Synthesis of α-helix-containing PPEGMEA-g-PBLG, well-defined amphiphilic graft copolymer, by sequential SET-LRP and ROP

A series of well-defined polypeptide-based amphiphilic graft copolymers containing hydrophilic poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA) backbone and hydrophobic poly(gamma-benzyl-L-glutamate) (PBLG) side chains was synthesized by successive single electron transfer-living radical polymerization (SET-LRP) and ring-opening polymerization (ROP) via the combination of grafting-through and grafting-from strategies. The brush-like main chain was firstly constructed by SET-LRP of PEGMEA macromonomer in THF/H2O followed by post-polymerization modification to PPEGMEA-NH2 macroinitiator. The target well-defined PPEGMEA-g-PBLG graft copolymers with narrow molecular weight distributions (M-w/M-n = 1.06-1.21) were obtained via ROP of BLG-NCA monomer initiated by PPEGMEA-NH2 macroinitiator in 1,4-dioxane and the molecular weights of the backbone and side chains were both controllable. PBLG side chains were found to adopt alpha-helix conformation with a maximum helix content up to 99%. Critical micelle concentrations (cmc) of PPEGMEA-g-PBLG amphiphilic graft copolymers were determined using fluorescence probe technology and their diverse self-assembled nanoscale morphologies were visualized using a transmission electron microscope (TEM). Micellar morphologies formed by PPEGMEA-g-PBLG amphiphilic graft copolymers were found to be dependant on the initial water content, composition of the organic cosolvent, and length of the PBLG side chains.