Study On The Influence Of Cocatalyst On The Active Site Distribution Of Supported Ziegler-Natta Catalyst

Study on the influence of cocatalyst on the active site distribution of supported Ziegler-Natta catalystAbstractThe present thesis includes the study on the influences of cocatalysts on the 1-hexene polymerization active site distribution of DQ type supported Ziegler-Natta catalyst for propylene polymerization, and the introduced study on that one of propylene polymerization.Various co-catalytic systems, e.g. triethyl aluminium(TEA), triisobutyl aluminium(TIBA), methylalumoxane(MAO) and the mixture of and TEA-TIBA, and different AI/Ti ratios are adopted in the investigation on the influence on the 1-hexene polymerization by DQ catalytic system. It is included that 4-5 types of active sites exist in the catalytic system and the active site produced polymer with low molecular weight is easy to be activiated while TEA is used as the cocatalyst. While TIBA, the active site produced polymer with high molecular weight and seldom active site produced polymer with low one is prone to be activiated. MAO tends to activiate the active site produced polymer with middle-level molecular weight. In TEA-TIBA catalytic system, TEA and TIBA activiate the corresponding active site and the weight of every active site gradationally varied with the change of the ratio of the two cocatalysts. And the activity of the active site produced polymer with high molecular weight is proportion to the concentration of TIBA.The study on the influence of polymerization temperature, external donor, polymerization time and hydrogen regulation on the polymerization behavior and active site distribution of 1-hexene polymerization is carried out. It can be included that decreases of the polymerization temperature and/or introduction of the external donor make the isotacticity of resulted polymer higher. Hydrogen regulation lowers the molecular weight of polymer and makes the molecular weight distribution changed. This express the influence of hydrogen regulation is different for different active sites. Different kinetic behaviors are exhibited in different active sites. Some of them deactiviated rapidly. On the other hand, others were relatively stable. The response of different active sites to polymerizationtemperature is different. The active site produced polymer with high molecular weight would be reduced while temperature increased.Based on the results of 1-hexene polymerizations, the active site distribution and the effect of hydrogen regulation of propylene polymerization by using TEA-TIBA as cocatalyst is investigated. The change of active sites distribution reflects the accumulation effect of TEA and TIBAto their corresponding active sties. Hydrogen regulation made the molecular weight lower and the molecular weight distribution narrower. Hydrogen regulation reduced the difference of the molecular weight distribution between TIAB and TEA co-catalytic system. At the same time, hydrogen regulation reduced the influence on the molecular weight distribution resulted from the change of composition of cocatalyst. Varying the cocatalyst for propylene polymerization system could regulate the molecular weight.According to the results of the present study, it is reasoned that the cocatalyst importantly influence the active sites distribution of supported Ziegler-Natta catalytic system. The application of various cocatalysts can regulate the active sites distribution of polymer. This strategy is simple and convenient to carry out and the commercial value can been foreseen.