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, DP arm , strongly affects the final R-helical secondary structure and the corresponding self-assembling of the block copolymers. Below 20 amino acid residues, a mixture of secondary structures (R-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 R-helical secondary structure, which ends up into an orthogonal lamellar phase or rods.

Star Polymers

“…Mezzenga et al synthesized various 3-arm star block copolymers consisting of PBLGA arms using trisamino poly(propylene oxide) cores (MW = 3 and 5 kDa). 136 Bulk self-assembly studies revealed that the length of the peptide arm influences the formation of lamellar phase, where samples with <20 repeat units per arm led to poorly ordered liquid-crystalline microphase structures because of the presence of mixtures of secondary structures (α-helices, β-sheets, and unordered segments). For stars with >20 amino acids per arm, almost only α-helical structure was observed that led to lamellar phase in which the helical peptide rods were closely packed into a hexagonal lattice.…”

Hybrid Block Copolymers Constituted by Peptides and Synthetic Polymers: An Overview of Synthetic Approaches, Supramolecular Behavior and Potential Applications

“…In particular, the α-helical conformation of peptides leads to mesogenic rods which possess dipole moments, potentially include kinks, and have extensively been employed in peptide/polymer hybrid systems [70][71][72][73]. The polymer topology and conformational asymmetry can also influence the final structure.…”

Solid state self-assembly of the single-walled carbon nanotubes and poly(γ-benzyl-l -glutamate)s with different conformations

“…Poly(γ‐benzyl‐ l ‐glutamate)s (PBLGs) are well‐known thermotropic/lyotropic liquid crystalline polymers (LCPs) . They can adopt α‐helical or β‐sheet conformations depending on the chain length . In the solid state, the polymer often form a nematic phase, although monodisperse PBLGs have been shown to self‐assemble into a more ordered smectic phase .…”