Theoretical and Experimental Studies on Elementary Reactions in Living Radical Polymerization via Organic Amine Catalysis

Abstract

The reaction mechanism of living radical polymerization using organic catalysts, a reversible complexation mediated polymerization (RCMP), was studied using both theoretical calculations and experiments. The studied catalysts are tetramethylguanidine (TMG), triethylamine (TEA), and thiophene. Methyl 2-iodoisobutyrate (MMA-I) was used as the low-molar-mass model of the dormant species (alkyl iodide) of poly(methyl methacrylate) iodide (PMMA-I). For the reaction of MMA-I with TEA to generate MMA• and •I-TEA radicals (activation process), the Gibbs activation free energy for the inner-sphere electron transfer mechanism was calculated to be 39.7 kcal mol–1, while the observed one was 25.1 kcal mol–1. This difference of the energies suggests that the present RCMP proceeds via the outer-sphere electron transfer mechanism, i.e., single-electron transfer (SET) reaction from TEA to MMA-I to generate MMA• and •I-TEA radicals. The mechanism of the deactivation process of MMA• to generate MMA-I was also theoretically studied. For the studied three catalysts, the theoretical results reasonably elucidated the experimentally observed polymerization behaviors.