Effects of denaturing agents on the molecular association of dextran. I. Aqueous solutions

Molecular association of aqueous dextran solutions have been investigated by viscosimetric measurements. Intrinsic viscosities of different concentrations of aqueous solutions of dextran with a variety of denaturing agents have been determined. Intrinsic viscosity numbers and Huggins constants of dextran solutions decreased with the addition of denaturing agents. The reducing effect of denaturing agents on the intrinsic viscosities and Huggins constants decreased in the order guanidinium sulfate > guanidinium carbonate > guanidinium chloride > thiourea > urea. The effect of temperature on the intrinsic viscosities of dextran and dextran denaturing agent solutions have also been investigated. A small change in the intrinsic viscosity values was observed for dextran in 1M of guanidinium carbonate and sulfate solutions with the increase of the temperature from 25 to 40 °C. Aqueous dextran solutions, however, showed a significant decrease in the intrinsic viscosities in the same temperature range. © 1995 John Wiley & Sons, Inc.     

Cohesive energy density of polytetrahydrofuran

Measurements have been conducted on radiation-crosslinked polytetrahydrofuran (PTHF) of stress-strain and of swelling coefficients in simple esters. For the linear polymer, measurements have been made of density and intrinsic viscosities in the esters. [η] was also determined under the θ conditions of 33.5°C. in diethyl malonate. The results have been incorporated into several (sometimes interdependent) approaches towards the evaluation of the solubility parameter δ_p of PTHF. The mean of the nine values obtained is 8.55 (cal./cc.)^1/2, whence the cohesive energy density is 5.17 kcal./mole. Seventeen experimental values of the Flory interaction parameter χ are also reported.     

A method for estimating both the solubility parameters and molar volumes of liquids

The solubility parameters and molar volumes of substances can be used, in conjunction with suitable theory, to provide estimates of the thermodynamic properties of solutions; the solubility characteristics of polymer-solvent systems and the estimation of the equilibrium uptake of liquids by polymers are examples of the type of practical problems that are amenable to treatment. For low molecular weight liquids, the solubility parameter, δ, is conveniently calculated using the expression δ = (ΔE_v/V)½, where ΔE_v is the energy of vaporization at a given temperature and V is the corresponding molar volume which is calculated from the known values of molecular weight and density. For high molecular weight polymers, the volatility is much too low for ΔE_v to be obtained directly and hence recourse must be made to indirect methods for estimating δ for these materials. One such widely used method is based on Small's additive group “molar-attraction constants” which when summed allow the estimation of δ from a knowledge of the structural formula of the material; however, the density must still be determined experimentally. The proposed method of estimating δ, also based on group additive constants is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of the structural formula of the compound.     

Solubility profiles of poly(ethylene glycol)/solvent systems. II. comparison of thermodynamic parameters from viscosity measurements

Solution thermodynamics of PEG samples in aqueous and nonaqueous (methanol, chloroform, tetrahydrofuran, and dimethylsulfoxide) solutions have been investigated by viscometric studies at 25, 30, 35, and 40°C. The hydrodynamic expansion factor, a_h, and the unperturbed root mean square end‐to‐end distance, , found for the system indicated that the polymer coils contract as the temperature is raised. The long‐range interaction parameter, B, was also evaluated and a significant decrease with increasing temperature was observed. The theta temperatures, θ, obtained from the temperature dependence of (1/2 ? χ) and the second virial coefficient, A₂, are quite good in agreement with the calculated values evaluated via extrapolation and interpolation methods. The thermodynamic interaction parameter, χ, was evaluated through the sum of the individual values of enthalpy and entropy dilution parameters for PEG samples. The restrictions applying to the establishment of concentration regimes, short‐range, and long‐range interactions are discussed. A parallelism is found between solubility profiles obtained by solution viscometry and solubility parameter approaches for PEG/solvent systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Sorption of low molar mass silicones in silicone elastomers

Elastomers based on polydimethylsiloxane (PDMS) are used as insulating material in outdoor electrical power applications. It is believed that migration of small molecule PDMS species plays an important role in the recovery of hydrophobicity of oxidized or polluted PDMS elastomer surfaces. This paper reports data on diffusivity and solubility of low molar mass PDMS liquids in PDMS rubbers (8000 < M _c < 16,000 g/mol) obtained by sorption measurements. It was found that the diffusivity (D) of linear PDMS liquids was approximately independent of the concentration of penetrant and that in the molar mass range 400 < M _c < 18,000 g/mol it decreased with molar mass (M _c) of the diffusing liquid according to D α M _c^−0.8. Theory and previous data for other oligomers and elastomers predict that D is proportional to M⁻¹. Linear PDMS liquids of lower molar mass exhibited a stronger molar mass dependence. The diffusivity of a given PDMS liquid increased with increasing elastomer crosslink density. The activation energy of the diffusivity was constant at 15.5 ± 2 kJ/mol for linear PDMS liquids of M _c larger than 1000 g/mol⁻¹ with only a negligible influence of network density and filler content. The activation energy of the lowest molar mass penetrant was considerably lower, 6 to 7 kJ/mol. The solubility increased markedly with decreasing molar mass of the penetrant and with decreasing elastomer crosslink density.     

Three-dimensional solubility parameters and chemical protective clothing permeation. II. Modeling diffusion coefficients,breakthrough times,and steady-state permeation rates of organic solvents in Viton® gloves

Three-dimensional (3-D) solubility parameters are used in separate models of the solubility, S, and diffusion coefficient, D, of organic solvents in polymers. Modeled values of these variables are then combined in Fickian diffusion equations to estimate solvent breakthrough times (BT) and steady-state permeation rates (SSPR). Published data on the permeation of 18 solvents through commercial Viton® glove samples are used to test the accuracy of the approach. Estimates of S are determined based on the model described in the preceding article. Of several empirical correlations investigated to model D, best results are achieved using the product of the solvent molar volume, V₁, and either the weighted solvent-Viton 3-D solubility parameter difference, A_w, or the Flory interaction parameter, X, also calculated from 3-D solubility parameters. To account for the change in the value of D over the course of the permeation test, D values are evaluated at breakthrough and steady state. Modeled BT values within a factor of three of experimental values (typically within a factor of two) are obtained for the 15 solvents for which analytical detection limits were reported. Modeled SSPR values within a factor of six of experimental values (typically within a factor of four) are obtained for the 15 solvents with valid SSPR measurements. © 1993 John Wiley & Sons, Inc.     

Spectrophotometric behavior of polyvinylpyrrolidone in aqueous solutions. II. The effects of denaturing agents

Electronic spectral behavior of aqueous polyvinylpyrrolidone solutions have been investigated by UV-vis spectrophotometry. n → * electronic excitations of the polymer were observed to shift longer wavelengths with a variety of denaturing agents. The shifting effect of denaturing agents on the λ_max increased in the order guanidinium carbonate ≡ guanidinium sulfate > guanidinium chloride > urea. Intrinsic viscosities of different concentrations of aqueous solutions of polyvinylpyrrolidone with the same denaturing agents have also been determined. Intrinsic viscosity number, [η], of polymer solutions decreased with the addition of denaturing agents. The slope, k_H[η]², of the polymer was also observed to decrease in the presence of denaturing agents. Shift to the longer wavelengths and decrease in the viscosity characteristics can be explained by the break of the molecular association between the polymer and the water molecules. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:1307–1311, 1997     

Use of a gee relationship in a diffusion study

Paul and Ebra-Lima⁶ reported on the pressure-induced transport of 12 organic liquids through a highly swollen rubber membrane. Gee¹⁰ examined the capability of a liquid to swell a rubber and the interaction between liquid and rubber from the standpoint of the Hildebrand-Scatchard solubility parameter. In this presentation, the swelling function of Gee was expressed by [V₀(δ₀ ? δ_r)²(1 ? v₀)²]^1/2 where V and δ are the molar volume and solubility parameter of the liquid 0 and the rubber r and (1 ? v) represents the volume fraction of rubber when the rubber is fully swollen by that liquid. The data of Paul and Ebra-Lima are analyzed in terms of the swelling function. It is principally assumed that the flux is a function of the swelling power of the liquid. The analysis indicates that the use of the Gee relationship provides values for the energetics of the various steps in the transport process and a means for differentiating between various types of penetrant liquids.     

Polymer miscibility in mixed organic liquids. An extension of the two-dimensional approach

Previous work on the two-dimensional approach to polymer miscibility in organic liquids is extended to polymer–mixed liquid system. From thermodynamic considerations methods for calculating δ_h of the mixed liquid and χ_H of the polymer–mixed liquid system from properties of pure components are proposed, where δ_h is the hydrogen-bonding solubility parameter of the liquid, and χ_H is a term which takes account of the dispersion and polar interactions between the liquid and the polymer and of effects due to temperature and molecular size of the liquid. Using these two calculated parameters, the solvent power of the mixed liquid can be determined from its location on the χ plane.     

Nitrogen solubilities in low-density polyethylene at high temperatures and high pressures

An apparatus for the determination of the solubility of gases in polymers at high pressure and high temperature is described. The solubilities of nitrogen in low-density polyethylene (PE800E) at 394–450 K at pressures between 10 and 125 atm are reported. Empirical correlations are obtained which represent the Flory–Huggins interaction parameter χ, solubility coefficient K_H, and activity coefficient of dissolved gas Ω₂ as functions of temperature and pressure for the above system. © 1995 John Wiley & Sons, Inc.     

Use of Hildebrand and Lamoreaux's theory to predict solubility and related properties of gas-liquid systems

There is a need in many fields such as chemical engineering, process chemistry and pharmacology for reliable data on the solubility, entropy of solution and partial molar volume of gases in liquids. Experimental data are not available for many systems of practical and academic importance and consequently a reliable theory to predict values for these properties would be of great use. Recent refinements of solubility parameter theory have been successful in predicting such values for several systems and in this paper results obtained from this theory are compared with experimental measurements on a large range of gas-liquid systems. The agreement found is satisfactory in the most part, but for helium, neon, xenon, hydrogen and deuterium, the predicted results deviate consistently from the experimental values. This is to be expected on the basis of some of the earlier results of solubility parameter theory and an empirical modification is proposed that yields significant improvements in the predicted values. This has also been used to predict values for carbon dioxide, tetrafluoromethane and sulphur hexafluoride to which the theory is not directly applicable. Values predicted by solubility parameter theory are compared with those obtained by Battino and co-workers from scaled particle theory. In general, the two theories are equally successful in predicting solubilities, but refined solubility parameter theory yields better values of entropy of solution. It is concluded that the theory provides a useful means of predicting solubility and entropy of solution but that prediction of partial molar volume results is limited because of the paucity of data for the thermal pressure coefficients of the solvents. Attention is drawn to apparent inaccuracies in certain experimental measurements. The interrelationship between the various forms of the entropy of solution used by different workers is clarified. A value of the energy of vaporisation of carbon dioxide, δE₂^v=2.64±0.15 kcal/mol is calculated.     

An approximate method for the determination of polymer–polymer interaction parameters of incompatible polymers in solution

A method is developed, based on Scott's equations for ternary systems of two polymers and a mutual solvent, for the calculation of values of the polymer–polymer interaction parameter, χ₂₃, for systems in which both polymer–solvent interaction parameters χ₁₂ and χ₁₃ are not known a priori. Equilibrium phase studies were carried out on ternary systems of polystyrene, polybutadiene, and tetrahydrofuran or toluene at 23°C and 1 atm. Typical interaction parameter values (χ₂₃) calculated by this new method were compared with the values of χ₂₃ determined earlier using standard equations and known χ₁₂ values for these systems, and were found to agree very well. It is concluded that the technique presented in this article can be used for mixed polymer systems in good mutual solvents where neither polymer–solvent interaction parameter is known, for determining an approximate value of the χ₂₃ parameter alone.     

Development of a correlation between the non-polar solubility parameter,refractive index and molecular structure. I. Aliphatic hydrocarbons

For non-polar liquids (e.g. the alkanes) the cohesion energy density (λ²) can be shown to be a function of the refractive index (nD ), molal volume (V) and molecular structure according to: where Δ is the non-polar solubility parameter and the increments g_ij are determined from molecular structure. The difference between values of Δ calculated by this formula and experimental data is <0.1% for the C₅–C₁₆ n-alkanes and <0.8% for the C₅–C₈ branched isomers. The main object of this correlation was to provide a method for estimating the London dispersion force contribution to the cohesive energy of branched polar liquids.     

Effect of molar size and solubility parameter of solvent molecules on swelling of a gel: a fluorescence study

Gels were swollen in various solvents with different molar volume V and solubility parameter δ. In situ steady state fluorescence (SSF) measurements were performed for swelling experiments in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM). Gels were prepared at 75 °C with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and slow release experiments were performed in various solvents with different V and δ at room temperature by time monitoring of the Py fluorescence intensity. The Li–Tanaka equation was used to produce time constant τ₁ values. Cooperative diffusion coefficients (D_c) were measured and found to be strongly correlated to the molar volume of the solvents used. Solvent uptake and degree of swelling were found to be dependent on the solubility parameter of the solvent. © 2000 Society of Chemical Industry     

Influence of solvent on measurement of cohesive energy density of polystyrene

The solubility parameter (δ₂) of polystyrene was measured by the maximum [δ] method in four series of solvents which were structurally different. In each case δ₂ varied with the solvent series used, from 8·75 to 9·25 (cal/ml)^1/2 The enthalpy parameter (X_H), which was calculated for polystyrene dissolved in at least one member of each series, was then used to derive δ₂, and little or no variation in δ₂, with solvent was observed. The average value was δ₂ = 9·16 ± 0·1 (cal/ml)^1/2 It has been shown that determination of δ₂, from [η]_max can be solvent-dependent because of the influence of the entropy term Xs. It was concluded that if reliable values of δ₂ are to be obtained, they should be estimated from X_H.     

Evaluation of thermodynamic theories to predict interfacial tension between polystyrene and polypropylene melts

The commonly used thermodynamic theories (mean field theory and the square gradient theory) to predict interfacial tension between polymers have been modified. The results of these theoretical developments have not yet been fully tested and compared to experimental data. In this paper, experimental data for the effects of temperature, molecular weight, and molecular weight dispersity on interfacial tension for polypropylene/polystyrene polymer pairs are compared with the predictions of the new versions of the above theories. To evaluate these theories, it is necessary to know the Flory-Huggins interaction parameter for the polymer pairs studied. The relation correlating the Flory-Huggins interaction parameter to the Hildebrand solubility parameter was not suitable for evaluating the theoretical predictions of interfacial tension. Instead, the Flory Huggins interaction parameter was expressed as the sum of an enthalpic contribution, χ_H, and entropic contribution, χ_s. In the absence of reliable experimental values, a method was developed to evaluate the two contributions, based on interfacial tension data. The procedure provided an interaction parameter that is allowed to depend on molecular weight. When this approach was used, the predictions of only the new version of the square gradient theory were in good agreement with the experimental data for the influence of temperature and molecular weight on interfacial tension. However, the theory predicted the effect of polydispersity on interfacial tension only at high temperatures.     

Compatibility of polymer blends. I. Copolymers with organic solvents

In this work, we present a theoretical discussion regarding the Flory–Huggins χ interaction parameter for 11 random copolymer‐solvent systems along with their corresponding polymer pairs. Copolymers studied are poly(acrylonitrile‐co‐butadiene) in acetonitrile, poly(styrene‐co‐acrylonitrile) in 1,2‐dichloroethane, poly(acrylonitrile‐co‐butadiene) in hexane, and poly(acrylonitrile‐co‐butadiene) in pentane. For ternary systems, the results are expressed in terms of χ_1,23, which is reduced to the classical Flory–Huggins χ₁₂ interaction parameter in case of binary mixtures. The data on χ_1,23 may be used for an approximate estimation of the χ′₂₃ interaction parameter for the limiting case of zero solvent concentration. For this purpose, at the end of each subsection of tables, the limiting value of is given. The limiting values of , , and χ′₂₃ also appear at the end of each table. It should be noted that these values are obtained by the graphical extrapolation of data to zero concentration of solvent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 492–498, 2006     

The solubility parameter of polypropylene

Solubility parameter values for polypropylene as reported in the literature cover a rather broad span, ranging from 7.9 to 9.4 (cal./cm.³)^1/2. This communication suggests the approximate value 8.2. This value is based on the swelling and dissolution characteristics of polypropylene films in various organic liquids. A calculated value of 8.1, obtained by Small's method, compares well with the experimentally determined value.     

Polymer miscibility in organic solvents and in plasticizers—a two-dimensional approach

From thermodynamic considerations based on associated solution models and from the Hansen's three-dimensional solubility parameter concept, it is found that the solvent power of an organic liquid for a given polymer can be characterized by two parameters, δ_h and χ_H, where δ_h is the hydrogen-bonding solubility parameter of the liquid, and χ_H is a term which takes account of the dispersion and polar interactions between the liquid and the polymer and of the effects due to temperature and molecular size of the liquid. It is also found that Hansen's solubility sphere for the polymer can be represented as a solubility circle in the proposed χ_H^?δ_h plane. The proposed approach is applied successfully to polymer–plasticizer systems.     

Thermodynamic characterization of poly (caprolactonediol) by inverse gas chromatography

Specific retention volumes, V _g ⁰, were determined for 21 solute probes on poly (caprolactonediol) (PCLD) in the temperature range 323.15–403.15 K by inverse gas chromatography. The retention diagrams drawn between ln V _g ⁰ versus 1/T are linear for all the solutes since PCLD with ten repeating units in its chain behaving like a non polymeric material under the conditions applied. The stationary phase with melting temperature ~321 K is in the liquid state in the GC column over the temperature range studied and hence found to be suitable to determine infinite dilution partial molar thermodynamic properties of mixing for solutes on PCLD. The V _g ⁰ values have been used to calculate weight fraction activity coefficients Ω^∞ and Flory–Huggins interaction parameters, χ ₁₂^∞. The average partial molar enthalpy of solution, [`(\Updelta H)]<sub>1</sub><sup>S</sup> , \overline{\Updelta H}_{1}^{S} , and partial molar enthalpy of mixing, [`(\Updelta H)]₁^￥ , \overline{\Updelta H}_{1}^{\infty } , are calculated using V _g ⁰ and Ω^∞ respectively. The average molar enthalpy of vaporization ΔH ₁ ^V for solutes have been calculated using [`(\Updelta H)]<sub>1</sub><sup>￥</sup> \overline{\Updelta H}_{1}^{\infty } and [`(\Updelta H)]₁^S \overline{\Updelta H}_{1}^{S} values and compared with the literature values at 363.15 K which is the average column temperature. The partial molar entropy of mixing, [`(\Updelta S)]<sub>1</sub><sup>￥</sup> \overline{\Updelta S}_{1}^{\infty } calculated at 363.15 K are in good correlation with the average [`(\Updelta H)]₁^￥ \overline{\Updelta H}_{1}^{\infty } values. The total solubility parameter due to Guillet and the Hansen solubility parameters (HSP) are calculated for PCLD using χ ₁₂^∞ values. In the present work the Hansen solubility parameters have been calculated using a new method following the Hansen theory and Huang method with less weight on polar and hydrogen bonding components. The errors in the solubility HSP are lower and the correlation coefficients are better in both the methods compared to unweighted three dimensional model.