Arborescent Micelles: Dendritic Poly(γ-benzyl L-glutamate) Cores Grafted with Hydrophilic Chain Segments

Amphiphilic copolymers were obtained by grafting arborescent poly(gamma-benzyl (L)-glutamate) (PBG) cores of generations G1-G3 with polyglycidol, poly(ethylene oxide) (PEO), or poly((L)-glutamic acid) (PGA) chain segments. The PBG substrates were synthesized by two methods: (1) subjecting PBG samples with a dispersity D = M-w/M-n < 1.1 to partial acidolysis of the benzyl ester groups, to produce randomly distributed carboxylic acid functionalities, and (2) using PBG chains containing a glutamic acid di-tert-butyl ester initiator fragment in the last grafting cycle of the PBG core synthesis, and selective acidolysis of the tert-butyl ester groups to obtain substrates with carboxylic acid termini. Linear polymers with D < 1.20 and a primary amine terminus were also synthesized to serve as hydrophilic shell materials: Polyglycidol and PEO by anionic polymerization, and PGA by N-carboxyanhydride ring-opening polymerization. These polymers, combined with the two different PGB substrate types, allowed the evaluation of the usefulness of random versus chain-end grafting in producing arborescent copolymers useful as unimolecular micelles in organic and aqueous media. Size exclusion chromatography served to determine the grafting yield, molar mass, dispersity, and branching functionality of the copolymers. Dynamic light scattering measurements provided information on their aggregation behavior in aqueous environments. (C) 2015 Wiley Periodicals, Inc.