Sorption of methanol/MTBE and diffusion of methanol in 6FDA-ODA polyimide

Kamaruddin, H.D.; Koros, William J.

doi:10.1002/1099-0488(20000901)38:17<2154::aid-polb60>3.0.co;2-8

Cited by 14 publications

(6 citation statements)

References 21 publications

(10 reference statements)

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“…From Table 2 it emerges that the diffusivity values estimated from gravimetric and FTIR data are in excellent agreement with each other; moreover, they also compare well with a previous literature report (Kamaruddin and Koros, 2000 ). The plot of D vs. C , constructed considering the average between the spectroscopic and the gravimetric values of , reveals a linear relationship in the concentration range of interest.…”

Section: Resultssupporting

confidence: 88%

Diffusion and molecular interactions in a methanol/polyimide system probed by coupling time-resolved FTIR spectroscopy with gravimetric measurements

Musto¹,

Galizia²,

Manna³

et al. 2014

Front. Chem.

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In this contribution the diffusion of methanol in a commercial polyimide (PMDA-ODA) is studied by coupling gravimetric measurements with in-situ, time-resolved FTIR spectroscopy. The spectroscopic data have been treated with two complementary techniques, i.e., difference spectroscopy (DS) and least-squares curve fitting (LSCF). These approaches provided information about the overall diffusivity, the nature of the molecular interactions among the system components and the dynamics of the various molecular species. Additional spectroscopic measurements on thin film samples (about 2 μm) allowed us to identify the interaction site on the polymer backbone and to propose likely structures for the H-bonding aggregates. Molar absorptivity values from a previous literature report allowed us to estimate the population of first-shell and second-shell layers of methanol in the polymer matrix. In terms of diffusion kinetics, the gravimetric and spectroscopic estimates of the diffusion coefficients were found to be in good agreement with each other and with previous literature reports. A Fickian behavior was observed throughout, with diffusivity values markedly affected by the total concentration of sorbed methanol.

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Section: Resultssupporting

confidence: 88%

Diffusion and molecular interactions in a methanol/polyimide system probed by coupling time-resolved FTIR spectroscopy with gravimetric measurements

Musto¹,

Galizia²,

Manna³

et al. 2014

Front. Chem.

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“…Negative deviations (i.e., a reduction) from the ideal responseknown as clusteringcan occur in systems where the penetrants exhibit strong intermolecular hydrogen bonding or other strong intermolecular interactions. 26 In clustering systems, the penetrants preferentially interact with penetrants already sorbed in the polymer, and additional activation energy is required to make the diffusive jumps through the membrane. In essence, clustering penetrants must overcome intermolecular attractions and the activation energy necessary to move into a free volume element.…”

Section: = D D P Qmentioning

confidence: 99%

Effect of Nonsolvent Treatments on the Microstructure of PIM-1

Jue¹,

McKay²,

McCool

et al. 2015

Macromolecules

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The combination of appreciable swelling at unit activity sorption, weak polymer−penetrant interactions, and high vapor pressure allows methanol to be effective at restoring free volume to glassy polymers compared to similar organics. Polymers of intrinsic microporosity (PIMs) are often soaked in methanol and then dried before permeation and sorption analysis to improve reproducibility and eliminate processing history. Here, surface area, pore volume, thermogravimetric analysis, sorption, and diffusion data are used to demonstrate the effectiveness of methanol treatments at removing nonsolvent-induced changes to PIM-1, specifically using dimethylformamide (DMF) as a candidate conditioning molecule. DMF clearly plasticizes PIM-1 while methanol does not. In addition, diethyl ether-conditioned PIM-1 showed marked increases in surface area and free volume higher than that found from methanol conditioning. Strongly plasticizing nonsolvents with low vapor pressures can be used as conditioning agents that promote polymer relaxations, accelerate chain packing, and remove additional nonequilibrium free volume. ■ INTRODUCTIONMicroporous polymeric materials have attracted significant interest for a variety of potential molecular separation applications due to their combination of synthetic tunability and unusually facile processability in the case of linear polymers. The most well-studied linear microporous polymer, PIM-1 (polymer of intrinsic microporosity 1, shown in Figure 1), has a characteristic spirocenter between cyclopentane rings that hinders efficient chain packing. These 90°bends in the polymer chain impart "intrinsic" microporosity and high free volume that is uncommon for amorphous, solution processable polymers. As a result, PIM materials have high permeabilities with moderate selectivities that helped redefine the Robeson upper bounds for many of the commonly studied gas pairs. 1 As polymers are cooled below their glass transition temperature (T g ), they retain excess free volume between the chains due to nonequilibrium packing defects. The concentration and nature of these free volume elements have been successfully used to describe the sorption, diffusion, and permeation of guest molecules through glassy polymers. 2−4 However, high free volume glassy polymers such as PIMs are particularly susceptible to aging and conditioningthe loss of permeability and concomitant gain in selectivity with time. After membrane formation, PIM-1 naturally begins to lose some of its excess free volume due to slow relaxations of the polymer chains toward their equilibrium packing. Lau et al. have shown that the CO 2 permeability of PIM-1 decreases by 62% over a period of eight months storage at ambient conditions. 5 However, not all of the free volume was lost, and there remained intrinsic microporosity to the polymers even after a year under ambient storage. 6 Moreover, PIMs are unusual linear polymers because they do not exhibit a measurable T g before decomposition. 7 As a result, near-T g annealing techniques used to alt...

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“…To start the experiment, the vacuum valve (valve 2) was shut off, and the vapor was introduced to the system by monitoring the system pressure as valve 3 was opened and closed. The amount of vapor sorbed at the equilibrium pressure was correlated, using Hooke's law, to the extension of the spring [31], which was recorded using a cathetometer.…”

Section: Vapor Sorptionmentioning

confidence: 99%