Synthesis and characterization of star-shaped block copolymer of poly-(ɛ-caprolactone) and poly(ethyl ethylene phosphate) as drug carrier

A series of novel 4-arm biodegradable star block copolymers of poly(ɛ-caprolactone) and poly(ethyl ethylene phosphate) were synthesized via ring-opening polymerization of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane using hydroxyl terminated 4-arm star-shaped poly(ɛ-caprolactone) and stannous octoate co-initiation system. Gel permeation chromatography (GPC), NMR and FT-IR were used to demonstrate the structure and analyze their compositions. The self-assembly behavior of these star-shaped copolymers in aqueous solution was studied by 1H NMR and fluorescence technique, and the results indicated those copolymers formed nanoparticles in aqueous solution with hydrophobic poly(ɛ-caprolactone) core and hydrophilic poly(ethyl ethylene phosphate) shell. The critical micelle concentration was relative to the length of poly(ɛ-caprolactone) and poly(ethyl ethylene phosphate) block. Paclitaxel was encapsulated in the micelles and the release behavior demonstrated that a longer hydrophobic block resulted in slightly slower release rate from the micelles. These copolymer micelles were biocompatible and potential as drug-delivery vehicles for pharmaceutical application.