Synthesis and properties of liquid crystalline polyurethane elastomers

Novel type of mesogenic chain extenders used in this study are N,N'-bis(4-h ydroxyphenyl)-3,4,3',4'-biphenyldicarboxyimide (BPDI) and N,N'-bis [4-(6-hy droxyhexyloxy) phenyl]-3,4,3',4'-biphenyldicarboxyimide (BHDI). BHDI has a flexible spacer of 6-methylene units but BPDI does not. The liquid crystall ine polyurethane elastomers were synthesized from BPDI or BHDI as a mesogen ic chain extender, 4,4'-diphenylmethane diisocyanate, and poly(oxytetrameth ylene)glycol (MW 1000) as a soft segment. Polyurethane based on BHDI exhibi ted two melting transitions. However, any melting behavior was not shown in the BPDI-based polyurethanes because of higher melting temperature than de composition temperature. The composition of polyurethanes was varied as a m eans of manipulating liquid crystalline behavior and physical properties. T he BHDI-based polyurethanes containing above 50 wt % of hard segment conten t exhibited nematic liquid crystal behaviors. As the hard segment content o f the BHDI-based polyurethanes increased, the glass transition temperature (T-g), strength, modulus, and the amount of hydrogen bonding increased. (C) 2000 John Wiley & Sons, Inc.