13 research outputs found
Rigidifying Cation-Tunable Nickel Catalysts Increases Activity and Polar Monomer Incorporation in Ethylene and Methyl Acrylate Copolymerization
In this study, we synthesized and
characterized two nickel complexes
featuring conformationally rigid bisphosphine mono-oxide ligands,
where one has an o-methoxyphenyl (Ni2) and the other has an o-(2-methoxyethoxy)Âphenyl
(Ni3) substituent on the PO moiety. We performed
metal binding studies using Ni3 and found that its reaction
with Li+ and Na+ most likely produced 1:1 and
1:1/2:1 nickel:alkali species in solution, respectively. The nickel
complexes were competent catalysts for ethylene homopolymerization
and copolymerization, with activities up to 3.8 × 103 and 8.1 × 10 kg mol–1 h–1, respectively. In reactions of ethylene with methyl acrylate (1.0
M), the addition of Li+ to Ni3 led to a 5.4-fold
enhancement in catalyst activity and a 1.9-fold increase in polar
monomer incorporation in comparison to those by Ni3 alone
under optimized conditions. A comparison with other nickel catalysts
reported for ethylene and methyl acrylate copolymerization revealed
that our nickel–alkali catalysts are competitive with some
of the most efficient Ni-based systems developed thus far
Fine-Tuning Nickel Phenoxyimine Olefin Polymerization Catalysts: Performance Boosting by Alkali Cations
To
gain a better understanding of the influence of cationic additives
on coordination–insertion polymerization and to leverage this
knowledge in the construction of enhanced olefin polymerization catalysts,
we have synthesized a new family of nickel phenoxyimine–polyethylene
glycol complexes (<b>NiL0</b>, <b>NiL2</b>–<b>NiL4</b>) that form discrete molecular species with alkali metal
ions (M<sup>+</sup> = Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>). Metal binding titration studies and structural characterization
by X-ray crystallography provide evidence for the self-assembly of
both 1:1 and 2:1 <b>NiL</b>:M<sup>+</sup> species in solution,
except for <b>NiL4</b>/Na<sup>+</sup> which form only the 1:1
complex. It was found that upon treatment with a phosphine scavenger,
these <b>NiL</b> complexes are active catalysts for ethylene
polymerization. We demonstrate that the addition of M<sup>+</sup> to <b>NiL</b> can result in up to a 20-fold increase in catalytic efficiency
as well as enhancement in polymer molecular weight and branching frequency
compared to the use of <b>NiL</b> without coadditives. To the
best of our knowledge, this work provides the first systematic study
of the effect of secondary metal ions on metal-catalyzed polymerization
processes and offers a new general design strategy for developing
the next generation of high performance olefin polymerization catalysts
Fine-Tuning Nickel Phenoxyimine Olefin Polymerization Catalysts: Performance Boosting by Alkali Cations
To
gain a better understanding of the influence of cationic additives
on coordination–insertion polymerization and to leverage this
knowledge in the construction of enhanced olefin polymerization catalysts,
we have synthesized a new family of nickel phenoxyimine–polyethylene
glycol complexes (<b>NiL0</b>, <b>NiL2</b>–<b>NiL4</b>) that form discrete molecular species with alkali metal
ions (M<sup>+</sup> = Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>). Metal binding titration studies and structural characterization
by X-ray crystallography provide evidence for the self-assembly of
both 1:1 and 2:1 <b>NiL</b>:M<sup>+</sup> species in solution,
except for <b>NiL4</b>/Na<sup>+</sup> which form only the 1:1
complex. It was found that upon treatment with a phosphine scavenger,
these <b>NiL</b> complexes are active catalysts for ethylene
polymerization. We demonstrate that the addition of M<sup>+</sup> to <b>NiL</b> can result in up to a 20-fold increase in catalytic efficiency
as well as enhancement in polymer molecular weight and branching frequency
compared to the use of <b>NiL</b> without coadditives. To the
best of our knowledge, this work provides the first systematic study
of the effect of secondary metal ions on metal-catalyzed polymerization
processes and offers a new general design strategy for developing
the next generation of high performance olefin polymerization catalysts
Visualization of miRNA-miRNA networks by Cytoscape.
<p>(<b>A</b>) Downregulated miRNA-miRNA network. (<b>B</b>) Upregulated miRNA-miRNA network. (<b>C</b>) Total miRNA-miRNA network. (<b>D</b>) The miRNA-miRNA interaction of hsa-miR-21. Green nodes represent downregulated miRNAs, while upregulated miRNAs are colored red. The size of the miRNA nodes corresponds to the node degree (the number of miRNAs that are connected). <i>P</i>-value strength is represented by edge line width, with wider edges representing more significant interactions.</p
The k = 12 clique from the downregulated miRNA-miRNA network and its co-regulated subpathways.
<p>Green nodes represent downregulated miRNAs, while upregulated miRNA is colored red. The size of the miRNA nodes corresponds to the node degree. <i>P</i>-value strength is represented by edge line width, with darker edges representing more significant interactions.</p
Power law of node degree distribution for the miRNA-subpathway networks.
<p>(<b>A</b>) Degree distribution of the downregulated miRNA-subpathway network. (<b>B</b>) Degree distribution of the upregulated miRNA-subpathway network. (<b>C</b>) Degree distribution of the total miRNA-subpathway network.</p
Network parameters of miRNA-subpathway and subpathway-subpathway networks.
<p>Network parameters of miRNA-subpathway and subpathway-subpathway networks.</p
Graphic representation of three miRNA-subpathway networks.
<p>(<b>A</b>) Downregulated miRNA-subpathway network. (<b>B</b>) Upregulated miRNA-subpathway network. (<b>C</b>) Total miRNA-subpathway network. Nodes colored in green are downregulated miRNA, and red nodes are upregulated miRNAs. Blue nodes represent the subpathways. The size of the miRNA nodes correspond to the node degree (the number of subpathways that miRNA connected). <i>P</i>-value strength is represented by edge line width, with wider edges representing more significant interactions. Hsa-miR-320b and hsa-miR-1248 had the biggest degree are shaded in yellow.</p
Schematic presentation of the analysis workflow to construct the miRNA-subpathway, miRNA-miRNA and subpathway-subpathway sub-networks.
<p>miRNA target genes were subjected to subpathway enrichment analysis to generate a miRNA-subpathway network. Then two sub-networks were constructed by the hypergeometric test.</p