Marcelo P. Gil

Copolymerization of Ethylene with 1‐Hexene Using Sterically Hindered Tris(pyrazolyl)borate Titanium (IV) Compounds

The copolymerization of ethylene/1-hexene was studied using {Tp Ms }TiCl 3 (1) (Tp Ms = hydriodotris(3-mesitylpyarzol-1-yl) and {Tp Ms* }TiCl3(2) (Tp Ms* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) compounds in the presence of methylaluminoxane at 65°C. for both catalysts it was observed that the productivities decreased with increasing the 1-hexene concentration in the milieu exhibiting a negative comonomer effect. The highest productivities and 1-hexene incorporations were achieved in the case of {Tp Ms* }TiCl3 catalyst system. The resulting copolymers were not soluble in TCB even at 165°C. 1-hexene incorporations were very low; ca. 1.2 and 3.3 mol-%, respectively (1) and (2). The r 1 and r 2 parameters for both (1) and (2)/MAO catalyst systems clearly indicated a strong tendency of these catalytic precursors to preferentially promote ethylene homopolymerization. According to X-ray photolectron spectroscopy, from the analysis of the Ti2p 3/2 peak, Tp Ms* catalyst seems to present a stronger cationic character after MAO treatment, which can explain in part its higher catalyst activity.

Structural stability of photodegradable poly(l-lactic acid)/PE/TiO2 nanocomposites through TiO2 nanospheres and TiO2 nanotubes incorporation

Photodegradation of PLA/PE, PLA/PE/TiO2 nanospheres and PLA/PE/TiO2 nanotubes was obtained under simulated sunlight. The nanocomposites were analyzed by infrared spectroscopy, scanning electron microscopy and tensile-deformation measurements. TiO2 nanospheres and TiO2 nanotubes were found to present different effects on the crystallinity of PLA and a straight correlation between structural organization and photostability was observed. According to the results, TiO2 promotes the degradation of PLA and PE, affecting the organizational level of the polymers. By adding TiO2 nanoparticles to the PLA/PE films, vibration modes characteristic of degradation products were promptly observed and the lifetime of the polymer decreased when compared to the PLA/PE without TiO2 nanoparticles. Mechanical measurements showed an improvement of the mechanical properties when adding the TiO2 nanoparticles.

Hydroruthenation of Propargyl Amines Promoted by the 16-Electron Complex RuHCl(CO)(PiPr3)2

Abstract The 16-electron complex RuHCl(CO)(PiPr3)2 (1) reacts with propargyl amines H‒C≡C(CH2) n Y (2–5) (n=1,2; Y = NMe2, N(Me)CH2Ph, or Py) by insertion to afford the five-coordinate vinyl-complexes RuCl{(E)‒CH˭CH(CH2) n Y}(CO)(PiPr3)2 (6, Y = NMe2, n = 1; 7, Y = N(Me)CH2Ph, n = 1; 8, Y = Py, n = 2; 9, Y = NMe2, n = 2) in good yield. Addition of CO to 7 produces the six-coordinate vinyl-complex RuCl{(E)‒CH˭CH(CH2) n Y}(CO)2(PiPr3)2 (10). The trans stereochemistry at the C˭C bond is observed in all compounds. All compounds were characterized by IR, 1H, 13C and 31P NMR spectroscopy.