Detailed studies of the initiation step in free radical polymerization of alpha-(substituted methyl)acrylates by electron paramagnetic resonance spectroscopy

摘要

Reactions of the adduct radical obtained by addition of the initiator-derived 2-carbomythoxy-2-propyl radical to methyl alpha-[(2-methyl-2-carbomethoxy)propyl]acrylate (the unsaturated dimer of methyl methacrylate (MMAD)) have been monitored by electron paramagnetic resonance spectroscopy. Rate constants for addition of the 2-carbomythoxy-2-propyl radical, and beta-fragmentation of the adduct radical were evaluated by steady-state and non-steady-state kinetic analysis in tandem with computer modeling and simulations involving parameter optimization procedures. The resulting rate constants showed that addition and radical-radical reactions between low molecular weight radicals are suppressed due to the marked steric congestion of the carbon-carbon double bond and radical center, respectively, and that beta-fragmentation can compete with radical-radical reactions of the adduct radicals depending on the radical concentration.