POS2-0994
pH-dependent conformational properties of poly(alkylacrylic acid)s in good/poor solvents
Topic
S2. High-End Characterization/Polymer Physics/Properties
When and Where
Sep 29, 2026
08:30 - 09:30
Room 301 (Grand Ballroom)
Session Chairs
Hae Jung SON
Boseok KANG
Presenter(s)
Seungbin Hong (Seoul National University)
Co-Author(s)
Abstract
Poly(alkylacrylic acid)s, including poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA), are ionizable, water-soluble polymers widely employed in water-based paints, superabsorbents, flocculants, and related applications. A defining feature of these weak polyacids is the progressive increase in apparent pKₐ with the degree of ionization, α′, indicating that the polymer becomes increasingly less acidic as titration proceeds. PAA typically exhibits an approximately linear dependence of apparent pKₐ on α′. In contrast, PMA displays a plateau near α′ ≈ 0.2, suggesting resistance to initial ionization. This behavior is associated with a coil-to-swollen-coil conformational transition, promoted by the relaxation effect of the additional alkyl side group. Measurements of the radius of gyration, Rg, as a function of α′ further reveal non-monotonic conformational behavior: after an initial expansion, Rg decreases near the ionization threshold. To elucidate these molecular mechanisms, we performed microsecond-scale molecular dynamics simulations with explicit solvent, sampling polyelectrolyte conformational transitions over a range of ionization levels. Our results reveal how local hydration, side-chain steric effects, and dynamic counterion distributions act cooperatively to reproduce the distinct titration profiles and anomalous Rg behavior of PAA and PMA in both aqueous and methanolic environments.
