Crystal forms in cold-crystallized syndiotactic polystyrene

Unique thermal treatments were performed and differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to characterize the dominating crystal form(s) being developed in cold-crystallized syndiotactic polystyrene (s-PS) in comparison with melt-crystallized polystyrene. The DSC results revealed that there are three (or fewer depending on the temperature of melt-crystallization) sharp melting peaks (Peak-1, -2, and -3) for the melt-crystallized s-PS samples, but only one peak (broad-based) for the cold-crystallized s-PS (when scanned at 10°C/min). The X-ray result suggested that cold-crystallization at higher than 200°C (200 approx. 250°C) produced only α-type crystal (or majority). This is in distinct contrast with melt-crystallization, which produced a combination of α-type (Peak-2 and Peak-3) and β-type (Peak-1) crystals at lower temperature (240°C or lower), or majority of β-type if at temperatures higher than 260°C.