Typical examples of such monomer include vinyl aromatic hydrocarbons containing 8 to 12 carbon atoms such as styrene, vinyl toluene, tert-butylstyrene, ??-methylstyrene or o-, m- or p-methyl ??-methylstyrene; aromatic cyclic vinyl monomers such as indene or methylindene, aliphatic monolefins containing 4 to 12 carbon atoms such as butene, pentene or hexene, aliphatic diolefins containing 4 to 12 c