PCL(10k)-mPEG(5k) is made of two distinct polymers with different hydrophilicity. One of the block is hydrophilic PEG and the other one is hydrophobic polycaprolactone (PCL). The different hydrophilicity allows the polymer to self-assemble in water with arrangement of PEG facing the water surface and PCL being shieled from the water. The core regions can be used to encapsulate hydrophobic drugs for sustained drug delivery. Reagent grade, for research purpose.