Formation of copper–polymer nanocomposite upon copper electrodeposition in the presence of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone)

The composition and structure of products formed on a cathode upon electrodeposition of copper from copper sulfate–poly(N-vinylpyrrolidone) mixed solutions have been studied. These products have been shown to be nanocomposites consisting of copper nanoparticles and the polymer. It has been suggested that the composite is formed by a pseudotemplate mechanism via noncovalent interaction between macromolecules and copper particles growing on the cathode. The interaction is accompanied by deceleration of subsequent growth of particles because of their screening by the polymer. This decreases the sizes of copper particles in the reaction product and the rate of metal reduction. The sonication of the reaction system yields a nanocomposite sol containing nanoparticles of copper(I) oxide. The oxide results from rapid oxidation of copper metal particles that have passed to the sol with copper(II) ions.     

Nanocomposite forming on the cathode in electrochemical reduction of copper ions from a polymer solution

Copper electrodeposition from a solution of a mixture of copper(II) sulfate and poly(N-vinylpyrrolidone) is accompanied by the formation of a nanocomposite on the cathode. The nanocomposite contains copper nanoparticles and up to 20 wt % polymer. The composite forms by a noncovalent interaction of polymer macromolecules with the surface of copper particles growing on the cathode.     

Interactions between macromolecules and metal nanoparticles in aqueous-saline media

The influence of the concentration of low-molecular-mass salt additives in the reaction medium on the size characteristics of copper nanoparticles in sols formed through the reduction of Cu²⁺ ions in the presence of a cationic polyelectrolyte and nonionogenic polymers with hydrophilic (poly(ethylene oxide) and hydrophobic (poly(N-vinylpyrrolidone)) main chains has been studied. Formation of sols with a narrow size (diameter) distribution of metal nanoparticle indicates the pseudomatrix character of formation of the metal phase under the studied conditions. Effects of the neutral salt and its concentration in the reaction medium on the synthesis of copper sols and on the mean size of metal nanoparticles are related to a change in the nature or character (when oppositely charged polyelectrolyte macromolecules and copper nanoparticles are involved in interaction) of noncovalent interactions stabilizing the macromolecule-nanoparticle complex on passage from the salt-free aqueous medium to the aqueous-saline medium with a sufficiently high concentration of the neutral salt.     

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.     

Competition between polyelectrolyte macromolecules and amphiphilic polymer micelles in interaction with copper nanoparticles

Competition between poly(1,2-dimethyl-5-vinylpyridinium methyl sulfate) polycationic macromolecules and micelles of amphiphilic polymers containing hydrophilic and hydrophobic blocks (polyethylene glycol-600 monolaurate and poly-N-vinylpyrrolidone monostearate) for copper nanoparticles was studied by means of electrophoresis and electron microscopy techniques. It was shown that, irrespective of the formation method, almost all copper nanoparticles were bonded to the polycation in polycation-polyethylene glycol-600 monolaurate mixed solutions but were distributed between the polymers in polycation-poly-N-vinylpyrrolidone monostearate mixtures. It was concluded that the stability of the complex of copper nanoparticles with the polycation is higher than that with polyethylene glycol-600 monolaurate and is comparable with that of the copper particle-poly-N-vinylpyrrolidone monostearate complex.     

Limiting stability temperatures for copper sols stabilized by poly(<Emphasis Type="Italic">N</Emphasis>-vinyllactams)

It has been shown that stable copper sols cannot be prepared through the reduction of copper ions in aqueous solutions of poly(N-vinyllactams) in the presence of poly(N-vinylpyrrolidone) in the temperature range 50–70°C, while in the presence of poly(N-vinylcaprolactam), the said sols cannot be prepared at temperatures below ～12°C. This tendency is related to the thermodynamic instability of complexes formed via noncovalent interactions of copper nanoparticles with polymer macromolecules in corresponding temperature ranges. Stable sols synthesized in the presence of the above polymers at other temperatures rapidly lose stability in the said temperature ranges, and this effect is accompanied by the aggregation of metal particles. The experimental results provide evidence that there is a relationship between the stability of complexes macromolecules-metal nanoparticles and the thermodynamic quality of the solvent.     

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).     

Effect of stability of nanosized catalyst-polymer substrate complex on hydrolysis of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) in copper sols

The causes of a high total conversion and the S-shaped pattern of the time dependence of conversion for copper sol-catalyzed hydrolysis of the lactam rings of poly(N-vinylpyrrolidone) have been studied. The high conversion of the hydrolusis is achieved via replacement of modified macromolecules in shields of catalyst particles with less modified macromolecules from the dispersion medium of a sol in the course of reaction owing to a decline in the stability of copper nanoparticle complexes with macromolecules with an increase in the degree of hydrolysis. A reduction in the complex stability leads to an increase in the lability of bonding of shielding polymer chains with the catalyst surface and to the growth of the rate of rearrangement and the overall rate of reaction after the induction period. This situation is also responsible for the enlargement of nanosized catalyst particles in the course of reaction and the destruction of the sol after a limiting conversion of units of ～40–50% is attained.     

The complexes of macromolecules and metal nanoparticles: pseudo-template synthesis and behavior

Metal sols composed of metal nanoparticles (1 - 10 nm in diameter) protected with polymer molecules may be regarded as dispersions of polymer-metal complexes formed due to cooperative non-covalent (e.g., hydrophobic, coulombic) interaction of polymer chains with the surface of metal nanoparticles. The sols are commonly prepared by reducing of metal ions in solutions of appropriate polymers. The interactions between macromolecules and nanoparticles are reversible. In the case of long polymer chains and minute particles, the equilibrium constant of the reaction exponentially depends on the surface area of the particle. The probability of mutual “recognition” (complex formation) of growing particle and a macromolecule rapidly increases from practically zero to practically unity in narrow interval of the particle's diameters. The recognition is followed with the shadowing of the particles and the stop of their growths. Such kind of processes was termed “pseudo-template”. In frame of the concept of pseudo-template processes can be estimated: (1) the conditions at which sol particles of desirable size can be prepared, (2) the influence of temperature, polymer concentration, nanoparticles size, and other conditions on the stability of polymer - particle complex having been prepared, and (3) the conditions at which stable sol does not exist and can not be prepared at all. The interactions between metal nanoparticles and macromolecules are highly selective regard to the structure of polymer chains. The property can be effectively used for the control the size characteristics of metal nanoparticles (in course of their formation) and the stability of metal sols. The selectivity provides high conversions in catalytic chemical modification reactions in which a macromolecule is the substrate and a component of the catalyst in the same time. As an example, the hydrolysis of lactame groups in monomer unites of poly(N-vinyl pyrrolidone) catalyzed with copper sols is discussed.     

Pseudotemplate synthesis of copper nanoparticles in solutions of poly(acrylic acid)-pluronic blends

It was found that the reduction of copper(II) ions in solutions of poly(acrylic acid)-pluronic blends results in a stable sol of metallic copper with a particle size below 10 nm, whereas a less stable sol with coarse aggregates of particles is formed in the presence of poly(acrylic acid) alone and an insoluble complex of this polymer with copper nanoparticles is produced in the presence of pluronic alone. The addition of poly(acrylic acid) to the complex causes the transfer of a portion of nanoparticles from the precipitate into the sol. In mixed poly(acrylic acid) and pluronic solutions, no formation of a polymeric complex with reasonable stability was detected. It was assumed that such a polycomplex is stabilized in the presence of copper nanoparticles. Owing to its amphiphilic nature, the complex forms stable protective shields on the surface of nanoparticles, and the stability of the sol is determined by free fragments of poly(acrylic acid).     

Gold nanoparticles as structurizing agents for the formation of hybrid nanocomposites

Two types of transparent gold-containing organo-inorganic hybrid gels (polymer nanocomposites) in which gold nanoparticles (nano-Au) are efficient species were synthesized. The stage of hybrid gel formation is preceded by the in situ chemical reduction of chloroauric acid in an aqueous solution of the synthetic linear polymer (polyvinyl alcohol or poly(N-vinylpyrrolidone)) affording a nano-Au. The presence of ultradispersed gold particles in the obtained nanocomposites was confirmed by UV-Vis spectroscopy and electron microscopy. The loss of solubility of the films in water confirms the formation of a gel network. The size of the gold particles and characteristics of the hybrid gel change depending on the molecular weight of the polymer. The interaction of the macromolecules and growing particles mainly determines the diameter and number of particles of the inorganic phase, whereas the content of chloroauric acid affects these parameters to a less extent. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 329–336, February, 2008.     

Interpolymer complexes of poly(N-vinylpyrrolidone) with copolyimide-grafted side chains of poly(methacrylic acid)

The process of formation and structural organization of interpolymer complexes formed by macromolecules of poly(N-vinylpyrrolidone) and poly(methacrylic acid) chains grafted onto polyimide in solution is investigated via the method of polarized luminescence. A luminescent label of anthracene structure is covalently bound to both polymers. Relaxation times characterizing intramolecular mobility of each of the components in their interpolymer complex are measured in relation to the composition of the system.     

Amphiphilic polymers as pseudotemplates in the synthesis of metal sols

The effects of poly(ethylene glycol) and its amphiphilic polymers on the products of copper ion reduction in aqueous solutions are studied. Whereas coarse metal dispersions are formed in poly(ethylene glycol) solutions, stable sols of metal nanoparticles with diameters of 2 nm and above are produced in the presence of poly(ethylene glycol monolaurate) and poly(ethylene glycol monostearate). A poly(ethylene glycol)-poly(propylene glycol) block copolymer (Pluronic) also stabilizes copper nanoparticles; however, the interaction product of this copolymer with nanoparticles forms a precipitate. According to the electron microscopy data, sol particles comprise polymer micelles containing included copper nanoparticles.     

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.     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Nanoporous polymer networks based on <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone

A method of preparing nanoporous polymer networks containing N-vinylpyrrolidone units via the crosslinking radical copolymerization in bulk performed in the presence of amphiphilic N-vinylpyrrolidone copolymers with the branched morphology and different physicochemical characteristics is developed. It is shown that macromolecular nanoobjects may be extracted from polymer composites using good solvents, such as chloroform and isopropyl alcohol. The physicomechanical, thermal, and diffusion–sorption properties of polymer composites before and after their extraction are compared. SEM and low-temperature nitrogen adsorption measurements reveal that nanosized pores are contained in the network copolymers after extraction of the polymer additives. The specific surface area, total pore volume, pore size, and pore-size distribution are determined. The maximum specific surface area of polymer networks attains ~26 m²/g, and mesopores compose the main type of pores.     

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.     

Dynamic surface properties of sodium N-acryloyl-11-amimoundecanoate and poly(sodium N-acryloyl-11-aminoundecanoate)

Adsorption layers of sodium N-acryloyl-11-amimoundecanoate and poly(sodium N-acryloyl-11-aminoundecanoate) (PAAU-Na) are studied using surface dilatational rheology measurements. It is established that the dynamic surface elasticity values of the studied systems are different, while their surface tension isotherms are almost the same. PAAU-Na solutions containing excess indifferent electrolyte (NaCl) exhibit a conformational transition in a surface layer due to the formation of loops and tails, which penetrate the bulk phase. Slow variations in the surface properties of PAAU-Na solutions with time seem to be caused by the aggregation of macromolecules in the bulk phase. The aggregation process is investigated by scanning probe microscopy.     

Fe-containing nanocomposites based on a biocompatible copolymer 1-vinyl-1,2,4-triazole with <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone

New polymer nanocomposites containing iron oxide nanoparticles stabilized with a biocompatible copolymer of 1-vinyl-1,2,4-triazole with N-vinylpyrrolidone were produced. The synthesis was conducted using the method of chemical reduction of iron ions with hydrazine hydrate in an aqueous medium in the presence of a polymer matrix. The ESR spectroscopy data showed that the core—shell type nanoparticles were obtained. The core generally consistsed of zero-valence iron coated with an oxide shell. According to the data of transmission electron microscopy, the obtained polymer nanocomposites consisted of nanoparticles of mainly spherical shape with a diameter from 1 to 14 nm. Aggregates formed from individual stabilized nanoparticles of up to 75 nm in size (in most cases) were also observed. These aggregated particles were found to self-organize and form branched chains. Nanocomposites were characterized by a different particle-size distribution, which was determined by the initial ratio of the copolymer and the precursor of iron nanoparticles.     

New polymer materials with controlled nanoporous structure based on N-vinylpyrrolidone

The polymer networks with nanoporous structure were obtained by the crosslinking free-radical copolymerization of N-vinylpyrrolidone with triethylene glycol dimethacrylate in bulk in the presence of amphiphilic copolymer and its fractions as templates. The templating agents consisted of copolymer or their fragments with similar monomer units and different molecular weight. Macromolecular templates were shown to be removed from the polymer composite by PrⁱOH leaving the pores. The values of the specific surface areas, the total pore volumes, pore size, and pore size distribution were measured by the method of low-temperature nitrogen absorption. The maximum value of the specific surface area was calculated to be ~26 m² g^–1. The value was significantly higher than that for the usual copolymer network. The relationship between specific surface area, parameters of pores, and macromolecular structure of template has been established. It is shown by Brunauer—Emmett—Teller method that the macromolecules having a branched architecture are more effective for the preparation of the polymer network with more developed specific surface area and narrow pore size distribution.