Polar Group-Promoted Copolymerization of Ethylene with Polar Olefins

Copolymerization of ethylene (E) and polar vinyl monomers is a great challenge but remains attractive, especially for early transition metal catalysts featuring strong oxophilicity. Herein, we present the copolymerization of E with 6-phenoxy-1-hexene (POH) by scandium precatalysts with different steric hindrances: (FluCH2CH2NHC)Sc(CH2SiMe3)2 (1), (FluCH2C5H4N)Sc(CH2SiMe3)2 (2), (FluCH2Ph)Sc(CH2SiMe3)2(THF) (3), and (C5Me4Ph)Sc(CH2C6H4NMe2-o)2 (4). In comparable conditions, precatalyst 1, activated by [Ph3C][B(C6F5)4] and AliBu3, shows high activity (1.4 × 105 g molSc–1 h–1) but gives a low POH incorporation ratio of 0.7 mol %. Under identical conditions, the activity of 2 drops to 0.1 × 105 g molSc–1 h–1. In contrast, the half-sandwich scandium precatalyst 3 displays a much higher activity (8.1 × 105 g molSc–1 h–1) and affords a copolymer with 7.0 mol % POH. The highest activity (18.0 × 105 g molSc–1 h–1) and incorporation ratio (8.6 mol %) are achieved by 4. After optimization of the reaction conditions, up to 16 mol % of POH could be incorporated into the copolymer produced with 4. The resultant copolymers are readily transformed into brominated products and, subsequently, ethylene-based ionomers featuring excellent mechanical properties. Density functional theory (DFT) simulations are employed to illustrate the mechanisms of polar group incorporation and the control of activity from kinetic, thermodynamic, and geometric viewpoints.