INVESTIGATIONS ON MONOTROPIC LIQUID-CRYSTALLINE POLYURETHANES BASED ON BIPHENYLOL

2,2'-Azobis-[2-cyano-(4-ethylphenol)] (ABCP) was prepared from parahyd roxyacetophenone, using hydrazine sulfate and sodium cyanide. Biphenyl ol ester of ABCP, 2,2'-azobis-[2-p-biphenyloxy-(4-ethylphenol) ] (BECP ) was synthesized via the acid route. Combined liquid crystalline poly urethanes (CLCPUs) were synthesized from 1,6-diisocyanatohexane (HDI) and BECP in dimethylformamide (DMF) at 110 degrees C under nitrogen at mosphere. The effect of partial replacement of BECP by 4,4'-dihydroxy biphenyl (DHBP) on liquid crystalline (LC) properties was studied. The polymers were characterized by proton and C-13 NMR, FTIR, and UV spec troscopy. Elemental analysis were done for determining the percentage content of C, H, and N and the molecular weights of the polymers were determined by gel permeation chromatography (GPC). Thermogravimetric i nvestigations (TGA) of the polyurethanes (PUs) were performed to study the decomposition. The LC nature of the PUs was confirmed by differen tial scanning calorimetry (DSC) and X-ray diffraction (XRD). Cross-pol arized optical microscopy studies demonstrated the existence of two di stinct crystalline morphologies, a spherulitic morphology with high mo le ratio of DHBP and a thread-like crystalline morphology with that of BECP. All the PUs synthesized showed a LC nature with a wide temperat ure range. Partial replacement of BECP by DHBP changed the mesomorphic nature, transition temperature, and temperature range of the mesophas e. (C) 1995 John Wiley and Sons, Inc.