Effect of sulfonation degree on molecular weight, thermal stability, and proton conductivity of poly(arylene ether sulfone)s membrane

Abstract

Direct copolymerization of sulfonated and non-sulfonated difluorodiphenyl sulfones as dihalide monomers with hydroquinone and also 4,4′-(4,4′-sulfonylbis-(1,4-phenylene)bis(oxy)) diphenol as diols led to preparation of two series of poly(arylene ether sulfone)s. Copolymers with different degrees of sulfonation (40, 50 and 60%) were synthesized in order to evaluate their potential for fuel cell application. 1H-NMR, FT-IR, and mass spectroscopy were used for characterization of prepared monomers and copolymers. Differential scanning calorimetry and thermogravimetric analysis were applied for investigation and comparison of the thermal properties of copolymers. Laser light scattering (LLS) was employed to calculate zeta potential, conductivity, and molecular weight of copolymers. Copolymers were obtained in high and sufficient molecular weight that was basic need to reach reasonable physical and thermal properties for applications as fuel cell membrane. The effect of similar structural repeating units with different sizes on the final properties of sulfonated poly(ether sulfone)s was investigated to compare their potential in fuel cell membrane.

Mechanical and morphological studies of sulfonated poly(arylene ether sulfone)s for potential application in fuel cell membrane

“…Nuclear Magnetic Resonance (NMR) study for estimation of the sulfonation content showed that the degree of sulfonation in Poly(ether sulfone) based on 4,4 0 -(4,4 0 -Sulfonylbis-(1,4phenylene)bis(oxy)) diphenol (PES-SPHD) series was lower than similar structures in Poly(ether sulfone) based on Hydroquinone (PES-HQ) series, resulting in lower IEC values in PES-SPHD chains. [49] Water uptake and dimensional stability showed a similar trend (Table 1); it means that both properties in two groups of copolymers increased as the degree of sulfonation increased, implying that more phase separation happened. Another assumption was that in SPHD-based copolymers, more free volume formed in copolymer structure and sulfonic acid groups become more accessible because of the presence of larger hydrophobic-hydrophilic segments.…”

“…The two protons next to the sulfonate group on SDFS monomer were considered as reference peaks for evaluation as they were well separated from the other aromatic protons of all the copolymers. After complete characterization of monomers and polymers, and film preparation, mechanical and morphological properties of the prepared membranes were studied for application in fuel cell …”

“…Ion exchange capacity was increased in both groups of copolymers as sulfonic acid groups content increased. Nuclear Magnetic Resonance (NMR) study for estimation of the sulfonation content showed that the degree of sulfonation in Poly(ether sulfone) based on 4,4′‐(4,4′‐Sulfonylbis‐(1,4‐phenylene)bis(oxy)) diphenol (PES‐SPHD) series was lower than similar structures in Poly(ether sulfone) based on Hydroquinone (PES‐HQ) series, resulting in lower IEC values in PES‐SPHD chains …”

“…After complete characterization of monomers and polymers, and film preparation, mechanical and morphological properties of the prepared membranes were studied for application in fuel cell. [49] Water uptake, dimensional stability, and ion-exchange capacity Water uptake, dimensional stability, and IEC are three important properties of polymer membrane fuel cell that related to the structure of polymer backbone and amount of sulfonation. Table 1 lists the IEC values of the copolymer membranes measured by a titration method.…”

“…Also, in a higher degree of sulfonation for each series, by the increase of the intermolecular interactions and the decrease of molecular weights, the elongation at break decreased, and the mechanical behavior inclined to a more rigid form. [49] Microstructure and morphology…”