ABSTRACTLinear poly(d-lactide) (PDLA) with various molecular weights is synthesized and incorporated into commercial poly(l-lactide) (PLLA) with different optical purities. And then, the crystallization, mechanical and thermal properties of the PLLA and PLLA/PDLA cast films are investigated. In the PLLA and PDLA/PLLA specimens with lower optical purity, few homochiral crystallites (HC) form in all the specimens and only a small amount of PLA stereocomplex crystallites (SC) are observed in the blends. The elongation at break of all the specimens is extraordinary high, >300%. Dynamic mechanical analyses indicate that the destruction temperature increases at first, and then depresses as enlarging the molecular weight of PDLA in these blends. For the PLLA and PLLA/PDLA with higher optical purity, more content of HC develops in neat PLLA, and both SC and HC produce in the PLLA/PDLA specimens. However, the strains of neat specimens and binary blends are much lower than that of specimens with lower optical purity. The specimens with higher optical purity exhibit higher destruction temperatures and lower loss factors. The high content of crystals (SC and HC) would act as the physical cross-linking points and provide a key factor to impede the deformation of neat PLLA and binary blends during stretching, which should result in the fragile behavior of the PLLA and PLLA/PDLA blends with higher optical purity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44730.

Linear and three-armed poly(L-lactide)/poly(D-lactide) (PLLA/PDLA, 3PLLA/3PDLA and 3PLLA/PDLA) specimens were prepared through a solution mixing method, and the morphology and the spherulite growth of poly(lactide) stereocomplex crystallites (PLA sc) from the melt with various structures and molecular weights were investigated. Polarized optical microscopy images revealed that regular spherulites and a visible boundary developed in all of the PLLA/PDLA blends with relatively lower molecular weights (Mn < 20 kg mol−1 for each branch), and irregular spherulites formed when the molecular weights of PLA polymers were higher than 60 kg mol−1. The growth rate of the spherulites (G) increased at first, and then decreased as the molecular weight increased in all of the PLLA/PDLA, 3PLLA/3PDLA and 3PLLA/PDLA specimens. The highest G value in all of the specimens was achieved when the average molecular weights of each branch were ∼10 kg mol−1. With similar molecular weights for each of the branches, the G reduced gradually as the three-armed PLA was added to the blend (i.e., PLLA/PDLA > 3PLLA/PDLA > 3PLLA/3PDLA).