The initiator efficiency of 2, 2′‐azobisisobutyronitrile in the polymerization of styrene and methyl methacrylate, and dicumyl peroxide as a polymerization initiator

The polymerization of styrene with 2,2′‐azobisisobutyronitrile (Azo I) as initiator has been studied at eight temperatures from 30° to 85°C. and methyl methacrylate at six temperatures from 30° to 67°C. With the use of the expression for the thermal rate of decomposition of Azo I given in a previous paper, the maximum scavenger efficiencies of styrene and methyl methacrylate have been calculated to be 60 and 80%, respectively. The efficiency is shown to be almost independent of initiator concentration except in styrene at very low concentrations of Azo I, where f, increases rapidly. If the true efficiency in methyl methacrylate is the same as in styrene, then the ratio of termination by disproportionation to overall termination is equal to about 0.3 for methyl methacrylate. The dicumyl peroxide‐initiated polymerization of styrene and methyl methacrylate has been studied from 60° to 100°C. The rate laws expressing the decomposition of initiator are: (for methyl methacrylate) kdf′ = 1.26 × 1016 exp { −36.4 kcal./RT} and (for styrene) kdf′ = 1.00 × 1016 exp { −36.4 kcal./RT}. Evidence is given to suggest that the initiator efficiency of DCP in styrene and methyl methacrylate is equal to unity.