Direct Formation of γ Form Crystal of Syndiotactic Polystyrene from Amorphous State in Supercritical CO₂

The crystallization behavior of amorphous syndiotactic polystyrene (sPS) in supercritical CO 2 was investigated in detail by using wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The pure γ form crystal was obtained directly after treating amorphous sPS in supercritical CO 2 in a range from 8 to 20 MPa and from 35 to 100 °C. This transformation in supercritical CO 2 was accelerated by increasing temperature. Supercritical CO 2 provided a moderate condition to crystallize the amorphous into the γ form, while liquid CO 2 could not induce the γ form even at the pressure as high as 20 MPa.