Polyisobutylene

Chemical properties

Polyisobutylene is composed of long-chain hydrocarbon formed by polymerization of isobutene, and is extremely stable under normal conditions. It is transparent non-noxious high-consistency semi-solid polymer free of impurities.

Chemical properties

The physical properties of polyisobutene are very dependent on molecular weight. Polymers with average molecular weight (Mw) of about 15 000 are sticky viscous liquids whilst those with molecular weight of 100000-200000 are rubber-like, resembling unmilled crepe rubber.
Polyisobutene is non-crystalline when unstretched and is therefore soluble at room temperature in hydrocarbons and halogenated hydrocarbons. The material 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:
Polyisobutene may be chlorinated but the reaction is accompanied by severe degradation.
A limitation of polyisobutene is its tendency to cold flow and, as a result, the polymer finds little use in self-supporting form. Applications are restricted mainly to adhesives, fabric and paper coatings, and blends with other polymers. Low molecular weight polyisobutene is also used in caulking compounds.

The Uses of Polyisobutylene

polyisobutene (hydrogenated) is an emollient.
Polyisobutylene, sometimes called butyl rubber, and other times PIB, is a vinyl polymer. It's 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.
Polyisobutylene is a synthetic rubber, or elastomer. It's special because it's the only rubber that's gas impermeable. That is, it's the only rubber that can hold air for long periods of time. You may have noticed that balloons will go flat after a few days. This is because they are made of polyisoprene, which is not gas impermeable. Because polyisobutylene will hold air, it is used to make things like the inner tubes, liner layers of tires, and the inner liners of basketballs.

Definition

ChEBI: A polymer composed of repeating 1,1-dimethylethylene units.

Preparation

Silicone rubbers are prepared as follows:

Other groups may replace the methyl groups. Silicone rubbers have excellent ozone and weathering resistance, good electrical properties, and good adhesion to metal.