BLOCK COPOLYMER IONOMERS .2. VISCOELASTIC AND MECHANICAL-PROPERTIES OF SULFONATED POLY(STYRENE-ETHYLENE BUTYLENE-STYRENE)

Ionomers prepared from a sulphonated poly(styrene-(ethylene-co-butylene)-styrene) triblock copolymer possessed a unique three-phase microstructure that consisted of 3-4 nm ionic domains within 20-30 nm polystyrene domains dispersed in a rubbery continuous phase. The ionic network resulted in an increase of the glass transition temperature, T(g), of the polystyrene-rich phase and the development of a new plateau region in the dynamic modulus above this T(g). The plateau modulus due to the block copolymer microstructure, i.e. the modulus between the rubbery block and polystyrene block T(g)s, decreased for the ionomers. These effects were accentuated by increasing the sulphonation level. Room temperature tensile properties were unaffected by sulphonating the block copolymer, but significant improvements were realized in the high temperature (70-200-degrees-C) tensile modulus, elongation and ultimate strength. The zinc salts exhibited the best combination of good processability and high temperature tensile properties. The ionomers were more hygroscopic than the unmodified block copolymer, but the reduction in tensile properties of saturated samples was generally < 20% of those of the dry ionomer.