Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymers prepared by living carbocationic polymerization and ionomers therefrom were analyzed using dynamic mechanical analysis (DMA) and tensile testing. The study encompassed five block copolymer samples, each with a PIE center block of approximately 52,000 g/mol, and PS weight fractions ranging from 0.127 to 0.337. Ionomers were prepared from two of these materials by lightly sulfonating the PS outer blocks. Sulfonation levels varied from 1.7 to 4.7 mol% and the sodium and potassium neutralized forms were compared to the parent block copolymers. DMA of the block copolymer films indicated the existence of a third phase attributed to PIE chains near the PS domain interface which experience reduced mobility due to their firm attachment to the hard PS domain. The relative amount of this phase decreased in samples with larger PS blocks, while the temperature of the associated transition increased. Tensile testing showed increased tensile strength but decreased elongation at break with larger PS blocks. DMA of the ionomers indicated improved dynamic modulus at temperatures above 90 degreesC. Tensile testing of the ionomers indicated slight improvements in tensile strength with little loss in elongation at break. (C) 2000 Elsevier Science Ltd. All rights reserved.