A novel class of living radical polymerizations with germanium, tin, and phosphorus catalysts were developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity (M(w)/M(n) approximately 1.1-1.3) polystyrene, poly(methyl methacrylate), poly(glycidyl methacrylate), and poly(2-hydroxyethyl methacrylate) with predicted molecular weight were obtained with fairly high conversion in a fairly short time. The pseudo-first-order activation rate constant kact for the styrene/GeI4 (catalyst) system was large enough, even with a small amount of GeI4, explaining why the system provides low-polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/GeI4 system was kinetically proven to be mainly due to the cross-termination between the propagating radical with GeI3*. Attractive features of the germanium, tin, and phosphorus catalysts include their high reactivity hence small amounts (1-10 mM) being required under relatively mild conditions (at 60-100 degrees 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 germanium and phosphorus catalysts may also be attractive for their low toxicity. The phosphorus catalysts may also be attractive for their low cost.
Simple phenols and hydrocarbons were used as novel and efficient organic catalysts for reversible chain transfer catalyzed living radical polymerization (RTCP). This is the first use of oxygen-and carbon-centered compounds as catalysts of living radical polymerization. The catalysts include such common compounds as phenol itself, phenol-based antioxidants for foods and resins (e.g., 3,5-di-tert-butyl-4hydroxytoluene (BHT)), phenol-based natural antioxidants (e.g., vitamin E), and dienes (e.g., 1,4-cyclohexadiene). Their cheapness, excellent environmental safety, and ease of handing may be quite attractive in practice. The catalysts were highly active and tolerant to functional groups. The required amounts of the catalysts were typically as small as 100-500 ppm, yielding low-polydispersity polymers (M w /M n ∼ 1.1-1.4) at moderate temperatures (40-100 °C), where M w and M n are weight-and number-average molecular weights, respectively. A wide variety of functional monomers with alkyl, aryl, hydroxyl, poly(ethylene glycol), alkylamino, amino, and carboxylic acid groups were adopted to the homo-and copolymerizations. Kinetic studies supported that, mechanistically, the polymerization is based on reversible chain transfer (RT) for these catalysts.
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