Asymmetric Self-Assembly of Functional Ionic Block Copolymers with Tailored Dense Charge Modification

Ionic block copolymers inherit the advantages of adjustable self-assembly from conventional block copolymers, along with additional functionalities from charge groups, which are broadly used in energy, separation, sensing, electronic, and biomedical fields. Past research has mainly limited to ionic block copolymers with low charge density, usually less than one charge per repeat unit. Increasing the charge density is a straightforward strategy to improve their performance. However, due to challenges in synthesis and processability, the effects of high-density charges on self-assembly and associated functional properties has not been well understood. To address this challenge, we established an efficient synthetic method to create densely charged cationic block copolymers and studied their self-assembly behaviors systematically. Each repeat unit can be modified with up to 9 fully charged ammonium cations. The self-assembly behaviors are precisely adjusted by charge density, the topological arrangement of charges, or partial charge modification. Strong electrostatic cohesion of dense charges plays a dominant role in creating highly asymmetric nanostructures and enhancing the crystallization of ionic groups within these nanostructures. We demonstrate that the tailored charge modification provides block copolymers with an increasing dielectric constant, distinct relaxor ferroelectric properties, and humidity-responsive photoluminescence. This study sheds fundamental insights into the molecular design and self-assembly of densely charged block copolymers, which paves an avenue for developing a new generation of ionic soft materials.