Regeneration of nanoporous crystalline syndiotactic polystyrene by supercritical CO2

Guest desorption procedures for s-PS clathrate samples, leading to formatio n and regeneration of the nanoporous delta phase, are compared. An extracti on procedure, based on supercritical carbon dioxide, allows an easy and fas t recovery of the guest molecules operating under relatively mild condition s (90-200 bar, 40 degrees C) and generates a completely empty delta form, a lso starting from the most stable s-PS clathrate forms. In agreement with a previously proposed crystal structure of the nanoporous delta form, X-ray diffraction patterns of delta form powders obtained by this procedure do no t show the peak, which is reduced but still apparent in samples extracted w ith previous procedures based on boiling solvents. (C) 1999 John Wiley & So ns, Inc.