Melting of crystallites in polymers with low degree of crystallinity under shear flow conditions I: Poly(vinyl chloride)

The aggregates found in dilute solutions of nearly atactic PVC have been shown to consist of 10 to 15 single molecules held together by a crystalline nucleus. Based on the postulate that the last crystallites in a PVC melt have the same structure as found in dilute solution, a relation between the melting temperature in shear ( T dyn ), the static melting temperature ( T m ) and the shear stress (τ) is found:\documentclass{article}\pagestyle{empty}\begin{document}$$ {1 \mathord{\left/ {\vphantom {1 {T_{{\rm dyn}} }}} \right. \kern-\nulldelimiterspace} {T_{{\rm dyn}} }} - {1 \mathord{\left/ {\vphantom {1 {T_m }}} \right. \kern-\nulldelimiterspace} {T_m }} = \frac{{\tau ^2 }}{{Q \cdot T_{{\rm dyn}} ^2 }} $$\end{document} where Q is a constant. The model predictions are in accordance with data from a Brabender rheometer and a Rheometrics mechanical spectrometer. Q is found to be a constant for samples with weight average molecular weights in the interval between 70,000 and 160,000 corresponding to polymerization temperatures between 40 and 70°C.