Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study

Carbon-centered radicals have been randomly generated on the chains of poly(acrylic acid), PAA, the simplest synthetic anionic polyelectrolyte, by pulse-irradiating its dilute, oxygen-free aqueous solutions by 6 MeV electron beam. In some experiments, oligo(acrylic acid), OAA, and propionic acid, PA...

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Autores principales:	Małgorzata Matusiak, Sławomir Kadłubowski, Piotr Ulański
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	reaction kinetics free radicals radiation chemistry pulse radiolysis polyelectrolytes poly(acrylic acid) Technology T Engineering (General). Civil engineering (General) TA1-2040 Biology (General) QH301-705.5 Physics QC1-999 Chemistry QD1-999
Acceso en línea:	https://doaj.org/article/f0ae599785a74713b3e05354ca7faf63
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spelling	oai:doaj.org-article:f0ae599785a74713b3e05354ca7faf632021-11-11T15:12:42ZRecombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study10.3390/app1121101422076-3417https://doaj.org/article/f0ae599785a74713b3e05354ca7faf632021-10-01T00:00:00Zhttps://www.mdpi.com/2076-3417/11/21/10142https://doaj.org/toc/2076-3417Carbon-centered radicals have been randomly generated on the chains of poly(acrylic acid), PAA, the simplest synthetic anionic polyelectrolyte, by pulse-irradiating its dilute, oxygen-free aqueous solutions by 6 MeV electron beam. In some experiments, oligo(acrylic acid), OAA, and propionic acid, PA, were used as PAA models. Recombination kinetics of PAA radicals has been followed by fast spectrophotometry. A strong pH dependence of radical lifetime on pH, and thus on the linear charge density due to deprotonated carboxylate groups, has been confirmed, while a weaker amplitude of pH dependence was observed for OAA and PA. Decay kinetics of PAA radicals in the protonated state, at pH 2, have been studied in some detail. At moderate doses of ionizing radiation, resulting in a moderate average initial number of radicals per chain, <i>Z<sub>R</sub></i><sub>0</sub>, the decay can be satisfactorily described by a second-order kinetic model, but a somewhat better fit is obtained by using a dispersive kinetics approach. While for a constant polymer concentration the reciprocal half-lives are proportional to the initial radical concentrations, such a data series for different PAA concentrations do not overlap, indicating that the overall radical concentration is not the decisive factor controlling the kinetics. Arranging all data, in the form of second-order rate constants, as a function of the average initial number of radicals per chain allows one to obtain a common dependence. The latter seems to consist of two parts: a horizontal one at low <i>Z<sub>R</sub></i><sub>0</sub> and another one of positive slope at higher <i>Z<sub>R</sub></i><sub>0</sub>. This is interpreted as two kinetic regimes where two distinct reactions dominate, intermolecular and intramolecular recombination, respectively. Comparison of the low <i>Z<sub>R</sub></i><sub>0</sub> data with calculations based on the translational diffusion model indicate that the latter is not the rate-controlling process in intermolecular recombination of polymer radicals; segmental diffusion is the more likely candidate.Małgorzata MatusiakSławomir KadłubowskiPiotr UlańskiMDPI AGarticlereaction kineticsfree radicalsradiation chemistrypulse radiolysispolyelectrolytespoly(acrylic acid)TechnologyTEngineering (General). Civil engineering (General)TA1-2040Biology (General)QH301-705.5PhysicsQC1-999ChemistryQD1-999ENApplied Sciences, Vol 11, Iss 10142, p 10142 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	reaction kinetics free radicals radiation chemistry pulse radiolysis polyelectrolytes poly(acrylic acid) Technology T Engineering (General). Civil engineering (General) TA1-2040 Biology (General) QH301-705.5 Physics QC1-999 Chemistry QD1-999
spellingShingle	reaction kinetics free radicals radiation chemistry pulse radiolysis polyelectrolytes poly(acrylic acid) Technology T Engineering (General). Civil engineering (General) TA1-2040 Biology (General) QH301-705.5 Physics QC1-999 Chemistry QD1-999 Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
description	Carbon-centered radicals have been randomly generated on the chains of poly(acrylic acid), PAA, the simplest synthetic anionic polyelectrolyte, by pulse-irradiating its dilute, oxygen-free aqueous solutions by 6 MeV electron beam. In some experiments, oligo(acrylic acid), OAA, and propionic acid, PA, were used as PAA models. Recombination kinetics of PAA radicals has been followed by fast spectrophotometry. A strong pH dependence of radical lifetime on pH, and thus on the linear charge density due to deprotonated carboxylate groups, has been confirmed, while a weaker amplitude of pH dependence was observed for OAA and PA. Decay kinetics of PAA radicals in the protonated state, at pH 2, have been studied in some detail. At moderate doses of ionizing radiation, resulting in a moderate average initial number of radicals per chain, <i>Z<sub>R</sub></i><sub>0</sub>, the decay can be satisfactorily described by a second-order kinetic model, but a somewhat better fit is obtained by using a dispersive kinetics approach. While for a constant polymer concentration the reciprocal half-lives are proportional to the initial radical concentrations, such a data series for different PAA concentrations do not overlap, indicating that the overall radical concentration is not the decisive factor controlling the kinetics. Arranging all data, in the form of second-order rate constants, as a function of the average initial number of radicals per chain allows one to obtain a common dependence. The latter seems to consist of two parts: a horizontal one at low <i>Z<sub>R</sub></i><sub>0</sub> and another one of positive slope at higher <i>Z<sub>R</sub></i><sub>0</sub>. This is interpreted as two kinetic regimes where two distinct reactions dominate, intermolecular and intramolecular recombination, respectively. Comparison of the low <i>Z<sub>R</sub></i><sub>0</sub> data with calculations based on the translational diffusion model indicate that the latter is not the rate-controlling process in intermolecular recombination of polymer radicals; segmental diffusion is the more likely candidate.
format	article
author	Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański
author_facet	Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański
author_sort	Małgorzata Matusiak
title	Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
title_short	Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
title_full	Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
title_fullStr	Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
title_full_unstemmed	Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study
title_sort	recombination of poly(acrylic acid) radicals in acidic aqueous solutions: a pulse radiolysis study
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/f0ae599785a74713b3e05354ca7faf63
work_keys_str_mv	AT małgorzatamatusiak recombinationofpolyacrylicacidradicalsinacidicaqueoussolutionsapulseradiolysisstudy AT sławomirkadłubowski recombinationofpolyacrylicacidradicalsinacidicaqueoussolutionsapulseradiolysisstudy AT piotrulanski recombinationofpolyacrylicacidradicalsinacidicaqueoussolutionsapulseradiolysisstudy
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Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study

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