Covalently cross-linked and mechanochemiluminescent polyolefins capable of self-healing and self-reporting

Abstract

Compared with non-cross-linked and dynamically covalent polymers, covalently cross-linked networks are irreplaceable in many areas; however, they are difficult to repair once fractured, due to limited polymer chain diffusion after cross-linking. Herein, the authors have reported a new kind of permanently cross-linked polyolefin, which when attached with amide side groups, yield mechanically robust yet readily repairable materials. A key is to use low cross-linking density, which enables satisfactory elasticity and chain mobility for thermodynamically favored healing. Another key is to incorporate dense hydrogen bonds that can undergo reversible associations. These factors jointly promise polyolefin networks with good mechanical properties and self-healing performance (recovered spontaneously up to 96% of its original tensile strength). More importantly, by means of mechanochemiluminescence from 1,2-dioxetane, which serves as the cross-linker and built-in self-reporting stress probe, a microscopic evaluation of how the chain entanglement proceeds upon healing and how failure occurs in the network can be obtained.