An official website of the United States government
Catalysts are essential for mediating a controlled polymerization in atom transfer radical polymerization (ATRP). Copper-based catalysts are widely explored in ATRP and are highly efficient, leading to well-controlled polymerization of a variety of functional monomers. In addition to copper, iron-based complexes offer new opportunities in ATRP catalysis to develop environmentally friendly, less toxic, inexpensive, and abundant catalytic systems. Despite the high efficiency of iron catalysts in controlling polymerization of various monomers including methacrylates and styrene, ATRP of acrylate-based monomers by iron catalysts still remains a challenge. In this paper, we review the fundamentals and recent advances of iron-catalyzed ATRP focusing on development of ligands, catalyst design, and techniques used for iron catalysis in ATRP.
more »
« less
Atom Transfer Radical Polymerization: A Mechanistic Perspective
Since its inception, atom transfer radical polymerization (ATRP) has seen continuous evolution in terms of the design of the catalyst and reaction conditions; today, it is one of the most useful techniques to prepare well-defined polymers as well as one of the most notable examples of catalysis in polymer chemistry. This Perspective highlights fundamental advances in the design of ATRP reactions and catalysts, focusing on the crucial role that mechanistic studies play in understanding, rationalizing, and predicting polymerization outcomes. A critical summary of traditional ATRP systems is provided first; we then focus on the most recent developments to improve catalyst selectivity, control polymerizations via external stimuli, and employ new photochemical or dual catalytic systems with an outlook to future research directions and open challenges.
more »
« less
- Award ID(s):
- 2000391
- PAR ID:
- 10348676
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- ISSN:
- 0002-7863
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)ATRP (atom transfer radical polymerization) is one of the most robust reversible deactivation radical polymerization (RDRP) systems. However, the limited oxygen tolerance of conventional ATRP impedes its practical use in an ambient atmosphere. In this work, we developed a fully oxygen-tolerant PICAR (photoinduced initiators for continuous activator regeneration) ATRP process occurring in both water and organic solvents in an open reaction vessel. Continuous regeneration of the oxidized form of the copper catalyst with sodium pyruvate through UV excitation allowed the chemical removal of oxygen from the reaction mixture while maintaining a well-controlled polymerization of N -isopropylacrylamide (NIPAM) or methyl acrylate (MA) monomers. The polymerizations of NIPAM were conducted with 250 ppm (with respect to the monomer) or lower concentrations of CuBr 2 and a tris[2-(dimethylamino)ethyl]amine ligand. The polymers were synthesized to nearly quantitative monomer conversions (>99%), high molecular weights ( M n > 270 000), and low dispersities (1.16 < Đ < 1.44) in less than 30 min under biologically relevant conditions. The reported method provided a well-controlled ATRP ( Đ = 1.16) of MA in dimethyl sulfoxide despite oxygen diffusion from the atmosphere into the reaction system.more » « less
-
Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X–Cu II /L). The role of PC was to trigger and drive the polymerization, while X–Cu II /L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X–Cu II /L, generating Cu I /L activator and PC˙ + . The ATRP ligand (L) used in excess then reduced the PC˙ + , closing the photocatalytic cycle. The continuous reduction of X–Cu II /L back to Cu I /L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X–Cu II /L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.more » « less
-
Efficient transfer of halogen atoms is essential for controlling the growth of polymers in atom transfer radical polymerization (ATRP). The nature of halogens may influence the efficiency of the halogen atom transfer during the activation and deactivation processes. The effect of halogens can be associated with the C–X bond dissociation energy and the affinity of the halogens/halides to the transition metal catalyst. In this paper, we study the effect of halogens (Br vs. Cl) and reaction media in iron-catalyzed ATRP in the presence of halide anions as ligands. In Br-based initiating systems, polymerization of methacrylate monomers was well-controlled whereas Cl-based initiating systems provided limited control over the polymerization. The high affinity of the Cl atom to the iron catalyst renders it less efficient for fast deactivation of growing chains, resulting in polymers with molecular weights higher than predetermined by Δ[M]/[RX] o and with high dispersities. Conversely, Br can be exchanged with higher efficiency and hence provided good control over polymerization. Decreasing the polarity of the reaction medium improved the polymerization control. Polymerizations using ppm levels of the iron catalyst in acetonitrile (a more polar solvent) yielded polymers with larger dispersity values due to the slow rate of deactivation as opposed to the less polar solvent anisole, which afforded well-controlled polymers with dispersity <1.2.more » « less
-
null (Ed.)The stringent control over the polymerization of less activated monomers remains one major challenge for Reversible Deactivation Radical Polymerizations (RDRP), including Atom Transfer Radical Polymerization (ATRP). Electrochemically mediated ATRP ( e ATRP) of a gaseous monomer, vinyl chloride (VC), was successfully achieved for the first time using a stainless-steel 304 (SS304) electrochemical reactor equipped with a simplified electrochemical setup. Controlled polymerizations were confirmed by the good agreement between theoretical and measured molecular weights, as well as the relatively narrow molecular weight distributions. Preservation of chain-end fidelity was verified by chain extension experiments, yielding poly(vinyl chloride) (PVC) homopolymers, block and statistical copolymers. The possibility of synthesizing PVC by e ATRP is a promising alternative to afford cleaner (co)polymers, with low catalyst concentration. The metal body of the reactor was also successfully used as a cathode. The setup proposed in this contribution opens an avenue for the polymerization of other gaseous monomers.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/jacs.2c05364
