Secondary Structure–Directed Bulk Self‐Assembly in Polystyrene‐ b ‐Polyproline Block Copolymers

ABSTRACT Bulk self‐assembly of block copolymers has been extensively studied, with factors such as intrinsic immiscibility, block composition, and chain length known to influence phase separation and dictate the resulting morphologies strongly. However, the role of secondary structure, particularly in blocks capable of conformational switching, remains underexplored. This study investigates the self‐assembly of a multistructured rod‐coil diblock copolymer consisting of poly(L‐proline) and polystyrene (PS) segments. The unique feature of these diblock copolymers is that the secondary structure of polyproline (PLP) blocks can independently be tuned into two distinct conformations (PPI and PPII). Furthermore, a high energy barrier associated with the conformational transition between PPI and PPII structures makes it of interest to study the influence of secondary structure on self‐assembly under thermodynamic equilibrium. A pair of diblock copolymers (PS m ‐ b ‐PLP n ) with differing polyproline block lengths has been synthesised. Among the two PLP‐containing block copolymers examined, the diblock with a trans‐polyproline (PPII) segment self‐assembled into a well‐defined lamellar morphology. In contrast, the same copolymer with identical molecular weight and composition but containing a cis‐polyproline (PPI) segment lacked long‐range order. These findings reveal secondary structure as a powerful, tunable parameter for programming block copolymer self‐assembly.