Evolution and Future Directions of Metal-Free Atom Transfer Radical Polymerization

Abstract

The increasing impact of atom transfer radical polymerization (ATRP) in fields beyond traditional polymer science has necessitated the development of alternative strategies for controlling polymer growth. Driven by applications that are sensitive to metal ion contamination, “greener” methodologies are emerging as a powerful alternative to conventional ATRP. Organic catalysis represents a major evolution of ATRP with metal-free systems holding significant potential as user-friendly methods for utility in biological and microelectronic applications. In addition, shifting from a combination of thermal activation/metal ions/ligands to simpler organic catalysis/light activation increases compatibility with functional monomers and allows the development of novel surface patterning strategies. Herein, we highlight key discoveries and recent developments in metal-free ATRP, while providing a perspective for future opportunities in this emerging area.

Synthesis of Hyperbranched Polymers via Metal‐Free ATRP in Solution and Microemulsion

“…Two seminal works in 2014 reported by Hawker and co‐workers [ 44 ] and Miyake and Theriot [ 45 ] opened the field of metal‐free ATRP as both 10‐phenylphenothiazine (Ph‐PTH) and perylene were successfully applied as photoredox catalysts for controlled polymerization of methacrylates, acrylates, acrylonitrile, styrene, and so on. [ 46,47 ] Various photoredox catalysts, including derivatives of phenothiazine, perylene, phenazine, [ 48 ] phenoxazine, [ 49 ] fluorescein, [ 50,51 ] carbazole, [ 52 ] and thienothiophene [ 53 ] photocatalysts, were subsequently developed, resulting in flourishing research of photomediated CRPs. [ 54–58 ]…”

“…As traditional ATRP has been used to prepare a variety of polymer architectures inaccessible via conventional radical polymerization, it is reasonable to expect that the development of metal‐free ATRP systems provides another opportunity to produce various polymer structures in greener and more efficient routes, [ 46,65 ] including block polymers, star polymers, [ 66,67 ] and (hyper)branched polymers. [ 68 ] Herein, we report the first homopolymerization of two inimers, 1 and 2, via photoinduced metal‐free ATRP using Ph‐PTH as photocatalyst in both solution and microemulsion media.…”

Surface‐initiated PET‐RAFT polymerization under metal‐free and ambient conditions using enzyme degassing

“…An efficient way to prepare densely grafted brush layers on surfaces is through a “grafting from” approach. This typically involves using surface‐initiated controlled radical polymerization (SI‐CRP), such as atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer (RAFT) polymerization, or nitroxide‐mediated polymerization (NMP) . The versatility of solution‐phase CRP techniques is transferable to surface‐initiated polymerization with many strategies taking advantage of established procedures for initiator synthesis and surface functionalization .…”

Metal‐Free Fast Azidation by Using Tetrabutylammonium Azide: Effective Synthesis of Alkyl Azides and Well‐Defined Azido‐End Polymethacrylates

“…PMMA‐Br was purified by reprecipitation and subsequently by preparative gel permeation chromatography (GPC) to remove traces of copper. Recently developed metal‐free photo‐ATRP may be used to seek the completely metal‐free synthesis of PMMA‐Br …”