Investigations on monotropic liquid crystalline polyurethanes based on biphenylol

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Abstract
2,2′‐Azobis‐[2‐cyano‐(4‐ethylphenol)] (ABCP) was prepared from parahydroxyacetophenone, using hydrazine sulfate and sodium cyanide. Biphenylol ester of ABCP, 2,2′‐azobis‐[2‐p‐biphenyloxy‐(4‐ethylphenol)] (BECP) was synthesized via the acid route. Combined liquid crystalline polyurethanes (CLCPUs) were synthesized from 1,6‐diisocyanatohexane (HDI) and BECP in dimethylformamide (DMF) at 110°C under nitrogen atmosphere. 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 13C NMR, FTIR, and UV spectroscopy. 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 investigations (TGA) of the polyurethanes (PUs) were performed to study the decomposition. The LC nature of the PUs was confirmed by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Cross‐polarized optical microscopy studies demonstrated the existence of two distinct crystalline morphologies, a spherulitic morphology with high mole ratio of DHBP and a thread‐like crystalline morphology with that of BECP. All the PUs synthesized showed a LC nature with a wide temperature range. Partial replacement of BECP by DHBP changed the mesomorphic nature, transition temperature, and temperature range of the mesophase. © 1995 John Wiley & Sons, Inc.