Polyurethane hard domain composed of mixed hard segments

The packing of hard segment in polyurethane hard domain has not been resolved or seen clearly yet. In this work, we prepared polyurethane blends, which were composed of different weight ratios of crystallizable 1195A and non-crystallizable EG85A, to study the structural evolution and crystallization in mixed hard domain. Time and temperature dependent differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction results were used to record the micro-phase evolution and crystallization processes. It was very surprising to find that the multiple melting temperatures in these blends were similar. We deduced that the packing of hard segment tended to separate into different groups, probably dependent on their segmental length. The crystalline nucleus was consist of 1195A hard segments with similar length, and the out-layer structure was consisted of mixed hard segments of varying lengths. The FTIR results demonstrated that crystallinity did not affect the degree of hydrogen bonding association (HBA), and the stacking of hard segments may be only differed in the degree of ordering. Moreover, the degree of HBA of the blends was always higher than the calculated number based on weight ratio of pure samples. The crystallizable 1195A and non-crystallizable EG85A were blended to study the packing of mixed hard segments. Hard segment with different chemical structures could be stacked together to form hard domains, in which the "nucleus and out-layer" model was still applicable. The hard segments seemed to separate into different groups according to their lengths, which caused distanced melting points. image