Polynuclear olefin polymerization catalysis: proximity and cocatalyst effects lead to significantly increased polyethylene molecular weight and comonomer enchainment levels.
Polynuclear olefin polymerization catalysis: proximity and cocatalyst effects lead to significantly increased polyethylene molecular weight and comonomer enchainment levels.
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DOI：
10.1002/anie.200460288
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发表时间：
2004-09
影响因子：
--
通讯作者：
Hongbo Li;Liting Li;T. Marks
中科院分区：
文献类型：
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作者：
Hongbo Li;Liting Li;T. Marks
非生物的尝试，模仿某些有利的酶的特点，最近集中在建设多金属催化中心，能够实现合作识别/激活/反应性之间的影响，接近过渡金属离子。[1]关于在单中心聚合催化中的这种效应，[2 - 4]我们最近报道了受限几何双核催化剂和双核助催化剂组合（C2-Zr 2 + B2）通过链转移途径的改性，与Zr 1 + B1的单核组合相比，在乙烯均聚中提供显著增强的支化，并且在乙烯和1-己烯共聚中提供增强的共聚单体掺入。[3c]然而，Zr的限制几何构型催化剂（CGC）通常产生不可接受的低Mw聚烯烃，[4c，d，5]（Mw是重均摩尔质量）提出了有趣的问题，即更接近的金属-金属接近和替代助催化剂可能具有什么影响。在这里，我们交流，在乙烯均聚反应在相同的反应条件下，亚甲基桥连的C1-Zr2提供显着更高的分子量的产品比-CH2CH2-桥连的C2-Zr2（% 70 Mw增加）和单核Zr1（% 130 Mw增加）。此外，用MAO（甲基铝氧烷）作为助催化剂，用C2-Zr2Cl 4和C1-Zr2Cl 4都实现了聚乙烯分子量的非常大的增加。
Abiotic attempts to mimic certain advantageous enzyme characteristics have recently focused on construction of multimetallic catalytic centers capable of achieving cooperative recognition/activation/reactivity effects between proximate transition-metal ions.[1] Regarding such effects in singlesite polymerization catalysis,[2–4] we recently reported that a constrained geometry binuclear catalyst and binuclear cocatalyst combination (C2-Zr2+ B2) affords, through the modification of chain-transfer pathways, significantly enhanced branching in ethylene homopolymerization and enhanced comonomer incorporation in ethylene and 1-hexene copolymerization versus a mononuclear combination of Zr1+ B1.[3c]Nevertheless, constrained-geometry catalysts (CGC) of Zr typically produce unacceptably low-Mw polyolefins,[4c, d, 5](Mw is the weight-average molar mass) raising the intriguing question of what effects closer metal–metal proximity and alternative cocatalysts might have. Here we communicate that in ethylene homopolymerizations under identical reaction conditions, methylene-bridged C1-Zr2 affords significantly higher molecular weight products than-CH2CH2-bridged C2-Zr2 (% 70 Mw increase) and mononuclear Zr1 (% 130 Mw increase). Furthermore, with MAO (methylaluminoxane) as cocatalyst, very large increases in polyethylene molecular weight are achieved with both C2-Zr2Cl4 and C1-