Miscible blends of polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were prepared by a solution casting method to examine the permeation characteristics for oxygen and nitrogen. Gas permeation characteristics of PS/PPO membranes prepared using two different methods, slowly cooled and quenched, after being treated at various annealing temperatures were examined with respect to the controlled free volume. A variety of compositions of PS/PPO membranes provided varying permeability coefficients and ideal separation factors. This indicates that the present miscible blends gave rise to a decrease in the free volume by the physical interaction between two polymer components. For the slowly cooled PS/PPO membranes, the permeability coefficient decreased but the ideal separation factor increased with decreasing annealing temperatures due to the fast macromolecular relaxation or the efficient packing effect of macromolecular chains. On the other hand, the permeability coefficient of the quenched PS/PPO membranes increased with increasing annealing temperatures, as the quenching from higher annealing temperatures led to the existence of more free volume. 相似文献
A high degree of nitration of polyphenylene oxide (PPO) was successfully achieved by carefully optimizing synthetic protocol. The reduction of nitro group to amino could be done quantitatively. The physical properties of formed polymers were investigated and correlated with gas sorption and permeation properties. The formed polymers were amorphous in nature as revealed by wide angle X-ray diffraction spectra. An increase in the packing density in comparison to unsubstituted PPO as a result of induced polarity was indicated by lowering of fractional free volume and d-spacing. The substitution by either nitro or amino group increased the chain stiffness as revealed by the dynamic mechanical analysis. Though both, nitro and amino group substitution on PPO led to a decrease in pure gas permeability, the selectivity of various gas pairs was increased by these substitutions. The gas sorption analysis revealed that both, solubility selectivity and diffusivity selectivity were increased by these polar group substitutions. The nitro group substitution was more effective in improving solubility selectivity, while amino group substitution was more effective in improving diffusivity selectivity. 相似文献
An environmentally friendly one-pot synthetic method based on green chemistry was developed to prepare thermodynamically partially compatible poly(2,6-dimethyl-1,4-phenylene oxide)/poly(methylmethacrylate) (PPO/PMMA) alloy in water. The oxidative polymerization of 2,6-dimethylphenol in alkaline aqueous solution was firstly conducted and then methyl methacrylate (MMA) was added into the reactor before the end of polymerization. MMA could penetrate into PPO particles and then in situ reverse atom transfer radical polymerization (RATRP) of methyl methacrylate was initiated by 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride after the oxidative polymerization. Both the oxidative polymerization of 2,6-dimethylphenol and RATRP of methyl methacrylate were catalyzed by the complex of CuCl2 and 4-dimethylaminopyridine. Finally, thermodynamically partially compatible PPO/PMMA alloy was successfully prepared which possessed a multi-layer core-shell structure with two polymers embedded in each other. 相似文献
A method of determining the quantity of ungrafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO®
1 Trademark of General Electric Company.
resin) in mixtures of such polyphenylene oxide or PPO resin, polystyrene (PS), and graft copolymers of PPO resin and PS is described. The technique is a combination of physical and chemical separations and gel permeation chromatographic (GPC) analysis. The extent of grafting on PPO resin and the quantity of ungrafted PPO resin were calculated from molecular weight data and compositional analysis. 相似文献
A new hybrid gas separation membrane was prepared from poly(2,6-dimethyl-1,4-phenylene oxide) modified with graft copolyimide with side poly(methyl methacrylate) chains. The changes in the membrane structure on introducing up to 15 wt % modifier were evaluated by atomic force microscopy and density measurements. The microphase separation in modified polyphenylene oxide films was demonstrated. Introduction of graft copolyimide leads to an increase in the density of the hybrid films. The gas transport properties of the membranes were evaluated for H2, CO2, O2, O4, and N2. Introduction of up to 10 wt % modifier does not noticeably alter the permeability of the hybrid membranes to all the gases but increases the selectivity in gas separation.
Benzoylation of polyphenylene oxide (PPO) was carried out with aromatic acid chlorides bearing specific groups at para-position (H, methyl, Br, Cl and nitro), which differ in their polarity and bulk. The reaction conditions were optimized individually to get the high degree of substitution. These materials were characterized for thermal as well as other physical properties that are known to affect the gas permeation. In a series investigated, the nitrobenzoyl substitution on PPO resulted in the highest increase in glass transition temperature and the lowest thermal stability. An estimation of the packing density parameters—fractional free volume by density measurement and the d-spacing by X-ray diffraction analysis showed an increase in the packing density. The gas permeability was found to decrease in all the cases of benzoylation. The helium and oxygen based selectivities were increased, while CO2 based selectivities were decreased. The unusual trend observed in the gas permeation properties is explained on the basis of nature of substituent and the degree of substitution. 相似文献
Summary: In this work, we report superior mass transport properties of polymers prepared by the covalent coupling of supermolecular carbon cages (e.g., fullerenes, bucky balls) to a poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) polymer. Dispersing the bucky balls into the polymer reduces gas permeability, whereas covalent bonding enhances permeability up to 80% in comparison to the pure PPO. Gas pair selectivity, however, is not compromised and stays constant.
Schematic representation of the PPO polymer membrane and the PPO‐covalently bonded C60 polymer membrane. 相似文献
The unperturbed chain dimensions of unfractionated poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly-(2,6-diphenyl-1,4-phenylene oxide) have been measured by combining molecular weight data from light scattering with intrinsic viscosity data in chloroform. The unperturbed chain dimensions of the former polymer were also measured directly by light scattering dissymmetry in a critical consolute solvent mixture (methyl cyclohexane: 1,4-dioxane 50:50 by volume). The results of these measurements and of measurements reported by other investigators are satisfactorily explained by postulating no dimension-expanding prejudice in azimuthal angle in chain conformers of the 2,6-substituted-1,4-phenylene oxide polymers. This corresponds to equal population of the two chain rotation energy minima at azimuthal angles 90° and 270°. Accepting this postulate, one calculates from the observed chain dimensions that the C? O? C bond angle is 118–120° in these aromatic polyethers in solution. 相似文献
PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) is a well-known membrane material showing good gas separation properties. The incorporation of nanoparticles can enhance or deteriorate the performance of composite membranes, sometimes depending only on the way of the composite preparation. We have modified the PPO polymer with C60 fullerenes up to a content of 2 wt %. Previous investigations showed a strong dependence of permeability on whether the C60 is simply dispersed in the polymer or chemically bonded to the polymer chains. Free volume effects were suggested as an explanation but not experimentally confirmed. Here, we present free volume studies by positron annihilation lifetime spectroscopy. An additional long positron lifetime shows the increased free volume of composite samples, while the high electron affinity of C60 helps to indicate the homogeneity of the samples. Combining the presented results with permeability measurements refines the understanding of this promising membrane material. 相似文献
Low-temperature internal motions of the following polyesters have been investigated by broad line nuclear magnetic resonance: poly(methylene terephthalates) (2–6 methylene groups), poly[1,4-(dimethylene)cyclohexylene terephthalate], poly(diethyleneglycol terephthalate), poly(1,2-propylene terephthalate), poly(1,4-phenylene terephthalate), poly(2,2,3,3,4,4-hexafluoropentamethylene terephthalate), poly[1,4-phenylenebis(dimethyl) siloxane], and poly(2,6-dimethylphenylene oxide). No complex line structure was found for any of the samples. Molecular motions in the polyesters appear to be restricted by polar forces arising from the ester groups. Above—196°C. the line width decreases smoothly with increasing temperatures for all polymers except poly[1,4-(dimethylene)cyclohexylene terephthalate] and poly[1,4-phenylenebis(dimethyl)siloxane]. These two show a definite transition in line width at ?20°C. and +12°C., respectively, caused by the onset of considerable internal motion. At ?196°C. the lattices are rigid except for polymers containing methyl groups: poly(1,2-propylene terephthalate), poly[1,4-phenylenebis(dimethyl) siloxane], and poly(2,6-dimethylphenylene oxide). Internal motion that can be ascribed to be a reorientation of the methyl groups is present at ?196°C. for these three polymers, as is demonstrated by comparison of experimental second moments and those calculated on the basis of various models. 相似文献
By fluorescence spectroscopy it is possible to investigate some of the photophysical processes, particularly the energy transfer, that occur during the photo-oxidative degradation of polystyrene (PS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and homogeneous blends of these. In connection with the irradiation, a part of the absorbed energy is transferred from excited phenyl groups in PS to PPO. The decrease in PS excimer fluorescence at 319 nm by admixture of PPO is greater than expected from the absorption of PPO at the excitation wavelength. A radiative energy transfer is suggested from PS to PPO which absorbs at 319 nm. Energy transfer also occurs to groups formed during photo-oxidation. The quenching of PS excimer fluorescence during the process has been studied for both the homopolymer and the blends, and in all cases the reactions occurring during photo-oxidation result in marked quenching at 319 nm. 相似文献
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. 相似文献