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

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 H NMR and FT-IR investigations demonstrated that the hydration of CH side chains in P(OEGMA-co-BVIm[SCN]) was enhanced due to the anion-dipole interaction between a chaotropic anion SCN and CH groups, and dehydration of C[double bond, length as m-dash]O groups served as the driving force of phase transition. In particular, the formation of C[double bond, length as m-dash]ODO-PIL hydrogen bonds was preferred in P(OEGMA-co-BVIm[SCN]) during the phase transition process considering the interaction of IL-DO associations and C[double bond, length as m-dash]O 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[NTf]), 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.