Metallocene supported on a polyhedral oligomeric silsesquioxane‐modified silica with high catalytic activity for ethylene polymerization

Abstract

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 (b-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 (XPS) was used to measure the amount of Si (2p) of POSS adsorbed on the SiO 2 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 ZrCl 2 , 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.

Metallocene supported on a polyhedral oligomeric silsesquioxane‐modified silica: Structural characterization and catalytic activity for ethylene polymerization

“…This means that some of the metallocene species adsorbed directly on POSS are also active in the ethylene polymerization. In a previous study, we compared the catalyst activity of homogeneous systems based on pure metallocene or unsupported POSS–metallocene complexes 16. The activity of the complexes in solution was significantly reduced with respect to the activity of the neat metallocene, meaning that interactions with POSS do not increase the activity of the catalyst.…”

“…Preliminary results on the activity of metallocene supported over POSS‐modified silicas for ethylene polymerization16 were extended showing the effect of large variations of the amount of both POSS and catalyst used in the silica modification. DRIFT results showed that at low concentrations (<1 wt %), POSS was physically adsorbed on SiOH groups present in the silica surface through H‐bonds.…”

“…On the other hand, the specific POSS shown in Chart can act both as a horizontal and a vertical spacer. We already used it for the surface modification of a silica used as a support of a metallocene for ethylene polymerization, carried out in the presence of methylalumoxane (MAO) as reaction cocatalyst 16. POSS modification of the silica surface improved the catalyst activity compared with the metallocene supported on an unmodified silica.…”

Preparation and characterization of polyurethane/POSS hybrid aqueous dispersions from mono-amino substituted POSS

“…Various copolymers and networks usually display enhanced viscoelasticity, mechanical properties, high thermal stability, oxygen permeability, low thermal conductivity, thermal expansion, dielectric permittivity [23], and surface energy [24]. Thus, these nanocomposites containing POSS units have been extensively applied as coatings [25], components in catalysis [26], and drug delivery systems [27].…”

Hybrid Nanocomposite Films from Mono‐ and Multi‐Functional POSS Copolyacrylates in Miniemulsion

“…[1] The resulting copolymers and networks usually display improved viscoelastic and mechanical properties, high thermal stability and oxygen permeability, and low thermal conductivity, thermal expansion, dielectric permittivity, [2] and surface energy. [3] As the result, POSS-based nanocomposite thermoplastics and thermoset resins have been investigated as high-performance coatings, [4] components in catalysis, [5] fuel cells, [6] lithium ion batteries, [7] nanolithography, [8] and drug-delivery systems. [9] Among the various reports on multifunctional POSS derivatives used as comonomers and cross-linkers, the vast majority involve stepwise addition or condensation copolymers, [10] while very few of them concern copolymers prepared by free radical initiated [11] or other fast propagating polymerization processes.…”