Gas transport properties of crown-ether methacrylic polymers: poly(1,4,7,10-tetraoxacyclododecan-2-yl) methyl methacrylate

Polymer membranes were prepared by radical polymerization of the 1,4,7,10-(tetraoxacyclododecan-2-yl) methyl methacrylate (CR4MA) monomer and a small quantity of a cross-linking agent ethyleneglycoldimethacrylate. High vacuum pressure techniques were used to evaluate oxygen and helium transport through these membranes at temperatures below and above its glass transition temperature, between 0 and 50 °C. The apparent values of both the permeability and diffusion coefficients are unusually low because of the high packing degree of these polymeric membrane materials. The results obtained were also compared with those determined for polymer membranes derived from their open chain counterparts, the polymer derivatives from methacrylate monomers with a number of oxyethylene units in the ester residue variable between 2 and 6, and with a set of other polymers.     

Diffusion of gases and vapors through methacrylates with oxyethylene units in the pendent chain

The diffusion of He, Ar, O₂, N₂, CO₂, CH₄, CH₃CH₃ and CH₂CH₂ has been determined in three polymethacrylates with one, two and three oxyethylene units as side chains. For these three rubbery polymers we have used the acronyms PEEMA, PDEMA and PTEMA, respectively. The results have been compared to those of poly(ethyl methacrylate) on one hand, and on the other with previous results on methacrylates of varying length alkyl side chains. It has been found that the oxyethylene units side chains methacrylates show diffusion coefficients which are slightly lower than those methacrylates bearing alkyl side chain, when comparing polymers with the same number of atoms in the side chain. These diffusion data are put in relation to relevant structural features such as the glass transition temperature and the fractional free volume of both families of rubbery methacrylates.     

Diffusion and solution of gases and vapors in styrene-butadiene block copolymers

The diffusion, solution, and permeation behavior of a series of inert gases (helium, argon, nitrogen, krypton, and xenon) in S-B block copolymer films was studied by transient permeability measurements and by the equilibrium desorption method. The morphologies of most of the samples used in the measurements were (a) polystyrene rods dispersed in a polybutadiene matrix and (b) alternating lamellae of styrene and butadiene components. It was indicated, as far as the kinetic nature at lower temperatures is concerned, that the diffusion and permeation processes of gases, except for helium, are governed primarily by behavior in the polybutadiene matrix. At lower temperatures, it was shown that the transient method counts only the mobile penetrant in the polybutadiene matrix, while the equilibrium method counts less diffusive species in the polystyrene domains as well. The diffusion behavior in the copolymer films was compared with that in homopolybutadiene and discussed in terms of two impedance factors: the tortuosity and the chain immobilization factors. From the homopolymer-block copolymer comparison along with results obtained from diffusion experiments using n-hexane as the penetrant, it was indicated that segmental motions in the polybutadiene phase in the copolymers are restricted relative to motions in homopolybutadiene. Also, from data on gas sorption in samples of various styrene contents, involving both S-B block copolymers and binary mixtures with homopolystyrene, it was suggested that the partial mixing of component block chains occurs at the interface between the domains, resulting in rather diffuse domain boundaries.     

Synthesis and solid state structures of macromolecular cylindrical brushes with varying side chain length

Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤P_n^sc≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d∼(M_n^sc)^0.476. The contour length of the cylindrical brush polymers per main chain monomer unit, l_m, was determined to slightly vary with side chain molar mass M_n^sc according to l_m∼(M_n^sc)^0.059. The resulting values are much less than the maximum extension, which is found to be almost independent of side chain molar mass. Also, supermolecular structure formation of a random copolymer brush prepared by radical copolymerization of methacryloyl end functionalized polyvinylpyridine and polymethylmethacrylate macromonomers has been observed and is interpreted as a consequence of intramolecular phase separation.     

Transport properties of organic vapors in nanocomposites of organophilic layered silicate and syndiotactic polypropylene

Syndiotactic polypropylene (sPP) nanocomposites were obtained by melt blending synthetic fluorohectorite modified octadecyl ammmonium ions (OLS), and maleic-anhydride-grafted isotactic polypropylene (iPP-g-MA) as compatibilizer. The composition of the inorganic material was varied between 5 and 20 w/w%. Films of the composites were obtained by hot press molding the pellets. Melt-direct polymer intercalation of sPP into the OLS gave rise to nanocomposites in which the silicate layers were delaminated at low clay contents, and ordered to intercalated structures at the highest clay content. The elastic modulus was higher than for the pure polymer in a wide temperature range and increased with the inorganic content. The transport properties were measured for dichloromethane and n-pentane. The sorption was reduced compared to pure sPP. There were not significative differences between the samples having different inorganic contents. The diffusion coefficient decreased with increasing clay content. Permeability (P) showed a strong decreasing dependence on the clay content. The improvement of the barrier properties was largely caused by the reduced diffusion.     

Transport of water and methanol vapors in alkyl substituted poly(norbornene)

This report examines the ability of aliphatic-substituted polynorbornenes to separate methanol vapor from water-wet air streams. Single component transport properties of water and methanol were measured for each candidate polymer at 30 °C. The diffusion coefficient, sorption coefficient, and permeability were determined by measuring the rate of mass gain or loss of a sample due to sorption or desorption. The ratio of the permeabilities of the pure components yielded the ideal selectivity. The materials studied in this were methyl-, nbutyl-, nhexyl-, and ndecyl-polynorbornene. These polymers were glassy, with T_gs of 150-380 °C, and have relatively high fractional free volumes (16-19%). The results of the study showed polynorbornenes were methanol selectivity with ideal selectivities of 1.2-9. This permeation selectivity is due primarily to the solubility selectivity of the materials.     

Diffusion of gases in metal containing carbon aerogels

Carbon aerogels containing Fe, Ni, Cu or no metal were prepared by carbonisation of polymer aerogels synthesised from 2,4-dihydroxybenzoic acid and formaldehyde and modified by CVD of benzene. Uptakes and diffusion coefficients of CO₂, CH₄, N₂ and O₂ were measured and the results compared with those obtained using a commercial carbon molecular sieve. The results indicated that the diffusion of light gas molecules in carbon aerogels cannot be interpreted solely on the basis of micropore diffusion, but that the very high mesopore volumes of the aerogel monoliths exert a strong influence on the kinetics of diffusion in these materials. The mesoporosity is decreased when the % solids used during synthesis of the polymer precursor increases and this resulted in kinetic behaviour which was more similar to that predicted by Fickian or LDF models. Increasing % solids was also accompanied by generally slower diffusion rates and generally lower uptakes. The single gas uptakes and diffusion coefficients could be altered by varying the % solids used during synthesis of the polymer precursor, by introducing different metals into the polymer hydrogel by ion exchange, or by CVD of benzene on the carbon aerogel.     

Transport in nonporous membranes

A theory is developed for isothermal, steady-state transport of solutes and solvents in nonporous membranes in the absence of electrical effects. The proposed equations, which include the effects of both concentration and pressure gradients, are used to analyze gas separations, ultrafiltration, solvent drag, and osmotic effects and negative anomalous osmosis.     

The effect of side chain length on hydrodynamic and conformational characteristics of polyimide-graft-polymethylmethacrylate copolymers in thermodynamically good solutions

Samples of graft-copolymers with polyimide backbones and poly(methyl methacrylate) side chains synthesized by ATRP of methylmethacrylate on polyimide macroinitiator are investigated by ¹H NMR, GPC, static and dynamic light scattering, sedimentation, and viscosimetry in chloroform and ethyl acetate solutions. Hydrodynamic and conformational behavior of graft-copolymers is well-described by the wormlike spherocylinder and Porod wormlike chain models. Samples of graft-copolymers have high equilibrium rigidity, the Kuhn segment length grows from 20 to 95 nm with the lengthening of side chains. The equilibrium rigidity and hydrodynamic diameter of the investigated graft-copolymers depend on the molar mass M of side chains as M ^0.7.     

Sorbate-induced structural rearrangements and permeation of gases in the polyphenylene oxide copolymer

Rearrangements of the porous structure of the glassy polyphenylene oxide copolymer occurring in the course of its swelling in the atmosphere of several gases and the subsequent relaxations were investigated using the low temperature nitrogen adsorption technique. The values of porosity (ε) and BET surface area (S_BET) were used to quantify the copolymer's free volume accessible to N₂ molecules at 77 K. The magnitude and the rate of changes of the copolymer's free volume invoked by its conditioning in vacuum, N₂, O₂, CH₄, CO₂ and C₃H₆, were analysed in terms of ε and S_BET. These characteristics of the polymer structure were found to depend upon the sorbate nature, its pressure, exposure time and temperature. Swelling of the copolymer that occurs in certain atmospheres results in the expansion of the free volume, which is reflected in the increased values of ε and S_BET. In accordance with the magnitude of the copolymer swelling under experimental conditions employed in this study, the gases can be qualitatively ranked as follows: C₃H₆>CO₂>CH₄>O₂≈N₂. The swollen polymer, being placed in the environment of a lower swelling ability, experiences structural relaxations. The relaxations result in a decrease of the free volume, which is reflected by a decrease in the values of ε and S_BET. Gas permeability of glassy polymer membranes is directly related to the conditioning history of a polymer: the state of the glassy polymer characterised by the increased values of porosity and BET surface area corresponds to the more permeable state of a membrane.     

Diffusion Transport Vector for Multicomponent Gas Separation in Ultracentrifuge

Abstract

Simplified diffusion transport vector expressions for multicomponent gas mixture mass transfer analysis have been derived. Approximate relations for the general diffusion coefficients for multicomponent gas separation in an ultracentrifuge for both isotope and nonisotope mixtures are developed. Taking into account that diffusion coefficients matrices are diagonally dominant, a simple relationship for diffusion transport vectors for the case of isotope separation is derived. It is shown that the relative inaccuracies in separative power and separation factors calculation are less than 1-2%. Analogous relationships for diffusion coefficients for the separation of a nonisotope mixture containing small admixtures in the main gas are suggested. These relationships can be used when the total mole fraction of the admixtures is less than 5%.     

Cyclolinear organosilicon copolymers with monocyclic fragments in the side chain

The reaction of heterofunctional condensation of organodichlorosiloxycyclotri(tetra, penta) siloxanes and organodichlorosililcarbocyclotrisiloxane with dihydroxydimethylsiloxanes in the presence of pyridine was investigated. It was shown that at small lengths of the linear dimethylsiloxane link (n ≤ 4) the reaction of heterofunctional condensation runs both intermoleculary with formation of polymers and intramoleculary with formation of bicyclo‐organosiloxanes. It was established that insertion of cyclic fragments in the side chain hinders the chain transfer reactions that proceed with release of the D‐type cycles during thermal depolymerization. The conformational and hydrodinamic properties of some polymethylsiloxane copolymers with cyclosiloxane fragments in the side chain have been studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 583–594, 1999     

Influence of silica and black rice husk ash fillers on the diffusivity and solubility of gases in silicone rubbers

The preparation of elastomeric compositions based on poly(methylvinyl siloxane) using silica and rice husk ash as fillers is reported. Permeation of oxygen, nitrogen, carbon dioxide and methane across the compositions was measured in the temperature interval 30-60° C under upstream pressures lying in the range 15-76 cm Hg. Permeation and diffusion coefficients were independent on the upstream pressure but both parameters were thermal activated processes described by the Arrhenius equation. It was found that the activation energy associated with the diffusion process is larger in the filled than in the unfilled rubbers. The results also showed that the fillers enhance gas solubility in polysiloxane compounds in such a way that in most situations the sorption process is exothermic. The analysis of the solubility and diffusivity of gases in the rubbers suggests very good adherence matrix-fillers that hinder micro-Brownian motions thus impeding the normal development of non-permanent holes through which the diffusive particles can easily jump. Neither the proportion nor the nature of the fillers alters the permselectivity characteristics of polysiloxane based compounds.     

Transport properties of silmethylene homo-polymers and random copolymers: experimental measurements and molecular simulation

A novel class of silicon-containing rubbers is proposed as membrane materials for separation of hydrocarbons of natural and associated petroleum gas. Homo-polymers of general formulas -Si(CH₃)₂CH₂- (PDMSM) and -Si(CH₃)₂CH₂CH₂CH₂- (PDMSTM) and the copolymers with the same randomly alternating repeat units were prepared by thermal initiated polymerization of strained silicon-containing four-member cycles. These polymers have low glass transition temperatures and reveal solubility controlled gas permeation properties. The highest permeability is characteristic for PDMSM, however, it has poor film forming properties. On the other hand, amorphous copolymers exhibit combination of good film forming properties and relatively high permeability. Transport properties of PDMSM were successfully simulated by molecular dynamics using a very efficient united-atom force field.     

Synthesis and characterisation of side chain liquid crystal copolymers containing sulfonic acid groups

A series of novel side chain liquid crystal copolymers, the poly[10-(4-methoxy-4′-oxy-azobenzene) decyl methacrylate]–co-poly[2-acrylamido-2-methyl-1-propanesulfonic acid]s (10-MeOAzB/AMPS-x/y) have been synthesised by free radical copolymerisation. The mol fraction of the sulfonic acid-based group, AMPS, has been varied over a broad range of composition in the copolymers, and these have been characterised using differential scanning calorimetry (DSC), polarised light microscopy (PLM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). The liquid crystal homopolymer and copolymers containing up to 0.54 mol fraction AMPS-based units, all exhibit a smectic A phase, while at higher mol fraction AMPS-based groups, liquid crystallinity is extinguished and the copolymers are amorphous. The local packing arrangements within the smectic A phase varies with composition attributed, in part, to phase separation between acid rich domains and liquid crystal regions. The dependence of the transitional properties on copolymer composition may be interpreted in terms of the packing efficiency of the mesogenic side chains and hydrogen bonding between the sulfonic acid groups, as a consequence of increasing the concentration of acid-based groups.     

Survey on transport properties of liquids,vapors, and gases in biodegradable poly(3-hydroxybutyrate) (PHB)

The transport properties of carbon dioxide, water, and different organic solvents in bacterial poly(3-hydroxybutyrate) (PHB) at 30°C were investigated. CO₂ sorption was measured by the gravimetric method using a recording microbalance at subatmospheric pressures. Results were adequately interpreted in terms of Henry's law. Organic solvent and water permeabilities for both vapors and liquid were measured using a gravimetric cell. The data were interpreted in different terms depending on the units in which permeability was measured. Most of the solvent-polymer systems showed the typical time-lag plot, but in liquid permeation experiments, some anomalous behaviors were observed, with a transient period of rapid permeation at the beginning of the experiment before reaching the steady state. The transport properties of PHB were compared with those of other polymers, either from synthetic or biodegradable origin. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1849–1859, 1997     

Cure properties of epoxies with varying chain length as studied by DSC

The cure of diglycidyl ether of bisphenol A (DGEBA) and a homologous series of poly(ethylene oxide) diglycidyl ether (PEODE) epoxy resins with 4,4′‐diaminodiphenyl sulfone (DDS) was studied by scanning and isothermal differential scanning calorimetry (DSC). The heat of polymerization was relatively independent of monomer structure and chain length when determined by isothermal DSC. Variations in the heats of polymerization determined by the scanning method were attributed to degradative reactions at higher temperatures during the scan. The activation energies determined by scanning DSC experiments were relatively constant at 61 ± 3 kJ/mol. However, using an isothermal cure method, the activation energies were found to vary with monomer structure and extent of cure. The isothermal kinetics were analyzed in terms of the autocatalytic model on the basis of competing reaction paths involving catalysis by either initial impurities or hydroxyl groups produced in situ. The activation energies of both reaction paths were found to vary with monomer structure and degree of conversion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1479–1488, 1999     

Incorporation of terpyridine into the side chain of copolymers to create multi-functional materials

Polymer architectures containing metal-ligands in their side chain represent a diverse approach to generating multi-functional materials. The ability to define a versatile synthetic platform will enable many chemistries and architectures to be studied. This report describes our latest efforts to prepare these unique polymers by either a direct polymerization of functionalized monomers or a post-polymerization attachment. Random and block copolymers have been successfully prepared. Subsequent functionalization with metal ions leads to a variety of properties including metal induced gelation and solvochromic sensors.     

Finite element analysis of oxygen transport in microfluidic cell culture devices with varying channel architectures, perfusion rates, and materials

Numerical simulations were done both as an exploration into the nature of oxygen transport within microfluidic cell culture devices and an investigation of the relative importance of various design parameters. A rectangular channel comprised of an oxygen permeable polymer layer bonded to a glass substrate seeded with a monolayer of oxygen-consuming cells was modeled. Oxygen transport by both convection and diffusion within the cell culture media and by diffusion in the polymer layer were explored using finite element analysis. Stiff spring analysis was applied at the interface between these two regions to ensure a continuous flux of O₂ across the boundary. The O₂ utilization of the cells was approximated by a constant flux of oxygen from the bottom of the channel. The model was verified against an analytical solution from the literature. Design parameters including flow rate, diffusive layer thickness, and material selection were manipulated within the model to determine their relative importance in ensuring adequate supplies of oxygen for cell growth. The solubility and diffusivity of oxygen within the polymer layer were found to be key parameters in determining the amount of oxygen available to the cells, along with the flow rate of the media perfusing the system. These explorations will enable rational design choices to be undertaken during the implementation of microfluidic devices for cell culture.