Cationic polymerization of bis(1‐alkylvinyl)benzenes and related monomers, 5. New thermostable polyindanes

The cationic cyclopolymerization of six monomers of the type “1,4‐bis(alk‐2‐en‐2‐yl)benzene” is described. The length of the unsaturated chains of the monomers ranges from 3 (propenyl) to 8 (octenyl) carbon atoms. The polymerization yields polyindanes containing different isomeric indane structure elements, which have alkyl substituents ranging from methyl to hexyl groups. The number of carbon atoms in the alkyl side chains greatly influences the glass transition temperature Tg, which is depressed from 246°C (methyl‐substituted polyindane) to 26°C (hexyl‐substituted polyindane). Thermal stability is also affected, though far less than Tg: the temperature, at which the material has lost 2% of its original weight is lowered from 420°C to 340°C. The polyindanes are soluble in a number of organic solvents. Their degree of polymerization is limited by a side reaction which provides non‐reactive end groups. Thus, the number‐average molar masses obtained are between 2800 and 4300 g/mol.