Synthesis of Imidazolium-Containing ABA Triblock Copolymers: Role of Charge Placement, Charge Density, and Ionic Liquid Incorporation

Imidazole-based ABA triblock copolymers prepared using nitroxide-mediated polymerization achieved a microphase-separated morphology with ion-conducting central blocks. Difunctional random poly(1-(4-vinylbenzyl)imidazole-co-n-butyl acrylate) (poly(VBIm-co-nBA)) central blocks provided low glass transition temperature (T-g) phases for ion conduction, and subsequent chain extension for polystyrene external blocks provided mechanical reinforcement. Selective incorporation of 1-ethyl-3-methylimidazolium ethylsulfate ([EMIm][EtSO4]) into the random poly(VBIm-co-nBA) central blocks reduced the T-g of both neutral and charged imidazole-containing central blocks. Mechanical properties for ABA triblock copolymers depended on quaternization, central block composition, and ionic liquid incorporation. Ionic conductivity increased over an order of magnitude due to quaternization of imidazole and additional ionic liquid.. Tuning central block composition, charge content, and ionic liquid content provided an avenue to tailor the thermomechanical properties and ionic conductivity of ABA triblock copolymers.