Influence of the Molecular Mass of Poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) on Formation of Cu<Subscript>2</Subscript>O Nanoparticles During Reduction of Divalent Copper Ions with <Emphasis Type="Italic">tert</Emphasis>-Butylamine Borane in Polymer Solution

The process of reduction of divalent copper ions with tert-butylamine borane in dilute aqueous solutions of poly(N-vinylpyrrolidone) is investigated. The influence of polymer molecular mass on properties of the resultant Cu₂O sols is studied. It is shown that Cu₂O nanoparticles with an average diameter of 6–8 nm independent of polymer molecular mass and a relatively narrow size distribution of particles are formed in the systems under study. The contour length of macromolecules and the hydrodynamic diameter of a poly(N-vinylpyrrolidone) macromolecular coil are compared with the diameter of Cu₂O particles. Poly(N-vinylpyrrolidone) with M ≥ 1 × 10⁴ can be used to produce Cu₂O nanoparticles. Poly(N-vinylpyrrolidone) with M > 4 × 10⁴ should be used for the formation of long-living Cu₂O sols.     

Organic-inorganic hybrid hydrogels based on linear poly(N-vinylpyrrolidone) and products of hydrolytic polycondensation of tetramethoxysilane

The initial stage of gelation of organic-inorganic hybrid hydrogels based on poly(N-vinylpyrrolidone) and the products of hydrolytic polycondensation of tetramethoxysilane has been studied by capillary viscometry. The development of strong bonds between polymer molecules and silica particles in aqueous solutions is proved by the electrokinetic sonic amplitude method. The molecular mass of poly(N-vinylpyrrolidone), the concentration of starting components, and their total amount affect the onset time of gelation in poly(N-vinylpyrrolidone)—water—tetramethoxysilane systems. The general scheme of formation of three-dimensional networks in such systems under the conditions of mutual penetration of poly(N-vinylpyrrolidone) coils is suggested. According to this scheme, nanoparticles of the general formula SiO _x (OH) _y (OR) _z linking poly(N-vinylpyrrolidone) macromolecules serve as junctions of the gel network due to the formation of hydrogen bonds between hydrogens of silanol groups of organosilanes and oxygens of carbonyl groups of poly(N-vinylpyrrolidone).     

Birefringence in solutions and films of poly[4,4'-bis(4'-<Emphasis Type="Italic">N</Emphasis>-phenoxy)diphenylsulfon]imide of 1,3 bis(3',4-dicarboxyphenoxy)benzene

Birefringence in solutions and films of poly[4,4'-bis(4''-N-phenoxy)diphenylsulfon]imide of 1,3-bis(3',4-dicarboxyphenoxy)benzene macromolecules is studied. The method of birefringence in the flow of polymer solutions in DMF allows one to determine the proper specific optical anisotropy of the repeating unit of chain β_M = +15 × 10^–27 cm³ mol/g. Spontaneous birefringence in polymer films of different thickness is studied under various incidence angles of a polarized beam. The total data analysis allows one to estimate the orientation order parameter of polymer chain fragments in the vicinity of surface S ₀ =–0.01, which is typical of flexible-chain polymers.     

Dynamic birefringence and rigidity of poly-p-benzamide molecules in solutions

Flow birefringence (FB) in solutions of a number of samples of poly-p-benzamide (PPBA) in sulphuric acid has been investigated; intrinsic viscosities [η] of the same solutions have been measured.Characteristic values of FB, [n], and orientation angles [χ/g] of the solutions were determined. Molecular weights of all the PPBA samples were calculated by using the values of [χ/g] and [η]. The dependence [η] = 1.6 × 10^?5 M^1.7 shows that the conformation of PPBA molecules in solution is close to that of a straight rod.The use of characteristic values of [n] and [χ/g] and the theory of optical anisotropy of persistent chains gives quantitative data on the equilibrium rigidity of PPBA molecules. It was shown that the number of molecular units in a statistical segment of the PPBA chain is 320 and the corresponding length of the segment is 2000 Å.     

Thermosensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone): Effect of transition-metal halides

The effect of the halides of a series of transition metals on the properties of aqueous solutions of poly(N-vinylpyrrolidone) is studied. It is shown that the introduction of ZnCl₂ into solutions of poly(N-vinylpyrrolidone) causes phase separation with an increase in temperature. In the presence of halides of other transition metals (CdCl₂, CuCl₂), this phenomenon is not observed. However, the addition of HCl and/or alkali-metal halides to these systems likewise gives rise to phase separation, and in the ZnCl₂-based systems, the cloud point of solution substantially decreases with the introduction of alkali-metal salts. The same situation is observed in the case of polyvinylcaprolactam. Thus, it is concluded that the observed phenomena are associated with the formation of MtCl₄²⁻ complex anions in solutions that promote the globulization of polymer chains with participation of water molecules surrounding polymer chains and cations of transition-metal salts bound to complexes with C=O groups of lactam rings of the polymers.     

Synthesis,characterization and self-assembly of amphiphilic block copolymer poly(4-vinyl benzene chloride)-b-poly(N-vinylpyrrolidone) in aqueous solution

The synthesis, characterization and self-assembly of a novel amphiphilic block copolymer containing a poly(N-vinylpyrrolidone) as a segment of hydrophilic and poly(4-vinyl benzene chloride) (PVBC) arms are reported. The copolymer was characterized by FT-IR spectroscopy ¹H NMR. The composition and the molecular weights of the block copolymers were established using gel permeation chromatography and ¹H NMR. The water-soluble fraction of poly(N-vinyl-2-pyrrolidone) (PVP)/PVBC block copolymers formed micelles which were investigated at 25 °C in water at 5 mg/ml concentration using a tensiometer. The morphology of micelles in aqueous solution was determined by the AFM, SANS, and SAXS methods.     

Flow birefringence and conformational characteristics of molecules of para-and meta-isomers of polyoxyphenyl-benzoxazoleterephthalamides

Flow birefringence (FB) has been used to study sulphuric solutions of two homologous series of polyoxyphenylbenzoxazoleterephthalamides (POPhBT) differing in the position (para- or meta-) of phenyl ring in the chain. In the framework of the FB method alone by using the theory of flow birefringence for kinetically rigid wormlike chains, it was possible to determine quantitatively the optical anisotropy of the monomer unit Δa = (330 ± 30) 10^?25 cm^?3 and the length of the Kuhn segment $\text{A = (330 ± 30)}\text{A}\text{?}$ and $\text{A = (115 ± 20)}\text{A}\text{?}$ for para- and meta-isomers, respectively. Analysis of possible mechanisms of flexibility in the chains of both polymers gives theoretical values of the rigidity parameter A in good agreement with experimental values of A. confirming the validity of the molecular models used.     

Flow birefringence and conformational characteristics of polyamide hydrazide molecules in dimethylsulphoxide

Flow birefringence (FB) and intrinsic viscosity of 19 samples of aromatic polyamide hydrazide (PAH) in dimethylsulphoxide (DMS), previously characterized by their weight-average molecular weights by the light scattering method, have been investigated. The molecular-weight dependence of reduced birefringence according to theory [12] was used to determine the optical anisotropy of a monomer unit Δa = (200 ± 20) 10^?25cm³ and the length of the Kuhn segment $\text{A = (250 ± 30)}\text{A}\text{?}$ of PAH molecules. The second independent evaluation of rigidity of the PAH chain $\text{A = (240 ± 30)}\text{A}\text{?}$ was obtained according to the theory of rotational friction of rigid wormlike chains by using the coefficients of rotational diffusion of PAH molecules determined from the characteristic values of orientation angles of FB. The value of rigidity of the PAH chain obtained by this method is in good agreement with the data on molecular dimensions obtained by light scattering.     

Viscosity of concentrated solutions of polystyrene and poly(vinyl acetate) (empirical equations)

The viscosity of solutions of polystyrene with M _w from 2.8 × 10⁴ to 7.8 × 10⁵ in toluene and of poly(vinyl acetate) with M _w from 2 × 10⁴ to 1.4 × 10⁵ in butyl acetate at 30–80°C is measured. The dependence of the activation energy of the viscous flow of the solutions on the molecular weight of the polymers and solution concentration is examined. This dependence is approximated by a cubic polynomial for polystyrene solutions and by a quadratic polynomial for poly(vinyl acetate) solutions. The dependences of the solution viscosity on the concentration, molecular weight, and temperature are approximated by exponential equations in which the exponents are sums of polynomials. The coefficients of the polynomials are determined.     

Photoinduced optical anisotropy in azobenzene methacrylate block copolymers: Influence of molecular weight and irradiation conditions

The photoinduced anisotropy in a series of azomethacrylate block copolymers with different molecular weights and azo contents has been investigated under several irradiation conditions. Depending on molecular weight and composition, different microstructures (disordered, lamellar, spherical) appear, due to block microsegregation. Measurements of birefringence (Δn) induced with linearly polarised 488 nm light show that the highest (and stable) Δn_N values (birefringence normalised to the azo content) are achieved in copolymers with a lamellar structure. Lower Δn_N are obtained in the copolymers in which azobenzene units segregate to nano spheres and the lowest (and less stable) Δn_N values, appear in disordered systems not showing any defined microstructure. Besides, higher Δn_N is obtained in the copolymers with larger molecular weight of the poly (methyl methacrylate) and the azo polymer blocks, both in the microspheres segregated polymers as well as in those without a clear microstructure. This behaviour is consistent with that of the photoinduced order of azobenzene units obtained from dichroism measurements. Irradiation temperature (from 30 to 90 °C) and light power (from 100 to 500 mW/cm²) also influence the photoinduced response. Photoinduced Δn_N growth rate is faster when both temperature and irradiation power increase. Furthermore, birefringence is only induced at temperatures up to 90 °C, the maximum value being obtained at about 70 °C. No clear dependence of the final Δn_N value with light power has been found.     

Dynamic birefringence of poly(styrene-4-sulfonate sodium) macromolecules in aqueous solutions at high ionic strengths

For samples of various molecular masses, the flow birefringence of poly(styrene-4-sulfonate sodium) macromolecules in aqueous solutions at various ionic strengths is studied in relation to the concentration of NaCl. It is shown that the sign of birefringence changes from negative to positive with an increase in the ionic strength of a solution. Application of the macroform theory to the Maxwell effect makes it possible to estimate the intrinsic optical anisotropy of the repeating unit of poly(styrene-4-sulfonate sodium) (a||- a⊥) = −17 × 10^-25 cm³), which nearly coincides with similar values known for atactic polystyrene and poly(κ-methylstyrene).     

Fullerene-containing macromolecular structures based on amphiphilic N-vinylpyrrolidone copolymers: Preparation and characterization

Fullerene-containing macromolecular structures have been obtained via aggregation of polymer colloids (micelles and intermicellar clusters), formed by amphiphilic of N-vinylpyrrolidone copolymers in isopropyl alcohol, with C₆₀ fullerene dissolved in toluene. Their structure and behavior in solution have been investigated.     

Water-soluble complexes of poly(N-vinylamides) of various structures with C60 and C70 fullerenes

By the example of the interaction of fullerene C₆₀ and poly(N-vinylpyrrolidone), the effect of formation conditions of water-soluble fullerene-containing donor-acceptor polymer systems on their composition and structure has been studied. On the basis of these results, a new technique has been developed for preparing water-soluble polymer systems of this kind with the use of o-dichlorobenzene as a component of the reaction medium. This technique has been employed to prepare water-soluble fullerene-containing complexes of poly(N-vinylamides) of various structures (polymers and copolymers of N-vinylpyrrolidone and N-vinylcaprolactam) containing up to 3–5 wt % of C₆₀ and C₇₀ fullerenes. These values are 3–6 times higher than those described previously.     

Electrochemical method for producing globules of ultrasmall rhodium nanoparticles with poly(N-vinylpyrrolidone) bound to the surface of nanocellulose fibers

The study concerns the preparation of Rh nanoparticles (NPs) by room-temperature, methyl viologen (MV²⁺) mediated electrochemical reduction of RhCl₃ in the presence of poly(N-vinylpyrrolidone) (PVP, 40000 Da) and nanocellulose (NC, d = 57±36 nm) at a controlled potential of generation of MV^·+ radical cations in aqueous medium. When a theoretical amount of electricity is passed, the mediator is not consumed, while Rh^(III) is quantitatively reduced to Rh⁽⁰⁾. The reduction results in the Rh@PVP (141–191 nm in size) and Rh@PVP/NC nanocomposites dispersed in the solution bulk. The Rh@PVP/NC nanocomposite represents PVP globules (42±13 nm in size) with encapsulated ultrasmall spherical Rh NPs (1.3±0.4 nm in size) bound to the surface of NC fibers. The Rh nanocomposites exhibited high catalytic activity in the model reaction, viz., reduction of p-nitrophenol with sodium borohydride in aqueous medium. The catalytic activity increased in the presence of cetyltrimethylammonium chloride (CTAC).

     

Poly-N-vinylamides,complexation and conformational changes in aqueous solution

Interaction between small molecules (iodine and 1-anilinonaphthalene-8-sulphonate) and poly-N-methylacetamide (PVMA), poly-N-vinylcaprolactam (PVCL), poly-N-vinylpyrrolidone (PVP) and copolymers of N-vinyleaprolactam with N-vinylpyrrolidone (CP VCL-VP) and with N-vinyl-N-methylacetamide (VMA) were studied. All the polymers formed complexes with the small molecules. The stability constant for the complexes with the probe increases in the series PVMA < PVP < copolymer < PVCL indicating the essential role of hydrophobic interactions in the complex formation. With increasing temperature of aqueous solution from 18 to 33°, the constant decreased for PVP, PVMA and copolymers with low VCL content and increased for PVCL. A folding of PVC coils was observed over the temperature range, demonstrating a relationship between the conformational changes of macromolecules and the polymer complex formation. Addition of PVCL, PVMA and PVP to aqueous I₃^? solution brings about a shift of λ_max from 350 nm for free triiodide ions to 372, 367 and 364 nm respectively. It is explained by different dipole moments of the side substituents. The stability constant for the polymers and I₃^? was estimated as approx. 10⁵ M. The ability of the polymers to form complexes depends on chainlength. The greatest loss of the ability was observed for PVCL with $\text{M}{}_{\mathrm{n}}$ changing from 6 × 10³ to 2 × 10³. Interaction of the polymers with I₃^? is accompanied by a conformational shrinking of coils. In the case of the probe, forces of electrostatic repulsion between negative charges of sulphonate groups result in an unfolding of polimer coils.     

Conformational effects in compounds with 6-membered rings—XII : The conformational equilibrium in n-methylpiperidine

The conformational equilibrium at nitrogen in N-methylpiperidines has been determined in the gas phase (ΔG°₂₈₈ ? 13.2 ± 0.4 kJ mol^?1) and for dilute solutions in several solvents (ΔG°₂₉₃ ranging from 12.5 ± 0.4 in dodecane to 10.1 ± 0.4 in chloroform) by kinetically controlled protonation of anancomeric model compounds 6 and 8 at the interface between the pipendine-containing phase and an immiscible strong acid. The conformational energy for N-methylpiperidine determined by this method is strikingly higher than earlier estimates based on less direct methods but is supported by independent evidence from the temperature dependence of ¹³C NMR chemical shifts. Reconsideration of the more important of the earlier methods indicates that these involved invalid or unproven assumptions and that the low values of ΔG° for N-methylpiperidine derived from them are not reliable.     

Zn|ZnI2| iodine secondary galvanic cells using iodine adducts of nylon-6 and other polymers as positive electrodes

Zn|ZnI₂| iodine galvanic cells using carbon plate electrodes coated with polymer + carbon powder mixtures are rechargeable with minor self-discharge when a positive ion exchanging film is used as the separator. Among the polymers tested (nylon-6, Poly(tetrahydrofuran), poly(acrylonitrile), poly(methly methacrylate), poly(vinly Alcohol), poly(N-vinylpyrrolidone), and poly(4-vinylpridine)), nylon-6 and poly(tetrahydrofuran) have the highest ability to absorb iodine and afford secondary galvanic cells showing the best rechargeability: the secondary galvanic cells are rechargeable more than 500 times with about 100% current efficiency and 81–83% energy efficiency when charged and discharged at 2 mA/cm² at 25°C. The average charging and discharging voltages of the secondary cell using nylon-6 are 1.42 and 1.18 V, respectively. The cell prepared by using nylon-6 generates about 80 mA/cm² of an initial short-circuit current and 0.3–80 mA/cm² of a steady-state short-circuit current when the cell is dipped into a aqueous solution containing I^?₃. The steady-state short-circuit current increases with increasing I^?₃ concentration and a linear correlation holds between the logarithm of the steady-state short-circuit current and the logarithm of [I^?₃] in the range of [I^?₃] = 0.05–0.5 mol/1.     

Polymer-analogous transformations of poly(N-vinylpyrrolidone) to produce new complexing macromolecular systems

A new polymer-analogous transformations of poly(N-vinylpyrrolidone) was used to prepare new complex-forming macromolecular systems containing thiourea and thio-semicarbazone sites. Two variants of modification were realized, namely, the method including the preliminary in situ activation of nucleophilic centres of the polymer amide fragments with dimethyl sulfate followed by introducing nucleophilic agents into the system, and the method including partial hydrolysis of poly(N-vinylpyrrolidone) followed by the amide coupling. The obtained modified polymeric materials react with silver ions in aqueous solution.     

Synthesis of poly(N-vinylpyrrolidone) and N-vinylpyrrolidone-methyl methacrylate copolymers in the presence of C-phenyl-N-tert-butylnitrone

The free-radical polymerization of N-vinylpyrrolidone and its copolymerization with methyl methacrylate have been studied at 60°C in the presence of C-phenyl-N-tert-butylnitrone as a chain-growth regulator. It has been shown that the above additive makes it possible to synthesize poly(N-vinylpyrrolidone) and its copolymers without any gel effect and to control molecular-mass characteristics of homo-and (co)polymers.     

Complexation in Water-Soluble Systems Poly-N-vinylpyrrolidone-Fullerene C60

Complexes of fullerene C_{6 0} with poly-N-vinylpyrrolidone were prepared by various procedures in the presence of additional agents in solution (systems C_{6 0}-poly-N-vinylpyrrolidone and ternary system C_{6 0}-tetraphenylporphyrin-poly-N-vinylpyrrolidone) and in the solid phase (C_{6 0}-polyvinylpyrrolidone and C_{6 0}-KBr-poly-N-vinylpyrrolidone). Formation of a donor-acceptor bond in the system C_{6 0}-poly-N-vinylpyrrolidone was studied by ¹³C NMR. The conditions under which the ternary complex C_{6 0}-tetraphenylporphyrin-poly-N-vinylpyrrolidone with fullerene content varied from 1 to 5 wt % can be obtained were found.