Effects of the Chiral Interface and Orientation-Dependent Segmental Interactions on Twisting of Self-Assembled Block Copolymers.

The chirality effect on the self-assembly of block copolymers (BCPs) composed of chiral entities, denoted as chiral BCPs (BCPs*), gives rise to the formation of the helical phase (H*) due to intermolecular chiral interactions. The corresponding twisting of self-assembled H* might be initiated from the microphase-separated chiral interface and/or attributed to chiral orientation-dependent segmental interactions. To examine the origins of the twisting mechanisms, a series of polylactide-containing BCPs* with different sequences and molecular weights of chiral block, poly(l-lactide) (PLLA), and achiral block, poly(d,l-lactide) (PLA), were designed for self-assembling. Accordingly, the impact of sequence and length of the blocks on self-assembled BCPs* can be scrutinized. For the ones with the PLLA as a middle block, polystyrene- b -poly(l-lactide)- b -poly(d,l-lactide), the formation of H* can be achieved even with a short PLLA segment. By contrast, the self-assembled morphology of polystyrene- b -poly(d,l-lactide)- b -poly(l-lactide) with the PLA as a middle block is dependent upon the length of the PLA block. On the basis of the self-assembled results, the chirality effect on the self-assembly of BCP* is originated from both the chiral interface and the chiral orientation-dependent segmental interactions. The present work on the study of the formation mechanisms of the H* thus provides insights into the intermolecular chiral interactions from the self-assembly of BCP*.