Synthesis and properties of liquid crystalline polyurethanes

Abstract

Abstract Liquid crystalline polyurethanes were prepared from 4,4′‐bis(2‐hydroxyethoxy)biphenyl (BHBP) and 2,4‐tolylene diisocyanate (TDI). The effect of partial replacement of BHBP by 25–75 mol % poly(oxytetramethylene) diol (PTMO, M n = 250) on the liquid crystalline properties was studied. The BHBP/TDI/PTMO polyurethanes were obtained by one‐ and two‐step polyaddition. The polyurethanes were investigated by DSC, polarizing microscopy, x‐ray, and IR spectroscopy. The molecular weight distribution was determined by GPC. The morphology of the polymers was investigated by the SALS method. Thermogravimetric investigations of the polyurethanes were also performed. All polyurethanes containing BHBP units have liquid crystalline properties. Partial replacement of BHBP by PTMO‐250 considerably changes the phase transition temperatures and the range of mesophase occurrence. More homogeneous polyurethanes were obtained, if the two‐step polyaddition method was applied. The polyaddition method affects the phase transition temperatures. © 1993 John Wiley & Sons, Inc.