Synthesis of block copolymers of ethylene with styrene and n-butyl acrylate via a tandem strategy combining ethylene Living polymerization catalyzed by a functionalized Pd-diimine catalyst with atom transfer radical polymerization

We report a new two-step tandem strategy combining two versatile living polymerization techniques, Pd-diimine catalyzed ethylene living polymerization and atom transfer radical polymerization (ATRP), for the synthesis of functionalized polyethylene (PE) diblock copolymers containing an ethylene block and a functional monomer block, such as styrene and n-butyl acrylate. The key to the success of this tandem strategy is the development of a novel functionalized Pd-diimine catalyst, [(ArN = C(Me)-(Me)C = NAr)Pd-(CH2)(3)C(O)O(CH2)(2)OC(O)C(CH3)(2)Br]+SbF6- (Ar = 2,6-(iPr)(2)C6H3) (3), which uniquely contains a 2-bro-moisobutyryl substituting group on its chelate structure. This catalyst was synthesized by convenient equimolar reaction of the acetonitrile Pd-diimine adduct, [(ArN = C(Me)-(Me)C = NAr)Pd(CH3)(N CMe)]+SbF6- (Ar = 2,6-(iPr)(2)C6H3) (1), with a functional acrylate monomer, 2-(2-bromoisobutyryloxy) ethyl acrylate (BIEA). The remarkable feature of 3 lies in its unprecedented ability to catalyze ethylene living polymerization that directly gives rise to telechelic PE chains bearing an end-capping 2-bromoisobutyryl group active for initiating ATRP. The resulting end-functionalized PEs can thus be directly used as macroinitiators to subsequently initiate ATRP of functional monomers, like styrene and n-butyl acrylate used in this work, in the second step of this tandem strategy to synthesize functionalized diblock copolymers. Because of the living polymerization nature of both steps in this tandem strategy, we demonstrate that the functionalized block copolymers synthesized possess well-defined structures with narrow molecular weight distributions and controllable lengths for both PE and functional monomer blocks.