硅桥联稀土—过渡金属异核茂金属催化烯烃聚合研究

【作者】 张志红；

【导师】 孙俊全；

【作者基本信息】 浙江大学 ， 工业催化， 2003， 硕士

【摘要】 茂金属催化剂是继Ziegler-Natta催化剂之后的一类性能优异的烯烃聚合催化剂，具有高活性、活性中心单一、催化合成的聚合物的结构和分子量及其分布可控等优点。然而，茂金属聚合物因分子量分布窄而致使加工困难，已是阻碍其工业化的重要原因之一。研究表明，双核茂金属催化剂能够生产分子量呈双峰或宽峰的分布的聚合物，从而改善聚合物的性能。因此，对于双核茂金属的烯烃聚合研究，已经成为一个热点。 本文合成了两个新型的硅桥联稀土—过渡金属异核茂金属化合物：[（C₅H₅）TiCl₂ⅡMe₂Si（C₅H₄）₂][Sm（C₅H₅）Cl]（A）和 [（C₅H₅）ZrCl₂][Me₂Si（C₅H₄）（C₉H₆）][Sm（C₅H₅）Cl]（B），并对其进行了一系列的烯烃聚合研究：A／MAO和B／MAO催化乙烯聚合；B／Al（i-Bu）₃催化MMA聚合；B／MAO催化乙烯和MMA、乙烯和苯乙烯共聚。 详细研究了Ti-Sm异核化合物A和Zr-Sm异核化合物B在乙烯聚合中的催化特性，发现此类催化剂显现了一些不同于单核和同核茂催化剂的聚合行为：在相同的聚合条件下，Zr-Sm体系的活性要比Ti-Sm高。异核茂体系的活性比二茂钛、二茂锆体系和相应的同双核体系活性要低。 体系A／MAO的催化活性随催化剂浓度和MAO／Cat比例增大而增大，而温度的上升则使活性和分子量都下降。体系所得的聚乙烯熔点为126℃左右，结晶度69-75％。体系B／MAO随着MAO／Cat比例增大，活性明显上升，分子量下降。在70℃时活性最高，分子量随温度升高而急剧下降。体系得到的聚乙烯的熔点为128℃，结晶度为69％，比相同实验条件下Cp₂ZrCl₂／MAO所得的略高。 硅桥联Zr-Sm异核化合物B在Al（i-Bu）₃作用下催化MMA聚合，得到高分子量的PMMA（M_n≈5×10⁵）。非极性溶剂石油醚是MMA聚合的良溶剂。高铝比（Al／Cat=20）下，单体转化率随MMA／Cat减小而迅速增加，最高接近100％。提高Al／Cat摩尔比和温度有利于聚合速率增加。体系具有拟活性聚合特征。得到的聚合物部分不溶于常规PMMA良溶剂。PMMA间规含量在76％左右，玻璃化转变温度T_g=112.71℃，低温（20℃）下得到分子量呈双峰分布的PMMA（Mw／Mn=7.94）。 采用体系B／MAO，对乙烯和MMA、苯乙烯等极性单体进行了共聚合的探索性实验，考察了两种不同的聚合方法对共聚合的影响。实验表明，共聚单体的加入对活性物种有毒化作用。对于MMA，有可能得到嵌段共聚物，但共聚量很少；进行无规共聚，则只能得到MMA的均聚物，乙烯不参加聚合反应。对于苯乙烯，无论是嵌段共聚还是无规共聚，都没有得到良好的共聚物，只得到乙烯均聚物。更多还原

【Abstract】 Metallocene catalysts have been established as excellent catalysts for the polymerization after the Ziegler-Natta catalyst. The produced polyolefins have narrow molecular weight distributions due to identical active sites of the catalyst. However, this can be disadvantageous for industrial processing. The dinuclear complexes, which has two different active sites in one molecule , should be able to produce polymer with bimodal or broader molecular weight distributions. Recently a variety of dinuclear metallocene compounds have been prepared to examine their catalytic properties.Two novel silicon bridged transitionmetal - rare earth heterodinuclear metallocene compounds [(C5H.OTiCl2][Me2Si(C5H4)2][Sm(C5H5)Cl] (A) and [(C5H5)ZrCl2][Me2Si (C5H4)(C9H6)][Sm(C5H5)Cl] (B) were synthesized for the first time. In order to investigate the catalytic behaviors of the prepared dinuclear catalysts, many of polymerization are conducted as follows: (1) A/MAO and B/MAO system for ethylene polymerization. (2) B/Al(i-Bu)3 system for methyl methacrylate (MMA) polymerization. (3) B/MAO system for Ethylene and MMA copolymerization, ethylene and styrene copolymerizaion.Catalyst A and B have been used for the polymerization of ethylene activated by MAO. Some special behaviors were found. Under the same polymerization condition, the activity of Zr-Sm system is higher than Ti-Sm system. The catalytic activity of dinuclear catalysts is lower than the corresponding mononuclear and homodinuclear metallocene of Ti or Zr. For the system A/MAO, high concentration of catalyst and amount of MAO were preferred to get high activity. The activity and molecular weight of polyethylene dropped quickly with the elevation of the temperature. The melting point and crystallinity of the polymer were about 126 and 69-75% respectively. For the system B/MAO. with the molar ratio of MAO/Cat rise, the catalytic activity increase while the molecular weight declined. The optimal temperature for polymerization was 70 . The melting point and crystallinity of the polymer were about 128 and 69%, somewhat higher than the Cp2ZrCl2/MAO.Polymerization of MMA was catalyzed by B, activated with Al(i-Bu)3, produce polymer with high molecular weight ( A 5 105). The nonpolar solvents were suitable for the polymerization. The monomer conversion was rised as the MMA/Cat molar ratio decreased. The polymerization rate increased with the elevation of the temperature and Al/Cat molar ratio. Some polymer sample obtained by this catalyst system was not good dissolve in CH3Cl. The vitrification point and syndiotactic content of the polymer were about 112.71 and 76% respectively. PMMA produced under the lower temperature (20 ) showed a bimodal distribution (Mw/Mn=7.94).Some research has been carried into the ethylene and MMA, ethylene and styrene copolymerization, by catalysts system B/MAO through two different polymerization method. The results show that the activity became lower as the monomer added. The block copolymer of PE and PMMA may be obtained. However, copolymerization of ethylene and styrene can only produce PE neither in block nor in random copolymerization.更多还原