Gas permeability of cardo-poly(ether-ether-ketone) and poly(phenylene sulfide)

The gas permeability and sorption of CO₂ and N₂O was measured on cardo-poly(ether-ether-ketone) (C-PEEK) and poly(phenylene sulfide) (PPS) at 298 K. The results are discussed on the basis of the dual-mode model. Results obtained from measurements at 308 K are compared with literature data of poly(phenylene oxide) (PPO), poly(sulfone) (PSU) and poly(carbonate) (PC). While C-PEEK shows similar transport properties as PC and PSU, the values of PPS are distinctly lower. The solubility of CO₂ in the various polymers as well as the correlation of the permeability coefficients of the same polymers for He, Ar, CO₂, N₂, and CH₄ with the kinetic molecular diameter of the gases indicate a simple relation of the transport properties with the polymer density.     

The influence of carbon dioxide cosolvent on solubility in poly(ethylene glycol)

Supercritical carbon dioxide (CO₂) and poly(ethylene glycol) (PEG) can be utilized as an environmentally friendly biphasic solvent system for catalysis reactions and subsequent product separation. To efficiently implement this technology, it is important to understand how solutes partition between these phases as well as how dissolved CO₂ in PEG affects the solvent properties. The work presented here explores the influence of CO₂ on the solubility of four different solutes in PEG. The transferable potentials for phase equilibria-united atom force field and configurational-bias Monte Carlo molecular simulation were employed to determine the solubilities of ethylbenzene, 1-octene, 1-pentanol, and 2-pentanone at 323.15 K and 15?MPa in PEG-600 using an ideal vapor phase with a Poynting-corrected vapor pressure. The effect of CO₂ concentration within the PEG phase was determined by varying the amount from no CO₂ to the saturation limit. The results indicate that while there is preferential solvation of CO₂ around the solutes, solubility of non-polar solutes is unchanged whereas there is a modest increase for polar solutes as the concentration of CO₂ increases. Increased solubility is analyzed in terms of both modified solvent structure and direct solute–CO₂ interactions.     

Swelling equilibrium of poly(acrylamide) gels in aqueous salt and polymer solutions

The influence of some single salts (NaCl, KCl, Na₂HPO₄ and K₂HPO₄) and poly(ethylene glycol) (PEG) on the swelling of aqueous poly(arcylamide)-gels was studied at 25°C in more than 600 experiments. The chlorides and phosphates cause a different behavior at high salt concentrations: The polyacrylamide gels swell in aqueous solutions of sodium and potassium chloride whereas they shrink when chloride ions are substituted by hydrogen phosphate ions. These differences are due to differences in the interactions of chloride and hydrogen phosphate ions with the network groups. In aqueous solutions of poly(ethylene glycol) the gels shrink continuously with increasing polymer concentration. At constant PEG mass fraction in the liquid phase, the swelling of the gel decreases with increasing molecular weight of PEG. The experimental results (degree of swelling, partitioning of solutes to the coexisting phases) are correlated by combining a model for the Gibbs excess energy for aqueous systems of polymers and electrolytes with a modification of the phantom-network theory. The correlation gives a good agreement with the experimental data for the degree of swelling, whereas in most cases, there is only a qualitative agreement for the partitioning of the solutes.     

Transport properties of poly(phenylquinoxalines) containing heterocyclic moieties

The transport behavior of a new class of membrane materials—a series of poly(phenylquinoxalines) containing heterocyclic fragments in the backbone—has been studied. These polymers contain moieties of a common chemical structure. Therefore, it is possible to follow how the transport parameters change upon introduction of various moieties into the backbone chain. The coefficients of permeability, diffusion, and solubility for H₂, He, O₂, N₂, CO, CO₂, and CH₄ along with the separation factors for the corresponding pairs of gases have been determined. The results are compared with the data for previously studied polymers of the poly(phenylquinoxaline) series.     

Diffusive desorption of small solute molecules from amorphous polymers: poly(methyl methacrylate), poly (vinyl acetate) and poly(n-alkyl 2-cyanoacrylates)

Diffusion coefficients of some aromatic substances in poly(vinyl acetate) and poly(methyl methacrylate) have been measured from desorption rates into aqueous buffers from solid solutions of diffusant in cast polymer films. With ordinary spectrophotometric instrumentation, extension of the measurable range of the diffusion coefficient at infinite dilution to below 10^?21 m² sec^?1 is sometimes possible. Measures values below 10^?12 m² sec^?1 are generally much more quickly obtained, and are apparently at least as reproducible as those obtained by time-lag methods, permitting differential effects of diffusant molecular weight and shape to be studied, with solutes of higher molecular weight than those to which previous published studies were confined. Diffusion coefficients of the same solutes in a number of poly(n-alkyl 2-cyanoacrylates) were measured by desorption from polymer particles and films. The rank order and general dependence of diffusivity upon molecular weight and shape is similar in all three polymers. There is a tendency for the ionic and basic solutes to become bound, probably by covalent linkage, to poly(n-alkyl 2-cyanoacrylate) molecular chain ends.     

Miscibility and surface characterization of a poly(vinylidene fluoride)‐poly(vinyl methyl ketone) blend by inverse gas chromatography

The miscibility of blends of semicrystalline poly(vinylidene fluoride)(PVF₂) and poly(vinyl methyl ketone) (PVMK) along with surface characterization were investigated using the inverse gas chromatography method (IGC), over a range of blend compositions and temperatures. Three chemically different families, alkanes, acetates, and alcohols, were utilized for this study. The values of the PVF₂‐PVMK interaction parameters were found to be slightly positive for most of the solutes used, although some degree of miscibility was found at all compositions. Miscibility was greatest at a 50:50 w/w composition of the blend. The interaction parameters obtained from IGC are in excellent agreement with those obtained using calorimetry on the same blends. The calculated molar heat of sorption of alkanes, acetates, and alcohols into the blend layer reveal the impact of the combination of dispersive and hydrogen bonding forces on the interaction of solutes with the blend's backbone. The dispersive component of the surface energy was found to range from 18.70–64.30 mJ/m² in the temperature range of 82–163 °C. A comparison of the blend's surface energy with that of mercury and other polymers is given. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1155–1166, 2000     

Polyethylene/poly(styrene-co-divinylbenzene) sodium sulphonate membranes : Part 1. Synthesis and properties

Transport properties of cation-exchange membranes have been studied. The self-diffusion coefficients of sodium and chloride ions, the transport numbers of sodium ions and water, and the conductivities were measured in 0.1 M sodium chloride at 25°C. The concentration potentials were determined in the system 0.05/0.15 M sodium chloride.The membranes were prepared by sulphonation of oriented polyethylene (PE) film modified with 30 wt % of styrene—divinylbenzene copolymer (poly(St-co-DVB)). The copolymer was introduced by interpolymerization of the monomers within the film without its dissolution. A sequence of membranes having similar ion-exchange capacity but differing in water content was then obtained from sheets of normal PE/poly(St-co-DVB)SO₃Na membranes by expanding them by heating in water followed by a thermal treatment in air.The deviations of the measured transport properties from the behaviour of homogeneous membranes and the analysis of the Kedem—Katchalsky relationships for composite membranes have led to the conclusion that in PE/poly(St-co-DVB)SO₃Na membranes a structure prevails with a series arrangement of layers with different properties.     

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes - structure and CO2 facilitated transport

Poly(vinylalcohol) (PVA)/poly(ethyleneimine) (PEI)/poly(ethyleneglycol) (PEG) blend membranes were prepared by solution casting followed by solvent evaporation. The effects of the blend polymer composition on the membrane structure and CO₂/N₂ permeation characteristics were investigated. IR spectroscopy evidenced strong hydrogen bonding interactions between amorphous PVA and PEI, and weaker interactions between PVA and PEG. DSC studies showed that PVA crystallization was partially inhibited by the interactions between amorphous PVA and PEI blend, in which PEG separated into nodules. The CO₂ permeability decreased with an increase in CO₂ partial pressure in feed gas, while the N₂ permeability remained constant. This result indicated that only CO₂ was transported by the facilitated transport mechanism. The CO₂ and N₂ permeabilities increased monotonically with the PEI content in the blend membranes, whereas the ideal selectivity of CO₂ to N₂ transport showed a maximum. When CO₂ is humidified, its permeability through the blend membranes is much higher than that of dry CO₂, but the change in permeability due to the presence of humidity is reversible.     

Gas transport in poly(vinyl methylbenzoates)

Permeation of eight gases (He, Ne, Ar, Kr, O₂, N₂, CO₂, and CH₄) in three isomeric poly(vinyl methylbenzoates) was measured by the time-lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. The p-methylphenyl side group of poly(vinyl p-methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinyl o-methylbenzoate) and poly(vinyl m-methylbenzoate), had lower gas diffusivities than poly(vinyl p-methylbenzoate) and poly(vinyl benzoate). The o-methyl and m-methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinyl m-methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was still negligible.     

Water-swollen cation-exchange membranes prepared using poly(vinyl alcohol) (PVA)/poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA)

A water-swollen type of poly(vinyl alcohol) (PVA)/poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA) cation-exchange membrane was prepared and characterized in terms of its electrochemical properties including ion-exchange capacity (IEC), electrical resistance, and transport number, etc. PVA/PSSA-MA membranes exhibited low electrical resistance and highly swelling property. In spite of 2–4 times higher water swelling ratio (WSR) than that of CMX (Tokuyama Corp., Japan), the transport number of the prepared membrane was comparable to that of the commercial membrane (t_n>0.93). Moreover, the electric resistance of PVA/PSSA-MA membrane was measured as low as 1.0–1.5 Ω cm². Further, in this study, interrelation between the membrane characteristics and crosslinking was investigated, and the result exhibited that the crosslinking degree is one of major factors affecting the ion transport through a water-swollen ion-exchange membrane (IEM).     

Gas separation properties of aromatic poly(amide-imide) membranes

Aromatic poly(amide-imide)s were synthesized using direct 2,2-bis[N-(4-carboxyphenyl)-phthalimidyl] hexafluoropropane (6FDIA) polycondensation with various diamines containing flexible ether groups and bulky substituents. The oxygen and nitrogen gas transport in the poly(amide-imide) membranes was investigate at 35 °C with the pressure between the interval at 2-10 atm. The proposed method is expected to promote the gas permeability of the poly(amide-imide) membrane and maintain the gas selectivity. It was found that both gas permeability and selectivity of poly(amide-imide) membranes increased with increasing fractional free volume and d-spacing. The gas permeability had good correlation with the γ-transition temperature. The bulky pendent group introduced into diamine moiety of poly(amide-imide) could efficiently promote the gas permeability. For the behaviors of gas separation, the gas diffusivity coefficient and solubility selectivity controlled the gas permeability and selectivity, respectively. The sorption behavior of the aromatic poly(amide-imide) membranes can be well explained using the dual mode sorption model. The Langmuir capacity constant and Henry’s law constant increase with FFV increasing. 6F-TBAPS has the best O₂/N₂ separation performance among the poly(amide-imide) membranes.     

Vibrational spectra and normal coordinate analysis of isotactic poly(alkyl ethylene)s. I. Modification I of poly(ethyl ethylene) and its deuterated derivatives

A new calculation of the vibrational frequencies of poly(ethy1 ethylene) based on the actual molecular geometry was performed. The calculation takes into account new experimental data such far-infrared spectra and Raman spectra of the stretched polymer, infrared spectra of poly(ethyl ethylene)-(2,2;d₂) (P-4-1-d₂) and poly(ethyl ethylene)-(3,3,4,4;d₄) (P-4-1-d₄), and Raman spectra of poly(ethyl ethylene)-(1,3,3;d₃) and poly(ethyl ethylene)-(3,3,4,4;d₄). Refinement produced a set of force constants; it is also applicable to poly(propyl ethylene).     

KINETICS OF NON-ISOTHERMAL CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY POLY (ETHYLENE GLYCOL)

The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m~0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.     

Polymers derived from fluoroketones. III. Monomer synthesis,polymerization, and wetting properties of poly(allyl ether) and poly(vinyl ether)

The synthesis and polymerization of a series of perhaloalkyl allyl and vinyl ethers derived from perhaloketones is described. Data on the critical surface tension of wetting (γ_c) for high molecular weight polymers of heptafluoroisopropyl vinyl ether and low molecular weight poly(heptafluoroisopropyl allyl ether) is also presented. Preparation of the allyl ethers is a one-step, high-yield displacement reaction between the potassium fluoride–perhaloacetone adduct and an allyl halide, such as allyl bromide. The vinyl ethersare prepared by a two-step process which involves displacement of halide from a 1,2-dihaloethane with a KF–perhaloacetone adduct and dehydrohalogenation of the 1-halo-2-perhaloalkoxyethane to a vinyl ether. Low molecular weight polymers were obtained with heptafluoroisopropyl allyl ether by using a high concentration of a free-radical initiator. The low molecular weight poly(heptafluoroisopropyl allyl ether) had a γ_c of 21 dyne/cm. No polymer was obtained with tributylborane–oxygen or with VCl₃–AIR₃, with gamma radiation, or by exposure to ultraviolet light. High molecular weight polymers were obtained from heptafluoroisopropyl vinyl either by using either lauryl peroxide or ultraviolet light but not by exposure to BF₃–etherate. The γ_c for poly(heptafluoroisopropyl vinyl ether) ranged from 14.2 to 14.6 dyne/cm., and the significance of this value is discussed in relation to the γ_c for poly(heptafluoroisopropyl acrylate).     

Gas transport in poly [bis(trifluoroethoxy) phosphazene] above the T(1) transition

Gas permeation measurements were performed by the time-lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO₂, O₂, and N₂ in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO₂ was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO₂ in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO₂ in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considered.     

A composite proton-conducting membrane based on a poly(vinylidene)fluoride-poly(acrylonitrile), PVdF-PAN blend

This paper reports on the synthesis and the properties of a new microporous, composite proton-conducting gel membrane, formed by swelling a poly(vinylidene)fluoride- poly(acrylonitrile), PVdF-PAN blend-based matrix containing a dispersed Al₂O₃ ceramic filler with aqueous acid solutions. We show that this membrane has a high and stable conductivity, a proton transport not critically influenced by the relative humidity level, and a projected low cost. Tests in a methanol-air laboratory cell also demonstrate that the membrane is basically suitable for application in direct methanol fuel cells.     

Gas transport properties of poly(arylether bissulfone)s and poly(arylether bisketone)s

The transport properties of the poly(arylether bissulfone) based on bisphenol A (PBSF) and the poly(arylether bisketone) s based on bisphenol A (PBK) and bisphenol S (PBK-S) are reported at 35°C. Comparisons are made with the polysulfone and the polycarbonate also based on bisphenol A to determine the effect of the long, rigid bisketone and bissulfone groups on polymer properties. A direct comparison also is made between PBK and PBSF, which differ only by their ketone and sulfone groups. The bulkier sulfone group increases free volume and T_g more than the ketone group. This results in higher solubility and diffusivity coefficients for the bissulfone versus the bisketone polymer, both of which contribute to higher permeability coefficients. © 1993 John Wiley & Sons, Inc.     

Poly(ethylene oxide) induced cross-linking modification of Matrimid membranes for selective separation of CO2

The novel cross-linker, poly(propylene glycol) block poly(ethylene glycol) block poly(propylene glycol) diamine (PPG/PEG/PPGDA), was employed to chemically cross-link Matrimid 5218 at room temperature. The cross-linking reaction process was monitored by FTIR. The XRD was used to indicate the changing of the polymer structure by cross-linking reaction. The effects of the cross-linking reaction on mechanical performance, gel content and H₂, CO₂, N₂ and CH₄ gas transport properties of the cross-linked Matrimid membranes were investigated. The cross-linked Matrimid membranes display excellent CO₂ permeability and CO₂/light gas selectivity compared with the uncross-linked Matrimid membrane. Finally, the potential application of the cross-linked Matrimid membranes for CO₂/light gas separation was explored.     

Novel rolltruded films. II. Effect of draw ratio on the gas transport properties of rolltruded isotactic poly (propylene)

Modification of the gas transport properties of rolltruded isotactic poly(propylene) films have been studied. Changes in the amorphous solubility, diffusivity, and the activation energies of CO₂, N₂, and CH₄ in iPP rolltruded at 150°C for draw ratios to ca. 20 are recorded. At this processing temperature variations in the transport coefficients have been found to be weakly dependent upon draw ratio and do not suffer the dramatic reductions often reported in uniaxially drawn polymers. In general, the morphological differences between uniaxially drawn and rolltruded films are subtle and are responsible for the significant difference in the measured transport properties. © 1994 John Wiley & Sons, Inc.     

Compatibility of Poly(vinyl chloride) with Polyalkyleneoxides. I. Poly(methylene oxide) and Poly(ethylene oxide)

The compatibility of poly(vinyl chloride) (PVC) with linear polyethers is examined over the entire composition range. This study examines blends with poly(methylene oxide) (PMO) and poly(ethylene oxide) (PEO) of medium (MMW) and high (HMW) molecular weight. The techniques used are dynamic mechanical analysis, DSC, and optical microscopy (phase contrast and polarizing). The results indicate that all polyethers show limited miscibility in the melt at high PVC contents. Proper analysis of the T_m data using the Kwei-Frisch and Hoffman-Weeks procedures allows the determination of the thermodynamic interaction parameter, which is found to be close to zero for all pairs of blends.