A SEMIEMPIRICAL STUDY ON ZIEGLER-NATTA CATALYST - CONCERNING THE INTERACTION ETIND(2)ZRCL(2) MAO/SIO2/

A modified extended Huckel method (EHMO), which includes core-core rep ulsion terms, was used to study a propylene polymerization heterogeneo us catalyst by modelling the adsorption of the ansa-metallocene ethyle n-bisindenylzirconium dichloride (C2H5(C9H6)(2)ZrCl2 from now on EtInd (2)ZrCl(2)) on SiO2 surfaces. The adsorption was considered to occur a t two faces of SiO2 (with geminal and isolated OH's) and at two differ ent temperatures for SiO2 pretreatment (200 and 600 degrees C). Taking into account that the interaction with Al compounds is considered as a way to improve the catalyst performance, specially with methylalumin oxane (MAO), a local model of aluminoxane (AlO) was added to Si-O bond with the subsequent metallocene adsorption. The results show that AlO improves the zirconocene adsorption on SiO2 modelled at 200 degrees C while it inhibits that process at 600 degrees C.