Miscibility of a liquid crystalline polyurethane with common segmented polyurethanes

The phase behaviour of blends of a liquid crystalline polyurethane A, based on 4,4'-bis(6-hydroxyhexoxy)-biphenyl (BHHBP) as the mesogenic diol and toluene 2,4-diisocyanate (TDI), with common segmented polyurethanes B (based on poly(tetramethylene adipate), methylene di-p-phenylene isocyanate (MDI) or toluene 2,4-diisocyanate (TDI) and 1,4-butanediol) with various segment lengths was studied by differential scanning calorimetry (d.s.c.) and electron microscopy. No miscibility of the polyurethane A and the hard segments of the different polyurethanes B, independent of the length of the hard segments and the type of diisocyanate used, was observed. With decreasing length of the soft segment an increasing amount of the liquid crystalline polymer (LCP) can be mixed with the amorphous phase of the soft segment in the case of the MDI-polyurethanes, whereas the TDI-polyurethanes B are completely immiscible with polyurethane A. Copyright (C) 1996 Elsevier Science Ltd.