Free radical polymerisation studies of 4‐substituted styrenes, 2. Termination and chain transfer in the polymerisation of styrene, 4‐methoxystyrene and 4‐methylstyrene

The bulk polymerisation of styrene, 4‐methoxystyrene and 4‐methylstyrene was investigated at 60°C using 2,2′‐azoisobutyronitrile (AIBN) as the initiator. Initial rates ( R i 0 ) and efficiencies ( f ) of initiation were calculated from the radioactive content of the polymer obtained by labelling the initiator as either [methyl‐ 14 C 4 ]AIBN or [cyano‐ 14 C 2 ]AIBN. Rates of polymerisation determined gravimetrically are in good agreement with rates determined by the dilatometer technique. An empirical linear relationship between the number of initiator fragments and the degree of monomer conversion was noted. Factors affecting the termination of polymer radicals are discussed and compared with other published work. The polymerisation reaction is terminated predominantly by combination in the case of all three monomers, and chain transfer constants to initiator and to monomer are of the order of 10 −3 and 10 −5 , respectively.