Self-assembled structures from PEGylated polypeptide block copolymers synthesized using a combination of ATRP, ROP, and click chemistry

Abstract

In this study, we used a combination of atom transfer radical polymerization, ring opening polymerization, and click chemistry to synthesize new PEGylated polypeptide block copolymers of polystyrene-b-poly(γ-propargyl-L-glutamate-g-ethylene oxide) [PS-b-(PPLG-g-MEO2)]. We employed Fourier transform infrared spectroscopy and wide-angle X-ray diffraction (WAXD) to determine the secondary structures of the α-helical conformations of these PEGylated polypeptide block copolymers in the solid state, and circular dichroism spectroscopy to characterize them in solution. Hierarchical self-assembly of the PS-b-(PPLG-g-MEO2) diblock copolymers in the bulk state (characterized using WAXD, small-angle X-ray scattering, and transmission electron microscopy) led to the formation of lamellar structures as a result of microphase separation of the diblock copolymers; the hexagonal cylinder packing nanostructure featured α-helical conformations of PEGylated polypeptide segments, which were oriented perpendicular to the director of the lamellar structure formed by the diblock copolymers. We obtained a range of micellar structures from the PS-b-(PPLG-g-MEO2) diblock copolymer in DMF (common solvent) upon the addition of selective solvents (H2O or MeCN). We observed only spherical micelles from the PS-b-(PPLG-g-MEO2) diblock copolymer in DMF–MeCN systems at all MeCN compositions. The micelle structures changed, however, from spherical structures to long wormlike, vesicles, and large compound micelles in the DMF–H2O system upon increasing the content of water. These different morphology transformations arose as a result of very different PS–solvent (H2O or MeCN) interaction parameters.