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Infrared Spectroelectrochemical Study of the Oxidation of Substituted Phenols of relevance to the Surface Oxidation of Polystyrene

Diallo, Mohamed; (2019) Infrared Spectroelectrochemical Study of the Oxidation of Substituted Phenols of relevance to the Surface Oxidation of Polystyrene. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This work explores the changes in chemical structure to polystyrene upon treatment with oxidising agents and to monitor the oxidation in situ on addition of these agents using FTIR spectroscopy technique in order to understand the oxidation mechanisms. The electrochemical oxidation of TBP, unsubstituted phenol and o,m,p-cresols presented as defect sites in surface microstructure of the polystyrene was first studied using cyclic voltammetry and a combined technique of chronoamperometry and in situ ATR-FTIR spectroscopy. The results obtained showed that the oxidation of TBP involves a one electron per proton transfer, leading to the formation of 2,4,6-tri-tert-butylphenoxy radical. Additionally, enhanced electron-transfer kinetics was observed at the EPPG in comparison to the GC and BDD electrodes and this was attributed to the presence of the edge sites in the surface microstructure of the EPPG. The electrochemical oxidation of the unsubstituted phenol studied under the same experimental conditions as the TBP reveals that the oxidation proceeds by a one electron transfer, leading to the phenoxy radical then to polymeric, dimer link through O ̶ O and quinone as oxidation products. The oxidation reaction was found to be dependent of the experimental conditions. The results obtained from the electrochemical oxidation of the cresols indicate that the oxidation is influencing by the substitution pattern in the phenyl ring and this was confirmed by the different oxidation products obtained for each cresol. While polymeric, dimer link through O ̶ O and quinone products oxidation products were obtained for o-cresol, the oxidation of m-cresol produces polymeric and dimer link through O ̶ O as oxidation products. Only dimer link through O ̶ O oxidation product was obtained for p-cresol. The formation of quinoid compound was not observed in both the m-cresol and p-cresol and this was probably due the fact that the molecule being too sterically crowded. The electrochemical oxidation of these phenolic compounds was monitored using a combined technique of chronoamperometry and in situ ATR-FTIR spectroscopy in order to confirm the mechanism proposed for these phenolic compounds. IR peaks consistent with the vibration stretch of the oxidations product resulting from the oxidation of these phenolic compounds were identified.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Infrared Spectroelectrochemical Study of the Oxidation of Substituted Phenols of relevance to the Surface Oxidation of Polystyrene
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10080370
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