Anionic Centers Research Articles

High-Efficiency Mono-Cyclopentadienyl Titanium and Rare-Earth Metal Catalysts for the Production of Syndiotactic Polystyrene.

Syndiotactic polystyrene (SPS) refers to a type of thermoplastic material with phenyl substituents that are alternately chirally attached on both sides of an aliphatic macromolecular main chain. Owing to its excellent physical and mechanical properties, as well as its chemical stability, high transparency, and electrical insulation characteristics, SPS is used in a wide variety of technical fields. SPS is commonly produced via the stereoselective transition metal-catalyzed coordination polymerization method mediated by stereospecific catalysts, which consists of anionic mono-cyclopentadienyl derivative η5-coordinated single active metal centers (referred to as "mono-Cp'-M"), with active center metals involving Group 4 transition metals (with an emphasis on titanium) and rare-earth (RE) metals of the periodic table. In this context, the use of mono-cyclopentadienyl titanocene (mono-Cp'Ti) catalysts and mono-cyclopentadienyl rare-earth metal (mono-Cp'RE) metallocene catalysts for the syndiospecific polymerization of styrene is discussed. The effects of the mono-cyclopentadienyl ligand structure, cationic active metal types, and cocatalysts on the activity and syndiospecificity of mono-Cp' metallocene catalysts are briefly surveyed.

Triggering Mixed Cationic‐Anionic Redox in Cu2‐xSe Cathodes via Tailored Charge‐Carrier for High Energy Density Aqueous Zn Batteries

AbstractThe further application of promising transition‐metal chalcogenides (TMCs) cathodes in dilute neutral aqueous Zn batteries (AZBs) is mainly plagued by unsatisfactory working voltages (usually <1 V vs Zn2+/Zn) and their conventional cationic redox centers reaching theoretical capacity limit. Hence, to break the confinement, a novel Zn‐Cu2‐xSe battery is developed in dilute neutral‐aqueous electrolyte by introducing a tailored charge‐carrier, which not only alters the intercalation potential of ions embedded into Cu2‐xSe (vs Zn2+/Zn, working voltage from ≈0.4 to ≈1.2 V) but also activates the anionic redox centers of Cu2‐xSe (capacity release from 143.4 to 323.2 mAh g−1 at 0.4 A g−1). In situ synchrotron X‐ray diffraction (SXRD) and substantial ex situ characterizations reveal the multi‐step phase conversion undergone by cathode and triggered additional Se‐based anionic (Sen2−/Se2−) reversible redox reaction. A multi‐electron synergistic transfer process established on the cationic‐anionic redox centers circumvents the slow relaxation of single‐ion charge compensation achieving high‐capacity and enhanced ion diffusion kinetics. As a result, an extraordinary energy density of up to 406.2 Wh kg−1 at 240 W kg−1 is implemented (calculated based on the mass of Cu2‐xSe cathode), which is ≈8.4 times higher than that of conventional Zn‐Cu2‐xSe batteries, representing an advanced development toward energetic AZBs.

Achieving Synergetic Anion‐Cation Redox Chemistry in Freestanding Amorphous Vanadium Oxysulfide Cathodes toward Ultrafast and Stable Aqueous Zinc‐Ion Batteries

AbstractFlexible aqueous zinc‐ion batteries (AZIBs) with high safety and low cost hold great promise for potential applications in wearable electronics, but the strong electrostatic interaction between Zn2+ and crystalline structures, and the traditional cathodes with single cationic redox center remain stumbling blocks to developing high‐performance AZIBs. Herein, freestanding amorphous vanadium oxysulfide (AVSO) cathodes with abundant defects and auxiliary anionic redox centers are developed via in situ anodic oxidation strategy. The well‐designed amorphous AVSO cathodes demonstrate numerous Zn2+ isotropic pathways and rapid reaction kinetics, performing a high reversible capacity of 538.7 mAhg‐1 and high‐rate capability (237.8 mAhg‐1@40Ag‐1). Experimental results and theoretical simulations reveal that vanadium cations serve as the main redox centers while sulfur anions in AVSO cathode as the supporting redox centers to compensate local electron‐transfer ability of active sites. Significantly, the amorphous structure with sulfur chemistry can tolerate volumetric change upon Zn2+/H+ insertion and weaken electrostatic interaction between Zn2+ and host materials. Consequently, the AVSO composites display alleviated structural degradation and exceptional long‐term cyclability (89.8% retention after 20 000 cycles at 40 Ag‐1). This work can be generally extended to various freestanding amorphous cathode materials of multiple redox reactions, inspiring development of designing ultrafast and long‐life wearable AZIBs.

In-Situ Analysis of Anionic Coordination Polymerizations by Electrospray-Ionization Mass Spectrometry.

Anionic coordination polymerizations proceed via highly reactive intermediates, whose in situ analysis has remained difficult. Here, we show that electrospray-ionization mass spectrometry is a promising method to obtain detailed information on the polymerization process. Focusing on polymerization reactions of 1,3-dienes initiated by CoCl2 /RLi (R=Me, nBu, tBu, Ph), we directly observe the growing polymer chains and characterize the active anionic cobalt centers by gas-phase fragmentation experiments. On the basis of these results, we suggest a plausible mechanism for the polymerization reaction. Moreover, the ESI mass spectra permit the determination of molecular weight distributions, which are in good agreement with those derived from NMR-spectroscopic as well as MALDI mass-spectrometric measurements, and afford a wealth of kinetic data.

Ionic Liquid Crystals As Solid Organic Electrolytes for Li-Ion Batteries: Experiments and Modeling

The development of the new electrolytes is essential to increase the energy density of the Li-ion batteries (LIBs)1. Solid electrolytes have attracted the interest of researchers as a next-generation electrolyte for LIBs due to their superior physical and chemical stability, large working potential windows, high transference number, and intrinsic safety2 3.In this study, we have designed and synthesized novel organic electrolytes for LIBs with a naphthalene mesogenic moiety bearing a lithium sulfonate group connected to two flexible long-alkyl chains. Starting from the lithium 4-aminonaphthalene-1-sulphonate building block, alkyl-tails were successfully doubly grafted on the amine function with N, N-di-isopropylethylamine in N, N-di-methylformamide. Once the reaction was completed, a washing, purification and neutralization step was carried out to obtain the desired product. Those electrolytes have been synthesized with 95 % purity as suggested from the NMR and mass spectrum. The chains length were differ by the number of alkyl groups in the chains from 8, 12, and 16, namely lithium 4 - (dioctylamino) naphthalene – 1 – sulfonate (BS-Li-8), lithium 4 - (didodecylamino) naphthalene – 1 - sulfonate (BS-Li-12), and lithium 4 - (dihexadecylamino) naphthalene – 1 – sulfonate (BS-Li-16). We have employed molecular dynamics simulations and various experimental techniques for a comprehensive understanding of the bulk structure and transport mechanism of those electrolytes. Simulated static structural factor, radial distribution functions, and experimental small angle x-ray scattering spectrum suggest that degree of aggregation, ionic correlations, and structural properties of materials at the nanoscale of the electrolyte molecules varies with the length of the alkyl chains. The Li+ ion mobility calculated from experimental Electrochemical Impedance Spectra, using a symmetrical cell with blocking electrodes and molecular dynamics simulations reveal that BS-Li-12 is the most conductive (approximately 10-3 S / cm at 1400 C) owing to the weaker cation-anion correlation than others. It was observed that the conductivity of the Li+ ions is directly related to the coordination number between Li+ and anionic centers, since, in BS-Li-12, Li+ coordinates with two anionic centers while for others, it is three. During the conduction, Li+ move from one anionic site to another by changing their coordination number with anion.We successfully synthesized next-generation organic electrolytes with well-organized Li+ conduction channels. The comprehensive study of the influence of the nonpolar alkyl chain on the bulk structural arrangement and conductivity of such electrolytes will contribute significantly to the development of future LIBs electrolytes.

Cover Picture

The cover picture displays two different copolymerizations of ε‐caprolactone (CL) with 1,3‐dioxolane (DO) catalyzed by rare earth triflates. The panda represents Janus polymerization which yields multiblock copolymers of CL and DO, while the red panda represents cationic copolymerization which yields random copolymers. Janus polymerization combines anionic and cationic polymerizations on the two ends of a single propagating chain, followed by a self‐triggered polycondensation of anionic and cationic centers. The mechanism of copolymerization is determined by the element of rare earth in catalyst and the presence or absence of an epoxide initiator. More details are given in the article by Ling et al. on page 705—712. image

Single-atom catalysts with anionic metal centers: Promising electrocatalysts for the oxygen reduction reaction and beyond

Ongoing efforts to develop single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) typically focus on SACs with cationic metal centers, while SACs with anionic metal centers (anionic SACs) have been generally neglected. However, anionic SACs may offer excellent active sites for ORR, since anionic metal centers could facilitate the activation of O2 by back donating electrons to the antibonding orbitals of O2. In this work, we propose a simple guideline for designing anionic SACs: the metal centers should have larger electronegativity than the surrounding atoms in the substrate on which the metal atoms are supported. By means of density functional theory (DFT) simulations, we identified 13 anionic metal centers (Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au, and Hg) dispersed on pristine or defective antimonene substrates as new anionic SACs, among which anionic Au and Co metal centers exhibit limiting potentials comparable to, or even better than, conventional Pt-based catalysts towards ORR. We also found that anionic Os and Re metal centers on the defective antimonene can electrochemically catalyze the nitrogen reduction reaction (NRR) with a limiting potential close to that of stepped Ru(0001). Overall, our work shows promise towards the rational design of anionic SACs and their utility for applications as electrocatalysts for ORR and other important electrochemical reactions.

Amorphous Redox-Rich Polysulfides for Mg Cathodes.

The lack of appropriate cathodes is restraining the advances of Mg batteries. Crystalline cathode materials suffer from sluggish reaction kinetics and low-capacity delivery. The finite type of crystalline structure further confines the rational design of cathode materials. Herein, we proposed amorphization and anion enrichment as a brand-new strategy to not only enhance the solid-state ion diffusion and provide more ion-storage sites in amorphous structure but also contribute to the local transfer of multiple electrons through the additional anionic redox centers. Accordingly, a series of amorphous titanium polysulfides (a-TiSx, x = 2, 3, and 4) were designed, which significantly outperformed their crystalline counterparts and achieved a highly competitive energy density of ∼260 Wh/kg. The unique Mg2+ storage mechanism involves the dissociation/formation of S–S bonds and changes in the coordination number of Ti, namely, a mixture of conversion and intercalation reaction, accompanied by the joint cationic (Ti) and anionic (S) redox-rich chemistry. Our proposed amorphous and redox-rich design philosophy might provide an innovative direction for developing high-performance cathode materials for multivalent-ion batteries.

Methane to Methanol Conversion Facilitated by Anionic Transition Metal Centers: The Case of Fe, Ni, Pd, and Pt.

Density functional theory and high-level ab initio electronic structure calculations are performed to study the mechanism of the partial oxidation of methane to methanol facilitated by the titled anionic transition metal atoms. The energy landscape for the overall reaction M- + N2O + CH4 → M- + N2 + CH3OH (M = Fe, Ni, Pd, Pt) is constructed for different reaction pathways for all four metals. The comparison with earlier experimental and theoretical results for cationic centers demonstrates the better performance of the metal anions. The main advantage is that anionic centers interact weakly with the produced methanol. This fact facilitates the fast removal of methanol from the catalytic center and prevents the overoxidation of methane. Moreover, a moderate or high energy barrier for the M- + CH4 → HMCH3- reaction step is observed, which protects the metal center from deactivation. Future work should focus on the identification of proper ligands, which stabilize the negative charge on the metal (electronic factors) and prevent the formation of the global CH3MOH- minimum (steric factors). Finally, a composite electronic structure method (combining size extensive coupled clusters approaches and accurate multireference configuration interaction) is proposed for computationally demanding systems and is applied to Fe-.

Tris(trichlorosilyl)tetrelide Anions and a Comparative Study of Their Donor Qualities.

Trichlorosilylated tetrelides [(Cl3 Si)3 E]- have been prepared by adding 1 equiv of a soluble Cl- salt to (Cl3 Si)4 Si (E=Si) or 4 Si2 Cl6 /GeCl4 (E=Ge). To assess their donor qualities, the anions [(Cl3 Si)3 E]- (E=C, Si, Ge) have been treated with BCl3 , AlCl3 , and GaCl3 . Both BCl3 and GaCl3 give 1:1 adducts with the anionic centers. AlCl3 leads to Cl- abstraction from [(Cl3 Si)3 E]- with formation of (Cl3 Si)4 E (E=Si or Ge). (Cl3 Si)4 Ge is cleanly converted to the perhydrogenated (H3 Si)4 Ge by use of Li[AlH4 ]. Another case of Cl- abstraction was observed for [(Cl3 Si)3 Ge⋅GaCl3 ]- , which reacts with GaCl3 to afford the neutral dimer [(Cl3 Si)3 Ge-GaCl2 ]2 .

Time-resolved photoluminescence of pH-sensitive carbon dots

Time-resolved photoluminescence emission were performed to study the ≥100 ps time-scale photophysics of water soluble carbon dots (CDs) dispersed in different pH solutions. Excitation of the core and high-energy edge states at excitation wavelengths λex ≤ 350 nm produce hole-electron excitonic charge-carriers but do not yield any photoluminescence emission, implying efficient non-radiative recombination mechanisms for the charge-carriers. Using λex ∼375 nm, surface fluorophores as well as low-lying edge-states are excited, producing emission over a broad range. However, the emission characteristics vary strongly depending on the pH condition and the choice of excitation wavelength. In particular, the edge state emission is abruptly extinguished at pH ≥ 5, which also marks the onset of deprotonation of surface-bound -COOH groups of the CDs, indicating that the -COO- anionic centers promote quenching of edge-state emission. Using λex ∼450 nm, only the surface fluorophores are excited. The deprotonation of phenolic -OH group at pH > 9 causes a sharp red-shift in the emission spectra at all excitation wavelengths. The pH-sensitive emission behavior of the CDs enable them to serve as optical pH sensors.

Macrocycle-Encircled Polynuclear Metal Clusters: Controllable Synthesis, Reactivity Studies, and Applications.

Macrocyclic ligands have been extensively applied to recognize single metal ions with high selectivity and good affinity based on the size-match principle. The resulting metal-macrocycle complexes play a significant role in mimicking the function of natural metal ion carriers and understanding and reproducing the catalytic activity of metalloenzymes. Because of the known macrocyclic effect, those single metal-macrocycle adducts often show an enhanced kinetic and thermodynamic stability in comparison with their open-chain analogues. By virtue of such extraordinary coordination properties of macrocyclic ligands, it is expected that larger macrocycles with multiple coordination sites could properly act as an outer scaffold to direct the formation of multiatom species inside, such as polynuclear metal cluster aggregates, whose assembly may largely depend on the template positioning of coordinative atoms in the macrocyclic ring. Thus, the employment of polydentate macrocyclic ligands may provide a convenient tool to access polynuclear metal clusters in a controllable way. In this Account, we review our studies of the metal ion binding process of a class of polydentate macrocyclic ligands, azacalixpyridines (Py[ n]s), and the application of Py[ n]s as an outer template to direct the controllable synthesis of polynuclear metal clusters. Our investigations revealed that Py[ n]s show a significant cooperative coordination effect in the metal ion binding process that facilitated the easy formation of a polymetallic assembled structure. Taking advantage of the cooperative coordination effect and the tunable and highly fluxional conformation of Py[ n]s, we laid our focus on control of the nuclearity number by tuning the size of Py[ n]s and the adoption of Py[ n]s with different anionic centers in metal cluster synthesis. As an important example for application, this new established macrocycle-directed method has been employed to achieve a variety of metal-cluster-centered capsule, rotaxane, catenane, polygon, and other supramolecular assemblies. Furthermore, a cluster-to-cluster transformation inside the cavity of Py[ n]s is presented to showcase the use of the acquired metal cluster-macrocycle complexes to achieve unconventional metal cluster entities. With regard to the application of the newly synthesized macrocycle-encircled metal clusters, examples of the fabrication of functional materials and catalysts are presented. With the assistance of Py[ n]s, a bulk-to-cluster-to-nanoparticle transformation of silver sulfide (Ag2S) and silver halides (AgX) has been conducted to produce a series of nonstoichiometric silver sulfide and halide nanoparticles. The resulting Ag-S nanoparticle material with a high Ag/S ratio, which is inherited from the Py[ n]-protected polysilver sulfide clusters, has a large energy gap relative to conventional Ag2S nanoparticles. Moreover, the nonstoichiometric silver halide nanoparticles can act as a new kind of electrocatalyst for the chlorine evolution reaction, showing excellent selectivity and high catalytic efficiency. Overall, in this Account we try to highlight the application of polydentate macrocycles as an outer template to guide the synthesis of polynuclear metal clusters in a controllable manner. This unique synthesis will provide a new avenue to access unconventional metal clusters of different metal kinds and diverse anionic centers, which are expected to have promising and significant applications in many interdisciplinary areas of chemistry.

Making a triple negative

Organic Chemistry The trifluoromethanesulfonyl (Tf) group is remarkably adept at stabilizing negative charge: It boasts highly withdrawing fluorines and sulfur-oxygen bonds that can delocalize electrons through resonance. Hofler et al. took full advantage of these properties in generating a molecule with three independent anionic carbon centers. The synthetic reaction coupled triformylmethane with three equivalents of Tf2CH2, after which a base deprotonated all three Tf-substituted carbon centers. The compound was characterized by crystallography and showed trigonal-planar geometries at each charged carbon. Angew. Chem. Int. Ed. 10.1002/anie.201803647 (2018).

Efficient Removal of Pb2+ from Aqueous Solution by an Ionic Covalent–Organic Framework: Molecular Simulation Study

An ionic covalent–organic framework (ICOF-1 containing sp3 hybridized boron anionic centers formed by spiroborate linkage and dimethylammonium ions) is explored as an ion exchanger for the removal of lead (Pb2+) ions from aqueous solution. From molecular simulations, the Pb2+ ions are observed to exchange with the nonframework DMA+ ions in the ICOF-1. At a concentration of 600 ppm, the Pb2+ ions are completely exchanged and reside in the ICOF-1, while the DMA+ ions are in a dynamic equilibrium with the solution. It is revealed that the exchange between Pb2+ and DMA+ is governed by the stronger attraction of Pb2+ with the negatively charged ICOF-1 framework. The radial distribution functions and mean-squared displacements further show that the exchanged Pb2+ ions are in a closer proximity to the ICOF-1 framework with a smaller mobility than DMA+ ions. The simulation study provides microscopic insight into the ion-exchange process between Pb2+ and DMA+, and it suggests that the ICOF-1 might be an intriguing...

Zinc(II) and cadmium(II) coordination polymers containing phenylenediacetate and 4,4′-azobis(pyridine) ligands: Syntheses, structures, dye adsorption properties and molecular dynamics simulations

Two new coordination polymers (CPs) – [Zn(µ4-ppda)(µ-abpy)0.5]n(1) and [Cd(μ3-opda)(µ-abpy)0.5(H2O)]n(2) (o/ppda = 1,2/1,4-phenylenediacetate, abpy = 4,4′-azobis(pyridine)) – have been synthesized by using Zn(II)/Cd(II) salts in the presence of o- and p-phenylenediacetic acid and abpy under hydrothermal conditions. Their structures have been characterized by FT-IR spectroscopy, elemental analysis, X-ray powder diffraction and single crystal X-ray diffraction techniques. The structural diversities were observed depending on anionic ligands and metal centers in the synthesized complexes. Complex 1 consists of a 2-fold interpenetrated 3D+3D→3D framework with pcu topology while complex 2 has a 2D structure with sql topology. The adsorption of methylene blue (MB) was studied to examine the potential of the title CPs for removal of dyes from aqueous solution. Molecular dynamics (MD) simulations were also performed to examine diffusion of MB in 1 and 2. Thermal and optical properties of two complexes were also discussed.

Influence of the interaction of calcium carbonate particles with surfactants on the degree of water pollution in small rivers

IntroductionThe influence of the interaction of calcium carbonate (CaCO3) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed.ResultsLaboratory simulations indicate reduced negative influences on cationic SAS nitrification/self-purification processes in the presence of anionic species. This suggests the role of complex ionic formation [anionic SAS * cationic SAS] as a cause of this effect. UV-Vis spectra of lauryl sulfate (LS) and of cetyltrimethylammonium (CTMA), as well as of their mixtures in ratios of 2:1 and 1:1, treated by fine particles of CaCO3, display decreased amounts of SAS in analyzed solutions and their presence on the surface of CaCO3 nanoparticles. UV-Vis spectra reveal the decomposition of the complex [anionic SAS (SAS-An) * cationic SAS (SAS-Ct)] in solutions when CaCO3 is added. CTMA can be bonded by LS through hydrophobic chains, on the surface of CaCO3 particles. Therefore, CaCO3 modifies the nature of LS and CTMA interactions. This leads to an increased degree of toxicity of cationic SAS in aquatic environment. The amounts of CTMA in aqueous solutions are diminished in the presence of ammonium ion NH4+ (2 mg/L). In the presence of two orders higher concentration of ammonium ion, this effect strongly increases, making the association obvious. The structure of cationic SAS does not influence this effect. The obtained results have been confirmed both by timed natural aquatic sample analysis and laboratory simulations using water from Moldovan small rivers (Isnovat, Raut, and Bic).ConclusionsUV-Vis spectra and laboratory simulations demonstrate the change due to the addition of calcium carbonate. Simulations and laboratory tests of water samples from Isnovat, Bic, and Raut Rivers, establish the cationic SAS negative influence on treatment and self-purification processes.

Ionic Covalent Organic Frameworks with Spiroborate Linkage

AbstractA novel type of ionic covalent organic framework (ICOF), which contains sp3 hybridized boron anionic centers and tunable countercations, was constructed by formation of spiroborate linkages. These ICOFs exhibit high BET surface areas up to 1259 m2 g−1 and adsorb a significant amount of H2 (up to 3.11 wt %, 77 K, 1 bar) and CH4 (up to 4.62 wt %, 273 K, 1 bar). Importantly, the materials show good thermal stabilities and excellent resistance to hydrolysis, remaining nearly intact when immersed in water or basic solution for two days. The presence of permanently immobilized ion centers in ICOFs enables the transportation of lithium ions with room‐temperature lithium‐ion conductivity of 3.05×10−5 S cm−1 and an average Li+ transference number value of 0.80±0.02. Our approach thus provides a convenient route to highly stable COFs with ionic linkages, which can potentially serve as absorbents for alternative energy sources such as H2, CH4, and also as solid lithium electrolytes/separators for the next‐generation lithium batteries.

Ionic Covalent Organic Frameworks with Spiroborate Linkage.

A novel type of ionic covalent organic framework (ICOF), which contains sp(3) hybridized boron anionic centers and tunable countercations, was constructed by formation of spiroborate linkages. These ICOFs exhibit high BET surface areas up to 1259 m(2) g(-1) and adsorb a significant amount of H2 (up to 3.11 wt %, 77 K, 1 bar) and CH4 (up to 4.62 wt %, 273 K, 1 bar). Importantly, the materials show good thermal stabilities and excellent resistance to hydrolysis, remaining nearly intact when immersed in water or basic solution for two days. The presence of permanently immobilized ion centers in ICOFs enables the transportation of lithium ions with room-temperature lithium-ion conductivity of 3.05×10(-5) S cm(-1) and an average Li(+) transference number value of 0.80±0.02. Our approach thus provides a convenient route to highly stable COFs with ionic linkages, which can potentially serve as absorbents for alternative energy sources such as H2, CH4, and also as solid lithium electrolytes/separators for the next-generation lithium batteries.

Mechanism of protodesorption—exchange of heavy metal cations for protons in a heterophase system of H2O–H2SO4–MSO4—cellulose sorbent

The influence of pH on the distribution of metal cations [Cd(II), Cu(II), Fe(II), Ni(II), Zn(II)] in a four-component heterophase system (H2O–H2SO4–MSO4–cellulose sorbent) was studied. Protodesorption of metal cations was studied with indicator and constant quantities of [MSO4] salts and constant solvent–sorbent ratio. Linear dependence lgКDМ2+=f(рН) with tgα=1/2 of the КDМ2+ metal ions distribution coefficients from the acidity of the aqueous phase is observed in logarithmic coordinates. Depression of the exponent corresponding to proton involvement in protodesorption from 2 (theory) to 0.5 (experiment) indicates that anions of the aqueous phase are involved in the process of exchange of metal cation for proton on the anionic centers of the sorbent, which corresponds to participation of the salt and acid components of the system in molecular non-dissociated form in an equivalent proportion H2SO4/MSO4=1/1.Different behavior of the salt and acid components in ion exchange of cations for cations and cations for protons is due to the differences in the constraint coefficients of their molecular and ionic forms which must be taken into consideration in equations describing thermodynamics of the interphase exchange.

Synthesis, characterization and properties of waterborne polyurethanes based on two different ionic centers

Two different series of waterborne polyurethanes based on anionic centers: dimethylol propionic acid (DMPA) and N,N-bis(2-hydroxy ethyl)-2-aminoethane sulfonic acid sodium salt (BES sodium salt) were prepared from hydrogenated MDI (H MDI), poly(e-caprolactone), and 1,4-butanediol (BDO). The BES-based dispersions showed a smaller average particle size, and higher viscosity in comparison to the DMPA-based series. Furthermore, the tensile strength, thermal stability, and modulus of the polyurethane films for the BES ionic center were higher than the DMPA-based films. These were due to the higher activity and more powerful degree of dissociation and electrostatic interaction of -SO Na groups in comparison to the quaternary ammonium carboxylate groups of the neutralized DMPA.