Synthesis and Characterization of Star-Shaped Block Copolymer sPCL-b-PEG-GA

Compared to linear polymers with the same molecular weight star-shaped polymers have the superiority of drug loading and delivery. The glycyrrhetinic acid (GA) from licorice is remarkably characteristic of liver distribution and liver cells targetability. In this paper four-armed star-shaped polycaprolactone was synthesized and amino polyethylene glycol was modified by glycyrrhetinic acid (NH2 -PEG-GA). Then the condensation reaction between the two above polymers finally produced four-armed star-shaped poly(ethylene glycol)-b-poly(epsilon-caprolactone) block copolymer (sPCL-b-PEG-GA). The structures of the intermediates and product were characterized by (HNMR)-H-1. The results indicated that the structure andmolecular weight of sPCL-b-PEG-GA can be controlled by the varied ratios of pentaerythritol (PTOL) to epsilon-caprolactone (epsilon-CL) in the presence of stannous octoate (Sn(Oct)(2)) and the amphiphilic copolymer sPCL-b-PEG-GA consists of PTOL as core PCL as inner hydrophobic segments PEG as external hydrophilic segments and terminal glycyrrhetic acid as targeting ligand. The work explored a new synthesis route of star poly(ethylene glycol)-b-poly(epsilon-caprolactone) copolymer with liver targetability. The star-shaped polymer is expected to be an efficient drug carrier.