Butyl rubber from isobutylene monomers

Butyl rubber (HR) is widely used for inner tubes and as a sealant. It is produced using the cationic polymerization with the copolymerization of isobutylene in the presence of a small amount (10%) of isoprene. Thus, the random copolymer chain contains a low concentration of widely spaced isolated double bonds, from the isoprene, that are later cross-linked when the butyl rubber is cured. A representation is shown in structure 5.20 where the number of units derived from isobutylene units greatly outnumbers the number of units derived from the isoprene monomer. The steric requirements of the isobutylene-derived units cause the chains to remain apart giving it a low stress to strain value and a low Tg. 

Butyl rubber is exclusively made by a solution polymerization process. Hence, nanoparticles can only be introduced as a dispersion with the butyl polymer before the solvent is removed, with the monomer, or in a standard compounding protocol. Butyl rubber is prepared from isobutylene. There are no double bonds available for cure after polymerization. A small amount of isoprene is added to the polymerization process to provide for the double bonds necessary for cure. Bromination of the polymer is also done to provide cross-linking sites. 

Butyl rubber n (1940). A synthetic elastomer produced by copolymerizing isobutylene with a small amount (ca 2%) of isoprene or butadiene. It has good resistance to hear, oxygen and ozone, and low gas permeability. Thus, it is widely used in inner tubes and to line tubeless tires. Butyl rubber is a vinyl polymer, and is very similar to polyethylene and polypropylene in structure, except that every other carbon is substituted with two methyl groups. It is made from the monomer isobutylene, by cationic vinyl polymerization. It can also go by the name of polyisobutylene. (1) Generic name for vulcanizable elastic copolymers of isobutylene and small amounts of diolefins. (2) Mixture of isobutylene, 98% and... 

Butyl Rubber. In butyl rubber, isoprene is enchained predominantly (90-95%) by 1,4-addition and head-to-tail arrangement (81-84). The remaining minor isoprene species may be interpreted spectroscopically either as 1,2-enchained (83,84) or as branched species from 1,4-addition (85). Depending on the grade, the unsaturation in butyl rubber is between 0.5 and 3 mol%. The glass-transition temperature of butyl rubber is about —65°C (86). With the low content of isoprene and a near-imity reactivity ratio between isoprene and isobutylene (87), a random distribution of enchained isoprene monomer in butyl rubber is achieved. The molecular weight distribution in butyl rubber is mostly with Mw/Mn of 3-5. 

There are many other industrial examples such as acrylic fibers made from polyacrylonitrile (with 7% vinyl acetate). The monomer is fairly water soluble at about 5% and the polymerization occurs in the aqueous phase. However, the polymer is insoluble in water. The primary particles precipitate and agglomerate, forming larger particles that are stabilized by ionic initiator end groups. Butyl rubber (isobutylene+ < 5% isoprene) is produced by cationic polymerization with aluminum trichloride catalyst in methyl chloride at about -100 °C. The polymer precipitates as fine polymer particles from the reaction medium. 

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