三种不同碳桥联双核茂钛配合物的合成及催化乙烯聚合研究

合成了3种不同结构的CnH₂n桥联双核茂钛配合物(CH₃)₂C[(C₅H₄)TiCl₂(C₅H₅)]₂(3),(CH₂)_n[(C₅H₄)TiCl₂(C₅H₅)]₂(6,n=3;7,n=4),并用1HNMR进行了表征.发现以甲苯为溶剂时,不仅提高了产率,而且有效地避免了副产物Cp₂TiCl₂的生成.研究了化合物7/MAO(甲基铝氧烷)催化乙烯聚合的反应,考察了反应条件对催化体系的影响.结果表明,催化活性随着n(Al)/n(Cat.)比的增大而提高,聚乙烯的分子量在n(Al)/n(Cat.)=500和50℃时达到最高值9.0102×10⁴;随着聚合时间的延长,催化活性下降,而产物分子量不断升高;随着温度的上升,50℃时催化活性和聚乙烯的分子量最高,分别为2.4074×10⁵gPE/(molTi·h)和6.8679×10⁴.随着桥联双核茂钛配合物碳桥的增长,催化活性增加,所得聚乙烯的分子量降低.

Synthesis of Three Different Carbon Bridged Dinuclear Titanocene Complexes as Catalysts for Ethylene Polymerization

Three different dinuclear titanocene complexes (CH₃)₂C[(C₅H₄)TiCl₂(C₅H₅)]₂(3),(CH₂)·n[(C₅H₄)TiCl₂(C₅H₅)]₂(6, n=3; 7, n=4) were synthesized by the reaction of the corresponding dilithiumed salts with two equivalents of CpTiCl₃in toluene. The yield of the corresponding dinuclear titanocene complex in toluene is higher than that in THF, in which CpTiCl₃may be disproportionated to form Cp²TiCl₂. All titanocenes are characterized by ¹HNMR. The catalytic properties of the dinuclear titanocene complexes for ethylene polymerization were investigated in the presence of MAO(methylaluminoxane). For the ethylene polymerization catalyzed by compound 7/MAO, the catalytic activity increases with the increase of n(Al)/n(Cat.), the moleculer weight of polyethylene reaches 9.0102×10⁴. With the prolongation of the polymerization time, the catalytic activity declines while the molecular weight of polyethylene increases. At50 ℃, the molecular weight of the polymer reaches up to 7.77×10⁴. However, it decreases rapidly along with rising reaction temperature. When the length of the bridged ligand increases, the polymerization activity increases with the increase of the bridge length while the molecular weight decreases accordingly.