Synthesis of a novel structural triblock copolymer of poly(gamma -benzyl-l-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone).

A novel structural triblock copolymer of poly(gamma-benzyl-l-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PBLG-PEO-PCL) was synthesized by a new approach in the following three steps: (1) sequential anionic ring opening polymerization (ROP) of ethylene oxide and epsilon-caprolactone with an acetonitrile/potassium naphthalene initiator system to obtain a diblock copolymer CN-PEO-PCL with a cyano end-group; (2) conversion of the CN end-group into NH2 end-group by hydrogenation to obtain NH2-PEO-PCL; (3) ROP of gamma-benzyl-l-glutamate-N-carboxyanhydrides (Bz-l-GluNCA) with NH2-PEO-PCL as macroinitiator to obtain the target triblock copolymer. The structures from CN-PEO precursor to the triblock copolymers were confirmed by FT-IR and 1H NMR spectroscopy, and their molecular weights were measured by gel permeation chromatography. The monomer of Bz-l-GluNCA can react almost quantitatively with the amino end-groups of NH2-PEO-PCL macroinitiator by ROP.