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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MDPI AG
2021-10-01
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| Online Access: | https://www.mdpi.com/2076-3417/11/21/10142 |
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| author | Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański |
| author_facet | Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański |
| author_sort | Małgorzata Matusiak |
| collection | DOAJ |
| 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. |
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| language | English |
| last_indexed | 2024-03-10T06:07:04Z |
| publishDate | 2021-10-01 |
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| spelling | doaj.art-f0ae599785a74713b3e05354ca7faf632023-11-22T20:28:30ZengMDPI AGApplied Sciences2076-34172021-10-0111211014210.3390/app112110142Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis StudyMałgorzata Matusiak0Sławomir Kadłubowski1Piotr Ulański2Institute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, Wróblewskiego 15, 93-590 Lodz, PolandInstitute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, Wróblewskiego 15, 93-590 Lodz, PolandInstitute of Applied Radiation Chemistry, Faculty of Chemistry, Lodz University of Technology, Wróblewskiego 15, 93-590 Lodz, PolandCarbon-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.https://www.mdpi.com/2076-3417/11/21/10142reaction kineticsfree radicalsradiation chemistrypulse radiolysispolyelectrolytespoly(acrylic acid) |
| spellingShingle | Małgorzata Matusiak Sławomir Kadłubowski Piotr Ulański Recombination of Poly(Acrylic Acid) Radicals in Acidic Aqueous Solutions: A Pulse Radiolysis Study Applied Sciences reaction kinetics free radicals radiation chemistry pulse radiolysis polyelectrolytes poly(acrylic acid) |
| title | 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_short | 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 |
| topic | reaction kinetics free radicals radiation chemistry pulse radiolysis polyelectrolytes poly(acrylic acid) |
| url | https://www.mdpi.com/2076-3417/11/21/10142 |
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