Microenvironment modulation of Zr sites in covalent organic frameworks for low-pressure preparation of UHMWPE

Abstract

The development of stabilized catalysts with one-dimensional meso-pore structures is important for advancing olefin polymerization. Covalent Organic Frameworks (COFs) are popular candidates for constructing single-site heterogeneous olefin polymerization catalysts due to their well-ordered structures and large channels. In this study, Zr–COF catalysts were applied for the first time to the production of ultra-high molecular weight (M_w = 1.71 × 10⁶ g mol⁻¹) linear polyethylene (UHMWPE) at 5 bar ethylene pressure, filling the gap of traditional catalysts for ethylene polymerization at low pressures. The microenvironment of nanoconfinement and electronic effects of Zr–COFs can directly affect the polymer properties, including product size, morphology, molecular weight and molecular weight distribution. Kinetic simulations show that a COF with a triazine ring skeleton can provide suitable receptors for forming hydrogen bonds to enrich ethylene monomers, leading to low-pressure ethylene polymerization. The continuous and uniform flow of monomers in the highly oriented channels lays a solid foundation for the full contact between the active centre and the monomer, which further facilitates the formation of conformational relationships.