Stereocomplex- and homo-crystallization behavior, polymorphism, and thermal properties of enantiomeric random copolymers of l- and d-lactic acids from the melt

Enantiomeric stereo random copolymers (SRCs), l-lactic acid-rich poly (lactic acid)s (L -PLAs) and d-lactic (D-PLAs) with major monomer unit fraction down to 85% were synthesized from mixtures of l- acids their stereocomplex (SC)- homo-crystallization the melt investigated. The obtained results compared those previously reported for enantiomeric SRCs, l-lactide-rich (l-lactide-co-d-lactide)s d-lactide-rich d-lactides acid cyclic dimers). Homo-crystallization L-PLAs occurred (MMUF) = 96.6–100% sequence length (MMUSL) 29.4–63.8 units. crystalline form transition δ α in MMUF 98.2 100% (MMUSL 55.6 63.8 units) between Tc 90 100 °C 110 °C, respectively, whereas only α-form formation took place L-PLA 96.6% 29.4 units). homo-crystallizability δ-form crystallizability determined by MMUSL rather than MMUF. SC crystallization L-PLA/D-PLA blends wider 84.4–100% 6.4–56.4 that unblended specimens, i.e., widened crystallizable ranges. was not or but also other factors, contrast homo- crystallizability. interplanar distance values decreased an increase α-form, crystallites remained unchanged range 100–180 °C. It is interesting note incorporated d-monomer units at ca. 3% caused compact packing chains α-form. equilibrium melting temperature (Tm0) [Tm0(S)] decreasing MMUSL. Tm0 homo-crystallites [Tm0(H)] Tm0(S) lower PLAs lactic monomers lactide monomers, when similar values. Tm0(H) In summary, found play a critical role determine blends.