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The development of conjugated polymers with wide absorption spectra is imperative to achieve high efficiency in polymer solar cells (PSCs), since most of these polymers usually absorb only a limited range of the solar spectrum. Random terpolymers consisting of three blocks (one electron-donor and two electron-acceptor blocks) are promising p-type polymers for PSCs, because the inclusion of a third block in the polymer macromolecules provides a synergistic effect of physical properties, such as absorption capacity, charge transfer, HOMO/LUMO energy levels, and photovoltaic characteristics. In this regard, we have developed and synthesized random terpolymers consisting of two different chromophores (DPP and BFCTP) with complementary absorption spectra as co-acceptor blocks in conjugated donor–acceptor (D–A) copolymers. Random copolymers exhibit both broad absorption and low HOMO levels favoring short-circuit current and idle voltage in PSCs. It is expected that new terpolymers consisting of one electron-donor unit and two electron-acceptor moieties will make a significant contribution to the development of highly efficient PSCs. It is expected that new ternary copolymers consisting of one electron-donor unit and two electron-acceptor fragments will make a significant contribution to the development of high-performance PSСs.

The dielectric properties of electrochromic composite material based on poly[4,4’-(1,4-phenylene)bis(2,6-diphenylpyridinium)triflate] (PV) and multi-wall carbon nanotubes (MWCNTs) have been studied. Negative permittivity was registered at low frequencies of the alternating electric field ( $$10^{-1}{-}10^{3}$$ Hz) in the PV/MWCNT nanocomposites of different composition. The frequency of transition from negative to positive permittivity, as well as the values of conductivity, increased in the case of application of direct-current (dc) voltage. The physical mechanism responsible for the unusual properties appears to be related to the delocalized charges located at the multiple insulator–conductor interfaces.

The effect of temperature on water sorption by gels based on the copolymers of N-isopropylacrylamide with sodium p-styrene sulfonate containing 1, 3, and 5 mol % of charged monomer units is studied in aqueous media in the presence of salt (NaCl, KCl) or urea. It is shown that the incubation of gels in salt solutions leads to compression of the gels. With increasing temperature, the collapse of gels is observed in all studied media. The difference in the gel collapse temperature in water and salt solution increases with an increase in the fraction of charged units in the polymer gel network and in the salt concentration in the solution. With a return temperature decrease and gel decollapse, the mass of all gels in salt solutions (0.5–5.0 wt %) is completely restored. The incubation of gels in aqueous solutions of urea (0.5–5.0 wt %) has practically no effect on water sorption by gels before the collapse and the collapse temperature. However, the degree of swelling of polyelectrolyte gels during decollapse caused by a temperature decrease is much lower than the initial value, in contrast to the completely reversible swelling of the poly(N-isopropylacrylamide) gel under similar conditions.

Two donor–acceptor (D–A) conjugated polymers designed on same 8,10-bis(2-octyldodecyl)-8,10-dihydro-9H-bisthieno[2′,3′:7,8;3″,2″:5,6]naphtho[2,3- d]imidazole-9-one donor and dissimilar acceptor uni...

This study is focused on two electrochromic poly(pyridinium triflate)s. They are aromatic rigid-rod polymer PV1 and PV12 containing alkyl linkages. Electrochromic behavior of both polymers was comparatively investigated by employing a three-electrode cell and «smart windows» prototypes. The electrochromic properties of polymer films were examined by electrochemical and spectroelectrochemical methods. Polymers with π-conjugate and non-conjugate structure demonstrate reversible redox process accompanied by a reversible color change both in three-electrode cell and electrochromic device (ECD). In general, introduction of the non-conjugated spacers to the PV12 backbone structure leads to deterioration in the optical contrast and switching time in comparison with π-conjugated PV1. The same effect was also detected for ECD. The reason behind this is thought to be a complication of electron transport in the system due to non-conjugated PV12 backbone structure.

We synthesized and characterized a series of new random terpolymers composed of two electron-accepting blocks, diketopyrrolopyrrole (DPP) and benzothiadiazolequinoxaline (BTQx), and one electron-donating benzo[1,2-b:4,5-b′]dithiophene (BDT) unit with different molar ratios of the BTQx block to DPP block (25%, 50%, and 75% BTQx). The random terpolymers compositional effects on the physicochemical properties and photovoltaic performances were studied. Different compositions of DPP and BTQx blocks in the conjugated backbone of the terpolymers had a crucial effect on the electrochemical and optical properties of the random terpolymers. These terpolymers were employed as a donor along with PC71BM as an acceptor for solution-processed polymer solar cells. Among all the terpolymers, P13 (BDT–DPP50–BTQx50) with a monomer composition of BTQx and DPP (50 : 50) blocks showed excellent light-collecting ability, high charge-carrier mobility, and a low-lying HOMO energy level. PSCs based on P13 (BDT–DPP50–BTQx50) exhibited a Voc of 0.86 V, a Jsc of 15.74 mA cm−2, and an FF of 0.68, leading to a high PCE of 9.20%, which is higher than that for D–A copolymers, i.e., P11 (7.37%) and P15 (8.11%). These results demonstrate that random terpolymerization is a simple and practical approach for optimization of a conjugated polymer donor for efficient polymer solar cells.

The influence of different salts and pH on the stability of the aqueous dispersion of multiwalled carbon nanotubes (MWCNTs) non-covalently modified by thermosensitive poly(N-vinylcaprolactam) (PVCL) was studied. The PVCL/MWCNT dispersion was prepared by adding MWCNTs into aqueous PVCL solution with the subsequent ultrasonication and centrifugation. The morphology of MWCNTs and MWCNT/PVCL composites was characterized by TEM. The aggregation temperatures of the MWCNT/PVCL dispersion and the lower critical solution temperature (LCST) of PVCL aqueous solution were determined for different salt types and concentrations as well as pH in the temperature range between 20 and 60 °C. Specific ion effect on LCST of PVCL was analyzed in terms of the Hofmeister series. In the presence of kosmotropes, both the MWCNT/PVCL dispersion aggregation temperature and the LCST of PVCL are well consistent with the Hofmeister series of ions. However, opposite trends were observed for LCST of PVCL and the MWCNT/PVCL dispersion aggregation temperature when adding chaotropic anions. The dynamic light scattering (DLS) technique was used to study the PVCL aggregation kinetics at a temperature above the LCST at different pH values. These results demonstrate that specific thermoresponsive properties of the MWCNT/PVCL dispersion at pH

A new carbazole-containing naphthodithiophene derivative—heteroaromatic compound 5,6- bis[9-(2-decyltetradecyl)-9H-carbazol-3-yl]naphtho[2,1-b:3,4-b']dithiophene (M1)—has been synthesized. The compound will be used by us as a weak donor structural block for fabricating narrow-bandgap D–A conjugated polymers. The composition and structure of M1 have been confirmed by elemental analysis data, IR spectroscopy, and 1H and 13C NMR. The synthesized compound has a low HOMO energy (–5.4 eV), which is favorable for a high open-circuit voltage. Monomer M1 can be used as a promising weak donor moiety in D–A conjugated polymers for solar photovoltaics.

Two new fused quinoxaline-containing monomers—2,3-bis(9-(2-decyltetradecyl)-9H-carbazol-3-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—have been synthesized in high yields of 88 and 83% as promising building blocks of D-A polymers for photovoltaic applications. The optical bandgaps, found from the absorption edge, are 2.79 and 2.88 eV, respectively. The HOMO/LUMO energies of М1 and М2 are–5.83/–2.96 and–5.83/–2.98 eV, respectively. Both monomers have low-lying HOMO levels, which is favorable for a high open-circuit voltage and a high stability in air in the development of PSCs. The E g ec values of monomers М1 and М2 are 2.87 and 2.85 eV and are consistent well with the optical bandgap (2.79 and 2.88 eV, respectively).

New derivatives of bis[1,3]thiazolo[4,5-f:5',4'-h]thieno[3,4-b]quinoxaline containing the fused thiadiazoloquinoxaline moiety have been prepared. Monomer M1 shows strong light absorption within 600–800 nm due to intramolecular charge transfer. The optical bandgap E g opt determined from the absorption edge in a film is 1.44 eV. The HOMO and LUMO levels are–5.44 and–3.12 eV, respectively. The new structural fragment has a rather low frontier molecular orbital energies and a small bandgap; therefore, it is a promising building block for the synthesis of polymers for organic electronics.

The electrochromic composite material based on poly(4,4′-(1,4-phenylene)bis(2,6-diphenylpyridinium) triflate) (PV) and multiwall carbon nanotubes (MWCNTs) was prepared by non-covalent interaction where PV acts as a functionalizing agent for MWCNTs. The increase in electrical conductivity and improvement of electrochromic properties of PV is attributed to the formation of MWCNTs networks. The percolation threshold for PV/MWCNTs occurred at 0.3 wt% of MWCNTs. Corresponding value of critical exponent was found to be 2.8 which is far from universal values. At practically the same electrochromic contrast the coloring and bleaching time for composites with higher polymer concentration (8 mg/mL) decreased from 600 ms to 300 ms and from 500 ms to 350 ms, respectively. It was demonstrated that further increase of MWCNTs weight content did not lead to the improvement of electrochromic properties.

The interaction of N-vinylcaprolactam–methacrylic acid copolymer hydrogel and N-vinylcaprolactam homopolymer hydrogel with alcian blue in aqueous solutions is studied. It is shown that copolymer gel are thermo- and pH-sensitive. Dye sorption by the copolymer gel and gel swelling degree depends on the pH of the solution. The features of the system behavior resulting from the pH sensitivity of both the gel and the dye are shown. The thermocollapse of gels incubated in aqueous solutions of alcian blue is studied. It is shown that the transition temperature of N-vinylcaprolactam–sodium methacrylate copolymer gel to the collapsed state decreases with the dye absorption. The temperature-induced collapse of homopolymer gels in dye solutions is reversible, while the copolymer gel mass restores incompletely during the return temperature decrease. The dye absorption by the copolymer gel leads to decreased hysteresis.

This paper represents a simple approach to modulate electrochromic properties of poly (4,4′-(1,4-phenylene)bis (2,6-diphenylpyridinium) triflate) (PV) by the formation of composite material with multiwalled carbon nanotubes. The polymer acts as a functionalizing agent for MWCNTs to prevent their agglomeration enabling the formation of stable dispersions. They were further used to prepare uniform electrochromic films by spin-coating method. The films were characterized by electrochemical and spectroelectrochemical methods. To evaluate the influence of MWCNTs on the electrochromic properties of PV the dispersions with various PV/MWCNTs compositions were studied. Upon the addition of MWCNTs the absorption bands and redox peak potentials of polymer did not change. However, the decrease of the peak separation between reductive and oxidative waves and the significant improvement of switching times (one of the most important properties of electrochromic materials) were demonstrated. At the practically identical optical contrast both coloration and bleaching times decreased that can be explained by the composite film morphology. This effect became significant for high PV concentrations in the initial solution. The decrease of coloration and bleaching times reached 30% and 50%, respectively. The resulting composite material exhibited fast (200–400 ms) response times and could be used as a promising candidate for novel electrochromic devices.

Smart polymer gels of microscale size are attracting a lot of attention since their properties, such as fast response to various external stimuli, make them suitable candidates for many potential applications including drug delivery, nanoreactors, or separation techniques. In this research, thermosensitive microgels of poly(N-isopropylacrylamide), poly(N-vinylcaprolactam), poly(N-isopropylacrylamide-co-sodium vinylsulfonate) and poly(N-vinylcaprolactam-co-1-vinylimidazole) were prepared via aqueous free-radical precipitation polymerization. The thermo-induced collapse of the microgels and subchain mobility were thoroughly investigated by means of proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as scanning electron microscopy and dynamic light scattering. It was found that in copolymer microgels a part of the thermosensitive monomer units does not collapse upon heating, and the critical temperature is not affected strongly by the addition of ionogenic groups. That could be explained by non-uniform monomer unit distribution, leading to the appearance of thermosensitive core-charged corona structure of the microgel particle. Сore-corona architecture of microgels results in film formation with the ordering of the self-assembly structure.

The temperature influence on the behavior of microgels based on poly-N-isopropylacrylamide (PNIPA) homopolymer, N-isopropylacrylamide copolymers with sodium methacrylate (PNIPA/MANa), sodium styrenesulfonate (PNIPA/SSNa), and sodium vinylsulfonate (PNIPA/VSNa) was studied. The comparative analysis of the temperature-induced collapse of macro- and microgels was conducted. The interaction between alcian blue and PNIPA, PNIPA/SSNa, PNIPA/VSNa, and PNIPA/MANa gels was studied. The research showed that dye sorption leads to the contraction of oppositely charged microgels. The sorption effectiveness depends on the nature of the ionogenic units. The dye sorption by PNIPA/SSNa microgels is more effective than the sorption by the corresponding macrogels. The AB sorption by PNIPA/MANa microgels is less than the sorption by the corresponding macrogels and by the PNIPA/SSNa microgels. The interaction properties are connected to the structure of the crosslinked polymer chains in the microgels.

The dielectric properties of polyacrylic acid were studied using dielectric spectroscopy method in the frequency and temperature ranges 0.2 Hz–2 MHz and 2–70°C (at heating), respectively. Thermogravimetric analysis and differential scanning calorimetry were also employed at 25–250°C. A linear dielectric dispersion has been observed at low frequencies. Analysis of electrical modulus showed that the main relaxation process is characterized by non-Debye relaxation time spectrum. The observed anomalies of dielectric properties (conductivity, electrical modulus, dielectric permittivity) are probably related to the presence of water in the sample.

Electrochromic behavior of poly(amine-amide) with pendant N-phenylcarbazole and triphenylamine units (A1) and its composites with multiwalled carbon nanotubes (MWCNTs) were investigated. Cyclic voltammetry showed four separate redox processes with oxidation peaks at Eox1 = 720 mV, Eox2 = 1070 mV, Eox3 = 1295 mV and Eox4 = 1730 mV vs Ag/Ag+. The first two reactions are reversible and spectroelectrochemical analysis demonstrated color changes. A1 exhibits a colorless initial state, a green radical cation state, and a blue dication state. The polymer exhibits a good stability during the electrochromic tests in the range of -400 to 1100 mV with minimal loss of the transmittance during 30 cycles. The potential increasing above 1100 mV induces the third and fourth redox reactions and results to coloring film to deep blue. However, these redox processes are chemically and electrochemically irreversible. Detailed calorimetric study and FTIR-spectra analysis of polymer before and after electrochemical measurements show change of the macromolecular structure induced by the redox processes at potentials above 1100 mV. The introduction of MWCNTs in the polymer films improves the kinetics of switching between the A1 color states while a slight decrease in the optical contrast. The FTIR spectroscopy, TG and DSC results of A1/MWCNT composites (in the range of the studied component composition) before and after electrochemical tests practically coincide with the data for pristine polymer and indicate a change in the polymer structure in the third and fourth redox reactions. Thus, the introduction of MWCNTs leads to an improvement in electrochromic characteristics during reversible redox reactions, but does not affect the destructive processes induced by the third and fourth oxidative reactions.

This paper represents a synthesis method of both soluble and insoluble interpolyelectrolyte complexes due to interaction of poly(4,4-(1,4-phenylene)bis(2,6-diphenylpyridinium) triflate) (PV) and sodium polystyrene sulfonate (PSS). Systematic evaluation of electrochromic properties of the both type complexes is given compared to the pristine electrochromic PV. The complexes composition and properties were studied as a function of polyanion and polycation concentrations and their ratios. It was demonstrated that non-stoichiometric insoluble complexes PV/PSS with an excess of PSS are formed in the initial mutual solvent DMF/H2O 5/1. Films prepared from that mixtures exhibit slower response times and deteriorated electrochromic stability. Non-stoichiometric interpolymer complexes PV/PSS with an excess of PV remain soluble in the initial solvent. Corresponding films have a superior electrochromic contrast than films obtained from the solution of pristine PV under identical conditions. Thus, optimum mixture ratios were found to obtain soluble interpolymer complexes with the advanced properties that may open up new possibilities for making novel electrochromic devices.

The behavior of sodium polyacrylate is studied via broadband dielectric spectroscopy. The non-Debye response in the frequency range 0.1 Hz–1.0 MHz, the non-Markovian dispersion in the infralow-frequency range, and the anomalies of dielectric permittivity and ac conductivity near “peculiar” temperatures of water (20, 35, 50, and 75°C) are ascertained experimentally. These facts make it possible to assign sodium polyacrylate to disordered media, in which the temperature behavior of dielectric parameters is described by the Kohlrausch–Williams–Watts relaxation function.

The interaction of lightly crosslinked polyelectrolyte hydrogels based on N-isopropylacrylamide copolymers with Alcian Blue in aqueous solutions is studied. The effects of the type and fraction of ionogenic groups of polymer network chains on the behavior of gels in aqueous solutions of the dye are analyzed. Dependences of the degrees of swelling of the gels and absorption of the dye on its concentration are measured. The effect of temperature on the collapse of the gels incubated in dye solutions is examined. It is shown that the temperature of gel collapse and its reversibility depend on the fraction of dye-bonded ionogenic units.

Electrochromic properties of poly(pyridinium triflate) PV and its polymer blend with poly(N-vinylcaprolactam) (PV/PVCa) are reported. PV films change their color from transparent slight yellow to blue in a reversible and reproducible manner upon application of potentials within the limits of 0.4 V and −1.2 V vs Ag/AgCl in a 3.5 KCl (aqu) solution. The main electrochromic properties of PV and PV/PVCa were evaluated by a series of cyclic voltammetry and chronoabsorptometry experiments of identical thin films. PV/PVCa films demonstrate electrochromic contrast enhancement (ΔT = 32% for pure PV and 40% for PV/PVCa) and narrowing of a colored cation absorbance peak. At the same time, PV/PVCa thin films exhibit slower switching time suggesting restrictions of counterion diffusion during charging/discharging processes. Coloring (transmittance change of 97–70% at 700 nm) and bleaching times for PV films are 0.26 and 0.77 s, respectively. The same values for PV/PVCa films (transmittance change of 97–61% at 700 nm) are about 1.20 and 13.50 s. Dramatic changes in electrochromic behavior of PV in the presence of PVCa can be attributed to the interaction between PVCa amide groups and PV radical cations induced by electrochemical reaction.

Semi-interpenetrating networks based on polyacrylamide gel and linear thermosensitive poly(N-vinylcaprolactam) are obtained for the first time and studied via the method of dynamic light scattering. Contributions associated with dynamic fluctuations and frozen inhomogeneities to scattering are determined. It is shown that the ensemble-average scattering intensity strongly depends on the quantity and dimensions of frozen inhomogeneities. As temperature increases, scattering due to both dynamic fluctuations and spatial inhomogeneities tends to increase. At the temperature of the conformational transition of poly(N-vinylcaprolactam), the intensity of scattering increases abruptly, whereas the correlation function assumes the shape of a strongly stretched exponent that corresponds to high relaxation times (∼1 s). It is found that the relaxation-time distribution restored with the use of the inverse Laplace transform contains several modes. For all the studied networks, the correlation length of the mode of cooperative motion (the fast mode) is independent of the concentration of poly(N-vinylcaprolactam) and coincides with the correlation length of the mode of collective motion for the polyacrylamide gel.

This paper describes the investigation of the behavior of polyelectrolyte thermosensitive hydrogels based on copolymers of N-isopropylacrylamide and sodium vinylsulfonate at different temperatures. The influence of ionogenic groups on the swollen gel-collapsed gel phase transition was studied by means of highly sensitive differential scanning calorimetry. It was demonstrated that the presence of ionogenic groups in the thermosensitive copolymer influences the reversibility and the amplitude of gel collapse, as well as the temperature, enthalpy, and increment of the transition heat capacity.

Thermosensitive ionic semi-interpenetrating polymer networks (semi-IPNs) based on poly(N-isopropylacrylamide) (PNIPAAm) and poly(styrene sulfonic acid sodium salt) (PSS) were synthesized, and their properties, such as conversion, swelling ratio and swelling/shrinking kinetics, were studied at different PSS fractions and molecular weight (MW). It is shown that studied semi-IPN hydrogels undergo shrinking under temperature increase. Swelling behavior and volume transition temperature of the semi-IPNs is controlled by the polyelectrolyte fraction. The increase of PSS MW allows obtaining of stable semi-IPN hydrogels. A novel phenomenon of collapse irreversibility in PNIPAAm-PSS semi-IPNs is reported. In contrast to PNIPAAm hydrogels, semi-IPNs of PNIPAAm with immobilized polyelectrolyte do not restore their volume when they reswell after shrinking. The magnitude of this effect is connected to the charged polyelectrolyte fraction.

The effect of the different kinds of ionogenic groups of copolymers of N-isopropylacrylamide with sodium methacrylate, sodium vinylsulfonate, and diallyldimethylammonium chloride on the temperature-induced conformation transition from a swollen gel to a collapsed gel is studied. The presence of different kinds of ionogenic groups in a thermosensitive copolymer is shown to affect the temperature, collapse amplitude, and reversibility of the transition between the swollen gel and the collapsed gel.

Using Mossbauer spectroscopy, we have studied iron complexes resulting from the interaction of aqueous iron salt solutions with poly(methacrylic acid) (PMAA) gel. In these complexes, the di- and trivalent Fe ions are linked to the PMAA through the COO− functional group. From the observed dynamics of the variation in the intensities of the di- and trivalent iron in the Mossbauer spectra of the gels with incubation time and iron concentration in solution, we have inferred a model for the incorporation of Fe ions into a gel matrix.

New triarylamino-containing bis(α-diketones) are synthesized. On the basis of these compounds, a series of electrochromic organosoluble polyphenylquinoxalines with glass-transition temperatures of 224–315°C are prepared. All polymers intensively fluoresce in solutions and thin films with maxima at 535–600 and 530–560 nm, respectively. Cyclic voltammograms of polyphenylquinoxalines exhibit reversible redox properties in the range E 1/2 = 0.92–1.25 eV. It is shown that, after 15 cycles, all polymers preserve high stability and reversibility of electrochromic characteristics, but their color changes from yellow (neutral form) to wine red (oxidized form).

The dielectric relaxation and conductivity of polyvinylcaprolactam (PVCL)-water systems of different compositions (with water contents of ∼1, 5, and 24 wt %) were studied by means of dielectric spectroscopy (10−1–107 Hz) at −100−50°C. It was found that the conductivity of samples with a low content of water upon cooling has an activation character, whereas a cooperative mechanism of conduction holds for the PVCL-water system with 24 wt % water, which switches to an activation character of interactions of water with polymer changes in the course of a glass transition.

A new aromatic diamine, 1,1-bis(4-aminophenyl)-1-{4′-bis(4″-bromophenyl)amino}phenyl-2,2,2-trifluoroethane, is synthesized. Its interaction with various dianhydrides of aromatic carboxylic acids via high-temperature polycondensation yields a number of new functionalized poly(imides) combining high thermal and mechanical characteristics with solubility in organic solvents. The values of Tg vary from 208 to 230°C, and temperatures corresponding to 10% weight loss fall within the intervals 330–370 and 550–660°C (in air and argon, respectively). Spectroelectrochemical characteristics of poly(imides) are studied by cyclic voltammetry and UV-VIS spectrometry. Poly(imides) exhibit high reversible stability of electrochromic properties, and their color changes from colorless (the neutral form) to green (the oxidized form) as the applied potential is varied from 0 to 1.25 V.

Interaction of water molecules and the polymer matrix of poly(N-vinylcaprolaktam) (PVCL), depending on temperature (−100 and 50°C) and water concentration (less than 1, 5 and 24 wt %), was investigated using the dielectric spectroscopy method (at 10−1–107 Hz). The presence of characteristic temperature points of changes of system properties, whose values depend on the quantity of water molecules in the polymer, was identified. It was found that the mechanism of temperature influence and water concentrations changes the characteristics of hydrogen bonds.

Local networks of κ-carrageenan adsorbed in the presence of an ionic surfactant and phenylalanine were examined by atomic force microscopy (AFM). Polymer chains of adsorbed carrageenan are aligned with crystallographic axes. The helical and globular conformations of carrageenan effectively bind the surfactant. Phenylalanine is not involved in the structuration of the carrageenan gel.

The interaction of weakly crosslinked gels of poly(methacrylic acid) and a nonionic gel based on N-vinylcaprolactam and N-vinylimidazole with Fe2+ ions in aqueous solutions has been studied. A comparative study of the conformational state and of the absorption ability of the gels for their interaction with iron and ferroin ions has been performed. It has been shown that Fe2+ ions are efficiently absorbed by both poly(methacrylic acid) gels and the gels based on N-vinylcaprolactam and N-vinylimidazole. In this case, the poly(methacrylic acid) gels undergo contraction, while nonionic gels derived from N-vinylcaprolactam and N-vinylimidazole experience swelling. During the interaction of gels containing immobilized Fe2+ ions with phenanthroline, the efficient absorption of the complexon and the formation of Fe2+-phenanthroline complexes in the gel volume take place, thus inducing the contraction of gels. The interaction of poly(methacrylic acid) gels with ferroin is accompanied by the absorption of the complex, the formation of the tertiary complexes, and the collapse of the gel. The efficiency of formation of tertiary complexes in the gel volume is independent of their preparation procedure.

The effect of amino acids, phenylalanine and lysine, and lithium ions on the conformation state of κ carrageenan has been studied by high-sensitivity DSC. The binding constants of lysine and lithium ions with the helical and coil forms of polysaccharide have been measured. The preferential binding of lysine molecules and lithium ions by the helical conformation of κ carrageenan has been demonstrated. The affinity of the helical form of κ carrageenan to lysine is much higher than that to lithium ions. The conformational state of κ carrageenan in the presence of cetyltrimethylammonium bromide has been investigated. The binding of cetyltrimethylammonium by κ carrageenan molecules leads to development of a new ordered structure of the polysaccharide.

A new classification for amino acid residues is proposed, based on interfacial and partitioning properties. Amino acid residues are characterized by two parameters: standard free energy of adsorption at the hexane/water interface and standard free energy of the partition between hexane and water. Theoretical approaches are used for the estimation of these parameters. As a result, several groups of amino acid units having close values of the parameters are distinguished. Classification of the amino acid units by such a method is believed to be able to provide promising results in the search of correlations in protein sequences. The comparison of experimental and theoretical studies of free amino acids at the hexane/water interface confirm the predictive power of the theory used, because a very good coincidence between theoretical and experimental data points is observed. The obtained values of standard free energies of adsorption are consistent with literature data.

The effect of poly(acrylic acid) and poly(methacrylic acid) on the molecular state of a cationic cyanine dye (3,3′-diethyl-2,2′-thiacarbocyanine iodide) was studied. Gels based on the above polymers were shown to efficiently absorb an oppositely charged dye. The absorption of dye ions by a gel induced their aggregation. It was shown that, in the acrylic acid-based gels, H-aggregates, dimers, and single ions of the dye coexist. In gels containing methacrylic acid units, dye ions mainly formed H-aggregates. A comparison of aggregation of dye ions in the gels with that in aqueous solutions of corresponding polyelectrolytes was performed. When dye ions were immobilized in a gel network, the proportion of the ions forming the H-aggregates was considerably larger than that in solutions. The effect of the gel network charge density on the aggregation of dye ions was investigated. It was shown that an increase in the fraction of charged units in network chains facilitates aggregation.

Phase and conformational behavior of poly(N-vinylcaprolactam) was studied as a function of polymer concentration, concentration of NaCI, and concentration of sodium dodecyl sulfate (SDS). Precise measurements of the partial heat capacity of the polymer were first carried out within the temperature range 10-125 °C. Thermodynamic parameters of the phase separation transition (transition temperature, enthalpy, and heat capacity increment) do not change with variations in polymer concentration. In the presence of salt the transition temperature decreases, the enthalpy increases, and the heat capacity increment does not vary significantly. Beginning with the SDS concentration of 0.005 M, the phase separation is suppressed and the heat capacity peak splits into two peaks. Upon further increase in surfactant concentration the amplitude of the low-temperature peak increases while that of the high-temperature peak vanishes. Phase separation transition in aqueous solutions of N-vinylcaprolactam-methacrylic acid copolymers of different compositions were studied at different polymer concentrations and pH (4-12). The transition parameters do not depend on polymer concentration and pH.

Formation of core-shell poly(N-vinylcaprolactam) (PVCL) single-molecule nanostructures due to interaction of PVCL with metal ions was studied using transmission electron microscopy, 13C NMR, and light scattering. This study demonstrates that addition of CoCl2 to PVCL in its globular conformation yields unimolecular core-shell polymer particles with the core decorated with Co(II) ions. The crucial condition for formation of well-defined unimolecular nanostructures is the presence of stable globular aggregates in aqueous solution. Moreover, the metal ions should have a sufficiently high coordination number (higher than 2) to provide a cross-linking and stabilization of the core.

Poly(N-vinylcaprolactam-co-1-vinylimidazole) (PVCL−Vim) and poly(N-isopropylacrylamide-co-1-vinylimidazole) (PNIPA−Vim) are thermosensitive in water and water−2-propanol solutions. These copolymers are soluble at room temperature; however, they undergo phase transition at higher temperatures (Ttransition > 35 °C). Catalytic properties of PVCL−Vim and PNIPA−Vim as well as of 1-methylimidazole and poly(1-vinylimidazole) (PVim) in hydrolysis of p-nitrophenyl acetate were studied. Variation of the reaction rate with temperature was investigated at constant concentrations of substrate and catalyst (imidazole groups). It was found that the reaction catalyzed by the copolymers does not follow Arrhenius-type behavior: as temperature is increased over the aggregation temperature, the reaction rate increases faster than it could be predicted from the Arrhenius law. This was explained via the assumption that the substrate having an affinity to polymer/solvent interface can be adsorbed at the surfaces of polymer agg...

Laser light scattering and differential scanning calorimetry measurements have been performed for aqueous solutions of thermosensitive linear copolymers of N-vinylcaprolactam and methacrylic acid o...

Complexes of polyelectrolyte gels with oppositely charged surfactants form ordered polymer matrices with unique structure properties, which can be used in a wide range of medical, chemical and physical applications. Ordered matrices made of natural components are of special interest for medical and biological purposes. In the present study, self-organised complexes of native ι- and κ-carrageenans formed with oppositely charged cetylpyridinium chloride (CPC) are prepared and structurally characterised using small-angle X-ray scattering (SAXS). Starting from the molar ratio CPC/(charge of carrrageenan) of 0.2, the carrageenan gel shrinks and ordered motifs in its internal structure are formed. The internal order in the sample is reflected by the Bragg peaks in the scattering patterns which permit to compute periodicity and characteristic sizes of the ordered regions. Moreover, strong central scattering appears and the calculated fractal dimensions indicate that these regions are organised in well defined clusters. The periodicity of the ordered motifs computed from the Bragg peaks in the scattering patterns corresponds to the width of the surfactant bilayer (about 4.0 nm) for all the complexes. The crystallite size ranges from 25 nm to 40 nm depending on the type of carrageenan and on the amount of CPC. A model of the ordered fragments is proposed whereby the carrageenan/surfactant bilayers are regularly packed at the walls of hollow cylindric clusters with the outer radius of about 8 nm and height 40 nm. More detailed ab initio models indicate that these particles are formed by bent worm-like substructures with the cross-section coinciding to the thickness of the carrageenan/CPC bilayer. Thanks to a higher charge density per monomer, ι-carrageenans form more regular structures than κ-carrageenans.

Dynamic light scattering measurements have been performed for aqueous solutions of linear copolymer of N-vinylcaprolactam (VCa) and methacrylic acid (MA) with variable composition (i.e., charge degree of polymer chain). The swelling behavior of macromolecules was investigated as a function of both the solution pH value and fraction of methacrylic acid groups. It was shown that these copolymers are thermosensitive, and intermacromolecular aggregation takes place at the temperature increase. They exhibit compositionally dependent swelling behavior as a function of both pH and temperature. The behavior of studied copolymer was explained by the partial formation of ion pairs. The dependence of hydrodynamic diameter on pH of the solution is nonmonotonic. In acidic media at room temperatures we observed the intermolecular aggregation of copolymers accompanied by a sharp increase of the light scattering intensity. In alkaline media intermacromolecular aggregation is observed at higher temperatures. The effect of...

The complex formation of organogels based on poly(N-vinylcaprolactam) (PVCa) and organic dyes [5-(4-dimethylaminobenzylidene) rhodanine, α-nitroso-β-naftol, and dithizone] and the properties of the complexes in salt aqueous solutions were studied. PVCa gels absorbed these dyes in organic media (ethanol and chloroform). Our main focus was the behavior of the gel/dye complex immersed in a salt aqueous solution if the dye was the chelating ligand for metal ions. The behavior of the PVCa/dithizone (Dz)/chloroform system was studied in AgNO3 aqueous solutions. The absorption spectra of gel/dye and gel/dye/metal ion systems were investigated. The results obtained indicate that Ag+ ions penetrate the gel phase and that the Dz/silver complexes are indeed formed inside the gel. The dependence of the optical density of the gel/dye/metal ion systems on the AgNO3 concentration was observed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3238–3243, 2001

The behavior of slightly crosslinked poly(N-vinylcaprolactam) (PVCa) gels in a CuSO4 solution in water and ethanol was studied. The investigation was carried out for PVCa gels with polymer contents of 4% and 7%. The effective absorption of CuSO4 by PVCa hydrogel accompanied by gel shrinking was observed for the CuSO4 aqueous solution. It was shown that dendrite crystals of CuSO45H2O localized within the gel sample are obtained after placement of gels samples into ethanol. The crystal habit depends on gel concentration. It was found that slightly crosslinked PVCa gels are promising as media for the growth of crystals. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2838–2842, 2001

Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa–non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl. The behaviour of ternary systems PVCa macromolecules–ionic surfactant–pyrogallol and PVCa macromolecules–ionic surfactant–NaCl was studied. The addition of pyrogallol leads to the suppression of the intermacromolecular aggregation induced by temperature increase that is still observed at low surfactant concentrations and to the decrease of macromolecular hydrodynamic diameter. Also, the addition of NaCl to the PVCa/ionic surfactant systems results in the increase of the macromolecular hydrodynamic diameter. It is speculated that these results are due to the suppression of the cross-linking role of surfactant aggregates upon the addition of NaCl and pyrogallol.

We report the first accurate measurements of the partial heat capacity of poly(N-isopropylacrylamide) hydrogels with varying cross-link density. When the cross-link density is increased, the transition broadens and the transition temperature decreases, while the enthalpy, entropy, and heat capacity increment of the transition do not practically change. The transition heat capacity increment is negative, Δtcp = −0.63 ± 0.04 J/g/K. This indicates the formation of a hydrophobic core of the gel upon the transition. The partial heat capacity of polymer network in the gel approaches the partial heat capacity of the unfolded linear poly(N-isopropylacrylamide) at low temperatures, indicating a complete disordering of the gel under these conditions. On the basis of the calorimetric data, thermodynamic functions of the transition were calculated from 0 to 150 °C. They allow one to compare enthalpic and entropic contributions to the stabilization of the collapsed gel. This state is found to be most stable at about 1...

Small-angle X-ray scattering (SAXS) was used to study the structure of ι-carrageenan gels formed in the presence of cationic surfactant cetylpyridinium chloride (CPC) at various concentrations of the polysaccharide and as a function of the surfactant concentration. A physical gel of low ι-carrageenan concentration displays no characteristic peak at small angles. After addition of CPC to the ι-carrageenan solution central scattering and equidistant characteristic peaks appear due to ordering in the gel structure. This ordering is the result of complex hydrophobic and electrostatic interactions between the polymer chains and the charged surfactants. The ι-carrageenan gelation in the presence of CPC leads to self-assembly of surfactant molecules inside the physical gel similarly to micellization in a solution. In this case the shrinking or collapse of polyelectrolyte gels takes place. The additional central scattering emerges due to the process of surfactant micellization. The relative positions of the main ...

The present work is devoted to the study of the complex formation of polymer gel with organic dye and their properties in the aqueous salt solutions. Two systems were studied: 1) polyelectrolyte gel based on poly(diallyldimethylammonium chloride) and water soluble oppositely charged organic dyes (alizarin red S and catechol violet) and 2) organogel based on poly(N-vinylcaprolactam) and dithizone. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depends on the dye concentration. In the case of PVCa gel in organic media the dye absorption takes place. The main attention has been concentrated on the study of the behaviour of gel/dye complex immersed in the salt solution if dye is the chelating ligand for metal ions. It was shown that polyelectrolyte gels generally form stable complexes with oppositely charged dyes. The behaviour of PVCa-dithizone-chloroform system was studied in AgNO 3 aqueous solution. The release of dithizone to the external aqueous solution of AgNO 3 reservoir is completely suppressed. Absorption spectra of gel/dye and gel/dye/metal ion systems were studied. It was shown that metal ions penetrate inside the gel phase and the dye/metal ion complexes form within the gel. The dependence of the optical density for the systems of gel/dye/metal ion on the salt concentration is observed.