The First Example of a Poly(arylimidazole) by Polycondensation of AB-type Monomers: Control of Molecular Mass by End-Capping, and Functionalization to Poly(arylimidazolium)s

In this work, the first AB-type primary-chain poly(arylimidazole) (AB-PAI) homopolymers were synthesized by Debus-Radziszewski polycondensation. Control of the number-average molecular mass (M̅n) by ab initio stoichiometry of a monofunctional end-cap provides the first corroborating evidence for this polycondensation proceeding by Carothers' Step-Growth mechanism. Quaternization of imidazole units in AB-PAI yields statistical poly(arylimidazolium) (AB-PAIm) ionenes. Steric protection of the electrophilic imidazolium C2 is encoded in the AB-type monomer. Exceptionally harsh alkaline conditions are required to quantify degradation of the sterically protected AB-PAIm derivative (in 40 wt % NaOD at 80 °C, 20% loss of imidazolium units is observed by NMR after 72 h). All the AB-PAI and the AB-PAIm are thermally stable up to 250 °C in air. The sterically encumbered, polycationic poly(2-[2,6-dimethylphenyl]-1,3-dimethyl-5-phenylimidazolium) hydroxide (IEC(OH) = 2.08 mmol g–1) is a transparent red glass that can be solvated by polar organic solvents and is insoluble in water and aqueous alkali metal hydroxides.