Proton Conducting Crosslinked Membranes by Polymer Blending of Triblock Copolymer and Poly(vinyl alcohol)

Proton conducting crosslinked membranes were prepared using polymer blends of polystyrene- b -poly(hydroxyethyl acrylate)- b -poly(styrene sulfonic acid) (PS- b -PHEA- b -PSSA) and poly(vinyl alcohol) (PVA). PS- b -PHEA- b -PSSA triblock copolymer at 28:21:51 wt% was synthesized sequentially using atom transfer radical polymerization (ATRP). FT-IR spectroscopy showed that after thermal (120 oC, 2 h) and chemical (sulfosuccinic acid, SA) treatments of the membranes, the middle PHEA block of the triblock copolymer was crosslinked with PVA through an esterification reaction between the -OH group of the membrane and the -COOH group of SA. The ion exchange capacity (IEC) decreased from 1.56 to 0.61 meq/g with increasing amount of PVA. Therefore, the proton conductivity at room temperature decreased from 0.044 to 0.018 S/cm. However, the introduction of PVA resulted in a decrease in water uptake from 87.0 to 44.3%, providing good mechanical properties applicable to the membrane electrode assembly (MEA) of fuel cells. Transmission electron microscopy (TEM) showed that the membrane was microphase-separated with a nanometer range with good connectivity of the SO 3 H ionic aggregates. The power density of a single H 2 /O 2 fuel cell system using the membrane with 50 wt% PVA was 230 mW/cm 2 at 70 °C with a relative humidity of 100%. Thermogravimetric analysis (TGA) also showed a decrease in the thermal stability of the membranes with increasing PVA concentration.