Volumetric properties of dilute aqueous solutions of poly(ethylene glycols)

The densities of aqueous solutions of some poly(ethylene glycols) (mono-, di-, tri-, and tetraethylene glycol, and four carbowaxes with a mean molecular weight ranging from 600 to 15,000), and of di-, tri-, and tetraethylene glycol dimethyl ether have been determined at 25°C, in the concentration range 5–100 g/liter. From these data, the limiting partial specific and/or molar volume of the solute has been calculated. A value of 37.0 ml/monomole has been evaluated for the partial molar volume of the repeating unit ? CH₂CH₂O? , and has been found independent of both terminal groups and chain length. The results suggest that the ethylene units in higher polymers are accessible to the solvent as easily as in oligomers, and support an “open” or extended conformation of the poly(ethylene glycol) chain in aqueous dilute solution. This interpretation has been confirmed by a comparison of the experimental values of partial molar volume with the values calculated by semiempirical models.     

NMR spectroscopic,osmometric, and viscometric study of association of syndiotactic poly(methyl methacrylate) in dilute solutions

Association of syndiotactic (s) poly(methyl methacrylates) (PMMAs) in toluene, benzene, and acetonitrile has been studied by NMR spectroscopy, osmometry, and viscometry. It was found that in solutions of highly syndiotactic PMMA in toluene, most of the polymer exists in the associated state. Association takes place by means of stereospecific intermolecular and intramolecular interactions of long parallel syndiotactic sequences. The minimum length of syndiotactic sequences necessary for association of s-PMMA in toluene is 7–8 monomer units. Viscosity data indicate that in dilute solutions the associated structures appear as large formations which do not have the character of compact particles. The formation of the aggregates of PMMA is a relatively slow process. A model of the structure of the aggregates of s-PMMA in toluene is proposed. As compared with that in toluene, the tendency to aggregation in benzene and acetonitrile is negligible. Integral parameters currently used for the characterization of polymer-solvent interaction, like “good” or θ solvent, are not suitable for predicting the tendency of s-PMMA to aggregation. The formation of aggregates evidently has some connection with the effect of the solvent upon the conformational structure of syndiotactic sequences.     

A viscometric study of poly(methyl methacrylate) in 2-alkoxyethanols

θ-Conditions, the temperature coefficient of unperturbed dimensions of the macromolecules and the thermodynamic interaction parameters ψ and κ were determined for solutions of poly(methyl methacrylate) in 2-alkoxyethanols (methoxy, ethoxy and butoxy). The results for this series of solvents fit the data reported for other solvents and dln $\text{r}{}_0{}^2\text{/}\text{d}\text{T = 2.6 × 10}{}^{\mathrm{?3}}\text{K}{}^{\mathrm{?1}}$. The dependence of parameters ψ and κ exhibited deviations from the theoretical dependence, mainly near the limiting value ψ = 0.5.     

Viscometric study of gelatin in dilute aqueous solutions

The viscosities of aqueous solutions of gelatin at different temperatures were carefully measured in a common glass‐capillary Ubbelohde viscometer at dilute to extremely dilute concentrations. The adsorption effect that occurred in the viscosity measurements was theoretically analyzed and discussed. A theory based on Langmuir isotherms could adequately describe the existing data. Some structural information was obtained by the use of an iterative fitting procedure to treat the reduced viscosity data, which disclosed that individual gelatin chains underwent a coil‐to‐helix transition as the solution cooled from 40 to 15 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1804–1812, 2006     

A small-angle neutron scattering study of poly(ethylene oxide) microstructure in aqueous poly(styrenesulfonate sodium) solutions

Dilute aqueous solutions of d-PEO and PSSNa mixtures were studied by (2)H NMR spectroscopy and small-angle neutron scattering (SANS). The interactions between d-PEO and PSSNa were found to be negligible both in the presence and absence of NaCl. At very dilute concentration (0.7 mg mL(-1)), d-PEO chains were still found to be slightly collapsed at ambient temperature in water. Upon the addition of PSSNa, aggregates of d-PEO were observed with d-PEO coils loosely associated with each other. The average centre to centre distance between d-PEO coils, which was calculated from the maxima in SANS spectra, was similar to the size of the individual coils. The effect of a simple salt, NaCl, on d-PEO-PSSNa interaction was investigated. Salt addition induced a breakdown of the dilute d-PEO aggregates.     

Dynamic viscosity of dilute solutions of poly(L-glutamic acid)

The dynamic viscosity η′ of a dilute solution of poly(L-glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2–10 and in the frequency range 2–500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady-flow viscosity, relaxation time, and high-frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10^?3 obtained from the relation between reduced steady-flow viscosity and helical content. The high-frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady-flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix–coil transition region, indicating that the relaxation time for helix–coil equilibrium is less than 10^?6sec.     

Aggregation of sulfonated poly(p-phenylene terephthalamide) in dilute solutions

The viscosities of dilute solutions of poly(p-phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley & Sons, Inc.     

Dielectric polarization of a partially neutralized poly(methacrylic acid) in dilute aqueous solutions: Conformational transition

Dielectric permittivity ε′ (at a frequency of 1 MHz) of aqueous solutions of a partially neutralized poly(methacrylic acid) Na-PMAA was studied with varying the degree of ionization α_i from 0 to 0.78 and concentrations w ₂ (g/g) from 1.25 × 10^?4 to 6 × 10^?3 at 25°C. It was shown that the concentration dependence of ε′ for Na-PMAA aqueous solutions at all α_i values contains two regions corresponding to different changes in ε′, and the above regions are separated by the crossover point w*₂. In the first region, ε′ increases with the increasing concentration Δε′/Δw ₂ > 0; in the second region, ε′ decreases with the increasing concentration Δε′/Δw ₂ < 0. The sign inversion of Δε′/Δw ₂ is explained by different structures of water and mechanisms of hydration in regions I and II. In the region corresponding to the ascending branch of the ε′-w ₂ curve, the dipole moments of macromolecules per repeating unit, μ = (〈M ²〉/N)^1/2, were calculated according to the Buckingham theory. The μ value is high; as a macromolecule is saturated with ionized units, this value nonmonotonically changes from ～10 D at α_i = 0 to ～18 D at α_i ～ 0.24. This dependence peaks at ～30 D at α_i ～ 0.1. As is assumed, (〈M ²〉/N)^1/2 depends on the vector sum of partial dipole moments of hydrated nonionized monomer units (μ ～10 D) and fluctuation-induced dipole moments of ionized monomer units. The profile of μ as a function of the degree of ionization of Na-PMAA indicates the occurrence of the conformational transition in an individual macromolecule. This transition takes place at the degree of ionization α_i ～ 0.1. An analysis of molecular interactions in the (ionized coil)-solvent system explans the conformational transition in Na-PMAA.     

Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution

The dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short-time region and a rotational one in the long-time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition. The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short-range methyl–methyl bonding as well as “long-range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.     

Thermodynamics of aqueous solutions containing poly (N-isopropylacrylamide)

Hydrogels undergo reversible and discontinuous volume changes in response to variation of solution conditions such as solvent composition, temperature, salt concentration, and pH. In this contribution we focus our attention on the experimental and theoretical investigation of these swelling equilibria of aqueous cross-linked poly (N-isopropylacrylamide) solutions as well as on the connected demixing behavior of the linear polymer dissolved in water. For the experimental study of the (liquid + liquid) equilibrium an alternative method based on refractive index measurements is suggested. In order to calculate the swelling behavior a model combining an expression for the Gibbs free energy of mixing with an expression for the elastic network is applied. As a model for the Gibbs free energy of mixing the UNIQUAC-approach and the Koningsveld–Kleintjens model are used. For the elastic network contribution again two different theories, namely the phantom network theory and the affine network theory, were applied. Whereas the type of network theory has only a small influence on the calculation results, the Gibbs free energy of mixing has a large impact. Using the UNIQUAC-approach the swelling equilibria can be correlated close to the experimental data, however, this model predicts a homogeneous mixture for linear polymer chains in water. In contrast to this situation the Koningsveld–Kleintjens model does a good job in calculating the swelling equilibria as well as the demixing curve, however, the adjustable parameter must be changed slightly.     

Viscosity-temperature relationships for poly(vinyl chloride)-tetrahydrofuran dilute solutions

The viscous flow parameters for dilute PVC tetrahydrofuran solutions were determined in the temperature range 10–45°. The temperature dependence of the viscosity of the solutions obeys an Arrhenius-type equation. The concentration and the molecular weight dependence of the pre exponential factor of this equation is given by the following relationship:

$\text{A=A}{}_0\text{·}\text{exp}\text{[minus;K}{}_{\mathrm{a}}\text{(c·}\text{M}{}_{\mathrm{w}}\text{)}{}^2\text{]}$

.Both the values of the viscous flow parameters and the mathematical expression of the pre-exponential factor indicate, by comparison with other results, some stiffness of PVC chains in tetrahydrofuran.     

Molar heats of transport of dilute aqueous HCl solutions: A potentiometric study

Heats of transport for dilute aqueous HCl solutions at 25°C have been determined from the measurements of thermoelectric powers of the thermocell $$(T){\text{ }}Ag{\text{ - }}AgCl/HCl(ag.)/Ag - AgCl{\text{ (T + }}\Delta {\text{T)}}$$ The variation of the heat of transport with concentration has been examined up to 0.04M and the molar heat of transport at infinite dilution obtained by extrapolation. Present experimental results may be summarized by the equation $${\text{Q}}^ * = {\text{ }}3397 - 3734I^{1/2} {\text{ + }}33610{\text{I}}^{{\text{3/2}}}$$ whereQ ^* is the heat of transport in cal-mole^?1 andI is the ionic strength.     

Soluble-insoluble-soluble transitions of aqueous poly(N-vinylacetamide-co-acrylic acid) solutions

Several poly(N-vinylacetamide-co-acrylic acid)s with various copolymer compositions have been synthesized, and their unique phase-transition behavior in aqueous salt (Na2SO4 or NaCl) solutions was investigated. Copolymers containing more than 51 mol % N-vinylacetamide (NVA) show reentrant soluble-insoluble-soluble transitions with increasing temperature. The soluble-insoluble transition temperature (T(p1)) increased linearly with increasing NVA content, whereas the insoluble-soluble transition temperature (T(p2)) was almost constant irrespective of the NVA content. Potentiometric titration of the copolymer solutions suggested that the acrylic acid (AA) carboxyl groups form hydrogen bonds with the NVA amide groups even under soluble conditions. Dehydration of the NVA amides and their consequent hydrogen bonding with the AA carboxyl groups during the soluble-insoluble transition process was indicated by FTIR measurements. Addition of salt (Na2SO4 or NaCl) to the aqueous media reduces the solvent quality and enhances the intra- and interchain interactions of the copolymers. Thus, T(p1) was observed to decrease and T(p2) was observed to increase with increasing salt concentration. However, the addition of urea to the media reverses the concentration dependence of T(p1) and T(p2) by disturbing the intra- and interchain interactions of the copolymers.     

Studies on the dynamics of poly(carboxylic acids) with covalently bound thionine and phenosafranine in dilute aqueous solutions

The poly(carboxylic acid) bound phenosafranine and thionine dyes show that, the fluorescence intensity and lifetime increases first and starts to decrease after reaching a maximum at pH 4.0. The fluorescence decay curve of the fluorophore bound polymers follow the biexponential decay fit independent of pH, while poly(MAA-Th) follows single exponential function above pH 4.0. At low pH, a more compact environment of the fluorophore exerts a more hydrophobic environment. In the subnanosecond time domain the solvation process is found to be incomplete while in the nanosecond time scale the solvation of the macromolecular chains is found to be over. The time resolved fluorescence spectra of the polymer bound fluorophores at different pH indicate distinct hydrophobic and hydrophilic environments due to the dynamics of the macromolecules in dilute aqueous solutions. For the first time structural transitions involving solvent are observed in the nanosecond and picosecond time domains for the same macromolecule.     

Electronic spectra of dilute solutions of cationic and radicalic poly (n-vinylcarbazole)

Fluorescence spectra of liquid solutions of PVCA are dominated by two kinds of excimer emission which are characteristic for the mode of preparation of the polymer. Luminescence spectra of solid solutions are more monomer-like, indicating shallow exciton traps. Substantial hypochromic effects are reported for the two lowest energy singlet transitions of PVCA. No significant difference could be observed for PVCA samples of cationic and radicalic origin. Note a - Presented in part at the EUROANALYSIS V European Conference on Analytical Chemistry, Kraków, August 1984     

A multi-reflection Raman cell for studying dilute aqueous solutions

A cell for multi-reflection Raman measurements was constructed. This device consists of two rectangular prisms and, when applied to a rectangular sample cell, Raman signals were enhanced by seven to ten times compared with the single-pass measurement for a transparent solution. This system is readily applicable to studies of dilute aqueous solutions with low refractive indices. With this device, the CH stretching Raman bands of benzene in water were observed with sufficiently high S/N ratios. Combination of the multi-pass cell with an optical-fiber light-collecting device enabled us to determine reproducibly the shifts of Raman bands from some reference state with an accuracy of 0.006 cm⁻¹.