The syndiotactic polystyrene (sPS) 6 form was crystallized from mixtures with different compositions of p-chlorotoluene-chlorobenzene (p-CT-CB) and p-chlorotoluene-1,1,2-trichloroethane (p-CT-TCE). The presence of the delta form and TTGG helical conformation was confirmed by Fourier transform infrared and wide-angle X-ray diffraction (WAXD) analyses. In sPS/p-CT-CB and sPS/p-CT-TCE delta-form membranes, the relative absorbance (RA) of the p-chlorotoluene (p-CT) solvent peak was very high even at very low concentrations of p-CT in comparison with the RA of higher concentrations of chlorobenzene (CB) or 1,1,2-trichloroethane (TCE) in the mixtures. However, the RAs of both CB and TCE solvent peaks decreased with decreasing concentrations of CB and TCE in the mixtures. A negligible decrease in the RA of the TTGG helical content was observed with a decreasing concentration of CB or TCE. The WAXD results showed that the 2 theta peak positions of the [010] and [(2) over bar 10] planes of the sPS/p-CT-CB and sPS/p-CT-TCE delta-form membranes appeared in the same position and were almost equal to those of the sPS-p-CT delta-form membrane. The mesophases of the sPS-p-CT [p-CT (A-M)] and sPS-TCE [TCE (A-M)] membranes were used for the sorption studies with different concentrations of various solvents. The sorption amount of aromatic solvents by both p-CT (A-M) and TCE (A-M) mesophase membranes was higher than that of aliphatic solvents, regardless of the size, shape, and nature of the molecular cavity. The 20 peak of the [010] plane of the sPS membranes slowly approached the original delta-form value when the sPS mesophase membranes were immersed in various solvents of different concentrations for 48 h. The shifting of the 20 peak of the [010] plane to the original delta form depended on the nature and concentration of the immersion solvents. (c) 2005 Wiley Periodicals, Inc.