Crystallization kinetics of poly‐ε‐caprolactone from poly‐ε‐caprolactone/poly(vinyl chloride) solutions

The polymer–polymer solution of poly(vinyl chloride) and poly‐ε‐caprolactone yields an excellent system for studying the crystallization kinetics of a crystallizable component from a polymer–polymer solution. Unlike previous studies of isotactic–atactic polystyrene solutions for which the glass transition temperature is invariant with composition, this system exhibits a marked dependence of T g on the composition. The experimental data dE ⅓ (modulus)/ dt (psi ⅓ /min) were obtained over a composition range of 40 to 70 wt‐% poly‐ε‐caprolactone. With the appropriate modification of the spherulitic growth rate equation, the expression\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{dE^{{1 \mathord{\left/{\vphantom {1 3}} \right.\kern-\nulldelimiterspace} 3}}}{dt}=k'\left( {1 - C_d } \right)_e \frac{-\Delta F_{WLF}}{RT},\left( \Delta F_{WLF}=\frac{4120T}{51.6+T-T_g}\right)$\end{document} approximated a reasonable fit of the experimental data. This demonstrates a marked dependence of the crystallization rate on concentration. Secondary observations of this investigation show a slower crystallization rate for high molecular weight poly‐ε‐caprolactone and a slow secondary crystallization step. Both homopolymer poly‐ε‐caprolactone and poly‐ε‐caprolactone in the poly‐ε‐caprolactone/poly(vinyl chloride) solution show a slow (relative to the nucleation‐controlled step) crystallization stage considered to involve a slow diffusion mechanism.