Synthesis and characterization of star poly(ε-caprolactone)-b-poly(ethylene glycol) and poly(L-lactide)-b-poly(ethylene glycol) copolymers:: Evaluation as drug delivery carriers

Two types of 32 arm star polymers incorporating amphiphilic block copolymer arms have been synthesized and characterized. The first type, stPCL-PEG(32), is composed of a polyantidoamine (PAMAM) dendrimer as the core with radiating arms having poly(epsilon-caprolactone) (PCL) as an inner lipophilic block in the arm and poly(ethylene glycol) (PEG) as an outer hydrophilic block. The second type, stPLA-PEG(32), is similar but with poly(L-lactide) (PLA) as the inner lipophilic block. Characterization with SEC, (1)H NMR, FTIR, and DSC confirmed the structure of the polymers. Micelle formation by both star copolymers was studied by fluorescence spectroscopy. The stPCL-PEG(32) polymer exhibited unimolecular micelle behavior. It was capable of solubilizing hydrophobic molecules, such as pyrene, in aqueous solution, while not displaying a critical micelle concentration. In contrast, the association behavior of stPLA-PEG(32) in aqueous solution was characterized by an apparent critical micelle concentration of ca. 0.01 mg/mL. The hydrophobic anticancer drug etoposide can be encapsulated in the micelles formed from both polymers. Overall, the stPCL-PEG(32) Polymer exhibited a higher etoposide loading capacity (up to 7.8 w/w % versus 4.3 w/w % for stPLA-PEG(32)) as well as facile release kinetics and is more suitable as a potential drug delivery carrier.