Effect of Multivalent Cations on Intermolecular Association of Isotactic and Atactic Poly(Methacrylic Acid) Chains in Aqueous Solutions
Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia
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Polymers 2019, 11(4), 605; https://doi.org/10.3390/polym11040605
Received: 25 February 2019
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Revised: 22 March 2019
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Accepted: 26 March 2019
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Published: 2 April 2019
(This article belongs to the Special Issue Selected Papers from ECIS 2018)
The formation of nanoparticles of two poly(methacrylic acid) (PMA) isomers, atactic (aPMA) and isotactic (iPMA), was investigated in aqueous solutions in the presence of mono- (Na+) and multivalent cations (Mg2+ and La3+). Using dynamic (DLS) and static light scattering (SLS), we show that PMA nanoparticles have characteristics of microgel-like particles with a denser core and a swollen corona. iPMA aggregates are stable at a much higher degree of neutralization (αN) than the aPMA ones, indicating a much stronger association between iPMA chains. This is explained by proposing segregation of ionized and unionized carboxyl groups within the iPMA aggregates and subsequent cooperative hydrogen-bonding between COOH groups. The calculated shape parameter (ρ) suggests different behavior of both isomers in the presence of Mg2+ ions on one hand and Na+ and La3+ on the other. The microgel-like particles formed in the presence of Mg2+ ions have a more even mass distribution (possibly a no core-shell structure) in comparison with those in the presence of Na+ and La3+ ions. Differences between the aggregate structures in the presence of different ions are reflected also in calorimetric experiments and supported by pH and fluorimetric measurements. Reasons for different behavior in the presence of Mg2+ ions lie in specific properties of this cation, in particular in its strong hydration and preference towards monodentate binding to carboxylate groups.
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Keywords:
polymethacrylic acid; stereoregularity; atactic; isotactic; multivalent cations; microgel-like particles; light scattering
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MDPI and ACS Style
Hriberšek, P.; Kogej, K. Effect of Multivalent Cations on Intermolecular Association of Isotactic and Atactic Poly(Methacrylic Acid) Chains in Aqueous Solutions. Polymers 2019, 11, 605. https://doi.org/10.3390/polym11040605
AMA Style
Hriberšek P, Kogej K. Effect of Multivalent Cations on Intermolecular Association of Isotactic and Atactic Poly(Methacrylic Acid) Chains in Aqueous Solutions. Polymers. 2019; 11(4):605. https://doi.org/10.3390/polym11040605
Chicago/Turabian StyleHriberšek, Patricija, and Ksenija Kogej. 2019. "Effect of Multivalent Cations on Intermolecular Association of Isotactic and Atactic Poly(Methacrylic Acid) Chains in Aqueous Solutions" Polymers 11, no. 4: 605. https://doi.org/10.3390/polym11040605
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