Α-diimine Catalysts Research Articles

Radical co-polymerization of diiminedibromidenickel(II)-functionalized olefin with styrene: synthesis of polymer-incorporated nickel II α-diimine catalysts for ethylene polymerization

α-Diimine nickel catalyst bearing two allyl groups [ArN=C] 2C 10H 6NiBr 2 (Ar=4-allyl-2,6-(i-Pr) 2C 6H 2)] ( Cat-1) has been synthesized and characterized. The corresponding polymer-incorporated nickel catalysts PC and the SiO 2-supported shell-core structure catalyst SC-1 were obtained by the co-polymerization of the olefin groups of Cat-1 with styrene in the presence of a radical initiator. Radical co-polymerizations with styrene in solution were investigated in detail, and the compositions and molecular weight of the copolymers were determined. All three types of catalysts ( Cat-1, PC and SC-1) have been investigated for ethylene polymerization. These catalysts were found to exhibit high activity in the presence of modified methylaluminoxane (MMAO) as a co-catalyst. Among them, the polymer-incorporated PC and SiO 2 shell-core catalyst SC-1 displayed very high activity (∼2.62 and ∼1.11 kg (mmol Ni) −1 h −1, respectively) with product molecular weights ( M w) in the range 26×10 4 to 47×10 4 under 0.1 MPa ethylene pressure. The particle morphology of polyethylene produced by the shell-core structure catalyst SC-1 was improved.

Polymerization of methyl methacrylate with nickel α-diimine catalysts: Effect of the methyl position in the ligand

In the solution polymerizations of methyl methacrylate with (α-diimine)nickel(II)/methylaluminoxane (MAO), we observed effects of the position of two methyl substituents in the ligand on both the activities of the catalysts and the polymer microstructure. α-Diimine nickel(II) catalysts gave syndiotactic-rich poly(methyl methacrylate) with high molecular weight and narrow molecular weight distribution.

Living and Block Copolymerization of Ethylene and α-Olefins Using Palladium(II)−α-Diimine Catalysts

Living polymerizations of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium−polymer bond with various reagents provides a protocol for synthesis of mono- and di-end-functionalized, branched, amorphous polyethylenes. The functional initiator used is the chelate complex (Ar = 2,6-(iPr)2C6H3) (3). The alkyl chain is cleaved by insertion of alkyl acrylates or methyl vinyl ketone, followed by cleavage with Et3SiH to generate alkyl ester or methyl ketone end groups, respectively. Insertion of 5-hexen-1-ol, followed by chain running and β-elimination, results in formation of aldehyde end groups. Conditions for living polymerization of propylene, 1-hexene, and 1-octadecene have also been established. Rates of first monomer insertion and subsequent chain growth are shown to be a sensitive function of the palladium complex used for initiation and the nature and concentration of auxiliary nitrile ligands. Block copolymers of ethylene and 1-o...

Living Polymerization of Ethylene Using Pd(II) α-Diimine Catalysts

Living Polymerization of Ethylene Using Pd(II) α-Diimine Catalysts

Novel Branching Topology in Polyethylenes As Revealed by Light Scattering and 13C NMR

A group of polyethylenes synthesized using palladium α-diimine catalysts were studied using 13C NMR spectroscopy, intensity light scattering, dynamic light scattering, and viscometry. These catalysts are known to produce branched polyethylenes without α-olefin comonomers. The series of polymers studied were synthesized under conditions of varying ethylene pressure. The polymers are highly branched and completely amorphous and are thus soluble in common organic solvents at ambient temperatures. Light scattering determinations of the root-mean-square radius of gyration (Rg) and the molecular weight M of fractions eluting from a size exclusion chromatograph demonstrated that, at a given M, Rg decreased as ethylene pressure decreased. The hydrodynamic parametersthe Stokes radius (RH) from dynamic light scattering and the intrinsic viscosity ([η])also decreased. The change in Rg at a constant M results from the change in branching topology for the polymers synthesized at different ethylene pressures. The parameter Rg2/M varies by an order of magnitude for the polymers synthesized under ethylene pressures varying from 0.1 atm to 500 psi. However, the total branching (methyls per 1000 CH2) and the distribution of short branches (methyl, ethyl, propyl, etc.) determined by 13C NMR remained essentially unchanged. These observations indicate the branching topology changes with polymerization pressure. Polymer topology varies from predominantly linear with many short branches at higher ethylene pressures to a densely branched, arborescent globular structure at very low ethylene pressures. Polymers synthesized at the lowest ethylene pressure studied, 0.1 atm, exhibited dilute solution parameters similar to those observed for dendrimers or many-armed stars, with Rg/RH below unity, and a segment density approaching that of a hard sphere.

Preparation of Linear α-Olefins Using Cationic Nickel(II) α-Diimine Catalysts

Nickel(II) dibromide complexes containing para- and unsubstituted aryl α-diimine ligands in combination with modified methylaluminoxane (MMAO) are highly active and efficient catalysts for the oligomerization of ethylene to linear α-olefins. α-Olefins in the C4−C26 range have been prepared with selectivities as high as 94%. The Schulz−Flory product distributions and selectivities for α-olefins are a sensitive function of catalyst structure and reaction conditions. Details of this catalyst system are described, including the synthesis of initiators, catalyst activities, and α-olefin product distributions.

Polymer-bound stabilizers

This work describes a simple one-pot and controlled synthetic method to generate migration-resistant bio-friendly tailor-made antioxidants through ethylene–sterically hindered phenolic antioxidant (SHPA) copolymerization by coordination polymerization using MAO-activated nickel(II)-α-diimine catalyst. The antioxidant tethering into the polymer chain by chain walking catalysts leads to adjustable copolymer architectures possessing different thermal features. It was found that oxidation induction time could be fine-tuned (from 2 to 36 min) by appropriate SHPA content selection and PE altering (from 10 to 0.5 bar of gage). Furthermore, the chemical composition analysis of DPE–SHPA copolymer shows 0.6 wt% SHPA incorporation (approximately 80% conversion) besides a dendritic architecture, containing 123 branches per 1000 carbon atoms and AFM images resembling semi-spherical topology. The migration resistance of the synthesized copolymers and their application as non-releasing additives are also investigated.