Carbene-Mediated Polymer Cross-Linking with Diazo Compounds by C-H Activation and Insertion

Compared with linear thermoplastic polymers, thermoset polymers with three-dimensional network structures exhibit improved solvent tolerance, heat resistance, and mechanical strength. The radical mediated process is widely used to cross-link the linear polymer chains; however, this process requires high temperature (> 150 degrees C) or UV irradiation to generate highly energetic radicals, unavoidably leading to undesired side reactions and uncontrolled cross-linking behavior. This work proposes and achieves a carbene-mediated polymer cross-linking with diazo-based compounds by C-H activation and an insertion mechanism under relatively mild conditions. A simple route containing only one or two steps is established to synthesize three generations of diazo-based cross-linkers 1G, 2G, and 3G. The cross-linker 1G exhibits the lowest cross-linking efficiency due to the undesired self-coupling of carbenes. After optimizing the chemical structure and increasing the numbers of diazo moieties, the cross-linking efficiency significantly improves for 2G and 3G cross-linkers. These cross-linkers are applicable for any polymers containing C-H bonds. They are useful in a wide range of applications, from the adhesion of low surface energy ultrahigh molecular weight polyethylene (UHMWPE) to polymer modification by co-cross-linking. This versatile, convenient, and practical carbene-mediated cross-linking strategy provides new opportunities for modification, cross-linking, and adhesion in polymer science.