Accelerated\nCrystallization and Preferred Formation\nof a Thermally Stable Crystal Phase in Enantiomeric Blends of Long-Spaced\nChiral Polyesters

Enantiomeric blends of L- and D-type chiral polymers\nusually show\ndistinct crystallization behavior and physical properties from the\ncorresponding enantiopure polymers. However, the crystallization kinetics\nand crystalline structure of the enantiomeric blends of L- and D-polymers\nare not yet well understood, particularly concerning the chiral polymers\nwith low chiral moiety densities. Herein, we synthesized a series\nof long-spaced chiral polyesters with a relatively low chiral moiety\ncontent and investigated the effects of enantiomeric blending on the\ncrystallization kinetics and crystal polymorphism of chiral polyesters.\nDifferent from the other chiral polyesters with high chiral moiety\ncontent, the enantiomeric blends of long-spaced chiral polyesters\ndo not crystallize into the new stereocomplex crystals but have a\nfaster crystallization rate than the corresponding enantiopure polyesters.\nCompared to the enantiopure polyesters, the enantiomeric blends show\nthe preferred formation of thermally stable form-I crystals in the\ncooling process and the broader temperature range for generating the\nform-I crystals in isothermal crystallization. The effects of enantiomeric\nblending on crystallization become less obvious with decreasing the\nchiral moiety content or increasing the methylene spacer length. We\ninfer that the accelerated crystallization and facilitated formation\nof form-I crystals in enantiomeric blends are correlated with the\ninterchain interactions between L- and D-polyesters. This study provides\nnew insights into the crystallization of long-spaced chiral polyesters.