Structural study of syndiotactic polystyrene: 1. Polymorphism

The features of the crystallization of syndiotactic polystyrene were investigated by X-ray diffraction, differential thermal analysis, thermogravimetry and density measurements. This polymer exhibits polymorphism: there are principally four distinct crystalline phases. Melt-crystallization yields a planar zigzag form. As-cast samples from solutions with a variety of solvents are molecular compounds with the solvents used, in which the polymer chains assume a twofold helical conformation of type ( TTGG ) 2 . On annealing the molecular compounds at moderate temperatures below ∼130°C, they are transformed in common, by removal of the solvent molecules, to a ( TTGG ) 2 twofold helical form free from solvents. On annealing at higher temperatures, the helical form is transformed to a planar zigzag form, which is distinguished from the melt-crystallized planar zigzag form in terms of the mode of molecular arrangement.