CA1339778C - Radiation cured polymer composition - Google Patents

Abstract

A cured composition possessing excellent cohesive strength at high temperatures along with excellent adhesion, shear strength and solvent resistance is prepared by economically attractive low dosages of high energy ionizing radiation initiated curing of a polymer composition comprising a linear, radial or star polydiene and an oligomer such that the unsaturation index of the composition is minimized. The radiation initiated curing of the adhesive composition is preferably accomplished without requiring the aid of a coupling agent to promote crosslinking of the polydiene during exposure to the radiation.

Description

RADIATION CURE~ POLYMER COMPOSITION
The present invention relates to adhesive composi-tions and more particularly to adhesive compositions cured by subjection to ionizing radiation, which promote crosslinking of the elastomeric block copolymer therein during exposure to the radiation.
Such compositions are known from e. g. U. S. Patents Nos. 3,113,912; 4,133,731; 4,432,828 and from "Experimental Thermoplastic Rubbers for Enhanced Radiation Crosslinking of Hot Melt PSA's", presented at TAPPI 1985 Hot Melt Symposium, May 1985 and "EB Curable Rubber Has More Heat and Solvent Resistance", Adhesive Age, Vol. 29(4), p. 22 (April 1986).
However in these disclosed curable adhesive compositions crosslinking agents are applied, which cause several disadvantages e. g. the compositions are more cGstly and contained an ingredient that is an irritant at best and toxic at worse and cause a decrease in tackifying character-istics, attributed to increasing the crosslinking density, whereas for these co~,positions containing multiarm block copolymers, the required irradiation dose is rather high, which causes relatively high operating and equipment costs.
Morecver in particular applications, the adhesive substrate may degrade or be adversely affected when exposed to such required levels of irradiation.
According to alternative embodiments of the prior art, thermoplastic rubbers are applied in adhesive compositions by using a solvent coating process. According to such a *

X;

- la -process, a solvent dissolves both phases of a block copolymer and a relatively low viscosity solution results, allowing the adhesive to be applied at moderately high solids content.
However, these solvent based processes possess inherent disadvantages, primarily due to the addition and evaporation of the solvent itself. The addition of solvent requires storage and handling equipment, plus the cost of the solvent itself. The evaporation of the solvent involves substantial investment and cost ln the procurlng and the operatlon of drylng ovens, alr pollutlon equlpment, and flre and safety equlpment.
Therefore, there ls stlll a need to further reduce the requlred lrradlatlon dosage to lower levels and/or to ellmlnate the lncorporatlon of a radlatlon responslve coupllng agent.
It ls an ob~ect of the present lnventlon to provlde a new hlgh energy lonlzlng radlatlon curable adheslve composltlon whlch ls curable at low dosage for lowest cost, and whlch contalns no solvent, to be removed from the composltlon as part of the curlng process and uslng no coupllng agent, promotlng the crossllnklng of the elastomerlc block copolymer durlng exposure to the radlatlon, at all or only small amounts as small as posslble.
In accordance wlth the present lnventlon an adheslve composltlon has been found, whlch ls capable of belng cured by economlcally attractlve low dosages of hlgh energy lonlzlng radlatlon and more preferably wlthout the ald of a radlatlon sensltlve coupllng agent.
Accordlngly, the present lnventlon provldes a cured composltlon possesslng good processablllty, solvent reslstance and hlgh temperature coheslve strength prepared by hlgh energy lonlzlng radlatlon lnltlated curlng of a polymer composltlon, sald polymer composltlon comprlslng: (a) a branched block polymer as represented by the general structural formula Qq (B)s -. 70474-279 whereln Q represent a group [BA~ or [~m (AB)n Ap~, in whlch A represents a polymer block whlch ls predomlnantly a polymerlzed C8-C16 alkenyl arene having a molecular welght of from 1,000 to 125,000; B represents a polymer block whlch ls predomlnantly a polymerized C4-C12 con~ugated dlene, the total average molecular weight of the con~ugated dlene portlon of the branched polymer belng at least 0.3 mllllon; X represents a residual group of a polyfunctlonal coupllng agent havlng three or more functional groups; r ls an lnteger equal to 0 to 20, q is an lnteger equal to 0 to 40, s ls an lnteger equal to 0 to 40, m ls an lnteger equal to 0 or 1, n ls an lnteger equal to 1 to 10, p ls an lnteger equal to 0 or 1, and 3 < ~ + r + s s 40 and (b) 0 to 2,000 parts ~y weight per 100 parts by weight of sald branched polymer of an ollgomer compatlble wlth the con~ugated diene portion of said branched polymer, (c) wherein said composition has an unsaturation lndex of at most 6.0~, said compasltion unsaturatlon inde~
belng deflned by the following e~pression:
t 2~ ~ (wl) (Ui) U~
i -- 1 whereln:
"1" represents a partlcular oli~omer ln the compositlon, "wi" represents the welght percGnt of the partlcular 7Q474-Z7g 1 33~778 - 3a -ollgomer based on the total welght of components (a) and (b) of sald composition, "Ul" represents the unsaturation lndex of the partlcular ollgomer, "t" represents the total number of the ollgomer ln the composltlon, and "UT" represents the composltlon unsaturatlon lndex of the composltlon.
The branched polymer may be a graft, radlal or star polymer havlng at least three (3), preferably at least slx (6), branches or arms. Addltlonally, the branched polymer may be formed by coupllng two or more polymers together, such as coupllng two (2) radlal polymers together. Llkewlse, other branched polymers may be coupled together. Such branched ~ o ~
D polymers possess~shear stabllity than thelr llnear counterparts havlng llke molecular welght and alkenyl arene contents due to the compact structure of the branched polymer.
The star polymer ls a partlcularly preferred structure. The radlal and star polymers may be symmetrlc or asymmetrlc wlth respect to the arms radlatlng from lt nucleus.
Accordlng to a preferred embodlment of the present lnventlon a branched block copolymer ls applled, whlch may be graft, radlal or star polymer havlng at least three (3), and more preferably slx (6) branches or arms. Addltlonally, the branched block copolymer may be formed by coupllng two or more block copolymers, together, such as coupllng two (2) radlal block copolymers together.

Likewise, other branched block copolymers may be coupled together. The star block copolymer is a particularly preferred structure. The radial and star block copolymers may be symmetric or asymmetric with respect to the arms radiating from its nucleus.
Most preferably, the branched block copolymers comprise at least two polymer blocks A, each of said blocks A
being at least predominantly a polymerized alkenyl arene block and at least one polymer block B, said block B being at least predominantly a polymerized conjugated diene block.
In these block copolymers said at least one block B
is between said at least two blocks A and each of said blocks A having a weight average molecular weight of from 1,000 to 125,000 and each of said blocks B having a weight average molecular weight of from 10,000 to 250,000.
The blocks A comprise from 1 to 55 percent by weight of said branched block copolymer and said B blocks have a total weight average molecular weight of at least 0.3 million.
Furthermcre, it is essential to the present invention that the unsaturation index of the composition be maintained at a sufficiently low level to allow curing of the composition by exposure to high energy ionizins radiation without the aid of a radiation sensitive crosslinking agent to promote cross-linking of the branched polymer. As the unsaturation index of the composition (UT) decreases, the irradiation dosage tends to decrease. Thus, it has been found that when UT is at most about 6% irradiation dosages may be reduced by at least about - 4a -7% and reductions as high as about 20% have been observed, and produce compositions having excellent adhesive properties.
However, to further reduce the irradiation dosages to yield like properties in the compositions herein, UT is preferably at most 3% and more preferably at most 1.5%. As UT approaches zero, irradiation dosages of about 1 Mrad or possibly less may be adequate to yield such adhesive properties.
Additional components may be present in the composition including, among others, antioxidants, block A
compatible resins, pigments, fillers, thickeners, stabilizers and flow control agents.

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~ 339778 Furthermore, direct and indirect crosslink promoters may be added thereto to further decrease irradiation dosages.
It will be appreciated that one of the key components of the present invention is the polymer employed. The polymers of the present invention may be as well non-network forming polymers of conjugated dienes and optionally, of alkenyl arenes, as network forming polymers.
"Non-network forming polymers" means those polymers having effectively at most one alkenyl arene polymer block A. Conversely, "network forming polymers" means those polymers having at least two alkenyl arene polymer blocks A and at least one conjugated diene polymer block B between the at least two blocks A.
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 block B resulting in 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 phenomena 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 entanglements.
Moreover, when the alkenyl arene content is small resulting in a continuous elastomeric B phase, the strength of such polymers is derived primarily from the inherent entanglements of the various B
blocks therein and to a lesser extent the inherent entanglements of the optionally present A blocks therein.
Though a linear polymer could be utilized herein, there are certain practical drawbacks to doing so which favour the utilization of branched polymers, particularly, those branched polymers having at least three (3), preferably at least six (6), branches or arms. Due to the compact configuration of the branched polymer, the branched polymers possess lower melt and solution viscosity than linear polymer 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.
Branched polymers should also result in better adhesives than their linear analogs. When a linear block copolymer is crosslinked, its modulus will increase and result in a reduction in the 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 molecule be crosslinked to other molecules to form a covalently crosslinked network. Since the other 8 arms remain covalently uncrosslinked, the adhesive modulus remains low and the covalently crosslinked adhesive retains tack.
A typical group of various structures (not exhaustive) of suitable branched block copolymers in the present invention are represented by the following general structural formula for star-type branched block copolymers:

/ [A]r Qq - X
[ ]s wherein Q represents a group [BA] or [(B) (AB) A ], 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 is a residual group of a polyfunctional coupling agent having two or more functional groups, q is an integer equal to 0 to 40, r is an integer equal to 0 to 20, s is an integer equal to 0 to 40, and 3 c q + r + s < 40, and/or wherein:
m is an integer equal to 0 or l, n is an integer equal to l to lO, and p is an integer equal to 0 or l.
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 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 bl'ocks 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 preferably 100% by weight.
The alkenyl arenes in the blocks A are preferably monoalkenyl .--- 30 arenes The term "monoalkenyl arene" will be taken to include -~~ particularly those of the benzene series such as styrene and its analogs and homologs including o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, l,3-dimethylstyrene, alpha-methylstyrene and other ring alkylated styrenes, particularly ring-methylated styrenes, and other mono-alkenyl polycyclic aromatic compounds such as vinyl naphthalene, vinyl anthracene and the like. The preferred 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 predominate in conjugated diene units. Preferably, the amounts of randomly copolymerized alkenyl 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 preferably ones containing from 4 to 12, preferably from 4 to 8, carbon atoms. Examples of such suitable conjugated 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-echyl-1,3-hexadiene, 3-butyl-1,3-octadiene, l-phenyl-1,3-butadiene, and the like. Mixtures of such conjugated dienes may also be used. The preferred conjugated dienes are butadiene and isoprene.
~ When polymers of conjugated dienes and alkenyl arenehydrocarbons are utilized, these polymers include any of those which exhibit elastomeric properties. Such polymers may contain various ratios of conjugated dienes to alkenyl arenes. The proportion of the alkenyl arene blocks is preferably between 1 and 60 per cent by weight of the block copolymer, more preferably between 1 and 55 per cent by weight and yet more preferably between 5 and 40 per cent by weight. When the alkenyl arene content is not more than 60 per cent by weight, preferably not more than 55 per cent by weight, the block copolymer has characteristics as a thermoplastic elastomer; and, conversely, when the alkenyl arene "_ content is greater than 60 per cent by weight, preferably more than ,- 70 per cent by weight, the block copolymer has characteristics as a resinous polymer.

~' -i 339778 } g In adhesive compositions, the proportion of the alkenyl arene blocks 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 irradiation dosages and i 5 yet still to take advantage of the physical crosslinking afforded ,~ by the alkenyl arene domains without significant compromising tack.
Thus the proportion of the alkenyl arene blocks is preferably from 3% to 35% by weight and more preferably from 5% to 15% by weight.
In the event that non-network forming polymers are applied, once these 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 via at least two covalently crosslinked B blocks.
Thus, the proportion of the alkenyl arene blocks is preferably from 3~ to 35%, more preferably from 5% to 15%, by weight, so as not to significantly compromise the tack of the composition.
; The average molecular weights of the individual blocks may i vary within certain limits. In most instances, the alkenyl arene blocks (blocks A) will have average molecular weights in the order of from 1,000 to 125,000, preferably from 5,000 to 30,000, and most preferably from 8,000 to 20,000; while the conjugated diene blocks (blocks B) will have average molecular weights in the order of from 10,000 to 250,000, preferably from 20,000 to 130,000, and most preferably from 40,000 to 100,000. The total weight average molecular weight of the poly (conjugated diene) portion of the polymer is at least 0.3 million, and preferably from 0.4 million to 2.5 million, and most preferably from 0.8 million to 1.8 million.
These molecular weights are most accurately determined by gel permeation gel chromatography - low angle laser light scattering (GPC-LALLS)~
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 60% polymer gel content. With respect to commercial ;~ :

1 33~778 yardsticks, adhesives requiring more than 5 to 7 Mrads to reach the 60% gel threshold will not be of much value commercially.
Furthermore, the microstructure of the poly (conjugated diene) portion may be utilized to vary the probability of covalent crosslinking of the branched polymer, thereby affecting the amount of irradiation required to attain a satisfactory cure. For example, high vinyl polybutadiene (1,2 microstructure) and high vinyl polyisoprene (3,4 microstructure) are believed to cure a lower irradiation dosage than their low vinyl counterparts, i.e , 1,4 polybutadiene and 1,4 polyisoprene, respectively. Not 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 measurements of G (crosslink) by Bohm and others for natural rubber, polyisoprene, and polystyrene. G
(crosslink) is the number of crosslinks per mer per 100 eV/g absorbed by the polymer. The solubility of the polymer depends upon the molecular weight of the polymer and the probability of an individual molecule being linked to its neighbour. The relevant variable here is the average number of crosslinks per molecule.
The elastic modulus and swelling depend upon the density of crosslinks. Charlesby demonstrated that the solubility of linear homopolymers as measured by the sol fraction is related to the nature of the polymer, the molecular weight of the polymer, and the irradiation dosage by the following equation:
S f S~ = pO/qO + l/qOUlr 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 a 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 ~pO~ according to the following equations:
G(X) - (0.48 x 10 ) qO/w G(F) = (0.96 x 10 ) pO/w where "w" is the molecular weight of a mer.

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i~ 33~778 The following values have been obtained by various workers for the values of G(X) and G(F), PolymerG(X) qoa G(F) pOa Natural rubber1.1 to 1.91.6E-4 to 2.7E-40.22 1.6E-5 1,4 poly-isoprene0.9 to 2.0 1.3E-4 to 2.8E-4 0.22 1.6E-5 High 3,4 polyisoprene 13 to 38 -- -- --1,4 poly-butadiene2 to 3.82.3E-4 to 4,3E-4 0 0 High 1,2 poly-butadiene10 -- -- --Polystyrene 0.036 7.8E-6 0,01 lE-6 Poly(p-methyl-styrene)0.061 1.5E-5 -- --a) "E" and the number following same stands for a power 10; e,g,, 1.6E-4 is 1.6 x 10 From Table l, 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 polymerization, the polymerization involves only one carbon-carbon double bond of the conjugated diene monomer, The carbon atoms of that bond will be incorporsted within the polymer chain which will then contain a pendant vinyl group, The pendant vinyl groups are then readily available for covalent crosslinking. Examples of these type of polymerization are high 3,4 polyisoprene and high 1,2 polybutadiene. In what is termed low vinyl polymerization, the polymerization involves both carbon-carbon double bonds of the conjugsted diene which add head to tail. Each conjugated diene monomer which adds in 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 pendant group as in high vinyl polymerization. The foregoing provides a basis for rationalizing the difference in G(X~ values between poly-(conjugated 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 polymerized poly(conjugated dienes) may be utilized in the branched l~S polymers of the present invention. However, 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 minimum 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 the other hand, 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 polymer; and : (b) reacting the living 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 presence of an alkali metal or an alkali-metal hydrocarbon as an anionic initiator. Examples of such procedures include the well known sequential addition of monomer techniques, ~: i ~
: :

3 lncremental addltlon of monomer technlque or coupllng technlque as lllustrated ln, for example, US Re 28,246 (Gamewell Mechanical Inc; W F StockfordtH M Gamewell; November 1974), US 3,239,478 (Shell Oll Company; J T Harlan; March 1966), US 3,251,905 (Phllllps Petroleum Company; R P Zellnskl;
May 1966), US 3,390,207 (Shell 011 Company; F D Moss; JF
Matthews; June 1968), US 3,427,269 ~Shell Oll Company; F C
Davls/W B Luther~D L Martlson; February 1969), US 3,598,887 (Polymer Corporatlon Limited; J Darey/Y K Wel/R C MacKenzie;
August 1971), US 4,219,627 (The Firestone Tire and Rubber Company; A F Halasa/J E Hall/A Para; August 1980).
As is well known in the block copolymer art, tapered - copolymer blocks can be incorporated in the multiblock copolymer by copolymerizlng a mlxture of con~ugated dlene and alkenyl arene monomers utillzlng the dlfference ln thelr copolymerlzation reactlvlty rates. Varlous patents descrlbe the preparatlon of multlblock copolymers containlng tapered copolymer blocks and partlcularly the U.S. patents No.
3,251,905 and US 3,265,765 (Shell 011 Company; G Holden/R
Mllkovich; August 1966), US 3,639,521 (Phllllps Petroleum Company; H L Hsleh; February 1972), US 4,208,356 (Asahl Kasel Kogyo Kabushiki Kalsha; I Fukawa/K Satake/T Yamada/K
Hayakawa/Y Sato; June 1980).
The livlng polymers utlllzed hereln are preferably produced by anlonic polymerlzatlon employlng an organomonollthlum lnltlator, ln the presence of an lnert dlluent (solvent). The organomonollthium compounds 7 ~\ ,'1 7 A _ 7 7 o -- 13a -(lnltlators) that are reacted wlth the polymerlzable addltlve ln the flrst step of thls process are represented by the formula RLl; whereln R is an allphatlc, cycloallphatlc, or aromatlc radlcal, or comblnatlons thereof, preferably contalnlng from 1 to 20 carbon atoms per molecule. Exemplary of these organomonollthlum compounds are ethylllthlum, n-propylllthlum, lsopropylllthlum, n-butylllthlum, sec-butylllthlum, tertoctylllthlum, n-decylllthlum, n-elcosylllthlum, phenylllthlum, 2-naphthylllthlum, 4-butylphenylllthlum, 4-tolylllthlum, 4-phenylbutylllthlum, cyclohexylllthlum, 3,5-dl-n-heptylcyclohexylllthlum, 4-cyclopentylbutylllthlum, and the llke. The alkylllthlum compounds are preferred for employment accordlng to thls lnventlon, especlally those whereln the alkyl group contalns from 3 to 10 carbon atoms. A much preferred lnltlator ls sec-butylllthlum. See U.S. Pat. No. 3,231,635 (Shell Oll Company;
G H Anahelm/R. Mllkovlch; 1966). The lnltlators may be added to the polymerlzatlon mlxture ln one or more stages optlonally together wlth addltlonal monomer.
The llvlng con~ugated dlene polymers are oleflnlcally unsaturated.
The llvlng polymers may be llvlng homopolymers, llvlng copolymers, llvlng terpolymer~, llvlng tetrapolymers, etc. The llving homopolymers may be represented by the formula Bl-M, or Al-M, whereln M ls an lonlc group, e.g.
llthlum, and Bl ls ~;

~ :~

i 339778 polybutadiene, polyisoprene or the like and A is a poly alkenyl arene such as styrene.
As stated above, the living copolymers may be living block copolymers, living random copolymers or living tapered copolymers.
The living block copolymers 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 s monomer, e.g. butadiene, to form a living block copolymer having the formula polyisoprene-polybutadiene-M, or butadiene may be lO 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 15 mixture, comprising either the less reactive monomer 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 20 the polymerization mixture. Living random copolymers may also be prepared by carrying out the polymerization in the presence of a , so-called randomizer. Randomizers are polar compounds which do not; deactivate the catalyst and bring out a tendency to randomcopolymerization and which are known in the art from e.g. U.S.
25 Patent No. 3,251,905.
Living tapered copolymers are prepared by polymerizing a mixture of monomers and result from the difference in reactivity between the monomers. For example, if monomer A is more reactive than monomer B then the composition of the copolymer gradually 30 changes from that of nearly pure poly-A to that of nearly pure poly-B. Therefore, in each living copolymer molecule three regions can be discerned, which 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 :

1 ' 39778 relative amount of units derived from monomer B greatly increases and the 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; 3,265,765; 3,639,521; and 4,208,356.
Living tapered copolymers of butadiene and isoprene are preferred living tapered polymers.
The inert diluents in which the living polymers are formed are inert liquid solvents such as hydrocarbons e.g. aliphatic hydrocarbons, such as pentane, hexane, heptane, octane, 2-ethylhexane, nonane, decane, cyclohexane, 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 between wide limits such as from -50 ~C to 150 ~C, preferably from 20 ~C to 80 ~C. 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 0.5 to 10 bars.
The concentration of the initiator used to prepare the living polymer may also vary between wide limits and is determined by the desired molecular weight of the living polymer. Generally, the initiator concantration is in the range of 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 frequently depends upon the 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), with a multifunctional coupling agent. If the living polymers are all the same, the branched polymer shall be symmetric. On the other hand, if the l 33q778 living polymers are combinations of living polymers having different structures and/or 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 those disclosed in U.S. Patents - ~;
Nos. 3,281,383; 3,595,941; 3,468,972; 3,135,716; 3,078,254 and ':
. _ ~= ~ 3,594,452. Other polyfunctional coupling agents include the-- lO silicon halides, e.g. chlorosilanes, and the like disclosed in U.S.
Patent No. 3,244,664.
A much preferred coupling agent is a polyalkenyl aromatic coupling agent. Polyalkenyl aromatic coupling agents capable of forming radial and star-shaped polymers are known in the 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.
Polyalkenyl aromatic compounds that are preferably employed in this step of the process are those polyvinyl aromatic compounds which are known from e.g. U.S. Patent No. 4,010,226.
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 -~ 25 said isomers (and contains 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 polyalkenyl aromatic coupling 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 l to 15 moles, preferably from 1.5 to 5 moles are preferred. The amount, 1 33q778 which may be added in two or more stages, is usually such so as to convert at least 70~w of the living polymers into radial or star-shaped polymel-s, 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 coupling reaction step (b) temperature may also vary between wide limits, e.g., from 0 ~C to 150 ~C, preferably from 20 ~C to 120 ~C. The reaction may also take place in an inert atmosphere, e.g., nitrogen, and under pressure, e.g., a pressure of from 0.5 to 10 bars.
The radial or star-shaped polymers prepared in the coupling reaction step above are characterized by having a centre 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, preferably from 6 to 30 and more preferably from 10 to 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 terminators, e.g., water, alcohol or other reagents, for the purpose of removing the lithium radical forming the nucleus for the condensed polymer product. The product is then recovered such as by coagulation utilizing hot water or steam or both.
,,J 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.

1 33q778 ~ ~ - 18 -B-Block Compatible Oligomers For various purposes, such as enhancing tack or processibility of the compositions of the present invention, predominantly carbon-hydrogen based oligomers that are compatible with the blocks - 5 B of the branched block copolymer are incorporated into thecomposition. The oligomers include, for example, tackifying resins, plasticizers, oils, petroleum derived waxes, and combinations thereof. However, in the present invention, it is essential that the amount of the unsaturated carbon atoms from these sources be minimized. By carefully controlling the unsaturation content in the composition from these sources, the composition is capable of being cured by exposure of commercially acceptable levels of irradiation without the aid of a radiation sensitive coupling agent to promote crosslinking of the branched block copolymer therein.
The hereinbefore defined unsaturation index of the composition (UT) is equal to at most 6%, preferably at most 3%, and more preferably at most l.5%.
Normally, the oligomers contain substantially only carbon and hydrogen and 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 - 25 oligomers requires adjustment or compensation to an equivalent value based upon carbon-hydrogen oligomers. An adequate correction is to l) 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 Cl3-N.M.R. if the - structure of the oligomer is not known beforehand. In Cl3-N.M.R., the unsaturated carbon fraction is the integration of all signals from 200 ppm to lO0 ppm chemical shift relative to the intergration of all signals from 200 ppm to lO0 ppm plus 75 ppm to 5 ppm (with tetramethylsilane (TMS) at O 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, Ui. Table 2 provides a list of typical tackifying resins and oils and their corresponding unsaturation index (Ui).

-- TA~LE 2 Oligomers Oli~omer Unsaturation Index~ (%) Tackifyin~ Resins:
- EscorezCR 538(~ 1<
Regalrez~ lnl8C 6 Adtac~ ~10 ll EscorezCR' l310LCb 13 Wingtac ~ 95 14 Wingtac ~ Plusd 17 Wingtack~ 10 16 Flora ~ 85 lga Wingtac ~ 86 34 Piccova~R AP-25C 36 Oils:
Tuff 1$ 6056 1<
Sh llfl !R'371f a) Includes 5~ in oxygenated carbons which have been doubled and 9% in regular unsaturated 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 Chemical.
g) Determined utilizing C -N.M.R., except for Tufflo~ 6056 which ls determined utilizing its structure.

As earlier noted, the amount of poly(alkenyl arene) in the branched polymers may vary from 1 to 60 per cent. In general, the amount of poly(alkenyl arene) for example polystyrene in the branched polymer within the limits specified does not appreciably affect the irradiation cure dosage required even though polystyrene 1 33q778 has an unsaturation index of 75%, i.e., 75~ of the carbon atoms therein are unsaturated. The foregoing phenomena results from the polystyrene being micro-phase separated from the poly(conjugated diene) portion of the branched polymer, unlike the B block .~ 5 compatible oligomers which intimately mix therewith on a molecular - ~ level. This suggests that polymers with very small blocks or sequences of polystyrene (500 to 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 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 sequences are allowed to become small enough to allow some molecular mixing, the weight fraction of those potentially interfering blocks and sequences may be quantified, or at least estimated, and accounted for in the determination of the composition unsaturation index (~T). Alternatively, the composition unsaturation index (UT) may be maintained at lower levels in such situations to allow gel formation at low irradiation dosages without explicitly including the effect of these potentially interfering blocks and sequences in the determination . of the composition unsaturation index.
-~ l. Tackifying Resins The branched polymer or block copolymer by itself is not sufficiently tacky or sticky. Therefore, it is often necessary to - add a tackifying resin that is compatible with the elastomeric conjugated diene portion of the polymer. However, in the present invention, it is preferable that the tackifying resin have a low level of unsaturation in order to achieve low dosage radiation curing of the 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 0 to 1,000 parts per hundred rubber (phr), preferably from 5 to 500 phr and more preferably from 50 to 250 phr, so long as the prescribed limits of the composition unsaturstion index (UT) are satisfied.
Optionally, a tackifying resin that is compatible with the alkenyl arene blocks may 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 poly(conjugated diene) blocks.
Compatibility is judged by the method disclosed in U.S. Pat. No.
3,917,607. Normally, the resin should have a softening point above about 100 ~C as determined 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 0 to 200 phr, preferably from O to 50 phr. However, if appreciable molecular mixing of the A block compatible tackifying resin occurs within the B block portion of the branched block copolymer, the fraction of the tackifying resin should be factored into the determination of the composition unsaturation index (UT).
2. Plasticizers and Oils The adhesive 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 boch high saturates content and high aromatic content oils. The above 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 per cent and, more preferably, less than 15 per cent 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 200 and 10,000. Vegetable and animal oils include glyceryl esters of the usual fatty acids and polymerization products thereof.
i However, in the present invention, the best results (i.e., satisfactory cure achieved with minimum irradiation dosage) are achieved when, like the tackifying resins, the plasticers and oils contain low levels of unsaturation. Additionally, it is also preferable to minimize the aromatic contents thereof.
The amount of plasticizer and oil employed varies from 0 to -~ 2,000 phr, preferably 0 to 1,000, more preferably 0 to 250 and most : 15 preferably 0 to 60 phr, so long as 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 adhesive and flexibility to the set adhesive, and to serve as a wetting agent for bonding cellulosic fibres. The term "petroleum derived wax'~ includes both paraffin and microcrystalline waxes having melting points within the range of 54 ~C to 107 ~C as well as synthetic waxes such as low molecular weight polyethylene or Fischer-Tropsch waxes.
The amount of petroleum derived waxes employed herein varies from 0 to 100 phr, preferably 0 to 15 phr, so long as the prescribed limits of the composition unsaturation index (UT) are satisfied.
C. Crosslink Promoters (Irradiation sensitive couplin~ a~ents) Though according to the present invention, crosslink promoters are preferably avoided, they may, if desired, be utilized to possibly enhance even further the 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 agents 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 crosslinking 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; sulphur monochloride; metal oxides, such as zinc oxide and antimony oxide (promotes flame retardance); lithal~ge; 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 maleimides, 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 Hansen 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.
The amount of crosslink promoter which may be employed varies from 0 phr to 50 phr, preferably 0 phr to 15 phr. However, as earlier noted, such crosslink promoters tend to be irritants and/or toxic and are preferably avoided being that such are not necessary to achieve a satisfactory cure with an economically attractive irradiation dosage.
D. Supplementary Materials The compositions of this invention may be modified with , supplementary materials including pigments, fillers, and the like as well as stabilizers and oxidation inhibitors. Stabilizers and oxidation inhibitors are typically added to the commercially available compounds in order to protect the polymers against degradation during preparation and use of the adhesive composition. Combinations of stabilizers are often more effective, due to the different mechanisms of degradation to which various polymers are subject. Certain hindered phenols, organo-metallic compounds, aromatic amines and sulphur compounds are useful for this purpose. Especially effective types of these materials include the following:
1. Benzothiazoles, such as 2-(dialkyl-hydroxybenzylthio)benzo-thiazoles.
2. Esters of hydroxybenzyl alcohols, such as benzoates, phthalates, stearates, adipates or acrylates of 3,5-dialkyl-1 hydroxybenzyl alcohols.
3. Stannous phenyl catecholates.

4. Zinc dialkyl dithiocarbamates.

5. Alkyl phenols, e. g., 2,6-di-tert-butyl-4-methyl phenol.

6. Dilaurylthio-dipropionate.
Examples of commercially available antioxidants are "Ionox 220"
4,4-methylene-bis(2,6-di-t-butyl-phenol) and "Ionox 330"
3,4,6-tris(3,5-di-t-butyl-p-hydroxybenzyl)-1,3,5-trimethyl-* *
benzene, "Dalpac 4C" 2,6-di-(t-butyl)-p-cresol, "Naughawhite"
alkylated bisphenol, "Butyl Zimate" zinc dibutyl dithio-carbamate, and "Agerite Geltrol" alkylated-arylated bis-phenolic phosphite. From 0.01 percent to 5.0 percent by weight of one or more antioxidants is generally added to the adhesive composition.

Trade-mark - 25a -Being that such stabilizers and oxidation inhibitors are added primarily to protect the poly(conjugated diene) portion of the branched polymer, such materials shall be molecularly mixed therewith. Further, as is readily apparent from the foregoing, such materials contain unsaturation.
Thus, it is preferred that the unsaturation indices of the materials be accounted for in determining the unsaturation index of the composition (UT) when the amount thereof exceeds about 1 phr by including the multiplication product of the weight fraction (wi) thereof and its corresponding unsaturation index (Ui).

1 3~9778 _.... . ... .... ..
E. Preparation and ~se The adhesive compositions of the present invention may be applied to the substrate from a solution of up to 60% 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 of the present invention are especially suited for preparatioll as 100% solids hot melt adhesives since they give re]atively low processing viscosities, less than several hundred thousand centipoise, and adequate pot life, up to several hours, at processing temperatures of 150 ~C to 180 ~C. A
. 15 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 Korpman U.S. Pat. No. 3,984,509.
The compositions of the present invention are cured by exposure to high energy ionizing radiation such as electron beam radiation.
The high energy ionizing radiatLon 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 accelerator, 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 depressed or elevated - temperatures if desired. It is also within the spirit and scope of the invention to 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 surface 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 other hand, an oxidized surface 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 block copolymer employed and the composition unsaturation index (UT).
Suitable dosages of electron beam irradiation include l Mrad to 20 Mrad, preferably l Mrad to 7 Mrad and more preferably l Mrad to 3 Mrads. It should be noted that irradiation dosages of l Mrad and possibly less are believed attainable herein with the aid of , , r~, crosslink promoters.
_ 20 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 coatLngs and the like, which are used in the manufacture of pressure-sensitive adhesive tapes.
The features and advantages of the present invention are ~ further illustrated by the accompanying drawings, to which is further referred to in the examples. In these drawings:
Figure l is an x-y plot of Polymer Gel (~) versus Wéight Average Molecular Weight (Mw) of the polydiene at an electron beam : 35 (EB~ dose of 3.2 Mrad.

_. .. ~, .. , .. . ~ ., ) Figure 2 is an x-y plot of Polymer Gel (%) versus Mw of the polydiene at an EB dose of 5.3 Mrad.
Figure 3 is an x-y plot of Polymer Gel (%) versus Mw of the polydiene at an EB dose of 7. 5 Mrad.
Figure 4 is an x-y plot of R. T. Holding Power to Steel-utilizing a 500 g weight (min.) versus Polymer Gel (%).
Figure 5 is an x-y plot of SAFT-utilizing a 500 g weight (~C) versus Polymer Gel (%).
Figure 6 is an x-y plot of Polymer Gel (%) versus EB dose (Mrad) at various UT.
Figure 7 is an x-y plot of Polymer Gel (%) versus Composition Unsaturation Index, UT, (%) at various EB doses.
Figure 8 is an x-y plot of SAFT-utilizing a 500 g weight (~C) versus Polymer Ge]. (%)~
Figure 9 is an x-y plot of 95 ~C Holding Power utilizing a lkg.weight (min.) versus Polymer Gel (%).
Figure 10 is an x-y plot of 95 ~C Holding Power utilizing a 500 g weight (min.) versus Polymer Gel (~).
More particularly, the Figures 11-21 are relating to the preferred compositions of the present invention, comprising the hereinbefore described branched block copolymers, comprising at least two polymer blocks A, each of said blocks A being at least predominantly a polymerized alkenyl arene block, and at least one polymer block B, being at least predominantly a polymerized conjugated diene block, wherein one block B is situated between said at least two blocks A, each of the blocks A having a weight average molecular weight of 3,000 to 125,000 and each of the B
blocks having a weight average molecular weight of 15,000 to 250,000, said blocks A comprising from 1 to 55 per cent by weight of said branched block copolymer and said blocks B having a total weight average molecular weight of at least 0. 3 million.

Figure 11 is an x-y plot of Polymer Gel (%) versus Composition Unsaturation Index, VT, (%) at various electron beam irradiation dosages.
Figure 12 is an x-y plot of SAFT (~C) versus Polymer Gel (%).
Figure 13 is an k-y plot of 95 ~C Holding Power utilizing a 1 kg.weight (minutes) versus Polymer Gel (%).
Figure 14 is an x-y plot of 95 ~C Holding Power utilizing a 500 g weight (minutes) versus Polymer Gel (%).
Figure 15 is an x-y plot of Polymer Gel (%) versus Composition Unsaturation Index, UT, (%) at various electron beam irradiation dosages.
Figure 16 is an x-y plot of Polymer Gel (%) versus Composition Unsaturation Index, UT, (%) at various electron beam irradiation dosages.
Figure 17 is an x-y plot of Polymer Gel (%) versus Composition ~ Unsaturation Index, UT, (%) at various electron beam irradiation dosages.
Figure 18 is an x-y plot of Polymer Gel (%) versus Composition Unsaturation Index, UT, (%) at an electron beam irradiation dose of 2.8 Mrad.
Figure 19 is an x-y plot of Polymer Gel (%) versus Composition . Unsaturation Index, UT, (%) at various electron beam irradiation dosages.
Figure 20 is an x-y plot of SAFT (~C) versus Polymer Gel (%).
Figure 21 is an x-y plot of 95 ~C Holding Power utilizing a 1 kg.weight (min.) versus Polymer Gel (%).
Examples The invention is further illustrated by means of the following illustrative exa~ples, which are given for the purpose of illustration alone and are not meant to limit the invention to the particular reactants and amounts disclosed.
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 and casting the formulations onto 25 micron thick Myla ~ sheets. After air dryinv, n a hood for 1 hour, the samples were dried in a 40 ~C
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 humidity (25 ~C, 504 relative humidity) prior to electron beam curing. Electron beam (EB) curing was done using an Energy Sciences laboratory model CB150 Electocurtain~ system. 165Kev electrons and an inert atmosphere were used. The EB dose was varied by adjusting the magnitude of the electron beam current. The beam was directed against the adhesive surface. Testing was done to determine the test adhesives radiation responsiveness, solvent resistance, and high temperature performance. These 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 per cent of the polymel- that is not soluble in toluene and quantifies the covalent network formation caused by the radiation treatment.
Vnirradiated SIS and SBS based PSA's will completely 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 (SAFT): SAFT is defined as the temperature at which 1 in. x 1 in. overlap shear bond of the test adhesive tape to a Myla ~ substrate fails under a specified load, when placed in a cabinet whose temperature is increased by 22 ~C per hour. A load of 500 g was utilized.
3) 95 ~C Holding Power: 95 ~C Holding Power is the time at which a 1 in. x l in. overlap shear bond of the test adhesive tape ".-~, 1 33q778 to a Myla ~ substrate fails under a specified load when placed in a cabin~t ~hose temperature is held constant at 95 ~C Loads of 500 grams and 1 kilogram were used in the examples.
4) Room Temperature Holding Power to Steel: R.T. Holding Power to Steel is the time at which a 1 in. x 1 in. overlap shear bond of the test adhesive tape to steel fails under a specified load. A load of 500 grams was used in the examples.
In the examples 1 and 2, the following materials were employed:
I. Branched Polymers:
A. Polymer 1: A star-shaped isoprene polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having about 11 arms, a weight average molecular weight _, , , ,., . . , ~ .
of about 0.36 million, a 25% viscosity in toluene of 300 centipoise and less than 10% vinyl content (i.e., 3,4-polyisoprene).
B. Polymer 2: A star-shaped isoprene polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having about 15 arms, a weight average molecular weight of about 0.38 mil]ion, a 25% viscosity in toluene of 250 centipoise and less than 10% vinyl content (i.e., 3,4-polyisoprene).
C. Polymer 3: A star-shaped isoprene polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having about 19 arms, a weight average molecular weight of about 0.88 million, a 25% viscosity in toluene of 1040 centiposie and less than 10% vinyl content (i.e., 3,4-poly-isoprene) D. Polymer 4: 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, a 25~ viscosity in toluene of 1320 centipoise and less than 10~ vinyl content (i.e., 3,4-polyisoprene).
II. B-Block Compatible Resins and Oil:
A. Escore ~ 5380: A hydrogenated hydrocarbon resin from Exxon Chemical. A solid resin with Tg of about 29 ~C and a softening point of 80 ~C.

~ 339778 B. Regalre ~ 1018: A hydrogenated hydrocarbon resin from Hercules. A liquid with a Tg of about -25 ~C and a softening point of 18 o r C. Adtac~ B10: A aliphatic hydrocarbon resin from Hercules.
A liquid resin with a Tg of about -48 ~C and a softening point of 10 ~C.
D. Wingtack~ 95: A C5 hydrocarbon resin from Goodyear Chemical. A solid resin with a Tg of about 51 ~C and a softening point of 95-105 ~C.
E. Piccova ~ AP25: A low molecular weight alkylaryl resin derived from aromatic petroleum feedstocks from Hercules. A liquid resin with a Tg of about -21 ~C and a softening point of 25 ~C.
III. Stabilizers and Antioxidants A. Polygard~ HR: A tris(nonylated phenyl) phosphite from Uniroyal, Naugatuck Chemical Division, U.S.A., described as being a tris(mixed mono- and di-nonylphenyl) phosphite (Polygard Technical Bulletin No. 15; March 1964, ex Uniroyal).
Example l: Effect of Polymer Molecular Wei~ht In this example, Polymers 1, 2, 3, and 4 were formulated using only Wingtac ~ 95, Samples A-D, as shown in Table 3 to give a fixed polymer to oligomer (tackifying resin) ratio of 53:47 and a composition unsaturation index, UT, of 6.5~. Test films of each of these samples were sub;ected to varying doses of electron beam radiation, as shown in Table 3, and evaluated.
As is readily apparent from Table 3 and Figures 1-3, an increasing degree of cure is obtained, at any given dosage, as the weight average molecular weight (Mw) of the polymer is increased.
To obtain a useful degree of cure, about 60~ polymer gel content, at 3.2 Mrad (Figure 1), the polyisoprene Mw needs to be at least 0.8 million; at 5.3 Mrad (Figure 2), the Mw needs to be at least 0.4-0.5 million; at 7.5 Mrad (Figure 3), the Mw needs to be at ~ least 0.2-0.3 million. To achieve a very good cure of 80~ polymer _ gel content or above at 3.2, 5.3 and 7.5 Mrads respectively, the polyisoprene Mw's evidently must be at least l.l, 0.7, and 0.5 million, respectively. Thus, it is not possible to achieve ; ~
~ s ~.:

t 339778 satisfactory cure at less than 7 Mrads using a predominantly l,4 polyisoprene star polymer having a Mw of less than about 0.3-0.5 million, when using a conventional type formulation i.e., one with a UT ~f the 6.5% or more.
Figures 4 and 5 graphically present the relationship of room temperature Holding Power to steel using a 500 g weight and SAFT to Myla ~ using a 500 g weight, respectively. Satisfactory properties . are achieved at about 60% polymer gel content and better yet at - about 80% gel content.
Also in this example is a comparison using the same polymer, Polymer 3, between a composition with a UT of 0.4%, Sample E, to a composition with a UT of 6.5%, Sample G. This comparison is in Table 3 and shown in Figure 6. From the fit of the data in Figure 6, it is evident that by reducing the composition unsaturation index from 6.5% to 0.4% the polymer gel content at any dose in the 3.2-7.5 Mrad range increases the gel by 20%. This means that with a very low UT value the minimum molecular weight for satisfactory cure at less than 7 Mrads is 0.3 million. Thus, if the amount of the 3,4 content of the polyisoprene is increased or the polydiene is polybutadiene, good cures are possible at a Mw as low as 0.3 million.
Example 2: Effect of Composition Unsaturation In this example, Polymer 4 was formulated with various tackifying resins as shown in Table 4, at a fixed polymer to tackifying ratio of 45:55, to obtain adhesive compositions Samples H, J, and K having the same B block/resin Tg, but varying the composition unsaturation index. Test films of each of these samples were subjected to varying doses of electron beam radiation, as shown in Table 4, and evaluated. The B block/resin Tg was calculated using the Fox equation; namely, wi 1 i Tgi Tg As is readily apparent from Table 4 and Figure 7,-satisfactory cure is obtained at lower irradiation dosages as the composition unsaturation index is decreased. For example, referring to Figure 7, a gel content of 74% is obtained at UT of apart 12% at 4.8 Mrads while only 2.9 Mrads is needed at a UT of about 6%, and only 1.9 Mrad is needed at a UT of about 0.4%. These results demonstrate the beneficial effect of decreasing the composition unsaturation index to 6.0% and below to achieve dramatic reductions in the required irradiation dosage to achieve equivalent levels of cure.
Figures 8, 9 and 10 graphically present the relationship of SAFT to Mylar-500 g weight, and 95 ~C Holding Power to Mylar-l kg and 500 g weights respectively. Improved SAFT values are obtained at 60% gel or greater and 95 ~C Holding Power is dramatically increased between about 70% and about 80% polymer gel content.

.

Formulation(w) Sample A B _ D
Mw Viscosity Polymer (million) (CP) 1 .36 300 53.4 2 .38 250 53.4 3 .88 1040 53.4 53.4 4 1.2 1320 53.4 Oligomer:
Wingtack~ 95 46.6 46.6 46.646.6 Escorez@ 5380 _ 46.6 Total 100.0100.0 100.0100.0100.0 Composition Unsaturation Index, UT (~) 6.5 6.5 6.56.5 0.4 Polymer Gel Content (~' Irradiation Dosage (Mrad) O O O O O O
3.2 5 3 68 85 89 5.3 13 61 83 97 96 i.5 60 79 74 96 94 .

R.T. Holding Power-Steel -500g (Minutes) Irradiation Dosage (Mrad) 5.3 334 3212>4000>4000 >4000 SAFT -Mylar~ C
500~ (~C) Irradiation Dosage (Mrad) 0 38< 38<38< 38< 38<
5.3 59 67 130 138 157 a) Data plotted in Figures 1, 2, and 3 for Samples A-D. Figure 6 shows comparison between Samples C and E.
b) Data plotted in Figure 4 for Samples A-D.
c) Data plotted in Figure 5 for Samples A-D.
d) Polymers 1, 2, 3 and 4 known to have zero gel. Polymer Gel Content test not used for Zero Dose Adhesives.

.-~Formulation (%w) Sample .-- H J K
- Mw Polymer(million) Polymer 4 1 2 44.90 44 90 44.90 Oligomer:
Escorez~ 5380 53.87 Regalrex~ 1018 1.00 Wingtack~ 95 45.19 33.31 Adtack~ B-10 9.58 Piccova ~ AP-25 16.56 Polygard~ HR 0 23 0.23 0.23 Total lO0.00lO0.00 100.00 Composition Unsat~n-ation Index, UT (%) 0.4 7.4 11.4 Polymer Gel Content (%) Irradiation Dosage (Mrad) 1.9 74 0 2.9 83 79 57 4.8 88 81 71 ., , TABLE 4 (Cont'd) Formulation (%w) Sample H J K
SAFT-Myla 500~ (~C) Irradiation Dosage (Mrad) 0 38< 38< 38<

2.9 99 68 63 ~l 8 117 109 95 95 ~C Holding Power -Myla ~ - 1 k~ (minutes) Irradiation Dosage (Mrad) O 1< 1< 1<
1.9 30 1< 1<
2.9 113 15 10 4.8 430 113 43 95 ~C Holding Power -Myla ~ - 500g (minutes) Irradiation Dosage (Mrad~
1.9 583 6 7 4.8 >1000 400 103 a) Data plotted as Figure 7.
b) Data plotted as Figure 8.
c) Data plotted as Figure 9.
d) Data plotted as Figure 10.

: :-i339778 In the subsequent examples 3-6, the following materials were employed:
I. Block Copolymers:
A. Polymer 1: A symmetric star-shaped SIS polymer from Shell Development Company prepared using an alkenyl arene based coupling agent, and having 18 arms, a weight average molecular weight of 1.2 million, and a polystyrene content of 10% by weight.
B. Polymer 2: An asymmetric star-shaped SIS polymer from Shell Development Company prepared using an alkenyl arene based 10 coupling agent, and having 18 arms, a weight average molecular weight of 1.2 million, and a polystyrene content of 10% by weight.
C. Polymer 3: A symmetric radial SBS polymer from Shell Chemical Company prepared using a tetrafunctional coupling agent, having 4 arms, a weight average molecular weight of 0.18 million 15 and a polystyrene content of 23% by weight.
D. Polymer 4: A linear SBSBS polymer from Firestone (Stereon~ 840A) believed to be sequentially formed, and having a weight average molecular weight of O.10 million, and a polystyrene content of 43~ by weight. See U.S. Pat. No. 4,526,577.
E. Polymer 5: A commercially available star-shaped SIS
polymer from Shell Chemical Company (Krato ~ D 1320X rubber) prepared using an alkenyl arene based coupling agent and having greater than 6 arms, but less than 40 arms, a weight average molecular weight of 1.2 million, and a polystyrene content of 10%
25 by weight.
II. B-Block Compatible Resins and Oil:
A. Tufflo~ 6056: A paraffinic process oil from Atlantic Richfield Co. A liquid with a Tg of -64 ~C and a molecular weight of 530.
B. Escorez~ 5380: A hydrogenated hydrocarbon resin from ~ Exxon Chemical. A solid resin with Tg of 29 ~C and softening point of 80 ~C.

~ r~

1 '39778 C. Shellflex~ 371: A paraffinic-napthenic oil from Shell Chemical. A liquid with a Tg of -64 ~C.
D. Regalrez~ 1018: A hydrogenated hydrocarbon resin from Hercules. A liquid resin with Tg of -25~C and softening point of 18 ~C.
E. Adtac~ B10: An aliphatic hydrocarbon resin from Hercules. A liquid resin with Tg of about -48 ~C and softening point of 10~C.
F. Escorez~ 1310LC: A C5 hydrocarbon resin from Exxon Chemical. A solid resin with Tg of 42 ~C and softening point of 94 ~C.
G. Wingtac ~ 95: A C5 hydrocarbon resin from Goodyear Chemical. A solid resin with Tg of 51 ~C and softening point of 95 ~C.
H. Wingtack~ 10: A C5 hydrocarbon resin from Goodyear Chemical. A liquid resin with a Tg of -28 ~C and a softening point of 10 to 15 ~C.
I. Foral~ 85: A glycerine rosen ester resin from Hercules.
A solid resin with Tg of 40 ~C and softening point of 85 ~C.
J. Piccovar~ AP25: A low molecular weight alkylaryl resin derived from aromatic petroleum feedstocks from Hercules. A liquid - resin with Tg of -21 ~C and softening point of 25 ~C.
III. Stabilizers and Antioxidants:
A. Iono~: A phenolic antioxidant from Shell International having the formula 2,6-di-tertiary-butyl-4-methyl phenol (BHT).
B. Antioxidant 33 ~: A phenolic antioxidant from the Ethyl Corporation having the formula 1,3,5-trimethyl-2,4,6-tris-(3',5'-di-tertiary-butyl-4'-hydroxy-benzyl) benzene.
C. Polygard~ HR: A tris-(nonylated phenyl) phosphite from Uniroyal, Naugatuck Chemical Division, U.S.A., described as being a tris-(mixed mono- and di-nonylphenyl) phosphite (Polygard Technical Bulletin No. 15; March 1964, ex Uniroyal).
Example 3: Effect of Composition Unsaturation In this example, Polymer 1 was formulated with various tackifying resins as shown in Table 5 at a fixed polymer to tackifying ratio of 45:55 to obtain adhesive compositions Samples 1 33q778 A, B and C having the same B block/resin Tg, but varying the composition unsaturation index (UT). The weight average molecular - weight (Mw) of the diene portion of Polymer 1 was l.l million, since the weight average molecular weight of the entire polymer was about 1.2 million and the polystyrene content was 10%. Test films of each of these samples were subjected to varying doses of electron beam radiation, as shown in Table 3, and evaluated. The B
block/resin Tg, was calculated using the Fox equation; namely, _ \ wi Tg ~ i Tgi As is readily apparent from Table 5 and Figure 11, satisfactory cure is obtained at lower irradiation dosages as the composition unsatu]ation index (UT) is decreased. For example, referring to Figure 11, a gel content of 70% is obtained at 4.8 Mrads at a UT of about 11.2%, while only 2.9 Mrad is needed at a UT
of about 5.0%, and only 1.9 Mrad at a UT of about 0.8%. Likewise, referring to Figure 11, a gel content of 80% is obtained with 4.8 Mrad at a UT of about 6.5%, while only 2.9 Mrad is needed at a UT
of about 1.9%, and only l.9 Mrad at a UT of about 0.1%. UT is about 0.8 at 1.9 Mrads, 6.0 to 2.9 Mrad and 11.2 at 4.8 Mrad.
Likewise, referring to Figure 11 at a gel content of 80%, UT is about 0.1 at 1.9 Mrad, 1.9 at 2.9 Mrad, and 6.5 at 4.9 Mrad. These results demonstrate the beneficial effect of decreasing the composition unsaturation index (UT) to 6.0% and below by achieving dramatic reductions in the required irradiation dosage to achieve equivalent levels of cure.
Figures 12, 13 and 14 graphically present the relationship of SAFT and 95 ~C Holding Power using l kg and 0.5 kg weights to Polymer Gel Content, respectively. For the most part, satisfactory propertie~s are achieved at about 60% and better yet at about 70%
polymer gel content.

1 33~778 Sample Formulation (phb) A B C
Polymer:
Polymer 1 45.00 45.00 45 00 Oligomer:
Escorez~5380 69 30 RegalrezQ 1018 5.70 Wingtack~ 95 42.90 34.10 Adtac~ B-10 12.10 Piccovar ~ AP-25 20.90 Total 100.00 100.00 100.00 Antioxidant:
.--~~ Polygard )HR 0.23 0.23 0.23 ,~

Composition Unsaturation Index, UT (%) 0.8 7.3 12.3 .~

Polymer Gel Content (~) Irradiation Dosage (Mrad) l.9 70 1 2 2.9 85 55 7 4.8 92 80 67 ~ 3~9778 TABLE 5 (Cont'd) Samplef A B C
SAFT-Mylar~ (~C~
Irradiation Dosage (Mrad) 1.9 1]~4 95 78 2.g 118 106 81 4.8 117 127 105 95 ~C Holding Power Mylar~-l K~ (min.) Irradiation Dosage (Mrad) 1.9 166 29 100 2.9 378 116 10 4.8 >1000 410 63 ~ .
~~ 95 ~C Holding Power Mylar~ -0 5 K~ (Mrad) Irradiation Dosage (Mrad) 1.9 504 108 12 4.8 >1000 >1000 120 a) Parts per hundred blend, wherein the blend constitutes the polymer component plus the oligomer component. As between the polymer and the oligomer components, phb is equivalent to weight per cent thereof.
b) Data plotted as Figure 11.
c) Data plotted as Figure 12.
d) Data plotted as Figure 13.
e) Data plotted as Figure 14.

_.... .. .. . .

f) Samples B and ~ are outside the scope of the present invention.

Example 4- Effect of Polymer Structure and Molecular Weight In this example, Polymer 2 (star with polyisoprene Mw of about 1.1 million), Polymer 3 (radial with polybutdiene Mw of about 0.14 million), and Polymer 4 (linear with polybutadiene Mw of about 0.06 million) were formulated with various tackifying resins as shown in Table 4 at a fixed polymer to tac~ifying resin ratio of 50:50 to obtain Samples D-H, J-N, P and Q. By utilizing different tackifying resins, the composition unsaturation index (UT) was varied. Test films of each of these samples were subjected to varying doses of electron beam radiation, as shown in Table 6, and evaluated with respect to polymer gel content.
Several things are readily apparent from Table 6 and Figures 15-17. Firstly, regardless of the molecular weight of the poly(conjugated diene) portion of the respective polymer and associated structure, the effect of reducing the composition unsaturation index (UT) on reducing the irradiation dosage to effect equivalent levels of polymer gel content is evident even with relatively low molecular weight linear polymers. For example, in Samples M and N utilizing Polymer 4 (linear) at 8.6 Mrad dosage (Figure 17), a dramatic increase in polymer gel content is observed, from 6% to 53%, when UT is reduced from 3% to 0.4%. A
similar dramatic increase in polymer gel content is observed, from 19% to 73%, in Samples K and L at 8.6 Mrad dosage (Figure 16) when UT is reduced from 9.5% to 7%. However, practically speaking, irradiation dosages of greater than about 7 Mrads tend to be commercially unattractive. As such, there is considerable desirability to maintain irradiation dosages to at most about 7 Mrads, if not much lower when radiation sensitive substrates are being utilized.
Secondly, the role of the molecular weight of the polymers on election beam curing is very evident. In particular, samples 1 33q778 utili~ing Polymer 2 (polyisoprene Mw of about 1.1 million) will cure to about 73% polymer gel content at 3.2 Mrads when the UT is about 6.0%l while samples utilizing Polymers 3 and 4 thaving polybutadiene weight average molecular weights of only 0.14 and 0.06 million, respectively) do not form any gel at the same dose;
this is despite the fact that polybutadiene has a greater tendency to cure than polyisoprene. Although the polybutadiene molecular weight of Polymer 3 is too low to achieve about a 70~ polymer gel content at a UT of about 6.0% with less than about 7 Mrads (seen in Figure 16 where about 8.6 Mrads are required), it is still evident that Polymer 3 is considerably better than linear Polymer 4 that has a even smaller polybutadiene molecular weight. Considering how much better Polymer 3 is over Polymer 4, it is easy to extrapolate that a branched polystyrene - polybutadiene polymer having a polydiene molecular weight of about 0.3 million will readily crosslink at 7 Mrads when formulated to a UT of at most 6%.
Based on the foregoing, it is expected that linear polymers having such a minimum molecular weight poly (conjugated diene) portion or greater would adequately cure at lower dosages.
However, a disadvantage of such an increase in the molecular weight of a linear polymer is that the viscosity of compositions incorporating such a polymer, either in the melt or solution, would be undesirably excessive : ~

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~ 339778 ., ~.
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Example 5: Effect of UT at Constant EB Dose (with a Commercial Polymer) ~a this example, Polymer 4 (commercial Kraton~ Dl320X Rubber with polyisoprene Mw of about l.l million) was mixed with various oligomers, such as tackifying resins and oils, as shown in Table 7 at a fixed polymer to oligomer ratio of 50:50 to obtain samples R
though Z. By utilizing different oligomers, the composition unsaturation index (UT) was varied. Test films of each of the samples were subjected to 2.8 Mrad of elecron beam (EB) radiation ~ 10 as shown in Table 7, and evaluated with respect to polymer gel content.
It is readily apparent from Table 7 and Figure 18 that compositions having a UT of greater than 6 0% do not cure satisfactorily, having less than 60~ polymer gel content. Thus, if _. . 15 2.8 Mrads was the maximum dosage available due to a combination of equipment available and line speed requirements, a conventionally formulated composition (i.e. UT is greater than 6%) would not cure adequately to give ~ood performance. Likewise, if the composition were being coated onto a substrate that was significantly damaged by more than 2.8 Mrads of EB energy, the conventionally formulation (i.e. UT is greater than 6%) based upon commercial Kraton Dl320X
rubber could not be used successfully. However, at a UT of at mOSt 6.0%, a 60% or greater polymer gel content could be achieved; below a UT of about 3.0%, a 75% or greater polymer gel content could be obtained, and below a UT of about l.5, a 80% or greater polymer gel content could be achieved.

~ 339778 Composition Polymer Gel Unsaturation Content(~)b at Sample Oli~omerIndex, UT (~) 2.8 Mrad Dose R Tufflo~ 6056 0.4 92 S Escorezo~ 5380 0.4 84 T Shellflex~ 371 0.5 78 U Regalrez~ 1018 3.0 76 V Adtac~ B10 5.5 65 W Escorez~ 1310LC 6.5 24 X Wingtack~ 95 7.0 32 Y Wingtack~ 10 8.0 11 Z Floral~ 85 9 5 7 a) Formulation (phb) Polymer 5 (Kraton~ D1329X) 50 Oligomer 50 Total 100 Antioxidant:
Ionol~ (B~T) 0.15 Antioxidant 330 0.20 b) Data plotted as Figure 18.
c) Part per hundred blend, wherein constitutes the polymer component plus the oligomer component.

Example 6: Effect of Composition Unsaturation with Commercial Polymer In this example, Polymer 4 (commercial Kraton~ Dl320X rubber) was formulated with various combinations of oligomers as shown in ~ 5 Table 8 at a fixed polymer to oligomer ratio of 45:55 to obtain ~~ samples AA through GG. The resins were combined so as to maintain ' :

the T of the diene resin mixture at -28 ~C. By using these various combinations of tackifying resins and oils, the UT was varied from 0.5 to 8.3.
Behaviour similar to that seen in Example 1 is seen in Table 8 and in Figures 19-21. Satisfactory cure is obtained at lower irradiation dosages as the composition unsaturation index is decreased. For example, referring to Figure 19, by using the most preferred range of UT values, a gel content of 65-85% can be obtained at a very attractive dose of only 1.7 Mrads. A
conventional formulation with a UT of greater than 6% could not begin to be cured satisfactorily at such a low dose. In fact, as seen in Figure 19, a conventionally formulated adhesive using Polymer 4 that has a UT value of 8% requires a dose of about 6.5 Mrad to give the same degree of cure and properties as sample AA
(UT of about 0.5%) cured at 1.7 Mrad.
Figures 20 and 21 graphically represent the relationship of SAFT and 95 ~C Holding Power using 1 kilogram weights to Polymer Gel Content, respectively. Steady improvements in SAFT (Figure 21) are seen as the Polymer Gel Content increases. Although the 95 ~C
Holding Power test utilizing a 1 kilogram weight is a very severe test, significant improvements are achieved when the Polymer Gel Content reaches 60 to 70%, with very dramatic improvements occurring at Polymer Gel Contents of 80% and greater.
~hile 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. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

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Table g - (Continued~

Sampie Formulation (phb)a AA BB CC DD _E FF GG
SAFT - Mylar~ (~C)c Irradiation Dosage (Mrad) 1.7 116 1û4 113 94 9~ 97 93 3.8 117 112 109 1141ll~ 116 101 6.5 120 113 115 11311 :l 122 116 8.0 127 114 119 105 1,5 114 114 95~C Holding Power d Mylar9 - 1 Kg (min.) Irradiation Dosage ~Mrad) 1.7 150 50 120 10 3~ 50 26 3.8 ~1000 670 900 180 180 165 125 "
6.5 ~1000 800 >1000 198 191 290 128 8.û 1 >1000 >1000 >1000 315 650 500 140 a) Parts per hundred blend, wherein the blend constitutes the polymer component plus the oligomer component; Tg tFox) of B-block/oligomer is -28~C.
b) Data plotted as Figurel~. (Polymer Gel Content versus U ).
c) Data plotted as rigure 20 (SAFT versus Polymer Gel Con~ent).
d) Data plotted as Figure 21. (95~C Holding Power versus Polymer Gel Content).

BAP884801 c~

Claims (21)

1. A cured composition possessing good processability, solvent resistance and high temperature cohesive strength prepared by the high energy ionizing radiation initiated curing of a polymer composition, said polymer composition comprising:
(a) a branched block polymer as represented by the general structural formula wherein Q represent a group [BA] or [Bm (AB)n Ap], in which A represents a polymer block which is predominantly a polymerized C8-C16 alkenyl arene having a molecular weight of from 1,000 to 125,000;
B represents a polymer block which is predominantly a polymerized C4-C12 conjugated diene, the total average molecular weight of the conjugated diene portion of the branched polymer being at least 0.3 million;
X represents a residual group of a polyfunctional coupling agent having three or more functional groups;
r is an integer equal to 0 to 20, q is an integer equal to 0 to 40, s is an integer equal to 0 to 40, 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 or 1, and r ~ q + r + s ~ 40, (b) 0 to 2,000 parts by weight per 100 parts by weight of said branched polymer of an oligomer compatible with the conjugated diene portion of said branched polymer, (c) wherein said composition has an unsaturation index of at most 6.0% said composition unsaturation index being defined by the following expression t .SIGMA. (Wi) (Ui) = UT
i = 1 wherein:
"i" represents a particular oligomer in the composition, "wi" represents the weight percent of the particular oligomer based on the total weight of components (a) and (b) of said composition, "Ui" represents the unsaturation index of the particular oligomer, "t" represents the total of the oligomer in the composition, and "UT" represents the unsaturation index of the composition.

2. A cured composition possessing good processability, solvent resistance and high temperature cohesive strength prepared by the high energy ionizing radiation initiated curing of a polymer composition, said polymer composition comprising:
(1) a branched block copolymer which comprises (a) at least two polymer blocks A, each of said blocks A
being predominantly a polymerized C8-C16 alkenyl arene block, and (b) at least one polymer block B, said block B being predominantly a polymerized conjugated diene block, (c) wherein (i) said at least one block B is between said at least two blocks A
(ii) each of said blocks A having a weight average molecular weight of about 3,000 to about 125,000, (iii) each of said blocks B having a weight average molecular weight of about 15,000 to about 250,000, (iv) said blocks A comprise from about 1 to about 55 percent by weight of said branched block copolymer, and (v) said blocks B having a total weight average molecular weight of at least 0.3 million, and (2) about 0 to about 2,000 parts by weight per 100 parts by weight of said branched block copolymer of at least one oligomer compatible with said block B, (3) wherein said composition prior to irradiation having an unsaturation index of at most 6.0%, said composition unsaturation index being defined by the following expression:
t .SIGMA. (W1) (U1) = UT
1 = 1 wherein 1, w1, U1, t, and UT are as defined in claim 1.

3. The composition as defined in claim 1, wherein said high energy ionizing radiation is electron beam irradiation.

4. The composition as defined in claim 3, wherein the amount of radiation employed is between 1 and 20 Mrads.

5. The composition as defined in claim 4, wherein the amount of radiation employed is between 1 and 7 Mrads.

6. The composition as defined in claim 5, wherein the amount of radiation employed is between 1 and 3 Mrads.

7. The composition as defined in claim 1, wherein said composition unsaturation index, UT, is at most 3%.

8. The composition as defined in claim 5, wherein said composition unsaturation index, UT, is at most 1.5%.

9. The composition as defined in claim 1, wherein said branched polymer is a radial polymer having at least three arms.

10. The composition as defined in claim l, wherein said branched polymer is a star polymer having at least six arms.

11. The composition as defined in claim 1, wherein said branched block copolymer is represented by the general structural formula wherein "A" represents a polymer of block A, "B" represents a polymer of block B, "X" represents a residual group of a polyfunctional coupling agent having three 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 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 40, and 3 ~ q + r + s ~ 40.

12. The composition as defined in claim 1, wherein said branched polymer is a block copolymer as represented by the general structural formula wherein "A" represents a polymer block A, said block A being predominantly a polymerized C8-C16 alkenyl arene;
"B" represents a polymer block B, said block B being predominantly a polymerized conjugated diene, "X" represents a residual group of a polyfunctional coupling agent having three or more functional groups, "q" is an integer equal to 0 to 40, "r" is an integer equal to 0 to 20, "s" is an integer equal to 0 to 40, and 3 ~ q + r + s ~ 40.

13. The composition as defined in claim 11 or claim 12, wherein said block A has C8-C16 alkenyl arene content of from 80 to 100 percent by weight based on said block A.

14. The composition as defined in claim 13, wherein said block A has C8-C16 alkenyl arene content of 100 percent by weight based on said block A.

15. The composition as defined in claim 14, wherein said block B has C8-C16 alkenyl arene content of from 0 to 20 percent by weight based on said block B.

16. The composition as defined in claim 15, wherein said block B has C8-C16 alkenyl arene content of 0 percent by weight based on said block B.

17. The composition as defined in claim 1, wherein said branched block copolymer has C8-C16 alkenyl arene content of from 3 to 35 percent by weight based on said branched block copolymer.

18. The composition as defined in claim 1, wherein said oligomer is 5 to 500 parts by weight per 100 parts by weight of said branched polymer.

19. The composition as defined in claim 1, wherein said oligomer is 50 to 250 parts by weight per 100 parts by weight of said branched polymer.

20. A composition according to claim 1 wherein said branched block polymer comprises polyisoprene blocks.

21. A composition according to claim 1 wherein said branched block polymer comprises polystyrene and polyisoprene blocks.