Preparation and Characterization of Sulfonated Copolyamides Based on Poly(hexafluoroisopropylidene) Isophthalamides for Polymer Electrolytic Membranes

Abstract

A series of sulfonated random copolyamides with increasing sulfonation degree were synthesized from the aromatic diamine 4,4′-(hexafluoroisopropylidene)dianiline, HFA, reacted with 2,4-diaminobenzenosulfonic acid, DABS, by direct polycondensation using isophthalic diacid, ISO, as comonomer. Thin films of the sulfonated copolyamides were prepared by the solution-evaporation method using dimethylacetamide, DMAc. The structure of the resulting sulfonated copolyamides was confirmed by FTIR and 1H NMR which evidenced the presence of amide and sulfonic groups in the proposed concentrations. Thermal stabilities as characterized by TGA, showed the onset of decomposition at 320 °C for the ionic moieties and above 600 °C for the nonsulfonated part of the copolymers. The values of water uptake and ion exchange capacity, IEC, at room temperature for the copolymer with 50 mol % of DABS, HFAS55 membrane were higher than those obtained for Nafion 115. HFAS55 also presented a proton conductivity value of 3.3 (mS cm–1) which was similar to the one of Nafion 115 tested under the same conditions which situates it as a possible material for PEM membrane preparation.

Sulfonated poly(meta‐phenylene isophthalamide)s as proton exchange membranes

“…The polyelectrolyte effect results in lower inherent viscosities with an increase in the DS as has been observed for other sulfonated polyaramides. 33,42 SCHEME 1 Synthesis of random sulfonated copolyaramides MPDA-SIPA x .…”

“…The sulfonated random copolyaramide membrane, MPDA-SIPA 40 (H), exhibited low water uptake at room temperature compared with other sulfonated copolyaramides in the literature. [27][28][29][30][31][32][33] The random copolymer membrane had reasonably low water uptake at temperatures below 50 8C, but the water uptake increases sharply at higher temperatures. The water uptake increased by more than 90 wt % from 50 8C to 60 8C, and the membrane eventually became soluble in water above 70 8C.…”

“…[5][6][7] However, Nafion V R and other perfluorinated polymer membranes suffer from their relatively high cost, environmental concerns about their manufacture, and decreased performance at lower humidity. 8,9 Sulfonated engineering polymers, including poly(aryl ether sulfone)s, [10][11][12][13][14][15][16][17][18][19][20] poly(aryl ether ketone)s, 6,7,21,22 polyimides, [23][24][25][26] and polyamides 15,[27][28][29][30][31][32][33] have been investigated as alternative PEMs to replace perfluorinated membranes. The aromatic backbone of these polymers provides good mechanical properties and imparts good chemical stability, and the aromatic groups offer the possibility to introduce various functional groups to the backbones in different positions on the rings.…”

“…P erez-Padilla and coworkers prepared copolymers of sulfonated copolyamides from isophthalic acid, 4,4'-(hexafluoroisopropylidene)-dianiline and 2,4-diaminobenzenesulfonic acid where a mix of meta and para linkages are present in the polymer. 33 They used 2,4-diaminobenzenesulfonic acid, which produced sulfonic acid groups ortho to the backbone of the copolymer, but with the sulfonic acid groups on the electron rich aromatic ring. In this polymer, the water uptake was low for low degrees of sulfonated monomer incorporation, in part due to the fluorinated component.…”

Fluorinated Polyamides

“…The instability of sulfonated aromatic PA toward hydrolysis and heat limits their fuel cell application [75,76]. Although fluorinated PAs have the potential to be used as a PEM, only a few examples of sulfonated aromatic PA PEMs have been reported.…”