Multiple interaction regulated phase transition behavior of thermo-responsive copolymers containing cationic poly(ionic liquid)s

Abstract

The effect of multiple interactions including anion–macromolecule interaction, water-mediated ion–macromolecule interaction and hydrophobic interaction on the phase transition behaviors of random copolymers P(OEGMA-co-BVIm[X]) comprising oligo(ethylene glycol)methacrylate (OEGMA) and imidazolium-based ionic liquids is investigated in the present study. Temperature-variable ¹H NMR and FT-IR investigations demonstrated that the hydration of CH₂ side chains in P(OEGMA-co-BVIm[SCN]) was enhanced due to the anion–dipole interaction between a chaotropic anion SCN⁻ and CH₂ groups, and dehydration of CO groups served as the driving force of phase transition. In particular, the formation of CO⋯D₂O–PIL hydrogen bonds was preferred in P(OEGMA-co-BVIm[SCN]) during the phase transition process considering the interaction of IL–D₂O associations and CO groups. This water-mediated ion–macromolecule interaction acted as a “linkage” among polymers, resulting in the gradual dehydration of copolymers and the formation of stable small size micelles. As for P(OEGMA-co-BVIm[NTf₂]), water molecules were sequentially squeezed out of the polymer chains upon heating and the self-aggregation of polymer chains was carried out through hydrophobic interaction between OEGMA side chains with IL segments wrapped in the aggregates.