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), ¹H NMR, and gel permeation chromatography. The thermal properties (T _g and T _ms) 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 _ms. 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.