Synthesis and properties of polyurethanes containing 2,5-thiophenylene linkage

Abstract

A diisocyanate monomer, thiophenylene-2,5-diisocyanate was synthesized by specific reaction of adipic acid with thionyl chloride and pyridine followed by nucleophilic substitution and Curtius rearrangement. Polyurethanes containing 2,5-thiophenylene linkage were synthesized by the polycondensation of thiophenylene-2,5,-diisocyanate with various diols in N,N-dimethylformamide at 40-70℃. polymerization yields were 90-100%. The structures of thiophenylene-2,5-diisocyanate and resulting polymers were identified by IR and $H^1$-NMR spectroscopy. IR spectrum of thiophenylene-2,5-diisocyanate showed chracteristic absorption bands at $3100 cm^{-1}$ (C-H stretching) and $2250 cm^{-1}$ (-N=C=O stretching), those of polyurethanes were observed at $3300-3280 cm^{-1}$ (N-H stretching) and $1750-1710 cm^{-1}$ (carbonyl stretching) region. The physical properties of these polyurethanes were also investigated. The resulting polyurethanes had inherent viscosities in the range of 0.54-0.33 dl/g. Although most of these polymers were soluble in polar solvents, polyurethanes obtained from aromatic diols were quite insoluble in common organic solvents. These polyurethanes except for those obtained from aromatic diols revealed relatively good thermal stability. The TGA data showed 5% weight losses of polyurethanes at 252-327℃. The DSC curves showed that these polymers have melting and glass transition temperatures in the range of 120-232℃ and 35-85℃, respectively.