KINETICS OF FREE-RADICAL SOLUTION POLYMERIZATION OF METHYL-METHACRYLATE OVER AN EXTENDED CONVERSION RANGE

The low and intermediate conversion solution polymerization kinetics of methyl methacrylate in toluene and in 2-butanone are investigated. For this purpose, repetitively applied laser pulses are employed to stimulate initiation, and quantitative near infrared spectroscopy is used to determine methyl methacrylate concentrations. The monomer concentration change per pulse is measured; it is shown how this information may be converted into coupled values of the rate coefficient for propagation k(p), the rate coefficient for termination k(t), and the total efficiency of (photo)initiation. In the present case k(p) is already known from independent investigations, which enables our pseudostationary state methods to yield k(t) directly. The major thrust of this paper, therefore, concerns the effect of solvent on k(t): it is found that at both low and intermediate conversions, k(t) increases as the solvent concentration increases; possible causes of this are discussed. The effect of initial solvent fraction on the variation of k(t) with conversion is also reported. Although all our experimental measurements are carried out at an elevated pressure (1000 bar) and a single temperature (30 degrees C), there is no reason for suspecting that our findings regarding solution polymerization termination should not be representative for polymerizations of methyl methacrylate (and other methacrylate monomers) in general.