AN APPROACH TO SYNTHESIZE POLY(ETHYLENE GLYCOL)-b-POLY(ε-CAPROLACTONE) WITH TERMINAL AMINO GROUP via SCHIFF'S BASE AS AN INITIATOR

A new method to synthesize a degradable terminal amino group-containing copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL-NH₂), was developed in the following three steps: (1) the ring-opening polymerization (ROP) of ε-caprolactone from the Schiff base prepared from benzaldehyde and ethanolamine (Ph–CH=NCH₂CH₂OH) used as an initiator to obtain heterobifunctional poly(ε-caprolactone) with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH₂CH₂N=CH–Ph); (2) the coupling reaction of two reactive precursors, a hydroxy-terminated HO-PCL-CH₂CH₂N=CH–Ph and α-monocarboxy-ω-monomethoxy poly(ethylene glycol) (CMPEG) to synthesize MPEG-PCL-CH₂CH₂N=CH–Ph; (3) the conversion of the –N=CH–Ph end-group into NH₂ end-group by acidification of acetic acid to obtain MPEG-PCL-NH₂. The structures from the precursors to the terminal amino group-containing copolymer were confirmed by ¹H-NMR and their molecular weights were measured by gel permeation chromatography. The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell. The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.