Ethylene and Propylene polymerization using in-situ supported Me2Si(Ind)2ZrCl2 catalyst: Experimental and theoretical study

F. C: FRANCESCHINI; T. T. DA R. TAVARES; J. H. Z . DOS SANTOS; M. L. FERREIRA; J. B: P. SOARES

MACROMOLECULAR MATERIALS AND ENGINEERING (PRINT)

Wiley-VCH-Verlag

Lugar: Weinheim; Año: 2006 vol. 291 p. 279 - 287

1438-7492

Me2Si(Ind)2ZrCl2 was in-situ immobilized onto SMAO (MAO-modified SiO2) and used for ethylene and propylene polymerizatoin in the presence of TEA (triethylaluminum) or TIBA (triisobutylaluminum) as cocatalyst. The catalytic system Me2Si(Ind)2ZrCl2/SMAO exhibited different behavior depending on the amount and nature of the alkylaluminum employed, and on the monomer (ethylene or propylene). The catalyst activity was nearly 0.4 kg polymer/g cat.h with both cocatalysts in the propylene polymerization, and in the presence of TIBA in ethylene polymerization, independently of the Al/Zr molar ratio. However, when ethylene was polymerized using TEA at Al/Zr molar ratio of 250, the activity was 10 times higher (4.0 kg PE/g cat.h). The in-situ and homogeneous polyethylenes showed practically the same melting point (Tm). On the other hand, the in-situ polypropylenes had slightly lower Tm than the homogeneous one. The polydispersity of the polymers was higher when TIBA was used as cocatalyst. The nature and amount of the alkylaluminum also influenced the molar mass. The polypropylene molar mass was higher when TIBA was the cocatalyst. Nevertheless, opposite behavior was observed for the polyethylenes. Concerning the alkylaluminum concentration, the molar mass of the polymers decreased as the amount of TEA increased. In the presence of TIBA, the polyethylenes molar mass was almost the same, independently of the alkylaluminum concentration, and the polypropylene molar mass increased with increasing amounts of cocatalyst. The GPC curves deconvolution showed 2 peaks (2 different groups of active sites) for the homogeneous system, and 3 peaks for the heterogeneous in-situ system. The only exception was observed when TEA was used at Al/Zr molar ratio of 500, where the best fit was obtained with 2 peaks. Based on the GPC deconvolution results and on the theoretical modeling, a proposal for the active sites structure was made.