Solvent effects on free-radical polymerization, 1. Solvent effect on initiation of methyl methacrylate and N-vinyl-2-pyrrolidone

Initiation constant 2k_d · f, dissociation constant k_d, and efficiency factor f of AIBN were measured at 60°C for two model homopolymerization systems: methyl methacrylate (MMA) in N-methyl-2-pyrrolidone (NMP) and N-vinyl-2-pyrrolidone (NVP) in methyl isobutyrate (MiB) as the solvent. The stable Banfield radical was used as inhibitor. A pronounced solvent effect was observed on the side reaction of the inhibitor with the monomers. Particular solvent sensitivity of monomers in this reaction was identified, whereby opposite solvent properties of NMP and MiB as well as of MMA and NVP were found. The initiation constant 2 k_d · f depends mainly on the dissociation constant of the initiator k_d in regard to its solvent dependence. The efficiency factor f is influenced by monomer concentration, stability (reactivity) of primary radicals and by viscosity of the reaction medium (solvent cage effect).