SEGMENTED POLYURETHANES WITH 4,4'-BIS-(6-HYDROXYHEXOXY)BIPHENYL AS CHAIN EXTENDER .1. SYNTHESIS AND CHARACTERIZATION OF 2,4-TDI-POLYURETHANES

Polyurethanes composed of 2,4-toluene diisocyanate (TDI), poly(butylen e adipate) diols (PBA) of different molecular weights, and 4,4'-bis-(6 -hydroxyhexoxy)biphenyl (BHHBP) were prepared by a two-step solution p olymerization process. The polyurethanes were characterized by element al analysis, NMR, and SEC. The thermal properties were investigated by DSC, DMA, and optical polarizing microscopy. Dependent on the molecul ar weight of the PEA, a shift in the glass transition temperature T-g of the polyurethanes has been observed by DSC and DMA. Polyurethanes b ased on poly(butylene adipate)s of M(n) similar to 2000 exhibited a T- g nearly independent on the hard-segment content up to 50% LC hard seg ments, indicating the existence of mainly phase separated soft and har d segments. By shortening the PBA chain length up to 1,000 and further to 600, the T-g of the polyester soft-segment phase increases with gr owing hard-segment content, a consequence of enhanced interaction betw een the hard and soft segments. This tendency is observed to the great est extent at polyurethanes with the shortest polyester diol and can b e interpreted as a partial miscibility or compatibility of hard and so ft segments. Although in polyurethanes with PBA 2000 the mesophase can be proven at a hard-segment content of similar to 40%, its appearance in polyurethanes prepared with PBA 1000 or PBA 600 requires a hard-se gment content > 60%. (C) 1995 John Wiley & Sons, Inc.