Structure and properties of the mesophase of syndiotactic polystyrene V: preferential sorption performance of the mesophase for aromatic hydrocarbons

Toluene and benzene sorption properties of the syndiotactic polystyrene (sPS) membrane containing the mesophase structure were investigated in order to understand the preferential sorption properties of the mesophase. The mesophase was prepared from the sPS membrane having the clathrate type crystal, δ form complex with toluene as a guest molecule and then removing the guest molecule at 170 °C for 1 h. In vapor sorption study, the sorption isotherms showed sigmoid type and were concave toward activity axis at low activity region, although the both benzene and toluene are good solvents for polystyrene. The sorption behaviors of the sPS mesophase membrane from the pure solutions of toluene/methanol or benzene/methanol were explained in terms of Langmuir sorption type and the saturated sorption amounts of benzene and toluene were almost same. These findings suggested the presence of relatively strong sorption site for toluene and benzene, indicating the existence of molecular cavity of similar shape and size to a toluene molecule in the sPS mesophase. However, in the case of mixed solution of toluene, benzene, and methanol, the sPS mesophase membrane showed clearly the preferential sorption of toluene comparing to benzene. The sorption amount of toluene was about five times higher than that of benzene. From the present study, it could be concluded that the molecular cavity of the sPS mesophase has a preferential sorption capability for toluene. Furthermore, these results exhibited that fine separation and elimination of some organic molecules with slightly different molecular size and/or shapes might be possible.