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Aluminum Alkyls as Highly Active Catalytic Chain Transfer Agents
Macromolecular Reaction Engineering ( IF 1.8 ) Pub Date : 2020-01-07 , DOI: 10.1002/mren.201900047 Sean Ewart 1 , Ivan Konstantinov 1 , Teresa Karjala 1 , Dan Baugh 1 , Sarat Munjal 1
Macromolecular Reaction Engineering ( IF 1.8 ) Pub Date : 2020-01-07 , DOI: 10.1002/mren.201900047 Sean Ewart 1 , Ivan Konstantinov 1 , Teresa Karjala 1 , Dan Baugh 1 , Sarat Munjal 1
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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 (Cs) 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.
中文翻译：
烷基铝作为高活性催化链转移剂
在生产自由基引发的低密度聚乙烯（LDPE）的过程中，发现添加低含量的烷基铝化合物会导致LDPE的分子量急剧下降。进一步的研究表明，烷基铝化合物是有史以来最有效的链转移剂之一。还显示了转移至烷基烷基的聚合物链几乎仅包含乙烯基封端的端基。提出了一种催化链转移机理，其中从增长的聚合物链到铝中心发生链转移，然后消除β-氢化物以产生乙烯基封端的聚合物链和新的氢化铝键。然后，这种新的氢化铝键可进行进一步的链转移反应。这是首次报道这种催化链转移机理。仅有10–20 mol ppm的烷基铝物种使聚合度降低2倍，导致链转移常数（C s）值高达1000-2000。密度泛函理论（DFT）研究阐明了三乙基铝（TEA）的催化循环。已经发现，根据反应条件，TEA可以用作常规的以及催化链转移剂。
更新日期：2020-01-07
中文翻译：
烷基铝作为高活性催化链转移剂
在生产自由基引发的低密度聚乙烯（LDPE）的过程中，发现添加低含量的烷基铝化合物会导致LDPE的分子量急剧下降。进一步的研究表明，烷基铝化合物是有史以来最有效的链转移剂之一。还显示了转移至烷基烷基的聚合物链几乎仅包含乙烯基封端的端基。提出了一种催化链转移机理，其中从增长的聚合物链到铝中心发生链转移，然后消除β-氢化物以产生乙烯基封端的聚合物链和新的氢化铝键。然后，这种新的氢化铝键可进行进一步的链转移反应。这是首次报道这种催化链转移机理。仅有10–20 mol ppm的烷基铝物种使聚合度降低2倍，导致链转移常数（C s）值高达1000-2000。密度泛函理论（DFT）研究阐明了三乙基铝（TEA）的催化循环。已经发现，根据反应条件，TEA可以用作常规的以及催化链转移剂。
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