Secondary Structure-Induced Micro- and Macrophase Separation in Rod-Coil Polypeptide Diblock, Triblock, and Star-Block Copolymers

Abstract

Ten novel rod−coil block copolymers based on poly(γ-benzyl-l-glutamate) (PBLG), rod block, and poly(propylene oxide) (PPO), coil block, have been synthesized, and the influence on their secondary structure and solid-state organization have been studied in terms of their architecture (diblock, triblock, or star-block), molecular weight of the polymer coil block (from 2 to 5 kDa), and volume fraction of the rod block (0.50 or 0.75). The degree of polymerization of the polypeptide segment into the arms of the block copolymers, DParm, strongly affects the final α-helical secondary structure and the corresponding self-assembling of the block copolymers. Below 20 amino acid residues, a mixture of secondary structures (α-helices, β-sheets, and unordered segments) and microphase separation of the blocks is present. Above 20 repeating units, the microphase separation goes together with macrophase separation of the pure α-helical secondary structure, which ends up into an orthogonal lamellar phase or rods.