Tuning the hydrophilic-hydrophobic balance of block-graft copolymers by click strategy: synthesis and characterization of amphiphilic PCL-b-(PαN3CL-g-PBA) copolymers

The self-organization of amphiphilic block copolymers in water strongly depends on their molecular structure, particularly their hydrophilic-hydrophobic balance. This study proposes tuning the amphiphilicity of block copolymers by a click strategy. This work prepares novel amphiphilic block-graft PCL-b-(P alpha N3CL-g-PBA) copolymers that comprise poly(epsilon-caprolactone) (PCL) as the hydrophobic segment and poly(alpha-azido-epsilon-caprolactone-graft-propargyl benzoate) (P alpha N3CL-g-PBA) as the hydrophilic segment by ring-opening polymerization of 2-chloro-epsilon-caprolactone (CICL) with hydroxyl-terminated macroinitiator PCL, substituting pendent chloride with sodium azide. This copolymer is subsequently used for grafting propargyl benzoate (PBA) moieties by the Cu(I)-catalyzed Huisgen's 1,3-dipolar cycloaddition, thus producing a 'click' reaction. This research examines characteristics of these copolymers by H-1 NMR, FT-IR, GPC, contact angle measurement and differential scanning calorimetry (DSC). Increasing the length of the hydrophilic segment or decreasing the length of the hydrophobic segment significantly increases water uptake and decreases the contact angle of the copolymers. These amphiphilic copolymers self-assembled into micelles in the aqueous phase, which were then examined by fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The average micelle size ranges from 90 to 190 nm. The critical micelle concentration (CMC) is from 2.4 to 7.6 mg l(-1) at 25 degrees C. The length of the hydrophilic segment influences the shape of the micelle. The current study describes drug entrapment efficiency and drug loading content of micelles, dependent on the composition of block-graft polymers. Polymer Journal (2010) 42, 304-312; doi:10.1038/pj.2010.6; published online 24 February 2010