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

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.

The freeze-thaw stability of flavor high internal phase emulsion and its application to flavor preservation and 3D printing

Volatilization of flavor substances may reduce consumers' perception of flavor, and the research on preservation of flavor substances by high internal phase emulsions (HIPEs) under freeze-thaw conditions is still blank. Herein, flavor HIPEs prepared by adding more than 15% litsea cubeba oil in the oil phase could be used as food-grade 3D printing inks, and showed better stability after 5 freeze-thaw cycles, which could be interpreted as the reduced ice crystal formation, more stable interface layer, and more flexible gel-like network structure resulting from the protein binding to flavor substances. The constructed HIPEs system in this study could preserve the encapsulated flavor substances perfectly after 5 freeze-thaw cycles. Overall, this study contributes a food-grade 3D printing ink, and provides a new method for the preservation of flavor substances under freezing conditions and expands the application range of flavor HIPEs in food industry.

Quantification of branching within high molecular weight polymers with polyester backbones formed by transfer-dominated branching radical telomerisation (TBRT)

New branched polymerisations offer previously inaccessible macromolecules and architectural understanding is important as it provides insight into the branching mechanism and enables the determination of structure-property relationships. Here we present a detailed inverse gated 13C NMR characterisation of materials derived from the very recently reported Transfer-dominated Branching Radical Telomerisation (TBRT) approach to quantify branching and provide an insight into cyclisation.