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In this work, the static sorption technique has been extended to measure the diffusivity as well as the solubility of gases in polymers at elevated pressures. This has been accomplished by operating several static sorption capsules in parallel in order to measure the fractional mass uptake of a gas by a polymer with time. Equilibrium and diffusion data of propylene and ethylene in atactic polypropylene have been measured in the temperature range of 25−70 °C. The group-contribution, lattice-fluid equation of state (GCLF-EoS) was used to correlate the equilibria data with a single value of the binary interaction parameter for each of the systems. The Vrentas−Duda free-volume theory was employed to describe the propylene and ethylene diffusivity data. The chemical potential gradient used in the free-volume correlation of the diffusivity data was obtained from the GCLF-EoS.

Two new volumetric sorption techniques have been developed to measure thermodynamic and mass-transport properties in polymer−solvent systems at elevated pressures. They are both variations of the pressure-decay technique and differ in how the initial gas density is measured. In the first and simplest variation, the initial density is measured by extrapolation of the mass uptake curve from the region of usable data to the experiment starting time. In the second variation, the initial density is measured gravimetrically using a small titanium capsule. Concern has been voiced as to whether the extrapolation-type experiment is capable of measuring the initial gas density as accurately as a dual-chamber technique. To evaluate the accuracy of the extrapolation technique, solubility and diffusion data were collected for carbon dioxide, ethylene, and nitrogen in low-density polyethylene (LDPE) using both methods. The results indicate that the simpler extrapolation method produces the same diffusivity and solubility results as the more complicated dual-chamber method.

A new experimental technique has been developed to measure the solubility of gases and vapors in polymers and other sorbents at elevated pressures. The technique involves measuring the total weight of a vessel containing the sorbent material pressurized with a vapor, assessing the amount of vapor in the headspace of the vessel with an appropriate equation of state, and evaluating the total amount of vapor in (on) the sorbent material by the difference. Adsorption isotherms for carbon dioxide and nitrogen on an activated carbon were measured with the static sorption technique. These data were found to agree well with data taken with a standard volumetric technique. Sorption data obtained using this method for carbon dioxide in poly(vinyl acetate) and propylene in poly(propylene) compare well with data acquired by established techniques. The group-contribution lattice-fluid theory equation of state was used to predict solubility in these systems, and the Panayiotou−Vera equation of state was applied to correlate the solubility data.

The inverse gas chromatography method was used for the investigation of the partition and diffusion coefficients of polysulfone and polyetherimide with NMP, γ-butyrolactone, DMSO, acetic acid, propionic acid, THF, and water over a range of temperature from 200 to 270 °C. The weight-fraction infinite-dilution activity coefficients for the solvents, the Flory−Huggins interaction parameters, and the solubility parameters of the polymers are reported.

Diffusion and equilibrium coefficients in ternary polymer−solvent−solvent systems were measured using inverse gas chromatography (IGC). The technique provides a new approach to probe diffusion in ternary polymer−solvent−solvent systems. The self-diffusion coefficients of a solvent in a mixture of a polymer and a second solvent were measured. Experiments were performed for the diffusion of toluene and methanol in the poly(vinyl acetate) (PVAC)−toluene−methanol system and for diffusion of toluene and heptane in the polybutadiene (PDB)−toluene−heptane system. Predictions of diffusivities in ternary systems based on the free-volume theory are also critically analyzed and compared with the experimental data.