Synthesis and characterization of sulfonated poly(ether ether ketone) for proton exchange membranes Xing, P.; Robertson, Gilles; Guiver, Michael; Mikhailenko, S.; Wang, K.; Kaliaguine, S. AbstractSeries of sulfonated poly(ether ether ketone)s (SPEEKs) were prepared by sulfonation of commercial Victrex ® and Gatone ® PEEK for a comparative study of proton exchange membranes (PEM) intended for fuel cell applications. The degree of sulfonation (DS) of the sulfonated PEEK was determined from deuterated dimethyl sulfoxide (DMSO-d 6 ) solution of the purified polymers using 1 H NMR methods. The second method using a solvent suppression technique, in which DS results were obtained directly from 1 H NMR spectra of SPEEK dissolved in sulfuric acid (non-deuterated) reaction medium was evaluated. The variation between the two methods was determined. The room temperature sulfonation of PEEK, monitored directly by second 1 H NMR method, proceeded rapidly initially, reaching DS ∼ 0.8 within 1 week, but progressed slowly thereafter. A maximum DS of 1.0 was determined after 1 month at ambient temperature (∼22• C). The thermal properties of SPEEK were characterized by means of DSC and TGA. The mass averaged molecular weights M w of both Victrex ® and Gatone ® PEEK were estimated from intrinsic viscosities measured in sulfuric acid solutions. It was verified that higher temperature (55• C) did not induce any apparent chain degradation of Victrex ® (or Gatone ® ) PEEK by M w tests. The water uptake and swelling properties of prepared films were studied and the proton conductivities at different temperatures were measured. The conductivities of the SPEEKs were found to increase with increasing DS and temperatures. The effect of film casting solvents on the conductivities is also discussed.

A new method for the preparation of proton exchange membranes (PEMs), based on cross-linked sulfonated poly(ether ether ketones) is reported. The cross-linking involves thermally activated bridging of the polymer chains with polyatomic alcohols, which makes the polymer mechanically stronger and reduces its swelling by water. Although the cross-linking occurs through the sulfonic acid group, a major portion of acid functions is not involved in cross-linking and remains available for proton transfer. Owing to this, membrane conductivities are only somewhat reduced, leaving some with values above 2 × 10 −2 S/cm at room temperature.

Casting solvent interactions with sulfonated poly(ether ether ketone) during proton exchange membrane fabrication Robertson, G. P.; Mikhailenko, S.; Wang, K.; Xing, P.; Guiver, Michael; Kaliaguine, S. Abstract 1 H NMR spectroscopy revealed the formation of a strong interaction between sulfonated poly(ether ether ketone) (PEEK) and the casting solvents dimethylformamide (DMF) and dimethylacetamide (DMAc), commonly used in proton exchange membranes (PEM) preparation. The DMF amide function readily forms a hydrogen-bonding complex with sulfonic acid group starting at temperatures as low as 60 • C. DMAc is less susceptible to participate in this reaction and hydrogen-bonding occurs in this case only above 100 • C. Both solvents are prone to thermally activated decomposition possibly accelerated by sulfonic acid functions and the produced dimethylamine (DMA) also forms a strong association with SPEEK. The solvents' decomposition is strongly catalyzed by residual sulfuric acid originating from SPEEK preparation, with the resulting formation of N,N-dimethylaminium hydrogensulfate (DMAm). Both DMF and DMAc solvent interaction with SPEEK sulfonic acid groups significantly affect the properties of PEMs, lowering their proton conductivity.

Sulfonated poly(phthalazinone ether ketone) (SPPEK) copolymers and sulfonated poly(phthalazinone ether sulfone) (SPPES) copolymers containing pendant sodium sulfonate groups were prepared by direct copolymerization. The reaction of disodium 3,3′‐disulfonate‐4,4′‐difluorobenzophenone (SDFB‐Na), 4,4′‐difluorobenzophenone (DFB), and 4‐(4‐hydroxyphenyl)‐1(2H)‐phthalazinone (DHPZ) at 170 °C in N‐methyl‐2‐pyrrolidione containing anhydrous potassium carbonate gave SPPEKs. SPPESs were similarly obtained with 3,3′‐disulfonate‐4,4′‐difluorophenyl sulfone, 4‐fluorophenyl sulfone (DFS), and DHPZ as monomers. The sulfonic acid groups, being on deactivated positions of the polymer backbone, were expected to be hydrolytically more stable than postsulfonated polymers. Fourier transform infrared and 1H NMR were used to characterize the structures and degrees of sulfonation of the sulfonated polymers. Membrane films of SPPEKs with SDFB‐Na/DFB molar feed ratios of up to 60/40 and SPPESs with sulfonated 4‐fluorophenyl sulfone/DFS molar feed ratios of up to 50/50 were cast from N,N‐dimethylacetamide polymer solutions. Membrane films in acid form were then obtained by the treatment of the sodium‐form membrane films in 2 N sulfuric acid at room temperature. An increase in the number of sulfonate groups in the copolymers resulted in an increased glass‐transition temperature and enhanced membrane hydrophilicity. The sodium‐form copolymers were thermally more stable than their acid forms. The proton conductivities of the acid‐form copolymers with sulfonated monomer/unsulfonated monomer molar feed ratios of 0.5 and 0.6 were higher than 10−2 S/cm and increased with temperature; they were less temperature‐dependent than those of the postsulfonated products. SPPESH‐50 showed higher conductivity than the corresponding postsulfonated poly(phthalazinone ether sulfone). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2731–2742, 2003

As a novel class of proton exchange membrane (PEM) materials for use in fuel cells, sulfonated poly(phthalazinones) (SPPs), including sulfonated poly(phthalazinone ether sulfones) (SPPESs), sulfonated poly(phthalazinone ether ketones) (SPPEKs) and sulfonated poly(phthalazinone ether sulfone ketones) (SPPESKs), were prepared by modification of corresponding poly(phthalazinones) (PPs). Sulfonation reactions were conducted at room temperature using mixtures of 95-98% concentrated sulfuric acid and 27-33% fuming sulfuric acid with different acid ratios in order to get SPPs with degree of sulfonation (DS) in the desired range of 1.00-1.37. The presence of sulfonic acid groups in SPPs was confirmed by FT-IR analysis, and the DS and structures were characterized by NMR. The introduction of sulfonic groups into the polymer chains led to a decrease in the decomposition temperature. Membrane films were cast from SPPs solution in N, N-dimethylacetamide (DMAc). Water uptakes and swelling ratios of SPPs membrane films increased with DS and temperature. Proton conductivities of all SPPs increased with DS and temperature, reaching higher than 10 −2 Scm −1 at around DS 1.0.