PCL(3k)-PEG(5k)-MAL is a maleimide terminated amphiphilic polymer which can react with thiol (SH) at pH 6.5-7.5 via formation of thioether linkage. In water, the polymer self assembles to form micelles with polycaprolactone (PCL) core being shielded from the water by PEG shell. The polymer can be used to prepare drug loaded nanoparticles for drug delivery. Reagent grade, for research purpose.