ASPECTS OF HIGH-CONVERSION FREE-RADICALLY INITIATED POLYMERIZATIONS .2. COPOLYMERIZATION OF ACRYLONITRILE WITH METHYL ACRYLATE IN DIMETHYLSULFOXIDE USING AZOBISISOBUTYRONITRILE AS INITIATOR

The kinetic mechanism of the high-conversion free-radically initiated copolymerization of acrylonitrile with methyl acrylate in dimethylsulf oxide has been examined by using real-time C-13 nuclear magnetic reson ance (n.m.r.) spectroscopy to monitor individual monomer conversions. Computer simulation techniques have been used to generate model predic tions for comparison with experimental data. It has been found that th e kinetic behaviour of the copolymerization can be explained by using Walling's kinetic model with phi = 1 over the complete range of conver sion without the necessity to invoke the concept of the penultimate-un it effect. However, it has been found that the initiator efficiency de creases very significantly around 80% conversion, and this has a consi derable impact on the experimentally observed reaction rates over the last 20% conversion of monomers. The mathematical equations used to de scribe the influence of the initiator efficiency on the copolymerizati on reaction are an extension of those which successfully described the kinetic behaviour of the monomers in high-conversion homopolymerizati on reactions.