New complex crystals of chiral poly(L -lactic acid) and different tactic poly(methyl methacrylate)

Based on evidence from differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier-transform infrared (FTIR) spectroscopy, a new stereocomplex crystal (DSC T _m = 175 °C, with WAXD 2Î = 10.0°and 12.5°) is proven for the first time between structurally dissimilar chiral poly(L-lactic acid) (PLLA) and syndiotactic poly(methyl methacrylate) (sPMMA). There is a strong complexing capacity only between low molecular weight PLLA and sPMMA, in miscible state, at specific weight fractions (70:30). The complexing capacity is more significant when the mixtures are melt-crystallized at T _c = 110°C or lower, and the intensity of this complex can be further enhanced if it is annealed between 100 and 160°C, below its T _m = 175°C. The new complex crystal can be formed only between PLLA and sPMMA, but not with isotactic or atactic PMMA.