Carbene-Mediated Polymer Cross-Linking with Diazo Compounds by C–H Activation and Insertion
Shicheng Yang, Siyu Yi, Jie Yun, Ning Li, Yuan Jiang, Zhujun Huang, Chaoran Xu, Congze He, Xiangcheng Pan
Abstract
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 °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.