PTMSP Films Research Articles

Fouling of poly[-1-(trimethylsilyl)-1-propyne] membranes in pervaporative recovery of butanol from aqueous solutions and ABE fermentation broth

Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) dense films were evaluated for n-butanol recovery from aqueous solutions and acetone–butanol–ethanol (ABE) fermentation broth. Flux decline through PTMSP dense films due to polymer compaction under vacuum conditions, relaxation in alcohol and alcohol/water mixtures, and membrane contamination are discussed. Flux decline of a PTMSP film during pervaporation of 20 g/l BuOH/water mixture was fitted to the following function, y= At − b . PTMSP films change their geometry when exposed to alcohol and alcohol/water mixtures and then dried. As a result of the relaxation process, polymer film becomes thicker and denser, effecting membrane performance. PTMSP films that were treated with 70% iso-propanol/water show linear flux decline versus pervaporation time. Strong lipid adsorption seems to occur on the membrane surface when fermentation broth is used as a feed causing flux decline within short period of time.

Free-Volume Distribution of High Permeability Membrane Materials Probed by Positron Annihilation

Positron annihilation lifetime (PAL) spectroscopy was applied to measure free-volume size distribution in polymer samples with unusually long lifetimes: in dense films of poly(trimethylsilylpropyne) (PTMSP) and in porous membranes prepared from poly(phenylene oxide) (PPO). PAL data were treated by finite-term lifetime analysis (PATFIT program) and continuous lifetime analysis (CONTIN program). Lifetime distributions of positron annihilation in these samples consist of two positronium components: in the range 1−2 and 4−8 ns (PTMSP) and in the range 20−70 ns (porous PPO). In the case of PTMSP, the longer lifetimes correspond to continuous free-volume size distribution in the range R = 4.5−5.5 A. These radii are much larger than those characteristic for “normal” glassy polymers. A good agreement was obtained between the parameters of PAL distributions obtained by means of PATFIT and CONTIN programs in PTMSP and PPO dense films. An analysis of the CONTIN peak widths of free-volume size distribution in diffe...

Cross-linking of poly[1-(trimethylsilyl)-1-propyne] membranes using bis(aryl azides)

Cross-linkable poly[1-(trimethylsilyl)-1-propyne] (PTMSP) films were cast from toluene solutions containing PTMSP and either 4,4′-diazidobenzophenone or 4,4′-(hexafluoroisopropylidene)diphenyl azide. The composite films were clear and homogeneous and were cross-linked by UV irradiation at room temperature or thermal annealing at 180°C. Low levels of the bis(aryl azide) (1–5 wt %) were effective in rendering the films insoluble in toluene and THF, both good solvents for PTMSP. The process is simple and effective, and thus PTMSP can be readily converted to mechanically stable membranes with permeabilities and separation factors comparable or higher than those of poly(dimethylsiloxane). The films were characterized by measuring their density, their permeability toward O2 and N2, and their spectroscopic properties. Compared to PTMSP, films containing bis(aryl azide) cross-linkers had lower permeabilities and higher separation factors, consistent with a reduction in free volume. When the films were cross-linked photochemically, the permeabilities declined further and the separation factor increased. Films cross-linked thermally had permeabilities comparable to their PTMSP/azide precursors, and density and swelling measurements suggest that higher free volumes are obtained in thermally cross-linked films. All films stored in air suffered from a slow decline in permeability which may reflect slow surface oxidation of the films. When stored in vacuum, cross-linked films were stable and showed no loss in permeability, but the permeability of uncross-linked PTMSP films stored under the same conditions fell to 70% of their original value in 1 month. We attribute the permeability decline to densification accelerated by impurities and solvents. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 959–968, 1998

Molecular modelling of amorphous membrane polymers

New results of molecular modelling investigations on the transport of different small molecules in polyimides and polysiloxanes are discussed. The transition state Gusev-Suter Monte Carlo method reveals a reasonable coincidence between simulated and measured diffusivity and solubility values for the polyimides. A comparison between simulation data obtained for flexible chain polymers like poly(dimethyl siloxane) and polyimides shows that the lifetime of temporarily open channels is considerably longer for the stiff chain polymers than for the flexible chain polymers. This is probably a cause for the observed high rate of immediate back-jumps of permeating small molecules during diffusion processes in the polyimides. For amorphous poly(1-(trimethylsilyl)-1-propyne) (PTMSP), equilibrated packing models could be produced with a considerably higher density (1.22 g cm −3) than measured for respective polymer films. This indicates that the low density of the experimentally investigated PTMSP films (≈0.7–0.8 g cm −3) is not the intrinsic ‘equilibrium’ density but rather caused by the specific membrane preparation conditions. Low density PTMSP, unlike polyimides or polysiloxanes for example, seems to have a microporous morphology.

Effects of Physical Aging on Viscoelastic and Ultrasonic Properties of Poly[1-(trimethylsilyl)-1-propyne] Films

Effects of physical aging and heat-treatment on the viscoelastic and ultrasonic properties of poly[1-(trimethylsilyl)-1-propyne] (designated as PTMSP) films were examined. The loss modulus and loss tangent decreased with physical aging and heat-treatment, and the attenuation coefficient increased. However the storage modulus and ultrasonic velocity little changed with heat-treatment. This indicates that no conformational change occurs in backbone carbon with physical aging and heat-treatment, but aggregation of substituents may change. Accordingly, reduction in gas-permeability with physical aging is ascribable to the change in the aggregation of substituents. Furthermore, we found that casting solvents and catalysts affect viscoelastic and ultrasonic properties of PTMSP films as well as gas-permeability.

Substituted propyne polymers—part II. Effects of aging on the gas permeability properties of poly[1‐(trimethylsilyl)propyne] for gas separation membranes

AbstractPoly[1‐(trimethylsilyl)propyne] (PTMSP) is an unusual polyyne material which is optically clear, exhibits high solubility in nonpolar organic solvents, and good oxygen compatibility. By contrast, polyacetylene is black, insoluble, and is unstable in oxygen. The long term stability of PTMSP has been determined by a combination of thermal gravimetric analysis (TGA) and permeability test procedures under a number of different isothermal aging conditions. The use of commercial antioxidants at up to 2 weight percent improves the long term stability of PTMSP. The presence of the antioxidant has no effect on the surface fluorination of PTMSP. Testing of PTMSP films for over eight months shows no change in either permeability or selectivity in contrast to previously reported data.

Substituted propyne polymers

Poly[1-(trimethylsilyl) propyne] (PTMSP) has the highest gas permeability coefficient, P, of any known polymer. This high P is associated with a very low selectivity, α. We have found that contacting the surface of a PTMSP film with a dilute mixture of fluorine in nitrogen (∼ 0.1% F2) for 1–10 min results in chemical modification of the top 500–1000 Å of the surface into a highly selective composite material. The dilute F2 gas selectivity removes the trimethylsilyl groups and fluorinates the surface of the PTMSP. X-ray photoelectron spectroscopy (XPs) indicates that the surface fluorination process is effective at a F/C ratio of ⩾ 0.6 in the top 80 Å of surface material. The fluorinated layer separates the test penetrants on a basis of the Lennard-Jones diameter and can be considered to be size selective in separation characteristics. Typical a values of O2/N2 of 5.1 and for He/CH4 α values of 248 were achieved by this process for the fluorinated layer.