RADICAL CONCENTRATIONS, ENVIRONMENTS, AND REACTIVITIES DURING CROSS-LINKING POLYMERIZATIONS

Radical environments and concentrations during the crosslinking polyme rizations of multiethylene glycol dimethacrylates were characterized w ith electron spin resonance spectroscopy. The relative concentrations of free and trapped radicals were used as a measure of certain structu ral features in the evolving polymer, especially with respect to micro gel formation. The influence of monomer structure and crosslinking den sity on the polymer structure was studied by examining the radical beh avior during the polymerization of diethylene glycol dimethacrylate, p oly(ethylene glycol 200) dimethacrylate, and poly(ethylene glycol 600) dimethacrylate. The extent of radical trapping and microgel formation was found to increase with increasing crosslinking density. The influ ence of the rate of initiation on radical trapping was also investigat ed, and slower rates of polymerization led to a higher fraction of tra pped radicals with respect to the total radical population. Finally, t he termination mechanism of radicals was characterized (long-term and short-term) and the corresponding kinetic constants quantified.