The reactions of butadiene with the 1-cyano-1-methylethyl and 1-phenylethyl radicals

Abstract

Butadiene (BD) has been copolymerized with methyl methacrylate (MMA) using as initiator ^(13)C-enriched samples of either azobisisobutyronitrile at 60°C or 1,1′-azobis(1-phenylethane) (APE) at 100°C. The initiator fragments in the copolymers have been examined by ^(13)C-NMR and the numbers attached to units derived from the comonomers have been compared, making allowance for the fact that the BD units may possess 1,2- or 1,4-configurations. The ratio, k_(BD)/k_(MMA), of the rate constants for the reactions of the initiating radical with the monomers is 1.3 for the 1-phenylethyl radical and 7.0 for the 1-cyano-1-methylethyl radical; the former quantity is consistent with a value of 2.3 for k_(BD)/k_(STY) obtained from the examination of a copolymer of BD with styrene (STY), prepared using APE. The model radical approach is further tested and the reactivities of BD towards the initiating radicals are discussed in terms of its reactivities towards the polySTY and the polymethacrylonitrile radicals. In all the studied systems, most of the BD units adjacent to initiator fragments have the 1,4-structure.

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