Preparation of Highly Reinforced Pore-filling Electrolyte Membranes from Cross-linked Benzoxazine-Benzimidazole

Abstract

An ultrathin novel reinforced pore-filling polymer electrolyte membrane (20um, thick) based on sulfonated poly(arylene ether sulfone) (PAES60) impregnated porous substrate, was prepared by polymer filling method for using in proton exchange membrane fuel cells (PEMFCs) application. Cross-linked copolymer synthesized with poly[2,2–(m–phenylene)–5,5–bibenzimidazole] (PBI) and 3–phenyl–3,4–dihydro–6–tert–butyl–2H–1,3–benzoxazine (pBu) was selected as a substrate (P(pBu-co-BI)). Porous substrates were successfully fabricated by leaching out a low molecular weight compound using a selectively soluble solvent of the porogen from P(pBu-co-BI) / porogen mixtures. The pore size and porosity of the substrate were determined by the P(pBu-co-BI) / porogen ratio and confirmed by SEM, mercury intrusion method and density measurement method. Filling material, PAES60, was synthesized successfully via nucleophilic aromatic substitution polymerization. In comparison to a pristine PAES60 membrane, pore-filling membrane (PF-PAES60) showed extremely low dimensional change (4-13%), water uptake (10-18%), outstanding mechanical strength and increased chemically bounded water. However, the proton conductivity of PF-PAES60 was lower than that of pristine PAES60 membrane. All of these results can be attributed to the reinforcement effect of porous P(pBu-co-BI) substrate and acid-base interaction between imidazole groups in the substrate and sulfonic acid groups in the filling polymer.