Stability of crystal forms of syndiotactic polystyrene correlated with their formation in different media having different solubility parameters

The formation of crystal forms of syndiotactic polystyrene having different stability was investigated in different media having different solubility parameters with the help of wide-angle X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry. The starting sample was the γ form of syndiotactic polystyrene, and the solubility parameter of the media was adjusted by changing the temperature, pressure, cosolvent of supercritical carbon dioxide. With increasing solubility parameter, the stability of the resultant crystal forms was increased in the order from γ through α″ and β′ to β″ form.