Catalytic-chain-transfer polymerization of styrene revisited: The importance of monomer purification and polymerization conditions

The cobaloxime-mediated catalytic-chain-transfer polymerization of styrene at 60 degreesC was studied with an emphasis on the effects of monomer purification and polymerization conditions. Commonly used purification methods, such as column chromatography and simple vacuum distillation, were not adequate for obtaining kinetic data to be used in mechanistic modeling. A purification regime involving inhibitor removal with basic alumina, followed by polymerization of the styrene in the presence of the cobaloxime and subsequent vacuum distillation, was found to be essential to this end. It was then possible to quantitatively investigate effects such as the initiator concentration and conversion dependencies of the apparent chain-transfer constant that resulted from the occurrence of cobalt-carbon bond formation. A value of about 9 X 10(3) was found for the true chain-transfer constant to cobaloxime boron fluoride, that is, its value in the absence of cobalt-carbon bond formation. Furthermore, previous predictions were confirmed: the measured chain-transfer constant decreased with increasing initiator concentration and conversion. Finally, it was confirmed that the presence of light increased the amount of free Co(II) catalyst in agreement with other studies. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 752-765, 2003.