Synthesis of well-defined ABC triblock copolymers with polypeptide segments by ATRP and click reactions

Abstract

Well-defined ABC block copolymers consisting of poly(ethylene oxide) monomethylene ether (MPEO) as A block, poly(styrene) (PS) as B block and poly(γ-benzyl- l-glutamate) (PBLG) as C block were synthesized by the combination of atom transfer radical polymerization (ATRP) and click reactions. The bromine-terminated diblock copolymer poly(ethylene oxide) monomethylene ether-block-poly(styrene) (MPEO–PS–Br) was prepared by ATRP of styrene initiated with macro-initiator MPEO–Br, which was prepared from the esterification of MPEO and 2-bromoisobutyryl bromide, and converted into the azido-terminated diblock copolymer MPEO–PS–N 3 by simple nucleophilic substitutions in DMF in the presence of sodium azide. Propargyl-terminated PBLGs were synthesized by ring-opening polymerization of γ-benzyl- l-glutamate- N-carboxyanhydride in DMF at room temperature using propargyl amine as an initiator. ABC triblock copolymers MPEO–PS–PBLG with a wide range of number-average molecular weights from 1.55 to 3.75 × 10 4 and a narrow polydispersity from 1.07 to 1.10 were synthesized via the click reaction of MPEO–PS–N 3 and the propargyl-terminated PBLG in the presence of CuBr and 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. The structures of these ABC block copolymers and corresponding precursors were characterized by NMR, IR and GPC. The results showed that click reaction was efficient. Therefore, a facile approach was offered to synthesize ABC triblock copolymers composed of crystallizable polymer MPEO, conventional vinylic polymer PS and rod-like α-helix polypeptide PBLG.