Chemoenzymatic synthesis of a pentablock copolymer and its self-assembly behavior study

A triblock copolymer PCL-6-PEG-b-PCL was prepared by enzymecatalyzed ring-opening polymerization of ε-caprolactone in the presence of catalyst Novozyme 435 and initiator PEG. The α-bromoester terminated Br-b-PCL-b-PEG-b-PCL-6-Br macroinitiator was obtained in the subsequent esterification of end hydroxyl groups with a-bromopropionyl bromide and was used in the ATRP of 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate(HFMA). A pentablock copolymer consisting of poly(ethylene glycol) (PEG) , polycaprolacrone (PCL) and poly(2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate) (PHFMA) was synthesized. The structures of the polymers were characterized by NMR and GPC. Because of the industrial and scientific significance, increasing interest has been arising on the aggregates of complicated block copolymers in selective solvents. The self-assembly of the pentablock copolymer was investigated in aqueous solutions. The size and shape of the resulting micelles were investigated using dynamic light scattering and tapping-mode atomic force microscopy. The results demonstrated that the copolymeric micelles had a spherical shape with a mean diameter of about 77 nm. In addition, the micellar morphologies were influenced remarkably by changing the initial copolymer concentration in organic solvents.