A Water‐Soluble Organic Photocatalyst Discovered for Highly Efficient Additive‐Free Visible‐Light‐Driven Grafting of Polymers from Proteins at Ambient and Aqueous Environments

Abstract Since the pioneering discovery of a protein bound to poly(ethylene glycol), the utility of protein–polymer conjugates (PPCs) is rapidly expanding to currently emerging applications. Photoinduced energy/electron‐transfer reversible addition–fragmentation chain‐transfer (PET‐RAFT) polymerization is a very promising method to prepare structurally well‐defined PPCs, as it eliminates high‐cost and time‐consuming deoxygenation processes due to its oxygen tolerance. However, the oxygen‐tolerance behavior of PET‐RAFT polymerization is not well‐investigated in aqueous environments, and thereby the preparation of PPCs using PET‐RAFT polymerization needs a substantial amount of sacrificial reducing agents or inert‐gas purging processes. Herein a novel water‐soluble and biocompatible organic photocatalyst (PC) is reported, which enables visible‐light‐driven additive‐free “grafting‐from” polymerizations of a protein in ambient and aqueous environments. Interestingly, the developed PC shows unconventional “oxygen‐acceleration” behavior for a variety of acrylic and acrylamide monomers in aqueous conditions without any additives, which are apparently distinct from previously reported systems. With such a PC, “grafting‐from” polymerizations are successfully performed from protein in ambient buffer conditions under green light‐emitting diode (LED) irradiation, which result in various PPCs that have neutral, anionic, cationic, and zwitterionic polyacrylates, and polyacrylamides. It is believed that this PC will be widely employed for a variety of photocatalysis processes in aqueous environments, including the living cell system.