Reactivities of monomers toward the 2‐cyano‐2‐propyl radical by NMR study of end groups in copolymers

Copolymerizations of styrene (S) with methyl methacrylate (MMA) and methacrylonitrile (MAN) at 60°C were performed with azoisobutyronitrile as initiator, enriched in its methyl groups with 13C. From the NMR spectrum of a copolymer it is possible to compare the numbers of initiator fragments attached to the two types of monomer unit; this information can be used to study the competition between the monomers for capture of the radicals formed from the initiator. The velocity constants for addition of the 2‐cyano‐2‐propyl radical to S, MMA, and MAN are in the proportions 1:0.56:0.34; it is concluded that polar effects are of some importance in the reactions of the radical.