Synthesis of Poly(ethylene oxide)-b-polystyrene-b-poly(4-vinylpyridine) ABC Triblock Copolymers by Two-step Atom Transfer Radical Polymerization

A novel ABC triblock copolymer of poly(ethylene oxide)-b-poly(styrene)-b-poly(4-vinylpyridine) (PEO-b-PS-b-P4VP) was successfully synthesized via atom transfer radical polymerization (ATRP). First, polyethylene glycol monomethyl ether (PEO) terminated with a halogen atom (PEO-Br) was prepared by esterification of PEO with 2-bromoisobutyryl bromide. Next, bromo-terminated poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) diblock copolymers were obtained by the polymerization of styrene using PEO-Br as the macroinitiator and CuBr/bpy complex as the catalyst. Finally, PEO-b-PS-b-P4VP triblock copolymers were also prepared by ATRP of 4-vinylpyridine (4VP) using PEO-b-PS-Br as the macroinitiator and CuCl/tris[2-(dimethylamino)ethyl]amine (Me6TREN) as the catalyst. The triblock copolymers and precursors were characterized by H-1 NMR spectroscopy and gel permeation chromatography (GPC) techniques. The triblock copolymers prepared by this method have a well-defined structure. The results of GPC analysis showed that the as-prepared triblock copolymers had relatively narrow molecular weight distributions. The kinetics of copolymerization was also investigated. The results indicated that the ATRP process of 4VP is "living"/controlled in 2-propanol at conversions below 70%.