where V (in cm3) is the averaged volume of NaOH solution added
for the neutralization of the second proton, c (in mol cm−3) is the
NaOH concentration, wo (in grams) is the dry membrane weight,
Mm = 116 g mol−1 for ABPBI, corresponding to the molecular weight
of themonomer unit; and Mm = 142 g mol−1 for PBI, considering that
284 g mol−1 is the molecular weight of the monomer unit and there
are two imidazol ring in each monomer unit of PBI.