PCL(5k)-PEG(3k)-VS is a block amphiphilic polymer. In water, the hydrophilic PEG is shielding the hydrophobic polycaprolactone (PCL) from the water. Therefore, hdyrophobic drugs can be encapsulated in the core of the nanoparticles. The terminal viniylsulfone can react with thiol via thiol-ene chemistry. Reagent grade, for research purpose.