Physicochemical characterization of polymeric micelles constructed from novel amphiphilic polyphosphazene with poly(N-isopropylacrylamide) and ethyl 4-aminobenzoate as side groups

An amphiphilic graft polyphosphazene (PNIPAm/EAB-PPP) composed of oligo-poly(N-isopropylacrylamide) (PNIPAm) as hydrophilic segments and ethyl 4-aminobenzoate (EAB) as hydrophobic groups was synthesized via ring-opening polymerization and subsequent substitution reaction. The molar ratio of the PNIPAm segment to EAB group was 1.85:0.15. The lower critical solution temperature (LCST) of copolymer was 32.6 degrees C as determined by turbidity method. Micellization behavior of PNlPAm/EAB-PPP in an aqueous phase was characterized by fluorescence technique, H-1 NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration (CMC) of the graft copolymer in aqueous solution was 0.1 mg/ml. The number-averaged particle size of spherical micelles was 80 nm at 25 degrees C with a narrow distribution. TEM also revealed that inter-micellar aggregation was induced in the micelle solution at temperature above LCST of graft copolymer. The thermosensitive PNIPAm/EAB-PPP micelles may be of help to regulate the loading and release of hydrophobic drugs. (C) 2005 Elsevier B.V. All rights reserved.