Incorporation of a desired stimuli-responsive unit in a stereospecific manner at the specific location within a nonlinear block copolymer architecture is a challenging task in synthetic polymer chemistry. Herein, we report a facile and versatile method to synthesize AB(2) miktoarm block copolymers bearing a singlet oxygen (O-1(2))-labile regio and stereospecific beta-aminoacrylate linkage with 100% E-configuration at the junction via a combination of amino-yne click chemistry and ring opening polymerization. Using this strategy, a series of O-1(2)-responsive AB(2) amphiphilic miktoarm (MA) copolymers composed of hydrophilic polyethylene glycol (PEG) as the A constituent and hydrophobic polycaprolactone (PCL) as the B constituent (MA-PEG-b-PCL2) was synthesized by varying the block length of PCL. The self assembly characteristics of these well-defined MA-PEG-b-PCL2 copolymers in an aqueous condition were studied by solvent displacement and thin-film hydration method, and their morphologies were investigated using transmission electron microscopy. The copolymers formed spherical, cylindrical, or lamella morphologies, depending on the chain length and preparation conditions. A hydrophobic photosensitizer chlorin e6 (Ce6) and anticancer drug doxorubicin (DOX) were efficiently encapsulated into the hydrophobic core of MA-PEG-b-PCL2 copolymer micelles. These coloaded micelles were taken up by human breast cancer (MDA-MB-231) cells. Upon red laser light irradiation, the O-1(2)-generated by the Ce6 induced photocleavage of the beta-aminoacrylate moiety, leading to the dissociation of the micellar structure and triggered intracellular drug release for effective therapy. Overall, rapid disassembly upon O-1(2) generation and subsequent controlled intracellular drug release suggested that these micelles bearing beta-aminoacrylate linkage have a huge potential for on-demand drug delivery.