Determination of the velocity coefficients for polymerization processes II. The photosensitized polymerization of vinyl acetate by benzoyl peroxide

The photopolymerization of vinyl acetate has been found to be very much accelerated by the presence of small quantities of benzoyl peroxide. This is considered to be the result of a photochemical decomposition of the peroxide, to give free radicals such as phenyl and benzoate. The dependence of the rate of polymerization on the peroxide concentration suggests that there is a considerable inhibition of the reaction due to the presence of the peroxide. The value of the intensity exponent approaches unity as the concentration of the peroxide is increased, and the formal analysis of the reaction suggests that the inhibition is due to the peroxide molecules themselves. The analysis of the induction period and the dark period shows that these are identical and therefore real, so that it can be concluded that they depend essentially on the nature of the initiation step. The value of the initiation velocity coefficient is calculated, and the energy of activation for this step is found to be 8.4 kcal./g.mol.