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Well-defined thermoresponsive amphiphilic poly(DL-lactide)- b-poly( N- vinylcaprolactam) (PDLLA- b-PNVCL) block copolymers with various block compositions were synthesized via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Their structures were confirmed by proton nuclear magnetic resonance spectroscopy (H NMR) and gel permeation chromatography/multi-angle laser light scattering (GPC/MALLS) measurements. They exhibited reversible temperature-dependent aggregation behavior in aqueous media as characterized by turbidity and dynamic light scattering (DLS) measurements. Their lower critical solution temperatures (LCSTs) increased with the increase in the chain length of PNVCL block and the decrease of the copolymer solution concentrations. These amphiphilic block copolymers self-assembled into aggregates of various morphologies in their aqueous solution, depending on the compositions of the copolymers. As the PNVCL content in block copolymer increased, the morphology of the aggregates changed from spheres to large compound vesicles (LCVs)-like, to irregularly spherical micelles. The viscosity measurement and HNMR analyses proved that these copolymers were hydrolytically degradable and the degradation process was accelerated under basic and acidic environments, especially in acidic media. [ABSTRACT FROM AUTHOR]