Sulfonate Ionomers Research Articles

A highly aromatic and sulfonated ionomer for high elastic modulus ionic polymer membrane micro-actuators

A high modulus, sulfonated ionomer synthesized from 4,6-bis(4-hydroxyphenyl)-N,N-diphenyl-1,3,5-triazin-2-amine and 4,4′-biphenol with bis(4-fluorophenyl)sulfone (DPA-PS:BP) is investigated for ionic polymer actuators. The uniqueness of DPA-PS:BP is that it can have a high ionic liquid (IL) uptake and consequently generates a high intrinsic strain response, which is >1.1% under 1.6 V while maintaining a high elastic modulus (i.e. 600 MPa for 65 vol% IL uptake). Moreover, such a high modulus of the active ionomer, originating from the highly aromatic backbone and side-chain-free structure, allows for the fabrication of free-standing thin film micro-actuators (down to 5 µm thickness) via the solution cast method and focused-ion-beam milling, which exhibits a much higher bending actuation, i.e. 43 µm tip displacement and 180 kPa blocking stress for a 200 µm long and 5 µm thick cantilever actuator, compared with the ionic actuators based on traditional ionomers such as Nafion, which has a much lower elastic modulus (50 MPa) and actuation strain.

Mesoscale Modeling of Hydrated Morphology in Sulfonated Poly(phenylene sulfone) Ionomers

not Available.

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide)-based lithium polyether-ester-sulfonate ionomers

Nuclear magnetic resonance spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. (1)H and (7)Li spin-lattice relaxation times (T(1)) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T(1) values along with the presence of minima in T(1) as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and quasi-elastic neutron scattering experiments.

Electric-field-actuation of in situ composites that contain silver-coated carbon fibers in sodium sulfonate ionomers

In this research contribution, an electric-field-stimulated actuation system was developed by impregnating sodium-sulfonated ionomers, poly(styrene-co-butyl acrylate-co-sodium allyl sulfonate, PSBS) with in situ deposited silver-modified carbon fibers (SCCF). In the actuator, PSBS acts as an electrolytic medium for metal ion migration, and the SCCFs act as surface conductive electrodes on both sides of a sandwich configuration. The maximum bending angle of 98° is achieved after 11 s of stimulation when the electric potential difference is 5 V. This novel actuator has two outstanding characteristics: (1) in situ deposited SCCFs in PSBS form double-sided surface electrodes with high conductivity (10−3 Ω cm) and good interfacial binding with the PSBS matrix, which minimizes the drawbacks of electrochemical plating or electrode-less deposition of noble metals like Pt on the membrane surface of ionic polymer metal composites (IPMCs); and (2) it has the highest bending rate compared to currently existing IPMCs including Nafion and novel ones published recently. Additionally, the storage E′ and loss E′′ moduli of the PSBS–SCCF actuation system can be adjusted by selecting the appropriate ratio of butyl acrylate to styrene, where the latter comonomer increases the rigidity of the composite. The bending angle of this actuator can be controlled by the electric potential difference, water-uptake, and terpolymer composition. This fabrication technology exhibits significant advantages, such as process simplicity using non-toxic and low cost materials, rapid response, large bending angles, and reproducibility.

Synthesis and characterization of sulfonated telechelic bisphenol A polycarbonate ionomers

Bisphenol A polycarbonate telechelic sulfonated ionomers have been prepared by melt polycondensation using bis(methyl salicyl) carbonate (BMSC), bisphenol A (BPA) and the sodium salt of sulfobenzoic acid phenylester (SBENa). Using an activated carbonate such as BMSC it is possible to decrease both reaction temperature and time respect to a standard polycondensation that use diphenylcarbonate (DPC) as carbonate precursor. Using the activated carbonate, ionomers with low Fries by-products and with good color have been obtained. The addition of SBENa permits the preparation of telechelic ionomers with ionic contents up to 3 mol%. All the properties of the telechelic ionomer obtained using BMSC are superior respect to those of the telechelic ionomers obtained using DPC. In particular, the ionomers prepared using BMSC are stable up to 400 °C and present higher glass transition temperature and storage modulus respect to standard PC.

Thermally Driven Ionic Aggregation in Poly(ethylene oxide)-Based Sulfonate Ionomers

A series of sulfonate polyester ionomers with well-defined poly(ethylene oxide) spacer lengths between phthalates and alkali metal cations as counterions are designed for improved ionic conductivity. Ion conduction in these chemically complex materials is dominated by the polymer mobility and the state of ionic aggregation. While the aggregation decreases dramatically at room temperature as the cation size increases from Li to Na to Cs, the extents of ionic aggregation of these ionomers are comparable at elevated temperatures. Both the Na and Cs ionomers exhibit thermally reversible transformation upon heating from 25 to 120 °C as isolated ion pairs aggregate. This seemingly counterintuitive aggregation of ions on heating is driven by the fact that the dielectric constant of all polar liquids decreases on heating, enhancing Coulomb interactions between ions.

Low equivalent weight Friedel-Crafts cross-linked sulfonated poly(ether ether ketone)

Poly(ether ether ketone) (PEEK) was sulfonated by electrophillic aromatic substitution to produce a highly water soluble polymer. With an equivalent weight (EW) of 381 g/eq, the polymer is capable of a proton conductivity of 0.2 S/cm at 80 °C and 100% relative humidity (RH). High proton conductivity in polymer electrolyte membranes is a key factor for optimum hydrogen fuel cell performance. Under testing at saturating RHs, the highly sulfonated polymer absorbs water while simultaneously becoming swollen and mechanically weak. To maintain mechanical stability, a ZnCl 2 catalyst was used to catalyze a Friedel-Crafts-type cross-linking using benzenedimethanol(BDM) as cross-linking agent. Although membrane thermal properties did not improve substantially, solubility was decreased and mechanical strength increased. Membranes cross-linked with 12 and 24 wt.% BDM yielded polymers with equivalent weights of 395 and 416 g/eq and conductivities of 0.15 and 0.14 S/cm at 80 °C and 100% RH, respectively, without excessive water uptake shown by the pure 96% sulfonated PEEK. Characterization of the pure and cross-linked membranes were also studied using Fourier transform infrared spectroscopy, water uptake, thermogravimetric coupled mass spectrometry and differential scanning calorimetry. Membranes were covered with platinum on carbon catalyst ink, and further characterized using linear sweep voltammetry. Behavior comparable to perfluoroalkyl sulfonate ionomers was demonstrated.

Counterion Dynamics in Polyester−Sulfonate Ionomers with Ionic Liquid Counterions

Conventional sodium cations (Na+) in sulfonated polyester ionomers were replaced with ammonium-based ionic liquid counterions. Counterion dynamics were measured by dielectric spectroscopy and linear viscoelastic response via oscillatory shear. Ion exchange from sodium counterions to ionic liquid counterions such as tetramethylammonium and tetrabutylammonium showed an order of 104 increase in conductivity compared with sodium counterions, primarily attributed to weaker ionic interactions that lower the glass transition temperature. Electrode polarization was used in conjunction with the 1953 Macdonald model to determine the number density of conducting counterions and their mobility. Conductivity and mobility exhibit Vogel−Fulcher−Tammann (VFT) temperature dependences and both increased with counterion size. Conducting counterion concentrations showed Arrhenius temperature dependences, with activation energy reduced as counterion size increased. When ether−oxygen was incorporated into the mobile cation structure, self-solvating ability notably increased the conducting ion concentration. Weakened ion pairing interactions prove favorable for fundamental design of single-ion conductors for actuators, as ionic liquid counterions can provide both larger and faster strains, required by such electro-active devices.

Microsolvation and Proton Transfer in Highly Sulfonated Poly(phenylene sulfone) Ionomers

not Available.

Sulfonated poly(arylene ether sulfone) ionomers containing di- and tetrasulfonated arylene sulfone segments

Poly(arylene ether sulfone) (PSU) ionomers containing disulfonated aryl-SO2-aryl and tetrasulfonated aryl-SO2-aryl-aryl-SO2-aryl segments, respectively, were synthesized and studied to establish their structure–property relationships as proton-exchange membranes. High molecular weight PSUs with different distributions of sulfone bridges in the backbone were prepared by nucleophilic aromatic substitution reactions involving 4,4′-dichlorodiphenyl sulfone (DCDPS), 4,4′-bis[(4-chlorophenyl)sulfonyl]-1,1′-biphenyl (BCPSB), 4,4′-isopropylidenediphenol (bisphenol A), and 4,4′-(1,4-phenylenediisopropylidene)bisphenol (bisphenol P). The polymers were sulfonated viametallation and reaction with sulfur dioxide, followed by oxidation of the resulting sulfinates. This procedure allowed the introduction of two sulfonic acid units on electron-deficient aryl rings in ortho positions to each sulfone bridge of the PSUs. Analysis by small angle X-ray scattering of solvent cast membranes showed that ionic clustering was promoted in ionomers containing sulfonated BCPSB residues and flexible bisphenol P residues. The fully sulfonated PSUs had ion-exchange capacities (IECs) of 3.3–4.1 meq g−1 and were water soluble. However, partly sulfonated polymers with IECs of approx. 1.7 meq g−1 showed high proton conductivity at moderate water uptake and decomposed only above 240 °C during heating 1 °C min−1 under air. This work demonstrated that BCPSB residues can be conveniently and fully tetrasulfonated, which opens possibilities to prepare various aromatic copolymers and membranes with locally very high densities of hydrolytically stable sulfonic acid groups.

Poly(arylene ether sulfone)s ionomers with pendant quaternary ammonium groups for alkaline anion exchange membranes: Preparation and stability issues

A series of quaternized poly(arylene ether sulfone)s containing up to two pendant quaternary ammonium groups per repeat unit was prepared by cesium carbonate mediated direct aromatic nucleophilic substitution polycondensation of 2,2′-dimethylaminemethylene-4,4′-biphenol (DABP), 4,4′-biphenol (BP) and 4,4′-difluorodiphenylsulfone (DFDPS), followed by reaction with iodomethane. The anion exchange membranes formed from these polymers showed conductivities above 10−2Scm−1 at room temperature with a hydroxide conductivity of 6.5×10−2Scm−1 for QNPS-OH-80. At the test of alkaline stability, these poly(arylene ether sulfone) ionomers were more stable than our previous reported partially fluorinated poly(arylene ether sulfone) ionomers under highly basic conditions.

Sulfonated Low-Cost Ionomers as Acidic Cross-Linkers for High-Temperature PBIOO Membranes

The low-cost polymers poly(styrene) and poly(α-methylstyrene) have been sulfonated in a first step. Then both sulfonated ionomers have been blended with PBIOO® (30 wt% sulfonated ionomer, 70 wt% PBIOO), the sulfonated ionomer serving as acidic cross-linker which enhances the PBIOO stability. Both membrane types were treated with Fentons Reagent to investigate their oxidative stability. Of particular interest was whether the poly(α-methylstyrene) ionomer was more stable against radical attack. It was indeed found that the PBIOO-sulfonated poly(α-methylstyrene) blend membrane showed less weight loss during and after Fenton Test than the respective poly(styrene sulfonic acid) PBIOO-containing membrane. The macromolecules are partially degrading by radical attack to the main chain of the sulfonated poly(α-methylstyrene) polymers but still remain in the blend membrane matrix due to acid-base interactions. Since the PBIOO/sulfonated poly(α-methylstyrene) blend membranes conserved their integrity even after Fentons Test they can be regarded as interesting low-cost high-T fuel cell membranes.

Synthesis and properties of novel sulfonated poly(arylene ether sulfone) ionomers for vanadium redox flow battery

Novel sulfonated poly(arylene ether sulfone)s with electron-withdrawing sulfone groups in each repeat unit were synthesized via step polymerization followed by post-sulfonation using chlorosulfonic acid. The sulfonation degree can be readily controlled by adjusting the feed ratio of the repeat unit of polymers to chlorosulfonic acid. The synthesized polymers are soluble in common aprotic solvents such as dimethyl sulfoxide, N, N′-dimethylacetamide and dimethylformamide, and can be cast into transparent membranes from their solutions. The ion exchange capacity, water uptake, swelling ratio, sulfonation degree, mechanical property, oxidative property, thermal property and proton conductivity were investigated in detail using different methodologies. As an objective to apply these polymers as separators for vanadium redox flow battery, the VO 2+ permeability and cell performance for the single cell were examined and assessed.

Poly(arylene ether)s Containing Superacid Groups as Proton Exchange Membranes

A series of poly(arylene ether)s containing pendant superacid groups on fluorenyl groups were synthesized and their properties were investigated for fuel cell applications. Poly(arylene ether)s containing iodo groups were synthesized by the polymerization of 2,7-diiodo-9,9-bis(4-hydroxyphenyl)fluorene with difluorinated compounds such as decafluorobiphenyl, bis(4-fluorophenyl)sulfone, and bis(4-fluorophenyl)ketone, under nucleophilic substitution conditions. The iodo groups on the fluorenyl groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The degree of perfluorosulfonation was controlled to be up to 92%, which corresponds to an ion exchange capacity (IEC) of 1.52 meq/g. The ionomers yielded flexible, ductile membranes by solution casting. The ionomer membranes exhibited a characteristic hydrophilic/hydrophobic phase separation, with small interconnected hydrophilic clusters (2-3 nm), which is similar to that of the benchmark perfluorinated membrane (Nafion). The aromatic ionomers containing superacid groups showed much higher proton conductivities than those of the conventional sulfonated aromatic ionomers with similar main chain structures. Fuel cell performance with the superacidic ionomer membranes was also tested.

Multi-Length Scale Morphology of Poly(ethylene oxide)-Based Sulfonate Ionomers with Alkali Cations at Room Temperature

A series of Li-, Na-, and Cs-neutralized polyester ionomers with well-defined poly(ethylene oxide) (PEO) spacer lengths between sulfonated phthalates have been investigated by X-ray scattering at room temperature. As the spacer lengths are increased the PEO segments crystallize, as evidenced by multiple crystal reflections that are identical to those of pure poly(ethylene glycol) oligomers. This crystallization also produces multiple small-angle peaks, which correspond to the well-defined thickness of PEO crystallites. The ionomer peak (q = 1−5 nm−1) is absent in the Na- and Cs-neutralized ionomers, while the Li-neutralized ionomers show peaks at q = 2−3 nm−1, reminiscent of conventional ionic aggregates in ionomers. Detailed analysis of the normalized X-ray scattering intensity from these ionomers reveals a variety of ionic states that are highly dependent on the cation size. The states of ionic groups change from a majority of isolated ion pairs to aggregated structures as the cation size decreases from...

Synthesis and characterization of sulfonated poly(arylene ether sulfone) ionomers incorporating perfluorohexylene units for DMFC membranes

A new, sulfonated poly(arylene ether sulfone) ionomer with partially fluorinated groups (F-SPAES) was synthesized by the direct polymerization of 1,6-bis(4-fluororphenyl)-perfluorohexane (FPPFH) and 6F-bisphenol A (6F-BPA) with 3,3′-disulfonated 4,4′-difluorodiphenyl sulfone (SDFDPS). The effect of fluorination on the membrane properties and membrane-electrode assembly (MEA) performance for DMFC applications were investigated comprehensively and compared with the pristine SPAES sample. Deliberate control of the hydrophobicity as well as the degree of sulfonation in the F-SPAES membranes allows the effective suppression of water uptake and methanol permeability, while barely affecting the proton conductivity and IEC value. Such an improvement in the membrane properties contributes to the superior single cell performance of the F-SPAES compared to pristine SPAES and Nafion®.

Conductivity of highly sulfonated polyphenylene sulfide in the powder form as a function of temperature and humidity

Block-copolymers with highly sulfonated ionomer blocks are considered as leading candidates for low-humidity high-temperature Polymer Electrolyte Fuel Cell membranes. We present a new approach that allows for faster measurement of conductivity of powdered ionomers in a wide range of temperature and humidity with a single 10–30 mg sample. Our method is exemplified by a case study of polyphenylenesufide with a degree of sulfonation 0.70. This material shows 0.12 S/cm conductivity at 127 °C and 50% relative humidity. At higher temperatures and lower humidities, this polymer undergoes irreversible cross-linking. Further routes to improving conductivity, chemical and mechanical properties of the polymer are discussed.

Synthesis of Soluble Poly(arylene ether sulfone) Ionomers with Pendant Quaternary Ammonium Groups for Anion Exchange Membranes

A new bisphenol monomer, 2,2′-dimethylaminemethylene-4,4′-biphenol (DABP), was easily prepared by Mannich reaction of dimethylamine and formaldehyde with 4,4′-biphenol. Novel partially fluorinated poly(arylene ether sulfone)s with pendant quaternary ammonium groups were prepared by copolymerization of DABP, 4,4′-biphenol, and 3,3′,4,4′-tetrafluorodiphenylsulfone, followed by reaction with iodomethane. The resulting copolymers PSQNI-x (where x represents the molar fraction of DABP in the feed) with high molecular weight exhibited outstanding solubility in polar aprotic solvents; thus, the flexible and tough membranes of PSQNI-x with varying ionic content could be prepared by casting from the DMAc solution. Novel anion exchange membranes, PSQNOH-x, were obtained by an anion exchange of PSQNI-x with 1 N NaOH. All PSQNOH-x membranes showed conductivities above 10−2 S cm−1 at room temperature, for example, the hydroxide conductivity of PSQNOH-90 achieved to 8.4 × 10−2 S cm−1, which was thus comparable to the p...

From Solutions to Membranes: Structure Studies of Sulfonated Polyphenylene Ionomers

The structure of rigid sulfonated polyphenylene ionomers was investigated in bulk and in dilute organic solutions. The uniqueness of polyphenylene ionomers lies in their rigid backbone which prevents folding and therefore affects the partition into hydrophilic ionic domains and hydrophobic regions. This segregation dominates the structure of flexible ionic polymers. Small-angle neutron scattering studies of these ionomers have demonstrated that bundles of polymer molecules are formed in dilute organic solutions. This clustered building block persists in bulk dry and hydrated states of the ionomers. Hydration of these ionomers membranes results in segregation to hydrophilic and hydrophobic regions, where diffusion into interstitial spaces between the bundles of sulfonated and unsulfonated domains takes place followed by rearrangements of domains to yield locally bicontinuous regions. Only at very high sulfonation levels are fully bicontinues phases formed. With controlling the degree of continuity, the sti...

Anionic polysulfone ionomers and membranes containing fluorenyl groups for anionic fuel cells

Poly(arylene ether sulfone) ionomers containing fluorenyl groups and functionalized with benzyltrimethylammonium groups were synthesized through polycondensation, chloromethylation, and amination reactions. The resulting polymers were characterized by 1H NMR, FT-IR and TGA. Polymer membranes were solvent cast from DMF on Teflon plates to form clear, flexible anion exchange membranes (AEMs). Carbonate anions had conductivities in the AEMs up to 63.12 mS cm −1 at 70 °C and were used in a carbonate fuel cell. The membranes were stable in 1 M carbonate solution (pH 11). However, conductivity loss was observed during soaking in 1 M hydroxide solution (pH > 14) at 50 °C. A carbonate fuel cell operating at room temperature with H 2 at the anode and O 2 and CO 2 at the cathode had a maximum power density of 4.1 mW cm −2.