Segmented polyurethanes with 4,4′‐bis‐(6‐hydroxyhexoxy) biphenyl as chain extender. I. Synthesis and characterization of 2,4‐tdi‐polyurethanes

Abstract

AbstractPolyurethanes composed of 2,4‐toluene diisocyanate (TDI), poly (butylene adipate) diols (PBA) of different molecular weights, and 4,4′‐bis‐(6‐hydroxyhexoxy) biphenyl (BHHBP) were prepared by a two‐step solution polymerization process. The polyurethanes were char‐acterized by elemental analysis, NMR, and SEC. The thermal properties were investigated by DSC, DMA, and optical polarizing microscopy. Dependent on the molecular weight of the PBA, a shift in the glass transition temperature Tg of the polyurethanes has been observed by DSC and DMA. Polyurethanes based on poly (butylene adipate)s of Mn ∼ 2000 exhibited a Tg nearly independent on the hard‐segment content up to 50% LC hard segments, indicating the existence of mainly phase separated soft and hard segments. By shortening the PBA chain length up to 1,000 and further to 600, the Tg of the polyester soft‐segment phase increases with growing hard‐segment content, a consequence of enhanced interaction between the hard and soft segments. This tendency is observed to the greatest extent at polyurethanes with the shortest, polyester diol and can be interpreted as a partial miscibility or compatibility of hard and soft segments. Although in polyurethanes with PBA 2000 the mesophase can be proven at a hard‐segment content of ∼ 40%, its appearance in polyure‐thances prepared with PBA 1000 or PBA 600 requires a hard‐segment content > 60%. © 1995 John Wiley & Sons, Inc.