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 p oly(ethylene oxides) (PEOs), obtained by chemical modifications of alp ha-hydroxy-omega-amino PEO, were studied for block copolymerization wi th beta-benzyl-L-aspartate-N-carboxy anhydride (BLA-NCA); the block co polymers were obtained via polymerization of BLA-NCA with the primary amino end-groups of the PEOs as initiator in the mixture CHCl3/N,N- di methylformamide (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 wer e submitted to selective precipitation in 2-propanol; this method allo wed total elimination of oligomers as shown by GPC of the purified blo ck copolymers. Moreover, for each block copolymer, the number of BLA u nits determined by H-1 NMR spectroscopy (in CDCl3) was in good agreeme nt with the number calculated from the ratio BLA-NCA/amino end-groups of PEO. The polymeric micelles having hydroxy functions or methoxy gro ups on the outer-shell were prepared by dialysis against water of the corresponding solution of the pure block copolymers. These polymeric m icelles were characterized by dynamic light scattering (diameter) and by fluorescence spectroscopy (critical micellar concentration, cmc) us ing pyrene as a fluorescence probe. Both polymeric micelles have a sma ll diameter (< 50 nm) and a very low cmc (< 20 mg/L in water).