High performance, self-healing and recyclable polyisoprene rubbers enabled by modulating sulfide bond structures

Sulfide bonds in sulfur-vulcanized rubbers not only consisting of strong C–S or S–S bonds which maintain the network integrity, but also provide exchangeable polysulfide bonds under loading or heating, which enhance extensibility, strain-induced crystallization, and potential reprocessability. However, current methods for tuning the sulfide bond structures and distribution are limited, hindering further exploration of effective strategies to improve rubber performance. In this study, we present a straightforward strategy to adjust the content of weak sulfide bonds by incorporating vulcanization modifiers into conventional vulcanization formulations. Our findings indicate that the vulcanization rate, crosslinking density, and mechanical properties can be finely tuned across a wide range. Notably, at low blending contents of vulcanization modifier, the tensile strengths of PhDT-0.5 (30.22 MPa) and PhDT-1 (30.42 MPa) significantly exceed that of PIP (22.03 MPa) and are comparable to Malaysian NR. It is demonstrated that π-π interactions between benzene ring increase entanglement modulus which not only promotes the strain induced crystallization behavior, but also imparts excellent dimensional stability to the rubber samples. Furthermore, at high blending contents of vulcanization modifier, a high content of weak sulfide bonds can be achieved in the vulcanization network, leading to the successful production of self-healing and recyclable polyisoprene rubbers. The representative samples demonstrated a maximum self-healing efficiency of 89.8 %. Moreover, the remolded samples exhibited a high recovery efficiency of tensile strength, reaching up to 104 %, and a recovery of 82.6 % for elongation at break. These results suggest that high-performance, self-healing, and recyclable polyisoprene rubber can be realized by modulating the composition and content of sulfide bonds in the vulcanization network. This innovative method has the potential to be applied to other diene rubbers and in the development of next-generation rubber materials.