Effects of the external electron donor on the catalyst activity and polymer molecular weight for the ethylene polymerization

Abstract

In the present study, investigate effects of external electron donors on the ethylene polymerization with MgCl2-supported Ziegler-Natta catalysts synthesized by recrystallization method. External donors can be divided into 4 grouped such as alcohols, ketones, esters and di-ethers. The effects of the different kind of functional groups and molecular structure of external donors on catalytic activity and polymer properties were investigated and also compared with and without any donor. The results indicated that external electron donors remarkably affected on the catalytic activity not only improvement, but also deactivation, depending on the nature of each functional groups. The activities of catalysts are in the following order: di-ether > none > ester > alcohol > ketone. In addition, molecular structures of alcohol carbon were found to be effected; more bulkiness produced an evident deactivation effect lower than linear structures in comparison with the same numbers of carbon. The obtained polymer molecular weight after external electron donors is addition depending on the catalytic activity. It can be proposed that external electron donors decreased the catalyst activity leading to the reduction of polyethylene molecular weight. Furthermore, it was found that di-ether which acts as an external donor increased the catalyst activity and also enhanced polyethylene molecular weight. Therefore, this research plays an important role in developing catalyst efficiently and molecular weight desire of polymer for in olefin industries