Ethylene Oxide Spacer Research Articles

Phosphoric acid-doped cross-linked poly(phenylene oxide)-based membranes for high temperature proton exchange membrane fuel cells

In this study, a series of cross-linked poly (phenylene oxide) (PPO)-based membranes with and without rotatable ethylene oxide spacers are prepared. Both PPO-based membranes possess good thermal stability, excellent oxidative stability, and satisfactory dimensional stability in phosphoric acid (PA) owing to their cross-linked structure and PPO backbone. The cross-linked PPO-based membrane with a rotatable ethylene oxide spacer exhibits enhanced conductivity, higher tensile strength, and better oxidative stability compared with that without the rotatable spacer. Owing to a better trade-off effect, the cross-linked membrane with the rotatable ethylene spacer exhibits higher H2/air cell performance (maximum power density, 237 mW cm−2) than that without the rotatable spacer (maximum power density, 144 mW cm−2). The introduction of rotatable spacers is an effective method for enhancing the performance of high-temperature proton exchange membranes.

Novel Pyrrolidinium-Functionalized Styrene-b-ethylene-b-butylene-b-styrene Copolymer Based Anion Exchange Membrane with Flexible Spacers for Water Electrolysis

Anion exchange membranes (AEM) are core components for alkaline electrochemical energy technologies, such as water electrolysis and fuel cells. They are regarded as promising alternatives for proton exchange membranes (PEM) due to the possibility of using platinum group metal (PGM)-free electrocatalysts. However, their chemical stability and conductivity are still of great concern, which is appearing to be a major challenge for developing AEM-based energy systems. Herein, we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as a backbone and pyrrolidinium or piperidinium functional groups tethered on flexible ethylene oxide spacer side-chains (SEBS-Py2O6). This membrane reached 27.8 mS cm-1 hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium-functionalized SEBS reaching up to 10.09 mS cm-1. The SEBS-Py206 combined with PGM-free electrodes in an AWE water electrolysis (AEMWE) cell achieves 520 mA cm-2 at 2 V in 0.1 M KOH and 171 mA cm-2 in ultra-pure water (UPW). This high performance indicates that SEBS-Py2O6 membranes are suitable for application in water electrolysis.

Novel piperidinium-functionalized crosslinked anion exchange membrane with flexible spacers for water electrolysis

Anion Exchange membranes (AEM) are core components for alkaline electrochemical energy technology, such as the AEM water electrolysis and AEM fuel cell. They are regarded as promising alternatives for proton exchange membrane-based systems due to the possibility of using noble metal-free electrocatalyst. However, chemical stability and conductivity of the membrane are still the main challenge of the electrolyzer system. Here in we highlight an AEM with styrene-b-ethylene-b-butylene-b-styrene copolymer (SEBS) as its backbone and piperidinium functioned flexible ethylene oxide spacer structure as its side-chains (SEBS-P2O6). This membrane reached 20.8 mS cm−1 hydroxide ion conductivity at room temperature, which is higher compared to previously obtained piperidinium functionalized SEBS with 10.09 mS cm−1[1]. The SEBS-P206 was measured in a single cell AEM electrolysis cell with platinum group metal (PGM) catalyst. Current densities 275 mA cm−2 and 680 mA cm−2 at 60 °C and 2 V cell potential were achieved in ultra-pure ware (UPW) and 0.1 M KOH, respectively. Remarkably, in UPW the degradation rate was only 140 μA h−1 cm−2, which is the lowest reported up to know.

Gel Polymer Electrolytes Based on Crosslinked Networks by the Introduction of an Ionic Liquid Crosslinker with Ethylene Oxide Arms

The volatility of liquid electrolytes is a major obstacle in the fabrication of efficient lithium-ion batteries that are safe. Solid-state electrolytes such as solid polymer electrolytes have been studied as a potential substitute for liquid electrolytes. However, their practical application is impeded owing to their low ionic conductivity and high interfacial resistance between the electrolyte and electrodes. Herein, we synthesize a novel ionic liquid crosslinker and use thermal crosslinking to prepare a gel polymer electrolyte (GPE), which shows a higher thermal stability than that of liquid electrolytes and a better ionic conductivity than that of solid electrolytes. The crosslinker, IL2, is designed to have a pyrrolidinium-bis(trifluoromethyl sulfonyl)amide structure and an acrylate terminal group with an ethylene oxide spacer connected between them. IL2-GPE, which is prepared by in situ thermal crosslinking, shows an ionic conductivity up to 5.37 mS cm–1 and high thermal and electrochemical stabilities. A cell with IL2-GPE sandwiched between a LiFePO4 cathode and lithium anode exhibits a capacity above 160 mA h g–1 and a high rate capability. By combining a crosslinker having four acrylate terminals with the IL2 crosslinker, we obtain HIL2-GPE, whose ionic conductivity is 20% higher than that of IL2-GPE. The HIL2-GPE cell exhibits capacities of 165 and 146 mA h g–1 at 0.1 and 1.0 C, respectively, thereby demonstrating better performance than that of the cell with IL2-GPE. We also prepared a cell using high-voltage cathode LiNi0.6Co0.2Mn0.2O2 (NCM622). The result suggested that the cell based on the GPEs maintained superior long-term stability even with high-voltage cathode materials over 100 cycles.

Synthesis and application of novel gemini pyridinium ionic liquids as demulsifiers for arabian heavy crude oil emulsions

Ionic liquids (ILs) are environmentally friendly compounds and their gemini types exhibit high thermal stabilities and high surface and interfacial activity. The main objective of this work is to prepare, characterize and investigate the demulsification efficiency of two gemini pyridinium surfactant ILs. They were prepared by the introduction of long chain decanoyl chloride to aminopyridine followed by quaternization with two dichloro spacers containing different ethylene oxide units (DCDE and TEGDC) to form MEGPy and TEGPy ILs, respectively. The structure properties of the prepared demulsifiers were investigated using different spectral tools including 1HNMR and 13CNMR and DLS. Also, their solubility and surface activity were investigated to confirm their ability to reduce surface tension (ST) and interfacial tension (IFT). Gemini pyridinium IL with triethylene oxide spacer (TEGP) showed higher ability to reduce both ST and IFT than that with mono ethylene oxide spacer (MEGP). Thanks to the ability of both TEGPy and MEGPy surfactant IL to reduce ST and IFT, they were applied successfully as demulsifiers for W/O emulsions with different water percentages. Demulsification study indicated that both TEGPy and MEGPy were able to demusify W/O emulsions with high performance which reached to 100% at low concentrations (250 ppm) for some compositions with higher activity to TEGP IL than MEGPy surfactant.

Design of Clickable Ionic Liquid Monomers to Enhance Ionic Conductivity for Main-Chain 1,2,3-Triazolium-Based Poly(Ionic Liquid)s.

A series of clickable α-azide-ω-alkyne ionic liquid (IL) monomers with an ethylene oxide spacer were developed and applied to the synthesis of 1,2,3-triazolium-based poly(ionic liquid)s (TPILs) with high ionic conductivities via one-step thermal azide–alkyne cycloaddition click chemistry. Subsequently, the number of IL moieties in the resultant TPILs was further increased by N-alkylation of the 1,2,3-triazole-based backbones of the TPILs with a quarternizing reagent. This strategy affords the preparation of TPILs having either one or two 1,2,3-triazolium cations with bis(trifluoromethylsulfonyl)imide anions in a monomer unit. Synthesis of the TPILs was confirmed by 1H and 13C NMR spectroscopy and gel permeation chromatography. The effects of the length of the ethylene oxide spacer and the number of IL moieties in the IL monomer unit on the physicochemical properties of the TPILs were characterized by differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy. The introduction of a longer ethylene oxide spacer or an increase in the number of IL moieties in the monomer unit resulted in TPILs with lower glass-transition temperatures and higher ionic conductivities. The highest ionic conductivity achieved in this study was 2.0 × 10–5 S cm–1 at 30 °C. These results suggest that the design of the IL monomer provides the resultant polymer with high chain flexibility and a high IL density, and so it is effective for preparing TPILs with high ionic conductivities.

Mussel-Inspired Electro-Cross-Linking of Enzymes for the Development of Biosensors.

In medical diagnosis and environmental monitoring, enzymatic biosensors are widely applied because of their high sensitivity, potential selectivity, and their possibility of miniaturization/automation. Enzyme immobilization is a critical process in the development of this type of biosensors with the necessity to avoid the denaturation of the enzymes and ensuring their accessibility toward the analyte. Electrodeposition of macromolecules is increasingly considered to be the most suitable method for the design of biosensors. Being simple and attractive, it finely controls the immobilization of enzymes on electrode surfaces, usually by entrapment or adsorption, using an electrical stimulus. Performed manually, enzyme immobilization by cross-linking prevents enzyme leaching and was never done using an electrochemical stimulus. In this work, we present a mussel-inspired electro-cross-linking process using glucose oxidase (GOX) and a homobifunctionalized catechol ethylene oxide spacer as a cross-linker in the presence of ferrocene methanol (FC) acting as a mediator of the buildup. Performed in one pot, the process takes place in three steps: (i) electro-oxidation of FC, by the application of cyclic voltammetry, creating a gradient of ferrocenium (FC+); (ii) oxidation of bis-catechol into a bis-quinone molecule by reaction with the electrogenerated FC+; and (iii) a chemical reaction of bis-quinone with free amino moieties of GOX through Michael addition and a Schiff's base condensation reaction. Employed for the design of a second-generation glucose biosensor using ferrocene methanol (FC) as a mediator, this new enzyme immobilization process presents several advantages. The cross-linked enzymatic film (i) is obtained in a one-pot process with nonmodified GOX, (ii) is strongly linked to the metallic electrode surface thanks to catechol moieties, and (iii) presents no leakage issues. The developed GOX/bis-catechol film shows a good response to glucose with a quite wide linear range from 1.0 to 12.5 mM as well as a good sensitivity (0.66 μA/mM cm2) and a high selectivity to glucose. These films would distinguish between healthy (3.8 and 6.5 mM) and hyperglycemic subjects (>7 mM). Finally, we show that this electro-cross-linking process allows the development of miniaturized biosensors through the functionalization of a single electrode out of a microelectrode array. Elegant and versatile, this electro-cross-linking process can also be used for the development of enzymatic biofuel cells.

Self-aggregation properties of new ester-based gemini surfactants and their rheological behavior in the presence of cosurfactant — monolaurin

A series of new quaternary ammonium gemini surfactants having different ethylene oxide (EO) units as spacer linked with ester functionality have been synthesized and characterized. The self-aggregation and thermodynamic properties of these new gemini surfactants have been investigated in respect to the effect of increasing ethylene oxide spacer units. The critical micelle concentration increases with increase in EO spacer units and other surface properties have been found to be dependent on the length of EO spacer units. Micellar solutions of these surfactants demonstrated greater ability to solubilize a large amount of nonionic amphiphile monolaurin (ML) at 25°C. An addition of ML to the aqueous solutions of these surfactants in a dilute region reduces the micellar curvature to less positive and favors sphere to rod to transient networks (a transparent solution of viscoelastic wormlike micelles). Viscosity increases by three orders of magnitude of that of pure solvent. The rheology study shows that the length of the polar EO spacer units of these surfactants affects the rheology; the maximum viscosity is achieved with gemini surfactant/H2O/ML having single EO unit as spacer and regular decrease in viscosity is observed with increase in EO spacer units for gemini surfactant/H2O/ML system. These systems exhibit viscoelastic behavior described by the Maxwell mechanical model with a single stress relaxation mode.

Synthesis and dilute aqueous solution properties of ester functionalized cationic gemini surfactants having different ethylene oxide units as spacer

New series of ester functionalized quaternary ammonium gemini surfactants having different ethylene oxide units as spacer have been synthesized and investigated for their aggregation behavior and thermodynamic properties of micellization by surface tension, conductivity, and fluorescence methods. The critical micelle concentration (cmc) of these gemini surfactants increases with the increase in the length of polar hydrophilic ethylene oxide spacer. The micellization process has been found to be entropy-driven and dependent on both the tendency of the hydrophobic group of the surfactants to transfer from aqueous environment to interior of micelle as well as the rearrangement of flexible ester-linked ethylene oxide units (hydrophilic spacer) into aqueous phase. The polar ester functional groups and pairs of nonbonding electrons on oxygen atom of ethylene oxide spacer form hydrogen bonding with water molecules enhancing their solubility in aqueous system.

Bioaffinity Sensor Based on Nanoarchitectonic Films: Control of the Specific Adsorption of Proteins through the Dual Role of an Ethylene Oxide Spacer

The identification and quantification of biomarkers or proteins is a real challenge in allowing the early detection of diseases. The functionalization of the biosensor surface has to be properly designed to prevent nonspecific interactions and to detect the biomolecule of interest specifically. A multilayered nanoarchitecture, based on polyelectrolyte multilayers (PEM) and the sequential immobilization of streptavidin and a biotinylated antibody, was elaborated as a promising platform for the label-free sensing of targeted proteins. We choose ovalbumin as an example. Thanks to the versatility of PEM films, the platform was built on two types of sensor surface and was evaluated using both optical- and viscoelastic-based techniques, namely, optical waveguide lightmode spectroscopy and the quartz crystal microbalance, respectively. A library of biotinylated poly(acrylic acids) (PAAs) was synthesized by grafting biotin moieties at different grafting ratios (GR). The biotin moieties were linked to the PAA chains through ethylene oxide (EO) spacers of different lengths. The adsorption of the PAA-EOn-biotin (GR) layer on a PEM precursor film allows tuning the surface density in biotin and thus the streptavidin adsorption mainly through the grafting ratio. The nonspecific adsorption of serum was reduced and even suppressed depending on the length of the EO arms. We showed that to obtain an antifouling polyelectrolyte the grafting of EO9 or EO19 chains at 25% in GR is sufficient. Thus, the spacer has a dual role: ensuring the antifouling property and allowing the accessibility of biotin moieties. Finally, an optimized platform based on the PAA-EO9-biotin (25%)/streptavidin/biotinylated-antibody architecture was built and demonstrated promising performance as interface architecture for bioaffinity sensing of a targeted protein, in our case, ovalbumin.

Synthesis and Lithium Ion Conduction of Polysiloxane Single-Ion Conductors Containing Novel Weak-Binding Borates

Three borate monomers: lithium triphenylstyryl borate (B1), a variant with three ethylene oxides between the vinyl and the borate (B2) and a third with perfluorinated phenyl rings (B3) were synthesized and used to prepare polysiloxane ionomers based on cyclic carbonates via hydrosilylation. B1 ion content variations show maximum 25 °C conductivity at 8 mol %, reflecting a trade-off between carrier density and glass transition temperature (Tg) increase. Ethylene oxide spacers (B2) lower Tg, and increase the dielectric constant, both raising conductivity. Perfluorinating the four phenyl rings (B3) lowers the ion association energy, as anticipated by ab initio estimations. This increases conductivity, a direct result of 3 times higher measured carrier density. The ∼9 kJ/mol activation energy of simultaneously conducting ions is less than half that of ionomers with either sulfonate or bis(trifluoromethanesulfonyl) imide anions, suggesting that ionomers with weak-binding borate anions may provide a pathway to useful single-ion Li+ conductors, if their Tg can be lowered.

Influence of peptide ligand surface density and ethylene oxide spacer arm on the capture of porcine parvovirus.

In previous work, we identified two trimeric peptide ligands (designated WRW and KYY), which bound specifically to porcine parvovirus (PPV) and demonstrated their ability to capture and remove the virus from solutions containing 7.5% human blood plasma. This article examines the influences of peptide density and the presence of an ethylene oxide spacer arm on the efficiency of virus capture using these two ligands. The WRW peptide bound the most virus from plasma solutions at the lowest peptide density tested (0.008 mmol/g dry resin), and binding was enhanced by the presence of the spacer arm. On the other hand, the KYY peptide bound the most viruses at the same low peptide density, but it performed better in the absence of the spacer arm. Of the two, the binding efficiency of the WRW peptide was more sensitive to peptide density and spacer arm presence. These results indicate that low peptide densities enhance binding selectivity, facilitating specific peptide-virus binding even in the presence of plasma proteins which can theoretically bind nonspecifically.

Contribution of 1H NMR to the investigation of the adsorption of cationic Gemini surfactants with oligooxyethylene spacer group onto silica

The present study aims to investigate the behavior of a series of cationic Gemini surfactants with a hydrophilic spacer at liquid–gas and solid–liquid interfaces, with particular emphasis on the effect of spacer length. Gemini surfactants containing two quaternary ammonium groups bound by an ethylene oxide spacer chain, referred to as 12-EO x -12 with x = 1 , 3 , 7 and 12 were synthesized. Surface tension measurements were used to show that the hydrophilic spacer with oxyethylene moieties was not fully extended at the air–water interface. With increasing the spacer group size, it became sufficiently flexible to adopt a particular conformation with a loop at the water side of the interface. A combined study by adsorption isotherm measurements and 1H NMR spectroscopy allowed a detailed description of the adsorption mechanism of these investigated 12-EO x -12 surfactants, with NMR providing more precise information on the conformation of hydrophilic spacer at the solid–liquid interface. Binding to the silica surface involved one cationic headgroup for the surfactants with a short spacer and the two headgroups for the ones with a long spacer. The number of charged surface sites was estimated by considering the dimeric surfactant as a “molecular ruler.” The small density of adsorption sites gave rise to the formation of pinned surface micelles.

Self‐assembly of liquid crystalline triphenylene–oligo(ethylene oxide)–triphenylene molecules and their complexes with lithium triflate

Mesomorphic dimeric molecules consisting of discotic triphenylene rigid units and flexible ethylene oxide spacers have been prepared. The liquid crystalline behaviour is greatly dependent on the length of the ethylene oxide chains. The miscibility and phase behaviour have been examined for mixtures of the materials with lithium triflate.

Synthesis, characterization, and properties of new sequenced poly(ether amide)s based on 2‐(4‐aminophenyl)‐5‐aminobenzimidazole and 2‐(3‐aminophenyl)‐5‐aminobenzimidazole

AbstractA set of new aromatic poly(ether amide)s containing benzimidazole groups and ethylene oxide sequences of different lengths were synthesized and characterized. The new polymers were prepared from two benzimidazole diamines, 2‐(4‐aminophenyl)‐5‐aminobenzimidazole and 2‐(3‐aminophenyl)‐5‐aminobenzimidazole, and various oligo(ethylene oxide)dibenzoyl chlorides. They exhibited good solubility in polar aprotic solvents and glass‐transition temperatures in the range of 125–300 °C (the longer the ethylene oxide spacer was, the lower the glass‐transition temperature was). The new polyamides were essentially amorphous, as observed by X‐ray diffraction measurements and confirmed by differential scanning calorimetry measurements, by means of which no melting endotherm was observed in any case. The decomposition temperatures, as revealed by thermogravimetric analysis in nitrogen, were about 400 °C for all of them, regardless of the length of the ethylene oxide content or the phenylene ring orientation (meta or para) of the diamine moiety. The number of ethylene oxide linkages per repeat unit also determined the water uptake. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1414–1423, 2006

Sequence-Specific Binding of DNA to Liposomes Containing Di-Alkyl Peptide Nucleic Acid (PNA) Amphiphiles

We present a method to covalently attach peptide nucleic acid (PNA) to liposomes by conjugation of PNA peptide to charged amino acids and synthetic di-alkyl lipids ("PNA amphiphile," PNAA) followed by co-extrusion with disteroylphosphatidylcholine (DSPC) and cholesterol. Attachment of four Glu residues and two ethylene oxide spacers to the PNAA was required to confer proper hydration for extrusion and presentation for DNA hybridization. The extent of DNA oligomer binding to 10-mer PNAA liposomes was assessed using capillary zone electrophoresis. Nearly all PNAs on the liposome surface are complexed with a stoichiometric amount of complementary DNA 10-mers after 3-h incubation in pH 8.0 Tris buffer. No binding to PNAA liposomes was observed using DNA 10-mers with a single mismatch. Longer DNA showed a greatly attenuated binding efficiency, likely because of electrostatic repulsion between the PNAA liposome double layer and the DNA backbone. Langmuir isotherms of PNAA:DSPC:chol monolayers indicate miscibility of these components at the compositions used for liposome preparation. PNAA liposomes preserve the high sequence-selectivity of PNAs and emerge as a useful sequence tag for highly sensitive bioanalytical devices.

Linear Rheology of Water-Soluble Reversible Neodymium(III) Coordination Polymers

The rheology of reversible coordination polymer networks in aqueous solution is studied. The polymers are formed by neodymium(III) ions and bifunctional ligands, consisting of two pyridine-2,6-dicarboxylate groups connected at the 4-positions by an ethylene oxide spacer. Neodymium(III) ions can bind three of these terdendate ligand groups. At high concentrations, the polymer networks yield viscoelastic materials, which can be described with the Maxwell model. The scaling of the elastic modulus, relaxation time, and zero-shear viscosity with concentration are in good agreement with the predictions of Cates' model that describes the dynamics of linear equilibrium polymers. This indicates that the networks have only few cross-links and can be described as linear equilibrium polymers. The gels are also thermo-reversible. At high temperatures, fast relaxation was found, resulting in liquidlike behavior. Upon cooling, the viscoelastic properties returned immediately. From the temperature dependence of the relaxation time, an activation energy of 49 kJ/mol was determined for the breaking and reptation of the polymers.

Solution and latex properties of model alkali‐soluble rheology modifiers, synthesized via the reversible addition–fragmentation chain transfer process, and the effects of the ethylene oxide chain length on the rheological properties

AbstractModel alkali‐soluble rheology modifiers were synthesized through the reversible addition–fragmentation chain transfer polymerization of methyl methacrylate, methacrylic acid, and three different associative macromonomers containing 20, 50, and 100 ethylene oxide spacer units, respectively. The synthesized polymers showed well‐controlled molar masses and narrow molar mass distributions. The rheological properties of the model alkali‐soluble rheology modifiers were measured in alkali solutions and in the presence of a well‐characterized core–shell emulsion. The steady‐shear viscosity data for the emulsion solutions, thickened with the associative rheology modifiers, were described by the Carreau model. The rheology modifiers containing the macromonomers with the longest ethylene oxide spacer units produced the highest viscosity in the latex systems but the lowest viscosity in alkali solutions. The highest viscosities in alkali solutions were obtained for the rheology modifiers containing macromonomers with 50 ethylene oxide spacer units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2502–2512, 2004

Effects of Ethylene Oxide Spacer Length on Solution Properties of Water‐Soluble Fluorocarbon‐Containing Hydrophobically Associating Poly (Acrylic Acid‐co‐Rf‐PEG Macromonomer)

AbstractPoly (acrylic acid)s (PAAs) modified with a series of fluorocarbon group (Rf) end‐capped Poly(ethylene glycol) (PEG) macromonomers (number of ethylene oxide unit: 1, 9, 23, 45) and corresponding copolymers without fluorocarbon end groups were synthesized. It was found that the effect of the hydrophobic association of fluorocarbon groups on the solution viscosity prevailed over that of the hydrogen bond between grafted PEG and the backbone. Rheological measurement on the aqueous solutions of these poly (acrylic add‐co‐RrPEG macromonomer)s demonstrated that the best thickening performance was shown when the number of ethylene oxide unit (EO number) was 23.

Rheological Properties of Transient Networks Formed from Copolymers of Sodium Acrylate and Methacrylates Substituted with Amphiphiles: Comparison with Sodium 2-(Acrylamido)-2-methylpropanesulfonate Copolymers

Rheological properties of aqueous solutions of the random copolymer of sodium acrylate (NaAA) and a methacrylate substituted with HO(CH2CH2O)mC12H25 (C12Em), where m = 2, 6, or 25 (DEmMA), were investigated in comparison with those of the random copolymer of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and DEmMA of similar molecular weights focusing on the effect of the length of ethylene oxide (EO) spacer (i.e., the number of m in the DEmMA unit). The pendant C12Em moieties in these copolymers form micelles through intra- and interchain associations, and hence, polymer chains are cross-linked by the micelles, forming a network structure. Steady-shear and oscillatory rheological measurements were performed for the NaAA/DEmMA and NaAMPS/DEmMA copolymers with the DEmMA contents of 12 and 10 mol %, respectively, in 0.1 M NaCl aqueous solutions of pH 10 at varying polymer concentrations (Cp). For the NaAA/DEmMA copolymer, the network was formed more favorably when the EO spacer was shorter whereas the trend was completely opposite in the case of the NaAMPS/DEmMA copolymer. For m = 2, values of plateau modulus (G0) and rheological relaxation time (λ) for the NaAA-based copolymer were larger than those for the NaAMPS-based copolymer by more than 4 and 3 orders of magnitude (at Cp = 40−50 g/L), respectively. The NaAA copolymer of m = 2 exhibited gellike behavior with G0 and λ on the order of 102 Pa and 102 s, respectively (at Cp = 40 g/L), solutions showing shear thinning over the shear rate range studied (10-2−103 s-1). In contrast, solutions of the NaAMPS copolymer of m = 2 were much less viscous with G0 and λ on the order of 10-2 Pa and 10-1 s, respectively (at Cp = 40 g/L). For m = 6, the differences in G0 and λ between the two copolymers decreased to ca. 2 orders and 1 order of magnitude, respectively. When m = 25, however, G0 for the NaAMPS copolymer was found to be larger than that for the NaAA copolymer by more than 1 order of magnitude and λ values for the two copolymers were on the same order of magnitude. These striking differences in the rheological properties between the NaAA-based and NaAMPS-based copolymers were attributed to a much stronger tendency for interchain association in the NaAA-based copolymers.