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 (SnOct 2 ) as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), 1 H NMR, and gel permeation chromatography. The thermal properties ( T g and T m s) 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 T g , and an increase in T m s. 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 MPEG 12 ‐ b ‐PBOCL 12 ‐ b ‐PCL series, which have higher hydrophobic components in the copolymers. However, contrasting results were observed for MPEG 12 ‐ b ‐PBOCL 27 ‐ 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