Germanium- And tin-catalyzed living radical polymerizations of styrene and methacrylates

Ge and Sn (non-transition-metal) catalyzed living radical polymerizations were developed. Low-polydispersity (M_w/M_n ∼ 1.1-1.3) polystyrenes, poly(methyl methacrylate)s, poly(glycidyl methacrylate)s, and poly(2-hydroxyethyl methacrylate) with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. The pseudo-first-order activation rate constant k_act for the styrene/Gel₄ (catalyst) system was large enough, even with a small amount of Gel₄, to explain why the system provides low-polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/Gel₄ system was kinetically proved to be mainly due to the cross-termination between the propagating radical with Gel₃ ^.. Attractive features of the Ge and Sn catalysts include their high reactivity hence small amounts (1-5 mM) being required under a mild condition (at 60-80°C), high solubility in organic media without ligands, insensitivity to air hence sample preparation being allowed in the air, and minor color and smell. The Ge catalysts may also be attractive for their low toxicity.