Solvent effects on the propagation rate coefficient for free radical polymerization

The effect of solvent on the propagation rate coefficient (k(p)) for styrene and methylmethacrylate was examined using pulsed laser polymerization. Solvents used were ethanol and methanol over the range 25-50-degrees-C. Solvent:monomer ratios were increased until phase separation of the polymer was observed during the polymerization. A block copolymer was also used to stabilize the formed particle phase, there by simulating the early-time nucleation behavior of dispersion polymerization systems. There were no observable solvent effects on k(p). This can be rationalized in terms of the transition state for propagation, where the reaction coordinate comprises the incipient bond in a configuration such that solvent molecules can play no direct role in the reaction dynamics.