INITIATOR EFFICIENCIES IN 2,2'-AZOISOBUTYRONITRILE-INITIATED FREE-RADICAL POLYMERIZATIONS OF STYRENE

Results are presented from a comprehensive study of the variation with conversion, temperature and pressure of the initiator efficiency of 2 ,2'-azoisobutyronitrile in styrene bulk polymerizations. These efficie ncies were measured using a new method involving the use of infra-red spectroscopy to monitor directly the concentrations of various nitrile -group containing species. Our results are shown to be satisfactorily fitted by a simple model based on the idea that initiation follows as a result of primary radical fragments diffusing away from each other. Closer microscopic inspection of the variations with temperature and p ressure of the entire range of our initiator efficiencies implies the possibility that capture by monomer may also contribute as a mechanism of out-of-cage escape of primary radicals. Taking a wider view, the e xperimental method of this paper is shown to be of use for simultaneou s determination of other important kinetic parameters: it yields rate coefficients of initiator decomposition, and also, when initiator deco mposition is stimulated by pulse-laser irradiation, the method is capa ble of delivering individual values of the rate coefficients for termi nation and propagation.