INITIATION IN FREE-RADICAL COPOLYMERIZATION STUDIED BY THE NITROXIDE TRAPPING METHOD - STYRENE AND ACRYLONITRILE

The initiation steps in the copolymerization of styrene and acrylonitr ile with t-butoxyl radicals have been investigated using the nitroxide trapping technique. t-Butoxyl radicals add to styrene Eve times more rapidly than to acrylonitrile whereas methyl radicals, formed by beta- fragmentation of t-butoxyl radicals, add to acrylonitrile about four t imes faster than to styrene. Acrylonitrile also reacts fast with first generation styryl radical end groups. Trapped products containing bot h monomers can only be observed, however, by operating at very low nit roxide trap concentrations. This has been achieved by using a syringe pump to feed nitroxide trap to the reaction mixture at a controlled ra te. Some information on rate constants for second monomer addition has been obtained. Solvent effects on the relative rates of addition of t -butoxyl radicals have been observed and discussed. Copyright (C) 1996 Elsevier Science Ltd.