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Computational Evaluation of the Sulfonyl Radical as a Universal Leaving Group for RAFT Polymerisation

Abstract (Expand)

The present study investigates the performance of the sulfonyl radical, i.e. •SO2Ph, as a universal leaving group in reversible addition–fragmentation chain-transfer (RAFT) polymerisation. The sulfonyl … radical is widely used as a radical initiator and has already been proved successful as a leaving group in an atom-transfer radical polymerisation. Our results, obtained using high-level ab initio computational methodology under relevant experimental conditions, indicate superior performance of the sulfonyl compared with a reference cyanoisopropyl group in controlling RAFT of a wide range of monomers. Importantly, the presence of sulfonyl chain ends in the polymers so formed opens attractive possibilities for further functionalisation. Potential synthetic routes to the R-sulfonyl RAFT agents are discussed.

Authors: Ganna Gryn'ova, Tamaz Guliashvili, Krzysztof Matyjaszewski, Michelle L. Coote

Date Published: 2013

Publication Type: Journal

Use of Spin Trap Technique for Kinetic Investigation of Elementary Steps of RAFT-Polymerization

Abstract

Not specified

Authors: Anatoly Filippov, Elena Chernikova, Vladimir Golubev, Ganna Grynova, Ching Yeh, Michelle L.

Date Published: 12th Sep 2012

Publication Type: Book

New Insights into the Mechanism of Amine/Nitroxide Cycling during the Hindered Amine Light Stabilizer Inhibited Oxidative Degradation of Polymers

Abstract (Expand)

High-level ab initio molecular orbital theory calculations are used to identify the origin of the remarkably high inhibition stoichiometric factors exhibited by dialkylamine-based radical-trapping … antioxidants. We have calculated the free energy barriers and reaction energies at 25, 80, and 260 °C in the gas phase and in aqueous solution for a broad range of reactions that might, potentially, be involved in amine/nitroxide cycling, as well as several novel pathways proposed as part of the present work, including that of N-alkyl hindered amine light stabilizer activation. We find that most of the literature nitroxide regeneration cycles should be discarded on either kinetic or thermodynamic grounds; some are even inconsistent with existing experimental observations. We therefore propose a new mechanistic cycle that relies on abstraction of a β-hydrogen atom from an alkoxyamine (R1R2NOCHR3R4). Our results suggest that this cycle is energetically feasible for a range of substrates and provides an explanation for previously misinterpreted or unexplained experimental results. We also explore alternative mechanisms for amine/nitroxide cycling for cases where the alkoxyamines do not possess an abstractable β-hydrogen.

Authors: Ganna Gryn’ova, K. U. Ingold, Michelle L. Coote

Date Published: 24th Jul 2012

Publication Type: Journal

Computational Design of Cyclic Nitroxides as Efficient Redox Mediators for Dye-Sensitized Solar Cells

Abstract (Expand)

Cyclic nitroxide radicals represent promising alternatives to the iodine‐based redox mediator commonly used in dye‐sensitized solar cells (DSSCs). To date DSSCs with nitroxide‐based redox mediators … have achieved energy conversion efficiencies of just over 5 % but efficiencies of over 15 % might be achievable, given an appropriate mediator. The efficacy of the mediator depends upon two main factors: it must reversibly undergo one‐electron oxidation and it must possess an oxidation potential in a range of 0.600–0.850 V (vs. a standard hydrogen electrode (SHE) in acetonitrile at 25 °C). Herein, we have examined the effect that structural modifications have on the value of the oxidation potential of cyclic nitroxides as well as the reversibility of the oxidation process. These included alterations to the N‐containing skeleton (pyrrolidine, piperidine, isoindoline, azaphenalene, etc.), as well as the introduction of different substituents (alkyl‐, methoxy‐, amino‐, carboxy‐, etc.) to the ring. Standard oxidation potentials were calculated using high‐level ab initio methodology that was demonstrated to be very accurate (with a mean absolute deviation from experimental values of only 16 mV). An optimal value of 1.45 for the electrostatic scaling factor for UAKS radii in acetonitrile solution was obtained. Established trends in the values of oxidation potentials were used to guide molecular design of stable nitroxides with desired equation image, and a number of compounds were suggested for potential use as enhanced redox mediators in DSSCs.

Authors: Ganna Gryn'ova, Jonathan M. Barakat, James P. Blinco, Steven E. Bottle, Michelle L. Coote

Date Published: 11th Jun 2012

Publication Type: Journal

Reversible Addition–Fragmentation Chain Transfer Polymerization of Vinyl Chloride

Abstract (Expand)

Controlled/“living” radical polymerization (CLRP) of vinyl chloride (VC) via the reversible addition–fragmentation chain transfer (RAFT) process is reported for the first time. The cyanomethyl … methyl(phenyl)carbamodithioate (CMPCD) was found to be an efficient RAFT agent enabling the CLRP polymerization of VC monomer under certain experimental conditions. Two different radical initiators, having very distinct half-life times at room temperature, were employed in this study. The kinetic studies of RAFT polymerization of VC show a linear increase of the molecular weight with the monomer conversion and the lowest polydispersity (PDI) ever reported for poly(vinyl chloride) (PVC) synthesized with CLRP method (PDI ∼ 1.4). The resulting PVC was fully characterized using the matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), 1H nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC) techniques. The 1H NMR and MALDI-TOF-MS analysis of PVC prepared via RAFT polymerization method have shown the absence of structural defects and the presence of chain-end functional groups. The “livingness” of the PVC was also confirmed by a successful reinitiation experiment. The suitability of the RAFT agent was also confirmed via high-level ab initio molecular orbital calculations.

Authors: Carlos M. R. Abreu, Patrícia V. Mendonça, Arménio C. Serra, Jorge F. J. Coelho, Anatoliy V. Popov, Ganna Gryn’ova, Michelle L. Coote, Tamaz Guliashvili

Date Published: 27th Feb 2012

Publication Type: Journal

The Use of Spin Traps for the Kinetic Investigation of Elementary Events of Pseudoliving Radical Reversible Addition-Fragmentation Chain-Transfer Polymerization

Abstract (Expand)

The spin-trapping technique is used for the first time to study the kinetics and mechanism of addition and fragmentation elementary events in reversible addition-fragmentation chain-transfer pseudoliving … radical polymerization. As shown by the example of the spin-trap-reversible addition-fragmentation chaintransfer agent model system, the constants of addition (substitution) of the model tert-butyl radical to polymeric reversible addition-fragmentation chain-transfer agents (poly(styrene dithiobenzoate), poly(n-butyl acrylate) dithiobenzoate, etc.) are one to two orders of magnitude higher than the constants of addition reactions involving low-molecular-mass reversible addition-fragmentation chain-transfer agents (tert-butyl dithiobenzoate, benzyl dithiobenzoate, di-tert-butyl trithiocarbonate, and dibenzyl trithiocarbonate). This circumstance makes it possible to significantly widen the synthetic possibilities of reversible addition-fragmentation chain-transfer polymerization. Rate constants of the fragmentation reaction for a number of intermediates are estimated, and the relationship between their structure and stability is ascertained. For the model reaction of the interaction (addition and fragmentation) of the tert-butyl radical with low-molecular-mass reversible addition-fragmentation chain-transfer agents, equilibrium constants are calculated via the methods of computational chemistry.

Authors: V. B. Golubev, A. N. Filippov, E. V. Chernikova, M. L. Coote, C. Y. Lin, G. Gryn’ova

Date Published: 1st Sep 2011

Publication Type: Journal

Evaluation of the Dependence of Aqueous Solubility of Nitro Compounds on Temperature and Salinity: A COSMO-RS Simulation

Abstract (Expand)

The solubility in pure and saline water at various temperatures was calculated for selected nitro compounds (nitrobenzene, 1,3,5-trinitrobenzene, 2-nitrotoluene, 3-nitrotoluene, 4-nitrotoluene, … 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2,3-dinitrotoluene, 3,4-dinitrotoluene, 2,4,6-trinitrotoluene) using the Conductor-like Screening model for Real Solvents (COSMO-RS). The results obtained were compared with experimental values. The COSMO-RS predictions have shown high accuracy in reproducing the trends of aqueous solubilities for both temperature and salinity. The proposed methodology was then applied to predict the aqueous solubilities of 19 nitro compounds in the temperature range of 5–50 °C in saline solutions. The salting-out parameters of the Setschenow equation were also calculated. The predicted salting-out parameters were overestimated when compared to the measured values, but these parameters can still be used for qualitative estimation of the trends.

Authors: Yana A. Kholod, Ganna Gryn’ova, Leonid Gorb, Frances C. Hill, Jerzy Leszczynski

Date Published: 1st Apr 2011

Publication Type: Journal

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