Guo Lihua, Li Jiaxing, Zhao Wei, Wei Peng, Ju Yanping, Cui Xiaoru, Yuan Liqing, Ji Mingjun, Liu Zhe
Key Laboratory of Catalytic Conversion and Clean Energy in Universities of Shandong Province, School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu 273165, P. R. China.
Inorg Chem. 2024 Sep 23;63(38):17809-17827. doi: 10.1021/acs.inorgchem.4c02712. Epub 2024 Sep 12.
This study addresses the challenge of controlling branching density and branch-type distribution in late-transition-metal-catalyzed chain walking polymerizations. We explored α-diimine Pd(II) complexes with incrementally increased -aryl sterics for long-chain α-olefin (co)polymerization. - catalysts, which feature gradually increased -aryl sterics and at least one small CH substituent, exhibited similar 2,1-insertion fractions (44-50%), polymer branching densities (55-63/1000C), and melting temperatures (26-28 °C). In contrast, with bulky -aryl sterics covering all sides demonstrated a significant increase in 2,1-insertion fractions up to 82%, leading to "PE-like" polymers with high melting temperatures ( > 111 °C). This abrupt change in polymerization behavior, termed the "steric-deficient effect", contrasts with the gradual changes observed in similar Ni(II) systems that we reported previously. Furthermore, due to the rapid chain walking ability of Pd(II) catalysts in long-chain α-olefin (co)polymerization, these catalysts favor the production of polyolefins with higher proportions of methyl branches compared to those produced by Ni(II) catalysts. Particularly, these Pd(II) catalysts are capable of synthesizing functionalized semicrystalline copolymers by copolymerizing 1-octene with a variety of polar comonomers, thereby significantly altering the surface properties of the materials.
本研究解决了在晚期过渡金属催化的链行走聚合反应中控制支化密度和支化类型分布的挑战。我们探索了具有逐渐增加的芳基空间位阻的α-二亚胺钯（II）配合物用于长链α-烯烃（共）聚合反应。具有逐渐增加的芳基空间位阻且至少有一个小的CH取代基的催化剂，表现出相似的2,1-插入分数（44-50%）、聚合物支化密度（55-63/1000C）和熔点（26-28°C）。相比之下，具有全方位大位阻芳基的催化剂2,1-插入分数显著增加，高达82%，从而得到高熔点（>111°C）的“类聚乙烯”聚合物。这种聚合行为的突然变化，称为“空间位阻不足效应”，与我们之前报道的类似镍（II）体系中观察到的逐渐变化形成对比。此外，由于钯（II）催化剂在长链α-烯烃（共）聚合反应中具有快速的链行走能力，与镍（II）催化剂相比，这些催化剂有利于生产具有更高比例甲基支链的聚烯烃。特别地，这些钯（II）催化剂能够通过使1-辛烯与各种极性共聚单体共聚来合成功能化的半结晶共聚物，从而显著改变材料的表面性质。
