Making ATRP More Practical: Oxygen Tolerance

Abstract

Conspectus Atom-transfer radical polymerization (ATRP) is a well-known technique for the controlled polymerization of vinyl monomers under mild conditions. However, as with any other radical polymerization, ATRP typically requires rigorous oxygen exclusion, making it time-consuming and challenging to use by nonexperts. In this Account, we discuss various approaches to achieving oxygen tolerance in ATRP, presenting the overall progress in the field. Copper-mediated ATRP, which we first discovered in the late 1990s, uses a CuI/L activator that reversibly reacts with the dormant C­(sp3)–X polymer chain end, forming a X–CuII/L deactivator and a propagating radical. Oxygen interferes with activation and chain propagation by quenching the radicals and oxidizing the activator. At ATRP equilibrium, the activator is present at a much higher concentration than the propagating radicals. Thus, oxidation of the activator is the dominant inhibition pathway. In conventional ATRP, this reaction is irreversible, so oxygen must be strictly excluded to achieve good results. Over the last two decades, our group has developed several ATRP techniques based on the concept of regenerating the activator. When the oxidized activator is continuously converted back to its active reduced form, then the catalytic system itself can act as an oxygen scavenger. Regeneration can be accomplished by reducing agents and photo-, electro-, and mechanochemical stimuli. This family of methods offers a degree of oxygen tolerance, but most of them can tolerate only a limited amount of oxygen and do not allow polymerization in an open vessel. More recently, we discovered that enzymes can be used in auxiliary catalytic systems that directly deoxygenate the reaction medium and protect the polymerization process. We developed a method that uses glucose oxidase (GOx), glucose, and sodium pyruvate to very effectively scavenge oxygen and enable open-vessel ATRP. By adding a second enzyme, horseradish peroxidase (HPR), we managed to extend the role of the auxiliary enzymatic system to generating carbon-based radicals and changed ATRP from an oxygen-sensitive to an oxygen-fueled reaction. While performing control experiments for the enzymatic methods, we noticed that using sodium pyruvate under UV irradiation triggers polymerization without the presence of GOx. This serendipitous discovery allowed us to develop the first oxygen-proof, small-molecule-based, photoinduced ATRP system. It has oxygen tolerance similar to that of the enzymatic methods, exhibits superior compatibility with both aqueous media and organic solvents, and avoids problems associated with purifying polymers from enzymes. The system was able to rapidly polymerize N-iso­propyl­acryl­amide, a challenging monomer, with a high degree of control. These contributions have substantially simplified the use of ATRP, making it more practical and accessible to everyone.

Design of biointerfaces composed of soft materials using controlled radical polymerizations

“…6(a)). 34 Moreover, ARGET ATRP can proceed in aqueous media with tolerance to oxygen. These characteristics have allowed ‘grafting from’ modification of biomolecules, including proteins and nucleic acids under biologically relevant conditions (Fig.…”

“…31 Moreover, ARGET ATRP proceeds in an aqueous medium with tolerance to oxygen to some extent. 32–34 Thus, ARGET ATRP is a powerful technique for the design of biointerfaces, including large-area densely packed polymer brushes, surface-functionalised water-containing materials, and polymer/biomolecule hybrids. 35 Photo-induced electron transfer (PET) RAFT polymerization can also proceed in aqueous media and has been applied to cytocompatible cell-surface engineering.…”

A New Protocol for Ash Wood Modification: Synthesis of Hydrophobic and Antibacterial Brushes from the Wood Surface

“…Moreover, ATRP methods enable the creation of polymer chains with a strictly designed structure and architecture [33,34]. Therefore, polymers and biopolymers produced by the ATRP technique are characterized by a narrow molecular weight distribution (M w /M n ), control over their molecular weight (MW) [30,35], and topology (geometry) [36,37] to obtain structures ranging from linear chains, stars, cyclic structures, combs, and regular polymer networks [32,[37][38][39].…”

Research progress in self-oscillating polymer brushes

“…Despite the 'smart' function of self-oscillating polymer brushes, the research interest on it is far less than that of stimulation-responsive polymer brushes. [62][63][64][65][66][67][68][69] With a view to arousing more research interest in related aspects, this paper aims to systematically introduce the research progress of selfoscillating polymer brushes and summarizes its response mechanisms and classication. Additionally, the future prospective is also discussed.…”