Two-Dimensional Supramolecular Assemblies from pH-Responsive Poly(ethyl glycol)-b-poly(l-glutamic acid)-b-poly(N-octylglycine) Triblock Copolymer

Amphiphilic block copolymers containing polypeptides can self-assemble into a variety of nonspherical structures arising from strong interactions between peptide units. Here, we report the synthesis of a pH-responsive poly(ethyl glycol)-block-poly(l-glutamic acid)-block-poly(N-octylglycine) (PEG-b-PGA-b-PNOG) triblock copolymers by sequential ring-opening polymerization using amine-terminated poly(ethyl glycol) as the macroinitiator followed by selective deprotection of the benzyl protecting group. The obtained triblock copolymer can be directly dispersed in aqueous solution with hydrophilic PEG, pH-responsive PGA block, and hydrophobic PNOG. We present a systematic study of the influence of pH, molar fraction, and molecular weight on the self-assemblies. It was found that the PEG-b-PGA-b-PNOG triblock tends to form two-dimensional nanodisks and nanosheet-like assemblies. The nanodisk-to-nanosheet transition is highly dependent on the pH and molar fraction despite the different molecular weights. We demonstrate that the dominant driving force of the nanodisks and nanosheets is the hydrophobicity of the PNOG blocks. The obtained bioinspired 2D nanostructures are potential candidates for applications in nanoscience and biomedicine.