Effect of Heat Treatment of Molten Bi2O3 Containing 22 mol % SiO2 on the State of the Metastable δ*-Phase Forming during Solidification

Inorganic Materials - We have studied the effect of isothermal holding of a melt containing 78 mol % Bi2O3 and 22 mol % SiO2 and various melt cooling schedules on the morphology, microstructure,...     

Synthesis and gas transport properties of polypentafluorostyrene

Polypentafluorostyrene (PPFS) (M _w = 1.7 × 10⁵ Da, M _w /M _n = 1.6, and Т _g = 110°С) has been synthesized by radical polymerization of pentafluorostyrene. The chemical structure of the polymer has been confirmed by ¹H and ¹⁹F NMR data. The permeability and diffusion coefficients of gases (He, H₂, O₂, N₂, CO₂, and CH₄) have been measured on a barometric setup. The permeability, diffusion, and solubility coefficients of gases have been shown to increase with the increases in the fluorine content in the repeat unit of the polymer in the polystyrene–poly(p-fluorostyrene)–PPFS series. Such behavior of transport parameters in the polymer series is associated with the growth in the fractional free volume and decrease in the cohesive energy density. The investigated polymers on the basis of styrene and its derivatives including PPFS are located in the middle of clouds of Robeson diagrams for N₂/CH₄, CO₂/CH₄, and O₂/N₂ and are not of interest for their separation.     

Synthesis and gas permeation parameters of metathesis polytricyclononenes with pendant Me3E‐groups (E = C,Si, Ge)

Metathesis polytricyclononenes were synthesized via ROMP polymerization in the presence of the 1‐st generation Grubbs catalyst and their gas‐transport properties were studied for the first time. The aim of this work was to evaluate the influence of Me₃E‐groups (E = C, Si, Ge) on gas permeation parameters of ROMP materials. New metathesis poly(3‐tert‐butyltricyclononene‐7) and poly(3‐trimethylgermyltricyclononene‐7) were obtained with high yields (up to 95%) and high‐molecular weights (M_w～3–7×10⁵ g mol^?1). The glass transition temperatures of the ROMP polytricyclononenes with Me₃E‐groups decreased when E was changed from C to Si and then to Ge. It was shown that the polytricyclononene containing Me₃Si‐groups has the highest gas permeability while the polytricyclononene containing Me₃C‐substituents has the lowest gas permeability. In addition, the gas permeation parameters were estimated for ROMP Me₃Si‐ and Me₃Ge‐substituted polytricyclonona‐3,7‐dienes. So the influence of the second double bond in the monomer units on the permeability of the polymers obtained was studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41395.     

Crosslinking of addition copolymers from tricyclononenes bearing (CH3)3Si‐ and (C2H5O)3Si‐groups as a modification of membrane gas separation materials

Here, we report the synthesis and the study of gas‐transport properties of crosslinked highly permeable copolymers from Si‐containing norbornene derivatives. The initial high‐molecular‐weight copolymers were prepared via addition copolymerization of 3‐trimethylsilyltricyclo[4.2.1.0^2,5]non‐7‐ene (TCNSi1) with 3‐triethoxysilyltricyclo[4.2.1.0^2,5]non‐7‐ene (TCNSiOEt) in good or high yields using a Pd‐catalyst. The obtained copolymers included up to 10 mol% of TCNSiOEt units bearing reactive Si–O–C‐containing substituents. The crosslinking was readily realized by using simple sol–gel chemistry in the presence of Sn‐catalyst. The formed crosslinked copolymers were insoluble in common organic solvents. Permeability coefficients of various gases (He, H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, n‐C₄H₁₀) in these copolymers before and after crosslinking were determined and the influence of the incorporated TCNSiOEt units as well as the crosslinking on gas transport properties were established. As a result, it was found that only a small reduction of gas‐permeability was observed when TNCSiOEt units were incorporated into the main chains, and the copolymers were crosslinked. At the same time, the selectivity for C₄H₁₀/CH₄ pair was increased. The suggested approach has allowed obtaining crosslinked polymers from Si‐containing monomers without a loss of the main membrane characteristics. POLYM. ENG. SCI., 59:2502–2507, 2019. © 2019 Society of Plastics Engineers     

Catalytic transformations of mono- and bis-silyl substituted norbornadienes

Transformations of 2-trimethylsilylnorbornadiene-2,5 (SNBD) and 2,3-bis(trimethylsilyl)norbornadiene-2,5 (DSNBD) under metathesis and addition polymerization conditions were studied. In the presence of the WCl₆/1,1,3,3-tetramethyldisilacyclobutane-1,3 and Cl₂(PCy₃)₂Ru=CHPh catalysts, high-molecular-mass silicon-substituted poly(cyclopentylidene vinylene)s were obtained with yields up to 98%. Under addition polymerization conditions, SNBD and DSNBD dimerized on the nickel(II) naphthenate-methyl alumoxane catalyst to give pentacyclic dimers. Three dimers were detected in the case of SNBD, whereas the exo-trans-exo-cyclodimer alone was exclusively produced from DSNBD. Being inactive in addition homopolymerization, both SNBD and DSBND take part in addition copolymerization with norbornene.     

Synthesis and metathesis polymerization of 5,5-Bis(trimethylsilyl)norbornene-2

5,5-Bis(trimethylsilyl)norbornene-2 was synthesized in a yield of 60% via the scheme of diene condensation of cyclopentadiene with 1,1-bis(trimethylsilyl)ethylene and subsequent methylation of the resulting adduct with methyllithium. Its metathesis polymerization was first performed on W and Ru catalysts with yields of up to 98%. The structure of the new polymer was determined by means of the NMR and IR techniques. The tungsten catalyst makes it possible to prepare the polymer with a 40% amount of trans-double bonds, whereas the ruthenium catalyst is more selective and yields the polymer that contains almost 100% trans-double bonds. A high glass transition temperature as compared to other silicon-substituted metathesis polynorbornenes (196–203°C) indicates a high rigidity of the polymer chain and suggests that the polymer will have good gas-separation properties.     

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.     

Copolymerization of 5-(trimethylsilyl)norbornene and 5-ethylidene-2-norbornene

Addition and metathesis copolymerization of 5-(trimethylsilyl)norbornene (TMSNB) and 5-ethylidene-2-norbornene (ENB) has been studied. High-molecular-weight metathesis copolymers have been obtained on the first-generation Grubbs catalyst based on the Ru carbene complex Cl₂Ru(=CHPh)(PCy₃)₂ with nearly quantitative yields. Addition copolymerization has been carried out on the Ni(II) naphthenatemethylaluminoxane (MAO) catalytic system. In both cases copolymerization proceeded without participation of ethylidene double bond. Copolymers of this type are promising ones for manufacturing stable highly permeable polymeric membranes, since they are capable for crosslinking.