Poly(ε-caprolactone)-block-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, triblock) and Poly(ε-caprolactone)block-(poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide)-poly (ε-caprolactone) (PCL-PEO-PPO-PEO-PCL, pentablock) copolymers were synthesized by transesterification with reduction of PCL molecular mass, enabling fewer reactions, lower temperatures, and eliminating extensive purification steps. Free hydrophilic groups were removed from the samples by selective precipitation, and 1 H-NMR, FTIR, GPC and DSC analyses characterized the structure and properties of the resulting copolymers. The detection of remaining hydrophilic groups indicates the formation of the amphiphilic block copolymers (BCPs). Further, we obtained polymeric nanoparticles with monodisperse size distribution profiles by nano-precipitation from both the triblock and the pentablock copolymers using a microfluidic device, resulting 144.6 and 188.9 nm size and 0.093 and 0.102 nm polydispersity index, respectively. The nanoparticle assembly depends on the copolymer composition, and the possibility of nanoparticle assembly corroborates to the block structure of the copolymers, and the success of this synthesis route to obtain BCPs.