摘要
烯烃聚合催化剂种类繁多,改变金属离子或配位体能得到性能不同的烯烃聚合催化剂.可供选择的助催化剂主要有烷基铝,烷基氯化铝,铝氧烷和Cp_2MtMe化合物等(Mt=Ti,V,Zr,Hf).有实用价值的助催化剂只有烷基铝或烷基氯化铝.对丙烯聚合非载体钛系催化剂而言,AlEt_2Cl是较好的助催化剂,而对载体型MgCl_2/TiCl_4钛系催化剂,较好的助催化剂则是AlEt_3.
The kinetics of propylene polymerization has been studied with catalyst MgCl2/CeH4(COOC4H9)2/TiCl4 and cocatalyst MgBu2/AlEt2Cl under 7.1×104 Pa of propylene pressure and 50℃. The effect of the concentration of alkyl metal, CMg]/(AD and CAl)/[Ti] molar ratio on the catalyst activity, isotactic index and the molecular weight distribution of polypropylene was discussed. The increase of the activity of the catalyst system containing MgBu2 is primarily due to the improvement of kinetic behavior. The catalyst activity and the isotactic index of polypropylene decrease obviously when [Mg]/[Al] is less than 1/4. A decrease in[Mg]/[Al] leads to a narrowing of polydispcrsity index (Mw/Mn) and an increase in Mn. It is conceivable that MgEu2 plays an important role in the process of chain transfer.Whole isotacticity decreases no matter whether [Al]/[Ti] molar ratio is higher or lower than 40. This is different from the conventional polymerization of propylene with AlEt3 as cocatalyst. The dependence of the polymerization rate on the concentration of alkyl metal can be described by Langmuir-Hinshelwood mechanism.
