Nuclear magnetic resonance monitoring of chain-end functionality in the atom transfer radical polymerization of styrene

The evolution of the bromine end functionality during the bulk atom transfer radical polymerization (ATRP) of styrene [in the presence of the catalyst CuBr/4,4'-di-(5-nonyl)-2,2'-bipyridine] was monitored with 600-MHz H-1 NMR. A decrease in the functionality versus the conversion was observed. The loss of functionality was especially significant at very high conversions (>90%). The experimental data were compared with a kinetic model of styrene ATRP. The latter indicated that the loss of chain-end functionality was partly due to bimolecular terminations but was mainly due to P-H elimination reactions induced by the copper(II) deactivator. These elimination reactions, which occurred later in the reaction, did not significantly affect the polymer molecular weights and the polydispersity. Therefore, a linear evolution of the molecular weights and low-polydispersity lymers were still observed, despite a loss of functionality. Understanding these side reactions helped in the selection of the proper conditions for reducing the contribution of the elimination process and for preparing well-defined polystyrene (number-average molecular weight similar to10,000 g mol(-1); weight-average molecular weight/number-average molecular weight similar to1.1) with a high functionality (92%). (C) 2005 Wiley Periodicals. Inc.