To investigate the preferential complexing behavior of isomeric xylenes, syndiotactic polystyrene (sPS) membranes are prepared using varying compositions of p- and m-xylene. Complex formation between sPS and the xylenes was studied by means of thermogravimetric and FT-IR analyses to determine the exact amounts of solvent molecules present per styrene repeating unit. A preferential complexing ability of p-xylene was revealed one to its favorable interaction with sPS.