Theory and Applications of Thiyl Radicals in Polymer Chemistry

Coote, Michelle L.; Değirmenci, İsa

doi:10.1016/b978-0-12-815983-5.00006-4

Cited by 7 publications

(9 citation statements)

References 106 publications

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“…Thiol-ene reaction has appeared in literature since 1905 (30). Many experimental (12,(31)(32)(33)(34)(35)(36) or theoretical (15)(16)(17)19,21) studies have been carried out to elucidate the mechanism of thiol-ene polymerization. However, limited studies have focused on the role of the initiator on polymerization involving thiol-ene reactions (20)(21)(22)37,38).…”

Section: Resultsmentioning

confidence: 99%

“…Many experimental and theoretical studies have focused on the elaboration of steps of thiol-ene polymerization and factors affecting the process (12), such as the effect of solvent medium (13)(14)(15), the influence of substrate (12,16), or thiol reactivity (17)(18)(19). It was demonstrated that the main drawing force for the thiol-ene polymerization is the rate ratios for propagation and chain transfer reactions (kp/kct) (12).…”

Section: Introductionmentioning

confidence: 99%

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Role of Initiator Structure on Thiol-Ene Polymerization: A Comprehensive Theoretical Study

Değirmenci

2022

Journal of the Turkish Chemical Society Section A: Chemistry

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The effect of initiator nature on thiol-ene polymerization was elaborated in this work with two initiators, four thiols, and eight monomers by utilizing the M06-2X/6-31++G(d,p) level of theory. For this purpose, a comparative investigation was carried out by modeling hydrogen abstraction from thiols (kHA) and addition reaction to monomers (ki), which is considered a side reaction. It was confirmed that the 2,2-dimethoxy-2-phenylacetophenone (DMPA) initiator is a suitable thiol-ene initiator except for the polymerization of electron-deficient or conjugated monomers. It was determined that the azobis(isobutyronitrile) (AIBN) initiator could not give a homogeneous thiol-ene product regardless of the monomer structure. However, it has been found that aromatic thiols should be used to obtain relatively better results with this initiator.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Role of Initiator Structure on Thiol-Ene Polymerization: A Comprehensive Theoretical Study

Değirmenci

2022

Journal of the Turkish Chemical Society Section A: Chemistry

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“…Overall, UV absorption spectra correlate well with the thiol’s effectiveness at each wavelength, relative to the results with the acrylate polymerizations. The origin of this difference would have to be investigated more thoroughly to determine whether these trends are a result of solely photodynamics or an interplay of photodynamics and the TEC reactive nature of each thiol, since both the rates of chain transfer and propagation are drastically altered by the alkene substrate and aromatic thiol structures …”

Section: Resultsmentioning

confidence: 99%

“…The radical-mediated thiol–ene coupling (TEC) reaction of a thiol and an alkene has become a robust and popular transformation in bioconjugation as well as organic and materials synthesis due to facile access to a wide range of useful, reactive functional groups. Under the appropriate implementation conditions, the TEC reaction has been designated as a “click” reaction, e.g., possessing quantitative and rapid kinetics, insensitivity to oxygen, water, and most organic functional groups, full atom economy, and high chemo- and regioselectivity. − The reaction proceeds through a cyclic mechanism where in one step a thiyl radical, which is typically generated by exposure of a photoinitiator, propagates into the alkene to afford a 2 °C radical intermediate and C–S linkage. This C-radical intermediate then chain transfers to another thiol via H atom abstraction to regenerate the thiyl radical.…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, TEC reactions have been initiated by initiatorless direct irradiation either by the direct photolysis of the S–H bond by high-energy light centered about 254 nm or with lower energy light, i.e., >300 nm, through an unknown mechanism. , Just as the reactivity of thiols and their corresponding radicals varies substantially with the thiol’s structure (e.g, alkyl thiols, aromatic thiols, and thioacids), ,,, these subclasses also have profoundly different photochemistry/dynamics. Alkyl thiols undergo selective S–H homolysis by the excitation of a S lone pair electron into the SH antibonding orbital (σ* SH ) .…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Aromatic Thiols as Photoinitiators

2020

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The unique photodynamics of aromatic thiols (relative to alkyl thiols) allowed their employment as effective ultraviolet and visible light photoinitiators (PIs) for acrylate photopolymerizations, radicalmediated thiol−ene coupling (TEC) network polymerizations, solventless and initiatorless small-molecule TEC reactions, and hydrogel network polymerizations. Twenty-six thiol structures were evaluated as radical generating PIs in the polymerization of n-hexyl acrylate. Initiator effectiveness follows the trend nonheterocyclic aromatic thiols > heterocyclic aromatic thiols ≈ thioacids > alkyl thiols. Substituted versions of thiophenol exhibited the highest photoinitiation efficiency with electron-withdrawing substituents increasing effectiveness. Ortho-and para-substituted mercaptobenzoic acids and (trifluoromethyl)thiophenols were generally the most effective, leading to 100% acrylate conversion at a loading of 3 mM (0.1 mol % with respect to acrylate) when irradiated with 320−390 nm light and at loadings of 30 mM when irradiated with 405 nm light. Results demonstrate the potential of aromatic thiols as oxygen insensitive photoinitiators for bulk polymerizations and for specialty polymer synthesis via aromatic thiol-functionalized macroinitiators.

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Reversible Thiyl Radical Addition−Fragmentation Chain Transfer Polymerization

Wang,

Du,

Huang

2024

Angewandte Chemie

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Developing reversible‐deactivation radical polymerization (RDRP) methods that could directly control the thiyl radical propagation is highly desirable yet remains challenging in modern polymer chemistry. Here, we reported the first reversible thiyl radical addition‐fragmentation chain transfer (SRAFT) polymerization strategy, which utilizes allyl sulfides as chain transfer agents for reversibly deactivating the propagating thiyl radicals, thus allowing us to directly control a challenging thiyl radical chain polymerization to afford polymers with well‐defined architectures. A linear dependence of molecular weight on conversion, high chain‐end fidelity, and efficient chain extension proved good controllability of the polymerization. In addition, density functional theory calculations provided insight into the reversible deactivation ability of allyl sulfides. The SRAFT strategy developed in this work represents a promising platform for discovering new controlled polymerizations based on thiyl radical chemistry.

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Theory and Applications of Thiyl Radicals in Polymer Chemistry

Cited by 7 publications

References 106 publications

Role of Initiator Structure on Thiol-Ene Polymerization: A Comprehensive Theoretical Study

Role of Initiator Structure on Thiol-Ene Polymerization: A Comprehensive Theoretical Study

Evaluation of Aromatic Thiols as Photoinitiators

Reversible Thiyl Radical Addition−Fragmentation Chain Transfer Polymerization

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