助催化剂对负载型Ziegler-Natta催化剂催化丙烯高温聚合的影响

Influence of Cocatalyst on High Temperature Polymerization of Propylene Catalyzed by Ziegler-Natta Catalyst

在低温下通过三乙基铝和水在不同的AI／H2O摩尔比下分别制备了EAO1(2:1),EAO2(3:2), EAO3(5:4)和EAO4(10:9)等一系列乙基铝氧烷,并将其作为助催化剂用于丙烯在不同温度下的聚合反应。通过对不同助催化剂的研究,发现助催化剂对负载型Ziegler-Natta催化剂催化丙烯聚合有显著的影响。在70℃时,不同助催化剂所制备的聚合物的等规度相近,但聚合活性按AIEt3>EAO1>EAO2>EAO3> EAO4次序递减,而EAO制备的聚合物的分子量明显高于AIEt3;在100℃时,不同助催化剂(除EAO4外) 的聚合活性相差不大,但聚合物的等规度和分子量都按AIEt3≈EAO1<EAO2<EAO3次序递增。结果表明助催化剂的反应性和体积大小影响活性中心的状态,进而影响聚合物的性质。

A series of ethylaluminoxanes were synthesized by the reaction between AIEt3 and water under various molar ratios of HzO to A1 at -78 ℃. The aluminoxanes were used as cocatalyst for MgCl2-supported Ziegler-Natta catalyst for propylene polymerization at the temperature ranging from 70 ℃ to 100 ℃. It was showed that the isotacticities of polymers prepared by various cocatalysts were close to each other at 70 ℃, while the polymerization activity was in the following order, AIEt3〉EAO1 〉 EAO2 〉 EAO3 〉 EAO4, and the molecular weights of polymers obtained with EAO were higher than that with AIEt3. The polymerization activities obtained with various cocatalysts （ except EAO4） were similar at 100 ℃, while the isotacticity and molecular weight of polymer increased in the order of AIEt3≈EAO1〈EAO2〈EAO3. It is proposed that the reactivity and the size of ＇cocatalyst influence the properties of active site of Ziegler-Natta catalyst resulting in the different properties of polymer.