Investigation of poly(lactide) stereocomplexes: 3-armed poly(L-lactide) blended with linear and 3-armed enantiomers.

Stereocomplex poly(lactide)s (sc-PLAs) were obtained from solution blending of 3-armed poly(L-lactide) (3PLLA) and linear poly(D-lactide) (PDLA) and between enantiomeric 3PLAs. Differential scanning calorimetry and wide-angle X-ray diffraction results indicated that racemic crystallites were preferentially produced in all the binary blends. The melting temperature and fusion enthalpy of racemic crystallites were remarkably different through varying the structure, constituent, and molecular weight of PLA. Through this investigation, higher melting temperatures were obtained in the middle molecular weight binary blends, and the highest melt temperature of racemic crystallites reached to 246 °C, it was the highest reported value until now. In similar molecular weight blends (or the linear PLA was similar to each branch of 3PLA enantiomers), with the composition of 3PLA increasing, the phase separation molecular weight decreased gradually (M(linear/linear blends) > M(linear/3-armed blends) > M(3-armed/3-armed blends)). The structure distinction between 3PLA and linear PLA induced different thermal properties and phase behaviors of the 3PLLA/PDLA and 3PLLA/3PDLA blends. The thermal properties of these mixtures and its variations provided basic data for their industrial applications.