polyisobutylene

Polyisobutylene is an addition polymer derived from the monomer isobutylene (2-methylpropene). Its repeat unit is -CH2-C(CH3)2-, and the polymer is typically atactic. PIB is prepared mainly by cationic polymerization of isobutylene using strong Lewis acid catalysts such as boron trifluoride complexes, aluminum halides, or related systems, often in the presence of initiating halides or alkyl halides. Polymerizations are conducted at low temperatures to obtain high-molecular-weight products with controlled end groups depending on the initiator and quenching conditions. Commercial PIBs span a broad range of molecular weights, yielding liquids, waxy solids, or elastomeric materials.

Key properties include chemical inertness, low glass transition temperature, and very low gas permeability. PIB is resistant to oxidation and remains flexible over a wide temperature range, making it useful in applications requiring gas barriers and impermeable, stable polymers. The material is generally non-petroleum-based in polarity, hydrophobic, and compatible with many rubbers and plastics.

Common applications reflect PIB’s combination of stability and impermeability. It is used as a thickening agent and tackifier in lubricants and rubber compounds, helping to modify viscosity and adhesive properties. In the rubber industry, polyisobutylene forms the basis of butyl rubber when copolymerized with small amounts of isoprene, imparting excellent gas impermeability and air retention to tire inner liners and seals. PIB is also employed in sealants, caulks, and various coatings and adhesives where elasticity, impermeability, and chemical resistance are valued.

Safety and handling follow standard polymer practices; PIB is generally regarded as chemically inert, with handling considerations mainly related to dust or fine powders and process conditions.