Miscibility of poly(ethylene oxide) with poly(N-vinyl pyrrolidone): DMTA and DTA studies

Dynamic mechanical thermal analysis and calorimetric studies are reported on blends of poly(ethylene oxide) (PEO) with poly(N-vinyl pyrrolidone) (PVP) between 80% and 40% PEO. DMTA curves show a peak corresponding to a phase of pure PEO and another peak which can be attributed to blended material. The calorimetric analysis shows an appreciable melting point depression and a marked decrease in the crystallization rate as the PVP content increases. The melting point depression follows the Nishi-Wang equation, giving an interaction parameter of ?0.50. These studies suggest the existence of microphases in the blend.     

Cross-linking of poly(N-vinyl pyrrolidone) films by electron beam irradiation

Biocompatible hydrogels based on poly(N-vinyl pyrrolidone) (PVP) were synthesized by electron beam irradiation of the dry polymer under various conditions. Sol–gel analysis of the bulk gel (in mm range) gave a dose of gelation of 94 kGy. As seen for various other polymers, the network density rises with the increase in dose. At around 350 kGy, PVP began to decompose. Based on these observations, films in μm range on a silicon wafer were synthesized by electron beam irradiation. Due to irradiation, the films adhered irreversibly on the wafer. Their swelling behavior was analyzed by ellipsometry.     

High-performances membranes for pervaporation I. Poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) blends

Dense membranes were prepared from poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) (PVA–PVP) blends of different compositions and studied in swelling and dehydration by pervaporation of three organic solvents contaminated by 5 wt% water. The swelling generally increases with the PVP content. No extraction occurs in water–tetrahydrofuran (THF) and water–methyl ethyl ketone (MEK) mixtures. In ethanol containing 10 wt% of water, there is no extraction for blends containing less than 40 wt% PVP and an increasing extraction beyond this PVP content. The pervaporation flux of the water–ethanol mixture increases drastically at the same threshold whereas the water permselectivity falls to a low level. The values of the diffusion and permeability coefficients determined from transient permeation of the test water–ethanol mixture exhibit a similar sudden increase at the same PVP content threshold. This singular behavior of the blend membranes is interpreted by a strong affinity of the PVP component to ethanol, combined with a disappearance of crystallites in the blend at this threshold. Consequently the amorphous membrane can swell freely according to the affinity of the PVP component, leading to the observed behavior.     

Studies on poly(vinyl pyrrolidone) based solid polymer blend electrolytes complexed with various lithium salts

Solid polymer electrolytes (SPEs) with high ionic conductivity and acceptable mechanical properties are of particular interest for increasing the performance of batteries. In the present work, SPEs based on poly(ethylene oxide)/poly (vinyl pyrrolidone) (PEO/PVP) with various lithium salts were prepared by solvent casting technique. The amorphous nature of the polymer-salt complex was studied by X-ray diffraction analysis. The complexation of the prepared electrolytes was confirmed by Fourier transform infrared analysis. Ionic conductivity as a function of frequency was studied at various temperatures in the range of 303–353 K. The maximum ionic conductivity value was found to be 1.08 × 10^?5 S/cm for the film containing lithium bis trifluoromethane sulfonoimide (LiN[CF₃SO₂]₂) at room temperature and the temperature dependent ionic conductivity values seem to obey Vogel-Tamman-Fulcher relation. Thermogravimetry was used to ascertain the thermal stability of the electrolytes. Photoluminescence measurements demonstrated that the sample having maximum ionic conductivity shows the minimum luminescence intensity. Ultra violet-visible analysis reveals that the values of the band gap energies were changed with the addition of various lithium salts. Porosity of the sample containing lithium bis trifluoromethane sulfonoimide (LiN[CF₃SO₂]₂) was studied by Atomic force microscope.     

Studies of solution dynamics of poly(N-vinyl pyrrolidone) and its iodine adduct

Carbon-13 NMR spin-lattice relaxation times T₁ of poly(N-vinyl pyrrolidone) (PVP) and PVP-iodine have been studied in several solvents and at different temperatures. Three kinds of motion can be identified from the T₁ data: segmental motion, ring rotation, and ring puckering. The effective correlation time for segmental motion is calculated to be 1 × 10^?9s, in good agreement with published proton NMR data. Another solvent, 1,1,2,2-tetrachloroethane, behaves like D₂O, the segmental correlation time being 3 × 10^?9s. In benzene, however, the linewidths are very broad and tend to narrow with increasing temperature, but the T₁s are not very different from those of PVP in D₂O. The results suggest association of pyrrolidone rings in benzene that reduces chain dimensions and also restricts chain mobility. As for PVP-iodine in water, again broad resonances are observed which sharpen considerably at higher temperatures. The result agrees with previous suggestions of specific interactions between the pyrrolidone group and iodine.     

Spectrophotometric studies of some charge-transfer complexes of tetracyanoethylene with poly(N-vinyl halogenocarbazoles)

The results and numerical analysis of measurements of absorption spectra of charge-transfer complexes of poly(N-vinyl halogenocarbazoles) with tetracyanoethylene are presented. The absorption bands result from donor–acceptor interaction together with values of equilibrium constants, enthalpy, and oscillators strengths of investigated complexes allowed us to conclude that isomerism of complexing took place. The influence of halogen substituents (mono- and disubstitution) in positions 3 and 6 of the carbazole ring (polymeric donor) on the spectral properties of its complexes was observed.     

Separation of statistical poly[(N-vinyl pyrrolidone)-co-(vinyl acetate)]s by reversed-phase gradient liquid chromatography

Although size exclusion chromatography (SEC) has been used successfully to determine the molecular weight distribution (MWD) of statistical poly[(N-vinyl pyrrolidone)-co-(vinyl acetate)]s [PVPVAs], SEC cannot separate the copolymers according to their chemical composition. In this article, the separation of commercial PVPVAs with varying chemical compositions is reported, by aqueous reversed-phase gradient liquid chromatography (RPLC) using polystyrene-divinylbenzene-based wide pore columns. RPLC-SEC cross-fractionation indicates the presence of molar mass dependant effects during RPLC separation due to broad MWD for the copolymer studied; therefore the width of the RPLC peak could not be associated entirely with chemical composition distribution of the copolymer. Coupling of RPLC with online FTIR spectroscopy reveals the increase of VA content with increasing THF gradient, an indication of interaction mechanism between VA repeating units and the stationary phase for water soluble PVPVAs. Separation of water insoluble PVPVAs and PVAs by the RPLC are possibly based on both interaction and precipitation/redissolution mechanisms.     

Solvent effects on the formation of nanoparticles and multilayered coatings based on hydrogen-bonded interpolymer complexes of poly(acrylic acid) with homo- and copolymers of N-vinyl pyrrolidone

The formation of hydrogen-bonded interpolymer complexes between poly(acrylic acid) and poly(N-vinyl pyrrolidone) as well as amphiphilic copolymers of N-vinyl pyrrolidone with vinyl propyl ether has been studied in aqueous and organic solutions. It was demonstrated that introduction of vinyl propyl ether units into the macromolecules of the nonionic polymer enhances their ability to form complexes in aqueous solutions due to more significant contribution of hydrophobic effects. The complexation was found to be a multistage process that involves the formation of primary polycomplex particles, which further aggregate to form spherical nanoparticles. Depending on the environmental factors (pH, solvent nature), these nanoparticles may either form stable colloidal solutions or undergo further aggregation, resulting in precipitation of interpolymer complexes. In organic solvents, the intensity of complex formation increases in the following order: methanol < ethanol < isopropanol < dioxane. The multilayered coatings were developed using layer-by-layer deposition of interpolymer complexes on glass surfaces. It was demonstrated that the solvent nature affects the efficiency of coating deposition.     

Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by direct acid casting

We report the preparation of phosphoric acid doped poly(2,5-benzimidazole) (ABPBI) membranes for PEMFC by simultaneously doping and casting from a poly(2,5-benzimidazole)/phosphoric acid/methanesulfonic acid (MSA) solution. The evaporation of MSA yields a very homogeneous membrane having a better controlled composition, avoiding the use of solvent-intensive procedures. Membranes have been prepared with contents of up to 3.0H₃PO₄ molecules per ABPBI repeating unit. These membranes achieve a maximum conductivity of 1.5 × 10⁻² S cm⁻¹ at temperatures as high as 180 °C in dry conditions. These ABPBI membranes are more conveniently prepared than those conventionally formed and doped in separate steps while featuring comparable conductivities (ABPBI × 2.7H₃PO₄ prepared by the soaking method showed a conductivity of 2.5 × 10⁻² S cm⁻¹ at 180 °C in dry conditions).     

Antibacterial poly(D,L-lactide) (PDLLA) fibrous membranes modified with quaternary ammonium moieties

<正>Antibacterial poly(D,L-lactide)(PDLLA) fibrous membranes were developed via electrospinning,followed by surface modification which involved plasma pretreatment,UV-induced graft copolymerization of 4-vinylpyridine(4VP) and quaternization of the grafted pyridine groups with hexylbromide.The success of modification with quatemized pyridinium groups on the PDLLA fibrous membranes was ascertained by X-ray photoelectron spectroscopy(XPS).The antibacterial activities of these membranes were assessed against Gram-positive Staphylococcus aureus(S.aureus) and Gram-negative Escherichia coli(E.coli).The PDLLA fibrous membranes modified with quaternized pyridinium groups showed antibacterial efficiency against both bacteria as high as 99.999%.The results demonstrated that the antibacterial activity was based on the interaction of the positive charge of pyridinium group and negatively charged cell membrane of bacteria, resulting in loss of membrane permeability and cell leakage.     

Free-radical synthesis of poly(urethane-g-N-vinyl pyrrolidone)

Relatively high-molecular-weight segmented polyurethanes based on methylene bis(4-phenyl-iso-cyanate), poly(propylene glycol), butane-1,4 diol, and cis-2-butene-1,4 diol have been synthesized and characterized. These unsaturated polyurethanes were successfully grafted using N-vinyl pyrrolidone as monomer and 2,2′-azobisisobutyronitrile as free-radical initiator. However, grafting experiments involving benzoyl peroxide as initiator were unsuccessful. The graft copolymers were isolated from the ungrafted polyurethane and poly(N-vinyl pyrrolidone) by selective solvent extraction. Elemental microanalysis, IR, NMR, thermogravimetric analysis, and equilibrium water sorption measurements were used to characterize the graft copolymers.     

Antimicrobial activities of polymeric quaternary ammonium salts from poly(glycidyl methacrylate)s

Amino poly(glycerol methacrylate)s (PGOHMAs) were synthesized from linear and 8‐arm poly(glycidyl methacrylate)s (PGMAs) via ring opening reactions with methylethylamine (MEA), diethylamine, and dipropylamine, respectively, which were further modified by quaternization reaction using methyl iodide to obtain quaternized PGMAs (QPGMAs for short). The products were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, and thermogravimetric analysis. The amination percentage of amino PGOHMAs and the degree of quaternization of QPGMAs were calculated by elemental analysis and X‐ray photoelectron spectroscopy, respectively. According to the solubility test results, 8‐arm PGOHMA modified with MEA (S8‐MEA) is the only water‐soluble derivative of amino PGOHMAs and was employed as a positive control for the comparison with QPGMAs. Antimicrobial studies on these PGMA derivatives were carried out by testing the minimum inhibitory concentration and the bacteria inhibitive rate against Escherichia coli and Staphylococcus aureus. The results indicated that QPGMAs possessed higher antimicrobial activity than S8‐MEA and exhibited increased antimicrobial activity against both bacteria with an increased degree of quaternization in weak basic conditions. Moreover, the chemical structure of PGMA derivatives and pH value of the assay conditions were found to affect the antimicrobial activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and gas permeation properties of poly(vinyl chloride)‐graft‐poly(vinyl pyrrolidone) membranes

A series of amphiphilic graft copolymers consisting of poly(vinyl chloride) (PVC) main chains and poly(vinyl pyrrolidone) (PVP) side chains, i.e. PVC‐g‐PVP, was synthesized via atom transfer radical polymerization (ATRP), as confirmed by ¹H NMR, FT‐IR spectroscopy, and gel permeation chromatography (GPC). Transmission electron microscope (TEM) and small angle X‐ray scattering (SAXS) analysis revealed the microphase‐separated structure of PVC‐g‐PVP and the domain spacing increased from 21.4 to 23.9 nm with increasing grafting degree. All the membranes exhibited completely amorphous structure and high Young's modulus and tensile strength, as revealed by wide angle X‐ray scattering (WAXS) and universal testing machine (UTM). Permeation experimental results using a CO₂/N₂ (50/50) mixture indicated that as an amount of PVP in a copolymer increased, CO₂ permeability increased without the sacrifice of selectivity. For example, the CO₂ permeability of PVC‐g‐PVP with 36 wt% of PVP at 35°C was about four times higher than that of the pristine PVC membrane. This improvement resulted from the increase of diffusivity due to the disruption of chain packing in PVC by the grafting of PVP, as confirmed by WAXS analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical treatment of membranes of a polymer blend: Mechanism of the reaction of hypochlorite with poly(vinyl pyrrolidone)

Sodium hypochlorite solutions are used to treat membranes prepared from a polymeric blend containing poly(vinyl pyrrolidone) (PVP) to increase their water permeability. Sodium hypochlorite affects the membrane material in such a way that PVP is selectively removed from the membrane matrix. The mechanism of the reaction between hypochlorite and PVP is investigated by several chemical analysis techniques of the reaction products. Strong indications are found that the reaction involves chain scission of PVP according to a radical mechanism. © 1995 John Wiley & Sons, Inc.     

2-methylaminopyridine N-oxide complexes prepared from various cobalt(II) salts

2-Methylaminopyridine N-oxide (HL) complexes have been formed with CoX₂ (X = ClO₄, BF₄, NO₃ and Cl) using both 6:1 and 2:1 ligand-to-metal ion mole ratios. From the former preparative mixtures species with four ligands per Co(II) except with Co(BF₄)₂ which had six, were isolated while two ligands per Co(II) were found for the solids isolated from the latter mixtures. Characterization of the eight solids was accomplished by a study of their IR and electronic spectra as well as partial elemental analyses, molar conductivities and thermal measurements. Of note is that HL rarely functions as a bidentate ligand in these complexes.     

Photopolarization and depolarization characteristics of poly(N-vinyl carbazole)

The photoelectret properties of poly(N-vinyl carbazole) sandwiched between a conducting glass electrode and an aluminum electrode have been studied. Photoelectret polarization was carried out by simultaneous application of an electric field and ultraviolet illumination. The polarization exhibits a linear dependence on the polarizing voltage, polarization time, and illumination intensity, with saturation effects for large values of these parameters. The depolarization current decay is quite fast, which indicates the absence of deep-trap levels. The ratio of photoelectret charge to the dark polarization charge is found to be 100, which determines the image contrast if the polymer film is used in persistent internal polarization (PIP) electrophotography.     

The structure and electric characters of proton‐conducting chitosan membranes with various ammonium salts as complexant

The structural and electric properties of chitosan electrolytes doped by three different ammonium salts [CH₃COONH₄, NH₄Cl, and (NH₄)₂SO₄] were discussed. The chitosan electrolytes were prepared by solution casting technique. The results show that the addition of ammonium salts leads to: The formation of complexation between ammonium salts and chitosan matrix, the destruction of crystal forms, and the enhancement of amorphous nature. With the rise of salt content, both the glass transition temperature and the activation energy show a “V”‐type trend, whereas the conductivity exhibits a reverse trend. For different ammonium salts, the electric properties of the chitosan electrolyte are different due to the Coulomb force between anion of salts and functional groups. The CH₃COONH₄ doped chitosan electrolyte exhibits the optimum electric properties, whereas those of (NH₄)₂SO₄ doped chitosan electrolyte are worst. The chitosan electrolyte doped with 40 wt % CH₃COONH₄ has the lowest glass transition temperature of 369 K, the lowest activation energy of 0.19 eV, and the highest ionic conductivity of 2.87 × 10^?4 S cm^?1 at room temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 880–885, 2010     

Alkaline stability of poly(phenylene)-based anion exchange membranes with various cations

Anion exchange membranes comprised of a poly(phenylene) backbone and one of five different cationic head-groups are prepared, briefly characterized, and tested for stability in 4 M KOH at 90 °C. The two membranes with resonance-stabilized cations (benzyl pentamethylguanidinium and benzyl N-methylimidazolium) show large (>25%) decreases in both conductivity and ion exchange capacity (IEC) after just one day of testing. The membrane with benzyl trimethylammonium cations shows a 33% loss of conductivity (14% decrease in IEC) after 14 days while the membrane with trimethylammonium cations attached by a hexamethylene spacer shows the least degradation: a 5% loss of conductivity over 14 days with no accompanying loss in IEC. A similar membrane which has a six-carbon spacer and a ketone adjacent to the phenyl ring shows much lower stability, suggesting that the ketone takes part in degradation reactions. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1736–1742, 2013     

An ESR study of polymer-Cu(II) complexes in poly(vinyl alcohol), polyacrylamide,and poly(vinyl pyrrolidone) films

Optical and ESR spectra of polymer-Cu(II) complexes in polymer films have been studied. The dependence on F₁ = [Cu²⁺]/[MU] and F₂ = [OH^?]/[Cu²⁺], where [MU] is the molar concentration of monomeric units of the polymer, has been obtained. Optical spectra and potentiometric titration curves in solution have also been studied. There exists a buffer region 0 ? F₂ ? 2. Optical spectra in films are slightly different from those in solutions. At least five different ESR signals, designated as A, B, C or D, and E, have been found in poly(vinyl alcohol)-Cu(II). These signals appear successively with increasing F₂. Assignments are proposed as follows. Signal A (F₂ ≈ 0), also found in poly(acrylamide)-Cu(II) and poly(vinyl pyrrolidone)-Cu(II), is due to a single Cu(II) coordinated with two water molecules and chelated with two oxygens or nitrogens attached to the polymer. A chain of Cu(II) ions singly and double bridged with OH^? ions is responsible for the B signal (F₂ ≈ 1). The C and D signals (F₂ ≈ 2) appear to be caused, respectively, by a dimeric Cu(II) complex singly or doubly bridged with OH^? ions. The E signal (F₂ ≈ 7) appears to be due to a monomeric Cu(II) complex, different from that responsible for the A signal.     

Convectional, sedimentary, and drying dissipative patterns of colloidal suspensions of polymer complexes of poly(acrylic acid) with poly(ethylene glycol) and poly(vinyl pyrrolidone)

Convectional, sedimentary, and drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri dish during the course of dryness of aqueous suspensions of colloidal polymer complexes of poly(acrylic acid) (HPAA) with poly(ethylene glycol) (PEG) and poly(vinyl pyrrolidone) (PVP). With increase in the molecular weight of the polymer component, the complexes showed from transparent solution stable colloidal dispersion and the sticky aggregates. HPAA25K + PVP25K complex showed bluish colors and the colloidal crystal suspension. Size of the macroscopic broad rings of HPAA25K + PEG decreased as molecular weight of PEG increased. Furthermore, the size increased sharply as the polymer concentration increased in the complex systems HPAA25K + PVP25K. Characteristic microscopic patterns appeared for HPAA + PEG and HPAA + PVP complexes.