Extended Self-Assembled Long Periodicity and Zig-Zag Domains from Helix-Helix Diblock Copolymer Poly(γ-benzyl-L-glutamate)-block-poly(O-benzyk-hydroxyproline)

We describe the synthesis and self-assembly of particularly high periodicity of diblock copolymers composed of poly(benzyl-l-hydroxyproline) (PBLHyP) and poly(gamma-benzyl-l-glutamate) (PBLG), that is, two polypeptide blocks with dissimilar helical structures. The robust helicity of the PBLHyP block is driven by steric constraints of the repeat units, while PBLG forms alpha-helices driven by hydrogen bonding, allowing defects and deformations. Herein, high-molecular-weight diblock copolypeptides of PBLG-b-PBLHyP with three different volume fractions of the PBLHyP-blocks are discussed. For shorter PBLHyP blocks, hexagonal packing of PBLHyP helices is observed, while by increasing the length of the PBLHyP block, keeping at a similar PBLG block length, the packing is distorted. Zig-zag lamellar structures were obtained due to the mismatch in the packing periodicities of the PBLG and PBLHyP helices. The frustration that takes place at the interface leads the PBLHyP to tilt to match the PBLG periodicity. The zig-zag morphology is reported for the first time for high-molecular-weight helixhelix (rodrod) copolypeptides, and the self-assembled periodicity is uncommonly large.