Synthesis and properties of main-chain liquid crystalline polyurethane elastomers with azoxybenzene

Liquid crystalline polyurethane elastomers (LCPUE) were synthesized by a two-step block copolymerization reaction. The main-chain LCPUE were based on two azoxybenzene-type mesogenic diol chain extenders (HA(2) and HA(6)), a poly(tetramethylene oxide) (PTMO) soft segment, and different diisocyanates, including 4,4'-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI). The polyurethanes were characterized by FTIR, DSC, DMA, WAXD, UV, and polarized optical microscopy. Most of the polyurethane samples exhibited nematic thermotropic liquid crystal behavior and had physical properties typical of thermoplastic elastomers. The liquid crystal properties were strongly related to the interaction between the hard and soft segments of the poly urethane. 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. (C) 1996 John Wiley & Sons, Inc.