Synthesis and characterization of poly(ethylene glycol)-b-poly(ε-caprolactone) copolymers with functional side groups on the polyester block

This study reports the successful synthesis of amphiphilic MPEG‐b‐PCL based‐block copolymers bearing benzyloxy and hydroxyl side groups on the PCL block by ring‐opening polymerization of 4‐benzyloxy‐ε‐caprolactone (4‐BOCL) and ε‐caprolactone (ε‐CL) with methoxy PEG (550 g mol−1) as the initiator and Tin(II) 2‐ethylhexanoate (SnOct2) as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), 1H NMR, and gel permeation chromatography. The thermal properties (Tg and Tms) of the block copolymers depend on the polymer composition. Incorporating a greater amount of 4‐BOCL and/or ε‐CL was incorporated into the macromolecular backbone causes a decrease Tg, and an increase in Tms. The micellar characteristics in the aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). A lower critical micelle concentration (CMC) was observed in MPEG12‐b‐PBOCL12‐b‐PCL series, which have higher hydrophobic components in the copolymers. However, contrasting results were observed for MPEG12‐b‐PBOCL27‐b‐PCL systems. The micelle exhibited a spindle shape, with an average size of less than 200 nm. A weak drug entrapment efficiency and drug‐loading ability of these micelles were observed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012