A Versatile Synthetic Approach to Polypeptide Based Rod−Coil Block Copolymers by Click Chemistry

Abstract

Well-defined block copolymers composed of a rigid poly(γ-benzyl-l-glutamate) (PBLG) sequence and a poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) block were synthesized by Huisgen's 1,3-dipolar cycloaddition (click chemistry) from homopolymers containing azide and alkyne functionalities. These functional groups were introduced in the α-position of both PBLG and PDMAEMA precursors using appropriate α−ω-functionalized initiators to trigger the living/controlled polymerization of the corresponding monomers. Both α-alkyne- and α-azido-PBLGs were synthesized by ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride at room temperature from amino-containing α-alkyne and α-azide difunctional initiators, using dimethylformamide as solvent. As for α-alkyne-PDMAEMA and α-azido-PDMAEMA, they were obtained by copper-mediated atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate at 60 °C in tetrahydrofuran as solvent. The copper(I)-catalyzed 1,3-dipolar cycloaddition coupling reactions of the α-azido-PBLG with the α-alkyne-PDMAEMA, in the one hand, and of the α-alkyne-PBLG with the α-azido-PDMAEMA, on the other hand were conveniently performed in DMF, affording the targeted PBLG-b-PDMAEMA diblock copolymers. Removal of the residual PDMAEMA used in slight excess was facilitated by the retention of this homopolymer onto the stationary phase of the column chromatography. On the basis of size exclusion chromatography, IR and NMR analyses, click chemistry was found to be quantitative, yielding for the first time hybrid diblock copolymers based on a polypeptide and a vinylic polymer.