Temperature Coefficient Of Unperturbed Dimensions Research Articles

Solution and rheological properties of polyacrylamide in 1,4-dioxane + water mixed solvent media

The hydrodynamic properties of uncharged polymers of acrylamide has been investigated in 1,4-dioxane (DO) + water mixed solvent media at 303 K, 313 K and 323 K temperatures as probed by viscometry to explore the dimension and conformation of individual polymer molecules. In this study three different average molar masses of PAM, e.g., 8.9 × 106 (designated as Type-A), 1.6 × 106 (designated as Type-B), and 2.3 × 105 (designated as Type-C) g·mol−1 were employed. The unperturbed dimensions () under non-theta condition of polymer molecules has been determined for various solvent compositions clearly indicates that though DO acts as poor solvent in our system but some compositions of solvent acts as a good solvent. The temperature coefficient of unperturbed dimension has been found negative for polyacrylamide in the mixed solvent systems indicating a weak helical nature. Rheological stress sweep measurements of Type-A PAM solutions at 298 K reveal marked increase in elasticity upon addition of DO in the mixed solvent compared to that in pure solvent. In the shear viscosity profile a significant increase in critical shear rate is observed with increase in temperature from 293 K to 298 K. The results are discussed in the light of microstructural arrangement of the PAM aggregates under different physiological conditions.

Molecular Dimension and Interaction Parameters of Polyacrylamide in Water‐N,N‐Dimethylformamide Mixtures

The intrinsic viscosities [η] of polyacrylamide (PAM) having different average molecular weights are measured in various mixtures of water (good solvent) and N, N dimethyl formamide (DMF, nonsolvent) at different temperatures. The observed results show a significant variation of cosolvency as a function of solvent composition (ϕDMF). The nature of curves in [η] vs. ϕDMF plot at different temperatures indicates the existence of two antagonistic effects. The unperturbed dimensions (Kθ) of the polymer are determined by a number of methods, which agree well with each other. The temperature coefficient of unperturbed dimension (K′), molecular extension factors (αn), characteristic ratio (Cα) and chain rigidity (σ) are evaluated and the effects of temperature, solvent composition are discussed. The volume related parameter VE and shape factor ν were also computed, which shows the shape of polymer molecules to be more or less spherical in solution.

UNPERTURBED CHARACTERISTICS OF ATACTIC POLYPROPYLENE: SOME NEW THETA SOLVENTS BASED ON ALIPHATIC KETONES

Solution properties of atactic polypropylene were studied in thermodynamically good solvents (toluene, n-butyl chloride and decalin) and in theta solvents (ethyl-n-butyl ketone, methyl-n-hexyl ketone, 1-nonanol and 2-ethylhexanol). Mark-Houwink-Sakurada relations within the temperature range between 15°C and 60°C, unperturbed dimensions Kθ = 1.62×10−3 at Tθ = 19.7°C in methyl-n-hexyl ketone (the Kθ and Tθ values for ethyl-n-butyl ketone are the same) and the temperature coefficient of unperturbed dimensions d ln r−2 0/dT = −2.44×10−3K−1 were established.

Star branched polystyrenes: an evaluation of solvent and temperature influences on unperturbed chain dimensions

Temperature coefficients of unperturbed dimensions of three high molecular weight polystyrene stars have been evaluated from intrinsic viscosity measurements in six theta solvents and two solvent/nonsolvent mixtures over a temperature range of 10 to 70°C. Larger values of unperturbed dimensions were found in cyclic aliphatic solvents than in chloroalkanes at similar temperatures. Negative values of the temperature coefficient of unperturbed dimensions were found in both solvent series, values which were in essential agreement with those found for linear polystyrene. The values of the branching index, g′, were found to be independent of both temperature and solvent type.

The unperturbed molecular dimensions of poly(ethylene oxide) in aqueous solutions from intrinsic viscosity measurements and the evaluation of the theta temperature

Intrinsic viscosity measurements were carried out on five well characterized fractions of poly(ethylene oxide) in aqueous solutions at 24.9°, 34.9°, and 45.5°C. The Stockmayer-Fixman extrapolation was applied to the data: it yields the unperturbed dimensions K 0 of the chain. The unperturbed root-mean-square end-to-end distance 〈 R ̄ 2〉 1 2 0 calculated for the polymer fractions in water indicate that the polymer molecules are expanded in this solvent as the temperature is raised. The temperature coefficient of unperturbed dimension, d In〈 R ̄ 2〉 0 dt = 0.024 K −1 , calculated for poly(ethylene oxide) in water using the present data is about 100 times higher than the literature values of 0.23 (±0.02) × 10 −3 K −1 and 0.2 (±0.2) × 10 −3 K −1, respectively, obtained from force-temperature (‘thermoelastic’) measurements on elongated networks of the polymer in the amorphouse state and form viscosity measurements on this polymer in benzene. A value of θ=108.3°C was obtained from the temperature dependence of the interaction parameter B in the Stockmayer-Fixman equation.

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 r02/dT = 2.6 × 10−3K−1. The dependence of parameters ψ and κ exhibited deviations from the theoretical dependence, mainly near the limiting value ψ = 0.5.

Diphyl properties of polydecylacrylate in solutions

Molecular parameters of eight polydecylacrylate (PA-10) fractions were measured by light scattering and the viscosity method in n-propyl, n-butyl, n-amyl alcohols, n-decane and toluene. The absence of any relation between [ν] in toluene and temperature suggests that the temperature coefficient of unperturbed dimensions is very low and does not exceed ≈ × 10 −4. The difference in unperturbed dimensions of PA-10 spheres in alcohols is basically due to the specific polymer-solvent interaction. It was assumed that the incompatibility of θ conditions for the second virial coefficient A 2 = 0 and the exponent in the Mark-Kuhn-Hauwinck equation a = 1 2 in alcohols (where A 2 = 0 and a < 1 2 ) and in n-decane (where A 2 = 0 and a > 1 2 ) is due to the ability of PA-10 to undergo “self-adsorption” or vice versa, displacement from the sphere of lateral macromolecular chain groups. A similar inversion of the conformation of lateral groups may explain the diphyl nature of polydecylacrylate in solutions.

Conformational energy contribution to the heat of solution in polymer–solvent systems. Part II. Experimental results

AbstractHeats of solution (ΔHexp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔHexp of an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔUconf) to the heat of solution. ΔUconf appears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔUconf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elongation).

A note to the determination of the temperature coefficient of unperturbed dimensions of the polymers

A note to the determination of the temperature coefficient of unperturbed dimensions of the polymers

On the Temperature Coefficient of Unperturbed Dimensions of Atactic Polystyrene

On the Temperature Coefficient of Unperturbed Dimensions of Atactic Polystyrene

Temperature coefficient of unperturbed dimensions from solution properties

AbstractValues of d ln r02/dT, for polystyrene, poly(vinyl acetate), poly(methyl methacrylate), and polydimethylsiloxane recently obtained by different authors are compared. The large discrepancies among values reported are taken as an indication of the effects played by polymer–solvent interactions on unperturbed dimensions.