TRANSPORT-PROPERTIES OF DICHLOROMETHANE IN GLASSY-POLYMERS .3. DRAWN ATACTIC POLYSTYRENE FILMS

Transport properties of dichloromethane vapor were measured in atactic polystyrene (aPS) samples, oriented by drawing at 95-degrees-C to different draw ratios (3 and 4.5) and analyzed after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on vapor activity: In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration-dependent diffusion and by the appearance of non-Fickian sorption curves; and in Zone III, the strong interaction polymer-solvent induces disorientation of the samples. The diffusional behavior is very similar to that of undrawn aPS, and also the extrapolated parameters coincide, showing that in the case of amorphous polymers, the drawing does not influence the diffusion. The aging, both at room temperature and at 70-degrees-C, decreases the diffusion parameters and leads to the appearance of anomalous sorption curves. The sorption curve as a function of vapor activity does not show any difference for the fresh and aged at room temperature-oriented samples; furthermore, it coincides with that of aPS. At variance, the oriented samples aged at 70-degrees-C show a lower sorption at low activity. As in the case of aPS, the presence of ordered domains, impermeable to the penetrant at low activity, was suggested for the oriented samples.