Poly(bis-arylimidazoliums) possessing high hydroxide ion exchange capacity and high alkaline stability

Solid polymer electrolyte electrochemical energy conversion devices that operate under highly alkaline conditions afford faster reaction kinetics and the deployment of inexpensive electrocatalysts compared with their acidic counterparts. The hydroxide anion exchange polymer is a key component of any solid polymer electrolyte device that operates under alkaline conditions. However, durable hydroxide-conducting polymer electrolytes in highly caustic media have proved elusive, because polymers bearing cations are inherently unstable under highly caustic conditions. Here we report a systematic investigation of novel arylimidazolium and bis-arylimidazolium compounds that lead to the rationale design of robust, sterically protected poly(arylimidazolium) hydroxide anion exchange polymers that possess a combination of high ion-exchange capacity and exceptional stability.

The reaction mixture was heated to reflux for 18 h. The reaction was then cooled to room temperature and poured into water. The precipitate was recrystallized from acetonitrile/water to yield 6 (1.50 g, 78%) as white crystals. 1
The solution changed colour from initial dark green to light yellow within 10 min. After 30 minutes, iodomethane (0.2 mL, 3.2 mmol) was added and after 30 minutes, the solution was poured into 400 mL of water containing 4.0 g KOH.
The solution was heated at 80 °C while stirring for 20 h. After cooling, the solution was poured into 200 mL 6 M HCl, to consume the catalyst. And the solid was filtered and washed with water, aqueous sodium bicarbonate and acetone.
After drying in vacuo, the solid was dissolved in 5 mL DCM and 5 mL DMSO. 20 times equilvent MeI was added and the solution heated to 80 °C for three days. The polymer was precipated into 100 mL ethyl acetate washed with acetone and filtered to get brown solid 0.1695 g (100 % yield). The other polymers were prepared following the same way which PAImMB(11) was prepared in 100% yield, PAImEE(12) was prepared in 100% yield, PAImPP(13) was prepared in 99% yield, PAImBB (14) was prepared in 98% yield.
Thermal stability. The thermal stability of the membranes was measured by thermogravimetric analysis (TGA) using a SHIMADZU thermogravimetric analyzer apparatus under nitrogen atmosphere at a heating rate of 5 ˚C/minbetween the temperature range 25 to 800 ˚C.