Preparation and Characterization of Iron Oxides – Polymer Composite Membranes

Composite membranes of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) or ethyl cellulose filled with magnetic nanoparticles, that is, ferroferric oxides (Fe₃O₄) were prepared. These membranes were examined for nitrogen and oxygen permeability. In the case of ethylcellulose membranes the gas flow was too high, since the macropore were formed. In further permeation measurements PPO membranes with 1 to 10 w/w% magnetic particles content were investigated. For the higher concentration of magnetite (more than 20%) in PPO polymer solution sedimentation phenomenon was observed. Mass transport coefficients (permeation and selectivity) were evaluated. Selectivity of the investigated membranes changed with the weight fraction of magnetic particles from oxygen (plain) towards nitrogen (2 and more w/w%).     

Magnetic Mixed Matrix Membranes Consisting of PPO Matrix and Magnetic Filler in Gas Separation

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and magnetic neodymium powder particles MQP-14-12 have been used for the preparation of magnetic mixed matrix membranes. Permeability diffusion and sorption coefficients of O₂, N₂, and synthetic air components were estimated for homogeneous and heterogeneous membranes using the Time Lag method based on dynamic experiments in a constant pressure system. The influence of magnetic field and magnetic powder particles on the gas transport properties of MMMs was studied. The results showed that the membrane permeation properties were improved with the magnetic neodymium particle filling. It was observed that the magnetic ethylcellulose and poly(2,6-dimethyl-1,4-phenylene oxide) membranes showed higher gas permeability, while their permselectivity and solubility were rather maintained or slightly increased. The results also showed that the magnetic powder addition enhanced gas diffusivity significantly in EC and PPO membranes.     

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997     

Effects of polymer molecular weight and chemical modification on the gas transport properties of poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) of different intrinsic viscosities has been studied to understand the effect of polymer molecular weight on the permeability and permeability ratio of CO₂/CH₄ and O₂/N₂ gas pairs. The increase in permeability of dense films prepared from higher molecular weight PPO was explained in terms of increased free volume. Gas permeability for the high molecular weight was further improved by attaching bulky bromine groups to the phenyl ring of the PPO backbone. Permeability ratio of PPO was greatly improved by attaching polar groups such as —COOH or —SO₃H. The loss in permeability because of the presence of the polar groups was compensated by using PPO that was brominated and sulfonated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1137–1143, 2000     

Concentration dependence on viscosity of oligourethane diols

To obtain viscosity suitable for application, relatively low molecular weight polymers, i.e., oligomers, are used in the formulation of high solids coatings. To support this requirement, the concentration dependence of the viscosity of synthesized oligourethane diols in different solvents was analyzed using Erickson's models. By regression analysis, it was found that the correlation coefficients are fairly good and the plots of the residuals are more random. The weight intrinsic viscosity, [η_o], composed of the oligomer component, O_5[η]o, and the oligomer-solvent interaction component, I_[η]o, was calculated from the intercept of the plot of 1/ln η_r vs. 1/o₀. The parameter I_[η]o, related to the solvent molar volume and the distance between the oligomer and solvent partial cohesion parameter coordinates, indicates the degree of interaction between the oligomer and solvent. The partial cohesion parameters of the oligomers obtained by the group-contribution method were used for calculating the interaction component of oligourethane diols. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1343–1351, 1997     

Polymere Dispergiermittel I. Molmasse und Dispergierwirkung der Melamin- und Naphthalin-Sulfonsäure-Formaldehyd-Polykondensate

The effect of the molecular weight of naphthalenesulfonicacid- and melamine-sulfonicacid-formaldehyde-polymers on their properties as dispersing agents has been studied. The investigated systems consisted of portlandcement and anhydrous CaSO₄ (anhydrite) suspensions in water. The dispersing properties have been evaluated using viscosimetric determinations of the slurries and calculating a typical “dispersing index”. It has been shown that the synthetized condensation polymers exhibit their best dispersing activity only in a rather narrow molecular weight region expressed as intrinsic viscosity (limiting viscosity number) from [η] = 0,02 dl/g up to [η] = 0,10 dl/g. Higher molecular weight values lead to a significant increase in the viscosity and because of this to the stiffening of the cement and anhydrite slurry. Basing on adsorption studies using these polymers on the cement- and anhydrite- surface and on the DLVO-interaction theory a possible explanation for the experimental findings will be discussed.     

Lösungseigenschaften von statistischen Copolymeren aus Methylmethacrylat und n-Butylacrylat

Viscosity measurements and light-scattering measurements have been carried out on chemically homogeneous random copolymers of methyl methacrylate (MMA) and n-butyl acrylate (BA). In the good solvent chloroform, the copolymers in the composition range 79,5 ≥ [MMA] ≥ 20,5 wt.-% show a uniform relation between the viscosity [η] and the molecular weight (M), which lies between that of PMMA and that of PBA: [η] = 4,2 × 10^?3 M^0,8 (cm³ · g^?1), T = 20°C. In the fair solvent acetone the [η]-M function for MMA/BA = 56/44 wt.- % is above those of PMMA and PBA. The values of the second osmotic virial coefficient A2 behave in the same way. Using equations given by STOCKMAYER-FIXMAN , BURCHARD and KURATA et al., the effects of the short-range and the long-range interactions on the composition dependence of [η] and A₂ were estimated from the molecular weight dependence of A2 and [η]. It was found that the short-range interactions correspond to the mean of the values for the two comonomers, while the long-range interactions are considerably greater than those of the corresponding homopolymers. The increase in the viscosity and in A₂ in the random copolymers can be explained as a result of intramolecular incompatibility.     

The mechanism of thermal degradation of certain polyether-polyurethans

This paper is an account of some studies of the mechanism of degradation of an uncrosslinked polyurethan prepared from poly(propylene oxide) (PPO) and 2,4-tolylene diisocyanate (TDI) at temperatures up to 320°C in a vacuum or inert atmosphere. Fractionation of polymers before and after degradation provides information about the mechanism of degradation since the molecular weight distributions obtained are dependent on the mode and sites of bond scission. A recent publication describes the column elution method of fractionation developed for undergraded and slightly degraded PPG-TDI. PPO-TDI gives essentially most probable molecular weight distributions at an initial intrinsic viscosity [η] of ～ 0.68 dl/g and also after degradation to [η] ～ 0.24 dl/g. This invariancy of the distribution strongly suggests a randon scission process. Other types of degradation, e.g., free-radical unzipping initiated at the chain ends, could also give invariant most probable distributions. However, such depolymerizations would be accompanied by much larger extents of volatilization than were observed for these polymers (<5% volatilization).     

Preparation of polymer–ceramic composite membranes with thin defect-free separating layers

Polymer—ceramic composite membranes with essentially defect-free separating layers have been prepared by a solution deposition technique. Rigid polymers were used for the selective organic layer. These included high molecular weight samples of 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofuran-dione, isopropylidenedianiline (6FDA-IPDA), 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofuran-dione, methylenedianiline (6FDA-MDA), tetramethylhexafluorobisphenol-A polycarbonate (TMHFPC), and tetramethylhexafluoropolysulfone (TMHFPSF). Attempts to prepare composite membranes from lower molecular weight samples of bisphenol-A polycarbonate (PC) and tetrabromohexafluorobisphenol-A polycarbonate (TBHFPC) were unsuccessful. The PC and TBHFPC composites exhibited a decrease in the measured gas flux after polymer deposition; however, the selectivities of the composites were considerably less than that of a dense film of the same materials. A microporous ceramic membrane prepared by Anotec Separations was used as the support layer. This ceramic membrane provided minimal resistance to gas flow. The selective composite membranes were found to have high gas fluxes and gas separating abilities essentially equivalent to that of a dense isotropic film. The estimated, effective skin layer thicknesses for these membranes are on the order of 1500 Å to 1.0 μm. The formation of these composites is believed to occur through a sieving process in which large swollen polymer chains are sieved out of solution by the ceramic support. Polymer solutions that had swollen coil diameters that were smaller than that of the ceramic membrane did not produce selective composite membranes, while those solutions with swollen coil diameter that were larger than that of the ceramic membrane produced defect-free polymer layers. © 1992 John Wiley & Sons, Inc.     

Formation and analysis of a polyimide layer in composite membranes

Composite membranes containing a thin‐film layer of aromatic polyimides (PI) ensure an advantageous combination of selectivity and permeability in gas separation. A series of rigid‐chain PI with different chemical structures were studied as a thin active layer. Composite membranes were prepared by coating a solution of poly(amic acid) (PAA) and an imidization catalyst on a poly(phenylene oxide) (PPO) support with pores filled by decane. The subsequent stage of solid‐state catalytic transformation of the PAA/PPO membrane into the PI/PPO membrane determines the specific structure of the PI layer and the transport properties of the PI/PPO composite membranes. The structure of composite membranes was determined by scanning electron microscopy and analyzed in the terms of the resistance model of gas transport in composite membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1026–1032, 2000     

Preparation of polyethyleneglycol (PEG) and cellulose acetate (CA) blend membranes and their gas permeabilities

Miscible blend membranes containing 10 wt % PEG of low molecular weight 200, 600, 2000, and 6000, and 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, and 60 wt % of molecular weight 20,000 were prepared to investigate the effect of PEG on gas permeabilities and selectivities for CO₂ over N₂ and CH₄. The permeabilities of CO₂, H₂, O₂, CH₄, and N₂ were measured at temperatures from 30 to 80°C and pressures from 20 cmHg to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane, which contained 10% PEG 20,000, exhibited higher permeability for CO₂ and higher permselectivity for CO₂ over N₂ and CH₄ than those of the membranes that contained 10% PEG of the molecular weight ranging from 200 to 6000. The high PEG 20,000 content blend membranes showed remarkable permeation properties such that the permeability coefficients of CO₂ and the ideal separation factors for CO₂ over N₂ reached above 200 barrer and 22, respectively, at 70°C and 20 cmHg. Based on the data of gas permeability coefficients, time lags, and characterization of the membranes, it is proposed that the apparent solubility coefficients of all CA and PEG blend membranes for CO₂ were lower than those of the CA membrane. However, almost all of the blend membranes containing PEG 20,000 showed higher apparent diffusivity coefficients for CO₂, resulting in higher permeability coefficients of CO₂ than those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG 20,000 blend membranes that their ideal separation factors for CO₂ over N₂ were higher than those of the CA membrane in the temperature range from 50 to 80°C, even though the ideal separation factors of all CA and PEG blend membranes for CO₂ over CH₄ became lower than those of the CA membrane over nearly the full temperature range from 30 to 80°C. © 1995 John Wiley & Sons, Inc.     

Determination of solution viscosity characteristics of rubber seed oil based alkyds resins

Three medium oil alkyd samples of different oil length [(I) 45%, (II) 50%, and (III) 55%] were synthesized with rubber seed oil. Dilute solution viscosity measurements were carried out on the alkyd in acetone and in toluene. The parameters investigated include intrinsic viscosity [η], Huggins constant (k_H), and Mark‐Houwink Sakurada constants (κ and α). The [η] values for the alkyd samples were found to be larger in acetone than in toluene. The K_H values showed a regular order in acetone but not in toluene. The K_H values showed no regular order in their variation with the oil content of the alkyd samples and the solvent, but the values obtained are higher in acetone than in toluene. Correlation of molecular weight (M) with [η] was also examined. [η] was observed to increase with the increase in the molecular weight of the resins. The α values obtained are in reasonable agreement with the reported ranges of α values in good solvent. The characteristics examined suggest that acetone is a better solvent for rubber seed oil alkyd resin than toluene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3073–3075, 2006     

Number‐average molecular weight of branched polymers from SEC with viscosity detection and universal calibration

BACKGROUND: Number‐average molecular weight, M?_n, is an important characteristic of synthetic polymers. One of the very few promising methods for its determination is size‐exclusion chromatography (SEC) using on‐line viscometric detection and assuming the validity of the universal calibration concept. RESULTS: We have examined the applicability of this approach to the characterization of statistically branched polymers using 22 copolymers of styrene and divinylbenzene as well as 3 homopolymers of divinylbenzene with various degrees of branching. SEC with three on‐line detectors, i.e. concentration, light scattering and viscosity, enables us to evaluate experimental data by various computational procedures yielding M?_n and weight‐average molecular weight, M?_w. Analysis of the results has shown that the universal calibration theorem has limited validity, apparently due to the dependence of the Flory viscosity function on the molecular shape, the molecular weight distribution and the expansion of molecules. CONCLUSION: For complex polymers, the universal calibration, i.e. the dependence of the product of intrinsic viscosity and molecular weight, [η]M, on elution volume, can differ in values of [η]M from those obtained for narrow molecular weight standards by 10–15%. The method studied is helpful for the determination of M?_n of polymers, in particular of those with very broad molecular weight distribution, such as statistically highly branched polymers. Copyright © 2008 Society of Chemical Industry     

Effects of molecular structure on the permeability and permselectivity of aromatic polyimides

Permeability coefficients of H₂, O₂, and N₂ were measured under 10 atm at the temperature from ambient temperature up to 150°C in a series of structurally different aromatic homo-and copolyimides, which were prepared from 4,4′-oxydianiline (ODA) or 4,4′-methylene dianiline (MDA) with various aromatic dianhydrides. The study shows that the molecular structure of the polyimides strongly influences gas permeability and permselectivity. As a result, the permeability coefficients of the polyimide membranes for each gas vary by over two orders of magnitude. In general, among the polyimide membranes studied, the increase in permeability of polymers is accompanied by the decrease in permselectivity, and the MDA-based polyimide membranes have higher permeability than ODA-based ones. Among the polyimides prepared from bridged dianhydrides, the permeability coefficients to H₂, O₂, and N₂ are progressively increased in the order BPDA <BTDA <ODPA ∼ TDPA <DSDA <SiDA <6FDA, while H₂/N₂ and O₂/N₂ permselectivity coefficients are progressively decreased in the same order. The copolyimide membranes, which were prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA), and ODA, have favorable gas separation properties and are useful for H₂/N₂ separation applications. © 1996 John Wiley & Sons, Inc.     

Carbon molecular sieve membranes derived from trimethylsilyl substituted poly(phenylene oxide) for gas separation

Carbon molecular sieve membranes for gas separation prepared using poly(phenylene oxide) (PPO) as precursor have been examined. The PPO precursor was modified by introducing a trimethylsilyl (TMS) substituent and its effect on the gas transport property of the resulting carbon membrane was examined. TMS-substituted PPO (TMSPPO) was prepared in a high yield by a simple one-step reaction, and its carbon membrane was successfully fabricated. The modification improved the gas permeability of the resulting membrane which also exhibited excellent O₂/N₂ and CO₂/CH₄ separation performance comparable to those of polyimide-derived carbon membranes. From the analysis of the microstructure of the TMSPPO carbon membranes, it is believed that the TMS groups improve gas diffusivity by increasing the micropore volume.     

Development and characterization of homopolymers and copolymers from the family of polyphenylene oxides

Poly(2,6‐dimethyl‐1,4‐phenylene oxide), PDMPO, poly(2,6‐diphenyl‐1,4‐phenylene oxide), PDPPO, as well as their copolymers of different compositions, having both random and block structures, have been synthesized and characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and gel permeation chromatography. Solution‐cast films were prepared from all synthesized polymers using chloroform as a solvent. The thermal properties of the resulting films were characterized by differential thermal analysis and differential scanning calorimetry, whereas their morphology was investigated using X‐ray diffraction. Ultimately, the potential of the synthesized polymers for gas separation was studied by examining gas permeation properties of the respective thin films in single gas permeation tests involving N₂, O₂, CH₄, and CO₂. In general, the O₂ and CO₂ permeability coefficients decrease with the PDPPO content. However, the largest drop in the permeability coefficients occurs between PDMPO and a copolymer having the lowest PDPPO content, and the permeability coefficients PDPPO are comparable or even lower than the permeability coefficients of the copolymers having the largest PDDPO content. On the basis of combination of the permeability coefficients and their ratios for CO₂/CH₄ and O₂/N₂, random copolymers appear to be a better candidate for gas separation membranes than their block counterparts. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Significance of the intrinsic viscosity ratio of unsubstituted and nitrated cellulose in different solvents

It has been studied the intrinsic viscosity ratios of cellulose solutions in different solvents and of the corresponding nitrates dissolved in aceton using cellulose samples from different origins and with different degrees of polymerization. The results demonstrate that with FeTNa and CdEn as solvents, molecular dispersed solutions are only produced with cellulose having a DP≤3000. FeTNa is limited to cotton cellulose only. Contrary to this, the intrinsic viscosity ratio [η]/[η] shows independence from the range of degree of polymerization and the origin of cellulose, confirming thus once more the polymeranalogous course of nitration. Its value referred to a degree of substitution S = 2.90±0.02, to absolute dry and pure cellulose and to standardized viscosity measurements amounts [η]_Ac/[η]_CuEn = 1.95±0.05. Determination of the intrinsic viscosity ratio permits, therefore, to obtain information in respect of the polymeranalogous and homogeneous character of the cellulose nitrate, and, in connection with determinations of yield of nitration, in respect of the purity of the corresponding unsubstituted cellulose. Basing on the constant value of the intrinsic viscosity ratio [η]_Ac/[η]_CuEn, and using the quotients [η]_FeTNa/[η]_CuEn and [η]_CdEn/[η]_CuEn, there has been derived the [η]-DP-relationships for unsubstituted cellulose in the respective solvents.     

Gas permeation and positron annihilation lifetime spectroscopy of poly(ether imide)s with varying ether

A series of poly(ether imide)s are investigated using positron annihilation lifetime spectra [PALS] and gas permeation measurements. The glass transition temperature T_g, determined by differential scanning calorimetry, does not correlate with the void sizes calculated from density or determined by PALS, implying that in these materials polymer?polymer chain interactions and not free volume has a dominant role in determining the overall chain dynamics. Significant differences observed in the permeability process with respect to carbon dioxide and nitrogen, highlight the role of polar interactions between the diffusing gas molecule and the polymer matrix on the transport processes. Diffusion coefficients do not change in a simple manner with void size. The solubility parameters vary across the series of materials and produce a small variation in the solubility coefficients for nitrogen and argon, but significantly differences were observed for carbon dioxide, reflecting the influence of polar interactions plasticizing the matrix. This study indicates that whilst the void structure is important in influencing gas transport, chain–chain interactions are controlling many of the higher temperature physical properties of these polymers. High values of selectivity between carbon dioxide and nitrogen were observed indicating that these materials have potential applications as gas separation membranes. POLYM. ENG. SCI., 56:427–434, 2016. © 2016 Society of Plastics Engineers     

Reaktive membrancopolymere auf acrylbasis

The copolymerization of acrylonitrile with maleic anhydride was investigated to synthesize acylic reactive polymers for manufacture of membranes that serve as support for covalent enzyme immobilization. The free-radical copolymer synthesis was carried out in solution (N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), γ-butyrolactone, ethylene carbonate), by precipitation polymerization (dioxane) as well as bulk polymerization. The polymers were characterized using IR spectroscopy, elementary analysis, NMR spectroscopy, gel permeation chromatography, viscosity measurements, osmometry and potentiometry. The kinetic parameters were followed by dilatometric measurements up to high conversions. The anhydride content in the monomer mixtures showed a significant influence on the rate of polymerization and the molecular weight. With raised concentration of anhydride the polymerization rate and molecular weights decreased. Film forming polymers (M̄_η > 30 000 g/mol) can be obtained by all copolymerization procedures with exception of solution polymerization in DMF and DMAC, respectively. The content of maleic anhydride in the membrane polymers did not exceed 5 mol-%, even though the maleic anhydride content in the monomer mixtures was raised up to the equimolar mixture. Nevertheless, such low maleic anhydride content of prepared membranes is enough for successful enzyme immobilization with amyloglucosidase (copolymer was prepared in γ-butyrolactone, M̄_η = 49 000 g/mol, c = 0,3 mol-%).     

Membranes based on poly(styrene-N-phenylmaleimide)/poly(2,6-dimethyl-1,4-phenylene oxide) blends

Blend membranes were prepared by casting chloroform solutions of mixtures of styrene-N-phenylmaleimide copolymer containing ca. 10 mol % imide units with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and their phase behavior was evaluated. At a content of 20% PPO, the membranes were homogeneous; those having 40 or more % PPO exhibited phase separation. Membranes made of the parent polymers and their blends were tested in the pervaporation of aqueous ethanol solutions; permeabilities to oxygen, nitrogen, and carbon dioxide were also determined. The pervaporation characteristics and gas transport properties are discussed considering the interactions of polymer chains and the phase structure of the membranes. © 1995 John Wiley & Sons, Inc.