New thermoplastic poly(ether-urethane)s and poly(carbonate-urethane) s were synthesized by a one-step melt polymerization from poly(oxytetramethylene) diol (PTMO) and poly(hexane-1,6-diyl carbonate) diol (PHCD) as soft segments, 4,4'-diphenylmethane diisocyanate, and 2,2'-[methylenebis(1,4-phenylenemethylenethio)]diethanol, 3,3'-[ methylenebis(1,4-phenylenemethylenethio)]dipropan-1-ol or 6,6'-[methylenebis(1,4-phenylenemethylenethio)]dihexan-1-ol as unconventional chain extenders. The effects of the kind and amount of the polymer diol and chain extender used on the structure and properties of the polymers were studied. The polymers were examined by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis, atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), TGA coupled with FTIR spectroscopy, and Shore hardness and tensile testing. The obtained high-molecular-weight polymers showed elastomeric or plastic properties. Generally, the PTMO-based polymers exhibited significantly lower glass-transition temperatures (up to -48.1 vs -1.4 degrees C), a higher degree of microphase separation, and ordering in hard-segment domains in comparison with the corresponding PHCD-based ones. Moreover, it was observed that the polymers with the PTMO soft segments showed poorer tensile strengths (up to 36.5 vs 59.6 MPa) but higher elongations at break. All of the polymers exhibited a relatively good thermal stability. Their temperatures of 1% mass loss were in the range 270-320 degrees C. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 331-346, 2012