Nickel-mediated surface grafting from polymerization of α-amino acid-N-carboxyanhydrides

The feasibility of a living grafting from polymerization of a-amino acid-N-carboxyanhydrides (NCA) from a surface using nickel initiators was shown. The polymerization has been carried out on commercially available polystyrene resins as spherical substrates in two different ways. Firstly L-glutamic acid was bound to the surface as gamma-ester via a UV-labile linker and transferred into the NCA by treatment with triphosgene. The grafting from polymerization was then carried out as a "block copolymerization" by reaction of the surface bound NCA with an excess of the Ni amido-amidate complex initiator and subsequent addition of free NCA to grow the polymer chain. By this procedure polymer was formed at the surface and can be isolated after photolysis of the linker. The characterization of the polymer by size exclusion chromatography indicates a living polymerization at the surface. The second approach employs N-alloc-amides at the surface to prepare an initiating Ni amido-amidate complex directly at the surface. It can be shown that the latter approach is much more straightforward and gives smaller quantities of non-tethered polypeptide.