Monomer chain‐transfer constants from emulsion copolymerization data: Styrene and α‐methylstyrene

Radical chain‐transfer constants can be deduced from corresponding measurements of rates and degrees of polymerization in copolymerization experiments. It is particularly useful to carry out such copolymerization in emulsion systems where the normal termination reactions are relatively less important and chain‐transfer processes are significant in determining the number‐average degree of polymerization. The method is illustrated for copolymerization of styrene and α‐methylstyrene at three temperatures. Rate constants for transfer of styryl and α‐methylstyryl radicals to either monomer were measured. All the rate constants are consistent with the relative stabilities of the product radicals which could be formed by the various transfer reactions. The procedure described here can be extended for measurements of rate constants for reactions of other potential transfer agents.