PCL(3k)-PEG(5k)-VS is a vinylsulfone (VS) functional block copolymer. The reaction between VS and thiol occurs via thiol-ene reaction in the presence of photo/radical initiator. It contains two distinct polymers, a hydrophobic polycaprolactone (PCL) block and a hydrophilic PEG block. The polymer can be used for formulation of nanomicellar for sustained drug delivery. Reagent grade, for research purpose.