Magnetic Poly(ionic liquid)s: Bottlebrush versus Linear Structures

Magnetic poly(ionic liquid)s (MPILs) with FeCl4– as counterions show phase transition from paramagnetism to ferromagnetism by introducing strong π–π stacking groups. The neighboring Fe(III)–Fe(III) distance and the ordering degree of magnetic ions are crucial for the phase transition. In this work, linear and bottlebrush magnetic polymers are synthesized to study the effect of topological structure on the magnetic property of MPILs. Magnetic studies show that the bottlebrush MPILs are ferromagnetic at low temperature while the linear analogue is paramagnetic. With increasing of the grafting ratio, the phase transition temperature from paramagnetism to ferromagnetism is increased. Compared with linear structure, the bottlebrush polymers show high ordering and crowding of the side chains which are favorable to the ferromagnetic phase transition.