Cationic mechanism butyl rubber

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. 

Similarly, 2-methylpropene (isobutene) is an important monomer. It only polymerizes by a cationic mechanism, and its copolymers with dienes are known as butyl rubber. Higher 1-alkenes (1-butene, 1-hexene, 1-octene) are important copolymerization components [4, 5] they produce tailored branching of some polyethylene types prepared by a coordination mechanism. Longer-chain alkenes (Cjq, C,2, Cj ) are also sometimes used as comonomers... 

Although butyl rubber is by far the most important commercial elastomer to be synthesized by cationic polymerization, several heterocyclic monomers provide useful elastomeric materials via this mechanism also. Epichlorohydrin can be polymerized to high molecular weight using a complex catalyst formed from a trialkylaluminum compound and water as shown in Eq. (58) [64, 130-132], For copolymerizations with ethylene oxide, a catalyst formed from a trialkylaluminum compound, water, and acetylacetone is useful [64,130], The mechanism proposed for these polymerizations is... 

Polymers are produced by one of two processes, addition or condensation polymerization. Addition polymerization occurs by one of three mechanisms, radical (e.g., low density branched polyethylene), cationic (e.g., butyl rubbers), or anionic (e.g., polystyrene). Condensation polymerization is used to produce Nylon 6,6 from adipic acid and hexamethylenediamine with the elimination of water. Industrially,... 

Butyl rubber is prepared from 2-methylpropene [115-11-7] (isobutylene) and 2-methyl-1,3-butadiene [78-79-5] (isoprene). Isobutylene with a purity of >99.5 wt% and isoprene with a purity of >98 wt% are used to prepare high molecular weight butyl rubber. Water and oxygenated organic compounds are minimized by feed purification systems because these impurities interfere with the cationic polymerization mechanism. Copolymers of isobutylene can also be prepared from mixed C4 olefin containing streams that contain re-hutene. These copolymers are generically known as polybutenes. 

The principal feature that both anionic and radical polymerization have in common is that a highly reactive species reacts with a monomer containing an alkene to generate a chain-extended species that itself is a highly reactive species (e.g., an anion or a radical). The two other principal chain polymerization mechanisms that are widely used are cationic and metal-catalyzed polymerizations. Cationic polymerization is used for the preparation of butyl rubber and metal-catalyzed... 

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