Photo‐mediated metal‐free atom transfer radical polymerization: recent advances in organocatalysts and perfection towards polymer synthesis

Abstract

Atom transfer radical polymerization (ATRP) is a significant improvement over traditional radical polymerization, which lacked control over molecular weight distribution and molecular weight. However, with the increasing advancement in synthetic polymer chemistry and the requirement of doing away with metal catalysts, which on one hand remain as contaminants even in trace quantities and on the other are environmentally unsustainable, catalysts that are totally organic in nature are being explored and success is being reported in the literature although in a very sparse way. This review is an attempt to give an overview of all the organic photocatalysts employed in metal‐free ATRP reported from 2014. It covers the recent advancements in photoinduced metal‐free ATRP and explains about the two possible mechanisms, i.e. oxidative and reductive quenching pathways, and the future direction in which this unique polymerization technique is heading. © 2021 Society of Industrial Chemistry.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air

“…The same result was obtained when MB + was used without the copper catalyst (Table , entry 3). Direct activation of the dormant polymer chain end (C­(sp 3 )–X) by excited MB + was not possible, due to its high oxidation potential. , Furthermore, no monomer conversion was observed in the absence of the TPMA ligand. However, when CuBr 2 , TPMA, and MB + were used in a molar ratio of [OEOMA 500 ]/[HO-EBiB]/[MB + ]/[CuBr 2 ]/[TPMA] = 200/1/0.05/0.2/0.6, a well-controlled polymerization ( Đ = 1.23) with a molecular weight of M n,th = 75 000 and M n,MALS = 62 600 was achieved, reaching 75% monomer conversion within 30 min (Table , entry 5).…”

“…Herein, we report red-light-mediated ATRP using commercially available methylene blue (MB + ) as the PC and [X–Cu II /TPMA] + (TPMA = tris­(2-pyridylmethyl)­amine) complex as the deactivator (Figure A). MB + is a water-soluble and biocompatible cationic dye (note that in the literature MB + is often abbreviated as MB, without a positive charge) that is commonly used as a PC in organic and polymer synthesis. − Despite these attractive properties, it has not yet been successfully used in photo-ATRP due to its high oxidation potential . The developed dual-catalytic ATRP system exhibited excellent oxygen tolerance, allowing open-air polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50–250 μL).…”

“…98−103 Despite these attractive properties, it has not yet been successfully used in photo-ATRP due to its high oxidation potential. 104 The developed dual-catalytic ATRP system exhibited excellent oxygen tolerance, allowing open-air polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50−250 μL). The method was applied to the high-throughput synthesis of a library of well-defined polymers and DNA−polymer bioconjugates with low dispersities (Đ < 1.30) in an open-air 96-well plate in both water and dimethyl sulfoxide (DMSO).…”

Electrochemical Investigation of Iron-Catalyzed Atom Transfer Radical Polymerization

“…Examples of these methods include activators regenerated by electron transfer (ARGET) ATRP [ 13 , 14 , 15 ] and supplemental activator and reducing agent (SARA) ATRP (also known as SET LRP) [ 16 , 17 , 18 ], which use a homogeneous reducing agent and a zero-valent metal, respectively, and methods based on external stimuli via electrochemistry [ 19 , 20 ], photochemistry [ 21 , 22 , 23 ] and sonochemistry [ 24 , 25 ]. Metal-free photo-induced ATRP is also widely used [ 26 , 27 ].…”