SYNTHESIS AND PROPERTIES OF MAIN-CHAIN LIQUID-CRYSTALLINE POLYURETHANE ELASTOMERS

Liquid crystalline polyurethane elastomers (LCPUE) have been synthesiz ed by a two-step block copolymerization reaction. The main-chain LCPUE s are based on two biphenyl-type mesogenic diol chain extenders (HB2 a nd HB6), a poly(tetramethylene oxide) (PTMO) soft segment, and differe nt diisocyanates, including 4,4'-diphenylmethane diisocyanate (MDI), t oluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and 1,4-( 3,5,5-trimethyl) cyclohexane diisocyanate (IPDI). The polyurethanes we re characterized by FTIR dichroism, DSC, DMA, WAXD, and polarized opti cal microscopy. Most of the polyurethane samples exhibited nematic the rmotropic liquid crystal behavior and had physical properties typical of thermoplastic elastomers. The liquid crystal properties are strongl y related to the interaction between the hard and soft segments of the polyurethane. As the compatibility of the soft and hard segments incr eased, the thermal stability of the liquid crystal phase and the trans ition temperatures decreased and the range of the transition became na rrower. Uniaxial extension analysis shows that two orientation mechani sms exist in the LCPUE systems. These samples had fairly high strength and modulus and good membrane-forming ability. (C) 1994 John Wiley & Sons, Inc.