Crystallization of Long-Spaced Precision Polyacetals II: Effect of Polymorphism on Isothermal Crystallization Kinetics

• DOI: 10.1021/acs.macromol.0c01443
• Publication Date: 2020-08-31T17:41:00Z
• Authors: Xiaoshi Zhang; Stephanie F. Marxsen; Patrick Ortmann; Stefan Mecking; Rufina G. Alamo
• Keywords: Isothermal process

Under isothermal crystallization (Tc) from the melt, polyacetals spaced by 12, 18, 19, or 23 methylenes develop two three distinctive layered polymorphs. The polymorphs formed in lowest Tc range are kinetically favored (hexagonal and Form I) characterized highly nucleated small axialites up to very close their melting point. In higher of Tc, a thermodynamically more stable II develops that melts at 5–8 degrees temperatures forms large spherulites. I overlap Tc. While overall kinetics display usual negative temperature coefficient, an inversion dependence rate with occurs when approaching above narrow where coexist. is attributed competition nucleation between II. Just before inception II, so low it becomes basically extinguished. degree crystallinity recovers pure increase Although overlapping range, growth rates significantly lower than those compared fixed undercooling, one order magnitude difference six times energy barrier for calculated analysis data according surface theory. Such explains observed variation density A minimum PA-12, consistent effect "self-poisoning", point hexagonal phase above.