Red-Light-Induced PET-RAFT Polymerization to Afford (Meth)acrylamide-Based Poly( <i>N</i> -oxide) and Other Hydrophilic Polymers Featuring Neutral, Cationic, and Zwitterionic Groups as Solubilizing Side Chains

Amine-oxide-containing polymers, poly-(<i>N</i>-oxide), have emerged as an alternative to poly-(ethylene glycol) (PEG) for imparting biofouling resistance and enabling drug delivery applications. Poly-(<i>N</i>-oxide) can be obtained by thermally initiated controlled free radical polymerization and postpolymerization modification of the corresponding tertiary amine-containing polymers. However, unexpected side reactions between (meth)-acrylamide-based <i>N</i>-oxide monomers and chain transfer agents commonly used in thermally initiated reversible addition-fragmentation chain transfer (RAFT) polymerization present challenges for achieving controlled polymerization. Herein, this study exploits visible-light-induced photoelectron transfer (PET)-RAFT polymerization of <i>N</i>-oxide-containing (meth)-acrylamides by using two types of zinc-(II) porphyrin derivatives. This approach affords well-defined (meth)-acrylamide- and methacrylate-based <i>N</i>-oxide polymers with narrow molecular weight distributions even at a catalyst loading of less than 100 ppm. Successful one-pot chain- extension experiments confirm the good end-group fidelity. The optimized reaction condition can afford well-defined polymers with <i>M</i> _n up to 126 kDa. This method enables polymerization under complete oxygen tolerance, with excellent temporal control and the ability to conduct polymerization from low volume to large scale without diminishing the control over polymerization. In addition, such a method is also applicable to other hydrophilic methacrylate monomers featuring neutral oligo-(ethylene glycol), zwitterionic sulfobetaine, and phosphocholine, as well as cationic quaternary ammonium groups as side chains.