Degradation behaviors of star-shaped poly(ethylene glycol)-poly(?-caprolactone) nanoparticles in aqueous solution

Star-shaped poly(ethylene glycol) (PEG)-poly(?-caprolactone) (?-PCL) block copolymers were synthesized via a ring-opening polymerization. Nanoparticles prepared by the precipitation/solvent evaporation technique exhibit a core-shell structure. The hydrolytic degradation of 3-arm PEG-PCL copolymeric nanoparticles was studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). It was found that copolymers with shorter PCL block length degraded faster. The sizes of nanoparticles fluctuated during the initial degradation period, and then increased slightly before finally dropping off. The degradation mainly occurred at CL-CL linkages firstly then at the EO-CL linkages. The CL/EO molar ratios and the molecular weights of copolymers decreased as degradation time and a zero-order degradation behavior was observed.