CA1337218C - Stable radiation curable polymer composition - Google Patents

Abstract

A cured composition possessing good processability, solvent resistance and high temperature cohesive strength and oxidative stability both prior to and after curing is prepared by irradiating a polymeric composition. The polymeric composition contains (1) non-sulfur containing polymer having an effective amount of isolated ethylenic unsaturation for high energy ionizing radiation curing of the polymer, (2) a minor amount of a combination of at least one primary antioxidant and of at least one secondary antioxidant wherein the minor amount effectively stabilizes the polymeric composition both prior to and after radiation cure, and (3) optionally, an oligomer which is compatible with the polymerized diene portion of the polymer.

Description

~ 293--~nR~

STABLE RADIATION CURABLE POLY~ER COMPOSITION

Cross Reference to Copendin~ Applications The pr~sent inYention is related to the inventions disclosed in t~e copendin~ Canadia-- patent appli~ation, Serial No~ 591 ,û77 entitled Radiat~on Curable Polymer Con~position and Radiation Cured Polydiene Based Polymer Composition, and havio~ the same 10 assignee.
Field of the InveDtion The present in~ention relates to polymeric compositions, and more particularly, to polymeric compositions cured by subjection to ionizing --radiation, preferably, uithout requiring the aid of coupling agents ~hicb 1$ promote crosslinking of the elastomeric portion of the polymer therein during exposure to the radiation, and the means of stabilizing these cured polymeric co~positions against the long term effects of use at elevated temperatures Back~round of the Invention Polymers of coDjugated die~es ~polydienes) and copolymers of alken~l arenes aDd conjugated dienes have been formulated in the past ~o produce a number of types of adhesive compositions. Of particular interest herein are adhesive compositions based on such polymers which are cured by exposure to high energy ionizing radiation such as electron beam radiation.
The advent of the radiation curing process has presented new problems and needs peculiar to same. ~irstly, there is a need for a radiation respOQsive polydiene polymer or copolymer which may be melt processed and radiation cured ui~hout requiring the aid of a radiation sensitive coupling age~t at commercially acceptable radiation doses. Secondly, there is a need to further reduce the required radiation dosages to lo~er levels. This is motivated in part to reduce operating and e9uipment costs. Furthermore, in particular applications, the adhesive substrate may degrade or be adversely -`. 2 1337218 ~ . 63293- 3û89 : ... . .
-affected when exposed to certain levels of irradiation. Thirdly, there is a need for stabilizing means that not only protects tbe polymer and formulation containing same prior to radiation curing but also after.
Furthermore, it is also imperative that the stabiliziog means does not inte~fere with tbe radiation cure process to the point tbat ao undesirable increase in dose is required Polymers and copolymers of polydienes which address the first and second points have been disclosed in copending Can~dia~ a~plina~ion Serial No. 591,~77 10 - The polymers tberein were branched polymers wherein the polydiene portion thereof had a molecular weight in excess of 300,000. As such, it uas possible to eliminate the previously required (per prior arc) use of direct crosslink promoters sucb as multifunctional acrylate and me~hacrylate monomers uhich are an irritant at best and toxic at uorse. An lS importan~ aspect therein was to obtain a substantial polymer gel content at the lo~esc dose possible This result uas achieved by controlliug the unsaturation content of the formulations therein attributed to non-brancbed polymer coDstituents therein.
As such, the present invention is primarily directed to the above-mentioned third point - namely, stabilizing means for the polymer and formulations containing same. As earlier noted, there are three requirements for this stabilizing meaDs. The first requirement is that the stabilizing means protect tbe polymer and formulation prior to radiation curing. The second requirement is tbat the stabilizing means does not interfere uith the radiation cure process to the point that an ~ndesirable increase in dose is required. Finally, the stabilizing means mus~ be able to survive the curing process and protect the polymer and formulation afcer radiation curing.
An important aspect of radiation curing is to obtain a substantial polymer gel content, preferably at the lowest dose possible This substantial gel content imparts solvent resistance and good shear resistance -at elevated service temperatures to the cured polymer and formulation.
Certain characteristics or features of the polymer itself play a very impostant role in the formation of the initial gel content therein or in the formulation, particularly at low irradiation dosages. These features are the weight average molecular weight and a narrow molecular weight distribution, which will dictate the particular processing conditions for the formulation.
If the formulation is to be hot melt coated onto a substrate prior to radiation curing, the adhesive formulation shall experience a heat and shear history. Heat and shear shall be impressed upon the formulation ingredients durin~ the mixing process to manufacuure the adhesive and during the application of the adhesive onto the substrate. During these processes, it is vert important to maintain as closely as possible the initial moiecul2r weight and molecular weight distribution of the polymer. If these properties increase or decrease significantly, the viscosity of the polymer and of the formulation will increase or decrease accordingly causing a lack of control during this portion of the processing. Furthermore, if the weight average molecular weight of the polymer decreases, the required irradiation dosage to achieve an adequate gel level shall increase.
Similarl~-, if the molecular weight distribution widens even though maintaining the weight average molecular weight approximately constant, the required irradiation dosage to achieve an adequate gel level shall also increase. At this point, it is important to note that isoprene based polymers tend to undergo chain fracture (scission) upon aging, especially under heat and shear. On the other hand, butadiene based polymers tend to undergo crosslinking (coupling) upon aging, such as under heat aud shear.
Therefore, there is a need for utilizing a stabilizing means to prevent such degrzdation prior to and during application onto the substrate.
During this pre-radiation cure stage, conventional stabilization technology is applicable. Polymer stabilization is typically best achieved by the incorporation of a combination of primary and secondary antioxidants ~8891C', to minimize or reduce oxidation. The primary antioxidants are radical scavengers and terminate radical chains, formed during aging for instance.
The primary antioxidant competes with the polymer itself for peroxy radicals ~RO0 ) in the propagation step of the auto-oxidation process. However, a considerable amount of polymer oxidation takes place even with the best primary antioxidants. Such polymer oxidation may result from continued hydroperoxide formation depleting the primary antioxidant and/or from the initiation of polvmer radicals by the primary antioxidant radicals, particularly at elevated temperatures. For this reason, a secondary antioxidant is typically added and frequently said to provide a synergistic effect when combined with a primary antioxidant. The secondary antioxidant furt~er imprG~eS the stability of the polymer and for~ulations containing same by stopping the auto-oxidative chain through the decomposition of peroxides into stable non-radical products. Thus, secondary antioxidants are also known as hydroperoxide decomposers. The majority of primary antioxidants are sterically hindered phenols or secondary aromatic amines.
The secondary antioxidants are essentially sulfur compounds (mostly thioethers and esters of thiodipropionic acid~ or triesters of phosporous acid (phosphites such as tris(nonylphenyl) phosphites). See generally Plastics Additives Handbook; Hansen Publishers (Edited by R. Gacher and H.
Muller); Munich, ~ienna, New York; 1985, page 4-8, and J. L. Williams, ~. E.
Williams, and T. S. Dunn, "Investigation of Stabilizing Additives. IV. PEPQ
as a Primary Radical Scavenger," Journal of Applied Polymer Science, Vol. 27, page 951 (1982). Typically, high-molecular-weight phenols are favored over low-molecular weight ~ phenols, such as BHT
(2,6-di-tert-butyl-4-methvl-phenol)J due to the volatility of the latter.
See A. Patel and R. Thomas, "Stabilization and Basic Understanding of Stabilize Performance in SIS Based Pressure Sensitive Adhesives," Presented at TAPPI 1987 Polymers, Laminations and Coatings Conference (page 547-S2, 552); S. Mitton and C. Mak, "Stabilization of SIS-Based Pressure Adhesives", Adhesives Age, February 1983 (pages 12-15, 14); and G. Scott, "New - ~ 1337218 Developments in the Mechanistic Understanding of Antioxidant Behavior,"
Journal of Applied Polymer Science: Applied Polymer Symposium, Vol. 35, page 123-49, 130 (1979). Additionally, if discoloration is a consideration, the discoloration caused by aromatic amines is the main reason for the fact S that antioxidants of this type are rarely used in thermoplastics.
Plastics Additive Xandbook, page 14.
~ aving thus gone through great pains to obtain a radiation sensitive polvmer and formulating the composition so as to allow radiation curing without the aid of a crosslink promoter (radiation sensitive coupling agent) particularly at low dosages, it is important that the stabilizing means chosen to effect the above-referenced maintenance of the inltial molecular welght and molecular weight distribution of the polymer not interfere with the radiation cure process and protect the product thereof.
In this regard5 the state of the prior art is somewhat confusing at best.
lj ~owever, the following attempts to present same in an orderly, concise fashior..
In the prior art, whenever either a primary or secondary antioxidant has been found to effectively stabilize or protect a high energy ionizing radiation treated polymeric composition, the other type of antioxidant bas failed to provide any benefit. By this it is meant that this other type of antioxidant has either (1) interfered with the radiation cure process; (2) been destroyed, consumed or rendered inactive by the radiation cure process; (3) failed to protect the cured composition; or (4 some combination of the foregoing effects.
For instance, in U.S. Patent No. 3,888,752 issued to Eldred, substituted phenolic antioxidants (primary antioxidants) were found to be ineffective in protecting radiation cured styrene-butadiene elastomers. It was believed therein that the radiation process destroyed the ability of these compounds to combine with free radicals or other reactive groups.
3~ Furthermore, when candidates of this type of antioxidant were found to survive the radiation cure process, it was necessary to increase the ~ 13372~8 radiation dosage by as much as 25 percent to effectively crosslink the elastomer. On the other hand, Eldred found that certain phosphite esters were effective antioxidants (secondary antioxidants3 in radiation cured, styrene-butadiene elastomers when used in concentrations of preferably about 2 to 15 percent of the composition prepared for curing. These phosphites esters were selected from the group that consists of an alkyl pentaerythritol diphosphite, an alkyl trithio phosphite, and an alkyl hexathio diphosphite. As such, Eldred indicated that these two types of antioxidants, i.e., hindered phenols and the specified phosphite esters, were mutuall~ exclusive groups of antioxidants - with the former (primary antioxidants) suitable for protecting a sulfur-cured, styrene-butadiene elasto~er and the latter (secondary antioxidants) suitable for protecting a rad-a~.on-cured, styrene-butadiene elastomer.
With respect to standard amine and phenolic antioxidants (primary 1~ antioxidants), Grossman found that such primary antioxidants were of dubious value in radiation cured poly~eric compositions containing chlorosulfonated polyethylene or EPDM polymers. These antioxidants interfered with the radiation cure process and necessitated an appreciable increase in radiation dosage to reach a comparable state of cure (10 Mrad without antioxidant and Mrad ~ith antioxidant in EPDM). Additionally, these antioxidants (particularly hindered phenols) were destroyed or consumed and failed to protect the cured product. See R. F. Grossman, "Compounding for Radiation Crosslinking", Radiation Physical Chemistry, Vol. 9, pp. 659-74, 659-~1 (Pergamon Press, Printed in Great Britain, 1977).
The foregoing places a fairly negative light onto the utilization of primary antioxidants in radiation cured compositions due to interference ~ith cure and consumption during cure, thereby failing to protect the cured product, particularly at elevated temperatures. The sacrificial role of primary antioxidants during electron beam or gamma radiation exposure is reinforced by their beneficial utility in non-cured polypropylene based articles, particularly biomedical products such as syringes. Such articles B.~ o l n4 - 13372~8 may be sterilized bv utilizing such types of irradiation. However, such irradiation results in severe resin degradation, even following irradiation.
Polyprop~1ene undergoes chain scission UpOD exposure to irradiation producing free radicals. Furthermore, since the radiation induced radicals and perGxides formed in solid polymers are long lived, the potential for chain scission remains for time periods on the order of years following irradiation. Thus, hindered phenols (primary antioxidants) were inferred by the reduc,lon in their concentration following irradiation to be terminating the polvmeric free radicals formed, thereby inhibiting chain scission. See P. Horng anà P. Klemchuk, "Stabilizers in Gamma-irradiated Polypropylene", Plastics Engineering, pages 35-37, April 1984 and T. S. Dunn and J. ~.
~`illiams, "Radiation Stability of Polypropylene," Journal of Industrial Irradiation Technologv, Vol. 1(1), pages 33-49 (1983). However, it should be noted that isoprene and butadiene based polymers and copolymers preferentially undergo crosslinking, as opposed to chain-scission, when exposed to high energy ionizing radiation. Hence, if the polymer being utilized in a composition to be radiation cured were of the crosslinking type, this same type of antioxidant would be expected to also terminate the polymeric free radicals responsible for crosslinking (cure) and prevent crosslinking, thereby interfere with cure.
Furthermore, the prior art also demonstrates that only a selected few secondary antioxidants have shown some efficacy in the protection of the cured product containing same. For that matter, only sulfur containing pbosphites and phosphates in the absence of a primary antioxidant have proven effective. For example, Eldred discloses that alkyl thio phosphites are effective antioxidants in a radiation cured styrene-butadiene copolymer svstem. Along this same vein, Graham in U.S. Patent No. 3,261,804 discloses that a sulfur containing phosphate or phosphite provides i~proved heat stabilitv to polyethylene and propylene compositions over similar compositions containing analogous phosphates or phosphites without sulfur, whether or not the respective compositions have been irradiated.

BAP~Q'~

~ -- 1337218 Analogously, Horng and Klemchuk found that the phosphite (non-sulfur containing) utilized in their non-cured polypropylene articles provided inadeouate protection at best upon irradiation of the article with gamma radiation (2.5 ~rad) during sterilization thereof. Only 20% of the non-sulfur containing phosphite (tris (2,4-di-tert-butyl phenyl) phosphite) survived the initial exposure and was reduced to non-detectable concentrations within six months after the irradiation.
Though the foregoing places heavy reliance on the presence or absence of sulfur in phosphites or phosphates, other sulfur containing secondary antioxidants have not proven effective. ~or example, Eldred further discloses that the thioester (or thioether~ distearyl thio dipropionate is not effective in protecting a radiation cured styrene-butadiene copolymer system. Additionally, Horng and Klemchuk disclose that distearyl thio dipropionate is totally consumed upon irradiation of a non-cured polypropylene article (a syringe) with 2.5 Mrad of gamma radiation, therebv rendering this secondary antioxidant totally ineffective. Furthermore, Hansen et al. in U.S. Patent No. 4,133,731 disclose that zinc dibutyl dithio carbamate interfered with the radiation cure process (See Figure 2 therein).
In summary, no primary antioxidants and only sulfur containing phosphites and phosphates and pentaerythritol diphosphites have shown some effectiveness in protecting radiation cured compositions of unsaturated and saturated poly~ers. However, as earlier noted, there is still a need to provide improved protection to the polymer and formulation both before and after radiation cure and for these antioxidants not to interfere with the radiation cure process to any appreciable extent.
Summary of the Invention Accordingly, it is an object of the present invention to provide a new high energy ionizino radiation curable polymeric composition which is curable at low total dosages for lowest cost.

It is another object of the present invention to provide stabilizing means which protects the composition against degradation and oxidative attack prior to and after radiation cure, particularly at elevated temperatures, and has little or no detrimental effect on the radiation cure S process.
It is a further object of the present invention to provide a new radiation curable polymeric composition comprising a polymer, preferably an elastomer, containing ethylenic unsaturation; a combination of a primary and a secondary antioxidant for providing stabilizing means prior to and after radiation cure and which preferably does not appreciably interfere with cure; optionally, an oligomer, such as a tackifying resin, plasticizer, oil and aliphatic waxj and, optionally,' pigments, fillers, thickeners,' flow control agents, slip agents, flame retardants, anti-block agents, ultra-violet stabilizers, metal deactivators, and other additiv,~s which 1~ maintain or enhance the properties and processahility of the pol~er or formulation.
It is a further object of the present invention to provide a new high energv ionizing radiation curable po~ymeric composition containing no solvent thereby e7iminating the need to remove the solvent from the composition as part of the curing process.
It is yet another object of the present invention to provide a new high energy ionizing - radiation curable polymeric composition which is curable without the aid of a coupling agent which promotes crosslinking of the ethylenic unsaturated portion of the polymer during exposure to the radiation.
In accordance with the present inventlon, a polymeric composition is provided wnich is capable of being cured by high energy ionizing radiation, preferably, without the aid of a radiation sensitive coupling agent particularly at economically attractive dosages. The cured polymeric composition possesses excellent high temperature stability both prior to and after cure and high temperature cohesive strength along with excellent BAP~gl04 lo 1~37218 adhesion, shear strength and solvent resistance. In addition, by selecting the appropriate polymer, the composition may be processed as a liquid at moderate or room temperature. This is an important consideration in that it then becomes possible to use less expensive equipment also resulting in no air pollution and reduced energy requirements.
Thus, according to one aspect, the invention provides a cured composition possessing good processability, solvent resistance and high temperature cohesive strength and oxidative stability both prior to and after curing which is prepared by high energy ionizing radiation initiated curing of a polymeric composition, said polymeric composition comprising: (a) a non-sulfur containing polymer, said polymer containing an effective amount of isolated ethylenic unsaturation for high energy ionizing radiation curing of said polymer, and (b) a minor amount of a combination of at least one primary antioxidant and of at least one secondary antioxidant for effectively stabiliz-ing said polymeric composition both prior to and after radiation cure, wherein said primary antioxidant is selected from the group consisting of: (1) sterically hindered phenols, (2) hydroquinone derivatives, (3) quinolines, (4) aromatic amines, and (5) combinations thereof, and wherein said secondary antioxidant is selected from the group consisting of: (1) thio-ethers, (2) phosphites, (3) thiophosphites, (4) phosphonites, (5) phosphates, (6) thiophosphates, (7) dithiocarbamates, (8) disulfides, and (9) combinations thereof.
Broadly, the cured composition of the present invention is prepared by high energy ionizing radiation, such as electron beam radiation, initiated curing of a polymeric composition in which the polymeric composition comprises: (a) a non-sulfur containing polymer containing an effective amount of : lOa 1337218 isolated ethylenic unsaturation for high energy ionizing radiation curing of the polymer, thereby curing the polymeric composition, and (b) a minor amount of a combination of at least one,primary antioxidant and of at least one secondary antioxidant for effectively stabilizing the polymeric composi-tion both prior to and after radiation cure, and which preferably does not appreciably interfere with cure.
Thus, according to another aspect, the invention provides a method of producing a cured composition possessing good processability, solvent resistance, high temperature--cohesive strength and oxidative stability both prior to and after curing, said method comprising the steps of: (a) providing a polymeric composition comprising (1) a non-sulfur containing polymer, said polymer containing an effective amount of isolated ethylenic unsaturation for high energy ionizing radiation curing of said polymer, and (2) a minor amount of a combination of at least one primary antioxidant and of at least one secondary antioxidant for effectively stabilizing said polymeric composition prior to and after curing, wherein said primary antioxidant is selected from the group consisting of: (1) sterically hindered phenols, (2) hydroquinone derivatives, (3) quinolines, (4) aromatic amines, and (5) combinations thereof, and wherein said secondary antioxidant is selected from the group consisting of:
(1) thioethers, (2) phosphites, (3) thiophosphites, (4) phosphonites, (5) phosphates, (61 thiophosphates, (7) dithio-carbamates, (8) disulfides, and (9) combinations thereof; (b) irradiating said polymeric composition with high energy ionizing radiation to effect the curing of said polymeric composition, with said minor amount providing protection againgst oxidative degradation in said cured composition.

lOb 1337218 The polymer may be linear or branched in structure, preferably branched. The polymer is preferably selected from the group consisting of: (a) homopolymers of C4 to C12 dienes, preferably conjugated dienes, (b) copolymers of at least two C4 to C12 dienes, preferably conjugated dienes, (c) copolymers, preferably block copolymers, of at least one C4 to C12 diene, preferab'-y conjugated diene, and of at least one alkenyl arene, (d) copolymers of at least one C2 to C12 monoolefin and of at least one C4 to C12 diene, (e) copolymers of ethylene, at least one C3 to C6 ~-monoolefin, and at least one non-conjugated diene, and (f) combinations thereof. The polymer becomes particularly radiation sensitive when the polymerized diene, e.g. conjugate diene, portion of the polymer has a total weight average molecular weight of at least 0.3 million, thereby achieving cure at - ~ 1337218 much reduced irradiation dosages. At these molecular weights, a branched pol~er is preferred for viscosity and shear stability purposes, particularly in hot melt applications.
The branched polymer may be a graft, radial or star polymer having at least three (3), preferably at least six (6), branches or arms.
Additionally, the branched polymer may be formed by coupling two or more polymers together, such as coupling two (2) radial polymers together.
Likewise, other branched polymers may be coupled together. Such branched poivmers possess lower melt and solution viscosities and improved shear stability than their linear counterparts having like molecular weight and alkenyl arene content due to the compact structure of the branched pol~-mer.
The star polymer is a particularly preferred structure. The radial and star pGl~ers may be symmetric or as~nmetric with respect to the arms radiating from its nucleus.
The primary antioxidants include sterically hindered phenols, hydroquinone derivatives, quinolines and aromatic amines The sterically hindered phenols are preferred. Such phenols include thiobisphenols, alkylidene-bisphenols, alkyl phenols, hydroxy benzyl compounds, aminophenols and hydroxyphenyl propionates. Of these sterically hindered phenols, the alkyl phenols, aminophenols and hydroxyphenyl propionates are more preferred.
The secondary antioxidants include thioethers (or thioesters~, phosphites, thiophosphites, phosphonites, phosphates, thiophosphates, dithiocarbamates and disulfides. Preferred are the thioethers and phosphi-es, such as alkyl aryl phosphites and alkyl phosphites.
As noted above, a combination of a primary and a secondary antioxidant are required herein. Such a combination may be effected by utilizing antioxidants which contain both primary and secondary antioxidant fu~ctional groups in the same molecule.
The minor amount of the combination of primary and secondary antioxidants which effectively stabilizes the polymeric composition BAP$89104 ~ ~ 1337218 preferably ranges from about 0.2%W to about 4%w based on the polymeric composition with the ratio of primary to secondary antioxidant preferably ranging from about 8:1 to about 1:8. The ~ m amount of primary antioxidant is preferably about 0.1hw, and likewise the ~ini~ amount of S secondary antioxidant is preferably about 0.1%w based on the polymeric composition. More preferably, the ratio of primary to secondary antioxidant ranges from about L:1 to about 1:4 with the inimllm amount of primary antioxidant being about 0.3hw and of secondary antioxidant being about 0.2%w and a total maximum of about 3%w. Yet more preferably, the ratio of prlmary to secondary antioxidant ranges from about 2:1 to about 1:2 with a mi~imum amount of primary antioxidant being about 0.5/OW and of secondary antioxidant being about 0.3~w and a total maximum of about 2%w. --~
Being that the oligomer is optional, an oligomer which is compatible with the portion o~ the polymer containing the ethylenic unsaturation, e.g. polydiene portion, may be present in an amount from 0 to about 2000 parts by weight per 100 parts by weight of the polymer.
~ urthermore, the unsaturation index o.f the polymeric composition is preferably maintained at a sufficiently low level to allow curing cr the composition by exposure to high energy ionizing radiation without the aid of a radiation sensitive coupling agent to promote crosslinking of the poly~er As the unsaturation index of the composition (UT) decreases, the irradiation dosage tends to decrease. Thus, it is preferred that ~T is at most about 12%. It has be~n found that when UT is at most about 6% irradiation dosages may be reduced bv at least about 7b and reductions as high as about 20% have been observed, and produce compositions, for example, having excellent adhesive properties. However, to further reduce the irradiation dosages to yield like properties in the compositions herei~, ~T is preferably at most about 3h and more preferabl~ at most about 1.5%. As UT approaches zero, irradiation dosages of about 1 Mrad or possibly less ~ay be adequate to yield such adhesive properties.

The compositlon unsaturation index is defined by the following expression:

i=t ~ (wi) (Ui) UT
i=l wherein:
"i" represents a particular oligomer in the polymeric composition, "wi" represents the weight percent of the particular oligomer based on the total weight of components (a) and (b) of the polymeric composition, "Ui" represents the unsaturation index of the particular oligomer, "t" represents the total number of the oligomers in the polymeric composition, and "UT" represents the composition unsaturation index of the polymeric composition.
Additional components may be present in the composi-tion including, among others, alkenyl arene block compatible resins, pigments, fillers, thickeners, UV stabilizers, flow control agents, slip agents, flame retardants, anti-blocking agents, metal deactivators, antiozonants and other additives which maintain or enhance the properties and processability of the polymer or formulation. Furthermore, indirect crosslink promoters may be added thereto to further decrease irradiation dosages. Direct crosslink promoters are preferably avoided.
Not wishing to be bound to any particular theory, direct crosslink promoters are believed to consume or deactivate the primary antioxidants as the direct crosslink promoters become free radicals during irradiation and may form peroxy radicals which in turn are acted upon by the primary antioxidants.

: 13a 1337218 These and other objects, features and advantages of the present invention will become apparent from the subsequent description, and examples, and the appended claims taken in conjunction with the accompanying drawings.

"~ .,, . _.

In the Drawings Figure 1 is an x-y plot of 95C Holding Power (minutes) versus ~el Content (6).
Figure 2 is an x-y plot of 95C Holding Power (minutes) versus Gel Content (%).
Figure 3 is an x-y plot of 95C Holding Power (minutes) versus Gel Content (~).
~ igure 4 is an x-y plot of Total Primary Antioxidant (%~) versus Total Secondary Antioxidant (hw).
Detailed ~escription of the Invention A. Polymer The polymers employed in the present invention may have a Yariety of geometrical structures, since the invention does not depend on any specific geometrical structure, but rather upon the chemical constitution of the polymer itself. In particular, these polymers are capable of being cured or crosslinked upon exposure to high energy ionizing radiation, such as electron beam radiaticn ~s such, these polymers contain an effective amount of isolated ethylenic unsaturation for curing (crosslinking) the polymer or compositions containing same upon exposure to high energy ionizing radiation. Furthermore, these polymers may contain polar moieties containing hetero ato~s (atoms other than hydrogen or carbon). Xowever, such polymers are preferably non-sulfur containing polymers. Additionally, the sites of ethylenic unsaturation are preferably separated or isolated from the polar moieties b~ at least one - CR2 - group where R is preferably hydrogen or an alkyl group, thereby giving rise to the term "isolated ethylenic unsaturation." It is presently believed that sulfur containing polar moieties and/or polar moieties in conjugation with ethylenic unsaturation sites contribute significantly to the consumption of the antioxidants, particularly primary antioxidants, during the curing process Such a belief is baseà in part on the low activation energy of such structures to form free radicals.

~- 1337218 63293-3089 The polymers may be linear or branched in structure.
The polymer is preferably selected from the group consisting of:
(a) homopolymers of C4 to C12 dienes, preferably conjugated dienes, (b) copolymers of at least two C4 to C12 dienes, preferably conjugated dienes, (c) copolymers, preferably block copolymers, of at least one C4 to C12 diene, preferably conjugated diene, and of at least one alkenyl arene, ~ d) copolymers of at least one C2 to C12 monoolefin and of at least one C4 to C12 diene, (e) copolymers of ethylene, at least one C3 to C6 a-monoolefin, and at least one non-conjugated diene, and (f) combinations thereof.
The polymer becomes particularly radiation sensitive when the diene portion of the polymer-has a total weight average molecular weight of at least 0.3 million, thereby achieving cure at much reduced irradiation dosages without the aid of a crosslink promoter. At these molecular weights, a branched polymer is preferred for viscosity and shear stability purposes, particularly in hot melt applications, e.g. adhesives and sealants.
Examples of polymers designated (a), (b) and (c) above are disclosed in copending Canadian Patent Application Serial No. 591,077.
Examples of polymers designated as (e) above are disclosed in U. S. Patent No. 3,884,88~ with polymers designated as (d) being an obvious variant of these polymers.
For illustrative purposes, the following "Polymer I" disclosure relates to examples of polymers designated as (a), (b~ and (c) lSa 1337218 63293-3089 and "Polymer II" disclosure relates to examples of polymers designated as (e).
1. Polymer I
The polymers of the present invention may be either non-network forming or network forming. The non-network forming ~olymers may be ~ ;~

~ 16 1337218 polymers of conjugated dienes, copolymers of conjugated dienes or copolymers of conjugated diene and alkenyl arenes. When alkenyl arenes are presen~ in the non-network forming polymer, the non-network forming polymer is preferably a thermoplastic elastomer and has at most "effectively" one 5 alkenyl arene polymer block A. On the other hand, the network forming polymers are preferably ther00plastic elastomers and have at least two alkenyl arene polymer blocks A and at least one elastomeric conjugated diene polymer block B betweeD these at least two blocks A, thereby facilitating physical crosslinking via the alkenyl arene domains to form a network structure.
Additlonal1y, the macromolecular configuration of the polymer mav be linear or branched, preferably branched. Branched polymers include graft, radial or star configurations, depending upon the method by which the pGlymer is formed. It is preferred that the branched polymer have at least three (3), preferably at ieast six (~), branches or arms. In order to satisfy this latter preferred condition, a radial polymer having at least three (3) arms may be coupled with at least one other radial polymer also having at least three (3) arms. Likewise, other branched polymers may be coupled together. The coupling may occur between at least one branch or arm on each of the branch polymers to be coupled. With respect to radial and/or star polymers, the~nucleus of one may be coupled with either an arm or nucleus of another radial or star polymer.
'INon-network forming polymers" means those polymers having effectively at most one polymer block A which is thermodynamically incompatible with blocks B, for example, whe~e A is an alkenyl arene polymer block and B is a conjugated diene polymer block. Conversely, "network forming polymers" means those polymers having at least two polymer blocks A
and at least one polymer block B between the at least two blocks A. For example, when the content of the alkenyl arene is small in a network forming polymer, the produced block copolymer is a so-called thermoplastic rubber.

In such a rubber, the blocks A are thermodynamically incompatible with the BAP889~04 ~ 1337218 blocks B resulting ln a rubber consisting of two phases; a continuous elastomeric phase (blocks B~ and a basically discontinuous hard glass-like plastic phase ~blocks A) called domains. Since the A-B-A block copolymers have two A blocks separated by a B block, domain formation results in effectively locking the B blocks and their inherent entanglements in place by the A blocks and forming a physically crosslinked network structure.
Such a pheno~ena allows the A-B-A rubber to behave like a conventionally vulcanized rubber in the unvulcanized state.
On the other hand, non-network forming polymers have effectively at most one A block. Domain formation of these A blocks does not lock in the B blocks and their inherent engantlements. Moreover, when the alken~71 arene content is s~all resulting in a continuous elastomeric B phase, the strength of such polvmers is derived primarily from the inherent entangle-ments of the various B blocks therein and to a lesser extent the inherent entangiements of the optionally present A blocks therein.
Ihough a linear polymer may be utilized herein, there are certain features of branched polymers which favor their utilization particularly, those branched polvmers having at least three (3), preferably at least six (6), branches or arms. Due to the compact configuration of the brancheà
polymer, the branched polymers possess lower melt and solutlon viscosities than linear polvmer analogs having a like alkenyl arene content and molecular weight. Furthermore, branched polymers, of this type allow one to increase molecular weight with only a modest increase in viscosity. As such in a solvent coating process, these branched polymers may be applied at higher solids contents than their linear analogs. Thus, in either case, the branched polymers may be processed as easily as a relatively low molecular weight linear polymer. Additionally, in a hot melt process utilizing high shear equipment, the branched polymers possess greater shear stability.
Ir. adhesive applications, branched polymers should also result in bette. adhesives than their linear analogs. ~hen a linear block copolymer is crosslinked, its modulus will increase and res~lt in a reduction in the -~ 18 1337218 tack of the adhesive. However, if for example a star polymer having 10 arms is used in the adhesive, it is only required that 2 of the arms of each mclecule be crosslinked tG other molecules to form a covalently crosslinked network. Since the other 8 arms remain covalently uncrosslinked, the adhesive modulus remains loh and the covalently crGsslinked adhesive retains tack.
Typical examples (not exhaustive) of various structures of suitable network-forming branched block copolymers in the present invention are represented by the following general structural formula for star-type branched block copol~ers: -/ ~A]
[(B3m (AB~n (A)p~q X
~B]s wherein: A is a polymer block of an alkenyl arene, B is a pol~er block of a conjugated diene, X is a residual group of a polyfunctiGnal coupling agent having two or more functional groups, m is an integer equal to 0 or 1, n is an integer equal to l to lO, p is an integer equal to 0 or 1, --q is an integer equal to 1 to 40, r is an integer equal to 0 to 20, s is an integer equal to 0 to 39, and 3< q + r + s < 40.

Furthermore, the above-mentioned branched configurations may be either symmetrical or asymmetrical with respect to the polymer chains radiating from X. In an asymmetric configuration, the polymer chains may be of different moiecular weights and/or different structures.
Typical examples (not exhaustive) of various structures of suitable non-network forming branched block copolymers in the present B,~pR,R,C¦Q4 ~ 37218 invention are represented by the following general structural formula for star-type branched block copolymers:
IA]

~U
IB]W
wherein: A is a polymer block of an alkenyl arene, B is a polymer block of a conjugated diene, X is a residual group of a polyfunctional coupling agent having two or more functional groups, u is an integer equal to 0 to 40, v is an integer equal to 0 to 20, w is an integer equal to 0 to 40, and 3< u + v t w < 40.

Furthermore, the above-mentioned branched configurations may be either lS sy~metrical or as~metrical with respect to the polymer chains radiating from X. In an asymmetric configuration, the polymer chains may be of different molecular weights and/or different structures.
It will be understood that both blocks A and B may be either homopolymer, random or-tapered copolymer blocks as long as each block at least predominates in at least one class of the monomers characterizing the blocks defined hereinbefore. As such, blocks A may comprise copolymers of two or more alkenyl arenes, e.g., styrene/alpha-methylstyrene copolymer blocks, or alkenyl arene/conjugated diene random or tapered copolymer blocks as long as the blocks A individually at least predominate in alkenyl arenes, i.e., greater than 50% by weight. The~ alkenyl arene content of the individual blocks A is preferably from about 80% to 100~ by weight, more preferabiy 100/O by weight.
The alkenyl arenes in the blocks A are preferably monoalkenyl arenes. The term "monoalkenyl arene" will be taken to include particularly those of the benzene series such as styrene and its analogs and homologs ~ ~ 13372~8 including o-methylstvrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dime~hylstyrene, alpha-methylstyrene and other ring alkylated styrenes, particularly ring-methylated styrenes, and otber mono-alkenyl polycyclic aromatic co~pounds such as vinyl naphthalene, vinyl anthracene and the like.
The pre~erred monoalkenyl arenes are monovinyl monocyclic arenes such as styrene and alpha-methylstyrene, and styrene is particularly preferred.
The blocks B may comprise homopolymers of conjugated diene monomers, copolymers of two or more conjugated dienes, and copolymers of at least one of the dienes with at least one monoalkenyl arene as long as the blocks B at least predomin3te in conjugated diene units. Preferably, the amounts of randomly copolymerized alkenvl arene mers or short runs (sequences~ of such mers is minimized due to the retarding effect such mers have on radiation cure, preferably less than about 10% by weight of the blocks B and yet more preferably 0~ by weight of such mers.
The conjugated dienes are preferablv ones containing from 4 to 12, preferably from 4 to 8, carbon atoms. Examples of such suitable conjugzted diene monomers include: 1,3-butadiene (butadiene), 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene (piperylene), 1,3-hexadiene, 4-ethyl-1,3-hexadiene, 3-butyl-1,3-octadiene, 1-phenyl-1,3-butadiene, and the like- -Mixtures of such conjugated dienes may also be used. The preferred conjugated dienes are butadiene and isoprenè.
~hen polymers of conjugated dienes and alkenyl arene hydrocarbons are utilized, these pol~ers include any of those which exhibit elastomeric properties. Such polymers may contain various~ratios of conjugated dienes to alkenyl arenes. With respect to network forming polymers, the proportion of alkenyl arene blocks is preferably between about 1 and about 60 percent by weigh~ of the block copolymer, more preferably between about I and about 55 percent by weight and get more preferably between about 5 and about 40 percent by weight. With respect to non-network forming polymers, the proportion of the alkenyl arene blocks is preferably between about I and B~p88o~nb about 55 percent by weight of the block copolymer, more preferably between about 3 and about 35 percent by weight and yet more preferably between about 5 and about 15 percent by weight. When the alkenyl arene content is not more than about 60 percent by weight, preferably not more than abut 55 percent by weight, tbe block copolymer has characteristics as a thermoplastic elastomer; and, conversely, when the alkenyl arene content is greater than about bO percent by weight, preferably more than about 70 percent by weight, the block copolymer has characteristics as a resinous polymer.
In adhesive compositions, the proportion of the alkenyl arene bl~.s is preferably further reduced. The purpose of the further reduction is to enhance the probability of covalent crosslinking within the conjugated diene blocks at lower irrad.ation dosages. Once non-network forming polymers are covalently crosslinked, the composition shall take advantage of the physical crosslinking afforded by the fraction of the alkenyl arene domains now linked together Vi2 at least two covalently crosslinked B
blocks. Network formi~g polymers also take advantage of the physical crosslinking afforded by the alkenyl arene domains without significantly compromising tack. Thus, the proportion of the alkenyl arene blocks in either case is preferably from about 3% to about 35%, more preferably from about 5% to about 15~, by weight, so as not to significantly compromise the tack of the composition.
The average molecular weights of the individual blocks may vary within certain limits. In ~ost instances, the alkenyl arene blocks (blocks A) will have average molecular weights in the order of from about 1,000 to about 125,000, preferably from about S,OOO to about 30,000, and most preferably from about 8,000 to about 20,000; while the conjugated diene blocks (bloc~s B) wiil have average molecular weights in the order of from about 10,000 to about 250,000, preferably from about 20,000 to about 130,000, and most preferably from about 40,000 to about 100,000. The total weight average molecular weight of the poly (conjugated diene) portion of ~ ~ 1337218 the pcly~er is at least about 0.3 million, and preferably from about 0.4 million to about 2.5 million, and most preferably from about 0.8 million to aboLt 1.8 million. ~hese molecular weights are most accurately determined -by gel permeation gel chromatography - low angle laser light scattering (GPC-LhLLS).
Generally, it has been found that the greater the molecular weight of the branched polymer, the lower the irradiation dosage required to attain a satisfactory cure. A satisfactory cure is generally believed to be attained when the composition possesses at least about 60% polymer gel content. ~ith respect to commercial yardsticks, adhesives requiring more th~n about 5 to about 7 Mrads to reach the 60% gel threshold will not be of much value cor~ercially.
~ urthermore, the microstructure of the poly (conjugated diene) portion may be utilized to varv the probability of covalent crosslinking of lS the branched polymer, thereby affecting the amount of irradiation required to at-2in a satisfactory cure. For example, high vinyl pcl-~~butadiene (1,2 microstruc.lre) and high vinyl polyisoprene (3,4 microstructure) are believed to cure a lower irradiation dosage than their lo~ vinyl counter-parts, i.e., 1,4 polybutadiene and 1,4 polyisoprene, respectively. ~Tot wishing to be bound to any particular theory, the foregoing may conveniently be rationalized in terms of the crosslinking theory presented by Charlesby in "Atomic Radiation and Polymers" Pergaman Press ltd., 1960 and measure-ments of G (crosslink) b; Bohm and others for natural rubber, polyisoprene, and polyst~rene. ~ (crosslink) is the number of crosslinks per mer per 100 eV/g absorbed by the polymer. The solubil~y qf the polymer depends upGn the molecular weight of the polymer and the probability of an individual molecule being linked to its neighbor. The relevant variable here is the average number of crosslinks per molecule. The elastic modulus and swelling de~eDG upGn the density of crosslinks. Charlesby demonstrated that the solubilitv of linear homopolymers as measured by the sol fraction is related r~

~- 13~7218 to the nature of the polymer, the molecu7ar weight of the polymer, and the irradiation dosage by the following equation:
s ~ s~ = pO/qO + l/q ulr where "s" is the sol fraction, ~pO~ is the probability of a mer being a fracture site per unit dose, "qO" is the probability of a mer being 2 crosslink site per unit dose, "ul" is the number average degree of polymerization, and "r" is the irradiation dosage in Mrad. G(crosslink) [G(X)] and G(fracture) [G(F)] are related to "qO" and ~Pc~ according to the following equations:
G(X) = ~0.48 x 106) qO/w G(F) = (0 96 x 106) po/w ~-here "w" is the molecular weight o~ a mer.
The following values have been obtained by various workers for the values of G(X) and G(E).

TABLE A
Polymer G(X) qOa G(F) pOa Natural rubber1.1 to 1.9 1.6E-4 to 2.7E-4 0.221.6E-5 1,4 polyisoprene0 9 to 2.0 1.3E-4 to 2.8E-4 0.221.6E-5 High 3,4 polyisoprene 13 to 38 -- -- __ 1,4 polybutadiene2 to 3.8 2.3E-4 to 4.3E-4 0 0 High 1,2 polybutadiene 10 - -- -- __ Polystyrene 0.036 7.8E-6 0.01 lE-6 Poly(p-methylstyrene) 0.061 - 1.5E-5 __ __ a) "E" and th4 number following same stands-for a power 10; e.g., 1.6E-4 is 1.6 x 10 From Table A, it is apparent that high vinyl conjugated diene homopolymers are more sensitive to curing when subjected to irradiation.
Within a polymerized conjugated diene block, two modes of polymerization are possible and generally observed. In what is termed high vinyl polymeri-zation, the pol~erization involves onl~ one carbon-carbon double bond of the conjugated diene monomer- The carbon atoms of that bond will be incorporated within the polymer chain which will then contain a pendant ~ ~ i3~7218 vinyl group. The pendant vinyl groups are then readily available for covalent crosslinking. Examples of these type of polymerization are high 3,4 polyisopre~e and high 1,2 polybutadiene. In what is termed lo~ vinyl polymerization, the poly~erization involves both carbon-carbon double bonds of the conjugated diene which add head to tail Each conjugated diene monos,er which adds ln this manner will have a carbon-carbon double bond at the 2,3 carbons therein. As such, the ethylenic unsaturation of low vinyl polymerization resides in the backbone of the polymer, rather than on a pendent group as in high vinyl polymerization. The foregoing provides a basis for rationalizing the difference in G(X) values between poly-(conju~ate~ dienes) produced by low versus high vinyl polymerization.
Control of the two modes of polymerization is within the-skill of the art.
On the basis of the foregoing, either low or high vinyl polvmerized poly(conjugated dienes) may be utilized in the branched polvmers of the present invention. ~owever, as the vinyl content is increased in the branched polymer, the irradiation dosages for substantially the same level of cure are expected to decrease. Thus, as the ~inimllm poly(conjugated diene) molecular weights are approached, an increasing amount of vinyl content is preferred However~ it should be noted that in pressure sensitive adhesive applications high vinyl content has the drawback of reducing tack. On tbe otherhand, it is well within the skill of the art to enhance tack by the addition of suitable tackifying resins.
The branched polymers employed herein are generally produced by the process comprising the following reaction steps:
~a) polymerizing one or more conjugated dienes and/or one or more alkenyl arenes in solution in the presence of an ionic initiator to form a living polvmer; and (b) reacting the ~iving polymer with a multifunctional coupling agent to form a radial or star-shaped polymer.
As is well known, living polymers may be prepared by the anionic solution polymerization of conjugated dienes and/or alkenyl arenes in the B.~P88C 1 0~

presence of an alkali metal or an alkali-metal hydrocarbon as an anionic initiator. Examples of such procedures include the well known seguential addition of monomer techniques, incremental addition of monomer technique or coupling technigue as illustrated in, for cxample, U.S. Patent Nos. Re 28,246; 3,239,47B; 3,251,905; 3,390,20~; 3,427,269; 3,598,887; ~,2~9,627;
and in many other U.S. and foreign patents.

The living polymers utilized herein are preferably produced by anionic polymerization employing an organomonolithium initiator, in the presence of an inert diluent (solvent3. The organomonolithium compounds (initiators) that are reacted with the polymerizable additive in the first step of this process are represented by the formula RLi; uherein R is an aliphatic, cycloaliphatic, or aromatic radical, or combinations thereof, preferably cootaining from I to 20 carbon atoms per molecule. Exemplary of these organomonolithium compounds are ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tertoctyllithium, n-decyllithium, n-eicosyllithium, phenyllithium, 2-naphthyllithium, 4-butylphenyllithium, 4-tolyllithium, 4-phenylbutyllithium, cyclohexyl-lithium, 3,5-di-n-hepthylcyclohexyllithium, 4-cyclopentylbutyllithiu~, and the like. The alkyllithium co~pounds are preferred for employment according to this invention, especially those wherein the alkyl group contains frcm 3 to 1~ carbon atoms. A much preferred initiator is sec-butyllithium. See U.S. Pat. No. 3,231,635. The initiators may be added to the polymerization mixture in one or more stages optionally together witb additional monomer.
The living conjugated diene polymers are olefiuically unsaturated.
The living polymers may be liviog homopolymers, living copolymers, living terpolymers, living tetrapolymers, etc. The living oomopolymers may be represented by the formula Bl--M, wherein M is an ionic group, e.g.
lithium, and Bl is polybutadiene, polyisoprene or the like. Living polymers ~0 of isoprene are the preferred liviog ho~opoly~ers. The liviqg copolymers may be represented by the ~ormula Bl--B2--M, wherein Bl--B2 is a ~lock, ~p 26 1337218 random or tapered copolymer of two different conjugated dienes such as poly(butadiene/isoprene). Such formulae, withaut further restriction, do not place a restriction on the arrangement of the monomers within the living polymers. For example, living poly(isoprene~butadiene) copolymers may be living polyisoprene-polybutadiene block copolymers, living poly(isoprene/butadiene) random copolymers, or living poly(isoprene/butadiene) tapered copolymers. As an example of a living terpolymer may be mentioned living poly~isoprene~butadiene/isoprene)-terpolymers. Likewise, a living alkenyl polymer represented by the formula A--M, e.g. polystyrene--M, may be produced living copolym~rs of an alke~yl arene/conjugated diene within the scope hereof would be B--A--~, e.g. poly(isoprene/styrene)--M.
As stated above, the living copolymers may be living block copolvmers, living random copolymers or living tapered copolymers. The living block copolyme.s may be prepared by the step-wise polymerization of the monomers e.g. by polymerizing isoprene to form living polyisoprene followed by the addition of the other monomer, e.g. butadiene, to form a living block copolymer having the formula polyisoprene-polybutadiene-M, or butadiene may be polymerized first to form living polybutadiene followed by addition of isoprene to form a living block copolymer having the formula polybutadiene-polyisoprene-M.
The living random copolymers may be prepared by adding gradually the most reactive monomer to the polymerization reaction mixture, comprising either the less reactive moDomer or a mixture of the monomers, in order that the molar ratio of the monomers present in the polymerization mixture be kept at a controlled level. It is also possible to achieve this randomization by gradually adding a mixture of the monomers to be copolymerized to the polvmerization mixture. Living random copolymers may also be prepared by carrying out the polymerization in the presence of a so-called randomizer. ~andomizers are polar compounds which do not deactivate the catalyst aDd bring out a tendency to random copolymerization.

BAP8~^~104 i337218 27 63293-3n89 -Suitable randomizers are tertiary amines, such as trimethylamine, triett~ylamine, dimethylethylamine, tri-n-propylamine, tri-u-butylamine, dimethylaniline, pyridine, quinoline, N-ethylpiperidine, N-methylmorpholine;
thioe~hers, such as dimethyl sulphide, diethyl sulphide, di-n-propyl sulphide, di-n-butyl sulphide, methyl ethyl sulphide; and in particular etbers, such as dimethyl ether, methyl ethyl ether, diethyl etber, di-n-propyl ether, di-n-butyl ether, di-octyl etber, di-benzyl ether, diphenyl ether, anisole, 1,2-dimethyloxyethane, o-dimethoxy benzene, and cyclic ethers sucb as tctrahydrofuran.
Living tapered copolymers are prepared by polymerizing a mixture o~ monomers and result from the difference in reactivity betueen the .
monomers. For example, if monomer A is more reactive than monomer B then the cGmpoSitiOn of the copolymer gradually changes from that of nearly pure poly-A to tbat of nearly pure poly-B. Therefore, in each living copolymer lS molecule three regions can be discerned, wbich gradually pass into each other, and which have no sharp boundaries. One of the outer regions consists nearly completely of units derived from monomer A and contains only small amounts of units derived from monomer B, in the middle region the relative amount of units derived from monomer ~ greatly increases and the 2~ relative amount of units derived from monomer A decreases, while the outer region consists nearly completely of units derived from monomer B and contains only small amounts of units derived from monomer A. Various patents describe the preparation of multiblock copolymers containing tapered copolymer block, including U-S- Patent Nos- 3,251,905; 3,265,76S; 3,639,521;

and 4,208,356 Living tapered copolymers of butadiene and isoprene are preferred living tapered poly~ers.
The inert diluents in ~hich the living polymers are formed are inert liquid solven~s such as hydrocarbons e.g. aliphatic hydrocarbons, such as pentane, hexane, heptane, octane, 2-ethylhexane, nonane, decane, cyclo-hexane, methylcyclohexane or aromatic hydrocarbons e.g. benzene, toluene, ethylbenzene, the xylenes, diethylbenzenes, propylbenzenes. Cyclohexane is preferred. Mixtures of hydrocarbons may also be used.
The temperature at which the polymerization is carried out may vary b~tween wide limits such as from -50C to 150C, preferably from about 20C to about 80C. The reaction is suitably carried out in an inert atmosphere, such as nitrogen, and may be carried out under pressures sufficient to maintain the reaction mixture in the liquid phase, e.g. a pressure of from abou~ 0.5 to about lO bars.
The concentration of the initiator used to prepare the living polymer may also vary between wide limits and is determined by the des~red molecular weight of the living polymer. Generally, the initiator concentration is in the range of about 0;25 to 50 millimoles per 100 grams of monomer although both higher and lower initiator levels can be used if desired. The required initiator level freqnently depends upon the 1~ solubility of the initiator in the inert diluent (solvent).
The living polymers produced in reaction step (a) are then typically reacted, in reaction step (b), hith a multifunctional coupling agent. If the living polymers are all the same, the branched polymer shall be symmetric. On the other hand, if the living polymers are combinations of living polymers having different structures-andlor-molecular weights, the branched polymer shall be asymmetric.
There are a wide variety of coupling agents that can be employed.
Any polyfunctional coupling agent which contains at least two reactive sites can be employed. Examples of the types of compounds which can be used include the polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides, and the like disclosed in U.S. Patent No. 3,281,383. These compounds can contain two or more types of functional groups such as the combination of epoxy and aldehyde groups, isocyanate and halide groups, and the like. Various other substituents which are inert in the treating reaction can be present such as hydrocarbon radicals as exemplified by the alkyl, cycloalkyl, aryl, aralkyl and alkarvl ~ 29 1337218 groups and the alkoxy, aryloxy, alkylthio, arylthio, and tertiary amino groups. Many suitable types of these polyfunctional compounds have been ' deseribed in U.S Pat. Nos. 3,595,941; 3,468,972; 3,~3~,716; 3,078,254; and 3,594,452. Other polyfunctional coupling agents include the silicon halides, e g. chlorosilanes, and the like disclosed in U.S. Patent ~o.
3,244,664.
A preferred coupling agent is a polyalkenyl coupling agent. These polyalkenyl coupling agents are usually compounds having at least two non-conjugated alkenyl groups. Such groups are usually attached to the same or different electron-withdrawing groups e.g. an aromatic nucleus. Such compounds have the property that at least two of the alkenyl groups are capable of independent reaction with different living polym'e'rs'and'in''this respect are different from conventional conjugated diene polymerizable monomers such as butadiene, isoprene etc. Pure or technical grade poly-alkenyl coupling agents may be used. Such compounds may be aliphatic,aromatic or heterocyclic Examples of aliphatic compounds include the polyvinyl and polyallyl acetylenes, diacetylenes, phosphates and phosphites as well as the dimethacrylates, e.g. ethylene dimethacrylate. Examples of suitable heterocyclic compounds include dlvinyl pyridine and divinyl thiophene. - ~ ---A much preferred coupling agent is a polyal~enyl aromatic coupling agent. Polyalkenyl aromatic coupling agents capable of forming radial and star-shaped polymers are ~nown in tbe art. See generally Milkovich, Canadian Pat. No. 716,645; Crossland et al., U.S. Pat. No. 4,010,226;
Fetters et al., U.S. Pat. No. 3,985,830; and St. Clair et al., U.S. Pat.
Nos. 4,391,949 and 4,444,953.
The polyalkenyl aromatic compounds that are employed in this step of the process are those polyvinyl aromatic compounds that have any of the follcwing gene~al formulas:

~AP8~9104 - - -.~ 30 - - 13372~8 ~ (6-n) (a) Yn~
Yn ~ R'~8-n) (b) Yn ~ ~ R'(10-n) wherein Y is a vinyl group, and wherein each R' is hydrogen or an alkvl group cont2lning from 1 to 4 carbon atoms with a total of the alkvl substituents having not more than 12 carbon atoms, and wherein n is an integer of 2 or 3. The vinyl substituents in the above formulas (b) and (c) can be on one or both rings. Exemplary of suitable polyvinyl aromatic compounds are 1,2-divinylbenzene;
1,3-divinvlbenzene;
1,4-divinylbenzenej 1,2,4-trivinylbenzene;
1,3-divinylnaphthalene;
1,8-divinylnaphthalene;
1,3,5-trivinylnaphthalene;
20 2,4-divinylbiphenyl; : . . --3,5,4'-trivinylbiphenyl;
1,2-divinyl-3,4-dimethylbenzene;
1,5,6-trivinyl-3,7-diethylnaphthalene;

1,3-divinyl-4,5,6-tributylnaphthalene;
2,2'-divinyl-4-ethyl-4'-propylbiphenyl;
and the like. Divinyl aromatic hydrocarbons containing up to 26 carbon atoms per molecule are preferred for employment according to this invention;
particularly divinylbenzene in either its ortho, meta, or para isomer and commercial divinylbenzene which is a mixture of said isomers (and contains ,~ 31 ~337 218 various amounts of other monomers, e.g. styrene and ethyl styrene) is also quite satisfactory.
The polyalkenyl aromatic coupling agent is preferably added to the living polymer after the polymerization of the monomers is substantially complete, i.e., the agent should only be added after substantially all of the monomer has been converted to living polymers.
The amount of polyalkeny~ aromatic coopling agent added may vary between wide limits but preferably at least 0.5 mole is used per mole of unsaturated living polymer. Amounts of from 1 to 15 moles, preferably from 1.5 to 5 moles are preferred. The amount, which may be added in two or more stages, is usually such so as to convert at least 70bW of the living poly~ers into radial or star-shaped polymers, preferably at least 85%w.
The coupling reaction step may be carried out in the same solvent as for the polymerization reaction step (a). A list of suitable solvents is given above. The coup~ing reaction step (b) temperature may also vary between wide limits, e.g., from about 0C to about 150C, preferably from about 20C to about 120C. The reaction may also take place in an inert atmosphere, e.g., nitrogen, and under pressure, e.g., a pressure of from about 0.5 to about 10 bars.
The radial or star-shaped polymers prepared ~in the coupling reaction ste~ above are characterized by having a center or nucleus of crosslinked poly(polyalkenyl coupling agent) and a number of arms of substantially linear unsaturated polymers extending outwardly therefrom.
The number of arms may vary considerably but is typically between 3 and 40, 25 preferably from about 6 to about 30 and more preferably from about 10 to about 25. From the above it can be seen that X is preferably a poly (polyvinyl aromatic coupling agent) nucleus and more preferably a poly(divinylbenzene) nucleus. As stated above it is believed that the nuclei are crosslinked.
Following the coupling reaction the product is neutralized such as by the addition of ter~inators, e.g., water, alcohol or other reagents, for BAP8810~

the purpose of removing the lithium radical formiDg the nucleus for the condensed polymer product. The product is tben recovered such as by coagu1ation utilizing hot water or steam or both.
It should be observed that the above-described polymers and S copolymers may, if desired, be readily prepared by the methods set forth above. - However, since many of these polymers and copolymers are co~mercially available, it is usually preferred to employ the commercially available polymer as this serves to reduce the number of processiog steps involved in ~be overall proce~s.
2.- Polymers II ~ ~ - - - ~- -The copolymers of ethylene, at least one C3 to C6 ~-monoolefin, and at least one Don-conjugated diene are preferably~elasto~eric~and sucb poly~ers are uell-knoun in the art.
These copolymers have a substantially saturated hydrocarbon backbone chain uhich causes the copolymer to be relatively inert to ozone attack and oxidative degradation and have side-chain unsaturation available for radiation curing.
These copolymers are conveniently prepared by copolymerizing tbe monomers in the presence of a coordination catalyst system such as diisobutylalumi~ium chloride and vanadium oxytrichloride. Copolymeri2ation may be conducted in an inert solvent or in a slurry or particle form reactor. Details of their preparation are given, for example, in U.S. Pat.
No. 2,933,480; 2,962,451; 3,000,866; 3,093,620; 3,093,621; 3,063,973;
3,147,230; 3,154,528; 3,260,708; and in M. Sittig, "S~ereo Rubber and Otber Elastomer Processes," Noyes Development Corporation, Park Riade, N.J., 1967.

Propylene is normally selected as the ~-monoolefin in preparing such copolymers because of its availability and for reasons of economics.

Other lower n-monoolefins, such as l-butene, 1-pentene, and l-hexene can be selected in place of or in addition to propylene in preparing elastomeric copolymers ~hich are useful in practicing the invention. The term EPDM as used herein refers to the preferred copolymers of ethylene, propylene, and at least one nonconjugated diene.
An especially preferred class of EPDM is that in which the nonconjugated diene is moDoreactive. Monoreactive nonconjugated dienes have S one double bond which readily enters the copoly~erization reaction with ethylene and propylene, and a second double bond which does not, to any appreciable extent, enter the copolymerization reaction. Copolymers of this class have maximum side chain unsaturation for a given diene content, which unsaturation is available for radiation curing. Gel content of these copolymers is also minimal since there is minimal crosslinking during copolymerization.
Monoreactive nonconjugated dienes which can be selected in preparing this preferred class of EPDM copolymer include linear aliphatic dienes of at least six carbon atoms which have one ter~inal double bond and lS one internal double bond, and cyclic dienes wherein one or both of the carbon-to-carbon double bonds are part of a carbocylic ring. Of the linear dienes, copolymers of ethylene, propylene, and 1,4-hexadiene having an inherent viscosity of at least about 1.5 are preferred.
A class of cyclic dienes useful in preparing the preferred class of EPDM copolymers for radiation curln8 includes alkylidene bicycloalkenes, alkenyl bicycloalkenes, bicycloalkadienes,- and alkenyl cycloalkenes.
Representative of alkylidene bicycloalkenes are S-alkylidene-2-norbornenes such as 5-ethylidene-2-norbornene and 5-methylene-2-norbornene.
Representative of alkenyl bicycloalkenes are S-alkenyl-2-norbornenes such as 25 5-(1'-propenyl)-2-norbornene, 5-(2'-butenyl)-2-norbornene, and 5-hexenyl-2-norbornene. Dicyclopentadiene and 5-ethyl-2~5-norbornadiene are illustrative of bicycloalkadienes, and vinyl cyclohexene is representative of alkenyl cycloalkenes which may be selected as the diene monomer. EPDM
copolymers prepared from cyclic dienes preferably have an inherent viscosity 30 within the range of about 1.5 to 3.0, as measured on 0.1 gram copolymer dissolved in 100 milliliters of perchloroethylene at 30C., for optimum ~` 3~ 1337218 processing properties. Of the cyclic dienes, 5-ethylidene-2, norbornene is preferred.
Another class of preferred copolymers includes branched tetrapolymers made from ethylene, at least one C3 to C6 ~-monoolefin with propylene being preferred, at least one monoreactive nonconjugated diene, and at least one direactive nonconjugated diene such as 2,5-norbornadiene or 1,7-octadiene. By "direactive" is meant that both double bonds are capable of polymerizing during preparation of the copolymer. Tetrapolymers of this class preferably have an inherent viscosity of about 1.2 to 3.0, as measured on 0.1 gram copolymer dissolved in 100 milliliters of perchloroethylene at 30C , for optimum processing properties. A pleferred copolymer of this class is a tetrapolymer of ethylene, propylene, 1,4-hexadiene, and 2,5-norbornadiene. Such copolymers are described in Canadian Pat. Nos.
855,774 and 897,895.
CopGl~ers of the classes defined above have low gel content, a substantially saturated hydrocarbon backbone which is resistant to ozone and oxidative degradation, and hydrocarbon side-chain unsaturation which presents a situs for radiation curing. Low gel content is indicative of a polymer having favorable processing properties.
2C It should be observed that the above-described polymers and copolymers may, if desired, be readily prepared by the methods set forth above. However, since many of these- polymers and copolymers are commercially available, it is usually preferred to employ the commercially available polymer as this serves to reduce the number of processing steps involved in the overall process.
B. Antioxidants In the present invention~ it is essential that a combination of ce-tain primary and secondary a~tioxidants be utilized to stabili2e the pol~ers and compositions herein, preferably without causing any significant change in the irradiation dose required to attain the desired level of cure.
As earlier noted, gel formation is particul-rly important in adhesive ~ 5 i337218 applications Specifically, substituted phenols in combination . with thioe~t~ers t~hioctlcL~), thiophosphites and/or phosphites have been found to not interfere with cure. Furthermore, these antioxidant combinations not only provide superior performance prior to cure but also after cure as evidenced by a surprising retention of the initial gel content (a measure of cure) after accelerated heat aging when compared to either of the antioxidants utilized individually. These combinations of primary and secondary antioxidants perform particularly well in stabilizing the branched polymer containing compositions disclosed in the above-referenced copending applications in which minimizing the irradiation dose to attain the desired gel formation therein is of considerable importance.
Though not wishing to be bound to any particular theory, it generically appears from the foregoing that a combination of a primary and a secondary antioxidant has a synergistic and symbiotic effect in that the primary antioxidant appears to better survive the radiation cure process in the presence of a secondary antioxidant. Further, the combination 2~ provides superior antioxidative protection to the polymer and composition both before and after the cure process. All this is accomplished without any significant change in the irradiation dose required to attain the desired level of cure (gel content).
As such, a combination of a primary and a secondary antioxidant is required in the present invention. Examples of suitable primary antioxidants include sterically hindered phenols, hydroquinone derivatives, quinolines, and aromatic amines ~including naphthylamines, diarylamines, and para-phenylenediamines), as generally disclosed in Index of CommercialAntioxidants and Antiozonants, Goodyear Chemicals, 4th Ed. 1983 36 1 3372~8 (compiled by Paul R. Dean II). Preferred are the sterically hindered phenols, such as thiobisphenols, alkylidene-bisphenols, alkylphenols, hydroxybenzyl compounds, aminophenols, and hydroxyphenylpropionates. These subclasses of hindered phenolic antioxidants are more fully disclosed in the earlier referenced Plastics Additives Handbook, pages 8-12. Especially preferred are the alkylphenols, aminophenols, and hydroxyphenylpropion-ates. Quinolines and aromatic amines are less preferred because they tend to stain.
~xamples of suitable secondary antioxidants include C dithiocarbamates, thioe~t~ers (tl~ioc~hcrc), disulfides, phosphites (including aryl phosphites, alkyl-aryl phosphites, diphosphites, polymeric phosphites, and phenolic-phosphites~, thiophosphites, phosphonites, phosphates and thiophosphates, many of which are disclosed in 1) Index of Commercial Anti-oxidants and Antiozonants, 2) Plastic Additives Handbook, pages 8-13, and 3) U. S. Patent No. 3,261,804 issued to Graham.
However, it is noted that alkyl phosphites do not appear to be as effective as alkyl aryl phosphites and aryl phosphites herein. Preferred are the thioethers and aryl or alkylaryl phosphites. Also included are commercial blends of primary and secondary antioxidants as were described above. Further-more, the requirement that there be present a combination of a primary and a secondary antioxidant is satisfied by the inclusion of antioxidants containing both primary and secondary groupings in the same molecule.
The combination of the at least one primary anti-oxidant and of the at least one secondary antioxidant is present in the polymeric composition in a minor amount for -- effectively stabilizing the polymeric composition prior to and : 36a 1337218 ~ 63293-3089 after radiation cure. As earlier noted, the combination of antioxidants preferably does not appreciably interfere with cure.
Generally, this minor amount is a function of the minimum amounts of each type of antioxidant, the maximum total amount of antioxidant, and the relative amount of primary to secondary antioxidant. Broadly, the ratio of prlmary to secondary antioxidants ranges from about 8:1 to about 1:8 on a weight basis. Furthermore, the minimum amount of primary or secondary antioxidant required is about 0.1% by weight (%w) based on the polymeric ~ 37 1 3 3 7 2 1 8 composition. The total amount of both types of~antioxidants is preferablv at most a~cut 4~w. Referring now to Figure 4, range 1 is a graphical representation of the foregoi~g l~mits. Thus,~the minor amount which is effective in stabilizing the pol~meric composition is preferably about that S represen~ed by range 1 which is the polyhedral area within the polyhedron formed by lines connecting points:
a(X = 0.1, Y = 0.1~, b(X = 0.1, Y = 0.8), c(x = 0.45, Y = 3.s5)~
d(X = 3.55, Y = 0.45), e(X = 0 8, Y = 0.1) of an X-} plGt,where X is the total secondary antioxidant (~w) and Y is the total primary antioxidant (~w).
~ore preferably, the ratio of primary to secondary antioxidarlts 1~ ranges from about 4:1 to about 1:4 on a weight basis, the minimum amour,t of primary antioxidant is about 0.3%W~ the minimum amoùnt of secondar~
antioxidant is about 0.2%w and the total combined amount of antioxidants is at most about 3h~ This more preferred range is about that graphicallv represented as range 2 in ~igure 4 which is the polyhedron formed bv lines 0 connecting points:
f(X = 0.2, Y = 0.3), g(X = 0 2, Y = 0.8), h(X = 0.6, Y = 2 4), i(X = 2.4, Y = 0 6~, and j(X = 1.2, Y = 0 3) of an X-Y plo~ and the polyhedral area therein, where again X is the total secondary antioxidant ~w) and Y is the total primary antioxidant (/Ow).

Yet more preferably, the ratio of primary to secondary antioxidant ranges from about 2:1 to about 1:2 on a weight basis, the mjnjmllm amount of primary antioxidant is about 0.5%w, the rin;, amount of secondary ~ ~ ~ c O ~ ~

. 38 1 3 3 7 2 1 8 -~ antioxidant is about 0.3h~, and the total combined amount of antioxidants is - at most about 2bw. This yet more preferred {ange is about that graphically represented as range 3 in Figure 4 which is the polyhedron formed by lines connecting points:
k(X = 0.3, Y = 0.5), l(X = 0.3, Y = 0.6), m(X = ~.67, Y = 1.33), n(X = 1. 33, Y = 0.67), and o(X = 1.0, Y = 0.5) of an X-~ plot and the polyhedral area therein, where again X is the total secondary antioxidant (%w~ and Y is the total primary antioxidant (~w).
Only the more active combinations of primary and secondary antioxidants will perform satisfactorily near the extremes of Range 1, i.e.
outside of Range 2. Most combinations will perform satisfactorily over Range 2. Those combinations which perform satisfactorily near the boundaries of Range 1 ~ill generally give better results in Range 2. Most combinations will perform very well and most economically in Range 3.
Examples (not exhaustive) of antioxidant combinations that perform well in Range 1, particularly the extremes thereof, are sterically hindered phenols (e.g., B~T) (primary antioxidants) and secondary antloxidants containing more than one sulfur atom therein, such as a thioester (e.g.
pentaerythritol tetrakis (3-(dodecylthio) propionate)), di- and tri-thio phosphites, and di- and tri-thiophosphates.
Examples (not exhaustive) of antioxidant combinations that perform well in Range 2 are sterically hindered phenols (e.g. BHT) (primary antioxidant) and secondary antioxidants containing at least one sulfur atom therein, such as a thioester, mono-thiophosphites, and mono-thio phosphates, arvl phosphites and those indicated for Range 1.

Examples (not exhaustive) of antioxidants combination that perform well in Range 3 are sterically hindered phenols (e.g. BHT) (primary ~ -- 1337218 ~.
antioxidant) and secondary antioxidants such as diphosphites, alkyl aryl phosphites, zinc dibutyldithiocarbamate, and those indicated for Range 1 and - 2.
Several com~ercially available antioxidants contain both primary and secondary antioxidant functional groups within the same molecule. For the present purposes, it is adequate to construe these multi-functional molecules as consisting of an equal by weight mixture of a primary and a secondary antioxidant. In some instances, it is preferable to add additional primary antioxidant to the composition to assure adequate stability prior to radiation curing of the polymeric composition.
Prior to formulating the polymeric composition, it is preferable to include a portion of the required minor amount of the antioxidant combinatiGn, particularly at least some of the primary antioxidant, in the polvmer utilized in the pol~eric composition. The antioxidant in the polymer will provide same a longer shelf-life and protect the polymer during the initial stages of formulating the polymeric composition wherein the polymer experiences a heat and shear history of its own.
The alkylphenols include but are not limited to the following.
Alkylphenols of the general structures OH

R2 - - illl!
where R~, R2 and R3 are hydrocarbon groups; inclusive examples of which are 2~ 2,6-di-tert-butyl-p-cresol (BHT~, 2,4-dimethyl-6-tert-butylphenol, 2,6-dimethyl-4-tert-butylphenol, 2~4-dimethyl-6-(l-methylcyclohexyl)phenol~
2-methyl-4,6-di-tert-nonylphenol, 2,6-di-(1-phenylethyl)-4-nonylphenol, 2,6-di-(l-phenyl-1-methylethyl)-4-nonylphenol, 2,6-didodecyl-p-cresol, 2,6-dicctadecyl-p-cresol, and 2,4,6-trioctadecylphenol.
Other included alkylphenol types are 2,5-dimethyl-4-tert-~ 40 1337218 butylphenol, 4~5-dimethyl-2-tert-butylphenol~ styrenated phenol, 2-and 3-tert-butyl-4-methoxyphenol, 4-(hydroxymethyl~-2,6-di-tert-butylphenol, 3,5-di-tert-butyl-4-hydroxy-dodecylbenzoate, 3,5-di-tert-butyl-4-hydroxy-phenylbenzoate, and the reaction products of two moles of 4-methyl-2-tert-butylphenol with dicyclopentadiene, and higher molecular weight alkylated phenols, produced by reaction of a monoalkylphenol with an unconjugated diene to give an oligomeric intermediate whose terminal phenol molecules are alkylated with isobutene.
The aminophenols include 4-((4,6-bis-(octylthio)-s-triazin-2-yl)amino~-2,6-di-tert-butylphenol (Irganox~ 565 from Ciba-Geigy), 2,6-di-tert-butyl-alpha-dimethylamino-p-cresol ~ commercially available as Ethyl Antioxidant 703, and N-butyryl-p-aminophenol commercially available as Suconox~ 4 from Hexel.
Hydroxyphenylpropionates include but are not limited to octadecyl-~3,5-ter--butyl-4-hydroxy-phenyl) propionate (Irganox~ 1076 from Ciba-Geigy), tetrakis-(methylene 3-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methane (Irganox~ 1~10 from Ciba-Geigy, N,N'-hexamethylene-bis-(3,5-di-tert-butyl-4-hydroxy-hydrocinn~mide (Irganox~ 1098 from Ciba-Geigy~, 1,2-bis-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine . (Irganox~~:. MD1024 from Ciba-Geigy, thiodiethylene-bis-(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate (Irganox~
1035 from Ciba-Geigy), and lJ6-hexamethylene-bis(3-(3~s-di-tert-butyl-4 hydroxyphenyl)propionate) commercially available as Irganoxl~ 259.
The thioethers, sometimes referred to as thioesters, include those of the general formula .-Rl - O - (CH2)2 - S - (CH2)~2 - O - R2 where Rl and R2 are hydrocarbon groups or oxygen containing hydrocarbon groupsj examples include dilaurylthiodipropionate commerically available as Cyanox~ LTDP from American Cyanamid and distearylthiodipropionate. Other thioethers include B.~RR~9104 2,4-bis(n-octythio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine (also known as 4-((4,6-bis-(octylthio)-s-t~riazin-2-yl) amino)-2,6-di-tert-butylphenol) commercially avallable as Irganox~ 565, thiodiethylene-bis-(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate commercially available as Irganox~ ]035, pentaerythritol-tetrakis(B-laurylthiopropionate) commercially available as Seenox~ 412S, and disulfides such as dioctadecyl disulfide.
The aryl and alkylaryl phosphites include phenyl diisodecylphosphite commercially available as Weston~ PDDP, triphenyl phosphite available as Weston~ TPP, trisnonylphenhylphosphite available as Weston~ 399, tris~2,4-di-tert-butyl phenyl) phosphite available as Irgafos~
168, and phosphited polyphenols such as Vanox~ 13 from R. T. Vanderbilt.
Being that such stabilizers and oxidation inhibitors are added primarily to protect the elastomeric portion (i.e., that portion containing the ethylenic unsaturation) of the polymer, such materials shall be molecularly mixed therewith. Further, as is readily apparent from the foregoing, such materials typically contain~ unsaturation. Thus, it is preferred that the unsaturation indices of the materials be accounted for in determining the unsaturation index of the polymeric composition (UT) when the amount thereof exceeds about 1-phr -by including the multiplication product of the weight fraction (wi) thereof and lts corresponding unsaturation index (Ui).
C. B-Block Compatible Oligomers For various purposes, such as enhanclng tack or processibility of the compositions of the present invention, predominantly carbon-hydrogen based oligomers that are compatible with e~astomeric portion of the polymer, e.g. the blocks B of a branched block copolymer, are incorporated into the composition. The oligomers include, for example, tackifying resins, plasticizers, oils, petroleum derived waxes, and combinations thereof.

However, in the present invention, it is preferable that the amount of the unsaturated carbon atoms from these sources be minimized. By carefully 42 1 3 37 2 1~3293_3089 controlling the unsaturation content in the composition from these sources, the composition is capable of being cured by exposure to reduced levels of irradiation, preferably, without the aid of a radiation sensitive coupling agent to promote crosslinking of the polymer therein. As earlier noted, examples of such polymers are those disclosed in copending Canadian Patent Application Serial No. 591,077.
This unsaturation content is quantified in terms of a composition unsaturation index (UT) defined by the following expression: --i-t ~ (wi~ (Ui) UT
C i_l wherein:
"i" represents a particular oligomer in the polymeric composition, "t" represents the total number of oligomers in the polymeric composition, "wi" represents the weight fraction of the particular oligomer "i" based on the total weight of the polymer(s) and the oligomer(s), "Ui" represents the unsaturation index of the particular oligomer "i" as an equivalent percentage of unsaturated carbon atoms relative to the total carbon atoms therein, (units in ~), "UT" represents the unsaturation index of the polymeric composition (units in ~).
The unsaturation index of the polymeric composition (UT) is preferably equal to at most about 12~, more preferably at most about 6%, yet more preferably at most about 3%, and most preferably at most 1.5%.

42a Normally, the oligomers utilized herein contain substantially only carbon and hydrogen and as such every two unsaturated carbon atoms correspond to one double bond.
However, when double bonds occur between a carbon atom and a non-carbon atom, such as an oxygen, the correspondence between the number of unsaturated carbon atoms and multiple double bonds is upset. AS a consequence, the unsaturation index for such oligomers requires ` 43 _ ~337218 .;
adjustment or compensation to an equivalent value based upon carbon-hydrogen oligomers. An adequate correction is to 1) identify the portion of unsaturated carbons bonded via a double bond to a non-carbon atom, 2) double its value, and 3) add it to the portion due to carbon-carbon unsaturation.
The percentage of the carbon atoms that are unsaturated in each oligomer may be determined by quantitative C13-N.M.R. if the structure of the oligomer is not known beforehand. ln C13-N.M.R., the unsaturated carbon fraction is the integration of all signals from 200 ppm to 100 ppm chemical shift relative to the intergration of all signals from 200 ppm to 100 ppm plus 75 ppm to S ppm (with tetramethylsilane tTMS) at 0 ppm in chloroform solvent). The signal due to unsaturated carbon atoms bonded to non-carbon --- atoms, such as oxygen, may be identified by one skilled in N.M.R. and the ~fraction thereof determined. The fraction of unsaturated carbons in the respective oligomer is then multiplied by 100 to yield the percentage of unsaturated carbons therein. This percentage of unsaturated carbons is denoted as the unsaturation index of the respective oligomer, Vi. Table B
provides a list of typical tackifying resins and oils and their corresponding unsaturation index (Ui).

13372~ 8 TA~LE B
OligomersOligomer Unsaturation Indexg (%) Tackifying Resins:
Escorez~ 5380 1<
Regalrez~ 1018C 6 Adtac6 BlOC b 11 Escorez@ 131~LC 13 Wingtack~ 95 14 Wingtack~ Pl~sd 17 Wingtack~ 10 16 Floral685 d lga Wingtack~ 86 34 Piccovar~ AP-25C 36 Oils:
Tufflo$ 6056e f 1<
Shellflex~ 371 a) Includes 5% in oxygenated carbons which have been doubled and 9% in regular unsa;urated carbons.
b) Available from Exxon Chemical.
c) Available from Hercules.
d) Available from Goodyear Chemical.
e) Available from Atlantic Richfield Co.
f) Available from Shell C4~mical.
g) Determined utilizing C -N.M.R., except for Tufflo~ 6056 which is determined utilizing its structure.

As earlier noted, the amount of poly(alkenyl arene~ in suitable branched polymers may vary from about 3 to about 60 percent. In general, the amount of poly(alkenyl arene) for example polystyrene-in the branched poly~er within the li=its specifled does not appreciably affect the irradiation cure dosage required even though polystyrene has an unsaturation index OI 75%, i.e., 75% of the carbon atoms therein are unsaturated. The foregoing phenomPna results from the polystyrene being micro-phase separated from the poly(conjugated diene~ portion of the branched polymer, unlike the B block compatible oligomers which intimately mix therewith on a molecular level. This suggests that polymers with very small blocks or sequences of polystyrene (about 500 to about 5000 molecular weight) may interfere with cure as these sequences or small blocks of polystyrene may not entirely phase separate, but may being intermixing on a~molecular level. Therefore, it is preferred that polymers requiring a very low amount of poly(alkenyl ~ 1~37218 arene) be made asymmetric to a block size which will tend to properly phase separate and not interfere with cure. If the poly(alkenyl arene) blocks or se~uences are allo~ed to become small enough to allow some molecular mixing, the weight fraction of those potentially interfering blocks and sequences S may be quantified, or at least estimated, and accounted for in the determination of the composition unsaturation index (UT). Alternatively, the composition unsaturation index (UT) may be maintained at lower levels in suoh situations to allow gel formation at low irradiation dosages without explicitly including the effect of these potentially interfering blocks and seq~!ences in the determination of the composition unsaturation index.
1 Tackifying ~esins The pol~er in the polymeric composition by itself lacks the required adhesion for certain end-use applications, such as in adhesives or sealants. Th~refore, it is often necessary to add a tackifying resin that is compatible with the elastomeric, e.g polymerized conjugated diene, portion of the pol~er. However, in the present invention, it is preferable that the tackifying resin -have a lo~ level of unsaturation in order to achieve low dosage radiation curing of the polymeric composition. Mixtures of resins having higher and lower unsaturations and softening points may also be used. Examples of resins which are useful in the compositions of this invention include unsaturated and hydrogenated resins, esters of resins, polyterpenes, terephenol resins, and polymerized mixed olefins with hydrogenated resins preferred. The amount of tackifying resin or resins in total varies from O to about 1,000 parts per hundred rubber (phr), preferably from about S to about 500 phr and more preferably from about 50 to about 250 phr, preferably such that the prescribed limits of the composition unsaturation index (UT) are satisfied.
Optionally, in copolymers of alkenyl arenes and dienes, such as conjugated dienes, a tackifying resin that is compatible with the alkenyl arene blocks ~ay be added so long as it does not appreciably hinder the radiation curing process as a result of mixing on a molecular level with the -- 13372~8 poly(conjugated diene) blocks. Compatibility is judged by the method disclosed in ~.S. Pat. No. 3,917,607. Normally, the resin should have a sof~ening point above about 100C as deter~ined by ASTM method E28, using a ring and ball apparatus. Mixtures of arene-block-compatible resins having high and low softening points may also be used. Useful resins include coumarone-indene resins, polystyrene resins, vinyl toluene-alphamethylstyrene copolymers, and polyindene resins. Much preferred is a coumarone-indene resin. The amount of arene-block-compatible resin varies from O to about 200 phr, preferably from O to 50 phr. Ho~ever, if appreciable molecular mixing of the A block compatible tackifying resin occurs within the B block portion of the block copolvmer, the fraction of the tackifying resin should be factored into the determination of the composition unsaturation index (UT).
2. Plasticizers and Oils The polymeric compositions of the instant invention may also contain plasticizers such as rubber extending or compounding oils in order to provide wetting action and/or viscosity control. These plasticizers are well-known in the art and may include both high saturates content and high aromatic content oils. The a~ove broadly includes not only the usual plasticizers but also contemplates the use of olefin oligomers and low molecular weight polymers as well as vegetable and animal oil and their derivatives. The petroleum derived oils which may be employed are relatively high boiling materials and preferably contain only a minor proportion of aromatic hydrocarbons (preferably less than 30 percent and, more preferably, less than 15 percent by weight of the oil~. Alternatively, the oil may be totally non-aromatic. The oligomers may be polypropylene, polybutene, hydrogenated polyisoprene, hydrogenated polybutadiene, or the like having average weights preferably between about 200 and about 10,000 Vegetable and animal oils include glyceryl esters of the usual fatty acids and polymerization products thereof.

BAP8~9~04 ~p ~'1 1337218 However, in the present invention, the best results (i.e., satisfactory cure achieved with minimum irradiation dosage) are achieved when, li~e the tackifying ~esiDs, the plasticers and oils contain low levels of unsaturation. Additionally, it is also preferable to minimize the S aromatic contents thereof.
The amount of plasticizer and oil employed varies from 0 to about 2000 phr, preferably 0 to about 1000, more preferably 0 to about 250 and most preferably 0 to about 60 phr, preferably such that the prescribed limits of the composition unsaturation index (UT) are satisfied.
3. Petroleum Derived Waxes Various petroleum derived waxes may also be present in the composition in order- to impart fluidity in the molten condition of the polymeric composition and flexibility to the set (cured) polymeric composition, and to serve as a wetting agent for bonding cellulosic fibers.
1~ The term "petroleum derived wax" includes both paraffin and microcrystalline ~axes having melting points within the range of about 130 to about 225F as well as synthetic waxes such as low molecular weight polyethylene or Fisher-Tropsch waxes.
The amount of petroleum derived waxes employed herein varies from 0 to about 100 phr, preferably 0 to about lS phr,'preferably such that the prescribed limits of the composition unsaturation index (UT) are satisfied.
D. Crosslink Promoters (Irradiation sensitive coupling agents) Though not 'an essential component- of the present invention, crosslink promoters may be utilized to possibly enhance even further the 2~ rate at which the cure is performed and/or allow an even further decrease in the irradiation dosage required to satisfactorily cure the compositions herein. These crosslink promoters are cure promoting coupling which are activated by ionizing radiation. There are two major types of such crosslink promoters.
The first type of additive consists of catalyst-type promoters which do not enter directly into the crossllnking reaction but act to .

enhance the production of reactive species, such as free radicals which then lead to the formation of crosslinks. Such "indirect crosslink promoters"
which have been studied include among others halides; nitrous oxide; sulfur monochloride; metal oxides, such as zinc oxide and anitmony oxide (promotes flame retardance); litharge; and magnesia. The presence of indirect crosslink promoters effectively increase the G(X) value.
The second type of additive consists of crosslink promoters which enter directly into the crosslinking reaction and become the molecular link between two polymer chains. Such "direct crosslink promoters" include malei~ides, thiols, acrylic and allylic compounds,-for example, triallyl phosphate. Acrylates have been found to be more reactive than allylics.
Examples of such acrylates are the polyfunctional acrylate and methacrylate coupling agents disclosed in H2nsen et al., U.S. Patent No. 4,133,731, St. Clair et al. U.S. Patent No. 4,152,231, and U.S. Patent No. 4,432,848.
However, as earlier noted, such crosslink promoters tend to be irritants and/cr toxic and are preferably avoided.
Presently, it is unknown whether direct crosslink promoters may be utilized in the polymeric compositions embodying the present invention.
However, direct crosslink promoters are suspected of playing a role in counteracting or the consumption of the primary antioxidant during the radiation cure process and again are preferably avoided.
The amount of indirect crosslink promoter which may be employed varies from 0 phr to about 50 phr, preferably 0 phr to about 15 phr.
E. Supplementary Materials The compositions of this invention may be modified with supplementary materials including pigments, fillers, thickeners, W
stabilizers, flow control agents, slip agents, flame retardants, anti-blocking agents, metal deactivators, antiozonants, and other additives which maintain or enhance the properties and processability of the polymer or formulation (polymeric composition) both before and after radiation curing.

~ 49 F. Preparation and Use The polymeric compositions, particularly as adhesive compositions, of the present invention may be applied to the substrate from a solution of up to about 70~ weight solids of the ingredients in a solvent such as toluene, the solvent being removed by evaporation prior to crosslinking by exposure to the radiation. Alternatively, the ingredients may be mixed in a solvent, the mixture may be emulsified and the solvent evaporated, and the adhesive may be applied to the substrate as a 60-70% weight solids water-based emulsion, the water being removed by evaporation prior to crosslinking. Adhesives embodiments of the present invention are especiallv suited for preparation as 100% solids hot melt adhesives particularly when braDched polymers` are~ utilized since they give relatively low processing viscosities, less than several hundred thousand centipoise, and adequate pot life, up to several hours, at processing temperatures oi about 150C to about 180C. A preferred method for processing these adhesives to minimize gel formation during hot melt processing is to use an extruder to mix the adhesive and feed the coating die as is disclosed in Rorpman U.S. Pat. No.
3,9&4,509.
The compositions of the present invention are cured by exposure to high energy ionizing radiation such as electron beam radiation.
The electron beam radiation or high energy ionizlng radiation which is employed to effect the crosslinking reaction can be-obtained from any suitable source such as an atomic pile, a resonant transformer accelerator, a Van de Graaf electron accelerator, a Linac electron acceleratorJ a betatron, a synchrotron, a cyclotron, or the like. Radiation from these sources will produce ionizing radiation such as electrons, protrons, neutrons, deuterons, gamma rays, X rays, alpha particles, and beta particles.
The crosslinking reaction is conveniently effected at room temperature, but it can be conducted at depres-sed or elevated temperatures if desired. It is also within the spirit and scope of the invention to BAP88~104 ~ ~ 1337218 effect the crosslinking reaction within the confines of an inert atmosphere to prevent oxidative degradation of the block copolymer, particularly at an exposed surface. Additionally, crosslinking may be effected by irradiating the composition which is sandwiched between substrates such as when the composition is utilized as a tie-layer between these substrates. Similarly, when the crosslinking reaction is not conducted within the confines of an inert atmosphere, release paper may be placed over the exposed composition s~rface contacting and covering same. Thus, the composition may be crosslinked by irradiation through the release paper without worry of oxidizing the surface of the composition. On ~the otherhand, an oxidized surrace may be beneficial and desirous in a coatings application.
The amount of irradiation required to produce a satisfactory cure depends primarily upon the type and concentration of the polymer employed and the composition unsaturation index (~IT). Suitable dosages of electron beam irradiation include about 1 Mrad to about 20 Mrad, preferably about 1 Mrad to about 7 Mrad and more preferably about 1 Mrad to about 3 Mrads. It should be noted that irradiation dosages of about 1 Mrad and possibly less are believed attainable herein with the aid of indirect crosslink promoters.
A preferred use of the present formulation is in the preparation of pressure-sensitive adhesive (PSA) tapes or in the manufacture of labels.
The pressure-sensitive adhesive tape comprises a flexible backing sheet and a layer of the adhesive composition of the instant invention coated on one major surface of the backing sheet. The backing sheet may be a plastic film, paper or any other suitable material and the tape may include various other layers or coatings, such as primers, release coatings and the like, which are used in the manufacture of pressure-sensitive adhesive tapes.
Examples The invention is further illustrated by means of the following illustrative examples, which are given for the purpose of illustration alone an are not meant to limit the invention to the particular reactants and amounts disclosed.

~o~g~n~, ~ 5 1337218 For the purposes of comparison, test films of formulations within and outside the scope of the present invention were prepared by dissolving the formulation ingredients in toluene an casting the formulations onto 25 micron thick Mylar~ sheets to a dry adhesive film thickness of about 4~
microns. After air drying in a hood for 1 hour, the samples were dried in a 40C vacuum oven. By casting from toluene, a good solvent for all of the components of the formulations, the morphologies of the PSA films after solvent evaporation reasonably emulate those obtained from 100~ solids hot melt application. The test films were then stored at constant temperature and hu~idity ~25C, 50% relative humidity) prior to electron beam curing.
Electron beam ~EB) curing was performed at 4.8 Mrads using an Energy Sciences laboratory model CB150 Electrocur-ain~ system. 165 Xev electrons and an inert atmosphere were used. The beam was directed against the adhesiv~ surface. The test films were then covered with 25 micron thick sheets of silicone release paper and aged for various times at various temper2tures Por ele~ated temperatures, a forced-draft air electric oven was used. The elevated temperatures used in the examples that follow where ~0, 100~ 110, and 130C. The samples were randomly placed in the oven in such 2 manner that air could pass freely between each of the samples. After the desired aging time the samples were removed from the oven and testing was done to determine the polymer gel content, the adhesives high temperature performance and, tack and peel properties. The release paper ~as removed a fe~ minutes before testing. The tests-included:
1) Polymer gel content: The polymer gel content test is the primary test used to quantify the radiation~ responsiveness and solvent resistance of a formulation. It measures the weight percent of the polymer that is not soluble in toluene and quantifies the covalent network formation caused bv the radiation treatment- Unirradiated SIS and SBS based PSA's will completelv dissolve in this test. Irradiated PSA's based on conventional SIS and SBS polymers also completely dissolve, unless an extreme EB dose is used. Consistently, improved elevated temperature properties and solvent resistance require the gel content to be about 60% or greater. The gel test is described in the paper "Experimental Thermoplastic Rubbers for Enhanced Radiation Crosslinking of Hot Melt PSA's" by J. R.
Erickson, presented at the 1985 TAPPI Hot Melt Symposium, May 1985.
2) Shear Adhesion Failure Temperature (SAET): SAFT is defined as the temperature at which 1 in. x 1 in. overlap shear bond of the test adhesive tape to a Mylar~ substrate fails under a specified load, when placed ir. a cabinet whose temperature is increased by 22C per hour. A load of 1 kilogram was utilized.
3~ 5C Holding Power: 95C Holding Power is the time (in minutes) at which a 1 in. x 1 in. overlap shear bond of the test adhesive tape to a ~ylar~ substrate fails under a specified load when placed in a cabinet whose temperature is held constant at 95C. A load of 1 kilogram was used in the examples.
4) 180 Peel: 1~0 Peel is the force per unit width, pouDds per linear inch (pli), required to remove an inch wide test adhesive tape from a stainless steel panel when peeled at an angle of 180 at a rate of 12 inches per minute. The test follows method PSTC-1 in "Test Methods for Pressure Sensitive Tapes", 8th Edition, from the Pressure Sensitive Tape Council (PSTC).
- 5) Polyken Probe Tack: Polyken Probe Tack is the force (kg~
required to remove a 1 cm x 1 cm sect~on of~a test adhesive tape from a stainless steel surface (typically the end of a stainless steel rod) bv pulling the stainless steel surface away from the tape in a direction normal to the tape section at a rate of 1 cm per second after the steel surface had been brought into contact with the tape section for a dwell time of 1 second under a 1 kg. per sq. cm. load. The method is ASTM D-2979.
I~ the embodlments and examples, the following materials were emplo ed: -I. Block Copolvmers:

B ~D~;~C 1 ~L

~ 3 3 7 2 1 8 A. Polymer 1: A co~mercially available star-shaped SIS copolymer from Shell Chemical Company (Kraton~ D1320X rubber) prepared using an alkenyl arene based coupling agent and having more than about 6 arms, but less than about 40 arms, a weight average molecular weight of about 1.2 million, a polystyrene content of about 10% by weight, and containing about O.25hW of Ethanox~ 330 and about 0.25hW of BHT.
B. Poly~er 2: An asymmetric star-shaped SIS polymer from Shell Develop~ent Company prepared using an alkenyl arene based coupling agent, and having about 18 arms, a weight average molecular weight of about 1.2 million, a polystyrene content of about 10%, and having no antioxidants.
C. Polymer 3: A star-shaped isoprene polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having about 22 arms, a weight averaged molecular weight of about 1.2 million, and no antioxidant.
lj D. Polymer 4: A symmetric star-shaped SIS polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having about 18 arms, a weight average molecular weight of about 1.2 million, a polystryrene content of about 10% by weight, and about 0.3~w of Ethanox~ 330 antioxidant.
II. B-Block Compatible Resins:
A. Escorez~ 5380: a hydrogenated hydrocarbon resin from Exxon Chemical. A solid resin with TB of about 29C, a softening point of about oOC, and an unsaturation index value of about <1%.
B. Adtac~ B10: A aliphatic hydrocarbon resin from Hercules. A
liquid resin with Tg of about -48C, a softeni~g point of about 10C, and an unsaturation index value of about 11%.
C. Wingtack~95: A C5 hydrocarbon resin from Goodyear Chemical. A
solid resin with Tg of about 51C, a softening point of 95C, and an unsaturation index value of about 14%.
III. Stabilizers and Antioxidants:

B.~P~C~ 7~

~ 54 - 13~7218 A. Ethanox~ 330: 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl -4-hydroxybenzyl) benzene from Ethyl Corporation. A hydroxylbenzyl type of primary antioxidant.
B. BHT: 2,6-di-tert-butyl-4-methyl phenol (also known as 2,6-di-tert-butyl-p-cresol). A alkyl phenol type of primary antioxid2nt C. Irganox~ 1010: Tetrakis (methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) methane (also known as tetrakis (methylene 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate) methane) from Ciba-Geigy Corporation. A hydroxylphenylpropionate type primary antioxidant.
D. ZBDC: Zinc dibutyldithiocarbamate. A thiocarbamate type of secondary antioxidant.
E. Cyanox~ ~TDP: Dilaurylthiodipropionate from American Cyanamid.
A thioester type of secondary antioxidant.
F. Seenox~ 412S: Pentaerythitol tetrakis (~-7aurylthiopropionate) lj (also known as per.taerythritol tetrakis (3-(dodecylthio) propionate)) from Argus Chemical Division Witco Chemical Corporation. A thioester t~pe of secondary antioxidant.
G. Polygard~ HR: Tris-(mixed mono- and di-nonylphenyl) phosphite ~ith triisopropanol ami~ne from Uniroyal Chemical Group. An aryl phosphite t~Tpe of secondary antioxidant. - -H. Weston~ 399: Trisnonylphenyl phosphite containing about 0.75%wtriisopropanol amine from Borg-Warner Corporation. An aryl phosphite type of secondary antioxidant.
I. Weston~ 618: Distearyl pentaerythritol diphosphite from Borg-Warner Corporation. A diphosphite type of secondary antioxidant.
J. Irganox~ 565: 4-((4~6-bis-(octylthio)-s-triazin-2-yl)amino)-2~6-di-tert-butylphenol from Ciba-Geigy Corporation. A mixed type antioxidant having both aminophenol (primary) and thio triazin (secondary) structures in one molecule.
Example 1: Cure of Neat Branched SIS Polymer.

- - 1~37218 In tbis example, Polymer I was formul-ted using only a series of primary aad secondary antioxidants, Samples l-A~to 1-N as shown in Table 1.
Test films of each of tbese samples were subjected to 4.8 ~rads of EB
radiation, as shoun in Table 1, and tested for ioitial polymer gel content.
Contrary to what was expected, none of thc aotioxidants added inbibited the initial gel formation to a~y detectable extent when used at the 1%w to 2Xw level. The average gel conteot for the 13 samples with additional antioxidaot was 81.4% and the standard deviatioo for the same 13 samples was 3.3Z. Using tbese values the upper prediction limit (alpha - .05 for upper tail) for the next observation is 88X. The value obtained ~or Sample 1-~ containing only tbe minimal primary phenolic antioxidants already present in Polymer 1 from commercial maoufacture was 87%; within the upper prediction limit, indicating tbat it is not significantly higher than the other samples. Thus, the present example shows that none of the primary aod/or secondary antioxidants interfered with tbe radiation cure of tbe neat polymer.
Tbe primary antioxidants utilized herein were Irganox~ 1010 (a hydroxyphenyl propionate), BHT (an alkyl phenol), and Ethanox~ 330 (a hydroxybenzyl compound).
The secondary antioxidants utilized - berein were zinc -dibutyldithiocarbamate, Cyanox~ ~TDP (a thioester), Seenox~ 412S (a thioester), Polygard~ HR (an aryl phosphite), Weston~ 399 (an aryl phosphite~, Weston~ 618 (a diphosphite), and Irganox~ 565 (a hybrid 001ecule having both primary (aminopheool) snd secondary~ (thio triazin) antioxidant functional groups).
Example 2: Effect of Aotioxidaots on PSA's uoder VariouS Agin8 Conditions.
In this example, Polymer 1 was formulated either with Wingtack~ 95 and Adtac~ B10 or uith ~scorez~ 5380 resins~ and with and without added antioxidants, Samples 2-A to 2-D as shown in Table 2. According to copending Canadiarl Patent ~pplicati~n Serial No. 591,n77, formulations 2-A
and 2-B should require mc,re EB dose tharl 2--C and 2-D to attain the same level of crosslinking as measured by polymer gel content, since their U~ value is about 6.8%, while that of Samples 2-C and 2-D is only about 0.4%. ~est films of each of these samples were subjected to 4.8 Mrad of EB radiation, as shown in Table 2, and evaluated before and after a series of accelerated aging conditions.
A number of things are evident from examining the results in ~able 2.
First, the initial polymer gel content for the samples having the higher UT value (Samples 2-A and 2-B) are lower than those having the low UT
value (samples 2-C and 2-D).-- Hence, these can least afford any decrease in gel content that occurs upon heat aging.
Second, regardless of the oligomers (resins) used, the initial pol-~er gel content attainable at 4.& Mrads is not reduced by the addition of 0.5hW BHT (a primary antioxidant) and 0.5%~ Polygard~ HR ~a secondarv antioxidant).
Third, Samples 2-B, 2-C, aDd 2-D do not suffer any detectable loss in gel content when aged for up to 60 days at 70C, whereas Sample 2-A does.
Ordinarily these ~ould be considered outstanding results, since for standard rubber/resin based PSA's, 2-3 weeks aging at 70C is considered good. The 70C aging results indicate several additional important ~aspects. ~irst, the formulations (i.e., pol~eric compositions) with the higher ~T values have the greatest need for a good antioxidant package. Second, aging at 70C
will not allow the relative evaluation of better antioxidant packages that might be able to protect the polymer/adhesive under more severe aging/use conditions as may be desired by an adhesive manufacturer that has taken the extra step of EB radiation crosslinking to attain higher temperature service properties.
Fourth~ aging at 100 or 110C shows the clear superioritv of a good antioxidant package, and is obviously the temperature range required to compare various antioxidant packages in a reasonable length of time. It is also apparent that the formulation using the Wingtack~ 95 and Adtac0 B10 ~ - ~337218 resins will most readily show the advantages or disadvantages of any particular antioxidant package, and that a formulation like that of Samples 2-C and 2-D having a lower ~T value is preferably used in combination with a good combinat;on antioxidant pac~age to obtain the best performance.
S Example 3: Effect of Antioxidants on Asymmetric Star Polymer 2.
In this example, Polymer 2 was formulated using Wingtack~ 95 and Adtac~ B10 resins and a series of primary and secondary antioxidants, Samples 3-A to 3-~ as shown in Table 3. Test films of each of these samples were subjected to 4.8 Mrad of EB radiation, as shown in Table 3, and evaluated before and after accelerated aging at 100C for 7 days.
Again, none of the primary and/or secondary antioxidants inhibited the initial gel formation to any detectable extent when added alone or in combination in the 0.5 to 1%w range based on the polymeric compositior. The average gel content for the 7 samples, Samples 3-A to 3-G, containing the additional antioxidant was 81.0% and the standard deviatiou for the same was 3.4%. Using these values the upper prediction limit (alpha - .05 for the upper tail) for the next observation is 88~. The value obtained for Sample 3-H ~hich contains no additional antioxidant was 85%: within the upper prediction limit, indicating that it is not significantly higher than the other samples. Thus, -this example also de~onstrates-that none of the primary and/or secondary antioxidants utilized interfered with the cure of Polymer 2 in a typical adhesive formulation.
Fxamining the values for the ratio of the gel content after aging to the initial gel content, shows that the sterically hindered phenols, Samples 3-A and 3-B, provide a measure (although less than desirable) of polymer gel content protection during use at elevated temperatures, with the alkyl phenol ~BHT) being the more attractive. The secondary antioxidants when used essentially by themselves, Samples 3-C to 3-E, are of little value at best. The thioester ~Seenox~ 412S) provides less than adequate elevated temperature protection of the gel network, but the thiocarbamate (ZDBC) and the aryl phoshite (Polygard~ HR) actually caused additional gel loss above -~ - .
-- 13372~8 s that which occurs when no antioxidant is used in the adhesive formulation,- Samples 3-C and 3-E versus Sample 3-~ ~control). However? the approximatel-~
1:1 by weight combinations of a primary and a secondary antioxidant, Samples 3-~ and 3-&, show that excellent retention of the initial gel network can be 5 obtained upon heat aging using a total of 1%w additional antioxidant. The effect of maintaining a high gel content is not only important in its own right for solvent resistance but provides for the retention ~of elevated temperature holding power as seen in Figure 1, where 95C holding power to a Mylar~ substrate (minutes) after heat aging is shown to be strongly related 10 to aged polymer gel content (%).
Example 4: Effect of Antioxidants on Star Polymer 3.
In this example, Polymer 3 was for~ula'ted using Wingtack~ 95 and Adtac~ BlO resins and a series of primary and secondary antioxidants, Samples 4-A to 4-I as shown in Table 4. Test films of each of these samples 15 were subjected to 4.8 Mrad of EB radiation, as shown in Table 4, and e-valuated before and after accelerated aging at 100C for 7 days.
Again, none of the added primary and/or secondary antioxidants inhibited the initial gel formation to any detectable extent when added alone or in combination in the 0.5 to 1~w range based on the polvmeric 2C composition. The average gel content for the 8 samples,~'Sampl~es 4-A to 4-H,containing additional antioxidant was 79.9b and the standard deviation for the same was 2.0b. Vsing these values the upper prediction'limit (alpha =
.05 for the upper tail) for the next observation is 84~. The value obtained for Sample 4-I uhich contains no additional antioxidant was 82%: within the 25 upper prediction limit, indicating that it ls not significantly higher than the other samples.
Fx~mining the values for the ratio of the gel content after aging to the initial gel content, shows that the sterically hindered phenols, Samples 4-A and ~-B, provide a good measure of polymer gel content 30 protection during use at elevated temperatures, with the al~yl phenol (BHT) being the more attractive. The secondary antioxidants when used essentially ~q by themselves, Samples 4-C to 4-E, are of little value at best. The - thioester (Seenox~ 412S~ provides some though inadequate elevated te~.perature protection of the gel network, but the thiocarbamate (ZDBC) and the alkyl phoshite (Polygard~ HR) are quite ineffective. However, the approximately 1:1 by weight combinations of a primary and a secondary antioxidant, Samples 4-F and 4-G, show that excellent retention of the initial gel network can be obtained upon heat aging using a total of 1%w additional antioxidant. The control sample 4-I, containing no additional antioxidant, deteriorated so badly in the aging test, to the point of embrittlemeDt, that it was impossible to obtain meaningful results from the standard test methods being used.
Example 5: Effect of Antioxidants on Symmetric Star Polymer 4.
In this example, Polymer 4 was formulated using Wingtack~ 95 and Adtac~ B10 resins and a series of primary and secondary antioxidants, IS Samples 5-A to 5-O as shGwn in Table 5. Test films of each of these samples were subjected to 4.8 Mrad of EB radiation, as shown in Table 5, and evaluated before and after accelerated aging at 100C for 7 days.
Again, none of the primary and/or secondary antioxidants inhibited the initial gel formation to any detectable extent when added alone or in combination in the 0.5 to 1~w range based on the polymeric composition. The average gel content for the 14 samples, Samples S-A to 5-N, containing the additional antioxidant was 79% and the standard deviation for the same was 3.6%. Using these values the upper prediction limit (alpha = .05 for the upper tail) for the next observation is 86%. The value obtained for Sample 5-O which contains no additional antioxidant was 81%: within the upper prediction limit, indicating that it is not significantly higher than the other samples.
~ mining the values for the ratio of the gel content after aging to the initial gel content, shows that about 0.~5bw (including captive amount) of the sterically hindered phenols, Samples 5-A and 5-B, provide a useful measure of polymer gel content protection during use at elevated B.~P889104 w 1337218 .
temperatures, compared to Sample 5-O containing only the captive 0.15hw Ethanox~ 330 contributed by the poly0er and the captive primary antioxidant contributed by the oligomers ~approximately O.l~w of what is believed to be a hindered phenol), with the alkyl phenol (BHT~ being the more attractive.
The secondarv antioxidants when added to the small amount of captive Ethanox~ 330 contributed by the polymer and the captive primary antioxidant contributed by the oligomers (approximately 0.1%w of what is believed to be a hindered phenol), Samples 5-C to 5-E, are of some value. In this example, the ~BC and the thioesters (Cyanox~ LTDP and Seenox~ 412S~ provide some elevated temperature protection of the gel-~network, indicating that a 1:2 ratio cf primary (including captive amount) to secondary antioxidant will provide some measure of protection after EB radiation cure. However, the aryl phosphite (Polygard~ HR) and the diphosphites (Weston~ 618~ do not because they require the use of more primary antioxidant than that provided by the small amount of captive primary antioxidant. However, the about 1.5:1 to about 2:1 ratios by weight combinations of a primary and a secondary antioxidant, Samples 5-I and 5-L, show that excellent retention of the initial gel network can be obtained upon heat aging using between a total of about 0.75%w and a total of about 1.25~w total antioxidant (including captive antioxidants) when-utilizing thioester and phosphite secondary antioxidants. The mixed type of antioxidant having both aminophenol and thio triazin structure in one molecule (Irganox~ 565) also protects the EB radiation cured polymer well (Sample 5-N); adding additional secondary antioxidant (Samples 5-L and 5-M) to it provides no measurable improvement after EB radiation cure, although the combination would appear to protect the polymer better during formulation (mixing), storage, and application than the Irganox~ 565 used alone.
Again, the retention of polymer gel content provides for the retention of elevated te0perature holding power as seen in Figure 2, ~here 95C holding power to a Mylar~ substrate (minutes) after heat aging is shown to still be strongly related to aged polymer gel content (%).

~ 61 1337218 Example 6: Effect of Antioxidants on Polymer 1 Based Adhesives.
In this example, Polymer 1 was formulated using Wingtack~ 95 and Adtac~ B10 resins and a series of primary- and secondary antioxidants, Samples 6-A to 6-0 as shown in Table 6. Test films of each of these samples were subjected to 4.8 Mrad of EB radiation, as shown in Table 6, and evaluated before and after accelerated aging at lOO~C for 7 days.
Again, none of the added primary and/or secondary antioxidants inhibited the initial gel formation to any detectable extent when added alone or in combiration in the 0.5 to 1~w range based on the polymeric composition. The average gel content for the 14 samples, Samples 6-A to 6-N, containing added antioxidant was B1.4% and the standard deviation for the same was 3.0% Using these values the upper prediction limit (alpha =
.05 for the upper tail) for the next observation is 87~. The values obtained for replicated Sa~ple 6-0 (control) which contains no additional antioxidant 15 were 83, 8~, and 85%: within the upper prediction limit, indicating that it is not significantly higher than the other samples.
Examining the values for the ratio of the gel content after aging to the initial gel content, shows that the sterically hindered phenols, Samples 6-A and 6-B, provide a useful measure of polymer gel content protection during use at elevated temperatures, with the alkyl phenol (BXT) again being the more attractive. The-secondary antioxidants when added to the small amounts of both captive Ethanox~ 330 and BHT contributed by the poly~er and the sterically hindered phenol contributed by the oligomers, Samples 6-C to 6-G, are useful hith the ZDBC and the thioesters (Cyanox~
LTDP and Seenox~ 412S) in providing more elevated temperature protection of the gel network than the phosphites, indicating that about a 2:3 ratio of primary to secondary antioxidant will provide some measure of protection after EB radiation cure. ~he aryl phosphite (Polygard~ HR) and the - diphosphites (Weston~ 618) do not d~ as well because they prefer the use of someuhat more primary antioxidant than that provided by the captive primary antioxidants contributed by Polymer 1 and the resins. However, about 2:3 to BAP88~104 about 5:2 by weight combinations of a primary and a secondary ,antioxidant (including captive amounts), Samples 6-I and 6-L, show that excellent retention of the initial gel net~ork can be obtained upon heat aging using between a total of about 0.8Zw and total of about 1.3hw antioxidant (including captive amounts) when utilizing thioester and phosphite secondary antioxidants. The mixed type of antioxidant having both aminophenol and thio triazin structure in one molecule (Irganox~ 565) also protects the EB
radiation cured polymer well (Sample 6-H); adding additional secondary antioxidant to it provides no signif1cant improvement (Samples 6-M and 6-N) after gel formation, although the combination would appear to p~rotect' the polymer better than the Irganox~ 565 alone during formulation (mixing), storage prior to application, and application prior to EB radiation cure.
Again, the retention of polymer gel content provides for the retention of elevated temperature holding power as seen in Figure 3, where 95C holding power to a ~ylar~ substrate (minutes) after heat aging is shown to be strongly related to aged polymer gel content (%).

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Table 2 ~ ~4 ~~~~ ~- - -Sa~ple No. 2-A 2-P 2-C 2-D
~ Foroulation:*
Poly~r 1 50.0 50.0 5n.-o 50.0 - Wingtack 9544 5 44-5 ~~ ~~
Adt,ac B10 5.5 5.5 -- --: E~core2 5380 -- -- 50.0 50.0 BH~** 0.13 0.13 0.13 0.13 Etha~ox 330*:~ G.1.3 0.13 0.13 0.13 Artioxidant*** 0.1 0.1 0.1 0.1 DHT -- 0.5rJ -- Q.50 Polygard HR -- t).50 -- 0.50 Irrsdiation dose, ~rad 4 a 4.8 4.8 4.8 Agir,~ condltion~:
Gel Content, æ
O Hr6 81.3 80.5 88.7 91.0 60 Day6 @ 23 'C82.7 78.5 94.9 89.4 30 Days ~ 70 'C76.8 82.0 87.7 87.7 45 Days @ 7n C69.3 80.0 89.4 88.7 60 Day @ 7tl C71.7 82.0 89.9 86.1 4 Day6 @ 100 'C58.4 70.0 80.0 88.0 7 Day6 @ 100 C29.6 53.6 82.8 86.9 7 D2YE @ 100 'C46.3 74.2 -- --2 ~ay6 ~ llt) C63.2 74.0 80.3 80.0 4 Day~ @ 110 C35.0 74.2 71.8 82.9 95 de~ C HP, ixl~ g,min.
O Hr6 ~10(~0 ~1000 ~1000 ~1000 60 Day6 @ 23 C>1000 ~1000 >1000 >1000 30 ~ayE @ 70 C>lOOQ ~lOn~l >lOl)O ~1000 45 Day6 ~ 70 C90(~ ;1000 >1000 ~1000 60 Day6 ~ 70 'C~lOOn ~1-00~ ~1000 ~1000 4 Day6 ~ iO~ 'C45n ~1000 ~1000 >1000 7 Days @ 100 C 25 700 425 625 7 Days @ 100 'C 40 ~1000 -- --2 Day @ 110 C 650 ~1000 ~1000 ~1000 4 Day6 @ 110 C 25 ~1000 60C 900 laO P~el, pll Q Hrs 4.4 3.9 2.5 3.1 60 Day& @ 2.3 'C4.4 4.0 2.6 3.4 30 Day6 @ 70 C 4.1 3.9 2.6 2.4 45 Day6 @ 70 C -- -- -- --69 Day6 ~ 70 'C4.5 4.0 3.0 2.6 4 Dav6 @ 100 'C5 3 9.6 2.6 3.0 7 Days ~ lt)O 'C8.8 5.2 3.6 2.7 7 Days @ 100 'C4.3 4.9 -- __ 2 DaYs @ 110 'C5.8 4.9 3.0 2.9 4 Days @ 110 'C4.3- 4.9 2.9 3.0 Probe Tack, k~ ~
O Hrs 0.95 1.19 1.-00 0.86 60 DaY6 @ 23 C0.65 Q.81 1.07 1.07 30 Day6 @ 70 'C0.62 0.62 1.06 0.78 45 Days ~ 70 'C0.45 ().56 0.86 0.79 60 Day6 e 7U 'C0.41 0.84 l.nO 0.74 4 Days e loo ~c1.17 1.00 l.n~ 1.11 7 D~y6 ~ 100 'C1.33 1.3n 1.18 1.02 7 Day6 @ lnO 'C n.86 l.n6 -- --2 DaY6 @ 110 Cn.55 0.76 0.74~ 0.92 4 Days @ 110 C0.93 0.68 1.06 0.84 SAFT-~ylar, 'C
O Hr6 13n 116 125 121 60 Day~ @ 23 'C132 137 143 127 30 Days @ 7~i C128 138 130 133 45 Day6 ~ 70 'C122 138 127 134 fi~ Days e 70 'C172 127 139 142 4 Dayfi @ 100 'C116 129 133 126 7 Days ~ 100 'C 93 121 110 113 7 Days ~ 100 'C -- -- _- __ 2 Day6 ~ llQ C 117 133 141 135 4 Days @ llU C 83 130 114 124 _______________________ * Parts by welght ba6ed on lU(I ~art~ t~t,al of polymer & oligo~er~.
** Thi6 a~ount of antioxidant ~a6 contributed by Poly~er 1 . . . .. .. . . . . . ... ..
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' .' ' , ~ .................................. ~ :, ,, : I-- ' ~'' ; . 00 ~q 1~37218 While the present invention has been described and illustrated by reference to particular embodiments thereof, it will be appreciated by those of ordinary skill in the art that the same lends itself to variations not necessarily illustrated herein. ~or this reason, then, reference should be made solely tc the appended claims for purposes of determining the true scope of the present invention.

Claims (56)

1. A cured composition possessing good processability, solvent resistance and high temperature cohesive strength and oxidative stability both prior to and after curing which is prepared by high energy ionizing radiation initiated curing of a polymeric composition, said polymeric composition comprising:
(a) a non-sulfur containing polymer, said polymer containing an effective amount of isolated ethylenic unsaturation for high energy ionizing radiation curing of said polymer, and (b) a minor amount of a combination of at least one primary antioxidant and of at least one secondary antioxidant for effectively stabilizing said polymeric compositlon both prior to and after radiation cure, wherein said primary antioxidant is selected from the group consisting of:
(1) sterically hindered phenols, (2) hydroquinone derivatives, (3) quinolines, (4) aromatic amines, and (5) combinations thereof, and wherein said secondary antioxidant is selected from the group consisting of:
(1) thioethers, (2) phosphites, (3) thiophosphites, (4) phosphonites, (5) phosphates, (6) thiophosphates, (7) dithiocarbamates, (8) disulfides, and (9) combinations thereof.

2. The composition according to claim 1, wherein said polymer is selected from the group consisting of:
(c) homopolymers of C4 to C12 dienes, (d) copolymers of at least two C4 to C12 dienes, (e) copolymers of at least one C4 to C12 diene and at least one alkenyl arene, (f) copolymers of at least one C2 to C12 monoolefin and at least one C4 to C12 diene, (g) copolymers of ethylene, at least one C3 to C6 .alpha.-monoolefin, and at least one non-conjugated diene, and (h) combinations thereof.

3. The composition according to claim 2, wherein said polymer is a linear or branched polymer.

4. The composition according to claim 3, wherein said primary antioxidant and said secondary antioxidant are contained in a single antioxidant molecule.

5. The composition according to claim 3, wherein said primary antioxidant is a sterically hindered phenol.

6. The composition according to claim 5, wherein said sterically hindered phenol is selected from the group consist-ing of:
(1) thiobisphenols, (2) alkylidene-bisphenols, (3) alkyl phenols, (4) hydroxybenzyl compounds, (5) aminophenols, (6) hydroxyphenylpropionates, and (7) combinations thereof.

7. The composition according to claim 6, wherein said secondary antioxidant is selected from the group consisting of (1) thioesters,(2) alkyl aryl phosphites, (3) aryl phosphites, and (4) combinations thereof.

8. The composition according to claim 1, 2 or 3, wherein said minor amount is (1) a ratio of primary to secondary antioxidant ranging from about 8:1 to about 1:8 on a weight basis, wherein (2) said primary antioxidant is present in an amount of at least about 0.1%w based on said polymeric composition, (3) said secondary antioxidant is present in an amount of at least 0.1%w based on said polymeric composition, and (4) the total amount of said primary and secondary antioxidants is at most about 4%w based on said polymeric composition.

9. The composition according to claim 8, wherein (1) said primary antioxidant is a sterically hindered phenol, and (2) said secondary antioxidant contains more than one sulfur atom.

10. The composition according to claim 9, wherein said secondary antioxidant is selected from the group consisting of thioethers,thiophosphites, thiophosphates, and combinations thereof.

11. The composition according to claim 8, wherein:
(1) said ratio of primary to secondary antioxidant ranges from about 4:1 to about 1:4 on a weight basis, (2) said primary antioxidant is present in an amount of at least about 0.3%w based on said polymeric composition, (3) said secondary antioxidant is present in an amount of at least about 0.2%w based on said polymeric composition, and (4) the total amount of said primary and secondary antioxidants is at most about 3%w based on said polymeric compositions.

12. The composition according to claim 11, wherein (1) said primary antioxidant is a sterically hindered phenol, and (2) said secondary antioxidant is selected from the group consisting of a secondary antioxidant containing at least one sulfur atom, aryl phosphites, and combinations thereof.

13. The composition according to claim 8, wherein:
(1) said ratio of primary to secondary antioxidant ranges from about 2:1 to about 1:2 on a weight basis, (2) said primary antioxidant is present in an amount of at least about 0.5%w based on said polymeric composition, (3) said secondary antioxidant is present in an amount of at least about 0.3%w based on said polymeric composition, and (4) the total amount of said primary and secondary antioxidants is at most about 2%w based on said polymeric composition.

14. The composition according to claim 2, wherein said polymer is a branched polymer as presented by the general structural formula wherein "A" represents a polymer block A, said block A being at least predominantly a polymerized alkenyl arene, "B" represents a polymer block B, said block B being at least predominantly a polymerized conjugated diene, "X" represents a residual group of a polyfunctional coupling agent having two or more functional groups, "u" is an integer equal to 0 to 40, "v" is an integer equal to 0 to 20, "w" is an integer equal to 0 to 40, and 3 ? u + v +
w ? 40.

15. The composition according to claim 14, wherein said branched polymer is symmetric.

16. The composition according to claim 14, wherein said branched polymer is asymmetric.

17. The composition according to claim 16, wherein said block A has an alkenyl arene content of from about 80 to 100 percent by weight based on said block A.

18. The composition according to claim 17, wherein said block A has an alkenyl arene content of 100 percent by weight based on said block A.

19. The composition according to claim 18, wherein said block B has an alkenyl arene content of from 0 to about 10 percent by weight based on said block B.

20. The composition according to claim 19, wherein said block B has an alkenyl arene content of 0 percent by weight based on said block B.

21. The composition according to claim 14, wherein said branched polymer has an alkenyl arene content of from about 3 to about 35 percent by weight based on said branched polymer.

22. The composition according to claim 21, wherein said branched polymer has an alkenyl arene content of about 5 to about 15 percent by weight based on said branched polymer.

23. The composition according to claim 14, wherein the conjugated diene portion of said branched polymer has a total weight average molecular weight of at least about 0.3 million

24. The composition according to claim 23, wherein the conjugated diene portion of said branched polymer has a total weight average molecular weight of about 0.4 million to about 2.5 million.

25. The composition according to claim 24, wherein the conjugated diene portion of said branched polymer has a total weight average molecular weight of about 0.8 million to about 1.8 million.

26. The composition according to claim 14, wherein said branched polymer is a homopolymer of a C4 to C12 conjugated diene.

27. The composition according to claim 26, wherein said branched polymer is a radical polymer having at least three (3) arms.

28. The composition according to claim 27, wherein said branched polymer is a star polymer having at least six (6) arms.

29. The composition according to claim 14, wherein said branched polymer is a copolymer of at least two C4 to C12 conjugated dienes.

30. The composition according to claim 2, wherein said polymer is a branched block copolymer represented by the general structural formula wherein "A" represents a polymer block A, said block A being at least predominantly a polymerized alkenyl arene, "B" represents a polymer block B, said block B being at least predominantly a polymerized conjugated diene, "X" represents a resldual group of a polyfunctional coupling agent having two or more functional groups, "m" is an integer equal to 0 or 1, "n" is an integer equal to 1 to 10, "p" is an integer equal to 0 to 1, "q" is an integer equal to 1 to 40, "r" is an integer equal to 0 to 20, "s" is an integer equal to 0 to 39, and 3 ? q + r +
s ? 40.

31. The composition according to claim 30, wherein said branched block copolymer is symmetric.

32. The composition according to claim 30, wherein said branched block copolymer is asymmetric.

33. The composition according to claim 32, wherein said block A has an alkenyl arene content of from about 80 to 100 percent by weight based on said block A.

34. The composition according to claim 33, wherein said block A has an alkenyl arene content of 100 percent by weight based on said block A.

35. The composition according to claim 34, wherein said block B has an alkenyl arene content of from 0 to 10 percent by weight based on said block B.

36. The composition according to claim 35, wherein said block B has an alkenyl arene content of 0 percent by weight based on said block B.

37. The composition according to claim 30, wherein said branched block copolymer has an alkenyl arene content of from about 3 to about 35 percent by weight based on said branched block copolymer.

38. The composition according to claim 37, wherein said branched block copolymer has an alkenyl arene content of about 5 to about 15 percent by weight based on said branched block copolymer.

39. The composition according to claim 30, wherein said blocks B have a total weight average molecular weight of at least 0.3 million.

40. The composition according to claim 39, wherein said blocks B have a total weight average molecular weight of about 0.4 million to about 2.5 million.

41. The composition according to claim 40, wherein said blocks B have a total weight average molecular weight of about 0.8 million to about 1.8 million.

42. The composition according to claim 30, wherein said branched block copolymer is a radical block copolymer having at least three (3) arms.

43. The composition according to claim 42, wherein said branched block copolymer is a star block copolymer having at least six (6) arms.

44. The composition according to claim 2, wherein said polymeric composition further comprises:
about 0 to about 2,000 parts by weight per 100 parts by weight of said polymer of at least one oligomer compatible with the diene portion of said polymer.

45. The composition according to claim 44, wherein said polymeric composition prior to irradiation has a composition unsaturation index of at most 12%, said composition unsatura-tion index being defined by the following expression:

wherein:
"i" represents a particular oligomer in said polymeric composition, "wi" represents the weight fraction of said particular oligomer based on the total weight of components (a) and (b) of said polymeric composition, "Ui" represents the unsaturation index of said particular oligomer, as an equivalent percentage of unsaturated carbon atoms therein, "t" represents the total number of said oligomers in said polymeric composition, and "UT" represents the unsaturation index of said polymeric composition.

46. The composition according to claim 45, wherein said composition unsaturation index, UT, is at most about 6%.

47. The composition according to claim 46, wherein said composition unsaturation index, UT, is at most about 3%.

48. The composition according to claim 47, wherein said composition unsaturation index, UT, is at most about 1.5%.

49. The composition according to claim 44, wherein said oligomer is about 0 to about 1,000 parts by weight per 100 parts by weight of said branched polymer.

50. The composition according to claim 49, wherein said oligomer is about 5 to about 500 parts by weight per 100 parts by weight of said branched polymer.

51. The composition according to claim 50, wherein said oligomer is about 50 to about 250 parts by weight per 100 parts by weight of said branched polymer.

52. The composition according to claim 1, wherein said high energy ionizing radiation is electron beam irradiation.

53. The composition according to claim 52, wherein the amount of irradiation employed is between about 1 and about 20 Mrads.

54. The composition according to claim 53, wherein the amount of irradiation employed is between about 1 and about 7 Mrads.

55. The composition according to claim 54, wherein the amount of irradiation employed is between about 1 and about 3 Mrads.

56. A method of producing a cured composition possessing good processability, solvent resistance, high temperature cohesive strength and oxidative stability both prior to and after curing, said method comprising the steps of:
(a) providing a polymeric composition comprising (1) a non-sulfur containing polymer, said polymer containing an effective amount of isolated ethylenic unsaturation for high energy ionizing radiation curing of said polymer, and (2) a minor amount of a combination of at least one primary antioxidant and of at least one secondary antioxidant for effectively stabilizing said polymeric composition prior to and after curing, wherein said primary antioxidant is selected from the group consisting of:
(1) sterically hindered phenols, (2) hydroquinone derivatives, (3) quinolines, (4) aromatic amines, and (5) combinations thereof, and wherein said secondary antioxidant is selected from the group consisting of:
(1) thioethers, (2) phosphites, (3) thiophosphites, (4) phosphonites, (5) phosphates, (6) thiophosphates, (t) dithiocarbamates, (8) disulfides, and (9) combinations thereof, (b) irradiating said polymeric composition with high energy ionizing radiation to effect the curing of said polymeric composition, with said minor amount providing protection against oxidative degradation in said cured composition.