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

Herein, enantiomeric polylactide-containing chiral block copolymers (BCPs∗) with aliphatic and aromatic junctions are designed and synthesized for investigating the impact of junction π-π interactions on the self-assembly of BCPs∗. A profound effect on the microphase separation of the BCP∗ can be found by introducing the π-π interaction of junctions, resulting in reduced structural ordering due to the mixing of constituted blocks by the formation of junction π-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 π-π 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 π-π 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 π-π junctions on self-assembly.