Higher-order crystalline structures of poly(oxyethylene) in poly(d,l-lactide)/poly(oxyethylene) blends

Higher-order crystalline structures in blends of poly(lactide)/poly(oxyethylene) (PLA/PEG) were investigated using small-angle X-ray scattering (SAXS). For this purpose, the fact that two polymers are both crystalline makes situation much complicated. To simplify, we used non-crystalline PLA: poly(d,l-lactide) (DLPLA), which is a racemic copolymer comprising d- and l-lactide moieties. Higher-order peaks arising from the ordered lamellar stacking of PEG (i.e. the lattice peaks) were observed in the various blend samples, as well as in the PEG 100% sample, all of which were cast from their solutions in dichloromethane. Surprisingly, we found that the structure is more or less regular in the blend of DLPLA/PEG at compositions of 5-20 wt% of DLPLA than that in the PEG 100% sample. We further examined changes in such regular structures with temperature and found very peculiar SAXS profiles just 1 °C below melting temperature, which can be ascribed to a lamellar particle scattering. To our best knowledge, such a well-defined particle scattering has neither been reported for polymer blends, nor for the crystalline lamellar structure. Moreover, crossover from the lattice scattering to the particle scattering was observed in the temperature range from room temperature to 64 °C for the PEG 100% sample and blend samples with 5-20 wt% of DLPLA.

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