Oxidation of poly(1-trimethylsilyl-1-propyne)

The oxidation of poly(1-trimethylsilyl-1-propyne) (PMSP) proceeded normally in air at room temperature and under mild thermal conditions. Two different bands assigned to the carbonyl groups on a side chain and on a decomposed chain end were found in the IR spectra of the oxidized PMSP membrane. However, no band assigned to a hydroxyl group was observed. An allyl-type methyl group of the PMSP was mainly autooxidized without a decrease in molecular weight at room temperature. Only the former band assigned to the carbonyl groups appeared and it had a shoulder peak. In the case of mild thermal oxidation, the decomposition started in the backbone chain and both bands appeared. When the thermal oxidation proceeded further, all bonds were broken and various carbonyl and siloxane bonds were then randomly produced. © 1994 John Wiley & Sons, Inc.     

Bromination and gas permeability of poly(1-trimethylsilyl-1-propyne) membrane

The bromination of poly(1-trimethylsilyl-1-propyne) (PMSP) was carried out by immersing a PMSP membrane in bromine water at 25°C. The bromine mainly reacted at the carbon–carbon double bonds in the backbone chain, and carbon–carbon single bonds were produced, which was determined from the infrared (IR) and ultravilet (UV)–visible analyses. The glass transition temperature of the PMSP is above 350°C, but a new endothermic peak appeared between 50 and 80°C in the differential scanning calorimetry (DSC) curves of all brominated PMSPs. The permeability for 12 gases in the PMSP membrane and its brominated membranes was investigated between 30 and 90°C below 1 atm. With increasing bromine content in the membrane, the permeability coefficient for all gases decreased together with the diffusion coefficient, and the ideal separation factor for the industrially important gas pairs increased at 30°C. A distinct change in slopes at near the endothermic temperature determined by the DSC analysis was observed in Arrhenius plots of the permeability coefficients in all brominated PMSP membranes. © 1994 John Wiley & Sons, Inc.     

Gas transport properties of MgO filled poly(1-trimethylsilyl-1-propyne) nanocomposites

Magnesium oxide (MgO) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form polymer nanocomposites. Transmission electron microscopy was used to determine the extent of particle aggregation in the composites. Both nanocomposite density and CO₂, CH₄, N₂, and H₂ permeability were influenced by nanoparticle loading. Nanocomposite densities were markedly lower than predicted by a two phase additive model. For example, in films containing 75 nominal volume percent MgO, the polymer-particle composite density was 68 percent lower than expected based on an additive model. At this loading, gas permeability coefficients were, depending on the gas, 17-50 times higher than in unfilled PTMSP at similar conditions. The changes in permeability with particle content were interpreted in terms of measured changes in gas solubility with particle content and diffusion coefficients calculated from the permeability and solubility data.     

Molecular dynamics simulation of diffusion of gases in pure and silica-filled poly(1-trimethylsilyl-1-propyne) [PTMSP]

Nanocomposites have been extensively applied, and molecular dynamics simulation techniques have been applied to study the diffusion of gases (H₂, O₂, N₂, CO₂, CH₄, n-C₄H₁₀) through pure and filled with silica particle poly(1-trimethylsilyl-1-propyne) [PTMSP]. The aim for this research is to explore and investigate the effect of silica particle on the diffusion of gases in polymer. The diffusion coefficients of gases were determined via NVT molecular dynamics simulation using the COMPASS force field up to 500 or 1000 ps simulation time. We have focused on the effect of the concentration and the size of the silica particles on diffusion coefficients of gases and the changes of free volume and translational dynamics and intermolecular energies. It has been found that the addition of silica particle to PTMSP increased the diffusion coefficients of gases by enhancing the free volume of polymer.     

Poly(1-trimethylsilyl-1-propyne)/MFI composite membranes for butane separations

The separation of equimolar mixtures of i-butane and n-butane through poly(1-trimethylsilyl-1-propyne)/MFI composite membranes was studied. Membranes were characterized by XRD and SEM. Addition of 50 wt% MFI particles into a PTMSP matrix showed increased permeability and simultaneous improved selectivity in the temperature range 25–200 °C. The best improvement was seen at 150 °C for the composites, giving almost threefold increase in permeability and 56% higher n-butane/i-butane selectivity over the pure polymer. To our knowledge, this is the first successful demonstration of the incorporation of a molecular sieve into a polymer matrix for butane isomer separations. The composite membranes were also tested for separations of n-hexane/2,2-dimethylbutane and p-xylene/o-xylene.     

Crosslinking poly(1-trimethylsilyl-1-propyne) and its effect on solvent resistance and transport properties

Poly(1-trimethylsilyl-1-propyne) (PTMSP) has been crosslinked using 3,3′-diazidodiphenylsulfone to improve its solvent resistance. This study reports the influence of crosslinker content on the solubility properties of PTMSP, its density, and its gas sorption and transport properties. Crosslinking PTMSP renders it insoluble even in excellent solvents for the uncrosslinked polymer. Gas permeability and fractional free volume (FFV) decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decreases in diffusion coefficients. Permeability reductions due to crosslinking could be offset by adding nanoparticles to the films. The addition of 30 wt.% fumed silica nanoparticles increased the permeability of crosslinked PTMSP by approximately 80%. In mixed gas permeation experiments, when the composition of the feed gas was 98 mol% CH₄ and 2 mol% n-C₄H₁₀, uncrosslinked PTMSP had an n-C₄H₁₀/CH₄ selectivity of 31 and an n-C₄H₁₀ permeability of 114,000 barrers at 35 °C and 14 atm feed fugacity. At the same conditions, crosslinked PTMSP containing 5 wt.% crosslinker had an n-C₄H₁₀/CH₄ selectivity of 28 and an n-C₄H₁₀ permeability of 73,000 barrers, and crosslinked PTMSP containing 5 wt.% crosslinker and 30 wt.% fumed silica nanoparticles had an n-C₄H₁₀/CH₄ selectivity of 21 and an n-C₄H₁₀ permeability of 110,000 barrers.     

Composite membranes of poly(1-trimethylsilyl-1-propyne) and poly(dimethyl siloxane) and their pervaporation properties for ethanol–water mixture

A poly(1-trimethylsilyl-1-propyne) (PTMSP) membrane was systematically modified to prevent flux decline over time by incorporating poly(dimethyl siloxane) (PDMS) in three different ways: (1) semi-interpenetrating polymer network (I series), (2) PDMS sorption (S series), and (3) PDMS sorption and crosslinking (X series). The PTMSP and PDMS phases were partially mixed in the I series, which was confirmed by the measurement of density and glass transition temperature. The flux and separation factor in pervaporation of an ethanol–water mixture decrease with time for the I series, analogous to the behavior of pure PTMSP. However, the flux and separation factor remained steady with time in the case of the S and X series. The sorption method appears to be a good means for maintaining a time-unvarying flux and separation factor at a minimum expense. © 1994 John Wiley & Sons, Inc.     

Chemical modification of poly(substituted-acetylene). V. Alkylsilylation of poly(1-trimethylsilyl-1-propyne) and improved liquid separating property at pervaporation

In order to improve the separation characteristic at pervaporation, the introduction of several kinds of trialkylsilyl groups into poly(1-trimethylsilyl-1-propyne) (PTMSP) was achieved via metalation of PTMSP followed by treating with trialkylchlorosilanes to afford trialkylsilylated PTMSP. Ratio of TMSP monomer unit and trialkylsilylated unit, x/y, was in the range of 95/5 to 80/20. All the chemically modified PTMSP membranes showed ethanol permselectivity at pervaporation of aqueous ethanol solution. Introduction of appropriate length of alkyl groups (methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl groups) into PTMSP effectively enhanced the selectivity. However, excess introduction of octyl and decyl groups or introduction of dodecyl and octadecyl groups caused decrease of selectivity, of which the value was smaller than that of PTMSP membrane. Furthermore, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their aqueous solutions at pervaporation through trimethylsilylated PTMSP membrane.     

Chemical modification of poly(substituted-acetylene). VI. Introduction of fluoroalkyl group into poly(1-trimethylsilyl-1-propyne) and the improved ethanol permselectivity at pervaporation

In order to improve the separation characteristics of membranes for pervaporation, the introduction of fluoroalkyl groups into poly(1-trimethylsilyl-1-propyne) (PTMSP) was achieved by two methods. First, 3,3,3-trifluoropropyldimethylsilylated PTMSP was prepared via metalation of PTMSP followed by treating with 3,3,3-trifluoropropyldimethylchlorosilane. About 6 mol % of 3,3,3-trifluoropropyldimethylsilyl group was introduced by the polymer reaction. Second, the copolymerizations of 1-trimethylsilyl-1-propyne (TMSP) with 1- (3,3,3-trifluoropropyldimethylsilyl)-1-propyne (FPDSP) or 1- (1H,1H,2H,2H-tridecafluorooctyldimethylsilyl)-1-propyne (FODSP) were carried out to afford TMSP/FPDSP or TMSP/FODSP random copolymers. The ratio of TMSP monomer unit and the comonomer unit, x/y, was in the range of 99/1-85/15. All the chemically modified PTMSP membranes showed ethanol permselectivity for pervaporation of aqueous ethanol solution. In particular, the introduction of less than about 5 mol % of fluoroalkylsilylated units into PTMSP effectively enhanced the selectivity. However, excess introduction of FODSP comonomer unit caused a decrease of the selectivity, with the value being smaller than that of PTMSP membrane. Furthermore, tetrahydrofuran, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their dilute aqueous solutions using a TMSP/FPDSP copolymer membrane.     

Copper catalysed gelation of dilute poly(acrylonitrile) solutions

Metallic copper catalysed gelation of dilute poly(acrylonitrile) solutions in dimethylformamide was discovered and studied by infra-red spectroscopy and other techniques for the first time. It was observed that some cyano groups were converted to carboxyl groups. Gelation did not lead to any increase in molecular weight. An intermolecular hydrogen bonding model is proposed to explain the behaviour of the gelated polymer. The gelation mechanism is given on the basis that metallic copper has a catalytic effect on the hydration of nitriles and that the partially neutralized acid component tightly coils the chain to cause the precipitation of poly(acrylonitrile).     

Physico-chemical concept of drag reduction nature in dilute polymer solutions (the Toms effect)

The physicochemical concept of turbulent drag reduction (the Toms effect) integrates physicochemical characteristics of polymer solutions with hydrodynamic and rheological flow parameters into a generalized equation, where the increment in volumetric flow rate Q_P is a function of the external shear stress τ_w, temperature, volume of macromolecular coils with immobilized solvent V_c and a function of their volume fraction Ψ = C · [η]/(1 + C · [η]). The Q_P depends on the coil intrinsic elasticity [G] = kT/V_c as well. This model allows one: (1) to describe the Toms effect in terms of useful elastic work spent by macromolecular coils with immobilized solvent to overcome the frictional forces (i.e. the forces of intermolecular interactions), (2) to forecast the initial conditions of the Toms effect (τ_* ≈ (RT)/(M · [η])) and (3) to explain the unusual temperature dependence of the polymer solutions flow.     

Friction reduction degradation in dilute poly(ethylene oxide) solutions

Degradation of friction-reducing effectiveness of dilute poly(ethylene oxide) solutions subjected to continuous agitation is examined in disk flow. A residual or steady-state effectiveness is observed which disappears only at a sufficiently high Reynolds number. The onset of friction reduction appears to occur within the transition region and seems to be independent of solution concentration. The onset of degradation also appears to be independent of concentration. Prior shear working is shown to have a significant effect on residual friction-reducing effectiveness only when the shear working is performed in a more intense shear field than that in which the friction-reducing effectiveness is evaluated. Degradation of friction-reducing effectiveness is compared to corresponding changes in viscosity-average molecular weight. The experimental results are interpreted in terms of a model of the interaction between polymer molecules and the turbulent flow field.     

Fourier transform infrared spectroscopy study of poly(1‐trimethylsilyl‐1‐propyne) aging

The influence of various factors on the aging of poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) during long‐term storage in air was investigated with Fourier transform infrared spectroscopy. Most attention was paid to the differentiation of oxidation, the reduction of the free volume, and the absorption of low‐molecular‐weight compounds from the environment. IR spectra of PTMSP samples stored from 1–2 months to 6.5 years revealed C?O, C? O, and C? H bands that had been earlier attributed to polymer oxidation products. It was established, however, that these bands completely disappeared from IR spectra of the aged samples after their soaking in ethanol. Spectra of dried residues of ethanol extracts displayed all these bands and did not show any bands of polymer chain fragments. Gas chromatography/mass spectrometry analysis proved that the residues were composed mainly of various dialkyl phthalates. Special experiments showed that PTMSP films easily absorbed di‐n‐butyl phthalate vapors. IR spectra of the films stored for a long time showed no decrease in double‐bond and methyl group bands. It was concluded that the polymer did not undergo oxidation in air at room temperature for at least 6.5 years. The absorption of plasticizer vapors (and possibly other compounds) from the environment and the reduction of the free volume were the main reasons found for PTMSP aging. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2523–2527, 2007     

Crosslinking poly(ethylene oxide) in dilute solutions by gamma rays

A high molecular weight poly(ethylene oxide) is gelled by radiation from a ⁶⁰Co source. At concentrations of 0.25 to 1 wt-%, doses of 4.5 to 7.5 × 10⁴ rad cause gelation. The storage modulus of the gel formed increases linearly with additional dose to a plateau value and then remains constant during further irradiation. The does needed to reach the plateau, D_p in rads, and the plateau modulus G_p in dynes per square centimeter, are related to the concentration c, in weight per cent: D_p = 1.05 × 10⁶c and G_p = 1.75 × 10⁴c^2.5. The energy absorbed by the polymer per crosslink formed is about 80 ± 10 kcal/mol. The crosslink density produced by radiation is calculated from the measured modulus by using the theory of rubber elasticity. Both modulus and loss are measured in a special air-bearing, recording torsion pendulum with a coneplate geometry.     

Studies on thermo-acoustic parameters in the dilute solutions of poly(ethyleneglycol)

Ultrasonic velocities and densities have been measured for the dilute solutions of poly(ethylene glycol) of average molecular mass 400 g mol^?1 in benzene at different temperatures between 299 and 328 K. The experimental data have been used to compute the thermo-acoustical parameters namely isentropic compressibility (β), intermolecular free length (L _f), molar volume (V _m), Schoff’s available volume (V _a(s)), acoustic impedance (Z), molar sound velocity (R _a), and molar compressibility (W). Variation of these parameters with temperature of the sample and mole fraction of the solute in the solution, keeping one of the either constant has been discussed to collect the informations on molecular structure and intermolecular interactions.     

Molecular diffusion in ternary poly(vinyl alcohol) solutions

The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant–polymer and surfactant–rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.     

Pure and mixed gas CH4 and n-C4H10 permeability and diffusivity in poly(1-trimethylsilyl-1-propyne)

Pure and mixed gas n-C₄H₁₀ and CH₄ permeability coefficients in poly(1-trimethylsilyl-1-propyne) (PTMSP) are reported at temperatures from −20 to 35 °C. CH₄ partial pressures range from 1.1 to 14.6 atm, and n-C₄H₁₀ partial pressures range from 0.02 to 1.8 atm. CH₄ permeability decreases with increasing n-C₄H₁₀ upstream activity (f/f_sat) in the feed. For example, at −20 °C, CH₄ permeability decreases by more than an order of magnitude, from 52,000 to 1700 Barrer, as n-C₄H₁₀ activity increases from 0 to 0.73. In contrast, n-C₄H₁₀ mixed gas permeability is essentially unaffected by the presence of CH₄. The depression of CH₄ permeability in mixtures is a result of competitive sorption and blocking effects, which reduce both CH₄ mixture solubility and diffusivity, respectively. Diffusion coefficients of n-C₄H₁₀ and CH₄ in mixtures were calculated from mixture permeability and mixture solubility data. The CH₄ concentration-averaged diffusion coefficient generally decreases as n-C₄H₁₀ activity increases. On the other hand, the n-C₄H₁₀ diffusion coefficient is essentially unaffected by the presence of CH₄. Pure and mixed gas activation energies of permeation and diffusion of CH₄ and n-C₄H₁₀ are reported. The mixed gas n-C₄H₁₀/CH₄ permeability selectivity increases with increasing n-C₄H₁₀ activity and decreasing temperature, and it is higher than pure gas estimates would suggest. Mixture diffusivity selectivity also increases with increasing n-C₄H₁₀ activity. The difference between pure and mixed gas permeability selectivity arises from both solubility and diffusivity effects. The dual mode mixed gas permeability model describes the mixture permeability data reasonably well for n-C₄H₁₀. However, the model must be modified to accurately describe the methane data by accounting for the decrease in methane diffusivity due to the presence of n-C₄H₁₀ (i.e., blocking). Even though the penetrant concentrations are rather significant at some of the conditions considered, no evidence is observed for phenomena such as multicomponent coupling that would require a model more complex than the binary form of Fick's law. That is, Fick's law in its simplest form adequately describes the experimental data.     

Composite membrane of poly(1-(trimethylsilyl)-propyne) as a potential oxygen separation membrane

A special affinity of poly(1-(trimethylsilyl)-1-propyne), PMSP, toward other materials has been investigated. The oxygen permeability of PMSP thin membranes decreased with time, depending on the environmental conditions in which the membrane was kept. It was observed that PMSP has high gas solubility coefficients compared with other polymers from sorption measurements. From the results the deterioration of the membrane was explained essentially in terms of absorbance of some additives to PMSP membrane having a certain morphology. In composite membranes produced from such mixtures a generation of an interface layer between PMSP and an additive was demonstrated using a bilayered model membrane consisting of PMSP and porous polysulphone membrane. A three-layered composite membrane (silicone-copolymer/PMSP/polysulphone) designed on the basis of the results was shown to have high oxygen permeability, high separation factor and high durability.     

Shear thickening behavior of dilute poly(diallyl dimethyl ammonium chloride) aqueous solutions

Using dynamic light scattering (DLS) and capillary dynamic viscoelasticity (DVE) analyzer, we investigated dilute (0.5 mg/ml) poly(diallyl dimethyl ammonium chloride) (PDADMAC) aqueous solution properties for three different molecular weights of PDADMACs mixed with various concentrations of NaCl. The dependence of PDADMAC molecular chain conformations in aqueous solutions on polymer molecular weight and NaCl concentration were studied. By analyzing dynamic shear viscosity η′(ω), viscoelastic relaxation times t_r, and shear rate at tube wall ?_a(ω) of PDADMAC aqueous solutions in oscillatory flows, we proposed that polymer chain conformations varied with increasing shear frequency ω via the following steps: intra-polymer associations, dissociation of intra-polymer associations, stretching of polymer chains, inter-polymer aggregations, and dissociations of inter-polymer aggregations. The intra-polymer associations lowered the n′ exponent of storage modulus G′(ω) (G′(ω) ∼ ω^n′) with n′ < 2, and the polymer chain stretching and inter-polymer aggregations caused shear thickening (i.e. upturn of η′(ω)) of PDADMAC aqueous solutions. The behaviors of the lowering of n′ exponent with n′ < 2 and the shear thickening were favored by increasing ionic strength of solutions. By comparing η′(ω) data with DLS hydrodynamic radii (R_h) data, we also confirmed the possibility of inter-polymer aggregations in dilute solutions when polymer chains were stretched in oscillatory flows.