Supercritical CO2 conditioning promotes γ-crystal formation in amorphous syndiotactic polystyrene during further heating

The conditioning history of amorphous syndiotactic polystyrene (sPS) in mild supercritical CO2 (scCO2) changes significantly the thermal behavior and crystal phase transformation of sPS in further thermal treatment by inducing the formation of helical segments. The results of differential scanning calorimetry and temperature-dependent Fourier transform infrared spectroscopy show that polymer chains are preferred to arrange into crystalline γ-form with helical conformation in the conditioned sPS by heating under ambient pressure. Thus, mixed γ-form and α-form with all-trans conformation are formed in the amorphous sPS after conditioning instead of α-form in the amorphous sPS without conditioning, and the formation of α-form is totally suppressed in the conditioned sPS having only γ-form of small degree of crystallinity.