The Microscopic Structure–Property Relationship of Metal–Organic Polyhedron Nanocomposites

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)₂₄Cu₂₄ metal–organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined‐extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP‐composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs.     

Stimuli-Responsive Polymers in Solution Investigated by NMR and Infrared Spectroscopy

Summary: Temperature-induced and solvent composition-induced phase separation in solutions of poly(N-isopropylmethacrylamide) (PIPMAm) and other thermoresponsive polymers as studied by NMR and infrared (IR) spectroscopy is discussed. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters characterizing the coil-globule phase transition induced by temperature, were determined from reduced integrated intensities in high-resolution ¹H NMR spectra. This approach can be especially useful in investigations of phase separation in solutions of binary polymer systems. Information on behaviour of water during temperature-induced phase transition was obtained from measurements of ¹H NMR relaxation times of HDO molecules. NMR and IR spectroscopy were used to investigate PIPMAm solutions in water/ethanol (D₂O/EtOH) mixtures where the phase separation can be induced by solvent composition (cononsolvency). Some differences in globular-like structures induced by temperature and solvent composition were revealed by these methods.     

NMR Investigations of Temperature-Induced Phase Transition in Aqueous Polymer Solutions

The different dynamics of polymer segments forming phase-separated globular structures in aqueous (D₂O) solutions affects both the shape of NMR spectra and NMR relaxation times of polymer and solvent. Two types of the approach are discussed. The first one is based on the reduction of integrated intensities of polymer NMR lines in high-resolution NMR spectra in the system undergoing the coil-globule phase transition. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters ΔH and ΔS characterizing the coil-globule phase transition can be determined. The second approach is based on measurements of ¹H NMR relaxation times of water (HDO) which provide information on behaviour of water during phase transition. The power of both approaches is demonstrated on results obtained with solutions of several thermoresponsive homopolymers and copolymers.     

Role of the deuterium isotope in the formation of the behavior of thermosensitive poly(2-isopropyl-2-oxazoline)

Thermosensitive star-shaped poly(2-isopropyl-2-oxazoline) is studied via light scattering in D₂O solutions in a ten-fold concentration range at the temperatures from 21 to 60°С. The data are compared to the results of investigations on this polymer in Н₂O at close concentration values. A qualitative similarity in behavior of the polymer in the compared solvents is established; the changes that occur after the change from Н₂O to D₂O are quantitative. After changing to the deuterated solvent, the initial temperature of phase separation decreases by 0.5–1.0°С. The lower the solution concentration, the greater the width of the phase-separation interval.     

Decreased Water Mobility Contributes To Increased α-Synuclein Aggregation**

The solvation shell is essential for the folding and function of proteins, but how it contributes to protein misfolding and aggregation has still to be elucidated. We show that the mobility of solvation shell H₂O molecules influences the aggregation rate of the amyloid protein α-synuclein (αSyn), a protein associated with Parkinson's disease. When the mobility of H₂O within the solvation shell is reduced by the presence of NaCl, αSyn aggregation rate increases. Conversely, in the presence CsI the mobility of the solvation shell is increased and αSyn aggregation is reduced. Changing the solvent from H₂O to D₂O leads to increased aggregation rates, indicating a solvent driven effect. We show the increased aggregation rate is not directly due to a change in the structural conformations of αSyn, it is also influenced by a reduction in both the H₂O mobility and αSyn mobility. We propose that reduced mobility of αSyn contributes to increased aggregation by promoting intermolecular interactions.     

Effect of the solvent on the 13C NMR spectra of pyrimidine nucleosides

The ¹³C NMR spectra of uridine and cytidine in d₆-DMSO, d₇-DMF, d₉-trimethyl phosphate, d₄-methanol, d₅-pyridine, and D₂O were investigated. A linear correlation between the C₁' chemical shifts and the J₁' vicinal spin-spin coupling constants of the protons was established. From the experimental data it may be assumed that the chief reason for the effect of the solvent on the C₁'₂' chemical shift is the different contribution of the effect of the base as a consequence of a change in the conformational equilibrium of the ribose ring. Deviations from the correlation in aqueous solutions and solutions of cytidine in pyridine are observed as a result of a change in the electron density in the base. The effect of the nature of the solvent on the position of the conformational equilibrium of the base relative to the glycoside bond was demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1550–1552, November, 1980.     

A model for predicting solvent self-diffusion coefficients in nonglassy polymer/solvent solutions

Cohen-Turnbull diffusion theory is used to develop a model for predicting solvent self-diffusion coefficients D₁ in nonglassy polymer/solvent solutions. Polymer molecules are envisioned as hindering solvent mobility by reducing the average free volume per unit mass in the system and through the lower mobility of polymer segments relative to solvent molecules. The concentration dependence of D₁ predicted by the model is in reasonable agreement with data for the solvents heptane, hexadecane, benzene, cyclohexane, and decalin in polyisobutylene (PIB), and for toluene in polystyrene, poly(methyl mothacrylate), and PIB. Although none of the data is for high concentrations of polymer (volume fractions ?≥0.9) it is anticipated the model will be less representative in this regime where the assumptions in its development are unsure. The model also demonstrates the correct temperature and concentration dependence of the apparent activation energy for diffusion. The only experimental data needed to use the model are the viscosity and critical volume of the pure solvent, and the specific volume of both the solvent and mixture. No binary transport data are required.     

Nanocomposites of silver with arabinogalactan sulfate: Preparation,structure, and antimicrobial activity

Silver-containing nanocomposites based on sulfated arabinogalactan have been prepared under mild conditions. The products contain 2–12 nm silver nanoparticles stabilized by the polymer. The composites are readily water-soluble and reveal antimicrobial activity against a wide range of bacteria and fungi.

     

Investigation of the dynamics of poly(ether sulfone) membrane formation by immersion precipitation

Cast‐leaching experiments were carried out to investigate the dynamics of membrane formation by immersion precipitation, with an emphasis on the outflow of the solvent from casting solutions during the phase‐separation process. The casting solutions, consisting of poly(ether sulfone) as the polymer, N‐methyl‐2‐pyrolidone as the solvent, and water (H₂O), isopropyl alcohol, 1‐butanol, and diethylene glycol as nonsolvent additives (NSAs), were immersed in a coagulation bath. Two thermodynamically vastly different coagulants? H₂O, a strong coagulant, and ethylene glycol, a weak coagulant—were used to study the effect of the coagulant on the dynamics of membrane formation. The results showed that the outflow of the solvent during the initial stage of membrane formation was controlled by Fickian diffusion within the extremely wide range of conditions studied, that is, polymer concentrations of 10–38%, approaching ratios of 0–0.95, and thermodynamically vastly different NSAs and coagulants. The role of the initial state of the membrane‐forming solution, especially the conformational state of macromolecules in the membrane‐forming process, was examined. In contrast to those works on the behavior of small molecules, an attempt was made to qualitatively interpret membrane formation from the viewpoint of macromolecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 498–510, 2005     

Influence of the preparation conditions on the textural properties andn-hexane isomerization activity of Pt/SO42??ZrO2

The effect of Na₂SO₄ and PhCOONa on the aquation of [Fe(Me₄phen)₃]²⁺ has been investigated in pure Triton X-100 as solvent. The rate and mechanism of the aquation are explained in terms of changes in the mobility, activity and structure of H₂O in the restricted environment of water pockets in the Triton X-100 solvent.     

Effect of the Solvent on the Conformation of Isolated MEH‐PPV Chains Intercalated Into SnS2

Photophysical processes in conjugated polymers are influenced by two competing effects: the extent of excited state delocalization along a chain, and the electronic interaction between chains. Experimentally, it is often difficult to separate the two because both are controlled by chain conformation. Here we demonstrate that it is possible to modify intra‐chain delocalization without inducing inter‐chain interactions by intercalating polymer monolayers between the sheets of an inorganic layered matrix. The red‐emitting conjugated polymer, MEH‐PPV, is confined to the interlayer space of layered SnS₂. The formation of isolated polymer monolayers between the SnS₂ sheets is confirmed by X‐ray diffraction measurements. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of the incorporated MEH‐PPV chains reveal that the morphology of the incorporated chains can be varied through the choice of solvent used for chain intercalation. Incorporation from chloroform results in more extended conformations compared to intercalation from xylene. Even highly twisted conformations can be achieved when the incorporation occurs from a methanol:chloroform mixture. The PL spectra of the MEH‐PPV incorporated SnS₂ nanocomposites using the different solvents are in good agreement with the PL spectra of the same solutions, indicating that the conformation of the polymer chains in the solutions is retained upon intercalation into the inorganic host. Therefore, intercalation of conjugated polymer chains into layered hosts enables the study of intra‐chain photophysical processes as a function of chain conformation.     

Selective adsorption to cellulose in cadoxen solution

Refractive index and density increments at constant composition and also at constant chemical potential have been measured on solutions of cellulose in alkaline aqueous cadoxen. Apparent and true molecular weights of cellulose in this solvent have been determined by light scattering. The findings indicate that [Cd(en)₃]²⁺ ions are preferentially adsorbed to the polymer to the average extent of two ions per three anhydroglucose subunits. Molecular models have shown that this effect is feasible sterically. In cadoxen alone the specific conductance increased with increasing concentration of cadmium and, for a fixed cadmium concentration, the specific conductance was observed to decrease with increasing concentration of dissolved cellulose. This was attributed to reduced overall ionic mobility resulting from selective adsorption of complex cadmium ions to the polymer chain. An analysis has been proposed to quantify this interaction.     

Electrocatalytic properties of nanocomposites based on conducting polymers and titanium dioxide in oxygen reduction process

Electrochemical characteristics and electrocatalytic properties in the oxygen reduction reaction are studied on hybrid nanocomposites based on conducting polymers (polyaniline, polypyrrol) doped with phosphomolybdic acid (PMA), and TiO₂ and also their bifunctional analogs containing up to 5 wt % of nanosize platinum. It is found that the obtained nanocomposites in 0.5 M H₂SO₄ are capable of reversible electro-chemical redox transitions (in the range of potentials from ?0.6 to 1.0 V vs. Ag/AgCl), in which the main contribution is provided by the corresponding conducting polymer and dopant (PMA). It is shown that activity of the studied nanocomposites in the oxygen reduction reaction is caused by the joint catalytic effect of all their components: the polymer, TiO₂, H₃PMo₁₂O₄0, Pt.     

Extraction and sorption preconcentration of rare-earth elements(III) and scandium(III) with phosphorylmethyl-substituted butylphenylphosphinates from perchloric acid solutions

The interphase distribution of microamounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc perchlorates between aqueous HClO₄ solutions and solutions of bidentate phosphorylmethyl-substituted butylphenylphosphinates Oct₂P(O)CH₂P(O)Ph(OBu) (compound I) and Ph₂P(O)CH₂P(O)Ph(OBu) (compound II) in 1,2-dichloroethane is studied. The stoichiometry of extracted complexes is determined, and the efficiency of metal ion extraction into the organic phase is considered as a function of the HClO₄ concentration in the aqueous phase and the nature of the organic solvent. The possibility of concentrating rare-earth elements (REE)(III) and scandium(III) from HClO₄ solutions with the complexing sorbent synthesized by noncovalent immobilization of I and II compounds on a macroporuos polymer matrix is shown.     

Polymer–nanoparticle interfacial interactions in polymer nanocomposites: Confinement effects on glass transition temperature and suppression of physical aging

The effects of confinement on glass transition temperature (T_g) and physical aging are measured in polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(2-vinyl pyridine) (P2VP) nanocomposites containing 10- to 15-nm-diameter silica nanospheres or 47-nm-diameter alumina nanospheres. Nanocomposites are made by spin coating films from sonicated solutions of polymer, nanofiller, and dye. The T_gs and physical aging rates are measured by fluorescence of trace levels of dye in the films. At 0.1–10 vol % nanofiller, T_g values can be enhanced or depressed relative to neat, bulk T_g (T_g,bulk) or invariant with nanofiller content. For alumina nanocomposites, T_g increases relative to T_g,bulk by as much as 16 K in P2VP, decreases by as much as 5 K in PMMA, and is invariant in PS. By analogy with thin polymer films, these results are explained by wetted P2VP–nanofiller interfaces with attractive interactions, nonwetted PMMA–nanofiller interfaces (free space at the interface), and wetted PS–nanofiller interfaces lacking attractive interactions, respectively. The presence of wetted or nonwetted interfaces is controlled by choice of solvent. For example, 0.1–0.6 vol % silica/PMMA nanocomposites exhibit T_g enhancements as large as 5 K or T_g reductions as large as 17 K relative to T_g,bulk when films are made from methyl ethyl ketone or acetic acid solutions, respectively. A factor of 17 reduction of physical aging rate relative to that of neat, bulk P2VP is demonstrated in a 4 vol % alumina/P2VP nanocomposite. This suggests that a strategy for achieving nonequilibrium, glassy polymeric systems that are stable or nearly stable to physical aging is to incorporate well-dispersed nanoparticles possessing attractive interfacial interactions with the polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2935–2943, 2006     

Investigation of clay modifier effects on the structure and rheology of supercritical carbon dioxide‐processed polymer nanocomposites

Superior property enhancements in polymer–clay nanocomposites can be achieved if one can significantly enhance the nanoclay dispersion and polymer–clay interactions. Recent studies have shown that nanoclays can be dispersed in polymers using supercritical carbon dioxide (scCO₂). However, there is need for a better understanding of how changing the clay modifier affects the clay dispersability by scCO₂ and the resultant nanocomposite rheology. To address this, the polystyrene (PS)/clay nanocomposites with “weak” interaction (Cloisite 93A clay) and “strong” interaction (Cloisite 15A clay) have been prepared using the supercritical CO₂ method in the presence of a co‐solvent. Transmission electron microscopy images and small‐angle X‐ray diffraction illustrate that composites using 15A and 93A clays show similar magnitude of reduction in the average tactoid size, and dispersion upon processing with scCO₂. When PS and the clays are coprocessed in scCO₂, the “dispersion” of clays appears to be independent of modifier or polymer–clay interaction. However, the low‐frequency storage modulus in the scCO₂‐processed 15A nanocomposites is two orders of magnitude higher than that of 93A nanocomposites. It is postulated that below percolation (solution blended composites), the strength of polymer–clay interaction is not a significant contributor to rheological enhancement. In the scCO₂‐processed nanocomposites the enhanced dispersion passes the percolation threshold and the interactions dictate the reinforcement potential of the clay–polymer–clay network. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 823–831, 2010     

H NMR study of temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers

¹H NMR spectroscopy was applied to investigate temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) [P(IPMAm/AAm)] random copolymers in D₂O, D₂O/ethanol and D₂O/acetone. The NMR relaxation behaviour of water (HDO) was also examined. The effects of P(IPMAm/AAm) composition and the ethanol or acetone content in the mixed solvents on the temperature, width and extent of the phase transition as well as on the mobility of polymer segments and water molecules were characterized. For D₂O solutions of the copolymers prepared with the AAm fraction in the polymerization mixture not exceeding 25 mol% ¹H NMR spectra show dynamic heterogeneity of copolymer chains in mesoglobules where AAm sequences and surrounding short IPMAm sequences are hydrated and mobile, while sufficiently long IPMAm sequences are dehydrated and their mobility is strongly reduced. The obtained results are consistent with the idea that P(IPMAm/AAm) copolymer mesoglobules are rather porous and disordered.     

Nuclear magnetic resonance relaxation studies of polyacrylamide solution

 The cohesive interaction among polymer chains in a polyacrylamide (PAAm)–D₂O solution has been studied by NMR relaxation. The NMR relaxation times of PAAm in the good solvent D₂O were measured at different temperatures. The results show that the solution system has a high local viscosity and that its relaxation characteristic is soft-solid-like. The temperature dependence of the relaxation behavior of the solution is obviously different from that of ordinary polymer solutions. The difference lies in the relaxation behavior of the methylene protons in the main chain of PAAm, as shown by analyzing the relaxation process with single exponential and biexponential decays. As the temperature increases, the solvation is weakened, leading polymer chains to form curling coils, thus hindering the movement of the methylene protons among the main chains. It can be expected from the existence of 80% fast-relaxing protons that there are a zhigh number of entanglements among the polymer chains in PAAm solution. The information about entanglements among the polymer chains can be deduced from the biexponential dependence of the spin–spin relaxation on the concentration of the polymer solutions. Received: 14 April 1999/Accepted in revised form: 12 October 1999     

Correlation between solvent-induced vibrational frequency shifts of the CO moiety and solvent electron acceptor numbers: tetramethylurea

The CO stretching frequencies in the Raman spectra of 0.10 M solutions of tetramethylurea in seventeen solvents have been recorded. These frequencies exhibit a linear relationship with the solvent electron acceptor number. Comparison of the slopes of these lines and those obtained from analyzing literature data of ν(CO) reveals a correlation with the bond polarity. A linear correlation between (ν_hexane −ν_soln)/ν_hexane and the solvent acceptor number is also shown. The slopes of these latter plots can be related to ν_hexane and it is suggested that this approach be used to explain the specific solvent—solute interaction contributions to solvent-induced vibrational frequency shifts. This method is compared with the solvato-chromic method and it is shown that solvent acidity strongly influences the observed vibrational frequency shifts for the CO moiety of tetramethylurea.     

Improvement of thermal stability of poly(methyl methacrylate) by incorporation of colloidal TiO2 nanorods

The thermal degradation behaviour of oleic acid-capped colloidal anatase TiO₂ nanorods, poly(methyl methacrylate), and their nanocomposites has been studied. Thermogravimetric and differential thermal analysis have been carried out in nitrogen atmosphere for both nanorods, and nanocomposites with nanorod loading from 5 to 30 wt% relative to the polymer. Our study shows that the degradation of the oleic acid-capped nanorods in nitrogen is mainly endothermic and occurs in two steps. The thermal stability of the nanocomposites is improved on increasing the filler loading in the considered range, as the nanorods prevent rapid heat diffusion and limit further degradation. This effect seems to be favoured by the nanorods increased mobility, leading to enhanced dispersion in the matrix upon heating the samples during the thermal analysis.