Dataset Information

Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper.

ABSTRACT: It was recently reported that copper catalysts used in atom transfer radical polymerization (ATRP) can combine with anionic surfactants used in emulsion polymerization to form ion pairs. The ion pairs predominately reside at the surface of the monomer droplets, but they can also migrate inside the droplets and induce a controlled polymerization. This concept was applied to activator regenerated by electron transfer (ARGET) ATRP, with ascorbic acid as reducing agent. ATRP of n-butyl acrylate (BA) and n-butyl methacrylate (BMA) was carried out in miniemulsion using Cu^II/tris(2-pyridylmethyl)amine (TPMA) as catalyst, with several anionic surfactants forming the reactive ion-pair complexes. The amount and structure of surfactant controlled both the polymerization rate and the final particle size. Well-controlled polymers were prepared with catalyst loadings as low as 50 ppm, leaving only 300 ppb of Cu in the precipitated polymer. Efficient chain extension of a poly(BMA)-Br macroinitiator confirmed high retention of chain-end functionality. This procedure was exploited to prepare polymers with complex architectures such as block copolymers, star polymers, and molecular brushes.

SUBMITTER: Wang Y

PROVIDER: S-EPMC6029244 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper.

Wang Yi Y Lorandi Francesca F Fantin Marco M Chmielarz Paweł P Isse Abdirisak A AA Gennaro Armando A Matyjaszewski Krzysztof K

Macromolecules 20171103 21

It was recently reported that copper catalysts used in atom transfer radical polymerization (ATRP) can combine with anionic surfactants used in emulsion polymerization to form ion pairs. The ion pairs predominately reside at the surface of the monomer droplets, but they can also migrate inside the droplets and induce a controlled polymerization. This concept was applied to activator regenerated by electron transfer (ARGET) ATRP, with ascorbic acid as reducing agent. ATRP of <i>n</i>-butyl acryla ...[more]

PMID: 29983450

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Project description:In atom transfer radical polymerization (ATRP), dormant alkyl halides are intermittently activated to form growing radicals in the presence of a CuI/L/X-CuII/L (activator/deactivator) catalytic system. Recently developed very active copper complexes could decrease the catalyst concentration to ppm level. However, unavoidable radical termination results in irreversible oxidation of the activator to the deactivator species, leading to limited monomer conversions. Therefore, successful ATRP at a low catalyst loading requires continuous regeneration of the activators. Such a regenerative ATRP can be performed with various reducing agents under milder reaction conditions and with catalyst concentrations diminished in comparison to conventional ATRP. Photoinduced ATRP (PhotoATRP) is one of the most efficient methods of activator regeneration. It initially employed UV irradiation to reduce the air-stable excited X-CuII/L deactivators to the activators in the presence of sacrificial electron donors. Photocatalysts (PCs) can be excited after absorbing light at longer wavelengths and, due to their favorable redox potentials, can reduce X-CuII/L to CuI/L. Herein, we present the application of three commercially available xanthene dyes as ATRP PCs: rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G). Even at very low Cu catalyst concentrations (50 ppm), they successfully controlled PhotoATRP. Well-defined polymers with preserved livingness were prepared under green LED irradiation, with subppm concentrations ([PC] ≥ 10 ppb) of RB and RD-6G or 5 ppm of RD. Interestingly, these PCs efficiently controlled ATRP at wavelengths longer than their absorption maxima but required higher loadings. Polymerizations proceeded with high initiation efficiencies, yielding polymers with narrow molecular weight distributions and high chain-end fidelity. UV-vis, fluorescence, and laser flash photolysis studies helped to elucidate the mechanism of the processes involved in the dual-catalytic systems, comprising parts per million of Cu complexes and parts per billion of PCs.

Project description: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-CuII/L). The role of PC was to trigger and drive the polymerization, while X-CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X-CuII/L back to CuI/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-CuII/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.

Dataset Information

Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper.

Publications

Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper.

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