Development of Living Radical Emulsion Polymerization

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It is theoretically predicted that the degenerative chain transfer-mediated living radical polymerization (LRP) carried out in an emulsion or dispersion polymerization system under specific conditions will provide an elongated radical lifetime and an increased frequency of degenerative chain transfer. In other words, LRP carried out in the inhomogeneous system is predicted to give longer chains with a lower polydispersity and a higher fraction of chain end activity (livingness) than LRP carried out in a homogeneous system. In order to test these theoretical predictions, polymerization of methyl methacrylate (MMA) and styrene were carried out in an emulsion and a dispersion system. Notable results obtained in the dispersion system will be reported below.Optimization of the aqueous-phase solvent (75% ethanol), dispersant (polyacrilic acid), and temperature (70℃), resulted in PMMA with a number-average molecular weigh about 1.0 x 10^5 and a polydispersity index M_w/M_n about 1.1, verifying the theory. However, some mutual adhesion of the PMMA particles was observed, which remains to be a problem to be solved. In the styrene polymerization, in which polyvinyl pyrrolidone was used as a dispersant, no such adhesion of the particles was observed. The polymerization gave polystyrene particles of controllable and homogeneous size (typically 2μm) composed of well defined polystyrene. For both MMA and styrene, the polymerization was completed in a short time, meaning that the effective radical concentration was exceptionally high, and thus increasing the performance, and making better use, of the degenerative chain transfer type of LRP.