Polyisobutene

Polyisobutene is often referred to as butyl rubber and is produced in a wide range of molecular weights; the lower molecular weight Polyisobutenes are very viscous, soft, and tacky semi-liquids while the higher molecular weight Polyisobutenes are tough and elastic rubbery solids.

Polyisobutene is resistant to most acids, alkalis and aqueous solutions, as would be expected from its saturated hydrocarbon structure and absence of tertiary hydrogen atoms. The lack of tertiary hydrogen atoms renders polyisobutene more resistant to oxidation than polypropylene; also, the less numerous and partially shielded methylene groups in polyisobutene are less reactive than those in polyethylene. However, polyisobutene is rather susceptible to thermal degradation since chain scission is favoured by the greater stability of the resultant tertiary free radical:free radical of PolyisobutylenePolyisobutene may be chlorinated but the reaction is accompanied by severe degradation.

Polyisobutene is non-crystalline when unstretched and is therefore soluble at room temperature in hydrocarbons and halogenated hydrocarbons.

Polyisobutene can increase the thickness of the lipid (oil) portion of cosmetics and personal care products. It dries to form a thin coating on the skin, hair or nails, and is used to hold together the ingredients of a compressed cake.