Gas permeability of copolypeptide membranes composed of γ-methyl L-glutamate and γ-benzyl L-glutamate

Membranes of copoly(γ-methyl L -glutamate, γ-benzyl L -glutamate) (PMBLG) as well as the related homopolymer membranes were prepared, and permeabilities of oxygen, nitrogen, argon, and carbon dioxide were measured in the 0–70°C temperature range. The values of permeability coefficients and solubility coefficients of the copolymers were smaller than those of permeability coefficients and solubility coefficients of the two homopolymers for every gas studied. The diffusion coefficients of the gases showed a minimum at around 25 mole % benzyl glutamate. The temperature at a maximum of tan δ spectra for the membranes showed a maximum at around 25 mole % benzyl glutamate. The Arrhenius plots of diffusion coefficients and solubility coefficients for PMBLG, which contained 50 and 71 mole % benzyl glutamate, showed a break at about 50 and 40°C, respectively. This permeation behavior is explained by assuming a unique interaction between methyl glutamate and benzyl glutamate side chains.     

Polymers in contact lens applications VII. Oxygen permeability and surface hydrophilicity of poly(4-methylpent-1-ene) and related polymers

Some of the problems and advantages in the use of non-hydrogel polymers in contact lenses are discussed together with studies on a series of such polymers which have potential advantages over the established material, poly(methyl methacrylate), in that they are both more flexible and more oxygen-permeable. Of the polymers examined which are all too hydrophobic for direct use, poly(4-methylpent-l-ene) proved to be the most readily modified in such a way that its surface became sufficiently wettable to sustain a coherent tear film without reducing its optical qualities to an unacceptable level. The ‘dissolved’ and ‘gaseous’ oxygen permeability coefficients of this polymer were studied as a function of film thickness, surface hydrophilicity and temperature. A pronounced boundary layer effect was observed in ‘dissolved’ oxygen permeability studies, although this decreased as the surface was treated to make it more wettable (as indicated by the equilibrium advancing water contact angle). The ‘gaseous’ permeability coefficients of oxygen were found to be some 4-6 times greater than those for nitrogen. A discontinuity corresponding to the glass transition temperature was observed at 28°C with both permeants and apparent activation energies for permeation were determined both above and below this temperature.     

Permeability of polyglutamic acid ester membranes to benzene vapor

Permeability of poly(γ-methyl L -glutamate) (PMLG), poly(γ-hexahydrobenzyl L -glutamate)-(PHBLG), and poly(γ-n-amyl L -glutamate) (PALG) membrane to benzene vapor was studied. Permeability coefficients of all the membranes were large, of the order of 10^?9–10^?6 cm³(STP) cm/cm² sec cm Hg, and increased markedly with increasing relative vapor pressure and temperature. The large permeability was due to the large diffusion coefficient. The sorption behavior of the PALG–benzene system was interpreted in terms of the theory of the mixing of solvent with side chains. The Arrhenius plots of diffusion coefficients for PMLG and PHBLG showed a break at about 29 and 40°C, respectively, where the volume-expansion curves of each polymer also showed a break, which is thought to be related to the side-chain motion. The diffusivity data for PALG were examined in terms of Fujita's free-volume theory, and it was found that the value of the average free-volume fraction in the pure polymer for PALG was much larger than that for vinyl polymers. This means that the side-chain motion of PALG is easy and is the reason that the diffusion coefficients for PALG are large. These results indicate that the diffusion of benzene in these polypeptides takes place in the side-chain regions between helices.     

Studies on syntheses and permeabilities of special polymer membranes. 37. Permeabilities of poly(γ-methyl L-glutamate) membranes

The permeation characteristics of poly(γ-methyl L-glutamate) (PMLG) membranes in the separation of polymers, poly(ethylene glycol) and poly(vinyl alcohol), from their aqueous solutions were influenced by the compaction of membrane swollen with water under pressure. The rate of pure water permeability up to an operating temperature of 70°C was governed by a change in the secondary-structure of PMLG. In addition, the permeabilities of alcohols through PMLG membrane were discussed.     

The effect of casting solvent on the sorption and diffusion of water vapor in poly(γ-methyl L-glutamate)

Water vapor permeability of poly(γ-methyl L -glutamate) (PMLG) membranes prepared by using dichloroethane, trifluoroacetic acid, and formic acid as solvents was studied. The membranes prepared by casting dichloroethane and trifluoroacetic acid solutions of the polymer, designated as PMLG–DCE and PMLG–TFA, respectivley, had α-helical structures according to infrared absorption spectra, while the membranes prepared by allowing the PMLG–TFA membranes to swell in formic acid, designated as PMLG–FA, had mainly a β-sheet structure. The amounts of water sorbed by PMLG–DCE, PMLG–TFA, and PMLG–FA increased in that order. The isotherms of PMLG–TFA and PMLG–FA were sigmoidal-shaped isotherms, and the heat of sorption for PMLG–TFA and PMLG–FA was larger than that for PMLG–DCE, which suggested the presence of the sorption sites. The diffusion coefficients of water for PMLG–DCE increased and then decreased with increasing concentration. On the other hand, the diffusion coefficients for PMLG–TFA and PMLG–FA increased with concentration. The activation energies of diffusion for PMLG–DCE, PMLG–TFA, and PMLG–FA increased in that order. These results were discussed in connection with the molecular conformations of poly(γ-methyl L -glutamate) in the membranes. From these results, it is assumed that the molecular chains in the PMLG–TFA membranes are mainly in α-helical and partly random-coil conformations.     

Pervaporation of methanol–water mixture by poly(γ-methyl L-glutamate) membrane and synergetic effect of their mixture on diffusion rate

The pervaporation behaviors of methanol–water by poly(γ-methyl L -glutamate) (PMLG) membrane at non-steady- and steady-state permeation were investigated. The values of t_1/2 (time required to reach a half value of steady-state permeation flux) for methanol and water changed and did not change with the component in feed, respectively. Both of the average diffusion coefficients for methanol–and water–PMLG from the mixture changed exponentially with the sorption amount of methanol by the synergetic effect on diffusion. The difference in behavior of non-steady and steady state diffusion was explained by whether D_o (diffusion coefficient at zero penetrant concentration) was influenced by the concentration distribution of penetrant in PMLG membrane.     

Separation of liquid mixtures by using polymer membranes. III. Grafted poly(vinyl alcohol) membranes in vacuum permeation and dialysis

A series of poly(vinyl alcohol) membranes were modifed by radiation-induced graft copolymerization with acrylic acid and methacrylic acid monomers. These grafted poly(vinyl alcohol) membranes were then tested for their separation and permeability characteristics in vacuum permeation and dialysis experiments. The permselectivity of the membranes toward methanol and water was studied on a vacuum permeation apparatus at 30, 40, and 50°C. The permeation process was found to be a temperature-activated process. The logarithm of the permeation rate varied linearly with the reciprocal of the absolute temperature. The permeability of the grafted membranes was found to increase with the degree of grafting, with no appreciable selectivity toward water in binary mixtures. The acrylic acid-grafted membranes generally showed greater improvement in permeability than the methacylic-grafted membranes. The permeability of the grafted membranes toward methanol, sodium chloride, urea, creatinine, and uric acid was studied in a dialyzer. In all cases, the grafted membranes showed an improved permeability toward these solutes over the commercial poly(vinyl alcohol) membranes. The dialysis results were then compared with those obtained for dialysis-grade cellophane membranes. For the case of sodium chloride, urea, and methanol, the permeability of the grafted membranes was comparable to that of cellophane. A comparison of commercial and grafted poly(vinyl alcohol) membranes in their permeability toward ionic solutes exhibited somewhat anomalous behavior in that the permeability of the commercial membranes was higher than that of the grafted membranes. This related to the ionic nature of the modified membrane. The permeability coefficients determined in the dialysis experiments were found to be directly related to the degree of hydration of the grafted membrane. This behavior was attributed to changes in the size and shape of voids within the membrane structure.     

Permeability of water vapor and carbon dioxide gas through poly(n-alkyl L-glutamate)

To elucidate the permeation mechanism in polypeptide membranes, permeation of water vapor and carbon dioxide gas through a series of poly(n-alkyl L -glutamate) (polymers of methyl, ethyl, propyl, butyl, amyl, hexyl, and octyl glutamate) were studied. It was confirmed that diffusion of small molecular substances in polypeptides takes place through the side chain region between helices. The diffusion coefficient of carbon dioxide gas increases with increase in side chain length. As for water vapor, the diffusion coefficient is highest with poly(n-butyl glutamate), and the clustering effect of water may contribute to the diffusion coefficient with increase in the hydrophobic nature of the polymer.     

Poly(acrylic acid)–poly(vinyl alcohol) semi- and interpenetrating polymer network pervaporation membranes

A series of poly(acrylic acid) (PAA)–poly(vinyl alcoho) (PVA) semiinterpenetrating (SIPN) and interpenetrating (IPN) polymer network membranes were prepared by crosslinking PVA alone or by crosslinking both PVA and PAA. Glutaraldeyde and ethylene glycol were used as crosslinking agents for the PVA and PAA networks, respectively. The presence of PAA increases the permeability of the membranes while the presence of PVA improves their mechanical and film-forming properties. The mechanical properties of the membranes were investigated via tensile testing. These hydrophilic membranes are permselective to water from ethanol–water mixture and to ethanol from ethanol–benzene mixtures. The IPN membranes were employed for the former mixtures and the SPIN membranes for the latter, because the IPN ones provided too low permeation rates. The permeation rates and seperation factors were determined as functions of the IPN or SIPN composition, feed composition, and temperature. For the azeotropic ethanol–water mixture (95 wt % ethanol), the separation factor and permeation rate at 50°C of the PAA-PVA IPN membrane, containing 50 wt % PAA, were 50 and 260 g/m²h, respectively. For the ethanol–benzene mixture, the PAA–PVA SIPN membranes had separation factors between 1.4 and 1200 and permeation rates between 6 and 550 g/m²h, respectively, depending on the feed composition and temperature. © 1996 John Wiley & Sons, Inc.     

Preparation and permeability of a block copolymer dialysis membrane by poly(γ-methyl-L-glutamate) and poly(ethylene glycol)

The block copolymer (PMLG-b-PEG) of poly(γ-methyl-L -glutamate) (PMLG) and isocyanate-terminated poly(ethylene glycol) was synthesized. Membranes were prepared by casting 2% 1,2-dichloroethane solutions of the polymer onto a glass plate and by evaporating the solvent at room temperature. The structure and microdomain morphologies of the membranes were observed with IR spectroscopy and scanning electron microscopy, respectively. Measurement of the contact angles of deionized water on polymer membrane surfaces was made. The mechanical properties of the membranes were also determined. The permeability of the PMLG-b-PEG and PMLG membranes toward urea and creatinine was studied in a dialyzer. In all cases, the block membranes showed improved permeability toward those solutes in comparison with the PMLG membranes. The permeation coefficients of urea, through the PMLG-b-PEG300 and PMLG-b-PEG1000 membranes, were about 2.3 and 3.2 times larger than that of PMLG membranes, and for creatinine through PMLG-b-PEG300 and PMLG-b-PEG1000 membranes, were about 1.0 and 2.0 times larger than that of PMLG membranes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:75–82, 1998     

Gas permeability and side chain structure of poly(γ-benzyl L-glutamate)

Three structural modifications of poly(γ-benzyl L -glutamate) (PBLG), forms A, B, and C, were prepared by varying the casting solvents and casting temperature. From x-ray analysis, infrared absorption spectroscopy, differential scanning calorimetry, and viscoelastic measurements, it is concluded that form A of PBLG is characterized by intramolecular stacking between the benzene rings in the side chain, form B exhibits intermolecular stacking, and form C has no stacking. The transition which corresponds to the breakdown of stacking of form A at 135°C is irreversible, while that of form B at 110°C is reversible. The degree of stacking is larger for form A than for form B. These structural features of the side chain region reflect the permeation and sorption behavior of carbon dioxide. Breakdown of stacking between benzene rings causes an abrupt increase in permeability in both form A and form B, and the permeation behavior for form A is not reversible, as is suggested from the irreversibility of the transition. The larger the degree of stacking, the lower is the amount of sorption. Although stacking is considered to affect the sorption site (solubility) and molecular motion, its influence on solubility is more evident in the temperature range up to about 50°C.     

The effect of casting solvent and water on gas permeability of poly(γ-methyl L-glutamate) membrane

Gas permeability of poly(γ-methyl L-glutamate) (PMLG) membranes prepared by using dichlorethane, trifluoroacetic acid, and formic acid as solvents was studied. The membranes prepared by casting dichloroethane and trifluoroacetic acid solutions of the polymer, designated as PMLG—DCE and PMLG—TFA, respectively, had α-helical structures according to infrared absorption spectra, while the membranes prepared by allowing the PMLG—TFA membranes to swell in formic acid, designated as PMLG—FA, had mainly a β-sheet structure. The diffusion coefficients of each gas studied for PMLG—DCE, PMLG—TFA, and PMLG—FA decreased in that order, and the apparent activation energies of diffusion increased in that order. The apparent heats of solution for Ne,O₂, N₂, and CO₂ were negative in PMLG—FA. These results were discussed in connection with the molecular conformations of PMLG in the membranes. It is suggested that the diffusion of gases in PMLG—DCE takes place in the side-chain regions between helices, while in PMLG—FA the diffusion occurs across the polymer main chain whose mobility is depressed by the intermolecular hydrogen bonds. The effect of water on oxygen permeability of PMLG—DCE was small; on the contrary that of PMLG—FA was very large. Furthermore, it is assumed that the random-coil conformation partly exists in PMLG—TFA.     

SBS/VP homograft membrane for oxygen enrichment

The grafting of 4-vinyl pyridine (VP) onto styrene-butadiene-styrene triblock copolymers (SBS) by homografting irradiation with dissolved oxygen was studied. Homograft membranes of various degree of grafting were prepared from a casting solution of grafted copolymer in benzene. The mechanical properties of membranes, gas permeability, and the effect of operating temperature on gas permeation were investigated. The degree of grafting of 8.4% was the largest at an irradiation time of about 15.5 h. It was smaller at both shorter and longer duration because of the interference of dissolved oxygen. It was found that the tensile strength and elongation of SBS-g-VP were similar to those of SBS. The stress relaxation of SBS-g-VP was slower than that of SBS, and this might be due to the formation of rigid microphase separation domain of poly(4-vinyl pyridine), which acted as permanent crosslinking points to reduce the stress relaxation. Using the properties of high flux of SBS and high O₂/N₂ selectivity of poly(4-vinyl pyridine), the performance of gas permeation of 4-vinyl pyridine homografted SBS membrane was studied. The selectivity of SBS-g-VP membrane increased with increasing degree of grafting. However, it was done at the expense of a decrease in the gas permeability. When the operating temperature of gas permeation increased, the permeability of oxygen and nitrogen increased, and the O₂/N₂ permeability ratio decreased. The activation energy (Ep) for gas permeation through different degree of grafting of SBS-g-VP membrane (obtained by the Arrhenius law) increased with increasing degree of grafting. For ungrafted SBS membrane, Ep was 5.5 kcal/mol for oxygen and 7.2 kcal/mol for nitrogen. For 8.4% grafting degree SBS-g-VP membrane, Ep for oxygen and nitrogen, were 6.5 and 8.1 kcal/mol, respectively.     

Permeation of solutes in water-swollen poly(vinyl alcohol-co-itaconic acid) membranes

Partition and permeability coefficients of urea, NaCl, and saccharose in water-swollen poly(vinyl alcohol-co-itaconic acid) membranes with various water contents (0.25 ? H ? 0.86) were measured. Partition coefficients and permeability ratios in freezing and nonfreezing water were estimated based on a parallel permeation model. It was suggested that at 25°C the permeation of saccharose in the nonfreezing water was nearly zero due to its negligible partition coefficient, while NaCl and urea were found to be able to permeate even the nonfreezing water. The activation energies of diffusion for three solutes were found to increase with the decrease of water content of the membranes. Since the fraction of nonfreezing water increased with the decrease of water content of the membranes, it is assumed that the increased activation energy of diffusion is due to the fact that the diffusion in nonfreezing water needs higher activation energy than in the pure bulk water.     

Cellulose acetate (CA) hybrid membrane prepared by phase inversion method combined with chemical reaction with enhanced permeability and good anti-fouling property

The CA hybrid membrane with enhanced anti-fouling property and higher permeability was prepared by nonsolvent induced phase separation method combined with chemical reaction. The impacts of different solvents (N-methyl-2-pyrrolidone, N, N- Dimethylacetamide, Dimethyl sulfoxide and N, N-Dimethylformamide), organic acids (citric acid/fumaric acid) and titanium dioxide (TiO₂) nanoparticles (NPs) on the separation performance and thermal stability of CA hybrid membranes were investigated. Results showed that the introduction of organic acids to membrane matrix caused asymmetry in the membrane structure with more uniform pore size distribution and higher porosity (82.5%). This is attributed to the production of CO₂ bubbles by a reaction between organic acid in the casting solution and salt in the coagulation bath. Meanwhile, a tremendous rise in anti-fouling property (from 89.7% to 94%), pure water flux (from 329.7 to 821.5 L/m² h) and permeation flux (from 265.8 to 546.3 L/m² h) indicates a significant improvement in the hydrophilicity and the permeability of prepared membranes. In addition, a significant improvement in thermal stability (by 90°C) was achieved owing to the formation of dative bonds between TiO₂ NPs and CA polymer. Therefore, this approach can significantly improve the anti-fouling property and the separation performance of the CA membrane.     

Morphology and Properties of Poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol)/Poly(L-lactic acid) Blend Membrane

A series of poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol) (PBLG-block-PEG)/poly(L-lactic acid) (PLLA) blend membranes were prepared by casting the polymer blend solution in chloroform. Surface morphologies of the PBLG-block-PEG/PLLA blend membranes were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PBLG-block-PEG/PLLA blend membranes were studied by thermogravimetric analysis (TGA), tensile tests, and contact angle testing. It was found that the introduction of PLLA could exert outstanding effects on the morphology and the properties of polypeptide copolymer membrane.     

Cellulose–poly(acrylamide–acrylic acid) interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures. II. Effect of ionic group contents and cellulose matrix modification

The separation properties in the dehydration of a water–ethanol mixture and the swelling behavior of interpenetrating polymer network (IPN) pervaporation membranes based on a cellulose or cellulose–hydroxyethyl cellulose (HEC) matrix and poly(acrylamide and/or acrylic acid) were investigated depending on the ionic acrylate groups content (γ) in synthetic polymer chains (0–100 mol %), the HEC content in the matrix (0–50 wt %), and the temperature (25–60°C). The separation factor (α), permeation rate (P), and separation index (αP) significantly improved with increasing γ values only for the separation of concentrated ethanol solutions (～86 wt %). For more dilute solutions of ethanol (～46 wt %), the P and αP values also increased but no considerable increase in α was observed. All types of membranes based on the cellulose matrix were characterized by a drastic decrease in the values of P at [EtOH] ≥90 wt % and, as a result, a decrease in the separation index (kg m^?2 h^?1) from ～2000 (for 86 wt % EtOH, 50°C) to ～240 (for 95 wt % EtOH, 50°C), which correlates with a decrease in the degree of membrane swelling. The modification of the cellulose matrix by introducing HEC into it makes it possible to increase considerably the membrane swelling in concentrated EtOH solutions and, hence, the αP value to ～760 (95 wt % EtOH, 50°C). All types of IPN membranes exhibit a marked increase in both α and P when the temperature increases from 25 to 60°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1452–1460, 2001     

Dehydration of water–alcohol mixtures by vapor permeation through PVA/clay nanocomposite membrane

An organic/inorganic hybrid nanocomposite membrane, poly(vinyl alcohol)/clay (PVAC), was prepared. The morphology of PVAC nanocomposite membranes were characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), and atomic force microscopy (AFM). The crystallinity and surface roughness increases with an increasing clay content in the PVAC nanocomposite membrane. Compared with the pure poly(vinyl alcohol) (PVA) membrane, the hybrid nanocomposite membrane (PVAC) shows an improvement in the thermal stability and the prevention of the water‐soluble property. The oxygen permeability and the water‐vapor permeation rate decreases with an increasing clay content (1–3 wt %) in the PVAC nanocomposite membranes. In addition, the effects of the clay content on the vapor‐permeation performance of an aqueous ethanol solution through the PVAC nanocomposite membranes was also investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3632–3638, 2003     

Transfer of gas to dissolved oxygen in water via porous and nonporous polymer membranes

The transfer rates of oxygen via polymer membranes in gas–membrane–gas and gas–membrane–water (dissolved oxygen) were investigated with various porous membranes and compared with results of silicone rubber sheet (nonporous, homogeneous polymer membrane). With a nonporous membrane, the permeability constant obtained by gas–membrane–gas represents the true membrane permeability in gas–membrane–water system, and consequently the transport resistance due to boundary layer can be quantitatively estimated. With a porous membrane, the data in gas–membrane–gas system (under applied pressure) merely represent the gas effusion rate of the membrane and are not directly related to the dissolved oxygen transfer rate in gas–membrane–water system. The penetration of liquid water into the pores of porous membrane is the most important controlling factor for the dissolved oxygen transfer rate of a porous membrane. With a porous membrane in which liquid water does not penetrate into the pore, the overall transfer rate of dissolved oxygen reaches the level which corresponds to that of the boundary layer found with silicone rubber membrane.