Pyroglutamate pendant block copolymers: evolution of inverse and conventional morphologies from RAFT-mediated PISA

By emulating the complex hierarchical assemblies found in bio-derived materials, nanostructural synthetic designs expand material properties and enlarge their capability for versatile applications. Correspondingly, polymerization-induced self-assembly (PISA) emerges as a controllable, innovative pathway to realize such intricate nanostructures. The present study aims to design block copolymer nano/micro-objects spanning from typical micelles, worms, jellyfish, and vesicles to scarcely attainable large compound vesicles, spongosome-like complex structures, and inverted micelles through PISA formulation. To obtain these in situ self-assembled structures, a series of block copolymers was synthesized via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of a pyroglutamate-pendant styrenic monomer (VBPGA) using poly(N,N-dimethylacrylamide) (PDMA) as a steric stabilizer in an alcohol/water binary solvent mixture at 65 °C. Various parameters, including solvophobic and solvophilic chain lengths, monomer solid content, cosolvent, stirring rate, and salt addition, were used as levers to achieve the morphological diversification. Differing from the traditional hydrophobicity or solvophobicity-driven self-assembly of block copolymers, the introduction of VBPGA as a unique core-forming precursor creates a fuzzy interface between hydrophilic and hydrophobic domains in PDMA-b-PVBPGA block copolymers through hydrogen bonding among amide groups and hydrophobic interactions, enabling the realization of an extended morphological window with fascinating inverse structures at a relatively shorter length of the PVBPGA segment.