Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Abstract

The most straightforward and potentially ideal route to produce polar-functionalized polyethylene is direct copolymerization of ethylene with polar monomers. However, access to high-molecular-weight polar copolymers represents one of the biggest challenges in the field of olefin polymerization. In this contribution, we report a family of well-designed nickel catalysts that readily address this issue under convenient and highly desired ambient conditions. Under 1 bar at 30°C, polar-functionalized ultrahigh number-average molecular weight polyethylenes (UHMWPEs, Mn = 0.83-1.10 × 106 g mol-1) are directly generated. The highest average number of incorporated polar units per polymer chain is 122. This enhances copolymer molecular weights by two orders of magnitude relative to previous reports. Notably, this nickel catalyst family also exceptionally produces the highest number-average molecular weight polyethylenes (Mn = 6.04 × 106 g mol-1) at 1 bar. The Sterimol B1 steric parameter of nickel catalyst quantitatively correlates to polymer molecular weight. Mechanistic insights from density functional theory (DFT) calculation reveal that the low barrier (10.4 kcal mol-1) of ethylene insertion as the rate-limiting step should be responsible for high activity and the formation of UHMWPE. This coordination-insertion approach is a striking contrast to the high energy free-radical approach.