Unusual crystallization kinetics of long-spaced polyacetals

The overall crystallization kinetics of the major polymorphs of a series of polyethylenes with acetal groups precisely placed on each and every 12^th, 18^th, 19^thand 23^rdbackbone carbon (PA-12, PA-18, PA-19, and PA-23) have been studied by DSC and FSC with parallel studies using FTIR, real-time X-ray and POM. The crystallization kinetics is unusual because multiple minima of isothermal crystallization rates are observed at polymorphic transition temperature regions, which is reminiscent of previous observations of crystallization minima in precision polyethylenes with halogen. The inversion is mainly associated with a confinement effect that the kinetically favored Form I makes on the growth of the more stable Form II. Besides the effect on growth, data of induction time for crystallization indicates that the presence of Form I also retards the nucleation of Form II.