Synthesis and properties of hyperbranched polyurethane elastomers based on dimer fatty acid-ethylene glycol polyester diol

Hyperbranched polyurethane (HBPU) elastomers were synthesized from dimer fatty acid-ethylene glycol polyester diol (DFA-EG), toluene diisocyanate (TDI) and glycerol (GLY) by a two-step, solvent-free process. The effect of glycerol on phase separation was studied by Fourier transform-infrared (FT-IR) and differential scanning calorimetry (DSC). The thermal and viscoelastic properties of the HBPU were investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), respectively. The transparent HBPU elastomers presented a typical amorphous morphology, with a single glass transition temperature (T_g) about -25 °C. All TGA curves showed two distinct stages of degradation with the onset decomposition temperature at 275 °C. It was found that the increasing content of GLY resulted in a decrease in the thermal stability between 295 °C and 445 °C. The results for DMA revealed that HBPU crosslinked with GLY had high elasticity up to 5.12 MPa at 100 °C. The best mechanical and viscoelastic properties were achieved at the n_NCO(TDI)/n_{OH(DFA-EG+GLY)} of 0.95, with its hardness and tensile strength values of 83 A and 13.2 MPa, respectively and the storage modulus value of 32.8 MPa. In addition, the lowest water absorptivity was 0.24% when the nNCO(TDI)/nOH(DFA-EG+GLY) equalled 1.05.