Phase Equilibria and Selectivity of Sulfonated Poly (styrene-isobutylene-styrene) for Specialty Separations

Poly (styrene-isobutylene-styrene) (SIBS) of 22.5% polystyrene weight fraction and 65k number-average molecular weight (Mn) was sulfonated to very high ion exchange capacity (IEC). The sulfonated polymers were cross-linked with several +2 cations (Mg+2, Ca+2, Ba+2). The phase equilibria and selectivity of the resulting membranes were investigated for various energy-efficient specialty separation applications (e.g., water purification). Water swelling significantly increased (30%-200%) as a function of sulfonation (27-100%), but was drastically reduced with the cation substitution. FT-IR results show the interaction of the metal with asymmetric oxygen of the sulfonic group, creating a metal-ion complex that influences phase-equilibria and selectivity results. Acetone/Water effective permeabilities measurements provided extremely selectivities, making a membranes separation approach a very efficient, low-cost alternative for separation.