Biocatalytic “Oxygen‐Fueled” Atom Transfer Radical Polymerization

Enzyme Catalysis for Reversible Deactivation Radical Polymerization

Enzyme catalysis has been increasingly utilized in reversible deactivation radical polymerization (Enz-RDRP) on account of its mildness, efficiency, and sustainability. In this Minireview we discuss the key roles enzymes play in RDRP, including their ATRPase, initiase, deoxygenation, and photoenzyme activities. We use selected examples to highlight applications of Enz-RDRP in surface brush fabrication, sensing, polymerization-induced self-assembly, and high-throughput synthesis. We also give our reflections on the challenges and future directions of this emerging area.

Achieving Ultrahigh Molecular Weights with Diverse Architectures for Unconjugated Monomers through Oxygen-Tolerant Photoenzymatic RAFT Polymerization

Achieving well-defined polymers with ultrahigh molecular weight (UHMW) is an enduring pursuit in the field of reversible deactivation radical polymerization. Synthetic protocols have been successfully developed to achieve UHMWs with low dispersities exclusively from conjugated monomers while no polymerization of unconjugated monomers has provided the same level of control. Herein, an oxygen-tolerant photoenzymatic RAFT (reversible addition-fragmentation chain transfer) polymerization was exploited to tackle this challenge for unconjugated monomers at 10 °C, enabling facile synthesis of well-defined, linear and star polymers with near-quantitative conversions, unprecedented UHMWs and low dispersities. The exquisite level of control over composition, MW and architecture, coupled with operational ease, mild conditions and environmental friendliness, broadens the monomer scope to include unconjugated monomers, and to achieve previously inaccessible low-dispersity UHMWs.

p-Substituted Tris(2-pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization

A facile and efficient two-step synthesis of p-substituted tris(2-pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis, p-Cl substituents in tris(4-chloro-2-pyridylmethyl)amine (TPMA^3Cl ) were replaced in one step and high yield by electron-donating cyclic amines (pyrrolidine (TPMA^PYR ), piperidine (TPMA^PIP ), and morpholine (TPMA^MOR )) by nucleophilic aromatic substitution. The [Cu^II (TPMA^NR2 )Br]⁺ complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [Cu^II (TPMA)Br]⁺ , indicating >3 orders of magnitude higher ATRP activity. [Cu^I (TPMA^PYR )]⁺ exhibited the highest reported activity for Br-capped acrylate chain ends in DMF, and moderate activity toward C-F bonds at room temperature. ATRP of n-butyl acrylate using only 10-25 part per million loadings of [Cu^II (TPMA^NR2 )Br]⁺ exhibited excellent control.

An Oxygen Paradox: Catalytic Use of Oxygen in Radical Photopolymerization

A peculiar radical polymerization reaction is presented in which oxygen serves as a cocatalyst, alongside triethylamine, to provide activation with light in the far-red (690 nm, 3 mW cm^-2 ) of the PET-RAFT process in the presence of zinc(II) (2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin) as photocatalyst. Apart from the ability to exert temporal control by switching the light on or off, this system possesses the exciting capability of inducing temporal control by removal or reintroduction of oxygen. Furthermore, this multicomponent catalytic system was typified by controlled polymerizations of various acrylate and acrylamide monomers, which all resulted in well-defined polymers with low dispersity (<1.2). The process displayed excellent living characteristics that were demonstrated through chain extensions and a range of degrees of polymerization (200-1600).

A cocktail of vitamins for aqueous RAFT polymerization in an open-to-air microtiter plate

We report a highly biocompatible photoinitiation strategy based on Vitamin B₂ and Vitamin C. This two-component photoinitiator enables RAFT polymerization to be conducted in high throughput in an open-to-air microtiter plate.