Synthesis and characterization of amphiphilic poly(ɛ-caprolactone)-b-polyphosphoester diblock copolymers bearing multifunctional pendant groups

A series of parent block copolyesters poly(ɛ-caprolactone)-block-poly[2-(2-oxo-1, 3, 2-dioxaphospholoyloxy)ethyl acrylate] (PCL-b-POPEA) with different block lengths have been synthesized by ring-opening polymerization (ROP) and four kinds of mercaptans were then used in the postpolymerization modification via Michael-type addition reaction, resulting in several block copolyesters with various functionalities (e.g., hydroxyl, carboxyl, amine, and amino acid) in their pendant groups. The chemical structures of these block copolymers were characterized by FT-IR, NMR spectroscopy and GPC analysis. The self-assembly behaviors of PCL-b-POPEA have been studied by fluorescence probe technique, transmission electron microscopy (TEM) and high-performance particle size (HPPS) instrument. In vitro cytotoxicity test indicated that the block copolymers possess good biocompatibility. Initial in vitro drug loading and release studies using Doxorubicin (DOX) as a model drug demonstrated a faster release in the presence of phosphodiesterase I as compared to the system without enzyme. Moreover, it was found that DOX-loaded nanoparticles displayed higher inhibition to KB cell proliferation in comparison with free DOX. Therefore, the combination of ROP and Michael-type addition reaction provides a general access to various types of multifunctional and biodegradable materials.