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

Abstract

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 (M̅ n ) 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.

Assessing Electrocatalyst‐Ionomer Interactions: HOR/HER Activity of Pt/C Catalyst Layers incorporating Poly(imidazolium)s

“…The AB polymerization route enables good synthetic reproducibility and a well-defined polymer backbone for reasons discussed in detail in a previous report. [25] 2,6-dm-OPBA was polymerized using an excess of hexylamine and ammonium acetate, in an acidic environment. The lower reactivity of hexylamine towards imidazole condensation enables the high IEC β' unit to be combined with the improved solubility and processability of the hexyl-containing α' unit.…”

“…The difunctional monomer was synthesized via formylation. [38] Sonogashira [39] and oxidation reactions, [25,40,41] were high yielding (> 90 %) and had notably simple purification procedures. The monomer could be readily scaled to tens of grams.…”

“…Synthesis of 5-bromo-2-iodo-m-xylene: 5-bromo-2-iodo-1,3-dimethylbenzene (1 eq., 3.216 mmol, 4.00 g) and dry THF (32 mL) was bubbled with argon for 1 hour. The mixture was cooled to À 15 °C and i-PrMgCl (2 M in THF, 2 eq., 25.727 mmol, 12.863 mL) was added dropwise. The reaction was kept at À 15 °C for 2 hours whilst stirring, then DMF (3 eq., 38.590 mmol, 2.988 mL) was added dropwise.…”

“…An adequate assessment of the catalyst-ionomer interactions must be conducted when aiming to use those materials as an ion-conductor in HOR/HER-dedicated catalytic layers. Hence, in this work, based on a recently reported AB-type polycondensation synthetic route, [25] we specifically designed and synthesized a novel poly(imidazolium)-based ionomer that possesses only two aromatic rings per repeat unit. The ionomer was designed to be soluble in low boiling point solvents for processing into films and catalyst layers, yet insoluble in basic aqueous solutions, for use in devices.…”

“…From this, a family of high-performance poly(imidazolium)s have been systematically developed with high hydroxide stability and conductivity for integration into AEMFCs and AEMWEs. [8,21,24,25] Initially, a novel C2-protected novel poly(imidazolium), HMT-PMPI, [21] was synthesized with an analogous backbone structure to that of successful poly(benzimidazolium), HMT-PMBI. [26] The poly(imidazolium), HMT-PMPI, observed no degradation when immersed in 10 M KOH at 100 °C, over 7 days.…”