When vinyl acetate is polymerised in the presence of benzene the rate of polymerisation is noticeably lower than that for the bulk reaction even if the concentration of the solvent is as low as 2.5%. The benzene-vinyl acetate system has been studied using the non-stationary state thermocouple system in an attempt to elucidate the mechanism which causes this reduction in the rate of polymerisation. As a result kinetic chain lifetimes, rates of reaction, overall activation energies, intensity exponents and velocity coefficients of propagation and termination have been determined at arbitrary intervals throughout the photo-sensitised polymerisation for varying concentrations of benzene. The purity of the reactants is of great importance in polymerisation studies and both monomer and solvent have been rigorously treated. The removal of impurity from the solvent has been accomplished by the growth of single crystals of benzene. The melt from the single crystal has been subjected to an accurate melting point determination and found to have a melting point of 5.5
