Crystal structure of the clathrate form of syndiotactic poly(p-methylstyrene) containing o-dichlorobenzene

The crystal structure of the clathrate form of syndiotactic poly(p-methylstyrene) (s-PPMS) containing o-dichlorobenzene (o-DCB) is presented. The structure is characterized by polymer chains in s(2/1)2 helical conformation and o-dichlorobenzene molecules packed in a monoclinic unit cell with axes a = 23.4 Å, b = 11.8 Å, c = 7.7 Å, and γ = 115°, according to the space group P21/a. The calculated crystalline density is 1.07 g/cm3 for two polymer chains (eight monomer units) and two o-DCB molecules included in the unit cell. The o-DCB molecules occupy cavities delimited by the phenyl rings of two enantiomorphic polymer chains. A disorder in the positioning of the o-DCB molecules inside the cavity is present. A comparison with the crystal structure of the clathrate form of s-PPMS containing tetrahydrofuran is presented. Remarkable differences were found, confirming the previous hypothesis that two different types of crystal structures (α and β class) are presented by the clathrate forms of s-PPMS depending on the guest molecule