Polyurethanes containing sulfur. III. New thermoplastic HDI-based segmented polyurethanes with diphenylmethane unit in their structure

Three series of new thermoplastic, high molecular weight, segmented thiopol yurethanes were synthesized by a one-step melt polymerization from newly ob tained thiodiols, including bis [4-(2-hydroxyethyl)thiomethylphenyl]methane , bis[4-(3-hydroxypropyl)thiomethylphenyl]methane, and bis[4-(6-hydroxyhexy l)thiomethylphenyl]methane (BHHM), as chain extenders; hexamethylene diisoc yanate; and 20-80 mol % poly(oxytetramethylene) glycol (PTMG; number-averag e molecular weight = 1000) as the soft segment. Solution polymerization wit h the chain extender BHHM gave considerably lower molecular weight polymers . The structures of all the polyurethanes were determined with Fourier tran sform infrared and X-ray diffraction analysis. The thermal properties of th e polyurethanes were examined with differential scanning calorimetry and th ermogravimetric analysis. Shore A/D hardness and tensile properties were al so determined. All the polyurethanes showed partially crystalline structure s; those obtained with 40-80 mol % PTMG were elastomers. An increase in the PTMC content decreased hardness, modulus of elasticity, and tensile streng th, whereas elongation at break increased. BHHM-based polyurethanes obtaine d in the melt showed the best tensile properties. The polyurethanes exhibit ed definite glass transitions (-70 to -59 degreesC) that were nearly indepe ndent of the hard-segment content up to about. 50 wt % (40-80 mol % PTMG), indicating the existence of mainly microphase-separated soft and hard segme nts. (C) 2001 John Wiley & Sons, Inc.