Benzoyl peroxide initiated polymerization kinetics of vinyl monomers in various solvents

Initial rates of polymerization in the presence of benzoyl peroxide as initiator have been determined for methyl methacrylate, vinyl acetate, and vinyl chloride in order to determine the order of reaction with respect to the monomer concentration. In the case of methyl methacrylate, the order of reaction is 1 if benzene is used as solvent; with tert‐butylbenzene, the order of reaction is more complex, and can be interpreted by a “complex” formation mechanism (Mark‐Josefowitz) or by cage effect (Matheson). In the case of vinyl chloride and vinyl acetate in the presence, respectively, of ethyl chloride and ethyl acetate as solvent, the order of reaction has been evaluated to 3/2 vs. monomer concentration. On the contrary, addition of benzene, even in small quantities, produces a strong decrease in rate of polymerization in the case of vinyl acetate, and makes it illusory to determine the order of reaction at high monomer concentrations. Preliminary results using azo‐bis‐isobutyronitrile as initiator for vinyl acetate with benzene as solvent have shown that the considerable influence exerted by benzene in the previous case cannot be attributed to a difference of rate of decomposition of the peroxide only. The results are interpretd by the mechanism of chain‐transfer reactions on the solvent, with formation of radicals from which the relative stability is different from that of the growing chains.