Aluminum Alkyls as Highly Active Catalytic Chain Transfer Agents

链式转移 烷基 化学 低密度聚乙烯 高分子化学 聚合物 催化作用 聚合 催化链转移 聚乙烯 链端接 氢化物 活性聚合 动链长度 有机化学 光化学 自由基聚合
作者
Sean W. Ewart,Ivan A. Konstantinov,Teresa Karjala,Dan Baugh,Sarat Munjal
出处
期刊:Macromolecular Reaction Engineering [Wiley]
卷期号:14 (1) 被引量:1
标识
DOI:10.1002/mren.201900047
摘要

Abstract During the production of free radical initiated low‐density polyethylene (LDPE), it was discovered that the addition of low levels of alkyl aluminum compounds caused the molecular weight of the LDPE to drop precipitously. Further investigation demonstrated that aluminum‐alkyl compounds are among the most effective chain transfer agents ever utilized. It was also shown that polymer chains, which transfer to Al alkyl species, contain almost exclusively vinyl terminated end groups. A catalytic chain transfer mechanism is proposed in which chain transfer occurs from a growing polymer chain to an aluminum center followed by beta hydride elimination to produce a vinyl terminated polymer chain and a new aluminum hydride bond. This new aluminum hydride bond can then undergo further chain transfer reactions. This is the first time such a catalytic chain transfer mechanism has been reported. As little as 10–20 mol ppm aluminum alkyl species decreased the degree of polymerization by a factor of 2 resulting in chain transfer constant ( C s ) values as high as 1000–2000. Density functional theory (DFT) study elucidated the catalytic cycle of triethylaluminum (TEA). It is discovered that, depending on the reaction conditions, TEA can serve as a conventional as well as catalytic chain transfer agent.
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