NMR studies of self-organization behavior of hydrophobically functionalized poly(4-styrenosulfonic-co-maleic acid) in aqueous solution

Abstract

Specially designed hydrophobically functionalized polyelectrolytes (HF-PEs) provide an important area of study, their unique properties being similar to those of biological systems, among them the strong tendency toward self-organization in aqueous solution caused by a combination of electrostatic and hydrophobic forces. A significant issue in this context is the comprehensive physicochemical characterization of adsorption and aggregation properties of these amphiphilic polyelectrolytes. The main aim of the present research has been to synthesize and study aggregation properties in an aqueous solution of the hydrophobically functionalized poly(4-styrenosulfonic-co-maleic acid) (PSS/MA) with a differing degree of hydrophobization, side-chain lengths and pH-labile moiety type (i.e., ester (PSS/MA-g-CnOH) or secondary amide (PSS/MA-g-CnNH2) groupings). Comprehensive analysis of self-assembly properties, including utilization of high-resolution NMR techniques (diffusion-ordered and nuclear Overhauser effect spectroscopies, T1 and T2 relaxometry) and dynamic light scattering, revealed a strong dependence on concentration and type of labile linking group (ester or amide). It has been noticed that more rigid amide bonds hinder the formation of highly organized structures in aqueous systems compared to polyelectrolytes with ester moieties. Our results were supported by molecular modeling. The performed studies enabled us to obtain crucial information about the hydrophobized PEs structure and its influence on aggregation properties that are crucial for their application in pH-sensitive nanosized thin films and nanocarriers.