Modular synthesis of biodegradable diblock copolymers for designing functional polymersomes.

Polymer vesicles, or polymersomes, are promising candidates for applications in drug delivery and tissue imaging. While a vast variety of polymers have been explored for their ability to assemble into polymersomes, relatively little research on the functionalization of these polymers has been reported. We present here a novel route for the synthesis of poly(caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) diblock copolymers that allows for the insertion of functional groups at the block junctions and the assembly of functional membranes. This modular synthesis has been developed on the basis of solid-phase peptide synthesis techniques and is accomplished through the formation of two peptide bonds, one between an amine-terminated PEG and the carboxyl moiety of the functional group and the other between the functional group amine and a carboxy-terminated PCL. As a demonstration of the potential utility of the resulting vesicles, we incorporated two different amino acid functional groups at the junction. 2-Nitrophenylalanine was utilized to create UV-responsive membranes in which the vesicles were destabilized and released encapsulated contents upon irradiation. A fluorescein-conjugated lysine was also utilized to create stable fluorescent membranes in which the fluorescence was built into the polymer. This method should contribute to our ability to further develop smart, functional membranes.