Origin of the Difference in Structural Behavior of Poly(acrylic acid) and Poly(methacrylic acid) in Aqueous Solution Discerned by Explicit-Solvent Explicit-Ion MD Simulations

The conformational and hydration behavior of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA) in dilute aqueous solution, as a function of charge density, is studied using two different sets of force field parameters: FF-1 and FF-2. The two sets of force field parameters predict similar correlation distances between carboxylate groups and water. The simulations bring about the difference in the interaction of the counterions with the polyions PAA and PMA. FF-1 predicts that upon neutralization PMA shows stronger correlation with Na+ ions in comparison to PAA in aqueous solution. This difference in behavior agrees with the fact that, in poor solvents, the polyelectrolyte chain and the counterions interact strongly. The atomistic simulations using FF-1 parameters presented here bring about the difference in the conformational behaviors of PAA and PMA and the effect of solvent quality on the polyacrylate chain backbone structure.