Characterization of Syndiotactic Polystyrene Physical Gels Formed in Toluene/Chloroform Mixed Solvents

A syndiotactic-rich polystyrene (sPS) in a mixed solvent of toluene and chloroform converted to a thermoreversible gel from its semi-dilute solution. According to measurements of gel-melting temperatures, toluene behaved as a relatively poor solvent for sPS, while chloroform was a relatively good solvent. The critical gelation concentration C*, i.e., the minimum concentration for gel formation became higher with increasing the volume fraction of chloroform X-chloro. In order to characterize the sPS physical gel formed in a mixed solvent, the junction length zeta and rho sequence were estimated as a function of the volume fraction X-chloro using the thermodynamic theory derived by Tanaka and Stockmayer. The theory suggested that the junction size S (zeta x rho) was ca. 320-450 for sPS/toluene gel, 150-200 for sPS/chloroform gel, and the junction size S decreased with increasing X-chloro. In other words, the junction size S became larger when a gel was formed in a poor solvent. FT-IR spectral data suggest that sPS chain adopted the T(2)G(2) conformation in the mixed solvents of toluene and chloroform, and then gelation occurred. FE-SEM images show a fibrillar morphology of the sPS gel.