Viscoelastic and Transport Properties of Sulfonated PS-PIB-PS Block Copolymers

摘要

Morphology, viscoelastic, and transport properties of the sulfonated polystyrene-polyisob utylene-polystyrene (PS-PIB-PS) block copolymer were investigated with respect to sulfonation level and counter-ion substitution. Dynamic mechanical analysis (DMA) was used to examine the dynamic storage modulus E' and dynamic loss modulus E', as they relate to changes in sulfonation levels. Small-angle x-ray scattering (SAXS) results confirmed that at a certain percent of sulfonation, a phase transition occurs from hexagonally packed cylinders to lamellar structure due to swelling of the styrene domains caused by the higher sulfonation levels. Transport measurements using Fourier Transfer Infrared Spectrometer (FTIR) confirm that the sulfonation level directly dictates the transport rate of small molecules (alcohol and water) through the PS-PIB-PS triblock copolymer membrane. Faster water transport can be achieved by incorporating more sulfonic acid groups throughout the polymer backbone. In addition, infrared (IR) data clearly identifies molecular interactions between the solvating alcohol molecules and the PS-PIB-PS triblock copolymer. The observed properties suggest that these ion-containing block copolymers are worthy of further development as barrier membranes to be incorporated into chemical protective clothing.