Study on tunable crosslinking anion exchange membranes fabrication and degradation mechanism

A novel monomer who combined cross linker and functional groups together called 2,2'-(hexane-1,6-diyl)bis(2-methyl-2,3,3a,4,7,7a-hexahydro-1H-4,7-methanoisoindol-2-ium) iodide (HDHM-iodide) was synthesized and polymerized by Ring-opening Metathesis Polymerization (ROMP) to give a series of anion exchange membranes . The resulting monomers and polymers were characterized by 1 H and 13 C NMR, TGA . Directly cast from the polymerization solution on flat glass to form the clear, flexible anion exchange membrane. Swelling ratio and water uptake are only 6.2% and 28.04% at 60 °C for membrane with 2.32 mmol·g −1 ion exchange capacity (IEC). The conductivity of Poly (HDHM-Norbornene-hydroxide-12) and Poly(HDHM-Norbornene-chlorine-12) AEMs at room temperature up to 27 mS·cm −1 and 14 mS·cm −1 separately, and increased with temperature quickly. After 16 days immersed in 2 M NaOH solution, conductivity and IEC dropped at 60 °C in alkaline solution, 50% and 35% separately. The energy barrier of degradation pathways calculation reveled that Hofmann Elimination case 2 degradation pathway with the lowest energy barrier 12.181 kcal·mol −1 is most likely occurred when faced with hydroxide. Also, the energy barrier of Hofmann Elimination is lower than Nucleophilic Substitution degradation mechanism .