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%).     

Effect of molecular weight parameters on gas transport properties of poly(2,6-dimethyl-1,4-phenylene oxide)

The gas permeability of O₂ and N₂ for homogeneous and composite membranes prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) samples with different molecular weight parameters was investigated. Temperature dependencies of gas permeability coefficients and permselectivity were determined for homogeneous membranes. It was established that gas permeability coefficients of homogeneous membranes depend on molecular weight of the polymers used. The gas permeability of composite membranes with a PPO selective layer was investigated as a function of PPO intrinsic viscosity [η] and its casting solution concentration (c). It was shown that under the condition [η]·c = const it is possible to obtain composite membranes with the same transport properties by using polymers with different molecular weight parameters. © 1996 John Wiley & Sons, Inc.     

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.     

Gas sorption and transport in UV-irradiated poly(2,6-dimethyl-1,4-phenylene oxide) films

Gas sorption and transport properties at 35°C have been reported for a series of UV-irradiated films of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). UV irradiation induced crosslinking in all films. The gas permeability was reduced upon crosslinking while significant increases in gas permselectivity were observed. The addition of benzophenone to the PPO films did not result in marked improvements in crosslinking or the resulting gas transport properties of the film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:875–883, 1998     

Blends of head-to-head polystyrene with poly(2,6-dimethyl-1,4-phenylene oxide)

Blends of head-to-head polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) were prepared and found to be miscible as judged by a single T_g. The measurements were carried out by d.s.c. and dilatometry. At high concentrations of PPO (> 80%) the mixture is on the threshold of incompatibility as indicated by the increase of the width of the transition step increase by d.s.c. and the increase of the free volume as calculated from dilatometric data. The thermal stability studies of head-to-head polystyrene-(HH-PS)-poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends by thermal volatilization analysis show two decomposition processes in the temperature range characteristic for both homopolymers. The temperature of the maximum rate of decomposition for PPO in the blend is slightly shifted towards lower temperatures as compared with pure PPO. This can be explained by assuming that the PPO degradation is induced by radicals formed during the decomposition of HH-PS.     

Filled poly(2,6-dimethyl-1,4-phenylene oxide) dense membranes by silica and silane modified silica nanoparticles: characterization and application in pervaporation

The effects of silica and silane modified silica fillers on the pervaporation properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) dense membranes have been studied. Crystallinity, thermal and mechanical properties of unfilled and filled PPO membranes with silica and silane modified silica nanoparticles were investigated. The surface energy together with the solubility parameters of the membranes and the nanoparticles were determined. Pervaporation separation of methanol/methyl tert butyl ether (MTBE) mixtures over the entire range of concentration were carried out using both filled and unfilled membranes. The results are discussed in terms of the solubility and the diffusivity of each liquid component in the membranes. Flory-Huggins theory was used to predict the sorption methanol selectivity. Compared to the unfilled PPO membrane, the filled PPO membranes exhibit higher methanol selectivity and lower permeability. For methanol concentration in liquid feed mixture lower than 50 wt%, methanol selectivity of the filled PPO membranes with silane modified silica is better than that of the silica filled and unfilled PPO membranes.     

Thermo-optical analysis of poly(2,6-dimethyl-1,4-phenylene oxide)/triblock styrene–butadiene–styrene copolymer blends

Blending of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO resin) with a triblock butadiene–styrene–butadiene copolymer (Kraton 101) monotonically increases the softening temperature of the latter as measured by TOA. The TOA transition temperatures of the styrene/PPO resin phases closely approximate those of polystyrene/PPO resin blends having the same styrene/aromatic ether unit compositions. Uniform mixtures of the styrene blocks with the poly(2,6-dimethyl-1,4-phenylene oxide) molecules is inferred.     

Effect of sorption behavior on transport properties of gases in polymeric membranes

The purpose of this work was to study the relationships between the gas sorption and transport properties in polymeric membranes. The intrinsic gas transport properties: permeation, diffusion, and sorption in a series of dense membranes with various carbonyl group densities were investigated. The poly(methyl methacrylate) (PMMA), polycarbonate (PC), and cyclic olefin copolymer (COC) membranes have similar helium permeability, but the helium permeability of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membrane was very high. The variation of permeability for these four membranes consists with their fraction free volume. In this study, a direct relationship was found between the carbonyl group density and Langmuir affinity constant. Furthermore, dependence of the fractional free volume on the membrane Langmuir capacity constant was observed.     

Compatibilization of Poly(2,6-dimethyl-l,4-phenylene oxide) and Poly(2,6-dichloro-l,4-phenylene oxide) with Sulfonated Polystyrene and its Na and Zn-neutralized Ionomers

Compatibility of acidic (H), Na, and Zn neutralized sulfonated polystyrene ionomer blends with Poly(2,6-dimethyl- 1,4-phenylene oxide) (PPO) and Poly(2,6-dichloro- 1,4-phenylene oxide) (PDCIPO) was investigated by Dilute Solution Viscometry (DSV) and Differential Scanning Calorimetry (DSC). The intrinsic viscosities of the blends, are measured in suitable solvents. The degree of compatibility of the blends is characterized by Δb parameter. According to the results, PPO is completely miscible, except for Na-neutralized 1.7 mol% sulfonated polystyrene (Na1.7SPS) which is completely immiscible with PPO and PDClPO. PDClPO is completely miscible with Zn-neutralized sulfonated polystyrene (Zn4.8SPS) and partially miscible with acid sulfonated polystyrene (4.8SPS). Received: 12 August 2001/Revised version: 21 January 2002/Accepted: 11 March 2003 Correspondence to Leyla Aras     

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) multi-bonded carbon nanotube (CNT): Preparation and formation of PPO/CNT nanocomposites

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) multi-bonded carbon nanotube (CNT) (CNT-PPO) was prepared using brominated PPO under the condition of atom transfer radical polymerization. The structure and properties of CNT-PPO were characterized with FTIR, Raman spectroscopy and thermal analyzer. The PPO layer in a thickness of about 4.5 nm was observed covering on the side wall of CNT with a high-resolution TEM. The PPO modification warrants the good dispersion of CNTs in PPO in the formation of PPO/CNT nanocomposites, which demonstrated enhanced mechanical properties and increases in electrical conductivity. The developed approach of CNT modification with engineering plastics can be applied to other polymers and preparation of functional polymer/CNT nanocomposites.     

Ionic liquid modified poly(2,6-dimethyl-1,4-phenylene oxide) for CO2 separation

Ionic liquid modified poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was synthesized by introducing imidazolium-based, pyridinium-based, and ammonium-basd ionic liquid groups to the methyl position of PPO. Membranes were prepared from the different types of ionic liquid modified PPO (IPPO), and the permeability of CO₂ and N₂ in these membranes was characterized. For having the CO₂-philic ionic liquid groups in the structure, the CO₂ solubility of the IPPO is better than that of PPO, while the CO₂ diffusivity in the IPPO is proportional to glass transition temperatures. The adsorption and desorption of CO₂ in the IPPO were also investigated, and the results manifest that the adsorption and desorption of CO₂ in IPPO are completely reversible, which makes the polymer promising as solid adsorbent materials for CO₂ separation.     

Dual-phase polyphenylene oxide membranes with copolyimide branched modifiers

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes are attractive due to high permeability for gases; however, the selectivity of these membranes is insufficient. In this work, the gas selectivity was improved without significant loss of the permeability. For this purpose, PPO was modified via incorporation of the branched copolyimide filler–grafted copolyimide (PI-g-PMMA) with polymethyl methacrylate (PMMA) side chains. Two series of mixed self-supporting PPO/PI-g-PMMA films (with variation of the filler content) were prepared and studied as gas separation membranes. The length of the polymide (PI) chain and the density of PMMA grafting were the same in both series, however, in one series the grafted chains contained 50 MMA units, and in the other 150 units. The intermolecular interactions between the PPO matrix and the PI-g-PMMA fillers were investigated using viscometry, infrared (IR) spectroscopy, and scanning electron microscopy. The compatibility of the polymer components is limited; however, for both series, the contents of the respective filler are found, which ensures phase segregation only in a microscale. Therefore, the mechanical properties of the films allow their use as gas separation membranes. It is shown that the degree of the segregation as well as the mechanical and gas transport properties of the membranes depend on the length of the PMMA chains, and the membranes with filler-containing shorter branches (50 MMA units) show better selectivity.     

Blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with polystyrene-based thermoplastic rubbers: A comparative study

This work presents the first part of our study on the modification of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with styrenic thermoplastic rubbers. Polystyrene-b-polyisobutylene-b-polystyrene (SIBS), polystyrene-b-polybutadiene-b-polystyrene (SBS) and polystyrene-b-poly(ethylene/butylene)-b-polystyrene (SEBS) triblock copolymers were melt blended with PPO and the blends were characterized. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and transmission electron microscopic (TEM) studies revealed that PPO/SEBS blends displayed the most pronounced phase-separated morphology with largest rubbery domains. SBS showed the most miscibility, and the least detrimental effect on dynamic mechanical properties and tensile strength. The results of this comparative study guided us to develop optimum conditions for the impact modification of PPO by SIBS thermoplastic rubbers.     

Removal of hydrogen sulfide from methane using commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes

The performance of commercially available poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) and Cardotype polyimide (PI) hollow fiber membranes was investigated in removing hydrogen sulfide from methane in a series of bench-scale experiments. It was observed that in the concentration range of hydrogen sulfide in methane from 101 to 401 ppm, the methane permeability decreased in the presence of hydrogen sulfide for Cardo-type polyimide hollow fiber membranes, whereas the PPO membrane performance was not affected. The separation coefficients of hydrogen sulfide/methane were 6 and 4 for PI and PPO membranes, respectively. Effects of temperature on the performance of PI and PPO membranes were investigated. It was observed that the permeabilities of both components of the mixture increased by increasing temperature, whereas the selectivities remained constant.     

Thermally-stimulated depolarization current studies in chemically doped poly(2,6-dimethyl-1,4-phenylene oxide)

The electret properties of solution-grown poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) films doped with 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene, 2,4,7-trinitro-9-fluorenone and I₂ have been studied by measuring thermally-stimulated depolarization currents (TSDC) as a function of dopant concentration varying from 0.25 to 1.00 wt% for identical conditions of polarizing field, temperature and time. The depolarization behaviour of poled doped PPO film exhibits a dopant-concentration dependent single relaxation around 438 K maximum in the TSDC spectra. This is attributed to formation of charge-transfer complexes with the PPO chain by interstitially placed dopants. The existence of such a complex is confirmed by ultraviolet–visible and infrared absorption spectral measurements. The dopant-concentration dependent increase in the magnitude of the TSDC peak is attributed to the enhanced aligned dipole density. © 1999 Society of Chemical Industry.     

Chemical modification of poly(2,6-dimethyl- 1,4-phenylene oxide) by electrophitic substitution reaction with isocyanates

Summary The chemical modification of poly(2,6-dimethyl- 1,4-phenylene oxide) (PPO) has been carried out by incorporating amide groups on PPO backbone by electrophilic substitution reaction with isocyanates. The modified polymers obtained have been characterized by IR and ^IH-NMR spectroscopy, nitrogen analysis, solubility tests and X-ray diffraction studies.NCL Communication No. 4455     

Compositional determination of 2,6-dimethyl-1,4-phenylene oxide and styreen hompolymer blends by infrared spectrometry and pyrolysis gas chromatography

Compositional analysis of 2,6-dimethyl-1,4-phenylene oxide (PPO) and styrene homopolymer blends was accomplished using infrared spectrometry and pyrolysis gas chromatography. In infrared measurements the 1030/700 cm^?1 absorption ratio provides percent PPO in the blends within ±3% of the actual value but with a σ% of ±10. In pyrolysis GC measurements, four peaks resulting from the fragmentation of the PPO molecule have been investigated for quantitation. One of these peaks provides results with ±2% of the PPO present with a σ% of 7 when the percent PPO in the blend is above 20.     

Effect of chemical doping on the electrical conductivity of poly(2,6-dimethyl-1,4-phenylene oxide)

The electrical conductivity of solution-grown poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) films doped with TCNQ, TCNE, TNF, and I₂ has been studied as a function of dopant concentration, temperature (298–353 K), and field (50–2000 V). PPO forms a conductive complex on doping with these strong electron-acceptor organic molecules. As with PPO, two distinct ohmic and nonohmic conduction regions at low and higher fields, respectively, are observed. The conduction properties of doped PPo films result from the formation of an isotropic continuous charge-transfer complex. The existence of such a complex is confirmed by UV-visible absorption spectra measurements. A possible mechanism for the electrical conduction process is discussed. © 1994 John Wiley & Sons, Inc.     

Diffuse shear banded zones of blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide)

The formation, mechanical properties, thermal characteristics, and density of diffuse shear banded zones of polystyrene, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and their miscible blends were studied. A significant increase in density of 0.2 to 0.3 percent was found for the diffuse shear banded zones. Differential scanning calorimetry results revealed a volume recovery process that occurs below T_g for the diffuse shear banded zones. The post-yield-stress drop, anelastic shear strain within the zone, and anelastic tensile strain were all found to decrease with increasing PPO content in an identical manner. The sharp shear band to diffuse shear banded zone transition was related to chain mobility, molecular packing, and free energy as manifested in the post-yield-stress drop. The decrease in anelastic shear strain with increasing PPO content for the blends is possibly related to the beta transition and length between entanglements.     

Chitosan-Modified Poly(2,6-dimethyl-1,4-phenylene Oxide) for Anion-Exchange Membrane in Fuel Cell Technology

A series of cross-linking chitosan-modified quaternary ammonium poly(2,6-dimethyl-1,4-phenylene oxide)s membranes (CS-QAPPO) were prepared by the Menshutkin reaction. The mechanical property, dimensional stability, and alkaline stability of the CS-QAPPO membrane have been impressively improved by introducing CS into PPO backbone. Even the hydroxide conductivity of CS-QAPPO membranes is higher than that of the pristine QAPPO membrane. The 20% chitosan-modified QAPPO membrane shows the best performance, and the hydroxide conductivity is 32 mS cm^?1 at 90°C. The alkaline stability measurements demonstrated excellent chemical stability of the CS-QAPPO membrane in 2?M NaOH solution at room temperature after 2,000?h.