Metastability studies of syndiotactic polystyrene polymorphism

Polymorphic behavior (i.e., the development of alpha and beta forms) of mel t-crystallized syndiotactic polystyrene, sPS, has been studied by structure analysis of FTIR (Fourier transform infrared spectroscopy), WAXD (wide-ang le X-ray diffraction), and ED (electron diffraction) as well as thermal ana lysis of DSC (differential scanning calorimetry). Significant factors that influence the formation of polymorphism were examined and described. Isolat ed alpha crystals and beta crystals of sPS crystallized at different crysta llization temperatures from the melt have been obtained. The equilibrium me lting temperatures, T-m(o), of both forms were determined by using linear H offman-Weeks (H-W) extrapolation and nonlinear H-W treatment. The T-m(o) (i .e., structural metastability) of beta form in sPS was found to be higher t han that of alpha form. The occurrence of phase stability inversion with la mellar size (i.e., morphological metastability) in sPS was recognized. Tran sformations from alpha to beta phase in the stage of crystal growth or in t he heating scanning process have been evidenced. The interlinkage of struct ural metastability and morphological metastability in sPS polymorphism was examined. The behavior of phase transformation has been successfully interp reted in terms of the stability inversion phase diagram. The formation of t he alpha form is indeed a kinetic result of crystallization.