【易塑网咨讯中心】讯：美国休斯敦大学Do课题组设计了一类具有短链PEG修饰的席夫碱Ni催化剂，并设想与碱金属盐作用得到目标催化剂。

　　以Ni和Pd为代表的后过渡金属催化剂在催化乙烯聚合过程中表现出和前过渡金属(Ti,Zr and Hf)不同的结果，并体现出对于极性单体，溶剂和杂质等良好的耐受性。通过对后过渡金属催化剂的结构和聚合条件的调节，仅以乙烯为唯一单体即可值得支化或者超支化聚乙烯。通过一定的设计得到具有高稳定性和高催化效率的催化剂，并以此制备高分子量、高支化以及窄分布的聚乙烯是该领域的研究目标。

　　美国休斯敦大学Do课题组设计了一类具有短链PEG修饰的席夫碱Ni催化剂，并设想与碱金属盐MBArF4(M = Li+, Na+, and K+; BArF4?=tetrakis ( 3,5-trifluoromethylphenyl)borate)作用得到目标催化剂。在这样的杂双催化体系中，Ni部分催化乙烯聚合，而碱金属离子部分起到激发和极性修饰的功能。通过，金属滴定法(metal titration)和X射线衍射法均验证了碱金属盐可以与Ni催化剂反应形成杂双金属体系。聚合实验表明，杂双金属体系较单金属体系表现出良好的稳定性、更高的TOF(up to 20-fold enhancement)、更高的分子量和更高的支化度，充分证明了碱金属与Ni的协同催化效果。

　　该工作首次系统研究了非催化性金属离子作为第二组分在烯烃配位聚合中的作用，对于设计高性能烯烃聚合催化剂提供了新思路。

摘要速递：

Fine-Tuning Nickel Phenoxyimine Olefin Polymerization Catalysts: Performance Boosting by Alkali Cations

J. Am. Chem. Soc.

DOI: 10.1021/jacs.5b10351

November 12, 2015

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 (NiL0, NiL2–NiL4) that form discrete molecular species with alkali metal ions (M+ = Li+, Na+, K+). Metal binding titration studies and structural characterization by X-ray crystallography provide evidence for the self-assembly of both 1:1 and 2:1 NiL:M+ species in solution, except for NiL4/Na+which form only the 1:1 complex. It was found that upon treatment with a phosphine scavenger, these NiL complexes are active catalysts for ethylene polymerization. We demonstrate that the addition of M+ to NiL 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 NiLwithout 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.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

微信关注【易塑网】公众号，更多资讯活动等你来挖掘