Assessing Cobalt(II/III) Complex Purity Using XRD and Its Impact on Effectiveness of Catalytic Chain Transfer Polymerization

Abstract

Catalytic chain transfer polymerization (CCTP) of methacrylates using Co(II)/Co(III) catalysts has been established for over 30 years. These catalysts have been used in commercial products in diverse markets including automotive coatings, printing and dental composites. However, it has proved difficult routine and reliable tests of catalyst purity that indicate the activity and hence the amount of catalyst required to achieve a desired product. The catalysts are difficult to characterize due to being paramagnetic, sparingly soluble and highly symmetrical. This work set out to first determine the structure of “impurities” that might be present after synthesis or might form over time. Using this knowledge the work then used powder X-ray spectra and the deconvolution of obtained spectra to the known structures to obtain a measure of catalyst purity and activity. This was then correlated with the chain transfer constants from Mayo plots as a measure of activity. We discovered some new hitherto unknown cobalt structures and obtained structural data and developed a deconvolution algorithm that extracts the composition of the catalyst mixtures to give compositional data for 6 cobalt-containing compounds as well as starting materials and inorganic salts. Three of the cobalt species were shown to be active and thus the composition data was shown to be a measure of catalyst activity as tested against polymerization data. Catalyst samples from two laboratories were obtained which had been prepared at different times as well as a commercial sample. The powder X-ray method developed was subsequently used to validate the catalyst activity toward CCTP of methyl methacrylate. Thus, a relatively simple powder X-ray measurement on a catalyst sample can be used as a direct measure of activity and purity.