Synthesis and properties of main‐chain liquid crystalline polyurethane elastomers

Liquid crystalline polyurethane elastomers (LCPUE) have been synthesized by a two‐step block copolymerization reaction. The main‐chain LCPUEs are based on two biphenyl‐type mesogenic diol chain extenders (HB 2 and HB 6 ), a poly(tetramethylene oxide) (PTMO) soft segment, and different diisocyanates, icluding 4,4′‐diphencylmethane diisocyanate (HDI), and 1,4‐(3,5,5‐trimethyl)cyclohexane diisocyanate (IPDI). The polyurethanes were characterized by FTIR dichrosim, DSC, DMA, WAXD, and polarized optical microscopy. Most of the polyurethane samples exhibited nematic thermortopic liquid crystal behavior and had physical properties typical of thermoplastic elastomers. The liquid crystal properties are strongly related to the interaction between the hard and soft segments of the polyurethane. As the compatibility of the soft and hard segments increased, the thermal stability of the liquid crystal phase and the transition temperatures decreased and the range of the transition became narrower, Uniaxial extenstion analysis shows that two orientation mechanisms exist in the LCPUE systems. These samples had fairly high strength and modulus and good membrane‐forming ability.