Cp2TiCl-catalyzed radical chemistry: living styrene polymerizations from epoxides, aldehydes, halides, and peroxides

Four different Cp2TiCl-activated radical sources (1,4-butanediol diglycidyl ether, benzaldehyde, (1-bromoethyl)benzene, and benzoyl peroxide) were investigated as initiators in the Cp2TiCl-catalyzed living radical polymerization of styrene (St). The effect of reaction variables was investigated over a wide range of values ([St]/[I]=50/1-400/1, [I]/[Cp2TiCl2]=1/0.5-1/4, [Cp2TiCl2]/[Zn]=1/0.5-1/3 and T=40-130 °C). A linear dependence of molecular weight on conversion was observed for each initiator, but larger initiator efficiencies and lower polydispersities were obtained upon increasing [Cp2TiCl2] and [Zn] and decreasing temperature. The optimum conditions are initiator dependent but broadly correspond to [St]/[I]/[Cp2TiCl2]/[Zn]=[50-200]/[1]/[2-3]/[4-6] at 70-90 °C. The most robust initiators are aldehydes followed by peroxides, epoxides, and finally halides.