2022 Volume 55 Issue 3 Pages 121-131
Novel sulfonated diblock copolymers containing cross-linkable moieties were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization for proton exchange membranes (PEMs) in proton exchange membrane fuel cells (PEMFCs). The copolymers were synthesized using allyl acrylate (AA), and sulfonated styrene ethyl ester (ESS) as monomers and pentaerythritol 3-mercapto propionic ester (PMPE) as the cross-linker. The chemical structures of the diblock copolymers were analyzed by using 1H NMR spectroscopy. Membranes were obtained through cross-linking with a thiol–ene reaction via via copolymer heat curing. TGA was employed to characterize the thermal properties of the cross-linked membranes. Gel permeation chromatography (GPC) was employed to measure the molecular weight, and scanning electron microscopy (SEM) was employed to elucidate the morphological changes in the membranes with an increase in the of cross-linking degree. The liquid uptake was significantly suppressed by the cross-linked network. The decrease in the proton conductivity may have been caused by the enhanced barrier properties of the membranes due to the introduction of more cross-linkers duing the membrane formation. These decreases in the liquid uptake and proton conductivity were probably due to the increased cross-linking degree, leading to a relatively tortuous pathway for water and methanol transport. The water uptakes were higher than the methanol uptakes for all the studied membranes, which lead to increased water selectivities. The proposed B2 membrane showed advantageous mechanical properties, better proton conductivityin water or methanol, and significantly higher liquid uptake compared to those of recast Nafion®.
