Poly(lactic acid)−Poly(ethylene oxide) (PLA−PEG) Nanoparticles: NMR Studies of the Central Solidlike PLA Core and the Liquid PEG Corona

Abstract

NMR studies on a series of poly(lactic acid)−poly(ethylene oxide) (PLA−PEG) diblock copolymers have been carried out in d6-acetone and in D2O. Nanoparticles of the PLA−PEG copolymers were obtained using a modified interfacial polymer deposition−solvent evaporation technique (Fessi, H.; Devissaguet, J. P.; Puisieux, F.; Thies, C. French Patent 2 608 988, 1986). In D2O, the PLA block forms a central hydrophobic core, while the PEG block forms an hydrophilic corona layer. In D2O, the hydrophobic core of the nanoparticle is generally not seen, while the PEG corona is observed. Only the PLA methyl protons at the interface between the two regions are observed, and these are seen as a double doublet structure. For nanoparticles with a low molecular weight PLA block length, an additional methyl multiplet signal is seen suggesting that PLA methyl groups are in more than one chemical environment. This is not seen for nanoparticles with a high molecular weight PLA block length indicating more uniform structure in th...