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

Reactions of the adduct radical obtained by addition of the initiator-derived 2-carbomethoxy-2-propyl radical to methyl α-[(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-carbomethoxy-2-propyl radical to MMAD, mutual reactions between the adduct radicals, and reactions of the adduct radical and the 2-carbomethoxy-2-propyl radical, and β-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 β-fragmentation can compete with radical–radical reactions of the adduct radicals depending on the radical concentration.