Enhancing Thermal Stability and Living Fashion in α‑Diimine–Nickel-Catalyzed (Co)polymerization of Ethylene and Polar Monomer by Increasing the Steric Bulk of Ligand Backbone

Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the <i>N</i>-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-^<i>t</i>Bu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate

Synthesis of Polyethylenes with Controlled Branching with α‑Diimine Nickel Catalysts and Revisiting Formation of Long-Chain Branching

The synthesis of polyethylenes with precise branching, especially long-chain branching (LCB), using ethylene monomer as a single feedstock is of a significant academic and industrial interest. On the basis of the <i>ortho</i>-aryl effect, a series of α-diimine nickel complexes with monoaryl-substituted anilines has been designed and prepared for the synthesis of the polyethylenes with controlled branching. The introduction of the <i>ortho</i>-aryl on aniline moieties enhanced the branching control ability of the α-diimine nickel catalysts. A different mechanistic model was proposed to interpret the presence of methyl and LCB but absence of other short branches in the obtained polyethylenes. LCB was formed by ethylene insertion into the primary Ni-alkyl species originating from nickel migration to methyl terminal of the growing chain because of restricted ethylene insertion into secondary Ni-alkyl species with an α-ethyl or a bulkier alkyl group

Precision Synthesis of Ethylene and Polar Monomer Copolymers by Palladium-Catalyzed Living Coordination Copolymerization

Coordination insertion polymerization is unsurpassed as a straightforward method for synthesis of high-value polyolefins by the copolymerization of ethylene and polar monomers, but poison effects of polar groups on the metal center result in a lack of fine control over the polymer architecture. Herein we reported a thermally stable dibenzo­barrelene-derived α-diimine palladium catalyst for the precision synthesis of functionalized polyolefins by living copolymerization of ethylene and a variety of acrylate comonomers. The introduction of the bulky dibenzo­barrelene backbone can improve migratory insertion selectivity of methyl acrylate (MA) in a 2,1-mode, thus preventing polar groups from poisoning palladium centers by stable five-membered palladacycle intermediates formed by 1,2-insertion of MA. In this living chain-walking catalyst system, the composition, molecular weight, and branching topology of the copolymer can be facilely tunable by simple variation of the ethylene pressure

Influence of Cuprous Oxide on Enhancing the Flame Retardancy and Smoke Suppression of Epoxy Resins Containing Microencapsulated Ammonium Polyphosphate

In this work, Cu₂O exhibited better synergistic effect with microencapsulated ammonium polyphosphate (MAPP) than other metal oxides, such as CuO, ZnO, SnO, Fe₂O₃, Ni₂O₃, and Co₂O₃, on improving the flame retardancy of epoxy resins (EP). Moreover, the addition of cuprous oxide (Cu₂O) could further decrease the total smoke production and carbon monoxide production. The analysis of char residues and evolved gases indicated that Cu₂O was beneficial to enhance the formation amount, intumescent degree, and compactness of char. The protective layer of intumescent char residue could hinder the decomposition of EP and diffusion of gaseous products, such as hydrocarbons, aromatic compounds and carbon monoxide (CO). In addition, Cu₂O also played a role in conversion of CO to CO₂ through a redox cycle, involving the reduction of Cu²⁺Cu⁺Cu⁰ by CO and the oxidation of Cu⁰Cu⁺Cu²⁺ by O₂. The possible flame retardant, smoke suppression, and CO oxidation mechanisms were proposed