A hydroxyl group
containing new cardo diamine monomer was synthesized, namely 9,9-bis
(hydroxy- (4′-amino(3-trifluoromethyl)biphenyl-4-oxy)-phenyl)-9H-fluorene
(mixture of isomers, HAPHPF). HAPHPF, along with a sulfonated diamine
monomer, 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA),
was used to prepare a series of new sulfonated copolyimides by polycondensation
with 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). The degree
of sulfonation (DS < 1) was adjusted by the feed ratio of DSDSA/HAPHPF
and the copolymers were named as DHN-XX, where XX denotes the mole
percentage of DSDSA (XX = 50, 60, and 70). The copolymers showed high
molecular weights. The copolymer structure and composition were confirmed
by FTIR and NMR techniques. Copolymer membranes were prepared through
solution cast route by using dimethyl sulfoxide as a solvent. The
membranes showed high thermal, mechanical, hydrolytic and peroxide
radical stability, and low water uptake and low swelling ratios. Well-separated
hydrophilic and hydrophobic phase morphology was observed in TEM and
AFM images of the copolymer membranes and was further supported by
the SAXS studies. The proton conductivity of the DHN-70 was as high
as 97 mS cm–1 at 80 °C and the value is significantly
higher than that of the nonhydroxylated analogue. The membranes also
showed superior microbial fuel cell (MFC) performance, similar like
Nafion 117 under similar test conditions. The chemical oxygen demand
removal values provide substantial evidence that the fabricated membranes
can be utilized in bioelectrochemical systems.