We report on novel diblock copolymers of poly(N-vinylcaprolactam) (PVCL) and poly(N-vinyl-2-pyrrolidone) (PVPON) (PVCL-b-PVPON) with well-defined block lengths synthesized by the MADIX/reversible addition-fragmentation chain transfer (RAFT) process. We show that the lower critical solution temperatures (LCST) of the block copolymers are controllable over the length of PVCL and PVPON segments. All of the diblock copolymers dissolve molecularly in aqueous solutions when the temperature is below the LCST and form spherical micellar or vesicular morphologies when temperature is raised above the LCST. The size of the self-assembled structures is controlled by the molar ratio of PVCL and PVPON segments. The synthesized homopolymers and diblock copolymers are demonstrated to be nontoxic at 0.1-1 mg mL-1 concentrations when incubated with HeLa and HEK293 cancer cells for various incubation times and have potential as nanovehicles for drug delivery. © 2014 Wiley Periodicals, Inc. J. Polym. Sci.