ON THE CRYSTAL-STRUCTURE OF THE ORTHORHOMBIC FORM OF SYNDIOTACTIC POLYSTYRENE

The crystallization conditions for the preparation of different modifications of the orthorhombic form (beta-form) of syndiotactic polystyrene (s-PS) are described. Crystallizing from the melt produces the beta' or alpha-form depending on the cooling rate. Crystallization by casting a film from omicron-dichlorobenze solutions produces clathrate structures (delta-form) at low temperatures (T < 130-degrees-C) and ordered beta" modifications at higher temperatures. In particular, modification very close to the beta" limiting one are obtained in the temperature range 130-140-degrees-C. Recrystallization of the beta-form has been detected by differential scanning calorimetry and studied by X-ray diffraction analysis of the annealed samples. These studies indicate that the recrystallization of the beta' form in the melting region does not involve a beta' to beta" transition, but only morphological changes. Models for the chain packing of the limiting modifications of the beta-form are suggested, by quantitative comparisons of the X-ray diffraction intensities and calculated structure factors.