SYNTHESIS AND LIQUID-CRYSTALLINE PROPERTIES OF THERMOTROPIC POLYURETHANES PREPARED FROM 1,4-DIISOCYANATES AND 4,4'-BIS(OMEGA-HYDROXYALKOXY)BIPHENYLS

A new series of thermotropic polyurethanes was synthesized by reacting such para-substituted diisocyanate monomers as 2,5-tolylene diisocyan ate (2,5-TDI) and 1,4-phenylene diisocyanate (1,4-PDI), with 4,4'-bis( omega-hydroxyalkoxy)biphenyls (BPm: HOCmH2mOC6H4C6H4OCmH2mOH; m is the carbon number of the hydroxyalkoxy group) in DMF. Intrinsic viscositi es of the polymers were in the range of 0.41-0.99 dL/g. DSC thermogram s for these polymers exhibited two endothermic peaks corresponding to phase transitions of melting and isotropization. Mesomorphic behavior of the polyurethanes was also observed under a polarizing microscope. For example, polyurethane 1,4-PDI/BP6 with [eta] = 0.77 prepared from 1,4-PDI and 4,4'-bis-[(6-hydroxyhexyl)oxy]biphenyl (BP6) exhibited a l iquid crystalline phase from 247 to 259-degrees-C. Infrared study indi cated that the hydrogen bonding between urethane linkages affected the mesomorphism. Thermo-gravimetric analysis of 1,4-PDI/BPm showed that no weight loss of the polymer occurred up to 300-degrees-C under an ai r atmosphere.