Effect of Stereochemistry on Directed Self-Assembly of Poly(styrene‑<i>b</i>‑lactide) Films on Chemical Patterns

We demonstrated here for the first time that the stereochemistry of polylactide (PLA) blocks affected the assembly behaviors of PS-<i>b</i>-PLA on chemical patterns. Two PS-<i>b</i>-PLA block copolymers, where the PLA block is either racemic (PDLLA) or left-handed (PLLA), were synthesized and directed to assemble on chemical patterns with a wide range of <i>L</i>_s/<i>L</i>₀. PS-<i>b</i>-PDLLA was stretched up to 70% on chemical patterns, while PS-<i>b</i>-PLLA was only stretched by 20%. The assembly behavior of PS-<i>b</i>-PDLLA was different from AB diblock copolymer, but similar to that of ABA triblock copolymer. The high stretchability might be attributed to the formation of stereocomplexes in PDLLA blocks. Compared to ABA triblock copolymers, stereocomplexed diblock copolymers have much faster assembly kinetics. This observation provides a new concept to achieve large process windows by the introduction of specific interactions, for example, H-bonding, supramolecular interaction, and sterecomplexation, between polymer chains