The copolymerization of styrene and acrylonitrile in bulk at 60 °C has been investigated by measurement of the copolymer/comonomer composition relationship and of the monomer sequence distributions using 13C NMR. Alternative models for the mechanism of the copolymerization have been evaluated in the most general forms, with allowance for nonzero conversions, by deriving reactivity ratios from composition data and then comparing predicted and experimental sequence distributions. The system shows significant deviations from the terminal model. Compositions cannot differentiate between penultimate and complex participation models, both of which give significant improvement over the terminal model. The measured sequence distributions are quite close to the predictions of the penultimate model but substantially different from those of the complex participation model, showing clearly that the penultimate model is the most appropriate of the models considered. We have obtained rss = 0.22g, rM = 0.03g, r^= 0.634, and rSA = 0.09v No significant improvement was observed with the antepenultimate model.

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Poly[(R)-3-hydroxybutyrate] (PHB), a bacterial polyester, is subject to a detrimental ageing process, which hampers its application possibilities. This ageing phenomenon is usually studied using moulded specimens, and was found to be related to a loss in segmental mobility. The presence of additives and orientation in moulded PHB samples might influence this ageing process. As a reference for our ageing studies, we therefore conducted a study on the ageing effects in virgin PHB powder. For this purpose a method is required to measure the mobility in a powder without the employment of heat or mechanical strain, since these are known to induce deageing. This paper describes a suitable technique based on the principle that the variation of the radical concentration with temperature after y-irradiation at 77 K provides a measure of the changes in the segmental mobility of the polymer chains.

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