Substituent effect on the antimony atom in organostibine-mediated living radical polymerization

The substituent effect on the antimony atom in organostibine-mediated degenerative transfer living radical polymerization has been studied. 2-Diphenylstibanyl-2-methylpropionitrile (1a) was synthesized as an organostibine chain transfer agent (CTA), and its effect was compared with the previously reported dimethylstibanyl analogue 1b. Both CTAs successfully polymerized butyl acrylate (BA) in a highly controlled manner giving poly(butyl acrylate)s possessing number average molecular weights close to the theoretical values determined by BA/1 ratios and narrow molecular weight distribution. The controllability of styrene polymerization by 1a was slightly decreased but the decrease is still at an acceptable level. However, 1a did not control the polymerization of methyl methacrylate (MMA). The results are in sharp contrast that 1b can highly control the polymerization of styrene and MMA. Kinetic studies using diphenylstibanyl-substituted polystyrene macro-CTA 2 in styrene polymerization revealed that the degenerative chain transfer reaction of the diphenylstibanyl group takes place faster than that of the dimethylstibanyl group, suggesting that the reactivity of the diphenylstibanyl group is not the origin of the low control. Chain extension experiments revealed the formation of a considerable amount of dead polymers when 1a was used as a CTA, and the frequent occurrence of termination reaction is the most probable origin of the low control. The addition of tetraphenyldistibine significantly increased the control of styrene and MMA polymerization, and structurally well-defined polystyrene and poly(methyl methacrylate) were obtained by applying a binary system consisting from 1a and tetraphenyldistibine. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:307–315, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20681