Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity
Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity
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烯烃捕获期间的主链重排作为分子烯烃聚合催化中的限速步骤及其对共聚单体亲和力的影响
DOI：
10.1002/pola.28685
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
C. Ehm
中科院分区：
文献类型：
--
作者：
F. Zaccaria;R. Cipullo;P. Budzelaar;V. Busico;C. Ehm
现有的几种茂金属的实验数据表明，乙烯/丙烯的共聚比RC可能比竞争插入过渡态(TS)是速度限制的情况下预期的更依赖于温度。对反应路径的详细研究表明，在实际插入之前，在几种情况下存在一种“类似俘获”的过渡态，其自由能接近插入TS。围绕这些过渡态的运动不仅涉及单体和链，还包括配体骨架的明显扭曲，以允许单体进入。考虑到这些额外的TSS，对于一系列的茂金属和一个受约束的几何催化体系，其结果与实验的一致性大大提高。根据催化剂和温度的不同，选择性由竞争插入/插入、捕获/插入或捕获/捕获决定。这似乎是一种常见的情况，特别是对于高效催化剂来说，这使共聚性能的预测变得复杂(但不是阻碍)。©2017威利期刊公司J.Polym。科学，A部分：多晶硅。化学。2017年
Available experimental data for several metallocenes indicate that the ethene/propene copolymerization ratio rc can be much more temperature dependent than would be expected if competing insertion transition states (TS) are rate limiting. Detailed exploration of the reaction paths reveals in several cases the existence of a “capture-like” transition state before the actual insertion, with free energies close to the insertion TS. Movement around these transition states does not just involve monomer and chain, but also clear distortion of the ligand skeleton to allow entry of the monomer. Taking these additional TSs into account leads to much improved agreement with experiment for a series of metallocenes and a constrained geometry catalyst system. Depending on catalyst and temperature, selectivity is determined by competing insertion/insertion, capture/insertion or capture/capture. It seems likely that this is a common situation especially for highly efficient catalysts, complicating (but not preventing) prediction of copolymerization performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017