Microstructure of Ionomers based on Sulfonated Block Copolymers of Polystyrene and Poly(ethylene-alt-propylene)

Sudhir Mani
Robert Weiss, The University of Akron
C. E. Williams
S. F. Hahn

Abstract

Block copolymer ionomers were prepared by lightly sulfonating the polystyrene (PS) blocks of diblock and triblock copolymers of PS and poly(ethylene-alt-propylene) (PEP), followed by neutralization of the sulfonic acid groups with either sodium or zinc. The block copolymers contained between 10 and 50 wt % PS, and as the PS content increased, the mesophase texture varied from PS spheres to hexagonalclose-packed (hcp) PS cylinders to alternating PS and PEP lamellae. The sulfonation level was varied from 1 to 17 mol % of the styrene repeat units, which provided a range of functionalization (NS) of between 2 and 9 sulfonate groups per molecule. The microstructure was analyzed by small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). An ion-rich microphase formed within the PS microdomains, and that hindered the development of a well-ordered block texture. Sulfonation of a diblock copolymer containing ca. 20 wt % PS resulted in a transition of the block microphase texture from a hcp to lamellar. The order-to-disorder transition temperature, TODT, of the block copolymer was relatively insensitive to the choice of the cation, and TODT increased as NS increased.