Novel amphiphilic triblock copolymer based on PPDO, PCL, and PEG: Synthesis, characterization, and aqueous dispersion

Amphiphilic triblock copolymer, poly(p-dioxanone-co-caprolactone)-block-poly(ethylene oxide)-block-poly(p-dioxanone-co-caprolactone) (PPDO-co-PCL-b-PEO-b-PPDO-co-PCL) was synthesized by ring opening polymerization (ROP) of p-dioxanone and epsilon-caprolactone initiated through the hydroxyl end of poly(ethylene glycol) (PEG) in the presence of stannous 2-ethyl hexanoate [Sn(oct)(2)] as a catalyst. Polymerization and structural features of the polymers were analyzed by different physicochemical techniques (GPC, H-1 NMR, C-13 NMR, FT-IR, DSC and TGA). The splitting of H-1 NMR resonance at delta 2.3 and delta 4.1 ppm reveals the random copolymerization. Polymeric nanoparticles were prepared in phosphate buffer (pH 7.4) by co-solvent evaporation technique at room temperature (25 degrees C). Existence of hydrophobic domains as cores of the micelles were characterized by 1 H NMR spectroscopy and further confirmed with fluorescence technique using pyrene as a probe. Critical micelle concentration (CMC) of the polymer in phosphate buffer (pH. 7.4) was decreased from 2.3 x 10(-3) to 7.6 x 10(-4) g/L with the fraction of PCL. Polymeric nanoparticles observed by atomic force microscopy (AFM) were uniform and spherical, with smooth textured of around 50-30 nnn diameter. Dynamic light scattering (DLS) and electrophoretic light scattering (ELS) measurements showed a monodisperse size distribution of around 113-90 nm hydrodynamic diameters and negative zeta (xi) potential (-4 to - 14 mV), respectively. The investigations for the polymeric nanoparticles in aqueous medium showed that the composition of the hydrophobic segment of amphiphilic block copolymer makes a significant influence on its physicochemical characteristics. (c) 2006 Elsevier B.V. All rights reserved.