Influence of metal-coordinating comonomers on the coordination structure and binding in magnetic poly(ionic liquid)s

Abstract

A poly(ionic liquid) (PIL), poly(acrylamide-co-diallyl dimethylammonium chloride), was systematically complexed with Co²⁺, Fe³⁺, and Co²⁺/Fe³⁺ (mixed) at different molar equivalencies to form a series of magnetic PILs (MPILs). These novel MPILs were utilized to examine molecular structure and binding between the polymer and metal species using comprehensive spectroscopic studies in both dry and liquid states. FTIR, X-ray photoelectron, UV-vis, and Raman spectroscopies showed evidence of metal coordination of both the iron and cobalt chloride species with the acrylamide comonomer. Using AC susceptibility measurements, the MPILs were found to have magnetic properties within the range of typical MPIL homopolymers with magnetic mass susceptibilities dependent on metal cation type and concentration. This work demonstrates MPILs can be tuned using the metal ion species and concentration, to increase the magnetic mass susceptibility and alter metal-ion coordination structure and binding with the PIL copolymer. Furthermore, the coordination structure of the transition metal halide complex was determined to be dependent on metal halide concentration in the polymer for the iron-based system, and it was shown that both metal cations (Fe³⁺ and Co²⁺) bond not only electrostatically with the PIL monomer but also predominantly with the acrylamide comonomer. In particular, metal–oxygen and metal–nitrogen bonding was observed with the amide group present in the acrylamide. Understanding and controlling the coordination structure and binding in PILs is significant as these materials allow for the formability and flexibility advantages of polymers to be combined with properties atypical for polymers, such as high ion conductivity, electrical and thermal stability, antibacterial properties, and magnetic responsiveness, in the case of MPILs.