Addition of Lewis bases and acids. Effect on α-olefins polymerization with soluble metallocenes, 1 Ethylene

Abstract

In this paper the soluble system rac-Etnd 2 -ZrCl 2 /methylaluminoxane (MAO) was studied in propylene polymerization with additives. Lewis acid and base such as AlCl 3 and ethyl benzoate (EB) were used to evaluate their effects on polymerization kinetics, catalyst activities and polymer properties. The results obtained show a trend to improve the performance when AlCl 3 is added. The activity is decreased with EB, but the effect it not as strong a for ethylene (see Part 1). To further elucidate some of the different aspects of metallocene activation and reactivation in the reaction media, several reactions were carried out using different preactivation steps, with and without AlCl 3 . The preactivations were carried out taking account of the different results obtained with both additives (AlCl 3 and EB). The pretreatment with EB was not considered because the activity is decreased in the polymerization. AlCl 3 improves the activity when it is present during the preactivation step, but the presence of EB in the reactor during the polymerization step has a poisoning effect. These results show the importance of the preactivation step carried out without olefin. The molecular weight of polypropylene obtained remains almost unchanged in all the evaluated conditions. A complete discussion of ethylene and propylene results is included, taking account of Part 1 and 2.