CA2578586A1 - Peroxide curable butyl rubber compound - Google Patents

Abstract

A peroxide curable butyl rubber compound including a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group, for example an acrylate. The butyl rubber polymer has a multiolefin content of at least 3.0 mol %. The cured compound exhibits good resistance to compression set and low gas permeability, making it particularly useful as a replacement for divinyl benzene containing peroxide curable rubbers, such as XL-10,000.TM.

Description

Peroxide Curable Butyl Rubber Compound Field of the Invention The invention relates to a peroxide curable butyl rubber compound comprising a high multiolefin content butyl rubber and a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group. More particularly, the invention relates to a peroxide curable compound containing butyl rubber having at least 3.0 mol % multiolefin content and a peroxide curing co-agent comprising an acrylate or methacrylate.

Background Poly(isobutylene-co-isoprene), or IIR, is a synthetic elastomer commonly known as butyl rubber which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene (1-2 mole %) .
As a result of its molecular structure, IIR possesses superior air impermeability, a high loss modulus, oxidative stability and extended fatigue resistance.

Butyl rubber is understood to be a copolymer of an isoolefin and one or more, preferably conjugated, multiolefins as comonomers. Commercial butyl comprise a major portion of isoolefin and a minor amount, not more than 2.5 mol %, of a conjugated multiolefin. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a vehicle and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Patent No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295.

Peroxide curable butyl rubber compounds offer several advantages over conventional, sulfur-curing, systems. Typically, these compounds display extremely fast cure rates and the resulting cured articles tend to possess excellent heat resistance. In addition, peroxide-curable formulations are considered to be "clean" in that they do not contain any extractable inorganic impurities (e.g., sulfur). The clean rubber articles can therefore be used, for example, in condenser caps, biomedical devices, pharmaceutical devices (stoppers in medicine-containing vials, plungers in syringes) and possibly in seals for fuel cells.

Lanxess' XL-10,000T"" is a commercially available terpolymer based on isobutylene, isoprene and divinylbenzene. The presence of divinyl benzene in the terpolymer leads to significant crosslinking when peroxide cured. However, the high Mooney Viscosity (ca. 60-75 MU, ML1+8@ 125 C) and presence of gel particles makes this material difficult to process. The presence of significant amounts of divinyl benzene makes this polymer unsuitable for medical applications. As a result, XL-10,000TM is currently being phased out of production. There is therefore a need for a replacement isobutylene based polymer which is primarily peroxide curable, completely soluble, and devoid of free divinyl benzene. It would be desirable for compounds based on this replacement polymer to have similar physical properties to those provided in previous XL-10,000TM compounds, particularly its uniquely low gas permeability.

It is well accepted that polyisobutylene and butyl rubber decompose under the action of organic peroxides. Furthermore, US 3,862,265 and US 4,749,505 teach us that copolymers of a C4 to C7 isomonoolefin with up to 10 wt. % isoprene or up to 20 wt.
% para-alkylstyrene undergo a molecular weight decrease when subjected to high shear mixing. This effect is enhanced in the presence of free radical initiators. In spite of this, CA 2,418,884 describes the preparation of butyl-based, peroxide-curable compounds which have high multiolefin content. Specifically, CA 2,418,884 describes the continuous preparation of IIR with isoprene (IP) levels ranging from 3 to 8 mol %.
However, the physical properties of this rubber are not comparable to those of XL-1 O,OOOTM.

Co-pending Canadian patent application CA 2,508,177 describes a peroxide curable polymer blend comprising a high isoprene butyl rubber, an EPDM rubber, and an acrylate. The acrylate is included as a co-agent to enable peroxide curing of the blend. The inclusion of EPDM in the blend has a negative effect on permeability, making this blend unsuitable for replacement of XL-10,000TM

The need therefore still exists for a peroxide curable butyl rubber compound having physical properties, particularly permeability, comparable to XL-10,000rM
Summary of the Invention According to the present invention, there is provided a peroxide curable butyl rubber compound comprising: a butyl rubber polymer comprising repeating units derived from at least one isoolefin monomer and at least 3.0 mol % of repeating units derived from at least one multiolefin monomer; and, a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group.

According to another aspect of the present invention, there is provided a peroxide curable butyl rubber compound prepared by: providing a butyl rubber polymer comprising: repeating units derived from at least one isoolefin monomer and at least 3.0 mol % of repeating units derived from at least one multiolefin monomer;
providing from 1 to 20 phr of a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group; blending the butyl rubber polymer and the co-agent to form the peroxide curable compound.

According to yet another aspect of the present invention, there is provided a peroxide cured butyl rubber compound comprising: a butyl rubber polymer comprising:
repeating units derived from at least one isoolefin monomer and at least 3.0 mol % of repeating units derived from at least one multiolefin monomer; a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group; the article having a compression set of less than or equal to 25%.

Compounds according to the present invention exhibit compression set properties similar to compounds made from XL-10,000T"', with permeability in the same order of magnitude and superior elongation properties. Importantly, these compounds do not contain significant amounts of DVB, which makes them ideal candidates for replacing XL-10,000T"" in clean applications, such as in medical devices.

Further features of the invention will be described in the following detailed description.

Detailed Description of Preferred Embodiments Butyl rubber polymers are generally derived from at least one isoolefin monomer, at least one multiolefin monomer and optionally further copolymerizable monomers. In the present invention, a butyl rubber polymer having a high multiolefin content (at least 3.0 mol %) is used. This high multiolefin butyl rubber is peroxide curable.
The preparation of a suitable peroxide curable high multiolefin butyl rubber polymer is described in co-pending application CA 2,418,884, which is incorporated herein by reference.

The butyl rubber polymer is not limited to a special isoolefin. However, isoolefins within the range of from 4 to 16 carbon atoms, preferably 4-7 carbon atoms, such as isobutene, 2-methyl-l-butene, 3-methyl-l-butene, 2-methyl-2-butene, 4-methyl-1-pentene and mixtures thereof are preferred. More preferred is isobutene.

The butyl rubber polymer is not limited to a special multiolefin. Every multiolefin copolymerizable with the isoolefin known by the skilled in the art can be used. However, multiolefins with in the range of from 4-14 carbon atoms, such as isoprene, butadiene, 2-methylbutadiene, 2,4-dimethylbutadiene, piperyline, 3-methyl-1,3-pentadiene, 2,4-hexadiene, 2-neopentylbutadiene, 2-methly-1,5-hexadiene, 2,5-dimethly-2,4-hexadiene, 2-methyl-1,4-pentadiene, 2-methyl-1,6-heptadiene, cyclopenta-diene, methylcyclopentadiene, cyclohexadiene, 1-vinyl-cyclohexadiene and mixtures thereof, preferably conjugated dienes, are used. Isoprene is more preferably used.

As optional monomers, any monomer copolymerizable with the isoolefins and/or dienes known by the skilled in the art can be used. a-methyl styrene, p-methyl styrene, chlorostyrene, cyclopentadiene and methylcyclopentadiene are preferably used.
Indene and other styrene derivatives may also be used. (3-pinene can also be used as a co-monomer for the isoolefin.

The reaction mixture used to produce the high multiolefin containing butyl polymer further contains a multiolefin cross-linking agent. The term cross-linking agent is known to those skilled in the art and is understood to denote a compound that causes chemical cross-linking between the polymer chains in opposition to a monomer that will add to the chain. Some easy preliminary tests will reveal if a compound will act as a monomer or a cross-linking agent. The choice of the cross-linking agent is not restricted. Preferably, the cross-linking contains a multiolefinic hydrocarbon compound.
Examples of these include norbornadiene, 2-isopropenylnorbornene, 2-vinyl-norbornene, 1,3,5-hexatriene, 2-phenyl-1,3-butadiene, divinylbenzene, diisopropenylbenzene, divinyltoluene, divinyixylene and C, to C20 alkyl-substituted derivatives thereof. More preferably, the multiolefin crosslinking agent is divinyl-benzene, diiso-propenylbenzene, divinyltoluene, divinyl-xylene and C, to C20 alkyl substituted derivatives thereof, and or mixtures of the compounds given. Most preferably the multiolefin crosslinking agent contains divinylbenzene and diisopropenylbenzene.

Preferably, the monomer mixture used to prepare the high multiolefin butyl polymer contains in the range of from 80% to 95% by weight of at least one isoolefin monomer and in the range of from 4.0% to 20% by weight of at least one multiolefin monomer and/or (3-pinene and in the range of from 0.01 % to 1% by weight of at least one multiolefin cross-linking agent. More preferably, the monomer mixture contains in the range of from 83% to 94% by weight of at least one isoolefin monomer and in the range of from 5.0% to 17% by weight of a multiolefin monomer or R-pinene and in the range of from 0.01% to 1% by weight of at least one multiolefin cross-linking agent.
Most preferably, the monomer mixture contains in the range of from 85% to 93%
by weight of at least one isoolefin monomer and in the range of from 6.0% to 15%
by weight of at least one multiolefin monomer, including P-pinene and in the range of from 0.01 % to 1% by weight of at least one multiolefin cross-linking agent.

The weight average molecular weight of the high multiolefin butyl polymer (Mw), is preferably greater than 240 kg/mol, more preferably greater than 300 kg/mol, even more preferably greater than 500 kg/mol, most preferably greater than 600 kg/mol.

The gel content of the high multiolefin butyl polymer is preferably less than wt.%, more preferably less than 3 wt.%, even more preferably less than 1 wt.%, most preferably less than 0.5 wt.%. In connection with the present invention the term "gel" is understood to denote a fraction of the polymer insoluble for 60 min in cyclohexane boiling under reflux.

In addition to peroxide curable butyl rubber, the compound also contains a polyfunctional monomer containing an electron-attractive group that functions as a peroxide curing co-agent. The peroxide curing co-agent preferably comprises a non-nitrosamine retarded trifunctional crosslinking agent, more preferably comprising an acrylate or methacrylate compound. Examples include trimethylolpropane tri(meth)acrylate, polyethylene glycol di(meth)acrylate, ethylene di(methacrylate), ethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate, tetramethylolmethane tetracrylate and polypropylene glycol di(meth)acrylate.
Preferred cross linking agents are commercially available under the trade names Saret 517T"', Saret 519T"" or Saret 522TM. Most preferably, the peroxide curing co-agent is a non-nitrosamine retarded trimethylolpropane triacrylate crosslinking agent, such as Saret 519T""

The compound may contain from 1 to 20 phr, preferably from 5 to 20 phr, more preferably from 5 to 15 phr of the co-agent. The ingredients of the compound may be mixed together in any known manner. Many known methods for mixing polymers can be utilized. For example, an internal mixer like a Brabender or a Banbury can be used as well as a kneader or a mill. The mixing can be performed at an ambient or elevated temperature. The co-agent may have a low molecular weight and may be provided in liquid form. The co-agent may be added directly to the high isoprene butyl rubber during mixing. The co-agent may be added simultaneously with filler(s) (eg:
carbon black and/or clay) during the mixing process. Blending can alternatively be conducted with both the high multiolefin butyl rubber and the acrylate in solution.

In curing the compound, there are many suitable peroxide curing agents that may be used, for example, dicumyl peroxide, di-tert.-butyl peroxide, benzoyl peroxide, 2,2'-bis tert.-butylperoxy diisopropylbenzene (Vulcup 40KE), benzoyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, (2,5-bis(tert.-butylperoxy)-2,5-dimethyl hexane and the like. The best suited curing agents are readily ascertained by means of a few preliminary experiments. A
preferred peroxide curing agent comprising dicumyl peroxide is commercially available under the trademark DiCupTM 40C. The peroxide curing agent is suitably used in an amount of 10 to 30 parts per hundred parts of rubber (phr), preferably 10 to 20 phr, more preferably 10 to15 phr.

Vulcanizing co-agents can also be used. For example, triallyl isocyanurate (TAIC), commercially available under the trademark DIAK 7 from DuPont Or N,N'-m-phenylene dimaleimide know as HVA-2 (DuPont Dow), triallyl cyanurate (TAC) or liquid polybutadiene known as Ricon D 153 (supplied by Ricon Resins). Amounts can be equivalent to the peroxide curative or less.

An antioxidant may also be included, suitably in an amount up to 4 phr, preferably about 2 phr. Examples of suitable antioxidants include p-dicumyl diphenylamine (Naugard 445), Vulkanox DDA (a diphenylamine derivative), Vulkanox ZMB2 (zinc salt of inethylmercapto benzimidazole), Vulkanox HS
(polymerized 1,2-dihydro-2,2,4-trimethyl quinoline) and Irganox 1035 (thiodiethylene bis(3,5-di-tert.-butyl-4-hydroxy) hydrocinnamate or thiodiethylene bis(3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate supplied by Ciba-Geigy. Vulkanox is a trademark of Lanxess Inc.

The cured compound may contain further auxiliary products for rubbers, such as reaction accelerators, vulcanizing accelerators, vulcanizing acceleration auxiliaries, antioxidants, foaming agents, anti-aging agents, heat stabilizers, light stabilizers, ozone stabilizers, processing aids, plasticizers, tackifiers, blowing agents, dyestuffs, pigments, waxes, extenders, organic acids, inhibitors, metal oxides, and activators such as triethanolamine, polyethylene glycol, hexanetriol, etc., which are known to the rubber industry. The rubber aids are used in conventional amounts that depend, inter alia, on the intended use. The cured article may also contain mineral and/or non-mineral fillers.
Conventional amounts are from 0.1 to 50 wt.%, based on rubber.

The compounding and vulcanization may be carried out by a process known to those skilled in the art, such as the process disclosed in Encyclopedia of Polymer Science and Engineering, Vol. 4, S. 66 et seq. (Compounding) and Vol. 17, S.
666 et seq. (Vulcanization).

The invention is well suited for the manufacture of shaped articles, especially shaped articles for high-purity applications such as fuel cell components and medical devices.

The invention is further illustrated with reference to the following examples.
Examples Experimental Compounds were prepared using either a Brabender internal mixer set at 60 C
and 50 rpm or a 6 x 12" mill with a roll temp of 30 C. The recipes were of the following variations:

Rubber ( XL-10,000T'", RB 402T'" or high isoprene (>3.0 mol%) butyl 100 phr Trifunctional methacrylate or trifunctional acrylate (Saret 517T"', 0, 10, 15 or 20 phr Saret 519T"", Saret 522T"" or Saret 633TM.) Carbon Black (IRB #7) 50 phr Peroxide Curing Agent (DicupTM 40 C) 5, 10 or 15 phr The mixing was performed as follows. The rubber and the methacrylate or acrylate were added first. After 1.5 min the carbon black was added in 3 increments. At 7.0 minutes the peroxide was added. The mixture was removed from the mill or Brabender after 8 minutes. Some variation in the above times was permitted, depending on how well the ingredients mixed together. To prepare a compound suitable for curing from the mixture, it was passed 6 times through a 6 x 12" mill set with a tight gap.

Performance testing of the cured compound was performed as follows:
Compression set-Method B

Cure time (min) Depends on t90+10, from MDR
Cure temperature ( C) 160 Sample type solid Deflection (%) 25 Aging time (hours) 22 Ageing temperature ( C) 100 Aging type air oven Aging medium hot air Die tear C

Cure time (min) Depends on t90+10, from MDR
Cure temperature ( C) 160 Test temperature ( C) 23 Stress Strain (Dumbells) Cure time (min) Depends on t90+1 0, from MDR
Cure temperature ( C) 160 Dumbbell Die C
Test temperature ( C) 23 Permeability to Gases Cure time (min) Depends on t90+10, from MDR 7-771 Cure temperature ( C) 160 Specimen perm Conditioning time (hours) 16 Conditioning temperature ( C) 23 Test gas air Test pressure (psig) 65.5 MDR Cure Characteristics Frequency (Hz) 1.7 Test temperature ( C) 160 Degree arc ( ) 1 Test duration (min) 45 Test range (dN.m) 100 Example 1: Properties of peroxide cured compounds based on XL-10 000TM' (comparative) Lanxess' XL-10,000 is a terpolymer based on isobutylene, isoprene and divinylbenzene (DVB). This particular polymer is curable with peroxide and the cured compounds have carbon to carbon crosslinkages. The formation of carbon to carbon crosslinkages greatly favors this material in condenser cap applications.
Condenser cap seals made from XL-10,000TM are stable towards different electrolytes and provide excellent insulation properties. Table-1 shows the cured properties of a typical XL-10,000TM compound using 5phr dicumyl-peroxide.

Table 1: Properties of peroxide cured compound based on XL-10,00OTM

XL- Dicup Saret- MH- t95 Hardness Tensile Elongation Compression Die Permeability 10,000 (phr) 517 ML (min) Shore A2 (MPa) (%) set tear Z
(cm /atm.sec) (%) (phr) (d.Nm) (pts) (%) (kN/m) 100 5 0 14.14 3.91 53 7.98 181 7.43 16.46 2.6 - 3.1 x 10$
100 5 10 28.32 7.03 64 9.16 117 8.24 17.52 - 2.8 x 10-8 The first cured compound with XL-10,000TM exhibited the following properties:
delta torque = 14.14 dN.m, Shore A hardness =53 points, ultimate tensile = 7.98 MPa, ultimate elongation = 181 %, compression set 7.43 %, Die tear 16.46 kN/m and permeability between 2.6 and 3.1 x 10-8 cm2/atm.sec. These properties can be further adjusted by the level of peroxide in the cure. The addition of 10 parts Saret 517 lead to a significant increase in delta torque to 28.32 dN.m, an increase in tensile strength to 9.16 MPa and a decrease in elongation to 117 % due to increased cross-links. The compression set, Die tear and permeability values stayed about the same.

Example 2: Properties of peroxide cured compounds based on RB-402T "
(comparativej The XL-10,000T"' in Example 1 was replaced by regular butyl RB-402T'". As can be seen from Table 2, the tensile and compression set properties of cured articles prepared using this compound were inferior to those reported in Example 1. As expected, the peroxide cure was very poor due to insufficient crosslinking; in fact, compounds without any acrylate were not peroxide curable at all. This suggests that chain scission reactions are dominant over crosslinking reactions. The addition of 10-20 phr of Saret 517T"" as a coagent does not provide any significant improvement to the inferior tensile and compression set properties of the cured compound.

Table 2: Properties of peroxide cured compound based on Butyl RB-402T""

RB- Dicup Saret- MH- t95 Hardness Tensile Elonga6on Compression Die Permeability 402 517 ML (%) set tear (phr) (min) Shore A2 (MPa) (cm2/atm.sec) (%) (phr) (d.Nm) (pts) (%) (kN/m) 100 5 10 9.11 2.67 52 0.565 656 83.19 9.64 2.5 x 10-8 100 5 15 20. 2.77 61 0.755 511 84.66 12.37 2.6 x 10-8 100 5 20 38.67 3.34 67 1.08 599 80.57 17.26 2.6 x 10-8 Example 3: Properties of peroxide cured compounds based on high isoprene butyl rubber (invention) The rubbers used in comparative Examples 1 and 2 were replaced by a high isoprene (IP) butyl rubber (at least 3.0 mol% IP) that is described in Canadian patent application 2,418,884. In this Example, the high IP butyl rubber had an isoprene content of 5.0 mol%, DVB content of 0.11 mol%, with the balance being isobutylene. The presence of relatively large amounts of isoprene in the butyl backbone tends to stabilize the polymer against free radical mediated chain scission, making it peroxide curable.
The effect on physical properties of the peroxide cured compounds based on high IP IIR
is shown in Tables 3a, 3b, 3c and 3d.

Table 3a: Properties of peroxide cured high IP butyl compounds with Saret-High Dicup Saret- MH- t95 Hardness Tensile Elongation Compression Die Permeability Isoprene (phr) 517 ML (min) Shore A2 (MPa) ( %) set tear (cm2/atm.sec) Butyl (phr) (d.Nm) (pts) (%) (kN/m) (%) 100 5 0 2.11 8.47 39 4.93 570 37.8 17.77 3.1 x 10$
100 5 0 2.14 9.51 35 4.95 547 35.49 17.08 3.4 x 10$
100 5 10 12.78 7.51 58 5.69 351 26.81 19.77 3.0 x 10-8 100 5 15 22.98 7 66 5.85 290 28.32 22.19 2.8 x 10$
100 5 20 37.2 7 72 6.46 286 28.42 24.14 3.0 x 10$
100 10 0 4.16 11.61 38 7.43 385 16.64 18.11 3.1 x 10$
100 10 10 14.68 10.24 58 6.42 225 17.06 13.83 3.3 x 10$
100 15 0 7.19 10.88 42 6.93 244 17.81 15.93 3.9 x 10$
100 15 10 17.16 9.93 57 7.39 173 11.09 17.31 4.3 x 10-8 Table 3b: Properties of peroxide cured high IP butyl compounds with Saret-High Dicup Saret- MH- t95 Hardness Tensile Elongation Compression Die Permeability Iso rene hr 519 ML min Shore A2 MPa set tear p (P ) ( ) ( ) (%) (cm2/atmsec) Butyl (phr) (d.Nm) (pts) (%) (kN/m) (%) 100 5 0 2.14 9.51 35 4.95 547 35.49 17.08 3.4 x 10$
100 5 10 10.3 6.77 53 6.48 337 20.01 18.37 3.4 x 10 100 5 15 13.5 6.84 57 6.24 307 18.48 19.42 3.1 x 108 100 5 20 15.5 7.33 59 5.54 258 21.03 19.04 2.9 x 10-8 100 10 0 4.16 11.61 38 7.43 385 16.64 18.11 3.1 x 10$
100 10 10 13.7 7.16 55 6.95 219 12.65 17.01 3.8 x 10-8 100 15 0 7.19 10.88 42 6.93 244 17.81 15.93 3.9 x 10$
100 15 10 15.93 7.86 57 7.38 174 8.52 15.14 3.8 x 10-8 Table 3c: Properties of peroxide cured high IP butyl compounds with Saret-High Dicup Saret- MH- t95 Hardness Tensile Elongation Compression Die Permeability Iso rene hr 522 ML min Shore A2 MPa % set tear 2 p (p ) ( ) ( ) ( ) (cm /atm/sec) Butyl (phr) (d.Nm) (%) (kN/m) (%) 100 5 10 8.76 6.93 54 6.37 343 23.53 18,37 3.5 x 10$
100 10 10 11.28 7.43 56 6.68 243 17.91 15.4 4.0 x 10$
100 15 10 14.37 8 57 6.82 176 15.36 14 4.8 x 10$
100 5 0 2.14 9.51 35 4.95 547 35.49 17.08 3.4 x 10-8 100 10 0 4.16 11.61 38 7.43 385 16.64 18.11 3.1 x 10$
100 15 0 7.19 10.88 42 6.93 244 17.81 15.93 3.9 x 10$

Table 3d: Properties of peroxide cured high IP butyl compounds with Saret-633T""
High Dicup Saret- MH- t95 Hardness Tensile Elongation Compression Die Permeability Isoprene (phr) 633 ML (min) Shore A2 (MPa) (%) set tear (cm2/atm/sec) Butyl (phr) (d.Nm) (%) (kN/m) (%) 100 5 10 6.77 5.08 50 6.22 287 44.58 21.14 3.3 x 10-8 100 10 10 7.92 5.57 50 4.69 407 30.03 20.48 3.3 x 10-8 100 15 10 9.94 7.53 50 6.35 238 28.3 15.13 3.4 x 10-8 100 5 0 2.14 9.51 35 4.95 547 35.49 17.08 3.4 x 10-8 100 10 0 4.16 11.61 38 7.43 385 16.64 18.11 3.1 x 10-8 100 15 0 7.19 10.88 42 6.93 244 17.81 15.93 3.9 x 10$

Table 3a shows properties of peroxide cured high IP IIR based compounds with Saret 517T " as a co-agent. This table also provides the effect of peroxide and Saret 517T~~ levels in optimizing the desired properties as seen with XL-10,000T""
compounds.
The compounds with high levels of DicupTM and Saret-517T'" seem to provide acceptable compression set, die tear, elongation %, tensile and Shore A2 hardness properties.

Similarly, in Table 3b compounds with high levels of DicupTM and high levels of Saret 519T"' matched all the excellent cure properties of XL-10,000T"' compound. In particular, the compounds containing at least 10 phr of Saret 519TM cured with at least 10 phr of peroxide exhibited properties that most closely matched those of XL-10,000T"'. These two compounds have a compression set between 8.52-12.65% with excellent delta torque of 13.7-15.93 d.Nm, Shore A2 hardness of 55-57, tensile 6.95-7.38 MPa and die tear of 15.14-17.01 kN/m. Gas permeability values are within the same order of magnitude as XL-10,000T"'. Since all other properties are similar to those of XL-10,000T"", it is surprising to note the much improved ultimate elongation of these compounds, making them suitable for applications not previously available for formulations based upon XL-10,000T""

Table 3c shows the properties of high IP IIR based compounds with Saret 522r"' The trends suggest that improvements in compression set, tensile and Hardness Shore A2 are shown here with increasing levels of DicupTM and Saret 522TM. In the absence of Saret 522T"", the compounds are soft and shows weak cure. The compression set values are slightly higher compared to compounds made with Saret 519T"".

Table 3d shows the properties of peroxide cured high IP IIR compounds with Saret 633T"". This metallic coagent did not provide any improvement in cure properties and it is inferior to Saret 517T"', Saret 519T"" and Saret 522TM.

The foregoing describes preferred embodiments of the invention and other features and embodiments of the invention will be evident to persons skilled in the art.
The following claims are to be construed broadly with reference to the foregoing and are intended by the inventor to include other variations and sub-combinations that are not explicitly claimed.

Claims (20)

1. A peroxide curable butyl rubber compound comprising.
a) a butyl rubber polymer comprising repeating units derived from at least one isoolefin monomer and at least 3.0 mol % of repeating units derived from at least one multiolefin monomer; and, b) a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group.

2. The compound of claim 1, wherein the isoolefin comprises isobutylene and the multiolefin comprises isoprene.

3. The compound of claim 2, wherein the peroxide curing co-agent comprises an acrylate.

4. The compound of claim 3, wherein the peroxide curing co-agent is present in an amount of from 1 to 20 phr.

5. A peroxide cured butyl rubber compound prepared by, a) providing a butyl rubber polymer comprising. repeating units derived from at least one isoolefin monomer and at least 3.0 mol % of repeating units derived from at least one multiolefin monomer;
b) providing at least 10 phr of a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group; and, c) blending the butyl rubber polymer and the co-agent to form a peroxide curable compound;
d) curing the peroxide curable compound with at least 10 phr of a peroxide curing agent.

6. The compound of claim 5, wherein the isoolefin comprises isobutylene and the multiolefin comprises isoprene.

7. The compound of claim 5, wherein the peroxide curing co-agent comprises an acrylate.

8. The compound of claim 5, wherein the peroxide curing co-agent is a non-nitrosamine retarded trimethylolpropane triacrylate crosslinking agent.

9. The compound of claim 5, wherein the peroxide curing agent is an organic peroxide.

10. The compound of claim 8, wherein the peroxide curing agent is dicumyl peroxide.

11. A peroxide cured butyl rubber compound comprising:

a) a butyl rubber polymer comprising: repeating units derived from at least one isoolefin monomer and at least 3 0 mol % of repeating units derived from at least one multiolefin monomer;
b) a peroxide curing co-agent comprising a polyfunctional monomer containing an electron-attractive group; and, c) the peroxide cured compound having a compression set of less than or equal to 25%.

12.The compound of claim 11, wherein the isoolefin comprises isobutylene and the multiolefin comprises isoprene.

13. The compound of claim 11, wherein the peroxide curing co-agent comprises an acrylate.

14. The compound of claim 11, wherein the peroxide curing co-agent comprises a non-nitrosamine retarded trimethylolpropane triacrylate crosslinking agent.

15. The compound of claim 11, wherein the peroxide curing co-agent is present in an amount of at least 10 phr.

16. The compound of claim 11, having a compression set of less than or equal to 15%.

17. The compound of claim 11, having an ultimate elongation of at least 150%.

18. The compound of claim 11, having a gas permeability of less than or equal to 4.5 ×
-8 cm2/atm~s.

19. The compound of claim 11, having a tensile strength of at least 6.5 MPa.

20. A shaped article made from the peroxide cured compound of claim 11.