From α-Helices to Mesoscale Order: Structure–Packing Relationships in Polypeptide Block Copolymer Films

Polypeptide-based block copolymers are promising platforms for creating hierarchical nanostructures because their secondary structures can direct mesoscale self-assembly. This study investigates how polypeptide chain length and thermal annealing govern the hierarchical organization of poly(ethylene glycol)-b-poly(ε-benzyloxycarbonyl-l-lysine) (PEG-b-PZLL) thin films. Combined FTIR, AFM, AFM-IR, and synchrotron GIWAXS/GISAXS analyses reveal that PZLL segments predominantly form α-helical conformations that assemble into hexagonally packed domains with nearly constant lattice parameters across compositions. Increasing the PZLL degree of polymerization stabilizes the α-helical structure, promotes preferential in-plane orientation of cylindrical domains, and enables the formation of long-range ordered fibrillar morphologies, whereas short PZLL chains partially transform into β-sheet structures during film formation and after high-temperature annealing. These findings establish a direct relationship between the secondary structure, orientational ordering, and mesoscale morphology in self-assembled polypeptide block copolymer films.