pH-Responsive Rheology and Structure of Poly(ethylene oxide)-Poly(methacrylic acid) Interpolymer Complexes

This study investigates the rheological and structural properties of interpolymer complexes (IPCs) formed between poly(ethylene oxide) (PEO) and poly(methacrylic acid) (PMAA) at various pH levels and polymer ratios. Potentiometric titration showed that PMAA must remain over 90% protonated for IPC formation. Extensive rheological experiments revealed a sharp transition from viscous to elastic behavior between pH 5.75 and 4.75. The rheological response is attributed to PEO chain entanglements and PEO-PMAA hydrogen-bond cross-links, with cross-links dominating at low pH and weakening as pH increases. Small-angle neutron scattering (SANS) highlights the structural changes, with dense, PMAA-rich domains forming at low pH and breaking down at higher pH. This work provides valuable new insights for the design of hydrogels, whose properties are easily tuned by the polymer mixing ratio and pH, offering potential for various pharmaceutical applications.