Polyaddition of bis(five-membered cyclic dithiocarbonate), 2,2-bis[4-(1,3-thioxolane-2-one-4-yl-methoxy)phenyl]propane (1), with diamines having soft oligoether segments and property of the obtained poly(thiourethane)s were examined. Treatment of 1 with equivalent diamines in tetrahydrofuran at room temperature gave poly(thiourethane)s having a mercapto group in each unit, which were further treated with acetic anhydride and triethylamine to give the corresponding S-acetylated poly(thiourethane)s in high yield. Exposing the mercapto group containing poly(thiourethane)s to benzoyl chloride and triethylamine provided the corresponding S-benzoylated poly(thiourethane)s effectively. Thermal properties of the obtained polymers were evaluated by thermogravimetric analysis and differential scanning calorimetry. The obtained polymers showed 10 wt % loss temperature (T-d10) in the range from 230 to 274 degrees C, which was relatively high when compared with the T-d10 of an analogous polymer prepared from 1 and 1,6-hexamethylenediamine. The polymers obtained here exhibited glass transition temperature (T-g) in the range from -16 degrees C to 40 degrees C, which was much lower than the analogous polymer described above, probably due to the soft oligoether segments. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1076-1081