Self-association behaviour of atactic polymethacrylic acid in aqueous solution investigated by atomistic molecular dynamics simulations

TLDR: In this article, the self-association behavior of atactic poly(methacrylic acid) (a-PMA) in water was investigated by atomistic molecular dynamics simulations.

Abstract: The self-association behaviour of atactic poly(methacrylic acid) (a-PMA) in water was investigated by atomistic molecular dynamics (MD) simulations. Simulations show that interchain association of a-PMA occurs only in its un-neutralised form, by hydrogen bonding between –COOH groups, which is in agreement with the experimental observation. Chain conformations, dihedral angle distributions, hydration behaviour, scattering structure factor and enthalpy-of-hydration (i.e. aqueous solvation) were analysed as a function of concentration for un-neutralised PMA, across dilute to concentrated regimes. The average 〈Rg〉 of the chain remains unaffected in solution and also for amorphous undissolved a-PMA phase, confirming the occurrence of the approximate theta-solution condition for the first time, as revealed by simulations, in a polar hydrogen-bonding polymer aqueous solution. Chain hydration behaviour and scattering structure factor show significant changes in concentrated regime. Scattering intensity collapse o...