PCL(5k)-PEG(2k)-MAL is a self-assembling block copolymer with polycaprolactone (PCL) as hydrophobic segment and PEG as hydrophilic block. The maleimide is reactive with thiol/cysteine to form a stable amide linkage. The polymer can be used to prepare nanoparticles for drug delivery. Reagent grade, for research purpose.