Kretschmer Winfried P, Meetsma Auke, Hessen Bart, Schmalz Thomas, Qayyum Sadaf, Kempe Rhett
Stratingh Institut for Chemistry and Chemical Engineering, Center for Catalytic Olefin Polymerization, University of Groningen, Nijenborgh 4 9747 AG Groningen, The Netherlands.
Chemistry. 2006 Dec 4;12(35):8969-78. doi: 10.1002/chem.200600660.
Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).
通过空间位阻较大的氨基吡啶与三烷基钇配合物发生烷烃消除反应，然后用硼酸铵夺取两个烷基官能团中的一个，可高产率地得到氨基吡啶配体稳定的有机钇阳离子。在80℃且存在少量烷基铝化合物的情况下，如果使用非常庞大的氨基吡啶配体，会观察到非常高的乙烯聚合活性。在这些聚合反应过程中，观察到有机钇阳离子与烷基铝之间存在可逆的聚乙烯链转移。此处描述的链转移催化剂体系能够制备相对长链（高达4000 g mol-1）的铝封端聚乙烯，其分子量分布<1.1。在合成高分子量聚乙烯时，由于较高粘度和聚合物链沉淀（80 - 100℃）导致可逆性降低，随着链长增加（15,600 g mol-1，约为1.4），多分散性略有增加。
