SOLVENT EFFECTS ON THE PROPAGATION RATE COEFFICIENT FOR FREE-RADICAL POLYMERIZATION

The effect of solvent on the propagation rate coefficient (k(p)) for s tyrene and methylmethacrylate was examined using pulsed laser polymeri zation. Solvents used were ethanol and methanol over the range 25-50-d egrees-C. Solvent:monomer ratios were increased until phase separation of the polymer was observed during the polymerization. A block copoly mer was also used to stabilize the formed particle phase, there by sim ulating the early-time nucleation behavior of dispersion polymerizatio n systems. There were no observable solvent effects on k(p). This can be rationalized in terms of the transition state for propagation, wher e the reaction coordinate comprises the incipient bond in a configurat ion such that solvent molecules can play no direct role in the reactio n dynamics.