Crystal structures of syndiotactic poly(p-methylstyrene) clathrates with two guest molecules having very similar shape and volume

In the present paper we report on the clathrate structures of syndiotactic poly(p-m ethyl styrene) (s-PPMS) containing chlorobenzene (cell constants: a = 23.5 angstrom, b = 12.0 angstrom, c = 7.9 angstrom and gamma = 112.4 degrees; space group: P2(1)/a) and toluene (cell constants: a = 19.5 angstrom, b = 13.5 angstrom, c = 7.9 angstrom and gamma = 90 degrees; space group: P2(1)). Despite the extreme similarity between the shape and volume of these two molecules, they give rise to completely different clathrate structures, the first belonging to ot class, the second belonging to class. Moreover the clathrate form containing chlorobenzene represent the first case in which a ot class clathrate form of s-PPMS contains two guest molecules in each cavity while the crystal structure here proposed for the s-PPMS/toluene clathrate represents a new example of chiral crystalline phase in which the polymer helices assume all the same chirality in the lattice. These results underline the fact that the choice of a particular structural organization in the process of clathrates' formation of s-PPMS is not easily referable only to steric effects but seems to be dependant even on the chemical structure of the guest molecules. A comparison with syndiotactic polystyrene is also done. (C) 2007 Published by Elsevier Ltd.