INITIATION PROCESSES IN COPOLYMERIZATION STUDIED BY THE NITROXIDE RADICAL-TRAPPING TECHNIQUE - ETHYL VINYL ETHER AND ACRYLONITRILE

The nitroxide free-radical trapping technique has been applied to an i nvestigation of the initiation mechanism of the copolymerization of et hyl vinyl ether and acrylonitrile initiated by t-butoxyl radicals. In addition to a range of products normally produced from reactions with individual monomers, four new trapped products each involving both mon omers have been observed. These arise because the strongly electron-ac cepting acrylonitrile reacts so fast with the strongly nucleophilic et hyl vinyl ether radical end groups that the reaction competes successf ully with radical trapping. t-Butoxyl radicals react 3-6 times faster with ethyl vinyl ether than with acrylonitrile depending on solvent, i llustrating the strong electrophilic nature of the t-butoxyl radicals. Reactions carried out in non-olefinic solvents show that polarity is not a major factor in the solvent effect. It is more likely to be due to selective interaction of one monomer with the radical end enhancing its electrophilic nature. A similar effect is caused by a hydrogen-bo nding solvent.