Hydrolytic stability of sulfonic acid-containing polyimides for fuel cell membranes

The long-term stability of sulfonic acid-containing polyimides has been investigated. The hydrolytic degradation of homopolyimide and the block copolyimide comprising 27 mol% of 2,2′-bis(trifluoromethyl)benzidine and 9 mol% ofm-phenylenediamine (BTFMB27mP10[7/(3+1)]), was quantified through viscosity measurements and FT-IR spectroscopic analyses. The viscosity decrease with respect to time and the degradation rate were similar. The degrees of degradation with respect to time under ambient conditions and at elevated temperature in water were monitored by FT-IR spectroscopy. A new absorption peak was observed at 1786 cm−1, which we corresponds to the presence of anhydride end groups formed by hydrolytic scission of the imide rings.