Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with M-n of 2000, 1,4-butanediol, and various diisocyanates. The diisocyanates used were pure 4,4＇-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4-isomer and 20% 2,6-isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4＇-diphenylmethane diisocyanate (HMDI), and 1,6-hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. in the segmented polyurethane materials with aliphatic KS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance. (C) 2000 John Wiley & Sons, Inc.