Free radical polymerisation studies of 4‐substituted styrenes, 1. The reactions of 2‐cyano‐2‐propyl radicals with styrene, 4‐methoxystyrene and 4‐methylstyrene

Only a limited amount of work has been previously published concerning the free radical polymerisation of 4‐methoxystyrene and 4‐methylstyrene initiated by 2,2′‐azoisobutyronitrile (2,2′‐azobis(2‐methylpropiononitrile)) (AIBN). The present investigation was, therefore, undertaken to establish whether the substituents have a considerable affect on the reaction of 2‐cyano‐2‐propyl radicals at 60°C, relative to styrene. Rates of polymerisation were determined gravimetrically and rates of initiation were calculated from the radioactivity of the polymer, obtained by labelling AIBN with carbon‐14. Number average molecular weights ( M n ) were determined by gel permeation chromatography (GPC). The order of reaction with respect to initiator concentration was found to be 0.50 for styrene and 0.48 for both 4‐methoxystyrene and 4‐methylstyrene, which was attributed to their susceptibility to primary radical termination. Polystyryl radicals were also found to undergo primary radical termination and values for the constant { k prt /( k i · k p )} were determined as 1.37 × 10 4 mol · s · dm −3 for styrene, 1.47 × 10 4 mol · s · dm −3 for 4‐methoxystyrene and 1.30 × 10 4 mol · s · dm −3 for 4‐methylstyrene. The rate of initiation for 4‐methoxystyrene is greater than for styrene, which in turn is greater than for 4‐methylstyrene.