FUNCTIONAL POLY[(ETHYLENE OXIDE)-CO-(BETA-BENZYL-L-ASPARTATE)] POLYMERIC MICELLES - BLOCK-COPOLYMER SYNTHESIS AND MICELLES FORMATION

Well-defined alpha-methoxy-omega-amino and alpha-hydroxy-omega-amino poly(ethylene oxides) (PEOs), obtained by chemical modifications of alpha-hydroxy-omega-amino PEO, were studied for block copolymerization with beta-benzyl-L-aspartate-N-carboxy anhydride (BLA-NCA); the block copolymers were obtained via polymerization of BLA-NCA with the primary amino end-groups of the PEOs as initiator in the mixture CHCl3/N,N- dimethylformamide (DMF) (vol. ratio 10/1). Gel-permeation chromatography (GPC) of both block copolymers showed the presence of BLA oligomers. alpha-Methoxy PEO/PBLA and alpha-hydroxy PEO/PBLA block copolymers were submitted to selective precipitation in 2-propanol; this method allowed total elimination of oligomers as shown by GPC of the purified block copolymers. Moreover, for each block copolymer, the number of BLA units determined by H-1 NMR spectroscopy (in CDCl3) was in good agreement with the number calculated from the ratio BLA-NCA/amino end-groups of PEO. The polymeric micelles having hydroxy functions or methoxy groups on the outer-shell were prepared by dialysis against water of the corresponding solution of the pure block copolymers. These polymeric micelles were characterized by dynamic light scattering (diameter) and by fluorescence spectroscopy (critical micellar concentration, cmc) using pyrene as a fluorescence probe. Both polymeric micelles have a small diameter (< 50 nm) and a very low cmc (< 20 mg/L in water).