Novel pH-responsive ABA triblock copolymers in which the outer A block comprises N,N-di-n-propyl-4-vinylbenzylamine (DnPBVA) and the central B block is 2-(methacryloyloxy) ethyl phosphorylcholine (MPC) were synthesized using atom transfer radical polymerization in methanol.The composition,structure,and molecular weight of the copolymer were characterized by 1H-NMR and GPC,respectively.The micellization of the triblock copolymer in aqueous solution was investigated using fluorescence probe technique,phase analysis light scattering (PALS) and transmission electron microscopy (TEM).The critical micelle concentration (CMC),the critical pH of various triblock copolymers and the influence of salt on the CMC were determined by fluorescence measurements.Above the critical pH,the PDnPBVA-b-PMPC-b-PDnPBVA triblock copolymers formed aggregates of PDnPBVA as core and PMPC as shell.Under the critical pH,spontaneous disassociation of the core-shell aggregates occurred,and the hydrophobic PDnPBVA cores became hydrophilic chains.The TEM images and phase analysis light scattering showed that the size of the copolymer micelles was about 50-100 nm.