Phototriggered Ring-Opening Polymerization of a Photocaged l-Lysine N-Carboxyanhydride to Synthesize Hyperbranched and Linear Polypeptides.

Abstract

Increasing efforts are being made on controlled photopolymerization methodologies; however, the previous polymerization systems need additional photoactive initiators or catalysts. The controlled synthesis of the hyperbranched polypeptide is still challenging, and developing a photopolymerization method to prepare a hyperbranched polypeptide is urgent for constructing biodegradable polymers and biomaterials. Without addition of any initiator/catalyst, we combine the inimer (initiator + monomer) ring-opening polymerization (ROP) and photocaged chemistry to prepare hyperbranched and linear polypeptides. The photocaged Nε-(o-nitrobenzyloxycarbonyl)-l-lysine-N-carboxyanhydride possesses intrinsic photosensitivity and will be transformed into an activated AB* inimer-type α-amino acid N-carboxyanhydride (NCA) containing a primary ε-amine, which further triggers ROP to produce linear and/or hyperbranched polypeptides in one pot and at room temperature. The microstructure and topology of the resulting polypeptide were clarified by means of mass spectroscopy and various NMR techniques including 1H NMR, 1H, 1H-COSY, and quantitative 13C NMR. By tuning the UV irradiation time or intensity, this methodology can produce a linear polypeptide with a high Mw,GPC of 109 kDa and/or (hyper)branched counterparts with tunable Mw,GPC's of 1.4-73.5 kDa and degree of branching of 0.09-0.60.