PCL(4k)-PEG(3k)-VS can be used to prepare nanoparticles for drug delivery applications. The polymer contains a hydrophobic polycaprolactone (PCL) block attached to a hydrophilic PEG block. The viniylsulfone group can react with thio via thiol-ene click chemistry in the presence of radical/photo initiator. Reagent grade, for research purpose.