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19 results on '"Sobieski, Julian"'

1. Better Together: Photoredox/Copper Dual Catalysis in Atom Transfer Radical Polymerization.

Author

Sobieski, Julian, Gorczyński, Adam, Jazani, Arman Moini, Yilmaz, Gorkem, and Matyjaszewski, Krzysztof

Subjects
*RADICALS (Chemistry), *POLYMERIZATION, *PHOTOCATALYSTS, *CATALYSIS, *ATOMS
Abstract

Photomediated Atom Transfer Radical Polymerization (photoATRP) is an activator regeneration method, which allows for the controlled synthesis of well‐defined polymers via light irradiation. Traditional photoATRP is often limited by the need for high‐energy ultraviolet or violet light. These could negatively affect the control and selectivity of the polymerization, promote side reactions, and may not be applicable to biologically relevant systems. This drawback can be circumvented by an introduction of the catalytic amount of photocatalysts, which absorb visible and/or NIR light and, therefore, controlled, regenerative ATRP can be performed with the dual‐catalytic cycle. Herein, a critical summary of recent developments in the field of dual‐catalysis concerning Cu‐catalyzed ATRP is provided. Contributions of involved species are examined mechanistically, followed by challenges and future directions towards the next generation of advanced functional macromolecular materials. [ABSTRACT FROM AUTHOR]

Published
2024
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2. ATRP with ppb Concentrations of Photocatalysts

Author

Coskun, Halil Ibrahim, De Luca Bossa, Ferdinando, Hu, Xiaolei, Jockusch, Steffen, Sobieski, Julian, Yilmaz, Gorkem, and Matyjaszewski, Krzysztof

Abstract

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.

Published
2024
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7. Comparison of mechano- and PhotoATRP with ZnO nanocrystals

Author

Cvek, Martin, Jazani, Arman Moini, Sobieski, Julian, Jamatia, Thaiskang, Matyjaszewski, Krzysztof, Cvek, Martin, Jazani, Arman Moini, Sobieski, Julian, Jamatia, Thaiskang, and Matyjaszewski, Krzysztof

Abstract

Zinc oxide (ZnO) was previously reported as an excellent cocatalyst for mechanically controlled atom transfer radical polymerization (mechanoATRP), but its photocatalytic properties in photoinduced ATRP (photoATRP) have been much less explored. Herein, well-defined ZnO nanocrystals were prepared via microwave-assisted synthesis and applied as a heterogeneous cocatalyst in mechano- and photoATRP. Both techniques yielded polymers with outstanding control over the molecular weight, but ZnO-cocatalyzed photoATRP was much faster than analogous mechanoATRP (conversion of 91% in 1 h vs 54% in 5 h). The kinetics of photoATRP was tuned by loadings of ZnO nanocrystals. PhotoATRP with ZnO did not require any excess of ligand versus Cu, in contrast to mechanoATRP, requiring an excess of ligand, acting as a reducing agent. ZnO-cocatalyzed photoATRP proceeded controllably without prior deoxygenation, since ZnO was involved in a cascade of reactions, leading to the rapid elimination of oxygen. The versatility and robustness of the technique were demonstrated for various (meth)acrylate monomers with good temporal control and preservation of end-group functionality, illustrated by the formation of tailored block copolymers.

Published
2023

10. Visible Light‐ATRP Driven by Tris(2‐Pyridylmethyl)Amine (TPMA) Impurities in the Open Air.

Author

Jazani, Arman Moini, Schild, Dirk J., Sobieski, Julian, Hu, Xiaolei, and Matyjaszewski, Krzysztof

Subjects
ETHYLENE oxide, AMINES, BLUE light, POLYMERS, RADICALS (Chemistry), METHACRYLATES, POLYMERIZATION, PYRAZOLYL compounds
Abstract

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500) in water is enabled using CuBr2 with tris(2‐pyridylmethyl)amine (TPMA) as a ligand under blue or green‐light irradiation without requiring any additional reagent, such as a photo‐reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18–1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co‐catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light. [ABSTRACT FROM AUTHOR]

Published
2023
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13. Understanding the Relationship between Catalytic Activity and Termination in photoATRP: Synthesis of Linear and Bottlebrush Polyacrylates

Author

Martinez, Michael R., primary, Sobieski, Julian, additional, Lorandi, Francesca, additional, Fantin, Marco, additional, Dadashi-Silab, Sajjad, additional, Xie, Guojun, additional, Olszewski, Mateusz, additional, Pan, Xiangcheng, additional, Ribelli, Thomas G., additional, and Matyjaszewski, Krzysztof, additional

Published
2019
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14. Pushing the Limit: Synthesis of SiO2-g-PMMA/PS Particle Brushes via ATRP with Very Low Concentration of Functionalized SiO2–Br Nanoparticles

Author

Wang, Zongyu, primary, Fantin, Marco, additional, Sobieski, Julian, additional, Wang, Zhenhua, additional, Yan, Jiajun, additional, Lee, Jaejun, additional, Liu, Tong, additional, Li, Sipei, additional, Olszewski, Mateusz, additional, Bockstaller, Michael R., additional, and Matyjaszewski, Krzysztof, additional

Published
2019
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19. Assessing steric bulk of protecting groups via a computational determination of exact cone angle and exact solid cone angle

Author

Sobieski, Julian Witold

Subjects
Chemistry, Steric, bulk, descriptor, computational, organic, protecting, exact, solid, cone, angle, Tolman,
Abstract

The exact cone angles and exact solid angles for 60 organic protecting groups were calculated and compared to previous methods of steric bulk approximation. Due to the lack of steric descriptors in literature for organic protecting groups, there was a need to develop a new approach. Recently reported computational techniques using Mathematica packages FindConeAngle and FindSolidAngle have allowed for the rigorous computation of several organic protecting group families. Functionalities analyzed by this method include, but are not limited to, silyl, acetal, halogenated, and aromatic protecting groups. Using Spartan '16, the approach uses equilibrium-optimized (B3LYP/LANL3DZ) structures of organic protecting groups coordinated to a single Pd atom in place of the protected O/N. Experimental evidence from a systematic study of steric influence by protecting groups on the synthetic yield of the Mitsunobu reaction is confirmed to correlate with the steric descriptors proposed in this work. The null conformation of equilibrium-optimized protecting groups is proposed as a concept for computationally determining the native behavior of organic protecting groups, the inclusion of which bears significance for computed steric bulks.

Published
2018

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