Swelling of ferrogels of poly(acrylic acid) with ferric oxide nanoparticles stabilized by chitosan

The processes of swelling of poly(acrylic acid) ferrogels prepared via radical polymerization in an aqueous suspension of ferric oxide nanoparticles with the weighted average size of 23.5 nm obtained by laser evaporation method and stabilized by chitosan (М = 5.3 × 10⁵ and degree of deacetylation of 62%) are studied. The swelling of washed ferrogels depends on the content of chitosan and decreases abruptly at a polymer concentration exceeding 1 g/L. At a chitosan concentration above 1 g/L, the chemical network of poly(acrylic acid) is formed on the fluctuation network of chitosan in solution. As pH increases, these ferrogels are contracted owing to formation of an interpolymer complex of chitosan with poly(acrylic acid) subchains.     

Characterization of stimuli-sensitive polymers for biomedical applications

Stimuli-sensitive polymers were synthesized by copolymerizing varying ratios of N-isopropyl acrylamide(NIPAAm) and acrylic acid(AAc). The influence of polyelectrolytes on the lower critical solution temperatures(LCSTs) of these temperature/pH sensitive polymers was investigated in the pH range of 2-12. Polyelectrolyte complexes were prepared by mixing poly(NIPAAm-co-AAc) as anionic polyelectrolyte with poly(allyl amine)(PAA) or poly(L-lysine)(PLL) as cationic polyelectrolytes, respectively. Back titration was performed to determine the pK_a values of PAAc in poly(NIPAAm-co-AAc) and to study the effect of comonomer ionization on the cloud point temperature. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). The swelling ratio of poly(NIPAAm-co-AAc) hydrogels as a function of pH at various temperature was obtained by measuring the weight of the hydrogels in buffer solutions. The LCSTs of the poly(NIPAAm-co-AAc) were strongly affected by pH, polyelectrolyte solutes, AAc content, and charge density. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm/water in the copolymer was stronger than that of poly(allyl amine)(PAA). Indomethacin was loaded into these hydrogels, and controlled release of this molecule from the hydrogel was determined under various temperature and pH conditions using UV/Vis spectrophotometry.     

改性壳聚精膜用于醇水混合液分离的研究──Ⅲ．超细粉末填充壳聚精膜

首次制备了用Ｓｉ３Ｎ４，ＳｉＯ２，ＴｉＨ４超细粉末填充的改性壳聚精膜，并将其用于乙醇／水混合液的分离中。实验表明壳聚糖膜经超细粉末填充后强度增大，溶胀度减小。用于乙醇／水混合液渗透蒸发分离时，分离因子和渗透通量都有提高，并在填充量为１６．７％附近出现极大值。随着料液中乙醇含量的增大，渗透通量减小，分离因子增大；随着料液温度的升高渗透通量显著增大，分离因子则稍有下降。并简单讨论了超细粉末在乙醇／水混合液分离中的作用。     

丙烯酸交联壳聚糖渗透汽化膜研究（Ⅰ）——膜结构及交联机理

报道了一种新型渗透汽化膜－－丙烯酸交联壳聚糖膜，通过溶胀、拉伸、渗透汽化分离以及红外光谱等手段研究了膜的结构和交联机理。实验结果表明，交联反应由两部分组成：丙烯酸的双键和壳聚糖的氨基的加成反应和丙烯酸另一端的羧基和壳聚糖的氨基的酸碱中和反应。     

N,N,N-trimethylchitosan iodide complexes with a weak or a strong polyacid and nanoparticles thereof

Polyelectrolyte complexes (PECs) were prepared from N,N,N-trimethylchitosan iodide (TMCh) of different molar mass and a weak polyacid-poly(acrylic acid) (PAA) or a strong polyacid-poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The quaternization of the amino groups of chitosan enabled the formation of water-insoluble PECs in a broad pH range—from 3 to 12 and from 1 to 12 for TMCh/PAA and TMCh/PAMPS, respectively. Whereas the stoichiometry of the TMCh/PAA complex was pH dependant, the stoichiometry of the TMCh/PAMPS complex did not depend on pH. The stoichiometry and the yield of the complexes were influenced by the molar mass of TMCh. PEC nanoparticles were produced by mixing dilute solutions of the oppositely charged polyelectrolytes as revealed by dynamic light scattering analyses. The size of the particles was in the range of 135–924 nm and depended on the polyelectrolyte molar mass, the initial polyelectrolyte concentration, and the molar fraction of the TMCh units. Microbiological screening against Staphylococcus aureus and Escherichia coli revealed that PECs between TMCh and PAA or PAMPS have a good antibacterial effect, which is more slowly pronounced than that of the starting TMCh of different molar mass.     

Design of composite films and ultrathin membranes of interpolymer complexes

The formation of stoichiometric interpolymer complexes (IPCs) between the poly(vinyl ether) of ethyleneglycol and the copolymer of acrylic acid–butyl vinyl ether, between copolymers of vinyl ether of ethyleneglycol–butyl vinyl ether, and the copolymer of acrylic acid–vinylbutyl ether is demonstrated by conductimetric, potentiometric, viscometric and spectroturbidimetric methods in aqueous solution. The swelling/deswelling behavior of composite films derived from the IPC has been studied in water, alcohol and water–alcohol mixtures, depending on various factors. The formation of polyelectrolyte complexes (PECs) between the copolymer of acrylic acid–vinyl butyl ether and poly(vinyl ether of monoethanolamine) on a dimeric interface of water–butanol has been studied by the potentiometric method. The kinetics of PEC formation on a dimeric interface was measured and the activation energy of this process was calculated. Copyright © 2000 John Wiley & Sons, Ltd.     

Use of polyelectrolyte multilayer systems for membrane modification

Membranes with designed surface and filtration properties were prepared by the adsorption of polyelectrolyte multilayer systems on membrane surfaces using the layer-by-layer electrostatic self assembly (ESA) technique. Microfiltration membranes with a first polyelectrolyte layer grafted onto the surface showed excellent stability during filtration process. Although a twofold higher permeate flux was observed for a three-layer polyelectrolyte complex membrane compared to a just grafted one the protein retention did not change remarkably. Additionally, a reduced protein adsorption was detected for repulsive electrostatic forces between the substrate and the protein under applied conditions. Pervaporation membranes with an anionically functionalized polyamide-6 support or Nafion^®-117 support and a dense separating layer consisting of poly(acrylic acid) and poly(ethylenimine) were prepared. Those membranes were used to separate aqueous organic mixtures. Six double layers were sufficient to obtain membranes with high water permselectivity. Membranes with similar properties but a lower number of deposited layers were obtained, when the adsorption process was carried out at 80°C.     

Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

The rheological properties of aqueous solutions of poly(acrylic acid), poly(diallyldimethyldiammonium chloride), and their mixtures at 25°C have been studied. The concentrated solutions of the mixtures contain 18 wt % of both polymers taken at different ratios. The ratio of cationogenic and anionogenic groups φ varied from 0 to 0.4 is taken as a criterion for selection of mixture composition. An increase in φ, reflecting a more intense formation of polyelectrolyte complexes in solution, is accompanied by a significant rise in the low-frequency loss modulus and, especially, in the storage modulus, as well as by an increase in viscosity over the entire studied range of shear rates. This behavior may be explained by the presence of an additional spatial structure with junctions formed by interacting complementary charged groups. In the general case, the formation of poly(acrylic acid)-poly(diallyldimethyldiammonium chloride) polyelectrolyte complexes is said to take place in solution. The excess of rheological characteristics of mixture solutions over the corresponding characteristics of poly(acrylic acid) solutions is found to be the power function of parameter φ. The additional spatial network derived from polyelectrolyte complexes and occurring in solution is destroyed at lower shear stresses than is the network of intermolecular entanglements. At high shear stresses, orientational effects may cause phase separation of the systems owing to a change in the hydrophilic-hydrophobic balance between complexes of poly(acrylic acid) with poly(diallyldimethyldiammonium chloride) and water.     

Studies on the interaction of poly(4-vinylpyridiniumchloride) with poly(sodiumphosphate) in an aqueous solution by conductometry

A reaction between poly(4-vinylpyridiniumchloride) and poly(sodiumphosphate) in the presence and absence of NaCl and NaBr salts was studied in aqueous solution by conductometry. The interaction of polycation and polyanion gave insoluble polyelectrolyte complex which contained polycation and polyanion in unit mole ratio in a salt-free solution. A deviation from stoichiometry was observed at high polyion concentration and in the presence of NaCl and NaBr salts. The resultant complex showed swelling property in different solvent mixtures. A maximum degree of swelling was obtained in the solvent mixture of NaBr + water and NaBr + water + acetone. Furthermore, polyelectrolyte complex sorbed salts from aqueous electrolyte solutions. The sorption of salts increased with increasing salt concentration. © 1996 John Wiley & Sons, Inc.     

pH-sensitive nanostructured architectures based on synthetic and/or natural weak polyelectrolytes

This study aims to evidence the influence of polyelectrolytes structure and the number of double layers on the properties of some new nanostructured architectures formed by layer-by-layer self-assembly of complementary weak polyelectrolytes on planar surfaces. For this purpose, we used chitosan and poly(allylamine hydrochloride) as polycations, and poly(acrylic acid) and poly(2-acrylamido-2-methylpropanesulfonic acid–co-acrylic acid) as polyanions. To get a direct image on the polyelectrolyte multilayers formation and properties, gravimetry, infrared spectroscopy, and atomic force microscopy have been used. The capacity of the polyions to overcompensate the complementary polyions charges, and thus to influence the swelling degree in water of thin films, was strongly influenced by the chain structure and flexibility. A special attention was paid to the responsiveness of the new composite materials to the pH of the swelling environment.     

SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURES THROUGH COPOLYMERIC MEMBRANES: Ⅰ. ACRYLIC ACID AND ACRYLONITRILE COPOLYMER AND ITS IONIZED MEMBRANES

The copolymer of acrylic acid and acrylonitrile has been synthesized and pervaporation properties of the copolymeric membranes have been investigated. In order to elucidate the influence of membrane-permeate interaction on the pervaporation of water-ethanol mixtures and to prepare much improved membranes, the membranes have been treated with alkali metal, alkali earth metal and transition metal salt aqueous solutions. The treated membranes (ionized membranes) exhibited higher separation factors than the untreated membranes. The separation factors of various alkali metal cation membranes decreased in the following order : Li~+>Na~+>K~+, and the permeation rates showed an opposite tendency. The dependence of pervaporation behavior on the copolymer composition ,feed concentration and operating temperature have been studied with both ionized and non-ionized membranes. The apparent activation energies of water and ethanol permeation were calculated.     

Network Paired Polymers Based on Poly(acrylic acid)

Network paired polymers (interpolymers) capable of limited swelling in aqueous media accompanied by the formation of polyelectrolyte hydrogels exhibiting рН and thermal sensitivity are synthesized by the reactions of poly(acrylic acid) with poly(methyl methacrylate) and poly(N-vinylcaprolactam) modified by the introduction of anchor oxirane moieties.     

Preparation and Characterization of pH-sensitive Hydrogel Film of Chitosan/Poly(acrylic acid) Copolymer

A hydrogel film of chitosan/poly(acrylic acid) (CS/PAAc) copolymer with the property of pH sensitivity, was prepared by irradiating the chitosan film, which was then swelled by aqueous AAc solutions of different concentrations. The effects of the feed ratio of chitosan and AAc on the properties of the hydrogels, such as swelling ratio and pH-sensitivity, were determined. Fourier transform infrared (FT-IR) spectroscopy was applied in the attenuated total reflectance (ATR) mode for analyzing the structure change of the hydrogels after the treatment in buffer solutions of different pHs.     

壳聚糖／聚丙烯酸聚电解质复合物膜对水／有机液体系的渗透汽化性能

以壳聚糖和聚丙烯酸为原料制备了聚电解质复合物膜，并对其分离水／乙醇体系的渗透汽化特性和浓度，温度，化学组成等因素的影响进行了研究，发现后处理方法对复合物膜的分离性能影响很大。同时对其它水／有机液体系，该膜也具备优异的分离性能。     

Membranes permselectives obtenues par greffage radiochimique des acides acrylique et methacrylique sur des films de poly(chlorure de vinyle)

Membranes were prepared by subjecting to gamma-rays PVC films swollen in a mixture of acrylic acid and methylene chloride. The kinetics of the reaction were investigated as a function of monomer concentration, temperature and dose-rate. The swelling properties of the resulting membranes were studied as well as those of PVC films grafted with methacrylic acid. It was found that PVC films grafted with methacrylic acid only swell slightly in water even for high grafting ratios and the swelling is very slow. At elevated temperatures the films swell more quickly and reach a higher limiting swelling, but the effect is small. PVC films grafted with acrylic acid swell much more quickly and reach much higher swelling ratios. The extent of swelling markedly increases with temperature but this effect is not reversible: once the membranes have reached a high swelling ratio at elevated temperatures, they keep the same ratio when dipped in water at 20°. The Arrhenius plot of the swelling ratio exhibits a break at 50–60° apparently corresponding to a glass transition temperature. In methanol the swelling is significantly higher for PVC films grafted with methacrylic than with acrylic acid. Swelling of the membranes was also investigated in mixtures of water with methanol and methanol with methylene chloride. The results are interpreted by assuming a strong dipole-dipole interaction between the grafted branches and the trunk polymer resulting in a quasimolecular dispersion of the carboxylic chains in the PVC matrix. The latter acts as a barrier against the penetration of water. Heat treatment favours a segregation of the two polymeric species into microphases and this non-reversible transformation is assumed to be responsible for the unexpected behaviour of PVC films grafted with acrylic acid. The significant differences between the properties of PVC films grafted with either acrylic or methacrylic acid are attributed to the much higher hydrophobic character of the methacrylic chains.     

Polyelectrolyte complex nanoparticles from chitosan and poly(acrylic acid) and Polystyrene‐block‐poly(acrylic acid)

Interpolymer polyelectrolyte complexes of chitosan (CS) with poly(acrylic acid) homopolymers and polystyrene‐block‐poly(acrylic acid) diblock copolymers were prepared and characterized. The influence of the positive/negative charge balance (charge ratio), pH, and ionic strength were thoroughly studied by dynamic light scattering. The existence of a strong polyelectrolyte effect was also highlighted in this study. Domains of stability, in which nanoparticle sizes are smaller than 100 and 200 nm for complexes of CS with the homopolymer and copolymer, respectively, were identified and confirmed by scanning electron microscopy and atomic force microscopy. The charged nature of the surface of the nanoparticles was evidenced by Zeta potential measurements. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Water-soluble complexes of star-shaped poly(acrylic acid) with quaternized poly(4-vinylpyridine)

The interaction of star-shaped poly(acrylic acid) having various numbers of arms (5, 8, and 21) and a strong cationic polyelectrolyte, viz., poly( N-ethyl-4-vinylpyridinium bromide), was examined at pH 7 by means of turbidimetry and dynamic light scattering. Mixing aqueous solutions of the oppositely charged polymeric components was found to result in phase separation only if their base-molar ratio Z = [N+]/[COO (-) + COOH] exceeds a certain critical value ZM ( ZM < 1); this threshold value is determined by the number of arms of the star-shaped polyelectrolyte and the ionic strength of the surrounding solution. At Z < ZM, the homogeneous aqueous mixtures of the oppositely charged polymeric components contain two types of complex species clearly differing in their sizes, with the fractions of these species appearing to depend distinctly on the number of arms of the star-shaped poly(acrylic acid), the base-molar ratio of the oppositely charged polymeric components in their mixtures, and the ionic strength of the surrounding solution. The small complex species (major fraction) are assumed to represent the particles of the water-soluble interpolyelectrolyte complex whereas the large complex species (minor fraction) are considered to be complex aggregates.     

Interpolymer complex formation of some nonionogenic polymers with linear and crosslinked polyacrylic acid

The formation of interpolymer complexes on the surface of crosslinked poly (acrylic acid) with some nonionogenic polymers is compared with the complex formation in analogous linear polymer systems. The behavior of these systems is compared with that of complexes of two oppositely charged polyelectrolytes. The concentration redistribution of the linear polymer in the system polyelectrolyte network-polymer solution and the degree of swelling of this network in these solutions were determined. © 1994 John Wiley & Sons, Inc.     

Pervaporation separation of water/alcohol mixtures using composite membranes based on polyelectrolyte multilayer assemblies

Composite pervaporation membranes composed of an asymmetric polyamide-6 membrane and an ultrathin self-assembled polyelectrolyte separating layer are described. The supporting membrane was prepared from both an unmodified polyamide-6 and a comb-like polymer with carboxyl terminated polyamide-6 side chains. A high end group concentration was found to be advantageous for sufficient adhesion of the multilayer systems on the supports. Up to 20 layers were deposited onto the membrane surface by dipping the membranes in aqueous solutions containing oppositely charged polyelectrolytes. The polyanions used were poly(acrylic acid), poly(styrene sulfonic acid) and alginic acid. The polycations used were poly(diallyldimethylammoniumchloride), chitosan and poly(ethylenimine). Performance of these membranes depends strongly on the layer number and on the type of polyelectrolytes. In general, membranes modified with two weak polyelectrolytes of high charge density gave the best separation properties while those modified with strong polyelectrolytes of low charge density led to poorer separation properties. However, the highest separation factor (≥10,000) for a water/2-propanol mixture (12/88 w/w) at permeate flux of 300 g/m²h was obtained with six double layers consisting of poly(ethylenimine) and alginic acid. These composite membranes were stable over an operating period of at least 400 h.     

Polyelectrolyte layer-by-layer self-assembly enhanced by electric field and their multilayer membranes for separating isopropanol–water mixtures

An electric field enhanced method is developed for fabricating layer-by-layer (LbL) self-assembly polyelectrolyte multilayer membranes. Three kinds of electric field enhanced polyelectrolyte multilayer membranes (EPEMs), poly(diallyl dimethylammonium chloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS), poly(diallyldimethylammonium chloride)/poly(acrylic acid sodium salt) (PDDA/PAA) and polyethylenimine/poly(acrylic acid sodium salt) (PEI/PAA), were self-assembled on a reverse osmosis membrane (ROM). The pervaporation performances of EPEMs for separating isopropanol–water mixtures (90/10, w/w) are all superior to those of corresponding normal self-assembled polyelectrolytes membranes (PEMs), and the selectivity increases with PDDA/PSS, PDDA/PAA and PEI/PAA in order. For (PEI/PAA)₄PEI EPEM, the separation factor is 1075 and permeation flux is 4.05 kg m⁻² h⁻¹ at 70 °C. This novel method speeds up the LbL process, which makes it promising for the practical application of the LbL multilayer membrane.