Synthesis and properties of transparent thermoplastic segmented polyurethanes

Various segmented polyurethanes with a hard segment content of about 50 wt% were prepared from 4,4'-diphenylmethane diisocyanate (MDI), a poly(tetramethylene adipate) glycol with an M, of 2000, and various combinations of aliphatic diols as chain extenders by a one-shot, hand-cast bulk polymerization method. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), ultraviolet-visible spectrometry, differential scanning calorimetry (DSC), and X-ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC data indicate rather good miscibility between the soft segments and the hard segments that accounts for the good transparency. The incorporation of a small amount of a second chain extender into MDI and 1-4-butanediol-based segmented polyurethanes decreases the crystallinity of the hard segment, thus enhancing the transparency. A segmented polyurethane derived from MDI and 1,6-hexanediol exhibits better transparency due to its relatively lower crystallinity of the hard segment. (c) 2007 Wiley Periodicals, Inc.