Photo-crosslinkable, self-healable and reprocessable rubbers

As a proof of concept, this study reports a facile method to prepare photo-crosslinkable, self-healable and reprocessable rubbers, which are rapidly crosslinked and patterned variform products via thiol-ene photoclick polymerization between the double bonds in polybutadiene and thiols in polysulfide. Disulfide linkages in polysulfide can dynamically rearrange the crosslinked networks through UV irradiation activated disulfide metathesis. The model small molecule experiments prove that disulfide metathesis is efficiently promoted by UV light and inclines to second-order reaction. The stress of photo-crosslinked rubbers is almost completely relaxed under UV irradiation at higher than 25 mW/cm(2). More interestingly, stress relaxation can be controlled by sequentially turning on/off UV light. The self-adhesion assisted self-healing property is revealed by repeated tensile shear tests. The content of disulfide bonds, transmittance, irradiation intensity and time have a synergistic effect on the self-healing ability. The healed samples can regain higher than 90% shear strength, and the efficiency is not significantly influenced by repeated healing. Due to the dynamic reversibility of disulfide metathesis, the molded rubbers can be transformed into other shapes under UV illumination. Moreover, the pulverized rubber can also be compressed into new items by means of UV induced disulfide metathesis. This study thus illustrates a feasible approach to endow photo-cured rubbers with UV triggered self-healing and reprocessing capacities.