Polyisobutylene

a polymer of isobutylene, [—C(CH₃)₂—CH₂—]_n.

Polyisobutylenes are viscous liquids with molecular weight of 10,000–50,000 or rubbery, amorphous products with a molecular weight of 70,000–225,000 that have cold flow. Their softening point is 185°-200°C and they do not decompose up to 350°C, although their mechanical properties deteriorate significantly even at 100°C; they retain their elasticity down to – 50°C.

The characteristic features of polyisobutylenes are low gas permeability and high resistance to the action of acids, alkalies, and solutions of salts, as well as high dielectric indexes (loss tangent, 0.0002 at 50 hertz). They degrade gradually under the action of sunlight and ultraviolet rays (the addition of carbon black slows this process). Polyisobutylenes are soluble in hydrocarbons, chlorinated hydrocarbons, and ether.

In industry, polyisobutylenes are produced by ionic polymerization of the monomer at temperatures from –80° to – 100°C; they are processed using the ordinary equipment of the rubber industry. Polyisobutylenes combine easily with natural or synthetic rubbers, polyethylene, polyvinyl chloride, and phenol-formaldehyde resins.

Polyisobutylenes are used in the production of electrical insulation and anticorrosion coatings for chemical apparatus and pipelines and in the preparation of adhesives and the production of waterproof fabrics and hermetic compounds. Polyisobutylenes with molecular weights of 10,000–20,000 are used as additives and thickeners in lubricants.

Polyisobutylenes are produced in the USSR, the Federal Republic of Germany (Oppanol and Dynagen), and the USA (Vistanex).