Doubly Charged ABA Triblock Copolymers: Thermomechanically Robust Physical Network and Hierarchical Microstructures

This manuscript describes the structure-property-morphology relationships of doubly charged 1,4-diazabicyclo[2.2.2]octane (DABCO) salt-containing ABA triblock ionomers. The triblock copolymers consist a soft poly(n-butyl acrylate) (PnBA) central block and two external styrenic hard blocks bearing amphiphilic pendant C₁₈-alkyl groups and doubly charged salt units. Surprisingly, the DABCO salt-containing ABA block copolymers preserved the thermomechanical integrity until degradation, which indicated the formation of a reinforcing physical network compared to the corresponding doubly charged random copolymers and singly charged block copolymer analogs. Small-angle X-ray scattering data revealed that the DABCO-based ABA block copolymers self-assembled into highly ordered hierarchical microstructures, in which the soft and hard domain of the block copolymers phase-separated into highly ordered lamellar morphologies. Moreover, a secondary structure that originated from the ordering of the amphiphilic pendant groups formed within the lamellar hard domain. The interesting thermal, thermomechanical, and morphological properties of doubly charged ionic block copolymers open promising avenues for the synthesis of novel thermoplastic elastomers.