A novel method for synthesizing cyano-functionalized polyethylenes through ethylene/acrylamide copolymerization using binuclear Nickel catalysts has been developed, presenting solutions to long-standing issues of catalyst poisoning and enhancing polymer performance.
The research, conducted by Y. Tao, X.-L. Sun, Y. Gong, and colleagues at the Chinese Academy of Sciences, has achieved remarkable advancements, enabling efficient synthesis of cyano-functionalized polyethylenes with over 99% purity and heightened catalytic activity—up to 4.1 × 106 g/(mol cat·h) under 20 atm of ethylene pressure.
Polymerization of functionalized polyethylenes is highly valued for applications across various industries, from packaging to automotive components, as they combine beneficial mechanical properties with functional characteristics. Traditional methods to synthesize these polymers often suffer from catalyst poisoning due to the presence of polar functional groups, which can cause significant decreases in performance metrics.
The innovative approach developed by the researchers employed binuclear Nickel catalysts, circumventing the detrimental effects associated with prior methods. By employing these catalysts during polymerization, they were able to achieve significant chain transfer reactions and confirm the conversion of the amido groups to cyano groups, as evidenced by extensive polymer characterization including nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC).
The findings, published on March 12, 2025, reveal the underlying mechanism of isomerization-mediated chain transfer polymerization (ICTP), which integrates tandem acrylamide enchainment, conversion of amido to nitrile groups, and active catalyst regeneration through diethylaluminum chloride (DEAC).
For example, initial experiments using one of the selected Nickel catalysts, identified as Cat.1, at 30 °C produced some cyano-functionalized polyethylenes with activity recorded at 0.9 × 105 g/(mol cat·h). An analysis of catalyst characteristics showed significant improvements when utilizing larger substituents on the catalyst; increasing the size of R1 from -Me to bulkier -iPr led to activity rising to 1.4 × 105 g/(mol cat·h).
Another pivotal aspect of this study is the reliance on DEAC, which was observed to facilitate both the transformation from amido to nitrile and the regeneration of active catalysts. The presence of DEAC was deemed necessary to maintain high activity levels, especially when the DEAC/Acrylamide ratio was adjusted—a factor contributing to the enhanced catalytic performance.
While testing under high ethylene pressure was expected to significantly increase polymer production, it also demonstrated how molecular weight (Mn) of the resulting materials could be fine-tuned, achieving much higher Mn values (from 2.4 to 48.5 kg/mol) without comprising the purity of cyano functionality, keeping the ratio of CN/CONH2 at approximately 99/1.
This breakthrough implies considerable promise not only for the field of polymer chemistry but for industries dependent on functional polymer materials. It paves the way for future research, aimed at exploring and optimizing configurations of these catalysts to yield even more exceptional results.
"This approach utilizes binuclear Ni catalysis for ethylene/acrylamide copolymerization, resulting in the synthesis of cyano-functionalized PEs with great activity," said the authors of the article.
Overall, the synthesis of cyano-functionalized polyethylenes through ethylene/acrylamide copolymerization marks a significant step forward, allowing enhanced properties of polymers and the potential for broader applications across material sciences. More broadly, these findings advance our comprehension of polymerization mechanisms and equip researchers with novel methodologies for crafting advanced functional polyolefins.