Polymer Mixtures In Solution Research Articles

Ionic polymers based on quaternized polysulfones: hydrodynamic properties of polymer mixtures in solution

Abstract Hydrodynamic properties developed in a series of mixtures, obtained from quaternized polysulfone and cellulose acetate phthalate or polyvinyl alcohol in N-methyl-2-pyrrolidone, were evaluated by viscometric investigations. Theoretical and experimental aspects concerning the viscometric data for binary polymer/solvent and ternary polymer/polymer/solvent mixtures have been discussed by the new Wolf model, as a function of the charge density of polyion, structural peculiarity of polymers, and polymer mixture composition. Intrinsic viscosity and also the hydrodynamic parameters obtained by the Wolf method offer new information on the competition between different types of interactions manifested in ternary polymer/polymer/solvent systems. The complex dependence of viscosity on polymer composition is influenced by conformational changes of constituent polymers from the mixture, as well as by cumulative effects of electrostatic interactions, hydrogen bonding or association phenomena. Additionally, the above-mentioned interactions indicate the compatibility of these polymers over a large composition domain. This study investigates the hydrodynamic functions from the perspective of some newly-issued theories and analyzes the choice of optimal polymer mixtures compositions for specific applications in biomedical domains.

Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy

Pulsed Field-Gradient Spin Echo (PGSE) NMR, which associates to a spectral dimension the measure of diffusion coefficients, is a convenient technique for mixture analysis. Unfortunately, because of relaxation, the quantification of mixtures by PGSE NMR is far from straightforward for mixtures with strong spectral overlap. Antalek (J. Am. Chem. Soc. 128 (2006) 8402–8403) proposed a quantification strategy based on DECRA analysis and extrapolation to zero of the diffusion delay. More recently, Barrère et al. (J. Magn. Reson. 216 (2012) 201–208) presented a new strategy based also on DECRA and on the renormalization of the intensities using estimates of the T1 and T2 relaxation times. Here we report an alternative quantification approach in which the fractions are obtained by analyzing the PGSE attenuation profile with a general Stejskal–Tanner equation that explicitly includes the relaxation effects. The required values of T1 and T2 relaxation times are either independently measured with conventional sequences or determined, along with the fractions and the diffusion coefficients, from the simultaneous analysis of up to 6 PGSE data sets recorded with different diffusion delays. This method yields errors lower than 3% for the fractions, even for complete spectral overlap, as demonstrated on model binary and ternary mixtures of polystyrene in the case of a convection compensating double stimulated echo (DSTE) sequence.

Influence of Temperature on the Rheological Behavior of Polymer Mixtures in Solution

This article investigates the viscoelastic behavior of poly(acrylonitrile) (PAN) and poly[N-(4-carboxyphenyl)maleimide] (PMI) solutions in dimethylformamide (DMF) in comparison with PMI/PAN/DMF ternary mixtures. Some rheological characteristics, such as viscosity and relaxation time, were investigated as functions of the polymer mixture composition at different temperatures in the range of 0–60 °C. The solutions of each polymer and their mixtures exhibit a Newtonian behavior throughout the studied frequency range. At low temperatures, the behavior of the solutions having high PAN contents in the polymer mixture is influenced by physical gelation of the solution. The activation energy of the flow gives indications about the intensity of polymer–polymer interactions as a function of the polymer mixture composition.

Hydrodynamic Properties of Polymer Mixtures in Solution

The paper investigates the hydrodynamic properties of polyacrylonitrile (PAN) and poly(N-(4-carboxyphenyl)maleimide) (PMI) solutions in dimethylformamide (DMF) in comparison with PMI/PAN/DMF ternary mixtures. The experimental data obtained by viscometry have been discussed by means of two methods: first, the plots obtained with the classical Huggins equation are analyzed, and in parallel, an evaluation of the parameters given by the new Wolf model is presented. The experimental data obtained for binary polymer/solvent and ternary polymer/polymer/solvent mixtures fit well with this last method and allow the calculation of intrinsic viscosities and other hydrodynamic parameters, which provide new information about the competition between different types of interactions for polymer mixtures in solution. The compatibility of the two polymers dissolved in a common solvent is also discussed on the basis of two parameters: Δb and α, reflecting the interactions between the polymer segments and polymer/polymer mis...

Coil Dimensions of Polystyrene Chains in Colloid−Polymer Mixtures at the Protein Limit: A SANS Study

A new combination of polymer chains and small colloids is presented in order to investigate the behavior of colloid−polymer mixtures in solution (CP) in the protein limit. To this end, hydroxy-functionalized silica particles (OHSil) were prepared according to a procedure [J. Am. Chem. Soc. 2003, 125, 3712], which led to colloid radii as small as 1.2 nm. Compared to this small size, the coil dimensions of the polystyrene (PS) chains used as the polymer component were larger by more than an order of magnitude. Investigation of the CP focused on the dimension of the PS chains in the presence of a varying amount of OHSil colloids. Chain size and shape were characterized by means of light scattering, viscosity experiments, and small-angle neutron scattering (SANS). Two solvents have been used. A mixture of dimethylformamide (DMF) with toluene was isorefractive to the OHSil particles, giving access to single chain behavior of PS. Pure DMF, on the other hand, allowed an efficient contrast matching of OHSil suitable for SANS experiments on fully deuterated PS. All characterization techniques provided clear evidence for a shrinking of the coil dimensions with increasing OHSil content in the solution. Particle scattering factors from SANS yielded a detailed picture of this chain compaction. The smallest coil dimensions were recorded close to the liquid−liquid phase boundary, occurring at an OHSil volume fraction of ∼0.17. This is considered to be a first experimental evidence for a shift of the liquid−liquid phase boundary toward lower colloid volume fractions if the colloid size increases. Altogether, present data extend earlier measurements on two chemically different CP in the protein limit, thus establishing the observed shrinking to be a universally valid feature of these systems. The results are in qualitative agreement with theoretical predictions.

Colloid-polymer mixtures in solution with refractive index matched acrylate colloids.

Colloid-polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius Rcol and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains Rg. In the present work, model systems are developed for the protein limit. The colloid-solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of Rg = 96 nm and Rg = 78 nm, respectively, are used. The radii of the colloidal particles are close to Rcol = 12 nm, leading to size ratios of Rg/Rcol = 8 and Rg/Rcol = 6.5. Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 degrees C, poly(ethyl methacrylate) in toluene at 7 degrees C and poly(ethyl methacrylate) in ETB at 40 degrees C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.

Degradation Kinetics for Polymer Mixtures in Solution

The degradation rate of a polymer mixture depends on the particular polymer mixture, and the presence of a second polymer can increase, decrease, or not affect the degradation rate of the first polymer. The degradation rates of poly(vinyl acetate) in both the presence and absence of polystyrene at various temperatures $(220-250^o C)$ were experimentally determined. The molecular weight distributions of the polymers were obtained by analyzing the samples by gel permeation chromatography. Continuous distribution kinetics were employed for determining the degradation rates of binary polymer mixtures. The results indicated that, because of the interaction of mixed radicals with polymer by hydrogen abstraction, the degradation rates of poly(vinyl acetate) are considerably enhanced in the presence of polystyrene, while the degradation rate of polystyrene decreases.

Viscometric study on the compatibility of polymer–polymer mixtures in solution

Abstract The viscosity behaviour of mixtures formed by two uncharged polymers in dilute solution has been studied at 25°C. The ternary systems assayed, and denoted solvent (1)/ polymer (2)/ polymer (3), have in common the poly(ether sulphone) (PES) as polymer 2, and poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) as polymer 3. The intrinsic viscosity and the viscometric interaction parameters have been experimentally measured for the binary (solvent/polymer) as well as for the ternary systems, and also theoretically evaluated for the latter. The estimation of the compatibility degree of the above polymer pairs have been done by means of three criteria: (i) the sign of Δbm, according to the traditional formalism developed by Krigbaum and Wall; (ii) the sign of a new defined Δb′m; and (iii) the sign of Δ[η]m. The two last criteria are proposed in this work and are based on treating the viscosity interaction parameter and the intrinsic viscosity as excess properties by similarity with those of real solutions. Both methods provide compatibility predictions in agreement with those made with the traditional one but they are much more simple in handling the calculations. Finally, the observed compatibility behaviour follows the order: (PES+PMMA)≫(PES+PVDF)>(PES+PS), in dimethylformamide as solvent, at least in the assayed composition range.

Mechanical behaviour of polymer mixtures in the phase separation region

The liquid–liquid phase transition triggered by changes in the composition of polymer mixtures in solution or melt is often accompanied by "critical" opalescence, which signals the appearance of a microemulsion in the mixture. The viscosity of the polymer mixture in this region is characterized by a sharp minimum, observed, as a rule, over an extremely narrow range of concentration. Depending on the concentration of the solution, the type of polymer, and the solvent, the viscosity may decrease by a factor of 8–10. On transition from micro- to macro-separation, viscosity rapidly increases back to the original level. Changes in the composition of the mixture can alter the concentration at which phase separation occurs, but the minimum in viscosity invariably corresponds to the moment of phase separation. The critical opalescence region represents the formation of phase particles up to 80–100 nm in size, and this corresponds to the point of viscosity drop. This effect is due to the appearance of thermodynamically stable microemulsions in the polymer mixture, in the region between the binodal and the spinodal in the phase diagram. These emulsions are characterized by lower molecular interaction of incompatible polymers in the highly developed interfacial layer. Extremal changes at the point of phase separation are also observed for other mechanical characteristics of polymer mixtures in solutions or melts, for example, G′ and G″ dynamic moduli or complex viscosity η*. Keywords: polyblends, critical phenomena, viscosity, emulsions, phase separation.

Dynamic scattering of ternary polymer mixtures in solutions: The χF interaction parameter and the single chain diffusion coefficient DS

AbstractThis work discusses the dynamic scattering properties of ternary polymer mixtures in solution and emphasizes on how can be extracted the value of the single chain diffusion coefficient DS and that of the interaction parameter χF when using Quasi Elastic Light Scattering (QELS) in any good solvent. This is the direct consequence of considerable efforts made during the past decade, in the understanding of dynamic properties of multicomponent systems from both theoretical and experimental points of view.

ESR Studies of the Competitive Adsorption Behavior of Poly(methyl methacrylate) and Polystyrene Mixtures at the Solid–Liquid Interface

Abstract The adsorption from solution of polystyrene and poly(methyl methacrylate) mixtures on a silica surface was studied in order to establish the competitive adsorption behavior of these polymers. The fractions of train segment for these polymers were determined from the ESR spectra analyses, and these values were compared with those of the individual adsorption. When the initial concentrations of the polymer mixtures in solution were fixed and the added amounts of silica adsorbent were varied, the adsorption of polystyrene did not take place until the poly(methyl methacrylate) in solution was completely exhausted. In the simultaneous adsorption, the amount of adsorption of poly(methyl methacrylate) was affected by the presence of polystyrene in the solution. On the other hand, the amount of adsorption of polystyrene was unaffected by the presence of poly(methyl methacrylate) in the system. The conformation of the adsorbed poly(methyl methacrylate) was also affected by the presence of polystyrene when they were simultaneously adsorbed on the silica surface. The conformation of the poly(methyl methacrylate) adsorbed from the mixed solution formed a more compressed polymer layer in comparison with that for the case where the poly(methyl methacrylate) was adsorbed alone.

Separation into Phases of Polymer Mixtures in Solution

Abstract When three different polymers are dissolved in a common solvent and the total polymer concentration is above a certain value, three liquid layers are obtained because of the limited compatibility of the polymer components with one another. Tests have been carried out at room temperature on solutions of polystyrene t polyvinyl acetate + polyvinyl chloride in tetrahydrofuran, and polystyrene t polyvinyl acetate t atactic polypropylene in benzene. Analysis of the individual layers yielded the following results: each polymer is always contained in each layer; the mixing ratios of the polymers in the three layers are generally different from one another and differ also from the mixing ratio of the starting mixture; each of the three layers is distinguished from the others by the fact that a specific polymer has been accumulated therein in preference to the other polymers. Concerning the quantitative distribution of the polymers among the layers, some laws could be found which can be explained qualitatively on the grounds of molecular-physical considerations. A solution of polystyrene t polyvinyl acetate t polyvinyl chloride t atactic polypropylene in tetrahydrofuran (equal amounts of polymers, total concentration about 10 g/100 ml) forms four layers, the composition of which was also determined by analysis. When solutions of polymer mixtures are evaporated, separation into phases takes place because the polumers become incompatible with one another when the concentration exceeds a certain value. As a result, strongly inhomogeneous films are obtained after evaporation of the solvent. If the inhomogeneity of the films is not taken into consideration, misleading results may be obtained in the analysis of the films. It is shown that in the system polystyrene + polyvinyl acetate, with tetrahydrofuran as solvent, surprising phenomena appear on the addition in stages of cyclohexane. The phenomena are due to the overlapping of separating and dissolving processes which have, in part, opposite actions.