Shape and volume of cavities in thermoplastic molecular sieves based on syndiotactic polystyrene

The empty space in different crystalline and clathrate phases of syndiotact ic polystyrene (s-PS) is evaluated by a numerical procedure. It is shown th at the delta form is nanoporous and includes two identical cavities per uni t cell, whose shape and volume are characterized. As a consequence of clath ration, the unit cell of the delta form is enlarged and the cavity is able to include molecules definitely larger than its starting size. Sorption exp eriments of nitrogen at 77 K for s-PS powders in different crystalline form s are also presented. These can be interpreted by inclusion of three nitrog en molecules per cavity of the delta crystalline phase and hence give an in dependent estimate of its volume.