Compatibility and neutron scattering studies of mixtures of polystyrene with poly(2,6-dimethyl 1,4-phenylene oxide) and its brominated derivatives

Several narrowly disperse polystyrenes (PS) were mixed with three series of random copolymers of 2,6-dimethyl phenylene oxide (also known as xylenyl ether (XE)) and 3-bromo-2,6-dimethyl phenylene oxide (BrXE), each series having a fixed chain length. The critical BrXE comonomer concentration necessary to induce phase separation, x_c′ was characterized for each blend series by a number of techniques. x_c was extrapolated to a value of about 0.5 at infinite chain lengths of each polymer of the blend. This finding supports the negative heat of mixing of PS with PXE reported by other workers. Small-angle neutron scattering studies were carried out using small amounts of perdeuteropolystyrene in several matrices for which single phase behaviour had been shown to exist. The radius of gyration R₂ and the second virial coefficient A₂ were greatest in the pure PXE matrix reflecting the goodness of this material as a ‘solvent’ for PS. In matrices containing $\text{50\%}\text{PS}\text{50\%}$ copolymer, A₂ extrapolated to zero at x_c ≥ 1 which was consistent with the phase behaviour of this series of blends.     

Microcellular foams from some high-performance composites

High-temperature composites were successfully prepared from aminated polysulfone, polyphenylsulfone, and a rod-like polymer polybenzimidazole (PBI). The single glass transition temperature T_g and the absence of evidence for phase separation in scanning electron microscopy suggested that these systems formed so-called ‘molecular composites’. The enhanced miscibility between the polymer pairs was probably due to hydrogen bonding interactions. Compared with the matrix polymers themselves, these composites have improved values of T_g and thermal stability due to a synergistic effect upon incorporation of polybenzimidazole into the polymer matrices. Microcellular foams were successfully prepared from these composites. The foaming behavior and morphologies of the resulting composite foams were much more complicated than those of the pure polymers. In particular, they had unusual bimodal cell size distributions, and some open or partially open-cell structures.     

The dilute solution properties of maleic anhydride and maleic acid copolymers: 1. Light scattering, osmotic pressure and viscosity measurements

Dilute solution behaviour of poly(maleic anhydride-co-ethyl vinyl ether) and poly(maleic acid-co-ethyl vinyl ether) has been investigated by light scattering, osmotic pressure, and viscosity measurements. The molecular weights ($\text{M}\text{?}{}_{\mathrm{w}}$ and $\text{M}\text{?}{}_{\mathrm{n}}$), the second virial coefficients A₂, and the intrinsic viscosities [η] have been determined for three states of this copolymer: anhydride-form, H-form, and Na-salt independently. The constants in the Mark-Houwink relations were obtained for the above three states under different solvent conditions. The molecular weight of the anhydride-form is found to be higher than that of the acid-form or the Na-salt, suggesting the degradation in a process of hydrolysis. The second virial coefficient A₂ as well as the Mark-Houwink relation indicates that the anhydride-form and H-form behave as flexible polymer chains in good solvents. However, the polymer coil of Na-salt is highly expanded even at saturated NaCl concentration.     

Concentration dependence of static and hydrodynamic screening lengths for three different polymers in a variety of solvents

We have used small angle neutron scattering and dynamic light scattering to measure the static and hydrodynamic screening lengths of polystyrene, polymethylmethacrylate and polydimethylsiloxane solutions ranging from marginal to good solvent quality. A universal plot is found for the scaled static screening length when the concentration is scaled using the second virial coefficient in the way suggested by renormalization group theories. The same concentration units do not produce a universal plot for the hydrodynamic screening length at the molecular weights that we have studied (all around 1-2×10⁵ g/mol). However, when the concentration is expressed in terms of k_Dc, where k_D is the virial expansion coefficient for the cooperative diffusion coefficient and c is the concentration, most of the variation between different polymer-solvent combinations is eliminated. The ratio of hydrodynamic screening length to static screening length increases with concentration for all of the polymer solvent pairs studied, and its value differs for different polymer solvent pairs.     

Depletion potential between two attractive plates mediated by polymers

Depletion interactions in polymer-colloid mixtures in the presence of the attraction between polymers and particle surfaces are computed from the simulation data on polymer partitioning. The gap between two large colloid particles is approximated by the slit plates immersed in a dilute polymer solution. The difference between the intra-slit and bulk pressures of polymers Δp (net pressure) and the effective pair potential of plates W is calculated as a function of the plate separation D and the attraction strength ε of plates to polymer segments. Weak attraction strengths ε are considered, including the region around the compensation point ε_c (the depletion/adsorption threshold) where the partition coefficient of polymers K=1. A fit of the simulation data for the free energy confinement ΔA=−k_BT ln K served as a base of computations of the above depletion characteristics. The analytical functions deduced for Δp(D,ε) and W(D,ε) predict a reduction of the range and depth of depletion interaction by an increase in the attraction strength |ε|. Variation of the thickness δ of depletion layers near the plates with attraction ε was also determined. Consequences of reduced depletion interaction for the effective second virial coefficient B₂ and for the stability of colloidal suspensions were discussed. At the compensation point ε_c the depletion effect disappears and the stability of polymer-colloid mixtures in dilute solution is not affected by the polymer concentration.     

Temperature dependence of unperturbed dimension and interaction parameters of polyester resin in solvents

The flow behaviour of a polyester in various solvents was studied at temperatures ranging from 10 to 80°C. The practical data obtained from the temperature dependence of limiting viscosity number [η] were used to calculate unperturbed dimensions and interaction parameters of the polyester resin in poor, moderate and good solvents. The data provided information regarding conformational transitions in the polymer chains in terms of exothermic or endothermic local ordering of solvents on resin segments and their fixation on polymer coils. The temperature dependence of unperturbed dimensions K_e, Flory–Huggins interaction parameter χ₁₂, the second virial coefficient A₂, entropy parameter U₁, enthalpy parameter K₁, and viscosity expansion factor α_n, has been used to estimate the solvent quality for the resin.     

Interaction between polymers in dilute solutions of two polymers in a single solvent measured by light scattering and the compatibility of polymers

The intensity of light scattered from dilute solutions of mixtures of two nonidentical polymers in a single solvent was measured. The parameter A₂₄ characterising the thermo-dynamic interaction of two nonidentical polymer molecules in solution was calculated for several systems polymer 2 - polymer 4 - solvent. For chemically strongly different polymers, A₂₄ is independent of molecular weights of the polymers and probably also of solvent. A₂₄ is related to the compatibility of both polymers and decreases contrary to expectation with increasing chemical difference between polymers 2 and 4.     

Thermotropic liquid crystalline polymers with quasi-rigid chains: 2. Chain flexibility

The melting points of polymers with quasi-rigid rod-like chains can be depressed below their decomposition temperatures by increasing their relative flexibility. However, v_ni is also depressed and the subtle balance between the axial ratio of the mesogenic segments and the flexibility of the macromolecule must be taken care of. A number of poly-esters, -amides, and -esteramides were prepared and their thermal behaviour investigated. One of the polyesters melts at 240°C–270°C to give a nematic phase. The solubility of the polymers also improved with increasing flexibility of the macromolecules.     

Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Estimation of thermodynamic quality of the solvent from the concentration effect in gel permeation chromatography of polymers

Dependences of the elution volume, V_e, on the concentration of the injected polystyrene (PS), c, in gel chromatography with inorganic carriers were studied in various single and binary eluents. It was found that the dependence of V_e on c is approximately linear in the region of low concentrations and its slope depends on the thermodynamic quality of the eluent. This relationship is more pronounced for higher molecular weights. Correlation for the slope k with the limiting viscosity numbers [η] proposed earlier in the literature is not valid for thermodynamically poor eluents; however, a correlation was found for all the eluents employed between k and the product A₂M, where A₂ is the second virial coefficient of polymer in solution. This supports the interpretation of the concentration effect in gel chromatography of polymers as a consequence of the decreasing effective hydrodynamic volume of coils with increasing concentration. The link between the empirically found correlation of k with A₂M and the existing theory of the concentration effect in g.p.c. was examined. Comparison of the virial coefficients determined from the slope k for PS in various eluents with the literature data showed that gel chromatography could yield a rapid estimate of the value A₂. As has been shown by an analysis of the concentration effect on the distribution coefficient K the concentration effect leads to the formation of a non-linear isotherm and to the asymmetrical peak shapes. In the range of very low concentrations, deviations from the linear dependence of V_e on c can be expected as a result of both the sorption effect and the thermodynamic partition of the solute.     

Improved accuracy and precision in the light-scattering characterization of homo- and copolymers in THF

A one-point method was developed for the estimation of weight-averaged molecular weights from light-scattering data. The method is based on the calculation of the second virial coefficient from theoretical predictions of the dependence of A₂ on the molecular weight. The second virial coefficient is then regressed for a particular polymer—solvent combination from a series of preexisting measurements over a range of molecular weights. The one-point method is found to yield as accurate molecular weight estimates as obtained from a Debye plot using the conventional dilution technique. The variance in the estimation of the Rayleigh factor has also been found to be highly dependent on the measurement concentration. Therefore, the precision in the estimation of molecular weight can be improved by calculating molecular weights at or near the optimal concentration, which is itself molecular weight-dependent. The one-point method is demonstrated for poly(methyl methacrylate)s of various polydispersities in tetrahydrofuran. The molecular weight of polystyrene and polystyrene-co-acrylic acid were also estimated by the one-point method in THF. In the case of the polystyrene-co-acrylic acid, THF becomes a poorer solvent with increasing levels of acrylic acid in the copolymer, and the parameter (A₂M^0.5) is found to vary with the copolymer composition, as is theoretically predicted. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1303–1316, 1997     

Thermodynamic and hydrodynamic properties of the the systems polymer—tetrahydrofuran—water: 1. Solution properties of polystyrene

Tetrahydrofuran (THF) is a solvent widely applied in polymer science and technology. However, because of its hygroscopic nature THF may often contain water considerably influencing the properties of the corresponding polymer solutions. In the first part of a series devoted to this problem, cloud point titrations and viscosity measurements were performed in the system polystyrene (PS)-THF-water. The limiting viscosity numbers of polystyrene considerably depended on the water content already in the domain of azeotropic composition, i.e. at about 4.5 vol.% of water. The constants of the Mark—Houwink equation, K and a were determined in pure THF and in mixtures containing up to 8.2 vol.% of water and compared with those for PS-THF found in the literature. The corresponding unperturbed dimensions were determined by various extrapolation procedures and were found to depend on solvent composition. Simultaneously, polymer-mixed solvent interaction parameters B were determined and discussed. Two theta compositions were observed: at about 7.7 vol.% of water for second virial coefficient A₂ = 0, and about 8.12 vol.% for a = 0.5. This agrees with the hypothesis of Dondos and Benoit and indicates the presence of preferential solvation in the system.     

Thermodynamic parameters of poly(lactic acid) solutions in dialkyl phthalate

Some of thermodynamic parameters for poly(lactic acid) (PLA)/dialkyl phthalate systems have been investigated. Both poly(dl-lactic acid) (PDLLA) and poly(l-lactic acid) (PLLA), which are stereoisomers of PLA, were used and a series of 1,2-dialkyl phthalates with different alkyl chain, from methyl to hexyl, was adopted as a solvent. Theta temperatures of PLA/dialkyl phthalate system were determined and subsequently the second virial coefficient and the interaction parameter were evaluated. Theta temperature was determined by the extrapolation of the highest liquid-liquid phase separation temperatures and Zimm plots were constructed by static light scattering to obtain second virial coefficient and z-average radius of gyration. Second virial coefficient and z-average radius of gyration was examined quantitatively as a function of temperature and solvent. Thermodynamic parameters that could not be obtained experimentally were calculated based on the Flory-Huggins theory.     

Conformational behaviour of (styrene-p-chlorostyrene) triblock copolymers in dilute solutions. 2. Temperature dependence of conformational behaviour in a selective solvent

Intrinsic viscosity, osmotic second virial coefficient and light scattering of the B_mA_nB_m and A_mB_nA_m copolymers (A, styrene monomeric unit; B, p-chlorostyrene monomeric unit, m and n denote the number of units) in cumene which is a good solvent for polystyrene but a θ solvent for poly(p-chlorostyrene) at 59.0°C, were studied over the temperature range 65° to 15°C. The results suggested that conformational transition from a random coil form to a segregated form occurs at a critical temperature which appears to be in the range 40° to 30°C, depending on the composition, molecular weight and structure of the block copolymers; the θ condition could not be attained by cooling the block copolymer solutions, and micelle formations due to intermolecular associations were found in some cases below the transition temperature.     

The second virial coefficients of highly-purified ring polystyrenes in cyclohexane

The second virial coefficients A₂ of ring polystyrenes with high purity in cyclohexane were measured by light scattering in the temperature range 27.0-34.5 °C. The purity of four samples with M_w of 16k, 42k, 110k and 570k was determined to be all over 96% by HPLC. It has been found that A₂s of all the samples are definitely positive at the theta temperature of linear polystyrene, 34.5 °C, and the measured values for four samples converged to zero at 27.7 °C with decreasing temperature. This value is below the previously reported one, but it is quite consistent with the predicted value based on the topological repulsive interaction among the ring polymer molecules.     

Zur phasentrennung von polymergemischen in lösung

Usually, mixtures of solutions of two different polymers in the same solvent are incompatible. This incompatibility leads to an intensive turbidity of the mixture and finally, to the formation of two phases. The turbidity disappears on dilution with the same solvent, because the polymers are compatible below a certain polymer concentration c_kr. In principle, the same effects occur also with mixtures of polymers in the solid state (polymer blends), but here the aggregation of the microphases is impossible due to the high viscosity. Up to now, there is little known about the composition of the two phases above c_kr. Therefore, we studied the distribution of two different polymersin solution regarding molecular weight and concentration into both phases. It was varied the polymer ratio, the molecular weight, the overall concentration and the nature of the solvent. Polystyrene and polyvinyl acetate were used as polymers because they can easily be separated from each other which is necessary when analysing the different phases; this analytical separation was carried out for each individual phase. The following results were obtained: Each phase contains both polymers; in addition there occurs a fractionation according to molecular weight during the phase separation for both polymers. The polymer distribution in the two phases regarding molecular weight, amount of polymer, and concentration depends not only upon initial concentration, molecular weight and weight ratio of the two polymers but also upon the different degree of solvation of the macromolecules in different solvents. When mixtures of solvents are used, an additional partially separation of the solvent into both layers takes place.     

Phase behavior of the ternary system solvent: poly(γ-benzyl L-glutemate) and polystyrene

Summary Phase equilibria were investigated at 80°C for a ternary system involving a solvent benzyl alcohol, a rodlike polymer poly(-benzyl L-glutamate) (PBLG), and a flexible polymer polystyrene (PS). The fairly dilute solution of the two polymers was isotropic and monophasic. At greater concentrations, it was separated into two isotropic phases. Above an even higher critical concentration of the two polymers, three phases, a cholesteric (A₁) and two isotropic phases (I₁ and I₂), coexisted at equilibrium. PBLG was contained exclusively in the phases A₁ and I₁, while PS was in the phase I₂. The more concentrated solution was separated into a cholesteric phase and an isotropic phase. The latter contained PS but excluded PBLG, These features were discussed on the ground of the Flory theory by considering the polymer compatibility.     

Automated batch characterization of polymer solutions by static light scattering and viscometry

Using a programmable mixing pump, light scattering flow chamber, refractive index detector, and single capillary viscometer, the batch (unfractionated) characterization of polymers in solution has been automated. Three different schemes to produce polymer concentration gradients were used, and values for weight average mass M_w, root mean square radius of gyration 〈S²〉^1/2, second virial coefficient A₂, and intrinsic viscosity [η] were determined for a broad distribution sample of poly(vinyl pyrrolidone) (PVP) and a narrow fraction of poly(ethylene oxide) (PEO). High concentration experiments on the PVP also allowed determination of the third virial coefficient A₃. The method has several advantages over traditional manual methods in terms of accuracy, sample preparation, and amount of labor required. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2359–2368, 1999     

Small-angle neutron scattering of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers

Small-angle neutron scattering was used to characterize the structure of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers dissolved in methanol-d4 (CD₃OD). A radial density profile based on a power law functional form provided a good fit to the scattering data. While a model with homogeneous density profiles in the core and shell, respectively, and with a size distribution (a polydisperse core-shell model) also fits the data comparably well, the extra parameters required for this fit are difficult to justify on the basis of the data. In addition, unconstrained fits using the core-shell model failed to converge to values of the overall molecular size and molecular weight which agreed with values determined from independent light scattering measurements which leads to the conclusion that the power law model is a more appropriate function for describing the radial density function of these molecules. The density profile from either model showed that the polystyrene core of the molecules is not collapsed. Values of the second virial coefficient, A₂, have been calculated from Zimm plots and it was found that A₂ decreased as a function of generation to close to zero for the highest generation (i.e. highest molecular weight) polymers. Finally, it was found that the radius of gyration of the polymers increases with the molecular weight according to the scaling relationship, R_g∼M_w^v with v=0.24±0.04.     

Zur unverträglichkeit von polymergemischen. 1. Lichtstreuungsmessungen am system polystyrol/polymethylmethacrylat/benzol

A polystyrene (PS) with M?_w = 9,7 · 10⁴ was investigated by means of light scattering in the isorefractive polymer/solvens-mixture polymethylmethacrylate (PMMA)/benzene. It was found, that the second osmotic virial coefficient A₂ of PS was strongly dependent on the average viscosimetric molecular weight M?_v and on the concentration of PMMA, but scarcely on the temperature in the range of 20°C to 60°C. The θ-Point, where A₂ is zero, was independent of the temperature within experimental error. By defining the PMMA concentration at the θ-Point as c_θ, and by reducing the measured PMMA concentration c to c/c_θ, an unequivocal relation was obtained between A₂ and c/c_θ, which is independent of molecular weight and molecular weight distribution of PMMA. PS shows a high second virial coefficient in dimer and trimer MMA as well as in non-hydrogenated and hydrogenated MMA. The investigated PS constitutes a θ-System in PMMA of a degree of polymerisation of P?_w, ～ 17without the use of benzene.