Photocatalysis to synthesize, derivatize, depolymerize and degrade polymers Brent Sumerlin University of Florida, USA Post-polymerization modification strategies have advanced considerably in recent decades due to the discovery and development of highly efficient chemoselective reactions. These methods facilitate the synthesis of complex macromolecules by providing methods to transform pendent or terminal reactive groups of polymers into the desired functionality after polymerization. Post-polymerization modification often enables polymers with diverse properties to be generated from the starting material merely by using different reagents for functionalization. Ideal modifications to polymer structures are rapid, specific, efficient, and able to be performed catalytically to lead to functional polymers or copolymers inaccessible by direct polymerization. Relying solely on mild ultraviolet or visible light irradiation of thiocarbonylthio compounds, we have developed a new avenue to polymer-protein conjugates, semi-telechelic polymers, and well-defined ultrahigh molecular weight (UHMW) block polymers. Using either a photocatalyst or relying on the direct activation of photoactive functional groups, we devised a strategy to functional polymers with unprecedented molecular weights, complex architectures, and controlled microstructures. Photochemistry applied to commodity poly(meth)acrylates allowed us to (i) synthesize polymers by photoiniferter polymerization and (ii) install new functionality to these polymers to prepare copolymers of (meth)acrylates and olefins that are inaccessible by direct copolymerization. Extending these approaches to the rapidly growing field of photocatalytic decarboxylation, we were also able to prepare photodegradable polymers that have all-carbon backbones. Finally, we have demonstrated that by employing the traditional conditions of photopolymerization at elevated temperatures, we can achieve dramatically accelerated depolymerization to regenerate monomer, suggesting low-energy photochemistry can be leveraged to approach life-cycle circularity. We have also demonstrated that the end groups that result from reversible-deactivation radical polymerization allow depolymerization of polymethacrylates in the bulk at temperatures up to 250°C lower than traditional processes. We demonstrated that decarboxylation of copolymers possessing activated esters or carboxylic acids is a versatile method for the derivatization or degradation of polymer backbones. The process is attractive for polymer modification because it is rapid, involves mild conditions, and, in some cases, bypasses the need for preactivation, granting high atom economy. We established that the backbone radicals generated by direct decarboxylation can be converted into multiple functional groups or lead to chain cleavage, depending on the structure of the copolymer and the presence of other reagents. Extending these approaches to the rapidly growing field of photocatalytic decarboxylation, we can also exploit photochemistry for degrading polymers despite their all-carbon backbones. We have also demonstrated that by exploiting the end groups that result from controlled radical polymerization, we are able to achieve dramatically accelerated depolymerization to regenerate monomer, suggesting low-energy photochemistry or thermal treatment can be leveraged to approach life-cycle circularity
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© The Author(s), 2023
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