New architecture of supported metallocene catalysts for alkene polymerization

T. VELILLA; A. DELGADO; R. QUIJADA; D. BIANCHINI; G. BARRERA GALLAND; J. H. Z. DOS SANTOS; D. P. FASCE; R. J. J. WILLIAMS

JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY

Wiley

Año: 2007 vol. 45 p. 5480 - 5486

0887-624X

We report the synthesis of a supported-metallocene catalyst that exhibits the same activity than the homogeneous catalyst for the ethylene polymerization reactions. The key of this new catalytic system is a hybrid organic-inorganic polymer obtained by the co-condensation of an organotrialkoxysilane (OTAS, 40 moles %) with tetraethoxysilane (TEOS, 60 moles %). The particular organic group of OTAS enabled to avoid gelation when the hydrolytic condensation was performed with a thermal cycle attaining 150 ºC. The resulting product (SFS, soluble functionalized-silica) was a glass at room temperature, soluble in several organic solvents such as THF and toluene. 29Si NMR spectrum of SFS showed that OTAS units were fully condensed (T3 species) while TEOS units were mainly present as tri- (Q3) and tetra-condensed (Q4) units. SFS was grafted on activated silica by reaction of silanol groups. The metallocene ((nBuCp)2ZrCl2) was covalently bonded to the SFS-modified support. The polymerization of ethylene was carried out in toluene in the presence of methylaluminoxane (MAO). The activity of the supported catalyst was similar to the one of the metallocene catalyst in solution. The simplest explanation accounting for this fact is that most of the metallocene was grafted to SFS species issuing from the surface of the support, by reaction with their silanol groups. This improves the accessibility of the monomer to the reaction sites. Specific interactions of the metallocene species with neighboring organic branches of SFS might also affect the catalytic activity.