New thermoplastic polyurethane elastomers based on aliphatic–aromatic chain extenders with different content of sulfur atoms

Abstract

Three series of new thermoplastic polyurethane elastomers (TPUs) were synthesized by a one-step melt polyaddition from aliphatic–aromatic chain extenders with different content of sulfur atoms, i.e., 2,2′-[sulfanediylbis(benzene-1,4-diyloxy)]diethanol (OSOE), 2,2′-[oxybis(benzene-1,4-diylsulfanediyl)]diethanol (SOSE) or 2,2′-[sulfanediylbis(benzene-1,4-diylsulfanediyl)]diethanol (SSSE), 1,1′-methanediylbis(4-isocyanatobenzene) (MDI) and 40, 50 or 60 mol% poly(oxytetramethylene) diol (PTMO) of $$ \bar{M}_{n} $$ = 1,000 g mol−1 as a soft segment. The structures of all the TPUs were examined by FTIR and atomic force microscopy. Their thermal behavior was investigated by means of differential scanning calorimetry and thermogravimetry (TG). For the selected polymers, the gaseous products evolved during the decomposition process were analyzed by TG-FTIR. Moreover, their physicochemical, tensile and adhesive properties as well as Shore A/D hardness were determined. The resulting TPUs were high-molar-mass materials with structures, which were amorphous or had a low degree of ordering. TPUs based on OSOE and SOSE showed a higher degree of microphase separation and glass-transition temperatures almost independent of soft-segment content (at ~−38 and −31 °C) than those from SSSE (from −28 to 1 °C). All TPUs were stable up to 288–297 °C, as measured by the temperature of 1 % mass loss. Their decomposition occurred in a two-step process and began within the hard segments. The main volatile products were carbon dioxide, carbonyl sulfide, aromatic compounds as well as aliphatic ethers and aldehydes. The polymers with 40 and 50 mol% PTMO content showed good tensile strength (~27–46 MPa), in most cases better than their commercial PTMO/MDI/butane-1,4-diol analogs with similar hardness values.