Isobutylene rubber

Isoprene -isobutylene rubbers Cannot be made into ebonite... 

M. Onizawa. Method for crosslinking of isoprene-isobutylene rubber, ethyl-ene-propylene-diene rubber containing ethylidenenorbomene as unsaturated component, or mixture thereof and crosslinked rubber product obtained by said method. US Patent 6403 713, June 11, 2002. 

Butyl mbber, a copolymer of isobutjiene with 0.5—2.5% isoprene to make vulcanization possible, is the most important commercial polymer made by cationic polymerization (see Elastomers, synthetic-butyl rubber). The polymerization is initiated by water in conjunction with AlCl and carried out at low temperature (—90 to —100° C) to prevent chain transfer that limits the molecular weight (1). Another important commercial appHcation of cationic polymerization is the manufacture of polybutenes, low molecular weight copolymers of isobutylene and a smaller amount of other butenes (1) used in adhesives, sealants, lubricants, viscosity improvers, etc. 

Butyl and Halobutyl Rubber. Butyl mbber is made by the polymerization of isobutylene a small amount of isoprene is added to provide sites for curing. It is designated HR because of these monomers. Halogenation of butyl mbber with bromine or chlorine increases the reaction rate for vulcanization and laminates or blends of halobutyl are feasible for production of mbber goods. It is estimated that of the - 100 million kg of butyl (UR) and halobutyl (HIIR) mbber in North America, over 90% is used in tire apphcations. The halogenated polymer is used in the innerliner of tubeless tires. Butyl mbber is used to make innertubes and curing bladders. The two major suppHers of butyl and halobutyl polymers in North America are Exxon and Bayer (see ELASTOLffiRS,SYNTHETIC-BUTYLrubber). 

Butyl Rubber isobutylene—isoprene good good ... 

Butyl Rubber. Butyl mbber was the first low unsaturation elastomer, and was developed ia the United States before World War II by the Standard Oil Co. (now Exxon Chemical). It is a copolymer of isobutylene and isoprene, with just enough of the latter to provide cross-linking sites for sulfur vulcanization. Its molecular stmcture is depicted ia Table 1. 

Butyl rubber and other isobutylene polymers of technological importance iaclude various homopolymers and isobutylene copolymers containing unsaturation achieved by copolymerization with isoprene. Bromination or chlorination of the unsaturated site is practiced commercially, and other modifications are beiag iavestigated. 

Halogenated Butyl Rubber. Halogenation at the isoprene site ia butyl mbber proceeds by a halonium ion mechanism leading to a double-bond shift and formation of an exomethylene alkyl haUde. Both chlorinated and brominated mbber show the predominate stmcture (1) (>80%), by nmr, as described eadier (33,34). Halogenation of the unsaturation has no apparent effect on the isobutylene backbone chains. Cross-linked samples do not crystallize on extension due to the chain irregularities introduced by the halogenated isoprene units. 

Until the mid-1950s the only polyolefins (polyalkenes) of commercial importance were polyethylene, polyisobutylene and isobutylene-isoprene copolymers (butyl rubber). Attempts to produce polymers from other olefins had, at best, resulted only in the preparation of low molecular weight material of no apparent commercial value. 

Butyl rubber (BR) and polyisobutylene (PIB) are widely used in adhesives as primary elastomeric binders and as tackifiers and modifiers. The main difference between these polymers is that butyl is a copolymer of isobutylene with a minor amount of isoprene (which introduces unsaturation due to carbon-carbon double bonds), while polyisobutylene is a homopolymer. 

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

Functionalized rubbers. Butyl rubber (isobutylene with about 2% iso-prene) has been functionalized through the residual double bonds via the bro-mobutyl intermediate to produce a material with 2% conjugated diene (see Fig. 19). This resin shows high reactivity towards e-beam or UV (free radical or cationic [53]). The bromo butyl intermediate has also been used to attach acrylate or photoinitiator groups to the butyl backbone [54]. 

Cationic polymerizations work better when the monomers possess an electron-donating group that stabilizes the intermediate carbocation. For example, isobutylene produces a stable carbocation, and usually copolymerizes with a small amount of isoprene using cationic initiators. The product polymer is a synthetic rubber widely used for tire inner tubes ... 

Butyl rubber is a copolymer of isobutylene (97.5%) and isoprene (2.5%). The polymerization is carried out at low temperature (below... 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

Problem 31.6 Draw the structure of an alternating segment of butyl rubber, a copolymer of iso-prene (2-methyl-],3-butadiene) and isobutylene (2-methylpropene) prepared using a cationic initiator. 

Living polymerization of isobutylene (IB) by di- and trifunctional initiators to make the nearly uniform rubber mid-block... 

Jacob S., Majoros I., and Kennedy J.P., Novel thermoplastic elastomers Star-blocks consisting of eight poly(styrene-b-isobutylene) arms radiating from a calex[8]arenecore. Rubber Chem. TechnoL, 71, 708, 1998. 

FIGURE 11.12 Interaction energy density versus 4-methyl styrene content. (From Raboney, M., Gamer, R.T., Elspass, C.W., and Peiffer, D.G., Phase Behavior of Brominated Poly(Isobutylene-co-4-Methylstyrene)/ General Purpose Rubber Blends. Rubber Division, Proceedings of the American Chemical Society, Nashville, TN, Sept. 29-Oct. 2, 1998, Paper No. 36.)... 

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

The sol fractions occurring in a series of cross-linked Tutyl rubber copolymers consisting of a small proportion of isoprene with isobutylene units have been found to vary with y in accordance with Eq. (50). The unfortunately large experimental inaccuracy precluded a precise test, however. 

IIR Isobutylene-isopropene rubber PEG Poly (ethylene glycol)... 

Butyl rubber (a copolymer of isobutylene and 1-3 mole per cent isoprene) and its halogenated derivatives have unsaturation in the carbon-carbon backbone and consequently do not have as good aging properties as EPDM. There are also reports (9-12) that ozone-resistant butyl rubber with a high degree of unsaturation can be prepared by copolymerization of isobutylene with either cyclopentadiene or 9-pinene. 

The most industrially significant polymerizations involving the cationic chain growth mechanism are the various polymerizations and copolymerizations of isobutylene. In fact, about 500 million pounds of butyl rubber, a copolymer of isobutylene with small amounts of isoprene, are produced annually in the United States via cationic polymerization [126]. The necessity of using toxic chlorinated hydrocarbon solvents such as dichloromethane or methyl chloride as well as the need to conduct these polymerizations at very low temperatures constitute two major drawbacks to the current industrial method for polymerizing isobutylene which may be solved through the use of C02 as the continuous phase. 

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