Urethane Elastomers/Liquid Crystalline Polyurethane Blends

Abstract

Nonsegmented and segmented liquid crystalline polyurethanes have been studied in mixtures with conventional elastomeric polyurethanes. The nonsegmented liquid crystalline polyurethane LCPU is composed of 2,4-tolylene diisocyanate and 4,4′-bis(6-hydroxyhexoxy)biphenyl (BHHBP) as the mesogen. By incorporation of poly(butylene adipate) soft segments of molecular weight 2000 in the main chain by a prepolymer process the segmented liquid crystalline polyurethane SLCPU was obtained. Both liquid crystalline polyurethanes were mixed with conventional elastomeric polyurethanes based on tolylene diisocyanate (TDI) or 4,4′-diphenylmethane diisocyanate (MDI), poly(butylene adipates) of molecular weight 2000 or 600 and 1,4-butanediol as chain extender. The components and blends were characterized by differential scanning calorimetry (DSC), electron microscopy and measurements of mechanical properties. In each blend the existence of a separated phase due to TDI-BHHBP structures can be detected by DSC. LCPU is immiscible with the TDI polyurethanes but partially miscible with the MDI polyurethane containing a short chain polyester of Mn = 600 and a relatively high content of MDI-1,4 butanediol hard segments. SLCPU is partially miscible with TDI polyurethanes without changing the mesophase formation. In blends with MDI polyurethanes the formation of mesogenic hard segment domains is reduced. The LC properties can be obtained in miscible and immiscible blends and the high tensile strength of SLCPU can be transmitted to the blends in case of partial miscibility.