Surface Grafting of Poly(l-glutamates). 3. Block Copolymerization

This paper describes for the first time the synthesis of surface-grafted AB-block copolypeptides, consisting of poly( γ -benzyl l -glutamate) (PBLG) as the A-block and poly( γ -methyl l -glutamate) (PMLG) as the B-block. Immobilized primary amine groups of ( γ -aminopropyl)triethoxysilane (APS) on silicon wafers initiated the ring-opening polymerization of N -carboxyanhydrides of glutamic acid esters (NCAs). After removal of the BLG-NCA monomer solution after a certain reaction time, the amine end groups of the formed PBLG blocks acted as initiators for the second monomers. This method provides the possibility of making layered structures of surface-grafted block copolymers with tuned properties. Ellipsometry and small-angle X-ray reflection (SAXR) measurements revealed the thickness of the polypeptide layers ranging from 45−100 Å of the first block to 140−270 Å for the total block copolypeptides. The chemical composition of the blocks was determined by X-ray photoelectron spectroscopy (XPS). In addition, Fourier transform infrared transmission spectroscopy (FT-IR) revealed that the polypeptide main chains of both blocks consisted of pure α -helices. The average orientation of the helices ranging from 22−42° with respect to the substrate within the first block to 31−35° in the second block could be derived with FT-IR as well.