PCL(5k)-PEG(5k)-VS is a biodegradable block copolymer with hydrophobic polycaprolactone (PCL) and hydrophilic PEG. The polymer can be used for formulation of nanomicellar for sustained drug delivery. The terminal hydroxyl (OH) can be used for further derivatization while the terminal vinylsulfone can react with thiol in the presence of photoinitiator/catalyst. Reagent grade, for research purpose.