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Tacticity effects on conformational structure and hydration of poly-(methacrylic acid) in aqueous solutions-a molecular dynamics simulation study
Published in Taylor and Francis Ltd.
2016
Volume: 42
   
Issue: 9
Pages: 725 - 736
Abstract

The influence of tacticity on chain dimensions, backbone and side-group conformational states and relaxation dynamics, intermolecular hydrogen bonding and its relaxation dynamics was investigated for 30 repeat unit poly(methacrylic acid) (PMA) as a function of the degree-of-neutralisation, f (i.e. charge density) [0 < f < 1 range] in explicit water with Na+ neutralising counter-ions, using molecular dynamics simulations. Chain expansion with increase in charge density is observed. Simulation results, where applicable, compare well with experimental results in the literature. Isotactic (i-PMA) chain exhibits the largest expansion (89% change in Rg), and syndiotactic (s-PMA-RR-0.7) chain shows 31%. For fully neutralised chain (high charge density), the probability for trans conformation at backbone bonds follows the trend i-PMA > a-PMA > s-PMA. At high charge density, a higher probability of trans state is obtained at meso dyads as compared to racemic dyads and the side group in i-PMA relative to other tacticity is conformationally more extended. RR triads impart better hydrogen bonding with water. In the COOH side group, greater rotational mobility is observed for i-PMA as compared to s-PMA. Water coordination to PMA is invariant with tacticity at low f. For f = 1, s-PMA exhibits the best level of H-bonding, due to its 3D chemical structural configuration. Binding distance between water and PMA atoms and their coordination number remain unchanged with respect to ionisation of COOH groups. Isotactic (i-PMA) exhibits the fastest relaxation of polymer-water H-bonds. While counter-ion coordination on to PMA is unaffected by tacticity, the intensity of ion condensation as well as hydrogen bond relaxation time at f = 1 varies in the order i-PMA > a-PMA > s-PMA. © 2015 Taylor & Francis.

About the journal
JournalData powered by TypesetMolecular Simulation
PublisherData powered by TypesetTaylor and Francis Ltd.
ISSN08927022
Open AccessNo
Concepts (20)
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    Chains
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    Charge density
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    Chemical bonds
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    Conformations
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    Ionization of liquids
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    Ions
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    Molecular dynamics
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    Relaxation processes
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    Solutions
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    Structure (composition)
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    Water
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    CONFORMATIONAL STRUCTURES
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    Intermolecular hydrogen bonding
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    Molecular dynamics simulations
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    POLY (METHACRYLIC ACID)
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    Relaxation dynamics
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    Simulation
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    STRUCTURAL CONFIGURATIONS
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    TACTICITIES
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    Hydrogen bonds