Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
  • C08K5/3415—Five-membered rings

Definitions

• This invention relates to compositions of matter classified in the art of chemistry as bis-, tri- and higher poly-maleimides, as bis-, tri- and higher poly- citraconimides, as silicone elastomers, as p-phenylenediamine based antiozonants and as sulfur containing organic compounds which are accelerators for the sulfur curing (crosslinking) of polymers which are curable/crosslinkable by sulfur and also sulfur compounds which are polysulfide polymers.
• the invention also relates to compositions containing them, to processes for their use and to the products produced by such processes.
• Polymers and copolymers crosslinked with free radical initiators, organic peroxides and/or azo initiators, are known to have superior properties, particularly to polymers crosslinked by sulfur cure. These properties include high heat ageing resistance, low compression set, decreased staining of metal or coated metal sheet and easy production of colored products which have color stability during crosslinking and during long periods of use. These properties make use of peroxide cure of great practical importance particularly because crosslinking is through a carbon carbon bond rather than through a sulfur containing linkage and this bonding difference is responsible for the improved heat aging and compression set.
• the drawback for cure of polymers with free radicals from organic peroxides and azo initiators has always been that if air is not excluded from the surface of the material during cure, a tacky surface due to cure inhibition by the molecular oxygen in the air results.
• U. S. Patent 4,983,685 discloses the use of compounds selected from the following classes: (a) imidazole compounds, (b) thiourea compounds, (c) thiazole compounds, (d) thiuram compounds, (e) dithiocarbamate compounds, (f) phenol compounds, (g) triazole compounds and (h) amine compounds which are accelerators for sulfur vulcanization in the optional presence of antioxidants, anti- ageing compounds and the like for elastomers for reducing surface tack in the peroxide cure of elastomers in the presence of molecular oxygen.
• N,N'-m-phenylene bismaleimide is N,N'-m-phenylene bismaleimide.
• This is not the preferred optional coagent as a dimethacrylate compound is actually used in the examples.
• this latter bismaleimide compound might provide an enhanced effect on the ability of certain compounds of (a) through (h) to reduce surface tack during free radical cure in the presence of molecular oxygen.
• the use of the various sulfur accelerators, in particular with peroxide does provide tack free or reduced tack surfaces for the cured polymers in this reference but the important physical properties expected from a peroxide cure are also reduced. There is no recognition in U.S.
• Patent 4,983,685 that if the silicone elastomers, bismaleimides and biscitraconimides of the present invention are used in combination with p-phenylene diamine based antiozonants, sulfur containing sulfur vulcanization accelerators and antioxidants and/or polysulfide polymers in free radical cures of polymers, that tack free surfaces and improved physical properties will result and that of all the crosslinking aids mentioned, only these particular classes of compounds have that effect. Japanese Published Patent Application No.
• Hei 9[ 1997]- 169873 discloses that antioxidants of the benzimidazole type and of the polymeric 2,2,4-trimefhyl- 1 ,2-dihydroquinoline type used in combination with standard crosslinking aids such as methacrylate esters, triallylcyanurates and maleimides, such as this present invention's preferred component N,N'-m-phenylene bismaleimide, and standard crosslinking peroxides will result in cured peroxide crosslinkable elastomers with a tack free surface in the presence of air.
• standard crosslinking aids such as methacrylate esters, triallylcyanurates and maleimides
• N,N'-m-phenylene bismaleimide such as this present invention's preferred component N,N'-m-phenylene bismaleimide
• standard crosslinking peroxides will result in cured peroxide crosslinkable elastomers with a tack free surface in the presence of air.
• U.S. Patent 4,334,043 teaches the use of surface treatment of curable polymer compositions with organo-metallic compounds, inorganic metallic salts, or lanthanides prior to crosslinking with organic peroxide crosslinking initiators in air to prevent surface tack after crosslinking. Other means of controlling surface tack are not mentioned except for the previously known techniques for surface tack free curing by simply excluding air contact with the rubber surface.
• U.S. Patent 4,814,384 and 4,973,627 disclose cures of rubber blends for tire treads and sidewalls using a combination of sulfur and peroxide cures.
• Sulfur accelerators are also employed. Coagents of any type are not mentioned, nor is cure in the presence of air discussed.
• elemental sulfur is required in the practice of these inventions. We have found, however, that the use of elemental sulfur adversely affects the final physical properties of the cured elastomer to the point where they are more typical of sulfur cure than peroxide cure.
• U.S. Patent 4,743,656 also discloses a mixed sulfur/peroxide cure agent for elastomers, which cure agent also includes sulfur accelerators as well as elemental sulfur and the peroxide. Coagents are not mentioned, nor are crosslinking in air and surface tackiness discussed.
• U.S. Patent 4,575,552 claims the use of specific combinations of hindered phenol antioxidants, metal salts of dithiocarbamates and m-phenylene- dimaleimide to provide a peroxide crosslinked polymer with superior hydrolytic and thermal stability for geothermal applications. There is no mention of crosslinking in the presence of air, air-inhibition or surface tackiness as a result of air-inhibition.
• U.S. Patent 5,849,214 discloses the use of sulfur compounds, sulfur accelerators and hydroquinones with the optional presence of crosslinking aids (coagents) in the retardation of scorch during compounding of free radical crosslinkable polymers in the presence of free radical initiators.
• crosslinking aids coagents
• Bismaleimides, and biscitraconimides are not specifically discussed nor is there any mention of the possible effect on surface tackiness during cure in the presence of molecular oxygen (air) for any of the compositions disclosed.
• composition comprising: a) At least one compound (A) selected from the group consisting of silicone elastomers and a compound having the formula (I):
• n is 1 , or 2 and R is divalent, or trivalent and is selected from the group consisting of acyclic aliphatic groups having from about 2 to 16 carbon atoms, cyclic aliphatic groups having from about 5 to 20 carbon atoms, aromatic groups having from about 6 to 18 carbon atoms and alkyl aromatic groups having from about 7 to 24 carbon atoms, and wherein those divalent, or trivalent groups may contain one or more heteroatoms selected from 0, N and S, replacing a carbon atom, or atoms, and each R ] is identical and is hydrogen or an alkyl group of 1 to 18 carbon atoms; and
• sulfur accelerators sulfur accelerators
• the tangible embodiments of the first composition aspect of the invention possess the inherent applied use characteristic of being suppressors of surface inhibition of free radical induced cure of polymers in the presence of gaseous molecular oxygen, (i.e., oxygen present in the atmosphere) thereby permitting tack free cures of polymers by free radical curing agents in the presence of air while maintaining the final physical properties associated with a conventional peroxide cure.
• gaseous molecular oxygen i.e., oxygen present in the atmosphere
• the invention provides in a subgeneric aspect of the first composition aspect of the invention, a composition formed by mixing as the essential ingredients thereof at least one member of compound (A) and at least one member of compound (B) of the first composition aspect of the invention.
• the invention provides in a second composition aspect, a composition comprising a composition as defined in the first composition aspect and a free radical initiator selected from the group consisting of organic peroxides and azo initiators.
• the tangible embodiments of the second composition aspect of the invention possess the inherent applied use characteristic of being curing or crosslinking agents for those polymers capable of being crosslinked by free radical initiators and of being capable of effecting such cures in the presence of air (molecular oxygen) without the polymer being cured experiencing surface inhibition by the presence of air (molecular oxygen), thus, providing a cured or crosslinked polymer having a substantially tack free surface without the necessity for avoiding contact of said surface with air (molecular oxygen) during cure.
• the invention provides a subgeneric aspect of the second composition aspect of the invention.
• composition being one prepared by mixing in any order, at least one member of compound (A) and at least one member of compound (B) of the first composition aspect of the invention and a free radical initiator as defined for the second composition aspect of the invention.
• the invention provides in a third composition aspect a curable composition comprising a polymer curable by free radical initiators and a composition as defined in the second composition aspect of the invention.
• the invention provides in a subgeneric composition aspect of the third composition aspect of the invention a curable composition prepared by mixing in any order at least one member of compound (A) and at least one member of compound (B) of the first composition aspect of the invention, a free radical initiator as defined for the second composition aspect of the invention and a polymer crosslinkable by a free radical initiator.
• the invention provides in a first process aspect a process for the preparation of the second composition aspect of the invention which comprises mixing in any order at least one member of compound (A) and at least one member of compound (B) of the first composition aspect of the invention and a free radical initiator as defined in the second composition aspect of the invention.
• the invention provides in a second process aspect of the invention, a process for the preparation of the third composition aspect of the invention which comprises mixing in any order at least one member of compound (A) and at least one member of compound (B) of the first composition aspect of the invention, a free radical initiator as defined in the second composition aspect of the invention and a polymer crosslinkable by a free radical initiator.
• compound (A) is selected from bismaleimides and compound (B) is selected from sulfur accelerators, where compound (A) is selected from biscitraconimides and compound (B) is selected from sulfur accelerators, where compound (A) is selected from bismaleimides and compound (B) is selected from polysulfide polymers, where compound (A) is selected from biscitraconimides and compound (B) is selected from polysulfide polymers, where compound (A) is selected from silicone elastomers and compound (B) is selected from polysulfide polymers.
• chlorinated polyethylene and/or chlorosulfonated polyethylene are included as optional supplemental ingredients in addition to compounds (A) and (B).
• the ingredients which are all in dry powder form (the LUPEROX® 231 XL is in the form of 40% by weight peroxide dispersed on calcium carbonate), may be mixed in any order and then compounded by standard methods (Banbury, two roll mill, extruder and the like) into the VISTALON® polymer.
• the Sulfads®, HVA-2 and LUPEROX 231 XL may also be compounded directly into the VISTALON either simultaneously or sequentially in any order.
• any two of the Sulfads, HVA-2 and LUPEROX 231 XL ingredients may be mixed and compounded into the VISTALON separately or simultaneously with the third ingredient. This compounding, if done separately, may also be performed in any order of ingredient addition to the polymer, but it is preferred if the peroxide is added last.
• the compounded mixture may be cured simply by placing it in a hot air oven at a suitable temperature for initiating cure by decomposition of the peroxide, conveniently, in this case, at about 365 °F (about 185°C), for a sufficient period of time to permit the desired degree of crosslinking to take place, conveniently, in this case, about
• trimaleimides and tricitraconimides as well as the higher polymaleimides and citraconimides may be prepared by analogous techniques if they are not commercially available.
• the trimaleimide, N,N',N"-(l,3,5-triazine- 2,4,6-triyl)trimaleimide has CAS number C AS(67460-81 -5).
• Some primary amines suitable for synthesis of the di, tri- and higher polymaleimides and analogous citraconimides are polyfnctional primary amines such as melamine and the various polyoxypropylene amines such as the polyoxypropylene diamines and the polyoxypropylene triamines sold under the JEFFAMINE tradename by Huntsman Corporation.
• N,N'-ethylenebismaleimide N.N'-hexamethylenebismaleimide, N,N'- dodecamethylene-bismaleimide, N,N'-(2,2,4-trimethylhexamethylene) bismaleimide, N,N'-(oxy-dipropylene)bismaleimide, N,N'-
• Biscitraconimides which may be substituted in whole or in part for the N,N'-m-phenylenebismaleimide referenced above include as representative examples:
• the biscitraconimides contemplated by the invention are all well known compounds and where not commercially available, they may be readily synthesized by methods detailed in the art.
• U.S. Patent 5,292,815 in column 4 provides a detailed list of such methods.
• the tri- and higher polycitraconimides may be prepared by analogous methods and substituted in whole or in part in the compositions of the invention and such compounds and substitutions will be understood by one of skill in the art as being a full equivalent to those specifically illustrated herein and well within the scope contemplated as equivalent by the invention.
• silicone elastomers contemplated as useful in the aspects of the invention are the peroxide crosslinkable dimethyl vinyl substituted silicone derivative elastomers which are well known in the art. See, for example, "Kirk Othmer Encyclopedia of Chemical Technology", Vol. 20, pp. 943 et seq., John
• Sulfur containing organic compounds capable of accelerating sulfur vulcanization of polymers, which are capable of being crosslinked by sulfur contemplated for use in the invention are well known in the art. Many different classes of these compounds are known and all are contemplated as equivalent.
• Vanderbilt Rubber Handbook thirteenth edition, 1990, R.T. Vanderbilt Company, Inc., publisher lists many types. Illustrative of these are derivatives of benzothiazoles, thiadiazoles, sulfenamides, sulfenimides, dithiocarbamates, thiurams, imidazoles, xanthates, and thioureas. Also included in this general class of sulfur compound sulfur accelerators are sulfides, disulfides (e.g., diallyldisulfide) polysulfides and arylpolysulfide compounds such as the amylphenol polysulfides e.g. VULTAC® products from ATOFINA Chemicals, Inc.
• disulfides e.g., diallyldisulfide
• arylpolysulfide compounds such as the amylphenol polysulfides e.g. VULTAC® products from ATOFINA Chemicals, Inc.
• one sulfur accelerator class suitable for use in the practice of the invention are salts of disubstituted difhiocarbamic acid.
• X is an ion derived from a metal selected from the group consisting of nickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium, selenium and tellurium, or X is a quaternary ammonium ion, n may vary from 1 to 6 and is equal to the number of formal positive charges on the X ion, and
• R j and R 2 are independently alkyl of 1 to 7 carbon atoms.
• Examples of the salts of disubstituted difhiocarbamic acid are: bismuth dimethyldithiocarbamate; cadmium diethyldithiocarbamate; cadmium diamyldithiocarbamate; copper dimethyldithiocarbamate; lead diamyldithiocarbamate; lead dimethyldithiocarbamate; selenium diethyldithiocarbamate; selenium dimethyldithiocarbamate; tellurium diethyldithiocarbamate; piperidinium pentamethylene dithiocarbamate; zinc diamyldithiocarbamate; zinc diisobutyldithiocarbamate zinc diethyldithiocarbamate; zinc dimethyldithiocarbamate: copper dibutyldithiocarbamate; sodium dimethyldithiocarbamate; sodium diethyldithiocarbamate; sodium dibuty
• R 3 is an alkyl group of from 1 to about 7 carbon atoms or the R 3 groups on each particular nitrogen atom may be concatenated to form, together with the nitrogen atom on which they are attached, a five, six or seven membered heterocyclic ring containing 4, 5 or 6 carbon atoms respectively and n may have a positive value from greater than zero up to 6.
• thiuram sulfur accelerators are: dipentamethylenethiuram tetrasulfide and hexasulfide; tetrabutylthiuram disulfide; tetramethylthiuram disulfide; tetraethylthiuram disulfide; tetramethylthiuram monosulfide; isobutylthiuram disulfide; dibenzylthiuram disulfide; tetrabenzylthiuram disulfide; tetraisobutylthiuram disulfide; isobutylthiuram monosulfide; dibenzylthiuram monosulfide; tetrabenzylthiuram monosulfide; tetraisobutylthiuram monosulfide.
• thiadiazoles are, but not limited to, monobenzoyl derivatives of dimercaptothiadiazole (2,5-dimethyl-1.3.4-thiadiazole); the proprietary thiadiazole of the Vanderbilt Rubber Company identified as VANAX® 189; 1,2,4-thiadiazole, 5-ethoxy-3-(trichloromethyl) thiadiazole; and alkyl mercaptothiadiazoles, e.g. methyl mercapto thiadiazole.
• M is a direct bond between two sulfur atoms, H, or an ion derived from a metal selected from the group consisting of nickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium, selenium and tellurium; and when M is H, x is 1 ; when M is a direct bond between two sulfur atoms, x is 1 or 2; and when M is an ion derived from a metal, x is equal to the formal valence of the metal ion; and if M is a direct bond between two sulfur atoms and ⁇ ; is 1 , then the second sulfur atom to which the M bond is attached is also bonded to a 4-morpholinyl radical.
• Illustrative compounds are: 2-(4-morpholinodithio) benzothiazole; benzothiazyl disulfide; 2-mercapto-benzofhiazole; 2-mercaptobenzofhiazole disulfide; sodium-2-mercaptobenzothiazolate; zinc-2-mercapto-benzothiazole; copper-2-mercaptobenzothiazolate; 2-N-cyclohexylaminobenzothiazole; N- cyclohexylamino-2-benzothiazole polysulfide; 2-bisbenzothiazole-2;2-polysulfide and 2-bisbenzothiazole-2, 2-disulfide; bis(2,2'-benzothiazyldislufide).
• the sulfenamide accelerators are also well known. Illustrative examples are: N-oxydiethylene-2-benzothiazole sulfenamide; N-oxydiethylene fhiocarbamyl-N-oxydiefhylene sulfenamide; N-cyclohexyl-2-benzofhiazole sulfenamide; N-t-butyl-2-benzothiazole sulfenamide; N-cyclohexyl-2- benzothiazylsulfeneamide; N,N-dicyclohexyl benzthiazyl sulphenamide; N-t- butyl-2-benzothiazole sulfenamide. There are also sulfenimide compounds, e.g., N-t-butyl-benzothiazole-2-sulfenimide.
• Typical imidazoles are: 2-mercaptobenzimidazole, 2- mercaptomethylbenzimidazole; and the zinc salt of 2-mercaptobenzimidazole.
• Zinc isopropyl xanthate is a typical xanthate sulfur accelerator.
• Typical thioureas are: trimethylthiourea; 1,3-diethylthiourea and 1,3- dibutylthiourea; ethylene thiourea; blend of dialkyl thioureas; diphenyl thiourea; diorthotolyl thiourea; dimethyl thiourea; diethyl thiourea; dibutyl thiourea.
• Alkylphenoldisulfide types of sulfur accelerators are illustrated by the compounds available from ATOFINA Chemicals, Inc., under the designation
• VULTAC® 2 VULTAC 3 and VULTAC 5.
• Thiophosphate sulfur accelerators are illustrated by such compounds as copper dialkyldithiophosphate; zinc dialkyldithiophosphate; zinc amine dithiophosphate; zinc dibutyldithophosphate; copper O,O-diisopropyl- phosphorodithiolate; zinc O,O-diisopropylphosphorodithiolate.
• miscellaneous sulfur accelerators include 4,4-dithiodimorpholine; N,N'-caprolactam disulfide; dibutylxanthogen disulfide.
• the polymers which can be cured (crosslinked) in the presence of molecular oxygen include all those natural and synthetic polymers capable of being crosslinked either by abstraction of hydrogen (or other extractable atoms, such as with iodo and bromo substituted fluoroelastomers) or by polymerization through double bonds.
• Polymers which are currently understood to not be crosslinkable by these mechanisms and which undergo degradation in the presence of free radicals generated from organic peroxides and the azo initiators defined herein below and whose presence should be substantially avoided in the curable compositions of this invention include: poly( vinyl chloride), poly-(propylene), butyl rubber, epichlorohydrin polymers and epichlorohydrin ethylene oxide polymers.
• Polymers crosslinkable by free radicals from organic peroxides and azo initiators as defined herein below include ethylene-propylene terpolymer (EPDM), ethylene-propylene copolymer (EPM) natural polyisoprene rubber (NR), styrene butadiene rubber (SBR), polybutadiene rubber (BR), synthetic polyisoprene rubber (IR), poly(ethylene) (PE), ethylene-vinyl acetate (EVA), acrylonitrile-butadiene- styrene (ABS), unsaturated polyester, styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), neoprene rubber (CR), nitrile rubber (NBR), polysulfide rubber (T) chlorinated poly-(ethylene) (CM), polyurethane (AU, EU), vinylidene fluor
• the free radical initiators (organic peroxides and azo initiators) suitable for use in the invention include all those classes of organic peroxides and azo initiators suitable for curing (crosslinking) polymers, both thermoplastics and elastomers.
• the azo initiators are those known in the art, such as 2,2'-azobis-(2- acetoxypropane), to generate free radicals on heat decomposition capable of inducing the desired curing (crosslinking) reaction.
• the azo initiators of U.S. Patents 3,862,107 and 4,129,531, the disclosures of which are incorporated herein by reference, are also suitable.
• hydroperoxides and liquid peroxydicarbonates all those organic peroxides known to undergo decomposition by heat to generate radicals capable of initiating the desired curing (crosslinking) reactions are contemplated as suitable for use in the invention.
• Dialkyl peroxides, diperoxyketals, mono-peroxy carbonates, cyclic ketone peroxides, diacyl peroxides, organosulfonyl peroxides, peroxyesters and solid, room temperature stable peroxydicarbonates are the preferred initiators.
• the most preferred initiators are dialkyl peroxides, peroxyketals, cyclic ketone peroxides and diacyl peroxides.
• dialkyl peroxide initiators are: di-t-butyl peroxide; t-butyl cumyl peroxide; 2,5-di(cumylperoxy)-2,5-dimefhyl hexane;
• Illustrative solid, room temperature stable peroxydicarbonates are, but not limited to: di(2-phenoxyethyl) peroxydicarbonate; di(4-t-butyl-cyclohexyl) peroxydicarbonate; dimyristyl peroxydicarbonate; dibenzyl peroxydicarbonate; di(isobornyl) peroxydicarbonate.
• dialkylperoxides which may be used singly or in combination with the other free radical initiators contemplated by the invention are those selected from the group represented by the formula:
• R 4 and R 5 may independently be in the meta or para positions and are the same or different and are selected from the group hydrogen or straight or branched chain alkyl of from 1 to 6 carbon atoms.
• Dicumyl peroxide and isopropylcumyl cumyl peroxide are illustrative.
• Other dialkyl peroxides are:
• the preferred initiators are: 1,1 -di(t-butylperoxy)-3 ,3,5-trimethylcyclohexane;
• peroxides falling within the general class defined as useful in the invention include benzoyl peroxide, OO-t-butyl-0-hydrogen-monoperoxy-succinate and 00-t-amyl-O-hydrogen-monoperoxy-succinate.
• Illustrative cyclic ketone peroxides are compounds having the general formulae (II), (III) and/or (IV).
• R x to R 10 are independently selected from the group consisting of hydrogen, C j to C 20 alkyl, C 3 to C 20 cycloalkyl, C 6 to C 20 aryl, C 7 to C 20 aralkyl and C 7 to C 20 alkaryl, which groups may include linear or branched alkyl properties and each of R ] to R 10 may be substituted with one or more groups selected from hydroxy, C j to C 20 alkoxy, linear or branched C j to C 20 alkyl, C 6 to C 20 aryloxy, halogen, ester, carboxy, nitride and amido, preferably, at least 20% of the total active oxygen content of the peroxide mixture used for a crosslinking reaction will be from compounds having formulas (II), (III) and/or (IV).
• Suitable cyclic ketone peroxides are:
• Illustrative monoperoxy carbonates are: O0-t-butyl-0-isopropylmonoperoxy carbonate; 00-t-butyl-0-(2-ethyl hexyl) monoperoxy carbonate;
• diacyl peroxides are: di(4-methylbenzoyl) peroxide; di(3-methylbenzoyl) peroxide; di(2-methylbenzoyl) peroxide; didecanoyl peroxide; dilauroyl peroxide;
• the compounds of formula (a) (the bismaleimide and biscitraconimides) in the composition of the invention in quantities which will provide from about 0.2 parts by weight per part of polymer by weight (phr) to about
• 10.0 phr preferably from about 1.0 phr to about 5.0 phr, most preferably from about 1.5 phr to about 3.0 phr.
• sulfur containing organic compound capable of accelerating sulfur vulcanization in polymers capable of being crosslinked by sulfur in compositions of the invention in quantities which will provide from about
• 0.01 phr to about 20 phr preferably from about 0.1 phr to about 1.0 phr, most preferably from about 0.1 phr to about 0.5 phr. It is understood by those of skill in the art that these compounds are of two types. Those that donate sulfur to the vulcanization and those which simply accelerate sulfur vulcanization. Either class of compound or mixtures thereof are contemplated as equivalents by the invention.
• Alkyl phenol disulfide polymers of the VULTAC® type are preferably used at from about 0.5 phr to 20 phr when used alone or at from about 0.1 phr to about 10 phr when in combination with other sulfur accelerators.
• the free radical initiator organic peroxide and/or azo initiator
• the free radical initiator in quantities of from about 0.04 to about 10 phr preferably from about 1 to about 4 phr.
• the time-temperature conditions necessary for curing largely depend on the structure of the free radical curing agent.
• suitable conditions are detailed in U.S. Patents 3,632,107 and 4,129,531.
• compositions of the invention appropriate time and temperature conditions may be determined for crosslinking a particular polymer composition by running a small number of well controlled rheometer studies and selecting values from the results of those studies where the time/temperature relationship is from five to fifteen times the half life value for the free radical initiator in the system.
• the invention contemplates that other conventional additives such as antioxidants (hindered phenols and polymeric quinoline derivatives are preferred), aliphatic process oils, and other process aids, pigments, dyes, tackifiers, waxes, reinforcing aids, UV stabilization agents, blowing agents and activators and antiozonants may also be present in the compositions before, after and during the curing step.
• antioxidants hindered phenols and polymeric quinoline derivatives are preferred
• aliphatic process oils and other process aids, pigments, dyes, tackifiers, waxes, reinforcing aids, UV stabilization agents, blowing agents and activators and antiozonants may also be present in the compositions before, after and during the curing step.
• polysulfide polymers contemplated by the invention are those known polysulfide polymers which are prepared by the reaction of an ⁇ , ⁇ ) - dihaloalkyl (or dihaloheteroalkyl) compound with a metallic, preferably an alkali metal, polysulfide.
• the common commercially available polysulfide polymers are either liquids or solids, are either thiol or hydroxy terminated and are derived from materials produce by the reaction of 1 ,2-dichloroethane, 2,2'-dichloro-diethyl ether or bis(2-chloroethyl)formal with an alkali metal polysulfide (MSx x ) wherein M is an alkali metal ion, preferably derived from sodium and x is a number greater than 1 up to about six.
• MSx x alkali metal polysulfide
• polysulfide polymers may be used in place of or in admixture with the other compounds (B) in equal quantities to those previously specified for those compounds. Since an excess of polysulfide polymer is not contemplated as detrimental to the practice of the invention, it is also contemplated that they may be preblended with the compound(s) (A) and optionally with the free radical initiator(s) to form masterbatches, either solid or liquid. The polysulfide polymers may also be preblended into the polymer to be cured and and the compound(s) (A) and also the free radical initiator(s) blended in simultaneously or subsequently at the option of the operator. Use of the polysulfide polymers in combination with the other sulfur accelerators contemplated by the invention permits reduction of the amount of sulfur accelerator required by the invention.
• Certain crosslinkable elastomer compositions which are highly filled with oil and/or carbon black are normally cured using sulfur vulcanization rather than free radical initiators. Free radical cure is more difficult because the radicals generated lack specificity and react with the filler and oil as well as the elastomer. This reduces efficiency of the free radical initiator.
• chlorinated polyethylene and /or chlorosulfonated polyethylene as supplemental ingredients to all the compositions of the various composition aspects of the invention surprisingly increases free radical cure efficiency in highly extended elastomer formulations and allows free radical cure of the systems with reduced or no surface tack.
• the amount of chlorinated and/or chlorosulfonated polyethylene as supplemental ingredients in the compositions of the first composition aspect of the invention may be from about 1% to about 50%) by weight, preferably 15% to 40% by weight and more preferably from 20% to 35% by weight.
• various known co-curing agents e.g., unsaturated monomeric crosslinking coagents, elemental sulfur, or sulfur donor compounds
• the elastomer used in this example was an ethylene propylene copolymer (EPM) marketed by Exxon, VISTALON® 504.
• EPM ethylene propylene copolymer
• Prior art U.S. 4,983,685 claims that use of high levels (2.5 to 20 parts) of specific sulfur containing compounds with or without optional unsaturated monomers can be used to crosslink elastomers with peroxide in the presence of air and produce a non-tacky surface.
• Other references employ sulfur.
• low levels of sulfur or sulfur donor compounds were evaluated alone or with some monomeric coagents.
• Table 1 shows these formulations produced a sticky surface, but also provided a crosslinked product with good physical properties (higher MH torque).
• a blend (as taught by the prior art) of an optional monomeric coagent, a high level of sulfur compound and peroxide was also evaluated. This produced a non tacky surface when crosslinking elastomers in the presence of air, however, the physical properties were unacceptable compared to a conventional peroxide monomeric crosslinking formulation.
• LUPEROX® 231XL [40% l,l-di(butylperoxy)-3,3,5-trimethylcyclohexane] dispersed on calcium carbonate, marketed by ATOFL A Chemicals, Inc.
• the level of crosslinking was determined using a Flexsys MDR® 2000E moving die rheometer. Samples were also cured in hot air at 365 °F for ten minutes and judged for surface tackiness by placing a paper towel on the surface, immediately after removal from the oven using moderate and consistent pressure. Surface tack was rated from 1-10, where 1 is considered non-tacky and 10 is very tacky.
• a combination of 0.3 parts elemental sulfur and 2 parts of HVA-2 (Table 1, run #5) provides further improvement in the level of crosslinking, (compared to run #2 using HVA-2 alone), but, unfortunately, provides high surface tackiness (7 out of 10).
• blends of coagent with low levels of elemental sulfur can improve crosslinking, but not surface tackiness.
• Prior art teaches 2.5 to 20 parts of sulfur accelerator or its equivalent is required.
• the use of the coagent HVA-2 and peroxide in the carbon black EPM formulation containing oil and antioxidant provided good crosslinking, but, unfortunately, also produced a sticky surface when curing in hot air.
• SR-350 is trimethylolpropanetrimethacrylate, marketed by Sartomer.
• This example illustrates that one cannot predict the effect of blending dissimilar co-curing agents such as peroxide, monomeric coagents and elemental sulfur or sulfur containing compounds with the objective of maintaining an acceptable level of crosslinking together with low surface tackiness when curing in the presence of air.
• dissimilar co-curing agents such as peroxide, monomeric coagents and elemental sulfur or sulfur containing compounds
• our data shows that one can improve the level of crosslinking while not improving the surface tackiness when curing in the presence of air.
• the surface tack was finally reduced using teaching from the prior art, it was found that the overall crosslinking was undesirable.
• Crosslinking within the sample (excluding air) and crosslinking the surface in the presence of air are two separate processes. Increasing or decreasing the level of crosslinking coagents or use of the various co-curing agents in combination with peroxide leads to unpredictable results. Crosslinking coagents such as HVA-2 help to increase the level of crosslinking with peroxides cures, but appear to provide a poor surface tack in air cure.
• monomeric coagents e.g., HVA-2 or SR 350 in combination with other co-curing agents, such as elemental sulfur or sulfur donor/accelerator compounds, as taught in the art, we find that the final physical properties are severely reduced, thus negating the advantages of a monomeric coagent-peroxide cure system.
• Example 2 Compounding of prior art peroxide formulations versus novel peroxide formulations for crosslinking fully saturated (no double bonds within the polymer chains) elastomers.
• novel peroxide formulation provides good physical properties associated with a conventional peroxide cure, plus an unexpected non-tacky surface when crosslinking in the presence of air.
• Table 2 run #3 prior art taught levels of 5 parts Vanox ZMTI (93% Zinc 2- mercapto-toluimidazole) with optional SR-206 coagent, improved compression set but gave a very sticky, unacceptable surface.
• Table 2, run #5 low levels of dipentamethylene thiuram tetra sulfide (at 0.4 parts which falls outside of U.S. 4,983,685), 0.4 parts of Durax (98% N-cyclohexyl-2-benzothiazolesulfenamide) and 5 parts DC40 (40% dicumyl peroxide), provides a tack free surface when cured in a hot air oven with an improved 41% compression set and better level of crosslinking.
• Table 2, run #6, shows that, unexpectedly, 0.4 parts Durax, 0.4 parts of
• Vanax A (98% 4,4'-difhiodimorpholine), 2.2 parts HVA-2 monomeric coagent and 5 parts DC40 (40% dicumyl peroxide), provided a tack free surface with 31% compression set.
• VULTAC 5 (75% alkyl phenol disulfide polymer from Elf Atochem) has not been taught by the art for use in hot air cure of elastomers together with peroxide and bismaleimide type coagent. Note that 0.4 parts of VULTAC 5 is equivalent to adding 0.3 parts of the alkyl phenol disulfide polymer, due to the 75% assay.
• the high 60%+ compression set values show that the prior art crosslinked polymer permanently deformed under applied pressure over 70 hours at 150°C, a standard test (ASTM D-395-61) for a peroxide cure.
• a tack free surface can be obtained in hot air by sulfur vulcanization for unsaturated polymers, but results in poor heat aging properties.
• There is no advantage to a peroxide cure system cured in hot air over a sulfur vulcanization if there are no significant differences in physical properties, e.g., low M H and/or high (poor) percent compression set values.
• Peroxide cures have been traditionally the choice for a number of high temperature and high performance applications. Peroxide crosslinking provides carbon-carbon bonds which allow the crosslinked polymer manufacturer to use the full engineering capabilities of the elastomer.
• Example 3 Novel peroxide-additive compositions produce solid or foamed crosslinked elastomer in hot air, with outstanding physical properties, e.g., percent compression set, while also producing a non tacky surface when curing in the presence of air.
• the elastomer used in this example was Uniroyal ® X3378 EPDM containing 4% dicyclopentadiene as the termonomer.
• Peroximon DC 40KEP 50% dicumyl peroxide on clay was used as the peroxide crosslinking agent.
• HVA-2 coagent constant (Table 3, runs #2 to #6).
• Sulfur vulcanization compression sets are measured at approximately 100°C - 120°C and rarely determined at 150°C due to constant poor performance at elevated temperature.
• the present 150°C, 70 hour desirable compression set data proves that these novel peroxide-additive compositions illustrated in the practice of this invention produce crosslinked EPDM with unexpectedly good heat aging properties.
• the novel peroxide-additive compositions surprisingly provide a way to produce both solid and foamed articles.
• Example 4 Novel peroxide-additive compositions are studied using a fast cure, higher ethylene EPDM (Rovalene 509 EPDM) using dicumyl peroxide and HVA-2 in Table 4.
• Example 5 Evaluation of common classes of coagents to demonstrate the uniqueness of the use of bismaleimide coagents with selected additives, for utility in providing good overall peroxide-type physical properties with the ability to cure the surface of a rubber (tack-free surface) in the presence of air.
• the bismaleimide is evaluated in combination with Sulfads® and VULTAC® 5 together with dicumyl peroxide for crosslinking a fast cure type
• the HVA-2 bismaleimide-type coagent
• tack free surface with the blend of 0.3 parts Sulfads and 0.2 parts of VULTAC 5.
• Use of other agents provided a sticky surface, e.g., TAC (triallyl cyanurate), SR-350 (trimefhylolpropane trimethacrylate), 1.2 BR (1 ,2 liquid butadiene rubber),
• Santolink XI- 100 allyl glycidyl ether alcohol resin
• TAP triallyl phosphate
• pBQ para benzoquinone
• Example 6 Use of low levels of prior art sulfur accelerators blended with HVA-2 and dicumyl peroxide does not provide tack free surface. Unexpectedly, use of low level prior art compounds with HVA-2 and select compounds provide a tack-free surface when crosslinking a fast cure EPDM (Royalene® 509 in the presence of air.
• VULTAC® 5 (75% alkyl phenol disulfide polymer) or Vanax® A (98% 4,4'dithiodimorpholine) is blended with these low levels of prior art compounds, e.g., Methyl Zimate or Unads, one obtains a tack-free surface when crosslinking in the presence of air.
• a unique blend of peroxide, HVA-2 coagent, and low levels of dithiocarbamates or thiurams with VULTAC 5 or Vanax A provides a crosslinked polymer with a cured surface in the presence of air.
• no gassing was noted, thus, solid crosslinked parts can be formed with these novel blends.
• Example 7 The use of low levels of prior art elemental sulfur with low levels of prior art Sulfads®. with or without optional HVA-2 monomeric coagent. provides good surface cure in hot air, however, poor physical properties (61% and 49% Compression Set .
• Example 8 In this example, it is shown that the novel peroxide-additive composition performs well in filled and non-filled EPDM formulations.
• Run #2 contains only EPDM and the novel peroxide-additive formulating, i.e., no oil, carbon black, ZnO or stearic acid.
• the novel formulation as taught in the practice of the invention, provides a completely tack free surface when cured in the presence of air, (1 out of 10) where 10 is tacky.
• Addition of normal levels of carbon black and oil (run #4) provides excellent tack free surface in the presence of air.
• Example 9 Novel peroxide-additive blends are used to hot air cure a very highly filled EPDM.
• This highly filled EPDM contains a large amount of carbon black and oil.
• Such formulations are only used for sulfur vulcanization, and are not typically used in peroxide cure.
• the successful use in these examples shows the unexpected tremendous utility of these novel peroxide-additive blends.
• the effectiveness of this system is illustrated by providing examples using four different organic peroxides.
• the peroxide controls (Table 9, runs #1, #3, #5 and #7) are all tacky due to an under cured surface when crosslinking in the presence of air. They also contain some gas bubbles in the interior of the sample.
• the novel peroxide-additive formulations used in this invention provide a fully cured surface (non-tacky) when crosslinking in the presence of air, see Table 9, runs #2, #4, #6 and #8. Unexpectedly, these formulations cure to a higher level of crosslinking to the point that there was no foaming (gas bubbles).
• the novel peroxide formulations provide a desirable, solid, crosslinked part with a non-sticky surface upon hot air cure. The cure times vary because of the different peroxides used, but unexpectedly the surfaces are always tack- free, despite the large amount of filler and oil used.
• Example 10 - ADA (Azodicarbonamide, is a blowing agent which is used to create foamed articles.
• ADA is used to produce hot air cured, free-rise, crosslinked EPDM sponge using our novel peroxide-additive formulations to create a tack free surface.
• the peroxide control with no additive or ADA is provided in Table 10, run #1.
• the Tangent delta for run #1 (peroxide control) was 0.064, a desirable low value.
• the MDR can measure tan ⁇ (tangent delta) which can be determined by dividing the viscous moduli by the elastic moduli.
• a cured compound with a very low tangent delta will be very resilient and exhibit low hysteresis.
• a higher tangent delta value means that the polymer chains can undergo permanent movement or deformation, after an applied stress.
• Captax (98% 2-mercaptobenzothiazole) as per prior art, Table 10 run #8, provides a non-tacky surface as well, however, with further degradation in final crosslinked physical properties (M ⁇ _ ⁇ and tangent delta).
• Example 11 Common coagents are evaluated by adding them to a sulfur donor - accelerator blend together with LUPEROX® 101 -XL .45% 2.5-dimethyl- 2.5-di(t-butylperoxy hexane].
• peroxide-coagent-accelerator blends are used to cure standard EPDM to show that the maleimide type coagent, HVA-2 or Vanax MBM is the only one of those tested which is capable of providing the all important combination of good cure with tack- free surface when crosslinking EPDM in the presence of air.
• Example 12 Various peroxide - sulfur cure blends used for other applications are rated for surface tack (quality) in air cure and percent compression set properties compared to the novel blends of this invention and to standard peroxide and sulfur cures.
• the novel peroxide cure system in Table 12, run #2 unexpectedly gives an excellent, tack-free surface in air (1 out of 10) with an outstanding compression set equal to the peroxide cures in Table 12, runs #1, #3 and #6. which are very tacky (10 out of 10) after curing in air.
• Example 13 Storage stability of novel peroxide formulations.
• novel peroxide compositions can be premixed and stored for later use without loss of activity or performance. Two different peroxide formulations were stored for three months.
• Example 14 Use of low levels of antioxidants (phenolic, metal dimethyldithiocarbamate type) in combination with bismaleimide coagents and low levels of sulfur donors provide excellent tack-free surfaces when curing elastomers in the presence of air and also provides desirable final physical properties (i.e., low % compression set ).
• antioxidants phenolic, metal dimethyldithiocarbamate type
• novel peroxide air curing formulations which consist of peroxide(s), bismaleimide coagents(s), sulfur donor - sulfur accelerator system can also include low levels of antioxidants.
• Table 4 run #11, (M. Niclate, i.e., Methyl Niclate) nickel dimethyldithiocarbamate was used at a low level of 0.2 phr, along with others, e.g., zinc (M. Zimate) and copper (M.
• Niclate is used in run #3 compared to a phenolic antioxidant and a sulfenamide accelerator; see run #6 MBPC (2,2'-methylene bis-4-methyl-6-t-butylphenol), and run #7, Santocure TBSI (N-t-butyl-2-benzothiazolesulfenimide).
• HVA-2 and Sulfads are also included in the formulation, as per the present invention.
• Methyl Niclate (nickel dimethyldithiocarbamate) with Sulfads (98% dipentamethylene thiuram tetrasulfide) or Morfax (98% 4-morpholinyl-2- benzothiazole disulfide) is an acceptable combination as per Table 14, runs #2, #3 and #4.
• Example 15 Crosslinking a fully saturated elastomer (ethylene-octene copolymer).
• run #3 and run #4 are only slightly tacky after curing which is a major improvement because most thermoplastic ethylene polymers would be very sticky in this test, simply because these polymers melt/soften at these temperatures.
• the oil is added to reduce stiffness but can make the surface more tacky. The oil can be left out at this low filler level. When cooled to room temperature, these samples (runs #3 & 4) were not tacky.
• Example 16 Evaluation of different bismaleimide compounds for use in novel peroxide formulations which can crosslink elastomers with a tack-free surface in the presence of air.
• Vanax A (®. T. Vanderbilt) 0.2
• VULTAC 5 (Elf Atochem) 0.7
• the 1,2; 1,3 and 1,4 (ortho, meta, para) isomers of N,N'-phenylene bismaleimide were evaluated for use in novel peroxide compositions which allow crosslinking elastomers in the presence of air and provide a fully cured tack-free surface.
• the elastomer used in this present example is Nordel®IP EPDM NDR- 4640. This is one of the new Dupont Dow metallocene type EPDM elastomers.
• Run #1 was the peroxide alone, runs #2 to #4 were the coagents and peroxide, run #8 was the peroxide and sulfur accelerator blend. In each case the surface of these formulations were tacky upon hot air cure at 400 °F cure.
• PDM N,N-(1,2 or 1,3 or l,4)-phenylenedimaleimide
• Table 18 shows the results of the evaluation of four coagent bismaleimide compounds for their effectiveness to provide a cured elastomer with tack- free surface upon curing in a hot air oven, when used with peroxides and select low levels of sulfur accelerators, as per the practice of this present invention.
• Dupont Dow Nordel IP NDR-4640 metallocene EPDM was chosen as the elastomer for evaluation work.
• the monomeric compounds are: l,l'(3,3-dimethyl-l,r-biphenyl-4,4'- diyl)-bismaleimide; N,N-(l,l'-biphenyl-4,4'-bismaleimide; 1,2- bismaleimidoethane and 1,6-bismaleimidohexane. They were compared no N,N'-l,3-phenylenebismaleimide or Vanax MBM, in Table 18.
• the final crosslinked elastomer had excellent final physical properties, based on the desirable, low percent compression set number which was obtained after heat aging the crosslinked EPDM for 70 hours at 150°C.
• Example 20 Use of Polysulfide in combination with select halogenated polymers or silicone rubber, used as additives with peroxide, sulfur accelerators and bismaleimide coagents. to produce a tack-free surface in highly extended EPDM formulations.
• Nordel IP 4520 (Dupont Dow Elastomers) blended with equal weight of carbon black and high levels of oil would be difficult to cure with ordinary peroxides and is representative of a sulfur cured hose compound formulation.
• Example 21 - In this example we show more data for curing the "difficult to cure by peroxide" highly filled EPDM formulations.
• Chlorosulfonated Polyethylene and Polysulfide as novel additives to crosslink a highly filled EPDM in the presence of air to provide a tack- free surface using organic peroxides
• Hypalon * a small portion of Hypalon (amount listed above) replaces an equal amount of 4570 EPDM
• Example 22- In this example we illustrate several new chemical and polymeric additives which are useful in developing a peroxide formulation for crosslinking elastomers in the presence of hot air.
• Vanax 6H N-cyclohexyl-N'-phenyl-p- phenylenediamine
• CAS 101-87-1 an antiozonant for diene based polymers
• PTE Polysulfide
• VMQ silicone rubber
• the antiozonant serves as a replacement for the sulfur containing compounds in the practice of this invention.
• the invention contemplates such substitution of this antioxidant and those of similar structure as full equivalents to the other compounds included within the scope of the definition of compound (B).
• polysulfide (PTE) also serves this same purpose.
• dialkyl peroxides can be used in the practice of this invention, besides the most commonly used dialkyl peroxide, dicumyl peroxide, which was extensively evaluated in the previous examples.
• compositions of the inventions may also be formulated as masterbatches for convenience in handling and compounding into the polymers for crosslinking in the presence of molecular oxygen.
• Typical masterbatch carriers include, for example, microcrystalline wax, polycaprolactone, Ethylene propylene diene monomers polymers (EPDM), ethylene propylene monomers polymers (EPM), ethylene vinyl alcohol polymer (EVA), polyethylene (PE), or mixtures thereof.

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