(397e) Magnetic and Biocompatible Polymerized Ionic Liquids

Polymerized Ionic Liquids (i.e., PILs) are an emerging class of materials with ionic liquid moieties covalently attached to a polymer backbone. As such, they synergistically combine the processability of polymers with the versatile chemical functionality of ionic liquids. PILs have been of interest for gas separation and electrochemical energy conversion due to the CO₂ solubility, ionic conductivity, and thermal and electrochemical stability intrinsic to ionic liquids. However, the ability to incorporate functionality through ionic liquid chemistry while retaining polymer properties turns PILs into a powerful platform for developing novel stimuli-responsive materials.

Herein, we present a magnetic and biocompatible PIL based on poly(ethylene glycol) (i.e., PEG) and the ionic liquid anion tetrachloroferrate(III) (i.e., FeCl₄^-). We illustrate a molecular design strategy based on a combination of epoxide ring opening anionic polymerization and thiol-ene click chemistry that allows for exquisite control over the molecular structure of the polymer and guarantees scalability appropriate for extensive physical characterization. PIL containing FeCl₄^- is paramagnetic with a magnetic susceptibility at 30 ^oC of 30x10^-6 emu/g.Oe, as characteristic of materials based on anions containing transition metals with partially filled d-orbitals. Additionally, the PIL significantly modifies the magnetic environment experienced by the ¹H of water, as revealed by a decrease in the spin-lattice relaxation time (i.e., T₁) of ¹H determined from Nuclear Magnetic Resonance (i.e., NMR) from 8 to 0.3 seconds. The structure-property relationships demonstrated in this work makes PILs based on PEG and FeCl₄^- suitable as a T₁-weighted MRI contrast agent. The magnetic and biocompatible nature of PILs is promising for development of novel therapeutic agents (i.e., drugs, proteins, antibodies) based on polymer conjugates that exhibit controlled residence time within the human body; and magnetic functionality for MRI imaging, and facilitated targeting.