Fundamental studies on the intermediate layer of a bipolar membrane: Part III. Effect of starburst dendrimer PAMAM on water dissociation at the interface of a bipolar membrane

Starburst dendrimer polyamidoamine (PAMAM) with ellipsoidal or spheroidal shape is structure-regular and has much more amino groups than conventional polymers. This paper investigates the possibility of these amino groups on water dissociation in a bipolar membrane interface. To do this, a bipolar membrane is prepared by casting the solution of sulfonated poly(phenylene oxide) (SPPO) in dimethyl formamide (DMF) on a commercial anion exchange membrane that is immersed in PAMAM aqueous solution in advance. The existence of PAMAM adsorbed on the membrane is proved by X-ray photoelectron spectroscopy (XPS), and the adsorption amount is evaluated by weighting method. The junction thickness of the prepared bipolar membrane is determined by electrochemical impedance spectroscopy (EIS), and the performance is evaluated by current–voltage curves. The experiments show that both the generation and concentration of PAMAM would strongly affect the characteristics of the bipolar membranes. There exists a transitional concentration for various generations PAMAMs to catalyze effectively the water dissociation, and above or below the transitional concentration the performance of bipolar membranes is decreasing. The higher the generation, the lower the concentration. Moreover, at a fixed solution concentration, there is not the simple relation of monotone decreasing or increasing between the performance of bipolar membranes and the generations of PAMAMs. All these can be explained according to the characteristics of PAMAMs combined with available water dissociation theory.     

Fundamental studies on the intermediate layer of a bipolar membrane. Part II. Effect of bovine serum albumin (BSA) on water dissociation at the interface of a bipolar membrane

This paper investigates the behavior of bovine serum albumin (BSA) during water dissociation on a bipolar membrane (BPM). BSA-modified BPM is prepared by immersing polyethylene anion exchange membrane in different concentration solutions of BSA, then casting the solution of sulfonated poly(phenylene oxide) (SPPO) in dimethyl formamide. The modification of BSA was evidenced by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The junction thickness was evaluated by electrochemical impedance spectroscopy (EIS). The results showed that the typical I-V curves for bipolar membranes were heavily affected by the BSA modifications: the more the adsorbed amount of BSA, the larger the potential drop across a bipolar membrane. The new phenomena is underlined by the intrinsic properties of BSA molecules: steric effects give rise to an increase in the thickness of the depletion layer, amphoteric properties weaken the electric field of the junction, and hydrophobicity makes the junction less wet. All of these cause negative effects on water dissociation on a bipolar membrane.     

PEG-catalytic water splitting in the interface of a bipolar membrane

This paper investigates the effect of polyethylene glycol (PEG) on the water dissociation of bipolar membranes. To do this, bipolar membranes were prepared by immersing anion exchange membranes in different-concentration solutions of different-molecular-weight PEGs and then casting the solutions of sulfonated polyphenylene oxide (SPPO) on the anion exchange membranes. All the bipolar membranes with PEG in the interface are evaluated by current-voltage curves. The experimental results prove that PEG has excellent catalytic function for water dissociation. Furthermore, this function is enhanced by both PEG amount (PEG concentration) and PEG molecular weight in the interface of a bipolar membrane.     

超支化聚酯低压纳滤膜的制备与表征

通过超支化聚酯(HPE)末端的羟基与戊二醛(GA)之间的羟醛缩合反应,采用简单的浸涂-交联方法,制备了一种以聚砜超滤膜为支撑层,交联的HPE为活性分离层的复合纳滤膜.采用衰减全反射红外光谱(ATR-FTIR)、接触角测定、扫描电子显微镜(SEM)对纳滤膜的表面化学组成、亲水性和膜形貌进行了表征.考察了HPE溶液浓度、GA溶液浓度对膜分离和渗透性能的影响,优化的HPE和GA溶液浓度分别为9.8 g/L和7.4 g/L,此时在0.4 MPa下膜的水通量达69.6 L/(m2.h),对Na2SO4脱除率为93.2%,表现出低操作压力、高通量、高脱盐率的优异性能.纳滤膜对无机盐的截留顺序为Na2SO4>NaCl>MgSO4>MgCl2,呈现明显的荷负电特征.     

Fundamental studies on the intermediate layer of a bipolar membrane V. Effect of silver halide and its dope in gelatin on water dissociation at the interface of a bipolar membrane

The effect of silver ions on the water dissociation of bipolar membranes was first investigated in this paper. To do this, the bipolar membranes were prepared by immersing the anion exchange layers in an AgNO3 solution and then coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers. XPS and AES observations indicated that silver at the intermediate layer was in the form of AgCl. The experimental results proved that AgCl has an excellent catalytic function for water dissociation in terms of I-V curves, and the quantity of AgCl played an important role in the behavior of a bipolar membrane. The bipolar membranes with gelatin and the gelatin doped with silver as a catalytic layer were also prepared in the same way, and their I-V behavior and the water dissociation pilot tests were also investigated. The experimental results showed that in the case of gelatin alone, the voltage drop increased slightly at high gelatin concentrations, due mainly to the steric effect and electrostatic interaction, but decreased at low gelatin concentrations due to the hydrophilicity. However, when gelatin was doped with AgCl, the bipolar membranes have an appreciable improvement in both stability and catalytic function, in comparison with those prepared from silver or gelatin.     

Correction of pH of diluted solutions of electrolytes by electrodialysis with bipolar membranes

The current efficiencies of the water dissociation water and the voltage-current characteristics of the bipolar (asymmetric bipolar) membranes were measured in a two-chamber electrochemical cell. The cell was formed of an MB-3 bipolar membrane or an asymmetric bipolar membrane, which is an MA-40 heterogeneous membrane with a thin surface layer in the form of a cation-selective homogeneous film and MA-40 and MA-41 heterogeneous monopolar membranes. The dissociation of water on MA-40 in 0.01 M sodium chloride decreased the current efficiency of the acid and alkali both in the channel with a bipolar membrane and in the channel with an asymmetric bipolar membrane. The effective ion transport numbers across MA-40 and MA-41 at different pH values were determined. The water dissociation rate on MA-40 decreased at pH > 9.5. A kinetic model of the electrodialysis of a dilute solution of sodium chloride in a two-chamber unit cell with a bipolar and anionite membranes was suggested.     

Encapsulation and controlled release of a hydrophobic drug using a novel nanoparticle-forming hyperbranched polyester

An amphiphilic, hyperbranched polymer suitable for use in controlled drug delivery is reported. This polymer was obtained by modification of the hyperbranched aliphatic polyester Boltorn H20 (H20) with succinic anhydride and then glycidyl methacrylate, and formed nanoparticles in aqueous solution. The critical association concentration was 7.4 x 10(-3) g . L(-1), as determined by fluorescence spectroscopy using pyrene as a molecular probe. A static/dynamic laser light scattering (LLS) study revealed that the average particle size was 39.4 nm with a low particle size distribution (PDI=0.04), and that each particle was composed of about 350 amphiphilic molecules. Daidzein, a hydrophobic traditional Chinese medicine, was encapsulated during particle formation and the release properties were determined. The optimal feeding concentration of daidzein to hyperbranched polyester was 4.9 x 10(-5) g . mL(-1) to 5.0 x 10(-3) g . mL(-1) with a loading efficiency of 76.1%. In the presence of the enzyme Lipase PS, the drug loaded nanoparticles degraded in a random one-by-one manner and released the drug over a few days. This system is therefore a novel controlled drug release system based on nanoparticles formed of hyperbranched polyester. Encapsulation of daidzein by hyperbranched polyester particles.     

New type of nanofiltration membrane based on crosslinked hyperbranched polymers

Novel nanofiltration (NF) membrane was developed from hydroxyl-ended hyperbranched polyester (HPE) and trimesoyl chloride (TMC) by in situ interfacial polymerization process using ultrafiltration polysulfone membrane as porous support. Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle (CA) measurements were employed to characterize the resulting membranes. The results indicated that the crosslinked hyperbranched polyester produced a uniform, ultra-thin active layer atop polysulfone (PSf) membrane support. FTIR-ATR spectra indicated that TMC reacted sufficiently with HPE. Water permeability and salts rejection of the prepared NF membrane were measured under low trans-membrane pressures. The resulting NF membranes exhibited significantly enhanced water permeability while maintaining high rejection of salts. The salts rejection increase was accompanied with the flux decrease when TMC dosage was increased. The flux and rejection of NF 1 for Na₂SO₄ (1 g/L) reached to 79.1 l/m² h and 85.4% under 0.3 MPa. The results encourage further exploration of NF membrane preparation using hyperbranched polymers (HBPs) as the selective ultra-thin layer.     

Preparation and enhanced properties of poly(propylene)/ silica‐grafted‐hyperbranched polyester nanocomposites

A series of poly(propylene) silica‐grafted‐hyperbranched polyester nanocomposites by grafting the modified hyperbranched polyester (Boltorn? H20), possessing theoretically 50% end carboxylic groups and 50% end hydroxyl groups, which endcapped with octadecyl isocyanate (C19), onto the surface of SiO₂ particles (30 nm) through 3‐glycidoxy‐propyltrimethoxysilane (GPTS) was prepared. The effect of silica‐grafted‐modified Boltorn? H20 on the mechanical properties of polypropylene (PP) was investigated by tensile and impact tests. The morphological structure of impact fracture surface and thermal behavior of the composites were determined by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The melt viscosity of composites was investigated by melt flow index (MFI). The obtained results showed that: (1) the modified Boltorn? H20 was successfully grafted onto the SiO₂ surface confirmed by FT‐IR and X‐ray photoelectron spectroscopy (XPS) analysis; (2) the incorporation of silica‐grafted‐modified Boltorn? H20 (3–5 wt% SiO₂) greatly enhanced the notched impact strength as well the tensile strength of the composites; (3) the incorporation of silica‐grafted‐modified Boltorn? H20 had no influence on the melting temperature and crystallinity of PP phase; (4) the MFI of PP composites increased when the silica‐grafted‐modified Boltorn? H20 particles were added compared with PP/SiO₂ or PP/SiO₂‐GPTS composites. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of a new hyperbranched,vinyl macromonomer through the use of click chemistry: Synthesis and characterization of copolymer hydrogels with PEG diacrylate

A new biodegradable, water‐soluble macromonomer based on the commercial hyperbranched polyester Boltorn^®H20 has been synthesized through the use of click chemistry. The macromonomer was developed with the aim of being injected with a comacromonomer, poly(ethylene glycol) (PEG) diacrylate, for in situ copolymerization to form biodegradable polymer hydrogels. Copolymer hydrogels were prepared from the macromonomer and PEG diacrylate (FW 700) by free radical copolymerization. A degree of phase separation of the hydrogels was observed during polymerization and with increasing incorporation of the Boltorn macromonomer an increasing tendency for the formation of macropores was observed. The swelling ratios of the gels in water and phosphate buffered saline solution, PBS, all increase with increasing Boltorn macromonomer concentration, as did the penetrant diffusion coefficients and the degradation rate in PBS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

超支化聚酯的改性及其结晶性能的研究

用十六酰氯和十八异氰酸酯分别对端羟基的超支化聚酯Boltorn^TMH20改性,可获得粉末状超支化低聚物,具有无定形“内核”及可结晶“外壳”的分子结构.实验结果表明,采用十八异氰酸酯改性的丙烯酸化超支化聚酯的熔点高于十六酰氯改性聚合物.     

Fundamental studies on the intermediate layer of a bipolar membrane part IV. Effect of polyvinyl alcohol (PVA) on water dissociation at the interface of a bipolar membrane

This paper investigates the effect of polyvinyl alcohol (PVA) as the intermediate layer of bipolar membranes on water dissociation. The bipolar membranes are prepared by coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers, which had been immersed in PVA aqueous solutions with different concentrations in advance. The experimental results show that the effect of PVA on water dissociation is significantly affected by its concentration: at low concentration range PVA solution catalyzes water dissociation and at high concentration range PVA solution shows a retardant effect. The phenomenon is different from the situation where polyethylene glycol (PEG) is used as the intermediate layer. Based on the adsorption data and the measurements of X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy, it is found that (1) the effect of PVA concentration on water dissociation can be explained by the competition and compromise of two effects--the catalytic and hydrophilic effect of the PVA molecule and the steric effect of the enlargement of junction thickness; (2) the reason that at high concentration range PVA and PEG show different effects on water dissociation is that the junction thickness is enlarged excessively by PVA, which is based on the intrinsic characteristics of PVA molecules.     

UV curable waterborne polyurethane acrylate dispersions based on hyperbranched aliphatic polyester: effect of molecular structure on physical and thermal properties

A novel waterborne hyperbranched polyurethane acrylate for aqueous dispersions (WHPUDs) based on hydroxy‐functionalized hyperbranched aliphatic polyester Boltorn? H20 was investigated. The effects of structural composition and crosslinking density have been studied in terms of swellability by water, thermal degradation, viscosity changes as well as transmission electron microscopy (TEM) morphology. The swell ratio showed an increasing trend with the higher concentration of ionic group, which is due to the increased total surface area of particles. The results of thermogravimetric analysis (TGA) for cured WHPUD films indicated good thermal stability with no appreciable weight loss until 200°C. The activation energies were evaluated and were found in the range 154–186 kJ mol^?1. It was observed that an increase in hard segment content provoked the increases in thermal degradation temperature and activation energy of waterborne dispersions. The transmission electron photographs revealed that the average particle sizes of aqueous dispersions were in the range 30–125 nm. Owing to the enlargement of the stabilization site, the particle size decreased as the content of carboxyl group and degree of neutralization increased. The viscosity of WHPUDs increased rapidly with increasing the degree of neutralization. Moreover, water showed a favorable viscosity reduction effect. Copyright © 2004 John Wiley & Sons, Ltd.     

An infrared spectroscopic study of H-bond network in hyperbranched polyester polyol

A FTIR study of aliphatic hyperbranched polyester of the fourth generation Boltorn H40 (BH40) is presented. In order to properly assign the main vibrational bands in infrared spectrum temperature measurements, hydration and H/D exchange experiments were performed. Beside these experiments, difference spectroscopy, 2D generalized correlation infrared spectroscopy (2-DGCS) and band fitting procedure were employed to study the main interactions in polymer. On the basis of the detected interactions between various groups the structure of a H-bond network in hyperbranched polyester is proposed. Three main H-bond interactions were detected. Besides CO?HO and HO?HO a third type of H-bond is present (CO?HO?HO). A minor type of interactions represent the hydrogen bond formed with the carboxyl COOH group and impurities, which may be present in lower concentration.     

Structure–property study of waterborne,polyurethane acrylate dispersions based on hyperbranched aliphatic polyester for UV-curable coatings

A series of waterborne, hyperbranched polyurethane acrylates for aqueous dispersions (WHPUDs) based on hydroxy-functionalized hyperbranched aliphatic polyester Boltorn H20 were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR). The aqueous dispersions were electrostatically stabilized with carboxyl groups incorporated into their structures, which were neutralized by triethylamine (TEA). The effects of chemical structures of end groups on various properties of WHPUDs, such as particle size, interfacial tension, and rheological behavior were investigated. The average particle sizes of aqueous dispersions, 43–237 nm, were determined by laser light scattering. Owing to the enlargement of the stabilization site, the particle size decreased as the content of carboxyl group, degree of neutralization, and dielectric constant of the dispersion medium increased. Moreover, the surface tension of aqueous dispersions of WHPUDs decreased as the TEA/COOH mole ratio and degree of neutralization increased. The investigations of the rheological behavior of the WHPUDs suggested that all the dispersions belong to pseudoplastic fluids, and each of them has viscosity much lower compared with the commercial water-based resin EB 2002.     

mCMC-PEG/mCS-PEG双极膜的制备与表征

以Fe3+改性羧甲基纤维素(mCMC)和聚乙二醇(PEG)共混为阳膜;以戊二醛改性壳聚糖(mCS)和聚乙二醇共混为阴膜,制备了mCMC-PEG/mCS-PEG双极膜.以FTIR测定了膜红外光谱,以扫描电镜观察了膜表面和界面层的形态,以TG进行膜的热重分析.测定了mCMC-PEG和mCS-PEG不同比例共混膜的含水率、离子交换容量、溶胀度,及mCMC-PEG/mCS-PEG双极膜的电性能.研究结果表明,在双极膜材料中引入亲水性的聚乙二醇后,因分子间的相容性增大,故而提高了双极膜的离子交换容量,并减小了膜的溶胀性.当CMC∶PEG质量比等于10∶1和CS∶PEG质量比等于2∶1时所制得的双极膜具有良好的电化学性能,在酸碱溶液中机械强度高、溶胀小.     

The dissociation rate of water molecules in systems with cation- and anion-exchange membranes

Within the framework of the mathematical model of Nernst-Planck-Poisson, an attempt is undertaken to theoretically describe the electrodiffusion of ions in the system diffusion layer/monopolar ionexchange membrane, which is accompanied by dissociation of water molecules. The formulas for estimating the current density transferred through a monopolar membrane by hydrogen or hydroxyl ions formed in dissociation of water in the space-charge region are derived. The rate constants and other parameters of dissociation of water molecules in the space-charge region of monopolar membranes under conditions of stabilization of the diffusion layer thickness are calculated. Their comparative analysis with the similar characteristics of bipolar membranes is carried out. For the phosphoric-acid heterogeneous membrane MK-41 in which the polarization conditions in the current density range under study are not so severe and the reaction layer is not being depleted as in the bipolar membrane MB-3 (contains the same phosphoric-acid groups), it is shown that only single-charged phosphoric-acid groups are involved in the water dissociation reaction. For MK-41, the calculated constants of the heterolytic reaction of water molecule dissociation are lower than for the heterogeneous membrane MA-40 containing ternary and quaternary amino groups. It is confirmed that the nature of ionogenic groups in membranes is a factor that determines the rate of water dissociation in systems with ion-exchange membranes.     

Influence of the chemical structure of fluorinated radicals in acrylated derivatives of Boltorn™ H20 hyperbranched polyesterpolyol on the surface energy of coatings prepared from UV-curable powder formulations

The surface and physicomechanical properties of polymeric coatings prepared from UV-curable powder formulations based on oligoester dimethacrylates were studied in relation to the chemical structure of a series of synthesized fluorinated modifiers of new generation, based on Boltorn? H20 hyperbranched polyesterpolyol. The surface energy of the coatings depends on the chemical structure of the derivatives obtained. The fluorinated derivatives of Boltorn? H20 are effective in low concentrations, 0.5–1.0 wt %.     

Study of pH correction process of chloride-bicarbonate dilute solutions by electrodialysis with bipolar membranes

The pH of a dilute chloride-hydrocarbonate solution and the concentrations of chloride ions and carbonic acid anions at the outlet of the alkaline and acid chambers of the electrodialysis cell formed by bipolar and anion-exchange membranes were determined. The decrease in the concentration of hydrocarbonate ions in the alkaline chamber with growth of current density was not equal to its increase in the acid chamber. This disbalance was caused by two concurrent processes: the electromigration ion transport through the anion-exchange membrane and the chemical reactions of hydrocarbonate ions with the water dissociation products formed on the bipolar and anion-exchange membranes. A mathematical model was suggested to describe the electrodialysis correction of the pH of a dilute chloride-hydrocarbonate solution. The experimental data on the correction of pH of the chloride-hydrocarbonate solution were well approximated by both the model that takes into account water dissociation on the anion-exchange membrane and the simplified model that neglects water dissociation. The experimental data agreed well with the results of calculations by the model in which the effective anion transport numbers were calculated only from ion concentrations and diffusion coefficients in solution. This reflects the outer diffusion character of the kinetics of ion transport through the anion-exchange membrane, with pH of dilute solutions corrected by electrodialysis.     

Modeling of hyperbranched polyesters as hosts for the multifunctional bioactive agent Shikonin

We employ fully atomistic molecular dynamics simulations to study in detail the mechanisms involved in the non-covalent association of the bioactive agent Shikonin with the commercially available hyperbranched polyesters (Boltorn?), in ethanol solutions. We examine effects of the (pseudo)generation of the hyperbranched polyester and mimic two different concentrations, under conditions corresponding to excess drug availability. The two mechanisms participating in the polymer/drug complexation are hydrogen bonding and spatial constriction of the drug molecules within the hyperbranched structure. Based on static, as well as on dynamic information obtained by the analysis performed, it is demonstrated that apart from the size of the polyester, factors like the degree of structural flexibility, the intrapolymer hydrogen bonding and the polymer concentration may affect decisively the polyester/shikonin associative behavior, as well as the behavior of the drug-molecules in the solution. The results from the present study offer a detailed picture of the relative importance of those parameters affecting the complexation, and may serve as a basis for the understanding of the behavior of more complex multi-polyester systems.