Solubility characteristics of poly(etheretherketone) and poly(phenylene sulfide)

The crystalline high-performance polymers poly(etheretherketone) (PEEK) and poly(phenylene sulfide) (PPS) are generally considered to be highly resistant to dissolution in most common solvents. This article reveals numerous compounds that dissolve in excess of 25 wt % of each polymer at elevated temperatures. Typical binary-phase diagrams depicting the minimum solubility temperature vs. concentration are also presented for several representative polymer–solvent mixtures for both PEEK and PPS. The phenomenon of the solvent-induced crystallization of PEEK is presented. The importance of these polymer–solvent systems for the preparation of permselective membranes is discussed.     

基于改进自由体积和无规因子贡献的聚合物热力学模型

给出了一个基于改进的自由体积和无规因子的聚合物溶液热力学模型，其无规因子项(NRF)用来描述聚合物溶液中聚合物与溶剂的局部交互作用对剩余Gibbs自由能的贡献，改进的自由体积项(Entropic-FV)用来描述聚合物溶液的混合效应对剩余Gibbs自由能的贡献。文中对45组二元聚合物与溶剂体系进行了关联计算，并与Zafarani-Moattar模型，Flory-Huggins模型和UNIFAC-FV模型的计算结果进行了比较，其平均绝对误差分别为1．910％，2．465％，3．738％和10．149％。     

Pressure-volume-temperature properties for binary and ternary polymer solutions of poly(ethylene glycol), poly(propylene glycol), and poly(ethylene glycol methyl ether) with anisole

Pressure-volume-temperature properties were measured for polymer solutions of poly(propylene glycol) (PPG)+anisole, polymer blends of PPG+poly(ethylene glycol methyl ether) (PEGME), and the blends of PPG+PEGME and poly(ethylene glycol) (PEG)+PPG with anisole at temperatures from 298.15 to 348.15 K and pressures up to 50 MPa. The Tait equation represents accurately the pressure effect on the liquid densities over the entire pressure range. The excess volumes change from positive to negative as increasing the mole fraction of PPG in the binary systems of PPG+anisole and PPG+PEGME. The volumetric data of the related binary systems were correlated with the Flory-Orwoll-Vrij and the Schotte equations of state to determine the binary parameters. By using these determined binary parameters, both equations predicted the specific volumes of the polymer blends with anisole to average absolute deviations of better than 0.13%.     

A modified entropic expression for the analysis of swelling behavior of polymeric membranes in solutions

The linear mixed relation for mixed molar volume and free-volume were modified to derive our new activity expression attributed to the combined combinatorial and free volume contributions. The validity and applicability of this expression were demonstrated by calculating the solvent activity in polymer solutions and analyzing the swelling behaviors for polymeric membranes. The average absolute deviation (AAD) of these calculated results from the experimental values of solvent activities for polymer solutions was employed for comparison. It is shown that the modified model can yield better results than the original one for most of the systems considered. The swelling behavior of poly vinyl alcohol (PVA) membranes in water/glycol (EG) mixture over a wide range of concentrations was analyzed. The activity of solvents in the liquid and the membrane was calculated by the UNIQUAC model and this present modified model, respectively. The estimations are consistent with experimental data roughly at temperatures of 333 and 343 K. It is found that the modified model is a suitable alternative to the Flory-Huggins equation for the analysis of the swelling behaviors of polymeric membranes in solutions.     

Theoretical consideration on the number of external degrees of freedom and its application to poly(dimethylsiloxane) solutions

Summary The Flory theory of polymer solution was modified by assuming the non-additivity of the number of the degree of external freedom for a binary mixture and applied the modified Flory theory to poly (dimethylsiloxane)-solvent systems. This theory can reproduce the experimental results of the interaction parameter and the excess volume of mixing, which the Flory theory failed to reproduce.     

Cohesive energy densities of poly(di-n-alkyl itaconates)

The solubility parameters of the first ten members of the homologous series of poly(di-n-alkyl itaconates) were determined from limiting viscosity numbers in various organic solvents, differing in structure, polarity and hydrogen bonding capacity. Numerical values from 9.58 to 8.10 (cal/cm³)^1/2 were obtained independently from measurements in hydrocarbon and oxygen containing solvents, close to solubility parameters calculated from polymer densities and molar attraction constants. The values obtained reflects the increasing paraffinic character within the series and can be correlated to solubility parameters published in the literature for structurally similar poly(alkyl acrylates) and poly(alkyl methacrylates).     

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems was investigated. Poly(DL ‐lactic acid) (PDLLA) and poly(L ‐lactic acid) (PLLA) with different molecular weights were used. A series of dialkyl phthalates, with different numbers of carbon atoms in the alkyl chain, were employed as solvents to control the interaction between polymer and solvent. The liquid–liquid phase‐separation temperature of the poly(lactic acid) solutions decreased systematically with a shorter alkyl chain in the phthalate. Based on the interaction between polymer and solvent and the molecular weight of polymer influencing liquid–liquid phase‐separation temperature significantly but crystallization temperature only slightly, proper thermal conditions were employed to investigate competitive phase separation and crystallization in PLLA solutions. Factors that can influence the final morphology of PLLA solutions were examined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2224–2232, 2003     

Effect of solvent balance on the surface properties of poly(vinyl chloride)

Films of poly(vinyl chloride) have been cast from solutions of varying thermodynamic quality and the film properties studied by inverse phase gas chromatography. The solvents included tetrahydrofuran, cyclohexanone, and mixtures of toluene with both tetrahydrofuran and cyclohexanone. The solvent composition was followed during evaporation and film formation for the mixed solvents, and it was shown that the slower evaporating solvent component has the greatest effect on the surface properties of the films. The porosity of the polymer film surfaces is interpreted in terms of the mobility of the polymer chains during film formation. At high concentrations, polymer chain–polymer chain interactions become stronger when thermodynamically less powerful solvents are used or are last to leave during film formation; therefore, the solvent balance has a critical influence on the film surface properties. Annealing the poly(vinyl chloride) above the glass transition temperature reduces the surface porosity of the cast polymer.     

Rheological properties of poly(ethylene oxide) aqueous solutions

This article describes the rheological properties of certain poly(ethylene oxide)s dissolved in water-based solvents. The experimental results show that the rheological properties in aqueous solutions are significantly affected by the solvent properties, which have been changed by the use of ethanol–water mixtures and electrolyte solutions and by the variation of the ambient pressure and temperature. The variation of the temperature and pressure is seen to change the polymer chain configuration and also the interactions of polymer segments with the solvent molecules. This gives rise to distinctive and apparently unusual rheological properties for these systems with the variation of the ambient temperature and pressure. The study generally illustrates that the rheology of these systems are, to a large degree, influenced by the hydrogen bonding in the solvent and between the solvent as well as the polymer. At a first-order level, the increase of the pressure and the temperature and also the addition of electrolytes, and the inclusion of an aqueous diluent, produce comparable effects. In essence, these changes seem to disrupt the hydrogen bonding structure in the solutions and, hence, the solvent quality in a comparable fashion. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 419–429, 1998     

聚L-乳酸在大分子体积溶剂中的结晶性能

聚L-乳酸(PLLA)的结晶性能影响着其生物降解速度和机械强度。采用广角X射线衍射(XRD)和差示扫描量热(DSC)方法研究溶剂分子体积对PLLA结晶性能的影响。以分子摩尔体积较大的聚乙二醇(PEG)为溶剂,PLLA在较高质量分数溶液(10%)中仍具有高的结晶度(73%)、高的非等温结晶温度和快的结晶速度,结晶速度系数CRC为0.659,高于从质量分数10%小分子溶剂中结晶的结晶速度。溶剂分子的摩尔体积对聚合物分子的构象有明显的影响,从而直接影响着PLLA的结晶速度和结晶度。     

Solvent activity coefficients at infinite dilution in polystyrene-hydrocarbon systems from inverse gas chromatography

Inverse gas chromatography was used to measure activity coefficients of solvents at infinite dilution over a temperature range from 373.15K to 423.15 K for monodisperse polystyrene-hydrocarbon systems. Polystyrene has average molecular weight 2.89 ×10⁵. Solvents include six aliphatic hydrocarbons such as cyclohexane, methylethylketone,n-hexane, carbon tetrachloride, acetonitrile and acetone and three aromatic ones as benzene, toluene andp-xylene. The measured data of activity coefficients of solvents were predicted by UNIFAC-FV model. We, also, presented a modified UNIFAC-FV model by empirically assigning to it a temperature-dependent C parameter in the free volume contribution of the model. Fitted results demonstrated that the modification of the model fitted the experiments better than the original one.     

Effect of recrystallization on the solubility of poly(vinylidene chloride)

A study of the crystallization of poly(vinylidene chloride) from dilute solution in various solvents was carried out. The temperature at which the polymer dissolved was dependent on crystallization history. The minimum solution temperature obtained by recrystallization at high undercooling and redissolving is the preferred parameter for characterizing solvents for poly(vinylidene chloride).     

Solubility parameters of poly(di-n-alkyl cyclohexyl-) and poly(di-n-alkyl phenyl itaconates)

Solubility parameters of poly(dicyclohexyl-), poly(diphenyl itaconate) and of the first three members of the poly(dialkyl cyclohexyl-) and poly(dialkyl phenylitaconate) homologous series were determined from limiting viscosity numbers in various solvents and solvent mixtures, differing in structure, polarity and composition. The values obtained are within limits of 19.0 and 16.7 (J^1/2. cm^-3/2). Phenyl groups in the substituents lead to slightly higher values than cyclohexyl rings and the introduction of alkyl groups in both series results in a progressive decrease of the solubility parameter. The experimental values are slightly lower than those obtained by calculation from molar attraction constants.     

Sorption of solutes by poly(ethylene oxide): 3. Partial molar entropy and enthalpy in poly(ethylene oxide) solution with benzene

The partial molar entropy and enthalpy of benzene in poly(ethylene oxide) solution have been determined over concentration ranges from 0 to 20 wt% for temperatures from 70° to 150°C using the corresponding-states theory of Prigogine and Flory. These results show that both the partial molar entropy and enthalpy of benzene in poly(ethylene oxide) increase as the segment fraction of poly(ethylene oxide) increases and decrease as temperature increases. The partial molar enthalpy is positive from 70° to 150°C.     

均三甲苯/二异丁基甲醇混合溶剂黏度测定及关联

采用乌氏黏度仪,在常压和293.15～323.15 K温度范围内测定了均三甲苯与二异丁基甲醇混合溶剂以及两种纯溶剂的黏度,计算了不同温度和组成下混合溶剂的超额黏度。用Redlich-Kister方程对超额黏度进行了关联;用Andrade方程、UNIFA-VISCO模型以及Grunberg-Nissan模型对黏度进行了关联与预测。结果表明,混合溶剂的黏度随温度升高和均三甲苯含量增加而减小。超额黏度均为负值,且随均三甲苯含量增加呈U形变化,约在均三甲苯摩尔分数为0.3时达到最低。Grunberg-Nissan模型对黏度数据的关联和预测性最好,预测值与实测值的最大和平均相对偏差分别为12.96%和5.74%。     

Resorbable materials of poly(L-lactide). II. Fibers spun from solutions of poly(L-lactide) in good solvents

Fibers of poly(L -lactide) (PLLA) with a tensile strength up to 1.2 GPa and Young's modulus in the range of 12–15 GPA were obtained by a hot drawing of fibers spun from solution of PLLA in good solvents such as dichloromethane and trichloromethane. The tensile strength of fibers was strongly dependent on the molecular weight of PLLA and on polymer concentrations in the spinning solution. Changing of the polymer concentration in the spinning solution gives rise to formation of fibers with different shape and porosity. Fibers spun from 10–20% solutions at room temperature exhibit a regular structurization, due to the melt fracture. These fibers had knot strengths up to 0.6 GPa, whereas fibers with a smooth surface spun from more dilute solutions had weaker square knots up to 0.3 GPa.     

Implication of solvent structure in the interaction of poly (vinylalcohol) and short chain monohydric alcohols

Viscosity and density data have been obtained for aqueous solutions of a monodisperse sample of 90% hydrolysed poly (vinylalcohol) PvOH and for solutions of PvOH in short chain alcohol/water mixtures. The results are interpreted in terms of a ‘dynamic’ flowing volume and a ‘static’ partial molar volume for the macromolecule. Changes in the size of the dynamic and static volumes of the polymer in alcohol/water solvent mixtures are shown to correlate closely with reported changes in the degree of solvent structure. A tentative explanation of the role of solvent structure in the solution behaviour of the polymer is proposed.     

Study of miscibility of poly(vinyl acetate) and poly(vinyl alcohol) blends by fluorescence spectroscopy

Secondary relaxation of poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), and their blends in different proportions (9 : 1, 1 : 1, and 1 : 9) were studied by photoluminescence of anthracene, fluorescein, and both probes dissolved in the polymer blends. The temperature of the glass transition in the homopolymers was determined by the radiationless deactivation of anthracene as T_g(PVAc) ? 304 K and the photobleaching of fluorescein as T_g(PVA) ? 350 K. The relaxation processes of the different phases of the polymer blends occur at temperatures close to the homopolymers, which may be explained by the localization of each molecular probe within the matrix. These deactivation curves, however, are not similar to those of the individual homopolymers, suggesting a partial miscibility between these polymers. © 1995 John Wiley & Sons, Inc.     

Structural and electronic properties of poly(3-thiophen-3-yl-acrylic acid)

This work presents a combined theoretical and experimental study of poly(3-thiophene-3-yl acrylic acid), a new polythiophene derivative soluble in polar solvents. Quantum chemical calculations on small oligomers were performed to propose a structural model for this polymer. Specifically, the minimum energy conformations and the rotational profiles of the different isomeric derivatives constructed for a model system formed by two monomeric units were calculated. The resulting model, which shows head-to-tail polymer linkages and the acrylic acid side group arranged in trans-conformation, were used to predict the π-π^∗ lowest transition energy of an infinite polymer chain. On the other hand, the polymer was prepared by chemical oxidative coupling using anhydrous ferric chloride and subsequent alkaline hydrolysis. The synthetized material, which is soluble in aqueous base and acetone solutions, was characterized by FTIR, ¹H NMR and UV-vis experiments. Both the structural information and electronic properties derived from such experiments are fully consistent with the theoretical model obtained using quantum mechanical calculations.