Pendant Sulfonate Research Articles

High-performance aromatic proton exchange membranes bearing multiple flexible pendant sulfonate groups: Exploring side chain length and main chain polarity

Fabrication of aromatic proton exchange membrane (PEM) with excellent conductivity and stability is a long-standing challenge. Here, we propose an aromatic PEM containing multiple sulfonated alkyl side chains (SAFPAEK-x and SAFPAEF-x), and then implement an ideal strategy to address the trade-off between conductivity and stability by optimizing the side chain length and main chain polarity. Specifically, the synthesized PEMs achieve an efficient proton transport (proton conductivity >0.124 S cm−1 at 80 °C) under the synergistic effect of multiple pendant sulfonate groups and a pronounced microphase separation structure. Meanwhile, regulating the polarity of the hydrophobic domain via introducing fluorinated structures can effectively suppress the swelling behavior, so that SAFPAEF-x display excellent dimensional stability (swelling ratio <10% at 80 °C). The theoretical calculations of molecular models and ex-situ experiments demonstrate that appropriate increases in side chain length and main chain polarity lead to noticeably improved radical stability of aromatic PEMs. Finally, the laboratory-assembled direct borohydride fuel cell using our rationally designed PEMs reaches the highest peak power density of 191.17 mW m−2 at room temperature, outperforming the Nafion 115 (95.87 mW m−2) under the same conditions. Therefore, this membrane design strategy stimulates great potential in designing high-performance aromatic PEMs for fuel cells.

Thermo-Responsive Polyion Complex of Polysulfobetaine and a Cationic Surfactant in Water

Poly(4-((3-methacrylamidopropyl)dimethylammonium)butane-1-sulfonate) (PSBP) was prepared via controlled radical polymerization. PSBP showed upper critical solution temperature (UCST) behavior in aqueous solutions, which could be controlled by adjusting the polymer and NaCl concentrations. Owing to its pendant sulfonate anions, PSBP exhibited a negative zeta potential of −7.99 mV and formed a water-soluble ion complex with the cationic surfactant cetyltrimethylammonium bromide (CTAB) via attractive electrostatic interaction. A neutral PSBP/CTAB complex was formed under equimolar concentrations of the pendant sulfonate group in PSBP and the quaternary ammonium group in CTAB. Transmittance electron microscopic images revealed the spherical shape of the complex. The stoichiometrically neutral-charge PSBP/CTAB complex exhibited UCST behavior in aqueous solutions. Similar to PSBP, the phase transition temperature of the PSBP/CTAB complex could be tuned by modifying the polymer and NaCl concentrations. In 0.1 M aqueous solution, the PSBP/CTAB complex showed UCST behavior at a low complex concentration of 0.084 g/L, whereas PSBP did not exhibit UCST behavior at concentrations below 1.0 g/L. This observation suggests that the interaction between PSBP and CTAB in the complex was stronger than the interpolymer interaction of PSBP.

High-Performance Aromatic Proton Exchange Membranes Bearing Multiple Flexible Pendant Sulfonate Groups: Exploring Side Chain Length and Main Chain Polarity

High-Performance Aromatic Proton Exchange Membranes Bearing Multiple Flexible Pendant Sulfonate Groups: Exploring Side Chain Length and Main Chain Polarity

Modulating the Properties of Fe(III) Macrocyclic MRI Contrast Agents by Appending Sulfonate or Hydroxyl Groups.

Complexes of Fe(III) that contain a triazacyclononane (TACN) macrocycle, two pendant hydroxyl groups, and a third ancillary pendant show promise as MRI contrast agents. The ancillary group plays an important role in tuning the solution relaxivity of the Fe(III) complex and leads to large changes in MRI contrast enhancement in mice. Two new Fe(III) complexes, one with a third coordinating hydroxypropyl pendant, Fe(L2), and one with an anionic non-coordinating sulfonate group, Fe(L1)(OH2), are compared. Both complexes have a deprotonated hydroxyl group at neutral pH and electrode potentials representative of a stabilized trivalent iron center. The r1 relaxivity of the Fe(L1)(OH2) complex is double that of the saturated complex, Fe(L2), at 4.7 T, 37 °C in buffered solutions. However, variable-temperature 17O-NMR experiments show that the inner-sphere water of Fe(L1)(OH2) does not exchange rapidly with bulk water under these conditions. The pendant sulfonate group in Fe(L1)(OH2) confers high solubility to the complex in comparison to Fe(L2) or previously studied analogues with benzyl groups. Dynamic MRI studies of the two complexes showed major differences in their pharmacokinetics clearance rates compared to an analogue containing a benzyl ancillary group. Rapid blood clearance and poor binding to serum albumin identify Fe(L1)(OH2) for development as an extracellular fluid contrast agent.

Polymer solar cells employing conjugated polyelectrolytes with different countercations

Conjugated polyelectrolytes based on benzotriazole (BT) and benzothiadiazole (BTz) alt unit with a pendant sulfonate ion but different countercations were synthesized and named PBTBTz-SO3Na and PBTBTz-SO3TBA. PBTBTz-SO3Na was used as a cathode interface applied to polymer solar cells (PSCs), and ITO/PEDOT:PSS/active layer/cathode interlayer/Al was set as a device structure. The PSCs displayed an average power conversion efficiency (PCE) of 7.7%, revealing an unchanged efficiency in comparison with that of the control device fabricated from a CH3OH interlayer. TBA+, a different counteraction, was used instead of Na+ to further study the influence of counterions on the electrical property of PBTBTz-SO3−. PBTBTz-SO3TBA was used as a cathode interface to fabricate two types of PSCs based on PTB7:PC71BM and PBDB-T:ITIC, and their improved average PCEs were 8.6% and 9.1%, respectively.

Ion-Pair-Directed Borylation of Aromatic Phosphonium Salts.

Control of positional selectivity in C–H activation reactions remains a challenge for synthetic chemists. Noncovalent catalysis has the potential to be a powerful strategy to address this challenge. As a part of our ongoing investigations into the use of ion-pairing interactions in site-selective catalysis, we demonstrate that several classes of aromatic phosphonium salts undergo iridium-catalyzed C–H borylation with a high selectivity for the arene meta position. This is achieved using a bifunctional bipyridine ligand bearing a pendant sulfonate group, which had previously been successful for borylation of aromatic ammonium salts. In this case, the phosphonium salts give a higher meta selectivity than the corresponding ammonium salts. We propose that the high selectivity occurs due to an attractive electrostatic interaction between the substrate and the ligand in the transition state for borylation.

Upper Critical Solution Temperature (UCST) Behavior of Polystyrene-Based Polyampholytes in Aqueous Solution.

Strong polyampholytes comprising cationic vinylbenzyl trimethylammonium chloride (VBTAC) bearing a pendant quaternary ammonium group and anionic sodium p-styrenesulfonate (NaSS) bearing a pendant sulfonate group were prepared via reversible addition-fragmentation chain-transfer polymerization. The resultant polymers are labelled P(VBTAC/NaSS)n, where n indicates the degree of polymerization (n = 20 or 97). The percentage VBTAC content in P(VBTAC/NaSS)n is always about 50 mol%, as revealed by 1H NMR measurements, meaning that P(VBTAC/NaSS)n is a close to stoichiometrically charge-neutralized polymer. Although P(VBTAC/NaSS)n cannot dissolve in pure water at room temperature, the addition of NaCl or heating solubilizes the polymers. Furthermore, P(VBTAC/NaSS)n exhibits upper critical solution temperature (UCST) behavior in aqueous NaCl solutions. The UCST is shifted to higher temperatures by increasing the polymer concentration and molecular weight, and by decreasing the NaCl concentration. The UCST behavior was measured ranging the polymer concentrations from 0.5 to 5.0 g/L.

Enhanced Performance of a Sulfonated Poly(arylene ether ketone) Block Copolymer Bearing Pendant Sulfonic Acid Groups for Polymer Electrolyte Membrane Fuel Cells Operating at 80% Relative Humidity.

The series of sulfonated poly(arylene ether ketone) (SPAEK) block copolymers with controlled F-oligomer length bearing pendant diphenyl unit were synthesized via a polycondensation reaction. Sulfonation was verified by 1H NMR analysis to introduce sulfonic acid group selectively and intensively on the pendant diphenyl unit of polymer backbones. The SPAEK membranes fabricated by the solution casting approach were very transparent and flexible with the thickness of ∼50 μm. These membranes with different F-oligomer lengths were investigated to the physiochemical properties such as water absorption, dimensional stability, ion exchange capacity, and proton conductivity. As a result, the SPAEK membranes (X4.8Y8.8, X7.5Y8.8, and X9.1Y8.8) in accordance to increasing the length of hydrophilic oligomer showed excellent proton conductivity in range of 131-154 mS cm-1 compared to Nafion-115 (131 mS cm-1) at 90 °C under 100% relative humidity (RH). Among the SPAEK membranes, proton conductivity of SPAEK X9.1Y8.8 (140.7 mS cm-1) is higher than that of Nafion-115 (102 mS cm-1) at 90 °C under 80% RH. The atomic force microscopy image demonstrated that number of ion transport channels is increased with increase in the length of hydrophilic oligomer in the main chains, and the morphology is proved to be related to the proton conductivity. The synthesized SPAEK membrane exhibited a maximum power density of 324 mW cm-2, which is higher than that of Nafion-115 (291 mW cm-2) at 60 °C under 100% RH.

Cyclopentane Formation from Flexible Precursors Using Samarium(II) Reagents

Three efficient methods for five‐membered ring carbocycle synthesis have been developed from simple starting materials using samarium(II) reagents. A Reformatsky aldol reaction proceeded efficiently with samarium(II) iodide using lithium bromide as an additive. A new intramolecular alkylation of a samarium enolate was realized with a pendant sulfonate ester leaving group. Pinacol cyclization of a simple diketone was also demonstrated giving a diol product in high stereoselectivity. A promising lead result has been established demonstrating enantioselectivity in a chiral ligand controlled Reformatsky aldol reaction.

Preparation of Water-soluble Polyion Complex (PIC) Micelles Covered with Amphoteric Random Copolymer Shells with Pendant Sulfonate and Quaternary Amino Groups.

An amphoteric random copolymer (P(SA)91) composed of anionic sodium 2-acrylamido-2-methylpropanesulfonate (AMPS, S) and cationic 3-acrylamidopropyl trimethylammonium chloride (APTAC, A) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. The subscripts in the abbreviations indicate the degree of polymerization (DP). Furthermore, AMPS and APTAC were polymerized using a P(SA)91 macro-chain transfer agent to prepare an anionic diblock copolymer (P(SA)91S67) and a cationic diblock copolymer (P(SA)91A88), respectively. The DP was estimated from quantitative 13C NMR measurements. A stoichiometrically charge neutralized mixture of the aqueous P(SA)91S67 and P(SA)91A88 formed water-soluble polyion complex (PIC) micelles comprising PIC cores and amphoteric random copolymer shells. The PIC micelles were in a dynamic equilibrium state between PIC micelles and charge neutralized small aggregates composed of a P(SA)91S67/P(SA)91A88 pair. Interactions between PIC micelles and fetal bovine serum (FBS) in phosphate buffered saline (PBS) were evaluated by changing the hydrodynamic radius (Rh) and light scattering intensity (LSI). Increases in Rh and LSI were not observed for the mixture of PIC micelles and FBS in PBS for one day. This observation suggests that there is no interaction between PIC micelles and proteins, because the PIC micelle surfaces were covered with amphoteric random copolymer shells. However, with increasing time, the diblock copolymer chains that were dissociated from PIC micelles interacted with proteins.

Microemulsion self-assembling of novel amphiphilic block co-polyarylene ether nitriles and photosensitizer ZnPc towards hybrid superparticles for photocatalytic degradation of Rhodamine B

Self-assembling of amphiphilic copolymers via microemulsion technique provides versatile platform for physical encapsulation of various sensitive functional molecules. In this work, a novel amphiphilic block poly(arylene ether nitriles) (b-PEN) has been firstly synthesized through the step-growth nucleophilic substitution polycondensation of bisphenol A (BPA) modified hydrophobic oligomer and the hydrophilic oligomer containing pendant sulfonate groups. Due to the incompatibility between the two segments, the isotropic b-PEN superparticles were prepared by a facile microemulsion self-assembly technique, which meanwhile allowed encapsulation of the hydrophobic photosensitizer of ZnPc into the polymeric superparticles. Finally, the stable aqueous solution containing b-PEN@ZnPc hybrid superparticles is obtained and demonstrates singlet oxygen generation ability, which ensures desirable photocatalytic degradation of rhodamine B (RhB). Based on the intrinsically chemical resistance, high mechanical strength and facile fabrication of b-PEN superparticles, the present work will open the way for the construction of robust PEN nanostructures, which could act as the template to assemble with various organic or inorganic functional particles to expand its environmental remediation application.

Solution Properties of Amphoteric Random Copolymers Bearing Pendant Sulfonate and Quaternary Ammonium Groups with Controlled Structures.

Amphoteric random copolymers P(AMPS/APTAC50) x, where x = 41, 89, and 117, composed of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and 3-acrylamidopropyltrimethylammonium chloride (APTAC) were prepared via reversible addition-fragmentation chain transfer radical polymerization. P(AMPS/APTAC50) x can dissolve in pure water to form small interpolymer aggregates. In aqueous solutions of NaCl, P(AMPS/APTAC50) x can dissolve in the unimer state. Amphoteric random copolymer P(AMPS/APTAC50)c with high molecular weight was prepared via conventional free-radical polymerization. Although P(AMPS/APTAC50)c cannot dissolve in pure water, it can dissolve in aqueous solutions of NaCl. In amphoteric random copolymers with high molecular weight, the possibility of continuous sequences of monomers with the same charge may increase, which may cause strong interactions between polymer chains. When fetal bovine serum (FBS) and polyelectrolytes were mixed in phosphate-buffered saline, the hydrodynamic radius and light-scattering intensity increased. There was no interaction between P(AMPS/APTAC50) x and FBS because corresponding increases could not be observed.

Impact of Nano- and Mesoscales on Macroscopic Cation Conductivity in Perfluorinated-Sulfonic-Acid Membranes

A mean-field local-density theory is outlined for ion transport in perfluorinated-sulfonic-acid (PFSA) membranes. A theory of molecular-level interactions predict nanodomain and macroscale conductivity. The effects of solvation, dielectric saturation, dispersion forces, image charge, finite size, and confinement are included in a physically consistent 3D-model domain geometry. Probability-distribution profiles of aqueous cation concentration at the domain-scale are in agreement with atomistic simulations using no explicit fitting parameters. Measured conductivities of lithium-, sodium-, and proton-form membranes with equivalent weights of 1100, 1000, and 825 g/mol(SO3) validate the macroscale predictions using a single-value mesoscopic fitting parameter. Cation electrostatic interactions with pendant sulfonate groups are the largest source of migration resistance at the domain-scale. Tortuosity of ionically conductive domains is the largest source of migration resistance at the macroscale. Our proposed tr...

Mixed conductivity of polythiophene-based ionic polymers under controlled conditions

The mixed conductivity behavior of polythiophene-based anionic and cationic polymers is studied under controlled atmospheres in this contribution. The conjugated polyelectrolytes are based on regioregular polythiophene backbones with either pendant sulfonate anions or imidazolium cations with counterbalancing tetrabutylammonium hexafluorophosphate and bromide anions, respectively. Direct current, four-point-probe measurements and impedance spectroscopy are performed to separate electronic and ionic conductivity. Optical absorption spectroscopy is used to make statements about the aggregation of the polymer chains and to visualize the electronic doping behavior. Similar to a pure conjugated polymer such as poly(3-hexylthiophene) the electronic conductivity can be tuned over a wide range from below 10−6 S/cm to 2.2 S/cm by external doping with the strong electron acceptor F4TCNQ by sequential solution doping. The ionic conductivity on the other hand is shown to be strongly dependent on the degree of water uptake. We show that values of up to 10−2 S/cm with effective ionic mobilities in the order of 10−8-10−7 cm2/(Vs) can be reached.

Missing metal-linker connectivities in a 3-D robust sulfonate-based metal-organic framework for enhanced proton conductivity.

A rare example of a robust, sulfonate-based metal-organic framework (MOF) with a prototypical primitive-cubic topology has been successfully synthesized. Importantly, one-fourth of the metal-ligand connectivities residing in the MOF are missing, resulting in the appearance of coordinatively accessible Cu2+ sites and pendant sulfonate groups. This unprecedented crystal irregularity phenomenon of MOFs substantially enhances their affinity towards water molecules, thus increasing the proton conductivity by two orders of magnitude.

Formation of Polyion Complex (PIC) Micelles and Vesicles with Anionic pH-Responsive Unimer Micelles and Cationic Diblock Copolymers in Water.

A random copolymer (p(A/MaU)) of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and sodium 11-methacrylamidoundecanate (MaU) was prepared via conventional radical polymerization, which formed a unimer micelle under acidic conditions due to intramolecular hydrophobic interactions between the pendant undecanoic acid groups. Under basic conditions, unimer micelles were opened up to an expanded chain conformation by electrostatic repulsion between the pendant sulfonate and undecanoate anions. A cationic diblock copolymer (P163M99) consisting of poly(3-(methacrylamido)propyl)trimethylammonium chloride (PMAPTAC) and hydrophilic polybetaine, 2-(methacryloyloxy)ethylphosphorylcholine (MPC), blocks was prepared via controlled radical polymerization. Mixing of p(A/MaU) and P163M99 in 0.1 M aqueous NaCl under acidic conditions resulted in the formation of spherical polyion complex (PIC) micelles and vesicles, depending on polymer concentration before mixing. Shapes of the PIC micelles and vesicles changed under basic conditions due to collapse of the charge balance between p(A/MaU) and P163M99. The PIC vesicles can incorporate nonionic hydrophilic guest molecules, and the PIC micelles and vesicles can accept hydrophobic guest molecules in the hydrophobic core formed from p(A/MaU).

Facile Doping of Anionic Narrow‐Band‐Gap Conjugated Polyelectrolytes During Dialysis

PCPDTBTSO3 K, an anionic, narrow-band-gap conjugated polyelectrolyte, was found to be doped after dialysis. The proposed doping mechanism involves protonation of the polymer backbone, followed by electron transfer from a neutral chain, to generate radical cations, which are stabilized by the pendant sulfonate anions. Formation of polarons is supported by spectroscopy and electrical-conductivity measurements.

Synthesis and ATRP of novel fluorinated aromatic monomer with pendant sulfonate group

Novel, fluorinated monomer with pendant sulfonate group was synthesized utilizing a two-step derivatization of 2,3,4,5,6-pentafluorostyrene (FS). The first step was a nucleophilic substitution of the fluorine atom in para position by hydroxyl group followed by sulfopropylation. The monomer was polymerized under aqueous ATRP conditions to yield phenyl-fluorinated aromatic homopolymer bearing pendant sulfonates on each repeating unit. Furthermore, this polymer was used as macroinitiator for the ATRP of poly(ethylene glycol) methacrylate. The polymers were characterized by 1H NMR, SEC and FTIR analyses. Their thermal properties were evaluated by differential scanning calorimetry and thermal gravimetric analyses.

(2,2′-Bipyridyl)-3-3′-diol in Nafion: Stabilization of Unusual Ground and Excited States

(2,2'-Bipyridyl)-3-3'-diol (BP(OH)(2)) undergoes excited state intramolecular double proton transfer (ESIDPT). The photophysics of this molecule has been investigated, in the highly acidic water channels inside nafion membrane. The dianionic enolate form of the dye, which is formed only in alkaline conditions in neat aqueous solutions, is found to be present in its excited state in native nafion membrane at low water content. This surprising phenomenon has been explained in the light of loss of protons from the fluorophore to the medium, due to increased electrostatic interactions with the pendant sulfonate groups of nafion, at the lower water content. This observation fortifies the model of microscopic interactions that we have proposed in recent past. Further, the ground state of the diketo form, observed only in neat aqueous solutions so far, is found to be present in Na(+)-exchanged membranes at lower levels of hydration. The steady-state spectral features of the dye is different in (CH(3))(4)N(+)-exchanged membranes than that of Na(+)-exchanged membranes, unlike in our earlier studies with coumarin 102 and 2-(2'-pyridyl)benzimidazole, here we observed formation of an unusual ground state in Na(+)-exchanged membranes, while no such feature was observed in (CH(3))(4)N(+)-exchanged membranes.

Synthesis, and Structural and Thermal Characterizations of Tetrasulfonated Poly(arylene biphenylsulfone ether) Copolymer Ion Conducting Electrolytes

Department of Physical Chemistry, School of Chemistry, Madurai Kamaraj University, Madurai, IndiaReceived September 14, 2011, Accepted September 21, 2011High molecular weight tetrasulfonated poly(arylene biphenylsulfone ether) (TsPBPSEH) copolymers contain-ing up to four pendant sulfonate groups per repeat unit were synthesized via aromatic nucleophilic displacementcondensation from 4,4'-bis(4-chloro-3-sulfonatophenylsulfonyl)biphenyl-2,2'-disulfonate (SBCSBPD), 4,4'-dichlorodiphenylsulfone (DCDPS) and 4,4'-(hexafluoroisopropylidene)diphenol (6F-BPA). The synthesizedcopolymers were structurally characterized using