Systematic Studies on (Co)Polymerization of Polar Styrene Monomers with Palladium Catalysts

Polymerization of polar styrene monomers and their copolymerization with ethylene are of great interest in both academia and industry. In comparison with hundreds of literature reports on palladium catalyzed (co)polymerization using polar vinyl monomers, studies on palladium catalyzed (co)polymerization using polar styrene monomers have received much less attention and remains almost unexplored. In this contribution, by employing the benchmark cationic α-diimine and neutral phosphine-sulfonate palladium catalysts 1 and 2, a comprehensive picture on (co)polymerization of polar styrene monomers including o -F, o -Cl, o -MeO, o -CN, o –OH, o -COOH, o -CHO, o -NO 2, o -NH 2, o -NMe 2, o -PPh 2, m -F, m -MeO, p -F, p -MeO, p -vinyl, and 2,3,4,5,6-F 5 functional groups was built. By utilizing the cationic catalyst 1, due to the formation of the cationic π–η 3 -benzyl chelate, homopolymerization of polar styrene monomers and the copolymerization with ethylene only generated atactic polar styrene homopolymers or produced no polymer, depending on the type of polar styrene monomers. In contrast, by using the neutral catalyst 2, homopolymerization of polar styrene monomers was not possible, but copolymerization with ethylene showed good activities (up to 290 kg mol –1 h –1 ) to afford a family of new ethylene/polar styrene copolymers with high incorporations (up to 6.3 mol %). Interestingly, the incorporated comonomer units are prone to an average distribution at the saturated chain end, in-chain, and unsaturated chain end. The origin of this unexpected observation was explored through stoichiometric insertion studies using selected polar styrene comonomers.