Photoinitiated atom transfer radical polymerization: Current status and future perspectives

Abstract

In macromolecular and material science, atom transfer radical polymerization (ATRP) has intensely influenced the research strategies facilitating fabrication of a wide range of polymers with well-defined structures and functions and their conjugation with biomolecules. Recently, the required copper (I) catalyst for ATRP process is generated by photoinduced redox reactions involving the in situ reduction of Cu(II) to Cu(I). Photochemically initiated reactions provide several distinct advantages, including temporal and spatial controls, rapid and energy efficient activation. The process is based on photoredox reactions of copper catalysts under various radiation sources with or without various photoinitiators. This Highlight focuses on the historical development, mechanistic aspects, limitations, and opportunities of photoinitiated ATRP along with selected examples.

Photocatalyzed Cu-Based ATRP Involving an Oxidative Quenching Mechanism under Visible Light

“…9 In particular, the development of atom transfer radical photopolymerization (ATRP2) has been a very active domain of research in the past few years. 10 The effect of light on ATRP was first demonstrated by Guan et al, who observed an acceleration of the polymerization rate as well as a better control under visible light. 11 Considering the well-known ATRP equilibrium, ATRP2 can recover actually several different strategies to introduce an effect of light in this mechanism, and a clear distinction between photoinduced and photocatalyzed mechanisms can be proposed.…”

Copper(II) thioxanthone carboxylate as a photoswitchable photocatalyst for photoinduced click chemistry

“…The process was realized in a ligand-free mode by the photogenerated intramolecular electron transfer reaction between the triplet state TX and Cu II leading to the in situ formation of Cu I species. The system offered temporal control over the click reaction as evidenced by alternating light and dark experiments, and the system may be adapted to light induced controlled/living radical polymerization processes, [33][34][35] specifically to Atom Transfer Radical Polymerization where initiating species and catalyst Cu I ions can be generated simultaneously. Further studies along these lines are now in progress.…”

Visible Light-Induced Atom Transfer Radical Polymerization for Macromolecular Syntheses

“…in the presence of oxygen, at room temperature or the use of catalyst at the level of parts per million (ppm). All of these methods are based on the in situ formation of activator via secondary reduction process including (I) the use of various reducing agents (either externally added (11) or monomers containing amine (12) or epoxide (13) groups as intrinsic reducing agents), (II) electrochemically redox processes (14), (III) copper-containing nanoparticles (15), and (IV) photochemically mediated redox processes (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27).…”

“…The use of UV and visible light irradiation for the in situ generation of activators for the photoinduced ATRP reaction has been researched extensively (16). Many copper (II) salts are light-sensitive compounds and can be photochemically reduced in the presence of the amine ligands.…”