Competitive Interactions of pi-pi Junctions and Their Role on Microphase Separation of Chiral Block Copolymers

Abstract

Herein, enantiomeric polylactide-containing chiral block copolymers (BCPs*) with aliphatic and aromatic junctions are designed and synthesized for investigating the impact of junction pi-pi interactions on the self-assembly of BCPs*. A profound effect on the microphase separation of the BCP* can be found by introducing the pi-pi interaction of junctions, resulting in reduced structural ordering due to the mixing of constituted blocks by the formation of junction pi-stacking. An ordered microphase-separated structure of the BCP* can be obtained by decreasing the number of aromatic rings of the junction or increasing the total molecular weight of the BCP*. Accordingly, competitive interactions of pi-pi junctions and microphase separation of the BCP* can be manifested by tuning the thermodynamic driving force for self-organization through molecular design. Most interestingly, the self-assembled morphology can be amended by self-assembling the BCP* from solution through the kinetic control of solvent evaporation. Fast solvent evaporation limits the formation of junction stacking while slow solvent evaporation enhances the stacking between junctions, and thus depresses the microphase separation of BCPs*. The self-assembled mechanisms are further evidenced by spectroscopic results and the corresponding induced circular dichroism (ICD) behaviors of the aromatic junctions. This work demonstrates a new approach to thermodynamically and kinetically regulate the self-assembled morphologies of BCP* by introducing the competitive interactions of pi-pi junctions on self-assembly.