A versatile synthetic approach to polypeptide based rod-coil block copolymers by click chemistry
Résumé
Well-defined block copolymers composed of a rigid poly(gamma-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 alpha-position of both PBLG and PDMAEMA precursors using appropriate alpha-omega-functionalized initiators to trigger the living/controlled polymerization of the corresponding monomers. Both alpha-alkyne- and alpha-azido-PBLGs were synthesized by ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride at room temperature from amino-containing alpha-alkyne and alpha-azide difunctional initiators, using dimethylformamide as solvent. As for alpha-alkyne-PDMAEMA and alpha-azido-PDMAEMA, they were obtained by copper-mediated atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate at 60 degrees C in tetrahydrofuran as solvent. The copper(I)-catalyzed 1,3-dipolar cycloaddition coupling reactions of the alpha-azido-PBLG with the alpha-alkyne-PDMAEMA, in the one hand, and of the alpha-alkyne-PBLG with the alpha-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.