Yu. P. Yampolskii

High transport parameters and free volume of perfluorodioxole copolymers

Abstract Permeability (P) and diffusion (D) coefficients of perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene copolymers were determined with respect to different gases (He, H2, O2, N2, CO2, hydrocarbons C1C3). The copolymers with large content of perfluorodioxole comonomer exhibit high permeability with respect to lighter gases comparable to that of poly(trimethylsilyl propyne). However, the copolymers studied are much more permselective than the latter polymer. Free volume as estimated via Bondis method and free volume size distribution parameters which were determined by means of positron annihilation lifetimes (PAL) method are also unusually high if compared with other glassy polymers. A novel correlation of the P and D values, as well as of the solubility coefficients S with the PAL parameter t 4 I 4 are reported.

Effects of film thickness on density and gas permeation parameters of glassy polymers

Abstract Dense films of poly(vinyltrimethyl silane) (PVTMS) and poly(trimethylsilyl norbornene) (PTMSNB) having different thicknesses in the range l = 5–150 μm were cast from hydrocarbon solutions. It was shown that a density is inversely proportional to the film thickness. The following equation holds for the density ϱ: 1/ϱ = 1/ϱ0 − b/l. Permeability and diffusion coefficients were determined using the time lag method in respect to different gases. For all the gases, diffusion coefficients decrease when film thickness decreases and film density increases. A correlation of diffusion coefficients with fractional free volume were demonstrated. On the other hand, permeability coefficients are nearly independent of the thickness and density. Possible mechanisms of this behavior are discussed.

Gas and vapor permeation and sorption in poly (trimetylsilylpropyne)

Abstract Permeability coefficients were determined and sorption properties were studied for poly (1-trimethylsilyl-1-propyne) (PTMSP), the most permeable of the known (rubbery or glassy) polymers. The values measured for PTMSP are compared with those for poly (vinyltrimethylsilane) (PVTMS), another glassy polymer with similar structure, which has high permeability, although lower than that of PTMSP and high diffusion coefficients. It was shown that permeability coefficients differ by 1-3 orders in favor of the former, depending on the nature of the diffusant molecules. This is due to the increase in diffusivity and sorption parameters or solubility coefficients. One can conclude that non-equilibrium free volume in a polymer with bulky Si (CH 3 ) 3 substituents is larger when the backbone chain is stiff (PTMSP) than when it is more flexible (PVTMS).

Pervaporation of alcohols through highly permeable PIM-1 polymer films

Polycondensation material PIM-1 has attracted the attention of researchers owing to its high transport parameters in gas separation and a high free volume. The pervaporation characteristics of PIM-1 have been systematically studied. Lower aliphatic alcohols (CH3OH, C2H5OH, and n-C4H9OH) and water were selected as objects of research. The rates of mass transfer for individual components at various temperatures have been estimated, and for the ethanol-water binary mixture, the process of separation has been examined. The films based on the polymer under study exhibit the properties of organophilic membranes and are characterized by high permeability with respect to alcohols. The apparent activation energy of permeability is low. This behavior is common for pervaporation membranes based on glassy polymers with a high free volume. The parameters of separation for the water-alcohol mixture surpass corresponding values for typical organophilic membranes based on PDMS. These parameters are commensurable with the values observed for membranes based on poly(trimethylsilylpropyne). At the same time, PIM-1 does not demonstrate a rapid decrease in permeability in the course of time.

Gas permeation properties of phenylene oxide polymers

Abstract Gas permeability (Pi) and diffusion (Di) coefficients in respect to several gases (H2, O2, N2, CO, CO2, CH4) have been measured for poly(2,6-dimethylphenylene oxide) (PMPO), poly(2,6-diphenylphenylene oxide) (PPPO), and phenylene oxide copolymers containing methyl, phenyl, and allyl radicals as side groups. X-ray diffraction study shows that both homopolymers are semicrystalline materials, whereas all the copolymers are completely amorphous. The results show that a replacement of methyl by phenyl groups in PMPO/PPPO pair is accompanied by decrease in the P values. A transition from semicrystalline PMPO to amorphous copolymers results in a decrease in permeability and solubility coefficients and not in a growth of these parameters as can be expected on the basis of the behavior of other semicrystalline polymers (e.g. polyolefins). It is supposed that the crystallites of PMPO, and possibly of PPPO are packed loosely and, hence, take part in sorption and gas transport. This assumption is in agreement with numerous X-ray data as well as the results of positron annihilation study of these polymers.

Development of the methods for prediction of gas permeation parameters of glassy polymers: polyimides as alternating co-polymers

Abstract A novel approach is described for prediction of gas permeation parameters (permeability and diffusion coefficients) of amorphous polyimides. The method is based on a search for the group contributions characteristic for various dianhydrides and diamines used in different combinations in the preparation of particular homopolymers of the polyimide class. In other words, all the polyimides are regarded as alternating co-polymers that include dianhydride and diamine sub-units. The group contributions were deduced from a database including about 120 polyimides prepared from nine different dianhydrides and about 70 diamines. The group contributions found allow the prediction of the transport parameters for six gases (He, H 2 , O 2 , N 2 , CO 2 , and CH 4 ) in about 400–500 polyimides only 25% of which have been prepared and tested. An improved accuracy of the predictions was also achieved. This enabled the predictions not only of gas permeability, but also permselectivity of various polyimides for different gas pairs.

Correlations with and prediction of activation energies of gas permeation and diffusion in glassy polymers

Three types of novel correlations for activation energies of gas permeation EP and diffusion ED in amorphous glassy polymers are considered and their application for prediction of the EP and ED values for different gases are examined. The first one is based on application of the group contribution method. Combined consideration of the equation of free volume and Arrhenius equation results in the correlation of EP and ED with free volume Vf and fractional free volume (FFV). At last, the correlations between EP and the permeability coefficient at a certain reference temperature P(Tref), as well as ED versus D(Tref), are based on the fulfilment of the so-called compensation effect between activation energies and preexponential factors in activated processes. Examples of applicability of the correlations considered and recommendations for their use in prediction of the EP and ED values are given for transport of various gases in glassy polymers and separately in amorphous glassy polyimides.

Synthesis and gas permeation properties of new ROMP polymers from silyl substituted norbornadienes and norbornenes

Abstract Using ring opening metathesis polymerization (ROMP) the novel linear polynorbornadiene and polynorbornene (PNB) derivatives bearing silicon-containing moieties were prepared in the presence of RuCl 3 ·3H 2 O, RuCl 2 (PPh 3 ) 3 , and WCl 6 /tetramethyldisilacyclobutane catalysts with the yields up to 98%. Gas permeation properties (permeability and diffusion coefficients) of the polymers obtained were measured. It was shown that polynorbornadiene containing the Si(CH 3 ) 3 group has the transport parameters similar to those of poly(trimethylsilyl norbornene) studied earlier. On the other hand, PNB bearing two Si(CH 3 ) 3 groups in each repeat unit reveals much greater gas permeability induced mainly by increased solubility coefficients. The latter result is consistent with the much higher glass transition temperature of this polymer.

On pressure dependence of the parameters of the dual-mode sorption model

Sensitivity of the parameters of the dual-mode sorption (DMS) model on the pressure range, in which sorption of gases in polymers have been studied, was analyzed. Different “gas-polymer” systems were considered but the most detailed analysis was performed for sorption of argon and nitrogen in poly[5,5-difluoro-6,6-bis(trifluoromethyl)] norbornene and polysulfone. It was shown that the model parameters depend upon the range of gas pressure studied. Expanding of the pressure range (0-pi) results in an increase in the Langmuir adsorption capacity C′H and in reduction of Henrys law solubility coefficient kD and Langmuir affinity parameter b. These behaviors does not depend on a choice of an experimental apparatus or software and procedure of nonlinear least squares treatment of the data. As statistical analysis indicated, a systematic error of the measurement cannot call forth the observed dependencies of the model parameters. Different physical reasons of these behaviors were considered, among them: the pressure dependence of the affinity parameter, and the dilation of a polymer. The results obtained showed that although the DMS model, as a rule, gives an excellent fit of the experimental curves, and, hence, can be used as a form of compact storage of information on gas sorption in polymers, one should be careful in using it outside the pressure range in which its parameters have been determined.

Studies in gas permeability and membrane gas separation in the Soviet Union

Abstract Trends in the investigations of diffusion, sorption, and permeation of gases in polymers having been carried out in the USSR for the last 10–15 years are reviewed. Emphasis is placed on the mechanism of permeation in glassy, polymers nonuniform and heterophase polymeric systems. The role of the specific interactions between a diffusant molecule and the polymer is outlined. New polymers, materials for gas separating membranes, as well as diverse membranes are described. Different types of membrane modules and their practical use are reviewed.