Add time:07/28/2019         Source:sciencedirect.com

There are two series of novel thermotropic liquid crystalline polyurethanes (LCPUs), obtained from the polyaddition reaction of 4,4′-bis(ω-hydroxyalkoxy) biphenyls (HBn, n: the number of methylene units in hydroxyalkoxy group) with 1,3-bis(isocyanatomethyl) benzene (XDI) and 1,3-bis(isocyanatomethyl) cyclohexane (H6XDI), respectively. The Fourier transform infrared spectroscopy, differential scanning calorimetry, wide angle X-ray diffraction, polarizing optical microscope and thermogravimetric analysis were used for characterizing these polyurethanes. All of the liquid crystalline polyurethanes exhibited enantiotropism. Except that XDI/HB11 showed trimorphism, all the other polyurethanes presented monomorphism in this study. The H-bonded urethane domain is stronger when the polyurethanes are composed of the benzene ring urethane moiety and longer alkoxy chain, and they show a higher transition temperature associated with the better stability in mesophase. All the thermal degradation of LCPUs are higher than 330°C. The polyurethanes of H6XDI/HB2 and XDI/HB2 show one-step degradation, while the others show two-step degradation.

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