Abstract
ABSTRACT In this study, three novel main-chain liquid-crystal polyurethanes based on mesogenic diol 4,4ʹ-bis(6-hydroxyhexoxy)biphenyl (BP6), azo diol 4,4ʹ-bis(6-hydroxyhexyloxy)-azobenzene (BHHAB) and 4,4ʹ-diisocyanato-3,3ʹ-dimethylbiphenyl (DMBDI) were synthesised via polyaddition method. The chemical structure, thermal properties, liquid-crystal behaviour and microstructure were fully characterised by FTIR, 1HNMR, UV spectrum, Differential scanning calorimetry (DSC), Thermogravimetric analyzer (TGA), Polarizing optical microscope (POM) and X-ray diffraction techniques. The resulted polyurethanes showed strong UV absorption at 313 nm ascribed to π–π* transition of azo group. All of the polyurethanes showed multiple transitions on DSC curve, which could be ascribed to crystal, melting and isotropization transitions combined with the POM observation. The thermal degradation of the polymers occurred at much higher temperatures (325–331°C) than the melting ones (144–154°C), making the melt processing feasible. The polyurethane showed semicrystalline structure based on diffraction and DSC results. The obtained polyurethanes exhibited smectic mesophase as verified by variable temperature WAXD results, and the mesophase temperature range was more than 25°C based on the POM observation. The obtained polyurethanes could be potentially used in optical and smart intelligence material area.
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