Studies On Preparation And Properties Of Acid-base Side-chain-type Aromatic Proton Exchange Membranes

Sulfonated aromatic polymers have been widely studied as a substitute for perfluorosulfonic acid polymers (PFSAs) due to their high thermal and chemical stability, excellent mechanical toughness, wide variety of chemical composition, and acceptable manufacturing cost. However, these sulfonated polymers exhibit relatively low proton conductivities due to the weak phase separation between hydrophilic and hydrophobic domains. Current researches have focused on the design of polymer structure to obtain well-defined nanochannels morphology responsible for ion transport. This work is aiming to design a series of side chain type sulfonated polymer with acid-base structure, which exhibited well-defined phase-separated structure, good proton conductivity and low methanol crossover as proton exchange membrane for DMFCs. The details are as follow:(1) A new sulfonated diamine monomer containing pyridine functional groupwas synthesized and polymerized to form copolymer containing pyridine groups in copolymer backbones and sulfonic acid groups in the side chains. The interaction between the N-bases and the sulfonic acid groups was expected to induce the formation of ionic cross-linking. Simultaneously, the sulfoalkylated side chains induced the formation of chemically stable microstructures resistant to chemical attacks. All the prepared membranes displayed high thermal stability, great oxidative stability and good mechanical properties. They exhibited appropriate water uptake (15.82%-30.2% at 80 ℃) and remarkable dimensional stability (2.48%-6.94% at 80 ℃). The proton conductivity of SPI-80 was 1.01 × 10-2 S cm-1 at room temperature, which is suitable for application. Moreover, the methanol permeability of SPI-80 membrane was 1.22 × 10-7cm2 s-1, which was lower than 12.22 × 10-7 cm2 s-1 of Nafion 117.(2) A normal bisphenol monomer,3,3’,5,5’-tetramethyl-4,4’-biphenol (TMBP) was used as precursors for preparing sulfonated poly(arylene ether ketone) copolymers containing clusters of sulfophenyl pendant groups. The acid and basic groups have been attached to the copolymer chains simultaneously by using click chemistry. Structures of the copolymers were confirmed by FT-IR and 1H NMR. Transmission electron microscopy (TEM) showed good phase separated morphology with ionic cluster sizes in the range of 2-15 nm. The sulfonated copolymers exhibited high proton conductivity in the range between 0.082 and 0.113 S cm-1 at 80 ℃ and 100% relative humidity (RH). The methanol permeability of these membranes was in the range between 4.07× 10-7 and 8.65×10-7cm2 s-1.