Studies on thermotropic liquid crystalline polyurethanes. II. Synthesis and properties of liquid crystalline polyurethane elastomers

Abstract

Abstract Three series of novel thermotropic liquid crystalline polyurethane elastomers (TLCPUEs) were studied. Hard segments were formed by using hexamethylene diisocyanate (HDI) reacted with a mesogenic unit, benzene‐1,4‐di(4‐iminophenoxy‐ n ‐hexanol), which also acted as a chain extender. Three diols: 1,10‐decanediol,poly(oxytetramethylene) glycol (PTMEG) M n = 1000 and PTMEG M n = 2000 were used as the soft segments. The effects of soft segments of polyurethanes on the liquid crystalline behavior were studied. Higher molecular weight TLCPUEs were obtained by adding 30−50 mol % of mesogenic segments to diisocyanates. In contrast to a conventional chain extender such as 1,2‐ethylene glycol or 1,4‐butyl glycol, the synthesized polyurethane elastomers exhibited a mesophase transition by using a mesogenic unit as the chain extender. Mesophase was found for all synthesized LC polyurethanes except of polymers H2‐A‐12 and H2‐A‐7. The structures and the thermal properties of all synthesized TLCPUEs were studied by using FTIR spectroscopy, wide‐angle x‐ray diffraction (WAXD) and DSC measurements, a polarizing microscope equipped with a heating stage, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). Mechanical properties were also examined by using a tensilemeter. © 1995 John Wiley & Sons, Inc.