A thermo-sensitive OEGMA-based polymer: synthesis, characterization and interactions with surfactants in aqueous solutions with and without salt

Abstract

The interactions between poly(2-(2-methoxyethoxy)ethyl methacrylate90-co-oligo(ethylene glycol) methacrylate10) (P(MEO2MA90-co-OEGMA10)) and sodium dodecyl sulfate (SDS) or dodecyltrimethyl ammonium bromide (DTAB) in aqueous solutions with and without salt are explored. The influence rule of surfactant on thermo-sensitive behavior of polymer and the corresponding mechanism is revealed. The results have suggested that both surfactants have moderate interactions with P(MEO2MA90-co-OEGMA10), which result in the formation of P(MEO2MA90-co-OEGMA10)/surfactant complexes. Meanwhile, the self-aggregation of polymer chains is hindered causing the lower critical solution temperatures (LCSTs) increase due to the electrostatic repulsion and “locking water” effect caused by surfactant head groups. Tetra-n-butylammonium bromide (Bu4NBr) and tetra-n-propylammonium bromide (Pr4NBr) can associate with SDS and form mixed micelles. Interestingly, the formed mixed micelles apt to attach on the polymer chain and the polymer-bound necklace-like structure forms in the ternary polymer/salt/surfactant system. The structure of the complexes formed in the ternary system is confirmed by 2D NOESY NMR and the interaction mode is proposed. The relations between LCST of different systems and surfactant concentrations are also established quantitatively.