STRUCTURAL-CHANGES INDUCED BY THERMAL TREATMENTS ON EMPTIED AND FILLED CLATHRATES OF SYNDIOTACTIC POLYSTYRENE

The solvent molecules included in the clathrates (delta-form) of syndi otactic polystyrene (s-PS) are removed by suitable extraction procedur es. An emptied delta-form is produced which is different from the know n gamma-form obtained by heating. The structural changes induced by th ermal treatments on emptied and filled clathrates of s-PS, have been f ollowed by thermogravimetry, X-ray diffraction analysis, differential scanning calorimetry and Fourier-transform infrared spectroscopy. It i s shown that, under suitable conditions, the emptied clathrates can be transformed into a mesomorphic form, which retains the chains in the helical conformation. This ''helical'' mesomorphic form, different fro m the previously known ''planar'' mesomorphic form, crystallizes by th ermal treatments into the ''helical'' crystalline gamma-form.