DETERMINATION OF PROPAGATION RATE COEFFICIENTS BY PULSED-LASER POLYMERIZATION FOR SYSTEMS WITH RAPID CHAIN GROWTH - VINYL-ACETATE

The pulsed-laser polymerization (PLP) technique for determination of free radical propagation rate coefficients (k(p)) by gel permeation chromatography analysis has been extended to systems with rapid chain growth. A mathematical model is developed to gain a better understanding of the relative importance of propagation, termination, and transfer events on the laser-generated molecular weight distributions. Insights from the model are used to define appropriate PLP experimental conditions for vinyl acetate (VAc), for which measured k(p) values are an order of magnitude higher than values measured for styrene and methyl methacrylate at the same temperature. The behavior of VAc is contrasted with methyl methacrylate, both by experimental means and through simulation. Results suggest that VAc radicals not only propagate quickly but also have a higher rate of termination than methacrylate or styrene monomer systems, explaining the formation of broad, featureless molecular weight distributions under typical PLP experimental conditions. This work demonstrates the value of mathematical modeling to aid in the design of optimal PLP experiments.