Stereocomplex formation between enantiomeric poly(lactic acid)s. X. Binary blends from poly(D‐lactide‐CO‐glycolide) and poly(L‐lactide‐CO‐glycolide)

Abstract

AbstractBinary blend films from lactide‐rich poly(D‐lactide‐co‐glycolide) (PDLG) and poly(L‐lactide‐co‐glycolide) (PLLG) were obtained by casting methylene chloride solutions of the two mixed copolymers with different D‐ and L‐lactide contents (XDI and XLI), and their crystallization was studied by differential scanning calorimetry (DSC). Four combinations were selected from the binary (A‐B) blends: mixing of the same polymer [XDI(A) = XDI(B) or XLI(A) = XLI(B)], blending under XDI(B) = XLI(A), blending of a D‐lactide homopolymer [XDI(B) = 1] with other PDLGs, and blending of a D‐lactide homopolymer [XDI(B) = 1] with other PLLGs. Racemic crystallites were exclusively formed between PDLG and PLLG when they had high lactide unit contents. The melting point and enthalpy of fusion of the racemic crystallites decreased with a decrease in XDI of PDLG or XLI of PLLG, suggesting that glycolide units in the polymer disturbed the growth of the racemic crystallites. A similar behavior was also observed for the homocrystallization in nonblended copolymer films. Homocrystallites composed entirely either of D‐lactide unit or L‐lactide unit sequences were formed when one component was crystallizable and the other component had the same sign of optical rotation or very different lactide content. An interesting finding was that even nonhomocrystallizable lactide‐poor PDLG and PLLG could form racemic crystallites when both were blended. © 1994 John Wiley & Sons, Inc.