Poly(styrene-co-alpha-methylstyrene)

Additive to sealants, caulks, adhesives, and coatings.

a-Methylstyrene is obtained from benzene and propylene by the following route:

a-Methylstyrene is not readily polymerized by free radical initiators but it is susceptible to cationic polymerization. Polymerization can be effected, for example, in ethyl chloride at -130C with aluminium chloride but poly(a-methylstyrene) prepared in this manner is a clear brittle solid which has little commercial application. Polymers with much lower molecular weight (300-600) obtained by using alkaline earth catalysts, however, are viscous liquids and have found some use as plasticizers in surface coatings and adhesives.
Styrene-a-methylstyrene copolymers are marketed for extrusion and injection moulding. Compared to polystyrene, these copolymers have the advantage of higher softening points (104-106C); they too are transparent and colourless.