Photocleavable amphiphilic diblock copolymer micelles bearing a nitrobenzene block

Amphiphilic diblock copolymers containing photocleavable nitrobenzene acrylate groups were synthesized by the reversible addition-fragmentation chain transfer (RAFT) method. The diblock copolymer (NBMA)(14)-b-(GLBT)(47) consisted of nitrobenzyl methacrylate as a hydrophobic block and carboxy methyl betaine, industrially known as GLBT, as a hydrophilic, zwitterionic block. The diblock copolymer was self-assembled into the micelles of 30-40 nm hydrodynamic radii in aqueous buffer solution of various pHs. The diblock copolymer showed non-surface activity in alkaline and acidic buffers but remained surface active at a neutral buffer (pH 7). On exposure to UV irradiation of 360 nm light, polymeric micelles were dissociated due to cleavage of the acrylate bond leaving the block as a hydrophilic acid group. Significant change in surface activity at pH 7 was observed after UV irradiation and the copolymer tended to be less surface active. Encapsulation of a model drug was shown using Nile red, a fluorescence probe, and light-stimulated release of the hydrophobic molecule was demonstrated. Our focus is to develop a photoresponsive nano-carrier utilizing the above system.