Quantitative Validation of the Living Coordinative Chain-Transfer Polymerization of 1-Hexene Using Chromophore Quench Labeling
Quantitative Validation of the Living Coordinative Chain-Transfer Polymerization of 1-Hexene Using Chromophore Quench Labeling
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DOI：
10.1021/acs.macromol.0c00552
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发表时间：
2020-07-28
期刊：
影响因子：
5.5
通讯作者：
Landis, Clark R.
中科院分区：
文献类型：
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作者：
Cueny, Eric S.;Sita, Lawrence R.;Landis, Clark R.
在这份报告中，我们应用发色团猝灭标记（CQL）技术的生活，均相聚合催化剂和生活的协调链转移聚合（LCCTP）的条件。我们观察到100%的活性位点计数，通过CQL的1-己烯聚合催化的两个不同的双脒（CPAM）4族金属配合物，以前报道的活性聚合催化剂。我们得到了1-己烯的传播的CPAM铪配合物催化的速率常数。聚合物链末端的选择性碘解和H-1 NMR分析使得能够量化Zn-聚合物基;在低转化率（类似于10%转化率）下，观察到每个Zn近2个聚合物链。通过马约分析和动力学模拟，我们估算了聚合反应中Hf-聚合基与Zn-乙基交换的速率。除了活性位点计数，发色团猝灭标记方法使得能够使用具有在线UV检测器的凝胶渗透色谱法（GPC）（UV-GPC）观察催化剂结合的聚合物基分子量分布（MMD）。催化剂结合的聚合物基和所有聚合物链的MMD的比较（使用折射率检测，RI-GPC测量）揭示了重要的机理细节。除了反应中的早期时间点之外，我们观察到UV-GPC和RI-GPC迹线之间的极好重叠。这些结果表明，在1-己烯的LCCTP中，使用CPAM铪络合物作为催化剂和二乙基锌作为链转移剂，聚合物链在Hf和Zn上的平衡迅速发生。动力学模拟表明，Hf-聚合物基的锌-聚合物基交换导致UV-GPC和RI-GPC的痕迹之间的良好的重叠，并粗略估计该过程的速率常数。
In this report, we apply the chromophore quench-labeling (CQL) technique to living, homogeneous polymerization catalysts and living coordinative chain-transfer polymerization (LCCTP) conditions. We observe 100% active site counts via CQL for 1-hexene polymerization as catalyzed by two different cyclopentadienyl amidinate (CPAM) group 4 metal complexes, both previously reported to be living polymerization catalysts. We obtain a rate constant for the propagation of 1-hexene catalyzed by the CPAM hafnium complex. Selective iodinolysis and H-1 NMR analysis of polymer chain ends enable the quantification of Zn-polymeryls; at low conversions (similar to 10% conversion), nearly 2 polymer chains per Zn are observed. Through Mayo analysis and kinetic simulations, we ks) estimate the rate of Hf-polymeryl for Zn-ethyl exchange in polymerization. Beyond active site counting, the chromophore quench-labeling method enables the observation of catalyst-bound polymeryl molecular mass distributions (MMDs) using gel permeation chromatography (GPC) with an inline UV detector (UV-GPC). Comparison of the MMDs of catalyst-bound polymeryls and all polymer chains (measured using refractive index detection, RI-GPC) reveals important mechanistic details. With the exception of early time points in the reaction, we observe excellent overlap between the UV-GPC and the RI-GPC traces. These results reveal that equilibration of polymer chains on Hf and Zn occurs rapidly in the LCCTP of 1-hexene using the CPAM hafnium complex as the catalyst and diethyl zinc as the chain-transfer agent. Kinetic simulations indicate that the Hf-polymeryl for Zn-polymeryl exchange leads to the good overlap between UV-GPC and RI-GPC traces and a crude estimate for the rate constant of this process.