Complexation between poly(acrylic acid) and poly(vinylpyrrolidone): Influence of the molecular weight of poly(acrylic acid) and small molecule salt on the complexation

Poly(acrylic acid) (PAA) with different molecular weight and poly(vinylpyrrolidone) (PVP) were prepared by free radical polymerization using 2,2′-azoisobutyronitrile (AIBN) as initiator in anhydrous methanol for PAA, and in distilled water for PVP. Then, the complexation between PAA and PVP in aqueous solution was studied by UV transmittance measurement and fluorescence probe technique. The result shows that (1) at low pH, the formation of complexation between PAA and PVP bases on the intermacromolecular hydrogen bond and the composition of the formed complex is around 3:2 (the unit molar ratio of PAA to PVP) at pH 2.60 over the range of pH investigated. (2) The cooperative interaction through the formation of hydrogen bond among active sites plays an important role in complex formation, and depends on the pH of solution, the required minimum chain length of poly(acrylic acid). (3) The hydrogen bond is not affected by small molecular salt, which only affects those carboxylic groups without forming hydrogen bond on the PAA chain.     

Controlled loading and release of methylene blue from LbL polyurethane/poly(acrylic acid) film

The layer‐by‐layer (LbL) assembled multilayer films are widely used in the biomedical field for the controlled drug delivery. Here, multilayer films were assembled by LbL technique through alternating deposition of cationic polyurethane (PU) and poly(acrylic acid) (PAA) on glass slides. Methylene blue (MB) was used as a model drug to investigate the loading and release ability of the prepared multilayer film. The results showed that the loading rate and loading amount of MB were greatly influenced by pH value of the dye solution, and the release rate of MB was controlled both by ionic strength and pH value of immersing solution. The result also indicated that the film had a good reversibility of drug loading and release. It suggested that the PU/PAA multilayer film had potential applications in drug delivery and controlled release. Copyright © 2011 John Wiley & Sons, Ltd.     

Self-assembly of multilayer films containing gold nanoparticles via hydrogen bonding

Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV-vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.     

Structure and sorption properties of the polyion complex between poly(acrylic acid) and poly(4-vinylpyridine)

A polyion complex was formed from poly(acrylic acid) (PAA) and poly(4-vinylpyridine) (PVP). Its structure and composition were examined by means of infrared spectroscopy (IR), x-ray photoelectron spectroscopy (XPS), and elemental analysis. The polyion complex was obtained by dissolving PAA and PVP together in methanol. The composition of the polyion complex was independent of stirring speed, mixing sequence, and standing time after mixing. However, the composition depended on the concentrations and the ratio of the components in the reaction mixture. Excess of PAA in the product was observed when concentrated solutions (2.0 × 10^?1M) were used for the preparation or when an excess of PAA was added to PVP. The sorption of water vapor by an equimolar PAA/PVP complex at 293 and 303 K was higher than that by the pure components, especially in the low- and middle-pressure regions. In the high-pressure region, however, the uptake was not affected by the complex formation. While hydrogen bond interactions in general decrease sorption, Coulombic interactions between polymer chains increased the sorption capacity.     

Thermosensitive behavior of amphiphilic triblock copolymers based on poly(acrylic acid) and poly(propylene oxide)

Self‐association in aqueous solution of amphiphilic poly(acrylic acid)‐b‐poly(propylene oxide)‐b‐poly(acrylic acid) (PAA‐b‐PPO‐b‐PAA) copolymers having various outer PAA block lengths are presented. These copolymers show two thermosensitive behaviors. The first one, due to hydrogen bonds between PAA and PPO resulting in large aggregates, was observed by visible spectroscopy. The second one, due to the association of PPO middle block into aggregates, was evidenced by dynamic light scattering and pyrene fluorescence. These critical temperatures both depend on the ionization and the length of PAA blocks. The characterization of the aggregates above the critical aggregation concentration by fluorescence quenching experiments showed a very low aggregation number corresponding to dimers or trimers association depending on the conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1507–1514     

Structure and pH‐sensitive properties of poly (vinylidene fluoride) membrane changed by blending poly (acrylic acid) microgels

pH‐sensitive poly (vinylidene fluoride) (PVDF)/poly (acrylic acid) (PAA) microgels membranes are prepared by phase inversion of the N, N‐dimethylformamide solution containing PAA microgels and PVDF in aqueous solution. The composition and structure of the blend membrane are investigated by Fourier transform infrared spectra, X‐ray photoelectron spectroscopy measurements, thermo gravimetric analysis, field‐emission scanning electron microscope and atomic force microscope. The results indicate the surface and cross section of the blend membranes have a porous structure with PAA microgels immobilized inside the pore and on the membrane surface. The blend PVDF membranes exhibit pH‐sensitive water flux, with the most drastic change in permeability observed between pH 3.7 and 6.3. The blend membranes are fouled by bovine serum albumin, and their antifouling property is enhanced by increasing PAA microgels, mainly derived from the improved hydrophilic property. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrogel characteristics of electron-beam-immobilized poly(vinylpyrrolidone) films on poly(ethylene terephthalate) supports

A novel strategy for the preparation of thin hydrogel coatings on top of polymer bulk materials was elaborated for the example of poly(ethylene terephthalate) (PET) surfaces layered with poly(vinylpyrrolidone) (PVP). PVP layers were deposited on PET foils or SiO2 surfaces (silicon wafer or glass coverslips) precoated with PET and subsequently cross-linked by electron beam treatment. The obtained films were characterized by ellipsometry, X-ray photoelectron spectroscopy, infrared spectroscopy in attenuated total reflection, atomic force microscopy (AFM), and electrokinetic measurements. Ellipsometric experiments and AFM force-distance measurements showed that the cross-linked layers swell in aqueous solutions by a factor of about 7. Electrokinetic experiments indicated a strong hydrodynamic shielding of the charge of the underlying PET layer by the hydrogel coatings and further proved that the swollen films were stable against shear stress and variation of pH. In conclusion, electron beam cross-linking ofpreadsorbed hydrophilic polymers permits a durable fixation of swellable polymer networks on polymer supports which can be adapted to materials in a wide variety of shapes.     

Interaction between poly(N-vinylpyrrolidone) and poly(acrylic acid)s: Influence of hydrogen and cupric ions on the adduct formation

Interpolymer adduct formation between poly(N-vinylpyrrolidone) (PVP) and poly(methacrylic acid) (PMAA) is mainly due to hydrogen bonding. It is found that the interpolymer adduct formation is enhanced in the presence of Cu(II). A simple turbidity measurement making use of a spectrophotofluorometer is described for the study of the interpolymer adduct formation. Enhanced adduct formation in the presence of Cu(II) is described by the empirical relation d[PAd]/D[PVP] = k × 10^4α[Cu(II)]^α, where PAd represents the interpolymer adduct and α and k are constants. Similar results have been obtained in the case of interpolymer adduct formation between poly(acrylic acid) (PAA) and PVP. In the above expression α signifies the influence of chelation on Cu(II)–PAA/PMAA–PVP-type complex formation and k is the extent of PVP–PAA/PMAA interaction. The enhancement of adduct formation in the presence of Cu(II) is more in PAA than in PMAA. Turbidity and viscosity measurements further indicate that the influence of Cu(II) on interpolymer adduct formation between PVP and PMAA or PAA is more in the case of PAA than PMAA, as PAA is a better chelating ligand. But the extent of adduct formation is more in the case of PMAA in the absence of Cu(II) ions due to hydrophobic interactions exerted by methyl groups.     

Self‐assembled complexes of poly(acrylic acid) and poly(styrene)‐block‐poly(4‐vinyl pyridine)

Polymer complexes were prepared from high molecular weight poly(acrylic acid) (PAA) and poly(styrene)‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) in dimethyl formamide (DMF). The hydrogen bonding interactions, phase behavior, and morphology of the complexes were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this A‐b‐B/C type block copolymer/homopolymer system, P4VP block of the block copolymer has strong intermolecular interaction with PAA which led to the formation of nanostructured micelles at various PAA concentrations. The pure PS‐b‐P4VP block copolymer showed a cylindrical rodlike morphology. Spherical micelles were observed in the complexes and the size of the micelles increased with increasing PAA concentration. The micelles are composed of hydrogen‐bonded PAA/P4VP core and non‐bonded PS corona. Finally, a model was proposed to explain the microphase morphology of complex based on the experimental results obtained. The selective swelling of the PS‐b‐P4VP block copolymer by PAA resulted in the formation of different micelles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1192–1202, 2009     

Self‐assembly of thermo‐ and pH‐responsive poly(acrylic acid)‐b‐poly(N‐isopropylacrylamide) micelles for drug delivery

Self‐assembled thermo‐ and pH‐responsive poly(acrylic acid)‐b‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM) micelles for entrapment and release of doxorubicin (DOX) was described. Block copolymer PAA‐b‐PNIPAM associated into core‐shell micelles in aqueous solution with collapsed PNIPAM block or protonated PAA block as the core on changing temperature or pH. Complexation of DOX with PAA‐b‐PNIPAM triggered by the electrostatic interaction and release of DOX from the complexes due to the changing of pH or temperature were studied. Complex micelles incorporated with DOX exhibited pH‐responsive and thermoresponsive drug release profile. The release of DOX from micelles was suppressed at pH 7.2 and accelerated at pH 4.0 due to the protonation of carboxyl groups. Furthermore, the cumulative release of DOX from complex micelles was enhanced around LCST ascribed to the structure deformation of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5028–5035, 2008     

Highly ion conductive poly(ethylene oxide)-based solid polymer electrolytes from hydrogen bonding layer-by-layer assembly

We report the development of a solid polymer electrolyte film from hydrogen bonding layer-by-layer (LBL) assembly that outperforms previously reported LBL assembled films and approaches battery integration capability. Films were fabricated by alternating deposition of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) layers from aqueous solutions. Film quality benefits from increasing PEO molecular weight even into the 10(6) range due to the intrinsically low PEO/PAA cross-link density. Assembly is disrupted at pH near the PAA ionization onset, and a potential mechanism for modulating PEO:PAA ratio within assembled films by manipulating pH is discussed. Ionic conductivity of 5 x 10(-5) S/cm is achievable after short exposure to 100% relative humidity (RH) for plasticization. Adding free ions by exposing PEO/ PAA films to lithium salt solutions enhanced conductivity to greater than 10(-5) S/cm at only 52% RH and tentatively greater than 10(-4) S/cm at 100% RH. The excellent stability of PEO/PAA films even when exposed to 1.0 M salt solutions led to an exploration of LBL assembly with added electrolyte present in the adsorption step. Fortuitously, the modulation of PEO/PAA assembly by ionic strength is analogous to that of electrostatic LBL assembly and can be attributed to electrolyte interactions with PEO and PAA. Dry ionic conductivity was enhanced in films assembled in the presence of salt as compared to films that were merely exposed to salt after assembly, implying different morphologies. These results reveal clear directions for the evolution of these promising solid polymer electrolytes into elements appropriate for electrochemical power storage and generation applications.     

Homogeneous blend membrane made from poly(ether sulphone) and poly(vinylpyrrolidone) and its application to water electrolysis

A homogeneous blend membrane has been successfully prepared from poly(ether sulphone) (PES) and poly(vinylpyrrolidone) (PVP), which have been usually thought to be immiscible to each other. The PES–PVP membrane possesses combined advantages of the hydrophobic and hydrophilic components; specifically, both good mechanical strength and excellent hydrophilicity have been achieved simultaneously. The success of achieving such special properties can be ascribed to the appropriate choice of solvent for membrane casting, N,N-dimethylformamide (DMF) in this case, and the post-treatment of the membrane in alkaline ethanol solution for obtaining hydrophilicity. Membranes with different blending ratios were characterized with tensile test, scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and electrochemical measurements. The membrane was found to function well as a diaphragm in water electrolysis. In comparison with the traditional asbestos diaphragm, an energy saving of ca. 10% can be reached upon employing PES–PVP membranes in water electrolysis.     

Mechanism of carbon nanotube dispersion and precipitation during treatment with poly(acrylic acid)

Carbon nanotubes have been shown to be easily dispersed within an acidic aqueous solution of poly(acrylic acid) but precipitate when the pH is increased. Transmission electron microscopy showed that the nanotubes were more exfoliated under the acidic condition but highly aggregated under the basic condition. Carbon K‐edge NEXAFS spectroscopy showed that the carbon nanotubes did not chemically react with poly(acrylic acid) during the dispersion or precipitation and that the dispersion mainly involved physical adsorption of poly(acrylic acid) onto the nanotubes. Together with the carbon K‐edge NEXAFS spectra, the cobalt L_{3, 2}‐edge NEXAFS spectra suggested that under the basic condition, the cobalt impurity within the nanotubes strongly reacted with poly(acrylic acid) resulting in complex formation. Cobalt reduces the adsorption of poly(acrylic acid) onto the nanotubes, which then reduced the nanotube dispersion and resulted in the precipitation. Copyright © 2008 John Wiley & Sons, Ltd.     

Complexation between poly(N,N-diethylacrylamide) and poly(acrylic acid) in aqueous solution

The complexation between poly(N,N-diethylacrylamide) (PDEA) and poly(acrylic acid) (PAA) in aqueous solution was studied by viscometric, potentiometric, and fluorescence techniques. It was found that an interpolymer complex formed between the two polymers through hydrogen bonding interactions with the stoichiometry of r=0.6 (r is unit molar ratio of PAA/PDEA), and the complex formation show the dependence on pH values. The phase behaviour studies showed that the lower critical solution temperature of the PDEA-PAA aqueous solution gradually increased with the increasing of r from 0.01 to 0.15, until a soluble system in the whole temperature region was obtained, which remained in the range of r=0.15-0.3. At higher PAA concentrations, when r is above 0.3, the system appeared phase separation, and almost no temperature dependence was observed. Based on these conclusion and structure characteristics of PDEA and PAA, a model containing only short sequences of monomer residues was proposed for the structure of PDEA-PAA complex.     

The radiation-induced peroxidation of poly(N-vinylpyrrolidone) in an aqueous solution

The radiation-induced peroxidation of poly(N-vinylpyrrolidone) (PVP) in its aqueous solution is reported. The amount of peroxides formed in PVP aqueous solution increased with radiation dose. The peroxides decomposed slowly at a low temperature. The molecular weight of PVP decreased with absorbed dose. The peroxidized PVP can function as initiators and crosslinkers for the syntheses of tough hydrogels.     

Composite thin film by hydrogen-bonding assembly of polymer brush and poly(vinylpyrrolidone)

Based on hydrogen-bonding layer-by-layer (LBL) assembly in aqueous solution, poly(vinylpyrrolidone) (PVPON) and a spherical polymer brush with a poly(methylsilsesquioxane) (PSQ) core and poly(acrylic acid) (PAA) hair chains were used to fabricate composite multilayer thin films. Hydrogen bonding as the driving force was confirmed by FT-IR spectrometry. A simple method (Filmetric F20) was introduced to determine the thickness and refractive index of the films. The film thickness was found to be a linear function of the number of bilayers. The average increase in thickness per bilayer is 28.3 nm. The film morphology was characterized with scanning electron microscopy and atomic force microscopy. The images obtained from the two instruments show a great resemblance. The films were further calcined to get an inorganic film by removing the organic components, or treated with tetrabutylammonium fluoride (TBAF) to remove the PSQ core and get an organic film. The optical properties and morphological changes induced by these treatments were also studied.     

Studies on interpolymer self-organisation behaviour of protoporphyrin IX bound poly(carboxylic acid)s with complimentary polymers by means of fluorescence techniques

Covalently bound protoporphyrin IX was used as a fluorophore to investigate the interpolymer complex formation between the poly(carboxylic acid)s, PMAA/PAA and poly(N-vinyl pyrrolidone), PVP, poly(ethylene oxide), PEO or poly(ethylene glycol), PEG. Absorption and emission spectral properties of protoporphyrin IX bound to PAA, PMAA and PVP have been studied. Protoporphyrin IX in poly(MAA-co-PPIX) was found to be present in the dimer or higher aggregated form at low pH due to the environmental restriction imposed by the polymer whereas in the case of poly(AA-co-PPIX) and poly(VP-co-PPIX), PPIX exists in monomeric form. The fluorescence intensity and lifetime of PPIX bound to poly(carboxylic acid)s increase on complexation through hydrogen bonding with PVP, PEO and PEG due to the displacement of water molecules in the vicinity of the PPIX. Poly(MAA-co-PPIX) shows longer fluorescence lifetime due to the more compact interpolymer complexation as compared to poly(AA-co-PPIX) due to the enhanced hydrophobicity of PMAA. Poly(VP-co-PPIX) shows a decrease in the fluorescence lifetime on complexation with PMAA or PAA due to the hydrophilic and microgel like environment of the fluorophore bound to PVP. The contrasting behaviour of the same polymer adduct with respect to the site of the fluorophore is interpreted to be due to the solvent structure which determines the environment of the fluorophore.     

A facile approach to synthesize poly(4-vinylpyridine)/multi-walled carbon nanotubes nanocomposites: highly water-dispersible carbon nanotubes decorated with gold nanoparticles

A facile approach to attach high-density and uniform gold nanoparticles on individual multi-walled carbon nanotubes (MWNTs) is achieved. By simple grinding, water-soluble linear polymers poly(4-vinylpyridine) (PVP)-wrapped around nanotubes and thus rendered them reversibly soluble in water, ethanol, and DMF. Individual tubes are clearly observed after PVP-wrapped nanotubes were spin-coated onto a silicon wafer. Subsequently, Au nanoparticles were densely decorated on the individual MWNTs by in situ reduction of HAuCl₄ in the homogeneous aqueous solution of MWNTs–PVP to form stable water-dispersible Au/PVP/MWNTs hybrid. Morphology of Au nanoparticles was determined by scanning electron microscope and atomic force microscope. The diameter of the Au nanoparticles is controlled in the range of 3.5 to 13.5 nm. The presence of gold nanoparticles with decreased particle size was also detected by UV–Vis spectroscopy.     

Ultradisperse catalytic layers supported by nanotubes and poly(diallyldimethylammonium)chloride polymer

A catalytic system consisting of carbon nanotubes, poly(diallyldimethylammonium)chloride, and a very thin layer of platinum or platinum-ruthenium is assembled layer-by-layer (LbL) on a glassy carbon (GC) electrode. Deposits of platinum metals are studied by electrochemical methods, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Such catalyst layers are shown to exhibit much higher activity in the methanol oxidation reaction as compared with commercial and electroplated catalysts. The currents compared are calculated per the surface area of deposited metals determined with respect to hydrogen adsorption.     

Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid)

An interpolymer complex was prepared by mixing aqueous solutions of poly(ethylene oxide) (PEO) and of a poly(carboxylic acid), i.e., poly(acrylic acid)(PAA), poly(methacrylic acid)(PMAA), or styrene-maleic acid copolymer(PSMA). The complexation mechanism was discussed on the basis of results of such experimental methods as viscosity, potentiometric titration, and turbidimetry. The hydrogen bond is primarily involved in these complexations, but the influence of hydrophobic interaction on complexation can not be ignored. If the degree of dissociation α of carboxylic acid or the degree of polymerization P_n of PEO was perceptibly changed, a stable complex was obtained at about α 0.1 or P_n (PEO) = 40 for PMAA, 200 for PAA. This fact indicates that more than a definite number of binding sites are necessary for a stable interpolymer complex to be formed and that cooperative interaction among active sites plays an important role in complex formation.