A gravimetric sorption apparatus is set up to measure solubilities and diffusivities in polymer−solvent systems, especially designed for measurements at low pressures and in glassy polymers. Interval sorption experiments are performed for the system toluene−polystyrene (PS) above and below the glass transition. Sorption isotherms (VLE) are obtained and diffusion coefficients are calculated in the Fickian diffusion region. Below the glass transition, non-Fickian sorption kinetics (sigmoid, two-stage) are observed.

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