Structural-changes Induced By Thermal Treatments On Emptied and Filled Clathrates of Syndiotactic Polystyrene

The solvent molecules included in the clathrates (delta-form) of syndiotactic polystyrene (s-PS) are removed by suitable extraction procedures. An emptied delta-form is produced which is different from the known gamma-form obtained by heating. The structural changes induced by thermal treatments on emptied and filled clathrates of s-PS, have been followed by thermogravimetry, X-ray diffraction analysis, differential scanning calorimetry and Fourier-transform infrared spectroscopy. It is 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 from the previously known ''planar'' mesomorphic form, crystallizes by thermal treatments into the ''helical'' crystalline gamma-form.