Ziegler-Natta催化剂制备低等规聚丙烯的研究

研究了不同Ziegler-Natta催化剂体系对淤浆聚合制备低等规聚丙烯的影响。实验结果表明，三异丁基铝作为助催化剂时催化剂的聚合活性高于三乙基铝。BCM-100催化剂具有较高的聚合活性和立构定向性能力，但制备的聚丙烯正己烷可溶物含量较低，而BCE制备的聚丙烯正己烷可溶物含量较高，且聚丙烯正己烷不溶物的等规指数最高。利用DSC、GPC、13C-NMR等表征手段对不同催化剂体系合成的低等规聚丙烯的结构进行了分析。表征结果显示，在相同聚合条件下，BCE催化剂制备得到的聚丙烯正己烷不溶物的立构规整性最高而结晶度最低；实验所考察几种催化剂制备的聚丙烯正己烷可溶部分的平均重均分子量均远小于正己烷不溶部分的平均重均分子量，通过比较发现，BCE催化剂得到的聚丙烯的正己烷不溶物的平均重均分子量最低，正己烷可溶物的平均重均分子量最高，而BCM-100得到的聚丙烯的正己烷不溶物的平均重均分子量最高，正己烷可溶物的平均重均分子量最低。

Preparation of low isotacticity polypropylene catalyzed by Ziegler-Natta catalysts

A study of the influence of different Ziegler-Natta catalyst systems on propylene polymerization in a slurry polymerization process has been investigated. It was found that Ziegler-Natta catalysts with triisobutylaluminium used as cocatalyst had a higher activity than the corresponding catalysts with triethylaluminum. The BCM-100 catalyst showed the highest activity and stereoregularity, but gave the lowest content of polypropylene dissolved in n-hexane. The BCE catalyst gave the highest content of polypropylene dissolved in n-hexane and the highest isotacticity index of the insoluble portion of polypropylene in n-hexane. The microstructure of the resulting low isotacticity polypropylene was investigated in detail by differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and carbon 13 nuclear magnetic resonance (13C-NMR) spectroscopy. The results showed that under the same conditions, the insoluble portion of polypropylene in n-hexane obtained with the BCE catalyst showed the highest stereoregularity and lowest crystallinity. With the catalysts studied, the average molecular weight of polypropylene dissolved in n-hexane was far lower than the average molecular weight of the insoluble portion. It was found that the BCE catalyst gave the lowest weight-average molecular weight of the polypropylene insoluble in n-hexane but the highest weight-average molecular weight of the polypropylene dissolved in n-hexane, whereas the BCM-100 catalyst gave the highest weight-average molecular weight of the polypropylene insoluble in n-hexane and the lowest weight-average molecular weight of the polypropylene dissolved in n-hexane.