Accelerated Crystallization and Preferred Formation of a Thermally Stable Crystal Phase in Enantiomeric Blends of Long-Spaced Chiral Polyesters

Abstract

Enantiomeric blends of L- and D-type chiral polymers usually show distinct crystallization behavior and physical properties from the corresponding enantiopure polymers. However, the crystallization kinetics and crystalline structure of the enantiomeric blends of L- and D-polymers are not yet well understood, particularly concerning the chiral polymers with low chiral moiety densities. Herein, we synthesized a series of long-spaced chiral polyesters with a relatively low chiral moiety content and investigated the effects of enantiomeric blending on the crystallization kinetics and crystal polymorphism of chiral polyesters. Different from the other chiral polyesters with high chiral moiety content, the enantiomeric blends of long-spaced chiral polyesters do not crystallize into the new stereocomplex crystals but have a faster crystallization rate than the corresponding enantiopure polyesters. Compared to the enantiopure polyesters, the enantiomeric blends show the preferred formation of thermally stable form-I crystals in the cooling process and the broader temperature range for generating the form-I crystals in isothermal crystallization. The effects of enantiomeric blending on crystallization become less obvious with decreasing the chiral moiety content or increasing the methylene spacer length. We infer that the accelerated crystallization and facilitated formation of form-I crystals in enantiomeric blends are correlated with the interchain interactions between L- and D-polyesters. This study provides new insights into the crystallization of long-spaced chiral polyesters.