Living/controlled free radical miniemulsion polymerization of styrene.

摘要

TEMPO-controlled living free radical polymerizations were studied in miniemulsion systems in this research. TTOPS was synthesized, and used as a macro-initiator. It was found that the polymerization rate is low. Molecular weight increases linearly with increasing conversion, and is narrowly distributed. The effect of TTOPS concentration was studied and it was found that the polymerization rate was independent of the TTOPS concentration. Lower molecular weights, with narrower distribution, were obtained with higher initial TTOPS concentration.; Particle size and size distribution were measured by CHDF and TEM. A broad particle size distribution was found. The particle size distribution was directly affected by the miniemulsion preparation method. With increasing surfactant concentration, the particle size decreased and the particle number increased. However, different surfactant concentrations had little effect on the molecular weight and the polymerization rate. The average number of active radicals per particle (n¯) in these systems was calculated by different methods. n¯ was estimated to be approximately 0.003.; The thermal self-initiation of styrene monomer was studied with the presence of TEMPO radicals at the polymerization temperature (125°C). An induction period was observed in styrene auto-polymerization with TEMPO radicals and the length of the induction period was found to increase linearly with increasing initial TEMPO concentration. Identical relationships were found for the miniemulsion and corresponding bulk systems. Faster initial polymerization rates were found in bulk than in the corresponding miniemulsion system; this can be explained by different thermal initiation rates resulting from different thermal initiation efficiencies.; Poly(styrene-block-n-butyl acrylate) copolymers were prepared by the living free radical miniemulsion polymerization process in the presence of ascorbic acid. It was found that the polymerization rate increased with increasing ascorbic acid concentration. A certain fraction of the polystyrene chains was dead at the beginning of the second step of polymerizations and did not participate in chain extension with n-butyl acrylate. The percentage of dormant TTOPS-1500 chains decreased with increasing ascorbic acid concentration.