Fast Photodegradable Block Copolymer Micelles for Burst Release

A novel photosensitive amphiphilic triblock copolymer (ABA) triblock copolymer was designed, synthesized and investigated. An amphiphilic ABA triblock copolymer of which the end block A is water-soluble poly (ethylene oxide) (PEO) and the middle block B is a hydrophobic polyurethane containing nitrobenzyl groups (PEO-b-PUNB-b-PEO) was synthesized. The photodegradable PUNB block was first prepared by using condensation polymerization of 2-nitro-1,3-benzene-dimethanol with tolylene 2,4-diisocyanate in slight excess. It was then terminated with monomethyl ether PEO to yield the triblock copolymer of PEO-b-PUNB-b-PEO. After irradiation of a BCP solution with UV light, the size exclusion chromatograph (SEC) trace shows dominant low molecular weight species while a remaining polymer peak matches the elution peak of PEO, indicating a complete separation of PEO chains from PUNB as well as the severe disintegration of the hydrophobic block into low-molecular-weight species.