Synthesis and characterization of glycidyl-polymer-based poly(ionic liquid)s: highly designable polyelectrolytes with a poly(ethylene glycol) main chain

Abstract

A series of glycidyl-polymer-based poly(ionic liquid)s (cationic GTPs) was synthesized via the click functionalization of a glycidyl azide polymer with alkyne derivatives of ionic liquids. Three types of cationic moieties (imidazolium, pyridinium and pyrrolidinium) and two types of spacers between the 1,2,3-triazole and cationic moiety (C₄H₈ alkyl chain (C4) and tetra(ethylene glycol) (EG4)) were examined. The cationic GTPs were characterized by NMR, IR, differential scanning calorimetry, thermogravimetric analysis and impedance spectroscopy. From the gel permeation chromatography analysis of the model polymer, the weight-average molecular weights of cationic GTPs were estimated to be 0.8–1.0 million Da. ¹H NMR analysis of the partially decomposed polymer confirmed that the thermal decomposition of the cationic GTPs with the C4 spacer begins with the detachment of the cationic moiety. Compared with the C4 spacer, the EG4 spacer decreases the glass transition temperature and increases the ionic conductivity. The cationic GTP with the EG4 spacer, pyrrolidinium cationic moiety and bis(trifluoromethanesulfonyl)imide (Tf₂N) counter anion exhibited the highest anhydrous ionic conductivity (1.1 × 10⁻⁵ S cm⁻¹ at 30 °C and 1.1 × 10⁻³ S cm⁻¹ at 120 °C). The conducting ion concentration and mobility were estimated by electrode polarization analysis. The imidazolium moiety gives a relatively higher conducting ion concentration because of the lower binding energy with the Tf₂N counter anion. Compared with other GTPs, the pyridinium GTPs showed greater temperature dependences of their conducting ion mobilities.