Radical concentrations, environments, and reactivities during crosslinking polymerizations

Radical environments and concentrations during the crosslinking polymerizations of multiethylene glycol dimethacrylates were characterized with electron spin resonance spectroscopy. The relative concentrations of free and trapped radicals were used as a measure of certain structural features in the evolving polymer, especially with respect to microgel formation. The influence of monomer structure and crosslinking density on the polymer structure was studied by examining the radical behavior during the polymerization of diethylene glycol dimethacrylate, poly(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 influence of the rate of initiation on radical trapping was also investigated, and slower rates of polymerization led to a higher fraction of trapped radicals with respect to the total radical population. Finally, the termination mechanism of radicals was characterized (long-term and short-term) and the corresponding kinetic constants quantified.