Dual-Chain Polymerization at an Early Transition-Metal Single-Site Catalyst

Abstract

The hafnium complex (N oct N dipp )Hf(Me) 3 (1, N oct N dipp = N-octyl-N′-(2,6-diisopropylphenyl)-1,4-diaza-2,3,3trimethyl-1-butene) contains a bidentate imino-anilido ligand. This complex undergoes protonolysis by the ammonium Brønsted acid [HN(Me)(C 18 H 37 ) 2 ][B(C 6 F 5 ) 4 ] to produce a competent alkene polymerization precatalyst, [(N oct N dipp )Hf(Me) 2 (N(Me)-(C 18 H 37 ) 2 )][B(C 6 F 5 ) 4 ] (2). Unlike most alkene polymerization precatalysts, 2 contains two Hf−Me groups, which have the potential to initiate and propagate two polymer chains simultaneously. Herein, we demonstrate that 2 does indeed grow two polymer chains at each hafnium center. Additional unusual characteristics for an early transition-metal catalyst include: (1) the numberaverage polymer molar mass (M n ) is independent of the concentration of monomer; (2) linear plots of monomer concentration as a function of time during polymerization indicate apparent zeroth-order dependence of rate on the monomer concentration; and (3) apparent first-order dependence of steady-state rate of polymerization on the initial concentration of monomer. While saturation behavior with respect to monomer concentration is common with late transition-metal-derived catalysts, propagation rate laws for early transition-metal complexes overwhelmingly are first-order in monomer concentration. Based on operando NMR kinetics, end group analysis, active site counting with chromophore quench labels, iodine quenching studies, and gel permeation chromatography, we propose a unified kinetic and mechanistic model for the polymerization of 1-octene with 2.

A commercially viable solution process to control long-chain branching in polyethylene

“…2): Group IV precatalysts supported by dianionic ligands have two methyl groups and, upon activation, have one growing polymer chain on the metal (single-chain catalysts). Precatalysts supported by monoanionic ligands have three methyl groups and form dialkyl metal cations upon activation, with the potential to grow two polymer chains from a single metal center (dual-chain catalysts) ( 27 , 28 ). We hypothesized that addition of an α,ω-diene to a catalyst capable of growing two polymer chains could add the diene sequentially across both polymer chains to effectively couple them together, creating long-chain branching with few pendant vinyl groups accessible for reactor fouling.…”

Best Practices for the Collection of Robust Time Course Reaction Profiles for Kinetic Studies

“…There are many programs that can be used for reaction modeling, such as DynoChem, , COPASI, , and Zeneth , and many valid approaches to kinetic modeling. As a starting point, we recommend first defining a minimal set of all kinetically relevant elementary steps to be input into the modeling software.…”

B(C6F5)3 grafted inorganic fillers for supported titanium-catalyzed synthesis of UHMWPE composites

“…[1][2][3][4] The development of high-performance polyolefin catalysts has always been the focus of academic and industrial research in this field. [5][6][7][8][9][10] The polyolefin materials produced based on these catalysts possess great mechanical properties and are widely used in various plastic products and polyolefin composite material devices. [11][12][13] Notably, various inorganic fillers such as SiO 2 and TiO 2 have been added to the polyolefin matrix to generate composite materials for cost reduction and property enhancement.…”