Permeation and sorption in polynorbornenes with organosilicon substituents

Gas sorption properties, permeability coefficients, and diffusion coefficients of a series of norbornene polymers are presented. Introduction of the Si(CH₃)₃ group into the polynorbornene (PNB) backbone chain results in significant increases in glass transition temperature, permeability, and diffusion coefficient for a number of gases (H₂, O₂, N₂, CO₂, CH₄, C₂H₆). The transport properties and sorption isotherms for poly(5-trimethylsilyl norbornene) (PTMSNB) are very similar to those for poly(vinyltrimethyl silane) (PVTMS), which contains the same side-chain group but differs from PTMSNB by the structure of its main chain. For another silicon-containing polymer poly[5-(1,1,3,3-tetramethyl-1,3-disilabutyl) norbornene] (PDSNB) having a bulkier side-chain group, the glass-transition temperature is decreased in comparison with that of PNB, presumably owing to self-plasticization. Both silicon-containing norbornene polymers (PTMSNB and PDSNB) have permeability coefficients for “rapid” gases like H₂ or CO₂ of about 10² Barrer. The high values of the Langmuir sorption capacity C′_H for PTMSNB and PVTMS, as well as the high diffusivity and mobility of spin probes in these polymers, were attributed to a large free volume related to the bulky Si(CH₃)₃ groups attached directly to the main chain. © 1993 John Wiley & Sons, Inc.     

Model of sorption of simple molecules in polymers

A model of simple molecule sorption in polymers is proposed which embraces both the glassy and rubbery regions, and incorporates the successful dual-mode model below the glass-transition temperature. Hole filling is shown to be an important sorption mechanism both above and below T_g, although saturation effects do not occur in the rubbery polymer. The model interprets the “dual-mode” Langmuir and Henry's law parameters at the molecular level, and a simple statistical mechanical analysis allows estimation of the parameter values, as well as specifying certain interrelationships between the parameters. Applications of the model to gas solubility data in five polymers are considered [polyethylene (PE), poly(ethylene terephthalate) (PET), polystyrene (PS), polymethacrylate (PMA), poly(vinyl acetate) (PVAc)] and semiquantitative agreement is obtained for PE, PET, and to a lesser extent, PS. For PMA and PVAc, the agreement is qualitative only.     

Determination of Polycyclic Aromatic Hydrocarbons in Vegetables by Headspace SPME-GC

Inverse gas chromatography (IGC) at infinite dilution is a powerful technique to characterize the superficial and interfacial properties of solid substrates as oxides, polymers or polymers adsorbed on oxides. It can also be used to determine the physicochemical properties and the transition phenomena of polymers. In this paper, IGC was used to determine the changes, as a function of temperature, of the specific free enthalpy ??G _a ^SP and deduce the specific entropy ??S _a ^SP of poly (methyl methacrylate) (PMMA) adsorbed on alumina or on silica for different tacticities of PMMA. The study of the surface properties of PMMA/SiO₂ and PMMA/Al₂O₃, revealed an important difference in the physicochemical behaviour of oxides covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the specific entropy of PMMA adsorbed on oxides.     

Thermodynamic interactions of water-soluble homopolymers and double-hydrophilic diblock copolymer

Thermodynamic interaction parameters of water-soluble poly[2-(dimethylamino)ethyl methacrylate] (DMA) and poly[2-(N-morpholino)ethyl methacrylate] (MEMA) homopolymers and their diblock copolymer (DMA–MEMA) were investigated at the temperatures above their glass-transition temperatures (T_g) by inverse gas chromatography (IGC) method. Sorption thermodynamic parameters of some aliphatic, alicyclic and aromatic hydrocarbons, weight fraction activity coefficients, Flory–Huggins interaction parameters, and solubility parameters for hydrocarbons and polymers were calculated. It was observed that sorption thermodynamic parameters on (co)polymers depend on the molecular structures of hydrocarbons. Evaluating both the calculated values of the weight fraction activity coefficients and Flory–Huggins interaction parameters, the solving ability of the hydrocarbons for DMA, MEMA homopolymers, and DMA–MEMA diblock copolymer decreased in the following sequence: Aromatic > alicyclic > aliphatic hydrocarbons.     

The effect of plasticization on the transport of gases in and through glassy polymers

The effects of plasticization on the transport of gases and vapors in and through glassy polymers are examined from the viewpoint of the “dual-mode” sorption model with partial immobilization. The analysis assumes the existence of two penetrant populations with different mobilities in the Henry's law and Langmuir domains of the glassy polymers. These mobilities are characterized by their mutual diffusion coefficients D_D and D_H. The plasticization of the polymer by penetrant gases is reflected in the concentration dependence of D_D and D_H. Expressions for the effective (apparent) diffusion and permeability coefficients are derived assuming that D_D and D_H are exponential functions of the penetrant concentration in the polymers. The results of this study are compared with a similar analysis which assumed the existence of a single mobile penetrant population. The present analysis provides information on the effects of plasticization on the penetrant transport in the Henry's law and Langmuir domains separately. The effects of antiplasticization or clustering of penetrant molecules on the effective diffusion and permeability coefficients are also examined.     

CO2 sorption in poly(ethylene terephthalate) above and below the glass transition

High-pressure CO₂ sorption data in semicrystalline poly(ethylene terephthalate) (PET) are presented for temperatures ranging from 25 to 115°C. The results are described by Henry's law above the glass-transition temperature of PET, while a dual-mode sorption model comprised of a Henry's law and a Langmuir isotherm applies in the glassy state. The disappearance of the Langmuir capacity of the polymer above T_g presumably results from the elimination of regions of localized lower density which are frozen into the glass upon quenching from the rubbery state. Exposure of PET to a high CO₂ pressure produced a systematic variation in the apparent sorption equilibria. Correlation of the Langmuir capacity of PET with the dilatometric parameters of the polymer provides a useful framework for understanding the origin of the Langmuir sorption mode and for interpreting annealing and conditioning effects in glassy polymers.     

Thermodynamics of the sorption of organic vapors in a carbosilane dendrimer and a hyperbranched polymer

Fluorinated derivatives of the carbosilane G6 dendrimer and the hyperbranched polymer of the same chemical structure are synthesized and characterized via the method of inverse gas chromatography. For various organic compounds (n-alkanes, aromatic hydrocarbons, partially fluorinated and perfluorinated organic compounds), the following thermodynamic parameters of their interaction with the above polymers are defined: solubility coefficient S, the sorption enthalpy, the partial molar enthalpy of mixing, the Flory-Huggins parameter, and the solubility parameter. The thermodynamic behavior of vapors in the dendrimer is similar to that in the hyperbranched polymer. For a dendrimer and a hyperbranched polymer, a linear correlation between the logarithm of S and T _cr ² is established, where T _cr is the critical temperature of a probe. For both polymers, the partial enthalpy of mixing of n-alkanes is shown to be independent of the dimensions of the probe molecules. This behavior is typical of the vapor sorption in linear polymers at temperatures above the glass transition temperature.     

An application of an homogenization method to a model of diffusion in glassy polymers

The sorption of gases in polymers below their glass-transition temperature T_g is known in many cases to be described by the “dual sorption” theory, according to which the gas is held in accordance with both the Langmuir and Henry's laws. Based on this theory, expressions for the “effective diffusion coefficient” in the glassy polymers have been obtained by investigators in the past, notably by Paul and Koros.² The present analysis regards the glassy polymers as inhomogeneous with regions on which the gas sorption follows the Langmuir law. Assuming that the linear dimensions of these regions, which are often referred to as “microvoids” (although they are not space filled by vacuum), are small compared to the macroscopic length of interest but large compared to the mean free path of the penetrant gas molecules, we derive a rigorous relation between the average flux and the concentration gradient in the polymer and show that this relation can be expressed in terms of an “effective diffusion coefficient” D_eff which depends on the details of the microstructure, i.e., the size, shape and spatial distribution of the “microvoids.” This expression for D_eff is shown to reduce to that of Paul and Koros² in two situations: (1) when the “voids” consist of slabs running parallel to the concentration gradient, and (2) when the “voids” are spherical and the temperature of the polymer is not too different from T_g. The results of the present study lead to an alternative procedure for interpreting the experimental data on sorption and permeation which may have some advantages over the procedure currently employed. Finally, the analysis presented here is also applicable to polymers containing adsorptive fillers.     

Gravimetric study of high-pressure sorption of gases in polymers

A gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N₂ and CO₂ in low-density polyethylene (LDPE); CO₂ in polycarbonate (PC); and N₂, CH₄, C₂H₆, and CO₂ in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time-dependent hysteresis in the sorption of CO₂, C₂H₆, and CH₄ in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high-pressure CO₂ on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual-mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.     

Thermodynamic and kinetic investigations of uranium adsorption on soil

In order to understand the mobility of uranium it is very important to know about its sorption kinetics and the thermodynamics behind the sorption process on soil. In the present study the sorption kinetics of uranium was studied in soil and the influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficient of uranium on soil was measured by laboratory batch method. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin?CRadushkevich (D?CR) models. The sorption energy for uranium from the D?CR adsorption isotherm was calculated to be 7.07?kJ?mol^?1.The values of ??H and ??S were calculated to be 37.33?kJ?mol^?1 and 162?J?K^?1?mol^?1, respectively. ??G at 30?°C was estimated to be ?11.76?kJ?mol^?1. From sorption kinetics of uranium the reaction rate was calculated to be 1.6?×?10^?3?min^?1.     

Sorption and partial molar volume of gases in poly (dimethyl siloxane)

Sorption of N₂, O₂, Ar, CH₄, CO₂, C₂H₄, and C₂H₆ in poly (dimethyl siloxane) liquid and rubber and the dilation of the polymers due to sorption of the gases are studied at 25°C under pressures up to 50 atm. In the liquid, the sorption isotherms for low-solubility and high-solubility gases are described by Henry's law and the Flory–Huggins equation, respectively. Gas sorption in the rubber, which contains a 29 wt % silica filler, follows the dual-mode sorption model, though marked hysteresis is observed in the sorption of O₂ and CH₄. The dilation isotherms increase linearly or exponentially in both polymers with increasing pressure. Considering that gas molecules adsorbed into micropores of the filler particles do not participate in the dilation, partial molar volumes of the dissolved gases in the rubber are determined from data of sorption and dilation. The values are nearly equal to the partial molar volumes in the liquid (48–60 cm³/mol).     

反气相色谱法测定聚环己基丙烯酸甲酯的热力学性质（英文）

In this work,some thermodynamic properties of poly(cyclohexyl methacrylate)were studied by inverse gas chromatography(IGC).For this purpose,the polymeric substance was coated on Chromosorb W and which was filled into a glass column.The retention times(tr)of the probes were determined from the interactions of poly(cyclohexyl methacrylate)with n-pentane,n-hexane,n-heptane,n-octane,n-decane,methanol,ethanol,2-propanol,butanol,acetone,ethyl methyl ketone,benzene,toluene and o-xylene by IGC technique.Then,the specific volume(V0g)was determined for each probe molecule.By using(1/T;ln V0g)graphics,the glass transition temperature of poly(cyclohexyl methacrylate)was found to be 373 K.The adsorption heat under the glass transition temperature(ΔHa),and partial molar heat of sorption above the glass transition(ΔHS1),partial molar free energy of sorption(ΔGS1)and partial molar entropy of sorption(ΔSS1)belonging to sorption for every probe were calculated.The partial molar heat of mixing at infinite dilution(ΔH∞1),partial molar free energy of mixing at infinite dilution(ΔG∞1),Flory-Huggins interaction parameter(χ∞12)and weight fraction activity coefficient(a1/w1)∞values of polymer-solute systems were calculated at different column temperatures.The solubility parameters(δ2)of the polymer were obtained by IGC technique.     

Relation of gas-transport parameters of amorphous glassy polymers to their free volume: Positron annihilation study

Correlations of transport parameters (diffusion coefficients D and permeabilities P of gases) and thermodynamic parameters (solubility coefficients S and parameters C′ _H of sorption isotherms) with the sizes of free-volume elements, v _h, as estimated via positron annihilation lifetime spectroscopy are analyzed for the first time on the basis of the data array obtained for glassy polymers. Correlations of logD and logP with 1/v _h that agree with the free-volume model under the condition of a weak change in the concentration of free-volume elements in different polymers are ascertained. Certain deviations from linear correlations with 1/v _h for polymers with high free volumes are interpreted as evidence that the connectivity (openness) of pores increases with the sizes of free-volume elements. For solubility coefficients and Langmuir parameters of sorption capacity C′ _H , good linear correlations with the value of v _h are demonstrated.     

Gas permeation parameters and other physicochemical properties of a polymer of intrinsic microporosity: Polybenzodioxane PIM-1

A detailed study of gas permeation, thermodynamic properties and free volume was performed for a novel polymer of intrinsic microporosity (PIM-1). Gas permeability was measured using both gas chromatographic and barometric methods. Sorption of vapors was studied by means of inverse gas chromatography (IGC). In addition, positron annihilation lifetime spectroscopy (PALS) was employed for investigation of free volume in this polymer. An unusual property of PIM-1 is a very strong sensitivity of gas permeability and free volume to the film casting protocol. Contact with water in the process of film preparation resulted in relatively low gas permeability (P(O₂) = 120 Barrer), while soaking with methanol led to a strong increase in gas permeability (P(O₂) = 1600 Barrer) with virtually no evidence of fast aging (decrease in permeability) that is typical for highly permeable polymers. For various gas pairs (O₂/N₂, CO₂/CH₄, CO₂/N₂) the data points on the Robeson diagrams are located above the upper bound lines. Hence, a very attractive combination of permeability and selectivity is observed. IGC indicated that this polymer is distinguished by the largest solubility coefficients among all the polymers so far studied. Free volume of PIM-1 includes relatively large microcavities (R = 5 Å), and the results of the PALS and IGC methods are in reasonable agreement.     

Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn₂(L1)(L2)₂]_n (PCP-1) and [Zn₂(L1)(L3)₂]_n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C₂H₂/CO₂ and C₂H₆/C₂H₄, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C₂H₂, CO₂, C₂H₆, and C₂H₄ gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions.     

Formation energies of molecules and anions of europium bromides

The content of saturated vapors above europium dibromide and Eu-EuBr₂, Eu-Ba-BaBr₂, EuBr₂-LaBr₃ systems is investigated by means of high-temperature mass-spectrometry in the electron ionization and thermoionic emission regimes. On the basis of the measured equilibrium constants for reactions with participation of molecules and negative ions, the enthalpies of formation ??_fH₂₉₈° (kJ/mol) are determined using the method of the third law of thermodynamics: ?59 ± 13 (EuBr), ?349 ± 19 (EuBr₂), and ?861 ± 24 (EuBr ₃ ^? ).     

Characterization and gas permeation of polycarbonateliquid crystal composite membrane

Polymer/liquid crystal composite membranes were cast from a 1,2-dichloroethane solution of polycarbonate (PC) and N-(4-ethoxybenzylidene-4'-n- butylaniline) (EBBA). The mixing state of the polymer/liquid crystal composite membrane was investigated on the basis of differential scanning calorimetry, x-ray, density, sorption isotherm and sorption—desorption studies and also by electron microscopic observations. EBBA molecules in the composite membrane exist in an almost molecularly dispersed state up to an EBBA fraction of 30 wt%, and in the case of EBBA fractions above 30 wt% form a crystal domain as the mutual continuous phase among the network of polycarbonate fibrils. The composite membrane containing EBBA of 60 wt% can be handled as a homogeneous medium when considering gas permeation.The diffusive permeability coefficient to water reveals a distinct jump in the vicinity of the crystal—liquid crystal phase transition temperature of EBBA. The permeability coefficients, P, to hydrocarbon gases increases 100-200 times over several degrees in the phase transition temperature range. P for hydrocarbon gases decreases with increasing number of carbon atoms below the phase transition temperature, but increases with increasing number of carbon atoms above it. These results suggest that the permeation process is predominantly controlled by diffusion mechanism below the transition temperature of EBBA, while the solubility factor significantly affects gas permeation above it.     

Thermodynamic properties of resveratrol in dimethyl sulfoxide

In this article, the enthalpies of dissolution of resveratrol in dimethyl sulfoxide (DMSO) were measured using a RD496-2000 Calvet microcalorimeter at 298.15?K under atmospheric pressure. The differential enthalpy (??_dif H _m) and molar enthalpy (??_sol H _m) of dissolution of resveratrol in DMSO were determined, and the relationship between heat and the amount of solute was also established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation, half-life, ??_sol H _m, ??_sol S _m, ??_sol G _m, the relative partial molar enthalpy (??_sol H _m(partial)) and the relative apparent molar enthalpy (??_sol H _m(app)) of the dissolution process were obtained. The results showed that this study not only provided a simple method for the determination of the half-life for a drug, but also offered a theoretical reference for the clinical application of resveratrol.     

Effect of penetrant-induced isothermal glass transition on sorption,dilation, and diffusion behavior of polybenzylmethacrylate/CO2

The effect of a penetrant-induced isothermal glass transition on sorption, dilation, and diffusion behavior was studied in a single experimental run for CO₂ in cast polybenzylmethacrylate films. The dual-mode type sorption isotherms below the glass transition temperature of the polymer changed to linear ones above a certain concentration. Meanwhile, partial molar volume of CO₂ determined from the dilation of the films above the concentration gave a value very close to the one reported for rubbery polymers, and diffusion coefficients became less concentration-dependent. The results were conformable to the concept of unrelaxed volume in glassy polymers. © 1996 John Wiley & Sons, Inc.     

Chromium (III) removal by microporous ion exchanger Amberlite.120 (Na+): kinetic, equilibrium and thermodynamic studies

Cr (III) sorption on microporous strong cation exchanger Amberlite.120 (Na⁺) is studied as a function of time and temperature. The pH changes show the co-sorption of H⁺ ions along with the chromium. The rate constant values for Cr (III) sorption are calculated for both film and particle diffusion processes. However, the particle diffusion is found to be more dominant than the film diffusion. The temperature is found to have a positive effect on both the diffusional processes. The low values of energy of activation also confirm the diffusional nature of the process. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (??H, ??S and ??G) for Cr (III) exchange on the resin are calculated. The ??G values are found to be negative, while both the ??H and ??S values obtained are positive.