Synthesis and characterization of poly(ethylene glycol)-b-poly (L-lactide)-b-poly(L-glutamic acid) triblock copolymer

A biodegradable amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-b-PLLA-b-PLGA) was obtained by catalytic hydrogenation of poly(ethylene glycol)-b-poly(L-lactide)-b-poly(gamma-benzyl-L-glutamic acid) (PEG-b-PLLA-b-PBLGA) synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with amino-terminated MPEG-b-PLLA-NH2 as a macroinitiator. MPEG-b-PLLA-NH2 converted from MPEG-b-PLLA-OH first reacted with tert-Butoxycarbonyl-L-phenylalanine (Phe-(BOC)-B-N) and dicyclohexylcarbodiimide (DCC) and then deprotected the tert-butoxycarbonyl group. MPEG-b-PLLA-OH was prepared by ROP of L-lactide with monomethoxy poly(ethylene glycol) in the presence of stannous octoate. The triblock copolymer and its diblock precursors were characterized by H-1 NMR, FTIR, GPC and DSA (drop shape analysis) measurements. The lengths of each block polymers could be tailored by molecular design and the ratios of feeding monomers. The triblock polymer PEG-b-PLLA-b-PLGA containing carboxyl groups showed obviously improved hydrophilic properties and could be a good potential candidate as a drug delivery carrier. (C) 2004 Elsevier Ltd. All rights reserved.