New thermoplastic segmented poly(thiourethane-urethane)s (SPTUUs) were prepared by a one-step melt polymerization from 20 to 80 mol % poly(tetramethylene oxide) of (M) over bar (n) = 1000 or poly(hexamethylene carbonate) diol (PHCD) of (M) over bar (n) = 860 as soft segments, hexamethylene diisocyanate (HDI) and bis[4-(mercaptomethyl)phenyl]methanone (BMMPM) as a. new dithiol chain extender at the NCO/(OH + SH) molar ratio of I in the presence of dibutyltin dilaurate as a catalyst. The structures of the SPTUUs were examined by FTIR, X-ray diffraction analysis, and scanning electron microscopy. The SPTUUs were also characterized by physicochemical, thermal, and tensile properties as well as Shore A/D hardness. The SPTUUs with the PHCD soft segments showed better tensile properties than those with the PTMO soft segments. A nonsegmented polythiourethane based on BMMPM and HDI is also described. (c) 2008 Wiley Periodicals, Inc.