Recent Developments and Future Challenges in Controlled Radical Polymerization: A 2020 Update

Abstract

This perspective summarizes the latest exciting developments in controlled radical polymerization during the last decade (2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020). Our focus is to critically highlight strengths and weaknesses of recent achievements and portray how these discoveries have expanded the scope of tailor-made polymeric materials. Our perspective on remaining future challenges and where we expect the field to grow toward in the next decade will also be discussed.100 years have passed since the landmark publication by Hermann Staudinger in 1920, after which the field of polymer chemistry was founded. One major revolution in the field has been controlled radical polymerization (CRP), also referred to as reversibledeactivation radical polymerization (RDRP), as it grants users the ability to regulate molecular weight, dispersity (Ð), composition, architecture, and end-group fidelity of vinyl polymers. Currently, numerous CRP techniques are available, most famously atom transfer radical polymerization (ATRP), 1 nitroxide-mediated polymerization (NMP), 2 and reversible addition-fragmentation chain-transfer (RAFT) polymerization. 3 Importantly, polymers synthesized by CRP find use as emulsifiers, dispersants, electrolytes, rheology, and surface modifiers and are applied in commercial products related to home care, beauty, health, paint, energy, and electronics. 4 The focus of this perspective is to acknowledge and critically review recent developments in the area of CRP (decade 2010-2020) (Figure 1). The order in which the developments are presented is not associated to their significance or date of their original report. USING LIGHT AS AN EXTERNAL STIMULUSAmong various stimuli, light is perhaps the most attractive due to its abundance, wide availability, mild nature, low cost, and environmental benignity while it offers tremendous possibilities for temporal and spatial control. In addition, light-mediated polymerizations might offer additional opportunities as they do not require high temperatures, which may facilitate side reactions and/or depolymerization. At the same time, however, light-mediated polymerizations suffer from limited depth penetration and scalability issues, although these have been considerably addressed through the development of flow photochemistry, which allows for faster polymerizations, enhanced control over the molecular weight distributions, and the possibility to be combined with on-orin-line monitoring characterization techniques (the reader is referred to a recent review in flow chemistry polymerization). 5 Furthermore, certain wavelengths and intensities may be disadvantageous for various biological systems. Currently, there are two main developments in this area, namely photo-ATRP (including metal-mediated and metal-free ATRP) and photoinduced electron transferThe Bigger Picture Challenges and opportunities:Universal catalysts compatible with a range of monomers and stimuli are urgently required to produce materials with enhanced control over monomer seq...

Ring-opening polymerization-induced crystallization-driven self-assembly of poly-L-lactide-block-polyethylene glycol block copolymers (ROPI-CDSA)

“…PISA is a scalable method that affords control over the BCP structure at high concentrations (10–50% solids w/w) 14 , 25 , 28 – 30 . To date, most PISA processes have been reversible-deactivation radical polymerizations (RDRP) 1 , 2 , 11 , 14 , 31 , primarily reversible addition-fragmentation chain-transfer polymerization (RAFT-PISA) 11 , 14 , 31 – 34 . However, PISA can theoretically be extended to all types of living polymerizations and has been demonstrated with living anionic polymerization 35 , ring-opening metathesis (ROMP) of norbornenes 13 , 29 , radical ring-opening copolymerization (rROP) of cyclic ketenes 36 , and ring-opening polymerization (ROP) of N-carboxyanhydrides 37 .…”

Biocatalytic nanoparticles for the stabilization of degassed single electron transfer-living radical pickering emulsion polymerizations

“…eversible deactivation radical polymerization (RDRP) techniques have emerged as one of the main tools for the efficient and precise synthesis of macromolecules with sophisticated and well-defined architectures for a wide range of macromolecular engineering applications [1][2][3][4][5][6] . Atom transfer radical polymerization (ATRP), reversible addition-fragmentation (RAFT) polymerization and single electron transfer-living radical polymerization (SET-LRP) offer high versatility to produce polymers, and the ability to minimize the termination events, while favoring equal propagation of polymeric chains during the polymerization process [7][8][9] .…”

Polymers in the Blender

“…Anionic poly merization demonstrates such features-as introduced by Szwarc almost 70 years ago [1] -yet it is tedious to perform and difficult to apply in most wet chemistry labs. The merger of living poly merization and radical polymerization, now coined reversible deactivation radical polymerization, [2,3] RDRP, has made such polymers available in abundance and broad variation, practically eradicating all noncontrolled polymerizations from contemporary advanced polymer synthesis. Since narrowness of polymer distributions (dispersity Ð < 1.5) is a trademark of living poly merization and RDRP, and is not achievable by uncontrolled polymerization, [4] low dispersity became soon a quality sign for any RDRP variant developed to yield such narrow distributions.…”

“…Equations for this behavior have been derived already when RDRP was introduced in the 1990s, even if their potential for material design had been largely neglected. [3] Based on this, any reversible termination or degenerative transfer system can be tuned to deliver specific dispersities. The problem rather lies in fact that the equilibrium constant, and hence the average lifetime of a radical between activation and deactivation, is typically constant for a given polymerization.…”