ASPECTS OF HIGH-CONVERSION FREE-RADICALLY INITIATED POLYMERIZATIONS .1. INITIATOR EFFICIENCY IN THE HOMOPOLYMERIZATION OF ACRYLONITRILE ANDMETHYL ACRYLATE IN DIMETHYLSULFOXIDE WITH AZOBISISOBUTYRONITRILE AS INITIATOR

The kinetic mechanism of the free-radically initiated homopolymerizati on of acrylonitrile and methyl acrylate in dimethylsulfoxide solution has been examined. All reactions have been taken to high conversions o f monomer. It has been found that the initiator efficiency is unity be fore the P scission of primary radicals occurs and is dependent on mon omer concentration after that reaction. A kinetic mechanism that expla ins the changes in the initiator efficiency with conversion has been p roposed, which makes use of the cage-effect concept. The proposed mech anism has made it possible to explain quantitatively the experimentall y observed variation in monomer concentration with time, which has not been possible previously. It has also been found that the termination step is not significantly diffusion-controlled in the homopolymerizat ions.