L. E. Starannikova

Highly permeable polymer materials based on silicon-substituted norbornenes

An approach to the manufacture of highly permeable polymers based on the synthesis and polymerization of norbornenes, norbornadienes, and tricyclononenes with different numbers and different positions of silicon-containing substituents has been developed. It has been found that these monomers are readily involved in metathesis polymerization yielding high-molecular-mass polymers possessing good filmforming properties. The addition (vinyl) polymerization of norbornenes is a more complex process; however, the product silylated polynorbornenes exhibit a higher gas permeability than the corresponding metathesis polynorbornenes. By the level of the gas-transport parameters, the silylated addition polynorbornenes obtained in the study are grouped with the most advanced high-permeability polymers. It has been shown that the presence of Me3Si substituent groups, their amount, and the main-chain structure are responsible for the enhancement of the gas permeability of polynorbornenes. Thus, a series of polymers with a regularly changing structure has been obtained, a result that makes it possible to reveal the polymer structure-property relations.

Hybrid gas separation polymeric membranes containing nanoparticles

Hybrid composite membrane materials and membranes on their basis containing various nanoparticles dispersed in polymer matrices attract significant attention of researchers. Different types of these materials in relation to their use for membrane gas separation are surveyed. The behavior of different types of additives is considered: nonporous oxides such as SiO2 and TiO2, metal-organic frameworks, and carbon nanotubes. It is shown that introduction of nanoparticles in many cases results in simultaneous enhancement of permeability and gas separation selectivity. The results obtained with hollow fiber membranes of this type are discussed. Problems arising during operation with this type of materials and possible ways of resolving them are considered.

Synthesis and gas separation properties of metathesis polynorbornenes with different positions of one or two SiMe3 groups in a monomer unit

The metathesis polymerization of 5,5-bis(trimethylsilyl)norbornene, 2,3-bis(trimethylsilyl)norbornadiene, and exo,endo-3,4-bis(trimethylsilyl)tricyclo[4.2.1.02,5]non-7-ene with the catalysts WCl6/1,1,3,3-tetramethyl-1,3-disilacyclobutane, RuCl3/EtOH, and the Grubbs Ru-carbene complex Cl2(PCy3)2Ru=CHPh has been studied. New polymers with yields of up to 98% and M w = (2−39) × 105 are prepared. New metathesis copolymers of 5-trimethylsilylnorbonene with 5-(hydroxymethyl)norbornene and 5-(trimethylsiloxymethyl)norbornene are synthesized in the presence of the Cl2(PCy3)2Ru=CHPh catalyst with yields of 78 and 98%. The gas-permeability study of the above series of the metathesis polymers containing one or two Me3Si substituents in each monomer unit shows that the introduction of the second SiMe3 group markedly improves their transport characteristics. A change in the character of the backbone (polynorbornadiene, polytricyclononene) has a small effect on the permeability of the polymers. The metathesis polynorbornene with two vicinal SiMe3 groups exhibits higher gas-permeability coefficients than its isomer with germinal substituents. The homopolymer of 5-trimethylsilylnorbornene is characterized by better transport parameters than its copolymers with -OSiMe3 and -OH substituents.

Synthesis and gas-separation properties of metathesis poly(3-fluoro-3-pentafluoroethyl-4,4-bis(trifluoromethyl)tricyclonene-7)

Metathesis polymerization of 3-fluoro-3-pentafluoroethyl-4,4-bis(trifluoromethyl)tricyclononene-7 (F-PTCN) and the properties of the resulting polymer, particularly gas permeability, have been studied. It has been found that F-PTCN exhibits high thermal stability. The gas separation parameters of the material (P(O2) = 60 Barrer, P(CO2) = 240 Barrer) are close to those of fluorinated polynorbornenes studied previously. The newly synthesized fluorinated metathesis polytricyclononene has a lower gas permeability than metathesis polytricyclononene bearing two Me3Si groups in the monomer unit, but it is significantly superior to the latter in gas separation selectivity for some gas pairs.

Membrane separation of gaseous C1-C4 alkanes

The separation of various gaseous hydrocarbons with the aid of polymer membranes is considered; attention is focused on the separation of gaseous C1–C4 alkanes, which are the components of natural gas and associated petroleum gases. It is noted that a practically important property of membrane materials is the thermodynamic selectivity of a membrane, which makes it possible to enrich a permeate with heavier alkanes. Up to this point, polyacetylenes exhibited the best transport parameters for the solution of this problem. The second experimental section of this paper describes a study of the separation of CH4 + C4H10 binary mixtures on films based on additive poly[3-(trimethylsilyl)tricyclononene-7]. It is demonstrated that this highly permeable saturated glassy polymer exhibits thermodynamic selectivity in experiments with both the individual gases (CH4 and C4H10) and their mixtures and provides fivefold butane enrichment of a permeate. The test polymer and others additive Si-containing norbornene polymers are of interest as membrane materials for the separation of hydrocarbon gases.

Membrane separation of multicomponent mixture of alkanes C1–C4

The membrane separation of the four-component mixture of gaseous alkanes C1–C4 is studied. Homogeneous films based on two high-permeable polymers, namely, addition-type poly[3-(trimethylsilyl)tricyclononene-7] and poly[3,4-bis(trimethylsilyl)tricyclononene-7], are used as membranes. Separation of the multicomponent mixture of hydrocarbons on these polymers follows the same trends as separation of binary mixtures CH4-C4H10 on polyacetylenes. In the presence of higher hydrocarbons, the permeability coefficients of methane decrease and the permeates become enriched with higher hydrocarbons. During separation of the multicomponent mixture, permeability coefficients P(C4H10) attain high values (up to 12000 Barrers).

Gas-transport properties of epoxidated metathesis polynorbornenes

The effect of postpolymerization epoxidation of metathesis polynorbornenes on their gas-transport behavior is studied. For two polymers, unsubstituted polynorbornene and poly(trimethylsilylnorbornene), postpolymerization modification via double bonds is implemented by epoxidation under the action of m-chloroperbenzoic acid to high conversions (95–100%). For initial polymers and their epoxidation products, the permeability and diffusion coefficients are measured and the solubility coefficients are estimated. It is shown that, for both initial polymers, functionalization leads to a marked reduction in permeability (by a factor of 2–10) and diffusion coefficients (by a factor of 3–10); simultaneously, the separation factors increase by a factor of 2–6. Although for all gases the solubility coefficients decrease as a result of epoxidation, the coefficients of CO2 solubility in both epoxidated polymers increase. This effect may be explained by specific interactions of a СО2 molecule possessing the quadrupole moment with С–О–С bonds appearing in a polymer.

Transport and physicochemical parameters of polypentenamer

Physicochemical properties of a cis-polypentenamer—a hydrocarbon polymer with a low glass transition temperature (T g = 168.8 K)—have been studied. Measurements of permeability coefficients P in rubbery material for a wide range of gases (He, H2, O2, N2, CO2, CH4, C2H6, C3H8, and n-C4H10) indicate a high permeability of this polymer for which the values of P are only slightly lower than those of the most permeable rubber—poly(dimethylsiloxane). The method of inverse gas chromatography has been employed to estimate solubility coefficients S for n alkanes C3–C10 and cycloalkanes in cis-polypentenamer in the range from 25 to 150°C. It has been shown that the solubility coefficients linearly increase in lnS-T cr 2 coordinates, where T cr is the critical temperature of a solute. In terms of the above correlation, the solubility coefficients of light gases have been estimated and the diffusion coefficients D of gases in the same polymer have been calculated via the formula P=DS. The free volume in cis-polypentenamer has been studied by positron annihilation lifetime spectroscopy. The temperature dependence of the positronium lifetime τ 3 that characterizes the size of the free volume element in a polymer demonstrates saturation at temperatures above 250 K. This effect is probably related to a rapid migration of fluctuation holes in the rubbery polymer at temperatures remote enough from its glass transition temperature.

Metathesis polymer based on 5-trimethylsilylbicyclo[2.2.2]oct-2-ene: Synthesis and gas-transport properties

A new silicon-containing bicyclic monomer 5-trimethylsilylbicyclo[2.2.2]oct-2-ene has been synthesized, and its metathesis polymerization and gas transport properties of the polymer based on it have been studied. The monomer is synthesized by the two-step scheme using the Diels–Alder reaction from 1,3-cyclohexadiene and vinyltrichlorosilane followed by methylation with a Grignard reagent. The resulting 5-trimethylsilylbicyclo[ 2.2.2]oct-2-ene is inactive in metathesis homopolymerization in the presence of first- and second- generation Grubbs catalysts and a Hoveyda–Grubbs catalyst, but it slowly polymerizes when norbornene is present in the reaction mixture. The high-molecular-mass copolymer (M w = 3.0 × 105, M w/M n = 2.8) of 5-trimethylsilylbicyclo[2.2.2]oct-2-ene and norbornene possesses good film-forming properties, and its glass transition temperature is 126°C. The gas-transport properties of the copolymer have been studied.

Microwave-assisted synthesis of mesoporous metal-organic framework NH2—MIL-101(Al)

The possibility of formation of the mixed matrix membranes NH2—MIL-101(Al) under the conditions of microwave activation of the reaction mixture at atmospheric pressure is studied. Microwave irradiation affects the morphology and crystallite size and significantly shortens the synthesis time (from tens of hours to 10—30 min). The obtained samples of NH2—MIL-101(Al) with a crystallite size of 100 nm were used as nanofillers for polymer matrix based on the PIM-1 polymer with intrinsic microporosity for the preparation of hybrid membrane materials. Gas permeability for a series of gases was measured on the synthesized membranes.