Scientists describe bio-based healable non-isocyanate polyurethanes driven by the cooperation of disulfide and hydrogen bonds.
A series of isocyanate-free polyurethanes (NIPUs), showing an intrinsic thermo-healing performance, have been synthesised from sustainable vegetable oil-based cyclic carbonates and bio-based amines. The bio-based contents of the NIPUs are higher than 78%. Their thermo-mechanical and self-healing performances are tailored simply by varying the feed ratios of the amines employed.
The biomass linoleic acid dimer-based diamine plays a positive role in maintaining the higher thermal stability and good elasticity of the prepared NIPUs, the cycloaliphatic isophorone diamine contributes to high tensile strength, and cysteine-derived disulfide-containing cystamine (CA) enhances the self-healing efficiency.
98.1% self-healing efficiency at 25 °C
The combination of intrinsic hydrogen bonds existed in the NIPU matrix with the dynamic exchange reactions of disulfide bonds and the enhanced flexibility of NIPU networks results in 98.1% self-healing efficiency at 25 °C. The contributions of disulfide bonds and hydrogen bonds to the healing efficiency were estimated by adjusting the composition of NIPUs, showing that the contribution of disulfide bonds to the healing ability is about 45.3% even at a low amount of CA (6.0 wt%).