Oxygen, light, and mechanical force mediated radical polymerization toward precision polymer synthesis

The synthesis of polymers with well-defined composition, architecture, and functionality has long been a focal area of research in the field of polymer chemistry. The advancement of controlled radical polymerization (CRP) has facilitated the synthesis of precise polymers, which are endowed with new properties and functionalities, thereby exhibiting a wide range of applications. However, radical polymerization faces several challenges, such as oxygen intolerance, and common thermal initiation methods may lead to side reactions and depolymerization. Therefore, we have developed some oxygen-tolerant systems that directly utilize oxygen for initiating and regulating polymerization. We utilize oxygen/alkylborane as an effective radical initiator system in the polymerization, and also as a reductant for the removal of polymer chain ends. Moreover, we employ the gentler photoinduced CRP to circumvent side reactions caused by high temperatures and achieve temporal and spatial control over the polymerization. To enhance the penetration of the light source for polymerization, we have developed near-infrared light-induced atom transfer radical polymerization. Additionally, we have extended photochemistry to reversible addition-fragmentation chain transfer polymerization involving ion-pair inner-sphere electron transfer mechanism, metal-free radical hydrosilylation polymerization, as well as carbene-mediated polymer modification through C-H activation and insertion mechanisms. Furthermore, we propose a new method for polymerization initiation synergistically triggered by oxygen and mechanical energy. This review not only showcases the current advancements in CRP but also outlines future directions, such as the potential for 3D printing and surface coatings, and the exploration of new heteroatom radical polymerizations. By expanding the boundaries of polymer synthesis, these innovations could lead to the creation of new materials with enhanced functionality and applications.