Journal of Polymer Science Part A: Polymer Chemistry, Vol.43, No.22, 5465-5476, 2005
Metallocene supported on a polyhedral oligomeric silsesquioxane-modified silica with high catalytic activity for ethylene polymerization
A polyhedral oligomeric silsesquioxane (POSS) consisting of a mixture of perfect and imperfect polyhedra with 8-10 Si atoms bonded to bulky and branched organic groups functionalized with (beta-hydroxy)-tertiary amines, was adsorbed on an activated silica from a toluene solution. POSS fixation was confirmed by measuring its concentration in the solutions resulting from filtering and repeatedly washing with toluene. Diffuse reflectance infrared Fourier-transformed (DRIFTS) spectra of the modified silica showed a decrease in the absorption of isolated SiOH groups. A POSS previously marked by reaction with an isocyanate was also used, and the presence of the carbonyl in the urethane group was recorded in the DRIFTS spectra of the modified silica, confirming the presence of adsorbed POSS. X-ray photoelectron spectroscopy (YPS) was used to measure the amount of Si (2p) of POSS adsorbed on the SiO2 surface as a function of the POSS concentration in the toluene solution. A linear increase of adsorbed POSS as a function of its concentration in toluene was found, even after successive washings with toluene. A metallocene, (nBuCp)(2)ZrCl2, was then adsorbed on the POSS-modified silica from a toluene solution, and the fixed Zr amount was measured by Rutherford backscattering spectrometry (RBS). The activity of the resulting catalyst for ethylene polymerization in toluene, using methylaluminoxane (MAO) as a cocatalyst, was determined in two different devices operating in the range of 1.6-7.0 bar. Under every experimental condition, POSS-modification of the silica support led to an increase of about 50% in the activity of the resulting catalyst when compared to the use of the unmodified support. Reasons for the observed increase in activity are discussed. The molar mass distribution and crystallinity of the resulting polyethylenes was not affected by the POSS modification of the silica support. (c) 2005 Wiley Periodicals, Inc.