Determination of the velocity coefficients for polymerization processes. - I. The direct photopolymerization of vinyl acetate

Abstract

This paper describes a method whereby the individual velocity coefficients of a vinyl polymerization reaction have been determined by a detailed analysis of the kinetics of the photo-polymerization of liquid vinyl acetate. The evaluation of the coefficients is made by the development of an accurate method for measuring the lifetime of the active polymeric molecules employing intermittent radiation. In addition, the kinetic chain length and the number average molecular weight of the polymers have been measured. It is shown that each absorbed quantum of radiation activates one vinyl acetate molecule probably as a diradical. The chain terminates by a disproportionation reaction between the polymer radicals. The size of the growth or propagation bimolecular coefficient decreases only slightly as the molecule grows, the energy of activation is 4400 cal. and the steric factor of the growth reaction is 10^-5. In the termination reaction there is likewise only a small decrease of velocity coefficient with increasing molecular size—no energy of activation is required and the steric factor has the surprisingly large value of 10^-2.