Equilibrium melting temperature of syndiotactic polypropylene

Isothermal crystallizations from the melt of samples of syndiotactic polypropylene having different degrees of syndiotacticity have been performed. The thermal behavior and the structural features of the melt-crystallized samples have been analyzed by differential scanning calorimetry and X-ray diffraction. According to this analysis, less stereoregular samples, crystallized in disordered modifications of form I with defects implying local arrangements of the chains such as in form II, present recrystallization phenomena during heating. For most stereoregular samples relevant recrystallization phenomena are absent. Extrapolation to the equilibrium melting temperature of syndiotactic polypropylene was attempted by using the Hoffmann-Weeks method, taking into account the occurrence of recrystallization and superheating phenomena. A value of nearly 182 degrees C has been obtained for the equilibrium melting temperature of the fully syndiotactic polypropylene