Letter pubs.acs.org/macroletters
Self-Folding Polymer Iron Catalysts for Living Radical Polymerization Yusuke Azuma, Takaya Terashima,* and Mitsuo Sawamoto* Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan S Supporting Information *
ABSTRACT: Iron-bearing self-folding polymers were created with amphiphilic random copolymers as active, versatile, and recyclable polymer-supported catalysts for living radical polymerization (LRP). The key is to build bis(imino)pyridine ligand cavities for iron complexes as linking units within self-folding polymers. Self-folding polymer ligands are synthesized by the intramolecular imine cross-linking of self-folded amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG), hydrophobic dodecyl, and urea/aniline pendants with 2,6-pyridinedicarboxaldehyde in water. The folding polymers efficiently formed iron complex catalysts in the cores to induce LRP and random or block copolymerization of various methacrylates. The self-folding polymer catalysts not only showed high activity and tolerance to functional groups such as acid, hydroxyl groups, and oxygen but also afforded easy product recovery and catalyst recycle thanks to hydrophilic PEG chains.
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folding polymers induced active, versatile, functionalitytolerant, and recyclable catalysis for precision polymer synthesis. Iron catalysts are potentially active for LRP12−14 and attract great attention as sustainable catalytic systems owing to their abundance on the earth and potentially low toxicity, whereas they have often suffered from low stability and tolerance to polar functional groups such as hydroxyl groups and carboxylic acid. To overcome these issues, bis(imino)pyridine ligands, allowing efficient coordination to iron metals,14 were built as cross-linking spacers into self-folding polymers. It should be noted that the ligand units not only serve as precision nanocavities to stably and individually support iron complexes but also allow us to robustly maintain self-folded structures in various environments (e.g., in organic solvents at high temperature). The folding polymer iron catalysts were thus effective for LRP of various methacrylates with high activity, stability, and functionality tolerance (e.g., acid, hydroxyl, and air), compared with core-forming model iron and other polymer-supported iron catalysts. To construct bis(imino)pyridine ligands in self-folding polymers, we designed an amphiphilic random copolymer
esign of nanospaces and environments around catalytic sites is a vital factor to create catalytic systems with high activity, functionality tolerance, and unique functions. In nature, enzymes perform highly active and selective catalysis with precision nanospaces/cavities that are comprised via the selffolding of amphiphilic polymer chains in water. Inspired by such a concept, various nanoreactors and polymer-supported catalysts have been developed for organic synthesis by using compartmentalized macromolecules including dendrimers,1 micelles,2 vesicles,3 microgel star polymers,4 and single chain polymeric nanoparticles (SCPNs).5−11 Among them, SCPNs uniquely have self-folded structures to carry inherent nanospaces and cavities, in which functional groups are sitespecifically placed and accumulated according to the primary structure. Thus, SCPNs bearing metal7−10 or organic11 catalysts serve as enzyme-like polymer-supported catalysts. SCPNs are generally created by the intramolecular self-assembly and/or cross-linking of functional random copolymers in solutions. In particular, amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) and functional pendants6d,7 autonomously self-fold in water by the hydrophobic effect and/or physical interactions even at high concentration (
