Synthesis, characterization, and olefin (co)polymerization behavior of unsymmetrical α-diimine palladium complexes containing bulky substituents at 4-position of aniline moieties

High molecular weight PE elastomers through 4,4-difluorobenzhydryl substitution in symmetrical α-diimino-nickel ethylene polymerization catalysts

The following family of N,N-diaryl-2,3-dimethyl-1,4-diazabutadienes, ArN[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]NAr (Ar = 2,6-Me2-4-{CH(4-FC6H4)2}C6H2L1, 2-Me-6-Et-4-{CH(4-FC6H4)2}C6H2L2, 2,4-{CH(4-FC6H4)2}2-6-MeC6H2L3, 2,4-{CH(4-FC6H4)2}2-6-EtC6H2L4, 2,4-{CH(4-FC6H4)2}2-6-iPrC6H2L5), each incorporating para-substituted 4,4-difluorobenzhydryl groups but differing in the ortho-pairing, have been synthesized and used as precursors to their respective nickel(ii) bromide complexes, Ni1-Ni5. Compound characterization has been achieved through a combination of FT-IR, multinuclear NMR spectroscopy (1H, 13C, 19F) and elemental analysis. In addition, L1, Ni1 and Ni5 have been structurally characterized with Ni1 and Ni5 revealing similarly distorted tetrahedral geometries about nickel but with distinct differences in the steric protection offered by the ortho-substituents. All nickel complexes, under suitable activation, showed high activity for ethylene polymerization with a predilection towards forming branched high molecular weight polyethylene with narrow dispersity. Notably the most sterically bulky Ni5, under activation with either EtAlCl2, Et2AlCl or EASC, was exceptionally active (0.9-1.0 × 107 g of PE per (mol of Ni) per h) at an operating temperature of 40 °C. Furthermore, the polyethylene generated displayed molecular weights close to one million g mol-1 (M w range: 829-922 kg mol-1) with high branching densities (86-102/1000 carbons) and a selectivity for short chain branches (% Me = 94.3% (EtAlCl2), 87.2% (Et2AlCl), 87.7% (EASC)). Further analysis of the mechanical properties of the polymers produced at 40 °C and 50 °C using Ni5 highlighted the key role played by crystallinity (X c) and molecular weight (M w) on tensile strength (σ b) and elongation at break (ε b). In addition, stress-strain recovery tests reveal these high molecular weight polymers to exhibit characteristics of thermoplastic elastomers (TPEs).

Efficient suppression of the chain transfer reaction in ethylene coordination polymerization with dibenzosuberyl substituents

Catalysts with dibenzosuberyl substituents possess a superior ability to suppress chain transfer in ethylene (co)polymerization, producing high molecular weight polyethylenes and functionalized polyethylenes (ethylene-MA copolymers).

Suppression of chain transfer via a restricted rotation effect of dibenzosuberyl substituents in polymerization catalysis

Catalysts with dibenzosuberyl substituents possess superior thermostability and outstanding ability to suppress chain transfer in ethylene (co)polymerization, producing high molecular weight polyethylene and functionalized polyethylene.

Bulky yet flexible substituents in insertion polymerization with α-diimine nickel and palladium systems

The bulky yet flexible substituent on the N-aryl moieties of α-diimine ligands may adopt different conformations and provide dynamic steric hindrance in the process of ethylene (co)polymerization.