Novel block ionomers. III. Mechanical and rheological properties

Abstract

Select rheological (dynamic viscoelastic) and mechanical properties of novel block cationomers and an-ionomers and their blends have been investigated. The block ionomers were linear di- and triblocks, and symmetric three-arm stars comprising hydrophobic polyisobutylene (PIB) blocks attached to ionized poly(methacrylic acid) (PMAA-X+, where X+ = Na+, Zn2+) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA +I-) blocks. The specific structures investigated were the well-defined diblocks PIB-b-PMAA- and PIB-b-PDMAEMA+ and their blends, the triblocks PMAA--b-PIB-b-PMAA- and PD-MAEMA +-b-PB-b-PDMAEMA+ and their blends, and the three-arm star anionomer φ(PIB-b-PMAA-)3. For comparison, the properties of the precursor PIBs and unionized blocks have also been studied. Hydrogen bonding between the carboxyl groups of the PMAA blocks in PIB-b-PMAA diblocks leads to inverse micelles. Neutralization of the PMAA by Zn(AcO)2 and quaternization of the PDMAEMA segments by CH3I in the triblock copolymers and star co-polymers yielded ionic domains, which self-assemble and produce physical networks held together by columbic interaction. The physical/chemical characteristics of the domains control the viscoelastic behavior and mechanical properties of these block ionomers. The mechanical properties of the various block ionomers were significantly enhanced relative to the precursors, and they were thermally stable below the transition temperature. Further, the thermomechanical properties of these novel materials were satisfactory even above 200°C.