Investigation of sequence isomer effects in AB-polybenzimidazole polymers

Abstract

In the present work, a unique series of random polybenzimidazole (PBI) copolymers consisting of the recently reported novel isomeric AB‐PBI (i‐AB‐PBI) and the well known AB‐PBI were synthesized. The i‐AB‐PBI incorporates additional linkages (2,2 and 5,5) in the benzimidazole sequence when compared with AB‐PBI. Random copolymers, varying in composition at 10 mol % increments, were synthesized to evaluate the effects of sequence isomerism in the polymer main chain without altering the fundamental chemical composition or functionality of a polymer chain consisting of 2,5‐benzimidazole units. Polymer solutions were prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. The resulting polymers were found to have high inherent viscosities (>2.0 dL/g) and showed elevated membrane proton conductivities (∼0.2 S/cm) under anhydrous conditions at 180 °C. Fuel cell performance evaluations were conducted, and an average output voltage ranging from 0.5 to 0.60 V at 0.2 A/cm2 was observed for hydrogen/air at an operational temperature of 180 °C without applied backpressure or humidification. Herein, we report for the first time glass transition (Tg) temperatures for AB‐PBI, i‐AB‐PBI, and an anomalous Tg effect for the series of randomized PBIs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 619–628

Solution polymerization of polybenzimidazole

“…Studies were then conducted with benzoic acid, as PBIs are commonly synthesized using diacid monomers. 7,14,29 GC/MS analysis of the reaction of benzoic acid and o-phenylenediamine showed multiple reaction products. After 48 h of reaction, <10% of the desired 2-phenyl benzimidazole product was obtained.…”

“…Since the early development, numerous variations of PBI derivatives have been reported . Of all the derivatives of polybenzimidazoles, aromatic PBIs have received the most attention due to their excellent thermal stabilities and chemical resistance …”

“…[4][5][6] Of all the derivatives of polybenzimidazoles, aromatic PBIs have received the most attention due to their excellent thermal stabilities and chemical resistance. [7][8][9][10][11][12][13][14][15][16][17] Fully aromatic PBIs exhibit very high decomposition temperatures (>500 8C), and do not show melting points due to their lack of crystallinity or have melting points above their decomposition temperatures. 18 Since PBI demonstrates excellent thermal stabilities, it is especially suited for hightemperature fabric applications, and is commercially produced as a high-performance, thermally stable fiber.…”

Characterizing Voltage Losses in an SO2Depolarized Electrolyzer Using Sulfonated Polybenzimidazole Membranes

“…PBI membranes have exceptional performance characteristics in various electrochemical devices due to their high ionic conductivity when imbibed with various acid electrolytes. [16][17][18][19][20][21] To date, a large variety of PBI polymers have been synthesized and studied, and a sulfonated polybenzimidazole was selected for use in SDE applications due to its stability in the sulfuric acid environments present in the electrolyzer, 13 which has resulted in an increased focus on PBI for SDE applications over the past several years. 19,[22][23][24] These works focused on including different blends of PBI with high H 2 SO 4 imbibed concentrations (80 wt%) 19,24 during membrane preparation, partially fluorinated PBI, 22,24 and crosslinked PBI.…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…Polymer solutions have been prepared in polyphosphoric acid (PPA) and cast into membranes using a sol gel PPA process [51]. Using this technique, PBI polymer doped with phosphoric acid (PA) are easily achieved and have been found to be a promising electrolyte material for high-temperature PEM fuel cells [52].…”