Self-healing polyurethane elastomers based on dynamic thiourethane and disulfide bonds

Abstract

Self-healable and reprocessable crosslinked PU (xPU) elastomer with robust mechanical properties were synthesized by the incorporation of dual dynamic covalent bonds (thiourethane bond and disulfide bond) in the network. The crosslinked PU network was obtained by solution blending of NCO-terminated PU prepolymer, dimethacrylate bearing a disulfide bond, a 6-functional thiol and a small amount of base catalyst, followed by solvent casting upon heating. Network bearing both thiourethane and disulfide bonds was formed through thiol-isocyanate and thiol-acrylate reaction, which were confirmed by FT-IR, Raman spectroscopy, and dynamic mechanical analysis. This molecular design endows the elastomer with high elongation at break (upto 600%) and tensile strength (upto 40 MPa), which can be regulated by varying the composition of the constituent materials. The xPUs with the dual dynamic bonds exhibit excellent self-healing properties under mild heating or UV irradiation, and a good recyclability with lower activation energy for stress relaxation behavior as compared to those with thiourethane bond only. Small amounts (0.1 wt%) of graphene oxide (GO) were added to fabricate xPU/GO nanocomposites, and the nanocomposites showed excellent self-healing effect under NIR irradiation due to the action of GO as NIR-triggered nanoheaters.