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Keywords:

  • clathrate;
  • crystal structures;
  • ortho-dichlorobenzene;
  • polystyrene;
  • syndiotactic

Abstract

Thumbnail image of graphical abstract

Schematic representation of the arrangement of the chains according to the orthorhombic (solid line) and to the monoclinic (dotted line) unit cells proposed for the crystal structure of the clathrate form of s-PS containing o-DCB.

Summary: The crystal structure of the clathrate form of syndiotactic polystyrene containing ortho-dichlorobenzene has been determined, and compared with those of the other crystalline clathrate structures of s-PS already known. This guest molecule, characterized by a quite different shape and volume from the others already described, gives rise to the only example of clathrate form of s-PS presenting a statistical orthorhombic symmetry (cell constants a = 17.5 Å, b = 22.9 Å, c = 7.8 Å and space group Ccmb). This symmetry is generated by the random coexistence in the crystals of domains, with the same monoclinic P21/a symmetry found for the other clathrate forms, that can be realized by two different but energetically equivalent packings of the chains. The unit cell constants are a = 17.5 Å, b = 14.4 Å, c = 7.8 Å and γ = 127.4°. The shape of the guest molecule produces a significant modification of the cavities (if compared to δ form) realized mainly through a shift of the ac layers of chains delimiting the cavities along the a axis direction that turns out in the highest γ value found for these kinds of structures.