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 investigation of the initiation mechanism of the copolymerization of ethyl 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 monomers have been observed. These arise because the strongly electron-accepting acrylonitrile reacts so fast with the strongly nucleophilic ethyl vinyl ether radical end groups that the reaction competes successfully with radical trapping. t-Butoxyl radicals react 3-6 times faster with ethyl vinyl ether than with acrylonitrile depending on solvent, illustrating 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 e®ect. It is more likely to be due to selective interaction of one monomer with the radical end enhancing its electrophilic nature. A similar e®ect is caused by a hydrogen-bonding solvent.