Kinetically Controlled Self-Assembled Superstructures from Semicrystalline Chiral Block Copolymers

Self-assembled superstructures resulting from the competition between crystallization and microphase separation of semicrystalline poly(styrene)-b-poly(L-lactide) (PS-PLLA) chiral block copolymers (BCPs*) were examined. A kinetically controlled process by changing nonsolvent addition rate was utilized to control the BCP* self-assembly. Single-crystal lozenge lamellae were obtained by the slow self-assembly (i.e., slow nonsolvent addition rate) of PS-PLLA BCP* with long PS chain (i.e., PS-rich PS-PLLA BCP*) whereas amorphous helical ribbon superstructures were obtained from the fast self-assembly (i.e., last nonsolvent addition rate). Moreover, amorphous flat ribbon superstructures were obtained in achiral BCPs, poly(styrene)-b-poly(DL-lactide) (PS-PLA), suggesting that the chirality plays an important role in the formation of the helical ribbon superstructures. By contrast, the self-assembly of PS-PLLA BCP* with short PS chain (i.e., PLLA-rich PS-PLLA BCP*) was dominated by PLLA crystallization regardless of the variation of nonsolvent addition rate, indicating that the PLLA crystallization rate is dependent upon the length of PS chain in PS-PLLA BCPs*. As a result, the formation of helical architectures from the self-assembly of PS-PLLA BCP* reflects the impact of chirality on microphase separation, but the chiral effect might be overwhelmed by crystallization.