WO2005080452A1

WO2005080452A1 - Peroxide curable rubber compound containing high-isoprene butyl rubber

Info

Publication number: WO2005080452A1
Application number: PCT/CA2005/000254
Authority: WO
Inventors: Rui Resendes; Adam Gronowski; Shunji Baba; Yong Siak Seow
Original assignee: Lanxess Inc
Current assignee: Arlanxeo Canada Inc
Priority date: 2004-02-23
Filing date: 2005-02-22
Publication date: 2005-09-01
Anticipated expiration: 2006-08-23
Also published as: CA2458741A1

Abstract

The present invention relates to a peroxide curable rubber compound containing polymers with a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt.% comprising repeating units derived from at least one isoolefin monomer, more than 4.1 mol% of repeating units derived from at least one multiolefin monomer, as well as optionally further copolymerizable monomers, and repeating units derived from at least one multiolefin cross-linking agent containing no transition metal compounds and no organic nitro compounds.

Description

PEROXIDE CURABLE RUBBER COMPOUND CONTAINING HIGH- ISOPRENE BUTYL RUBBER

FIELD OF THE INVENTION The present invention relates to a peroxide curable rubber compound containing polymers with a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt.% comprising repeating units derived from at least one isoolefm monomer, more than 4.1 mol% of repeating units derived from at least one multiolefin monomer, as well as optionally further copolymerizable monomers, and repeating units derived from at least one multiolefin cross-linking agent containing no transition metal compounds and no organic nitro compounds. Preferably the polymers have a multiolefin content of greater than 4.1 mol%, and a gel content of less than 10 wt.% and have been produced at conversions ranging from 70 % to 95%. Preferably, the polymers have a Mooney viscosity in the range of from 25-70 MU, more preferably 30-60 MU, even more preferably 30-55 MU.

BACKGROUND OF THE INVENTION Butyl rubber is understood to be a copolymer of an isoolefm and one or more, preferably conjugated, multiolefms as comonomers. Commercial butyl comprise a major portion of isoolefm and a minor amount, not more than 2.5 mol %, of a conjugated multiolefin. The preferred isoolefm is isobutylene. However, this invention also covers polymers optionally comprising additional copolymerizable co-monomers. 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. The methyl chloride offers the advantage that A1C1 , a relatively inexpensive

Friedel-Crafts catalyst, is soluble in it, as are the isobutylene and isoprene comonomers. Additionally, the butyl rubber polymer is insoluble in the methyl chloride and precipitates out of solution as fine particles. The polymerization is generally carried out at temperatures of about -90°C to -100°C. See U.S. Patent No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295. The low polymerization temperatures are required in order to achieve molecular weights which are sufficiently high for rubber applications. 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. 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 C 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. One approach to obtaining a peroxide-curable butyl-based formulation lies in the use of conventional butyl rubber in conjunction with a vinyl aromatic compound like DNB and an organic peroxide (see JP-A- 107738/ 1994). In place of DNB, an electron-withdrawing group-containing polyfunctional monomer (ethylene dimethacrylate, trimethylolpropane triacrylate, Ν,Ν'- -phenylene dimaleimide) can also be used (see JP-A- 172547/1994). A commercially available terpolymer based on IB, IP, and DNB, Bayer XL-

10000, is curable with peroxides alone. However, this material does possess some significant disadvantages. For example, the presence of significant levels of free DNB can present serious safety concerns. In addition, since the DNB is incorporated during the polymerization process a significant amount of crosslinking occurs during manufacturing. The resulting high Mooney (ca. 60-75 MU, M_L1+8@125 °C) and presence of gel particles make this material extremely difficult to process. For these reasons, it would be desirable to have an isobutylene based polymer which is peroxide curable, completely soluble (i.e. gel free) and contains no, or trace amounts of, divinylbenzene in its composition. White et al. (US 5,578.682) have previously claimed a process for obtaining a polymer with a bimodal molecular weight distribution derived from a polymer that originally possessed a monomodal molecular weight distribution. The polymer, e.g., polyisobutylene, a butyl rubber or a copolymer of isobutylene and para-methylstyrene, was mixed with a polyunsaturated crosslinking agent (and, optionally, a free radical initiator) and subjected to high shearing mixing conditions in the presence of organic peroxide. This bimodalization was a consequence of the coupling of some of the free- radical degraded polymer chains at the unsaturation present in the crosslinking co- agent. It is important to note that this patent was silent about any filled compounds of such modified polymers or the cure state of such compounds. Sudo et. al. (US 5,994,465) have claimed a method for curing regular butyl, with isoprene contents ranging from 0.5 to 2.5 mol %, by treatment with a peroxide and a bismaleimide species. In essence, this patent blankets all commercially available grades of butyl rubber. As will be shown by our comparative examples, the cure states (delta torques) achieved for formulations based on RB301 or RB402 (both of which are materials which fall under the specification window described in 5994465) are significantly inferior to those observed for the inventive high IP butyl analogues of this invention. Co-Pending application CA-2,418,884 discloses a continuos process for producing polymers having a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt. % comprising repeating units derived from at least one isoolefm monomer, more than 4.1 mol % of repeating units derived from at least one multiolefin monomer and optionally further copolymerizable monomers in the presence of A1C1₃ and a proton source and/or cationogen capable of initiating the polymerization process and at least one multiolefin cross-linking agent wherein the process is conducted in the absence of transition metal compounds. These polymers are well suited for the inventive rubber formulations of this invention and with regards to jurisdictions allowing for this method are enclosed by reference herein.

SUMMARY OF THE INVENTION The present invention provides a peroxide curable rubber compound containing polymers with a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt.% comprising repeating units derived from at least one isoolefm monomer, more than 4.1 mol% of repeating units derived from at least one multiolefin monomer, as well as optionally further copolymerizable monomers, and repeating units derived from at least one multiolefin cross-linking agent containing no transition metal compounds and no organic nitro compounds.

SHORT DESCRIPTION OF THE DRAWINGS Fig. 1 shows the MDR cure characteristics of Examples 3-9

DETAILED DESCRIPTION OF THE INVENTION The Mooney viscosity of the polymer is determined using ASTM test D1646 using a large rotor at 125 °C, a preheat phase of 1 min, and an analysis phase of 8 min (ML1+8 @ 125 °C) The invention is not limited to a special isoolefm. However, isoolefms within the range of from 4 to 16 carbon atoms, in particular 4-7 carbon atoms, such as isobutene, 2-methyl-l-butene, 3 -methyl- 1-butene, 2-methyl-2-butene, 4-methyl-l- pentene and mixtures thereof are preferred. Most preferred is isobutene. The invention is not limited to a special multiolefin. Every multiolefin copolymerizable with the isoolefm known by the skilled in the art can be used. However, multiolefms within 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-methyl-l,5-hexadiene, 2,5- dimethyl-2,4-hexadiene, 2-methyl-l,4-pentadiene, 2-methyl-l,6-heptadiene, cyclopentadiene, methylcyclopentadiene, cyclohexadiene, 1-vinyl-cyclohexadiene and mixtures thereof, in particular conjugated dienes, are preferably used. Isoprene is particularly preferably used. In the present invention, β-pinene can also be used as a co-monomer for the isoolefm. As optional monomers every monomer copolymerizable with the isoolefms and/or dienes known by the skilled in the art can be used, α-methyl styrene, jj-methyl styrene, chlorostyrene, cyclopentadiene and methylcyclopentadiene are preferably used. Indene and other styrene derivatives may also be used in this invention The multiolefin content is at least greater than 4.1 mol%, more preferably greater than 5.0 mol%, even more preferably greater than 6.0 mol%, yet even more preferably greater than 7.0 mol%. Preferably, the monomer mixture comprises in the range of from 80% to 95% by weight of at least one isoolefm monomer and in the range of from 4.0% to 20% by weight of at least one multiolefin monomer including β-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 comprises in the range of from 83%> to 94%> by weight of at least one isoolefm monomer and in the range of from 5.0%> to 17% by weight of a multiolefin monomer or β-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 comprises in the range of from 85% to 93 % by weight of at least one isoolefm monomer and in the range of from 6.0% to 15%> by weight of at least one multiolefin monomer, including β-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, M_w, is preferably greater than 240 kg/mol, more preferably greater than 300 kg/mol, even more preferably greater than 500 kg/mol, yet even more preferably greater than 600 kg/mol. In connection with this invention the term "gel" is understood to denote a fraction of the polymer insoluble for 60 min in cyclohexane boiling under reflux. The gel content is preferably less than 10 wt.%, more preferably less than 5 wt%>, even more preferably less than 3 wt%, yet even more preferably less than 1 wt%. There are no organic nitro compounds or transition metals present. The butyl polymer further comprises unites derived from one or more multiolefin cross-linking agents. 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 particularly restricted. Preferably, the cross-linking comprises a multiolefinic hydrocarbon compound. Examples of these are norbornadiene, 2-isopropenylnorbornene, 2-vinyl-norbornene, 1,3,5-hexatriene, 2-phenyl- 1,3 -butadiene, divinylbenzene, diisopropenylbenzene, divinyltoluene, divinylxylene and Ci to C₂₀ alkyl-substituted derivatives thereof. More preferably, the multiolefin crosslinking agent is divinylbenzene, diisopropenylbenzene, divinyltoluene, divinyl-xylene and Ci to C₂₀ alkyl substituted derivatives thereof, and or mixtures of the compounds given. Most preferably the multiolefin crosslinking agent comprises divinylbenzene and diisopropenylbenzene. The polymerization preferably is performed in a continuous process in slurry (suspension), in a suitable diluent, such as chloroalkanes as described in US 5,417,930. The monomers are generally polymerized cationically, preferably at temperatures in the range from -120°C to +20°C, preferably in the range from -100°C to -20°C, and pressures in the range from 0.1 to 4 bar. The use of a continuous reactor as opposed to a batch reactor seems to have a positive effect on the polymer. Preferably, the process is conducted in at least one continuos reactor having a volume of between 0.1 m and 100 m , more preferable between 1 m and 10 m . Inert solvents or diluents known to the person skilled in the art for butyl polymerization may be considered as the solvents or diluents (reaction medium). These comprise alkanes, chloroalkanes, cycloalkanes or aromatics, which are frequently also mono- or polysubstituted with halogens. Hexane/chloroalkane mixtures, methyl chloride, dicl loromethane or the mixtures thereof may be mentioned in particular. Chloroalkanes are preferably used in the process according to the present invention. Said polymers with a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt.% comprising repeating units derived from at least one isoolefm monomer, more than 4.1 mol% of repeating units derived from at least one multiolefin monomer, as well as optionally further copolymerizable monomers, and repeating units derived from at least one multiolefin cross-linking agent containing no transition metal compounds and no organic nitro compounds may be partially or fully chlorinated or brominated. Bromination or chlorination can be performed according to the procedures described in Rubber Technology, 3^r Ed., Edited by Maurice Morton, Kluwer Academic Publishers, pp. 297 - 300 and references cited within this reference. The rubber compounds presented in this invention are ideally suitable for the production of moldings of all kinds, in particular tyre components and industrial rubber articles, such as bungs, damping elements, profiles, films, coatings. The polymers are used to this end in pure form or as a mixture with other rubbers, such as NR, BR, HNBR, NBR, SBR, EPDM or fluororubbers. The preparation of these compounds is known to those skilled in the art. In most cases carbon black is added as filler and a peroxide based curing system is used. For the compounding and vulcanization it is referred to Encyclopedia of Polymer Science and Engineering, Vol. 4, S. 66 et seq. (Compounding) and Vol. 17, S. 666 et seq. (Vulcanization). The invention is not limited to a special peroxide curing system. For example, inorganic or organic peroxides are suitable. Preferred are organic peroxides such as dialkylperoxides, ketalperoxides, aralkylperoxides, peroxide ethers, peroxide esters, such as di-tert.-butylperoxide, bis-(tert.-butylperoxyisopropyl)-benzol, dicumylperoxide, 2,5 -dimethyl-2, 5 -di(tert. -butylperoxy)-hexane, 2,5 -dimethyl-2, 5 - di(tert.-butylperoxy)-hexene-(3), 1 , l-bis-(tert.-butylperoxy)-3,3,5-trimethyl- cyclohexane, benzoylperoxide, tert.-butylcumylperoxide and tert.-butylperbenzoate. Usually the amount of peroxide in the compound is in the range of from 1 to 10 phr (= per hundred rubber), preferably from 1 to 5 phr. Subsequent curing is usually performed at a temperature in the range of from 100 to 200°C, preferably 130 to 180°C. Peroxides might be applied advantageously in a polymer-bound form. Suitable systems are commercially available, such as Polydispersion T(VC) D-40 P from Rhein Chemie Rheinau GmbH, D (= polymerbound di-tert.-butylperoxy-isopropylbenzene). Even if it is not preferred, the compound may further comprise other natural or synthetic rubbers such as BR (polybutadiene), ABR (butadiene/acrylic acid-Cι-C4- alkylester-copolymers), CR (polychloroprene), IR (polyisoprene), SBR

(styrene/butadiene-copolymers) with styrene contents in the range of 1 to 60 wt%, NBR (butadiene/acrylonitrile-copolymers with acrylonitrile contents of 5 to 60 wt%, HNBR (partially or totally hydrogenated NBR-rubber), EPDM (ethylene/propylene/diene- copolymers), FKM (fluoropolymers or fluororubbers), and mixtures of the given polymers. The rubber composition according to the invention can 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, which depend inter alia on the intended use. Conventional amounts are e.g. from 0.1 to 50 wt.%>, based on rubber. Preferably the composition furthermore comprises in the range of 0.1 to 20 phr of an organic fatty acid, preferably a unsaturated fatty acid having one, two or more carbon double bonds in the molecule which more preferably includes 10% by weight or more of a conjugated diene acid having at least one conjugated carbon-carbon double bond in its molecule. Preferably those fatty acids have in the range of from 8- 22 carbon atoms, more preferably 12-18. Examples include stearic acid, palmic acid and oleic acid and their calcium-, zinc-, magnesium-, potassium- and ammonium salts. The ingredients of the final compound are mixed together, suitably at an elevated temperature that may range from 25 °C to 200 °C. Normally the mixing time does not exceed one hour and a time in the range from 2 to 30 minutes is usually adequate. The mixing is suitably carried out in an internal mixer such as a Banbury mixer, or a Haake or Brabender miniature internal mixer. A two roll mill mixer also provides a good dispersion of the additives within the elastomer. An extruder also provides good mixing, and permits shorter mixing times. It is possible to carry out the mixing in two or more stages, and the mixing can be done in different apparatus, for example one stage in an internal mixer and one stage in an extruder. However, it should be taken care that no unwanted pre-crosslinking (= scorch) occurs during the mixing stage.

The inventive compounds are very well suited for the manufacture of shaped articles, especially shaped articles for high-purity applications such as fuel cell components (e.g. condenser caps), medical devices,

The following Examples are provided to illustrate the present invention: Examples

Equipment Polymer unsaturation was determined through 1H NMR spectroscopy with the use of a Bruker 500 MHz NMR Spectrometer. NMR samples used to determine isoprene content were prepared in CDC1₃. NMR samples used to determine DVB content were prepared in THF-d₈. Microstructure information was calculated with the use of previously established integration methods. Peak shifts were referenced to a TMS internal standard. GPC analysis was performed with the use of a Waters Alliance 2690

Separations Module and Viscotek Model 300 Triple Detector Array. GPC samples were prepared by dissolution in THF. Polymer gel content was determined through conventional gravimetric analysis of the dry, hydrocarbon-insoluble fraction (insoluble in boiling cyclohexane, under agitation for a period of 60 minutes). ' Mixing was accomplished with the use of a miniature internal mixer (Brabender MIM) from C. W. Brabender, consisting of a drive unit (Plasticorder^® Type PL-V151) and a data interface module. Cure characteristics were determined with a Moving Die Rheometer (MDR) test carried out according to ASTM standard D-5289 on a Monsanto MDR 200 (E). The upper disc oscillated though a small arc of 1 degree. Curing was achieved with the use of an Electric Press equipped with an Allan- Bradley Programmable Controller. Stress-strain tests were carried out using an Instron Testmaster Automation System, Model 4464. The compounds presented in these examples employed the use of carbon black (IRB #1), a peroxide (DI-CUP 40C, Struktol Canada Ltd.) and a co-agent (HVA-2). All of the compounds studied were composed of: Polymer: 100 phr Carbon black (IRB #7; N330): 50 phr Peroxide (DI-CUP 40 C): 4 phr Optionally, 2.5 phr of HVA-2 was also used. Mixing was achieved with the use of a Brabender internal mixer (capacity ca. 75 g) with a starting temperature of 60 °C and a mixing speed of 50 rpm according to the following sequence: 0.0 min: polymer added 1.5 min: carbon black added, in increments 6.0 min: peroxide added 7.0 min: co-agent (HVA-2) added 8.0 min: mix removed In cases where no co-agent was present, the peroxide was added 7.0 min into the mixing process. The final compound was refined on a 6" x 12" mill.

Example 1 The following example illustrates our ability to produce, via a continuous process, a novel grade of IIR possessing an isoprene content of up to 5.0 mol %> and Mooney viscosity (ML 1+8 @ 125 °C) between 35 and 40 MU. The monomer feed composition was comprised of 2.55 wt. % of isoprene (IP or IC5) and 27.5 wt. %> of isobutene (IP or IC4). This mixed feed was introduced into the continuous polymerization reactor at a rate of 5900 kg/hour. In addition, DVB was introduced into the reactor at a rate of 5.4 to 6 kg/hour. Polymerization was initiated via the introduction of an AlCl₃/MeCl solution (0.23 wt. % of A1C1₃ in MeCl) at a rate of 204 to 227 kg/hour. The internal temperature of the continuous reaction was maintained between -95 and -100 °C through the use of an evaporative cooling process. Following sufficient residence within the reactor, the newly formed polymer crumb was separated from the MeCl diluent with the use of an aqueous flash tank. At this point, ca. 1 wt. %> of stearic acid was introduced into the polymer crumb. Prior to drying, 0.1 wt. % of Irganox® 1010 was added to the polymer. Drying of the resulting material was accomplished with the use of a conveyor oven. Table 1 details the characteristics of the final material.

Example 2 The following example illustrates our ability to produce, via a continuous process, a novel grade of IIR possessing an isoprene content of up to 8.0 mol %> and Mooney viscosity (ML 1+8 @ 125 °C) between 35 and 40 MU. The monomer feed composition was comprised of 4.40 wt. % of isoprene (IP or IC5) and 25.7 wt. % of isobutene (IP or IC4). This mixed feed was introduced into the continuous polymerization reactor at a rate of 5900 kg/hour. In addition, DVB was introduced into the reactor at a rate of 5.4 to 6 kg/hour. Polymerization was initiated via the introduction of an AlCl₃/MeCl solution (0.23 wt. % of A1C1₃ in MeCl) at a rate of 204 to 227 kg/hour. The internal temperature of the continuous reaction was maintained between -95 and -100 °C through the use of an evaporative cooling process. Following sufficient residence within the reactor, the newly formed polymer crumb was separated from the MeCl diluent with the use of an aqueous flash tank. At this point, ca. 1 wt. % of stearic acid was introduced into the polymer crumb. Prior to drying, 0.1 wt. % of Irganox® 1010 was added to the polymer. Drying of the resulting material was accomplished with the use of a conveyor oven. Table 2 details the characteristics of the final material. It is important to note that although the experimental high IP IIR elastomers described in Examples 1 and 2 contain trace amounts of DVB, (ca. 0.07 - 0.11 mol %) this level is less than 10 % of that found in commercial XL- 10000 (ca. 1.2 - 1.3 mol %).

Example 3 - Comparative This compound was based on a commercial butyl rubber (Bayer Butyl 301, isobutylene content = 98.4 mol %, isoprene content = 1.6 mol %) according to the recipe presented above. In this case, 2.5 phr of HVA-2 was employed in the formulation. As can be seen from Figure 1 and Table 3, moderate cure reactivity is observed for this system. This suggests that the presence of IP in the polymer main chain is an important factor in determining the peroxide-curability of polyisobutylene based copolymers. It is also important to note that a significant degree of reversion is seen for this system. This suggests that a chain degradation mechanism may be acting in conjunction with the crosslinking reaction.

Example 4 - Comparative This compound was based on a commercial butyl rubber (Bayer Butyl 402, isobutylene content = 97.9 mol %>, isoprene content = 2.1 mol %) according to the recipe presented above. In this case, 2.5 phr of HVA-2 was employed in the formulation. As can be seen from Figure 1 and Table 3, moderate cure reactivity is observed for this system. This suggests that the presence of IP in the polymer main chain is an important factor in determining the peroxide-curability of polyisobutylene based copolymers. It is also important to note that a significant degree of reversion is seen for this system. This suggests that a chain degradation mechanism may be acting in conjunction with the crosslinking reaction.

Example 5 - Comparative This compound was based on a commercial butyl rubber (Bayer XL- 10000, isoprene content = 1.6 mol %, DVB content = 1.2 - 1.3 mol %>, gel content 70 - 85 wt. %) according to the recipe presented above. In this case, a traditional XL- 10000 formulation was used in which HVA-2 was omitted from the formulation. As can be seen from Figure 1 and Table 3, significant cure reactivity is observed for this system.

Example 6 - Invention This compound was based on the experimental high IP IIR described in Example 1 (isoprene content = 5.0 mol %, DVB content = 0.07 - 0.11 mol %>, gel content < 5 wt. %>) according to the recipe presented above. In this case, HVA-2 was omitted from the formulation. As can be seen from Figure 1 and Table 3, evidence of cure reactivity with no reversion is observed for this system.

Example 7 - Invention This compound was based on the experimental high IP IIR described in Example 2 (isoprene content = 7.5 mol %, DVB content = 0.07 - 0.11 mol %>, gel content < 5 wt. %) according to the recipe presented above. In this case, HVA-2 was omitted from the formulation. As can be seen from Figure 1 and Table 3, evidence of cure reactivity with no reversion is observed for this system.

Example 8 - Invention This compound was based on the experimental high IP IIR described in

Example 2 (isoprene content = 5.0 mol %, DVB content = 0.07 - 0.11 mol %_>, gel content < 5 wt. %) according to the recipe presented above. In this case, 2.5 phr of

HVA-2 was added to the formulation. As can be seen from Figure 1 and Table 3, evidence of significant cure reactivity is observed for this system.

Example 9 - Invention This compound was based on the experimental high IP IIR described in

Example 2 (isoprene content = 7.5 mol %, DVB content = 0.07 - 0.11 mol %, gel content < 5 wt. %) according to the recipe presented above. In this case, 2.5 phr of

The preceding examples clearly demonstrate that both RB301 (Example 3) and RB402 (Example 4) undergo some cure reactivity on thermal treatment in the presence of HVA-2. However, following an initial rise in torque a rapid decrease in the elastic modulus is observed (Figure 1). This suggests that chain scission is the dominant mechanism operating in this system. On elevation of the IP content to 5.0 and 7.5 mol % (Examples 6 and 7 respectively), no reversion process was detected by rheometric analysis even in the absence of the HVA-2 co-agent. This suggests that the presence of elevated levels (cf. RB301 and RB402) of IP in the polymer backbones of these samples acts to stabilize these materials against free-radical mediated chain scission. The cure reactivity as detected for Examples 6 and 7 is significantly less than that observed for XL-10000 (Example 5). However, the inclusion of 2.5 phr HNA-2 into formulations containing the high IP IIR samples (Example 8 and 9) resulted in a dramatic increase in cure reactivity. As can be seen from Figure 1, the cure state achieved for Examples 8 and 9 is significantly higher than that observed for the XL- 10000 comparative formulation. Importantly, the stress-strain properties associated with the formulations described in Examples 8 and 9 are consistent with those observed for the standard XL- 10000 formulation. However, the ultimate tensile strength measured for Examples 8 and 9 is superior to that determined for the XL- 10000 control. In summary, the use of IIR with elevated levels of IP (5.0 and 7.5 mol % in this case) in conjunction with a co-agent such as HNA-2 allows for the preparation of peroxide curable butyl formulations with similar or better tensile properties as that observed for the XL- 10000 control compound. In addition, the processability of compounds based on experimental high IP IIR is far superior as a result of the significantly reduced gel content (cf. XL- 1000) present in these polymers.

Table 1.

Table 2.

Table 3.

Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Δ Torque (dNm) 4.32 4.69 15.24 5.95 7.09 22.4 23.09 Tensile 300% (MPa) 2.11 2.09 N/A 3.28 4.47 N/A N/A Ultimate Tensile (MPa) 7.81 6.14 4.81 7.35 9.16 9.24 8.58 Ultimate Elongation (%) 788 742 129 493 476 139 126 Hardness, Shore A (Pts) 42 42 61 40 43 62 63

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Claims

1. A peroxide curable rubber compound containing polymers with a Mooney viscosity of at least 25 Mooney-units and a gel content of less than 15 wt.%> comprising repeating units derived from at least one isoolefin monomer, more than 4.1 mol% of repeating units derived from at least one multiolefin monomer, as well as optionally further copolymerizable monomers, and repeating units derived from at least one multiolefin cross-linking agent containing no transition metal compounds and no organic nitro compounds.

2. A compound according to claim 1, where the polymer contains greater than 5 mol % of repeating units derived from a multiolefin and a gel content of less than 10 wt. %.

3. A compound according to claim 1, where the polymer contains greater than 7 mol % of repeating units derived from a multiolefin and a gel content of less than 5 wt. %>.

4. A compound according to any of claims 1-3, wherein said isoolefin monomer is isobutene.

5. A compound according to any of the claims 1-4 wherein said multiolefin crosslinking agent is divinylbenzene.

6. A compound according to any of the claims 1-5 where the polymer is either partially or completely chlorinated or brominated.

7. A compound according to any of the claims 1-6 further comprising at least one peroxide.

8. A shaped article comprising a compound according to any of claims 1-7. An article according to claim 8 in the form of a medical device or a condenser cap.