Poly(styrene-b-isobutylene-b-styrene) block copolymers produced by living cationic polymerization. Part III. Dynamic mechanical and tensile properties of block copolymers and ionomers therefrom

Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymers prepared by living carbocationic polymerization and ionomers therefrom were analyze d using dynamic mechanical analysis (DMA) and tensile testing. The study en compassed five block copolymer samples, each with a PIE center block of app roximately 52,000 g/mol, and PS weight fractions ranging from 0.127 to 0.33 7. Ionomers were prepared from two of these materials by lightly sulfonatin g the PS outer blocks. Sulfonation levels varied from 1.7 to 4.7 mol% and t he 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 exp erience reduced mobility due to their firm attachment to the hard PS domain . The relative amount of this phase decreased in samples with larger PS blo cks, 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 modu lus at temperatures above 90 degreesC. Tensile testing of the ionomers indi cated slight improvements in tensile strength with little loss in elongatio n at break. (C) 2000 Elsevier Science Ltd. All rights reserved.