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Cinnamic acid affects the initiation processes when methyl methacrylate is polymerized at 60 " C using benzoyl peroxide as initiator. Work with peroxide doubly-labelled with carbon-14 and tritium has shown that the balance between benzoate and phenyl end-groups is significantly shifted in favour of ester end-groups. On the other hand, study involving peroxide enriched with carbon-I 3 has given no evidence for the presence in the polymers of benzoate end-groups attached to units derived from cinnamic acid. It is proposed that the acid impedes the decarboxylation of the benzoyloxy radical. Cinnamic acid copolymerizes to some extent with styrene, methyl acrylate and acrylonitrile but less readily with the related monomers having a-methyl groups. The effect of the nature of the diluent is clearly shown for the copolymerization with styrene; the presence in the polymerizing system of N,N-dimethylformamide at quite low concentration causes appreciably less cinnamic acid to be incorporated than when bulk monomer or solutions of monomer in toluene are used.

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