Nitroxide-mediated living radical polymerization of styrene with fluorescent initiator

摘要

A fluorescence method was used for determination of marked chain ends in polystyrene samples prepared by 4-substituted TEMPO type nitroxide-mediated living free radical polymerization of styrene. 2,2,6,6-Tetramethyl-1-(1-phenylethoxy)-piperidin-4-yl-4-pyren-1-ylbutan oate (PYNOR) was prepared and used as an unimolecular initiator bearing pyrene as a fluorescence mark on mediating nitroxide fragment. The bulk polymerization of styrene at 120 degrees C, in the presence of new unimolecular initiator, was a typical nitroxide mediated living radical polymerization. For comparison, two different molar ratios of initiator and monomer (1:400 and 1:1000 initiator - monomer [I:M]) were used for polymerization. When I:M = 1:400, the obtained polydispersity was 1.12 and maximum molecular weight 27,000 g/mol was obtained at 62% conversion. For ratio 1:1000, slightly higher polydispersity was obtained -1.26 and the molecular weight was 53,000 g/mol at 70% conversion. The content of the polystyrene chains bearing mediating nitroxide fragment was determined by fluorescence spectroscopy. The intensity of pyrene fluorescence decreased as the molar mass, and the conversion increased as well. The extent of the incorporation of chromophore at propagating chain end or livingness of polymerization decreased despite the fact that the polydispersity did not change. The extent of side reaction leading to broadening of polydispersity is suppressed due to the high viscosity of the system at higher conversion. A low extent of livingness will have a very negative effect on possible preparation of block copolymers.