Adriana Curi Aiub Casagrande

UHMWPE-layered silicate nanocomposites by in situ polymerization with tris(pyrazolyl)borate titanium/clay catalyst

Polyethylene-MMT nanocomposites were prepared by in situ polymerization methodology using TpMs*TiCl3 (1) intercalated into the gallery of Cloisite® 30B (C30B) using methylaluminoxane (MAO) as activator. From the powder X-ray diffraction (XRD) analysis it was observed that the basal spacing of the activated organoclay changes from 1.85 nm (2θ = 4.8) to 2.18 nm (2θ = 4.0) indicating that the intercalation of the titanium catalyst into the gallery took place. The catalytic system 1/C30B/MAO was active in the ethylene polymerization under different reaction conditions. The exfoliated morphology of the PE-MMT nanocomposite was further examined and confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The presence of exfoliated clay (5 wt.%) in the PE matrix confers better mechanical properties (flexural modulus and storage modulus) when compared with the ones displayed by the neat PE produced using exclusively 1.

Styrene polymerization by nickel and titanium catalysts based on tris(pyrazolyl)borate ligands

= HB(3-mesitila-pirazolil) 2 (5-mesitila-pirazolil) foi estudada na presenca do cocatalisador MAO sob varias condicoes de polimerizacao. Todos complexos mostraram-se ativos na polimerizacao do estireno produzindo quase exclusivamente poliestireno atatico. As atividades cataliticas bem como as conversoes com os complexos de niquel foram maiores em relacao aquelas obtidas com os complexos de titânio. Maiores atividades foram encontradas a 80 °C. As propriedades dos poliestirenos sao substancialmente afetadas pelas condicoes de reacao tais como temperatura de polimerizacao, tempo e razao molar [Al]/[M]. Os resultados de GPC mostram que o peso molecular (M w ) dos poliestirenos e sensivel a temperatura de polimerizacao variando de 16.300 a 138.300 g mol -1 . Styrene polymerization with a series of nickel and titanium complexes based on sterically hindered tris(pyrazolyl)borate ligands, Tp Ms = HB(3-mesityl-pyrazolyl) 3 and Tp Ms* = HB(3-mesitylpyrazolyl) 2 (5-mesityl-pyrazolyl) have been studied in the presence of MAO cocatalyst under various polymerization conditions. All complexes showed to be active for styrene polymerization producing almost exclusively atactic polystyrene. The catalytic activities as well as the styrene conversions with nickel complexes were higher than those with the titanium analogues. Higher activities were found at 80 °C. Polystyrene properties are substantially affected by the reaction conditions such as temperature of polymerization, time, and [Al]/[M] molar ratio. The GPC results showed that the molecular weight (M w ) of the polystyrene is sensitive to the temperature of polymerization varying from 16,300 to 138,300 g mol -1