The experimental data available in the literature concerning syndiotactic-specific polymerization of styrene and the data reported in this paper, mainly concerning the comparison of the behaviour of different catalytic systems, lead to the tentative suggestion that the true catalytic species might be complex cations similar to those involved in a-olefin polymerization.
We recently succeeded in preparing highly syndiotactic polystyrene, similar to that described by Ishihara et al.'), in the presence of catalytic systems consisting of either tetrabenzyltitanium (TBT)Z) or tetrabenzylzirconium (TBZ),) and methylalumoxane (~~0 1 3 ) . E. g. 4,8 . lo-, mol of TBT plus 0,27 g of M A 0 dissolved in 40 ml of dry toluene and 20 ml of styrene under nitrogen atmosphere at 60°C after 1 h yield 0,9 g of highly syndiotactic polystyrene 97% of which is insoluble in boiling 2-butanone. The polymer was recovered after coagulation with methanol acidified with HCI, washed several times with methanol and dried under vacuum.
Some catalytic systems based on Ti or Zr compounds and methylalumoxane have been investigated with regard to their ability to promote styrene-ethylene copolymerization. 13C NMR analysis shows that the structure and the composition of the copolymerization products are dependent on the catalytic system and on the transition metal/methylalumoxane mole ratio. Polymers containing phenylethylene units bridging polyethylene sequences are generally obtained in the presence of Ti-based catalysts. In the presence of cyclopentadienyltitanium trichloridd methylalumoxane with high AVTi mole'ratio one can obtain copolymers of ethylene and syndiotactic polystyrene. Zr-based catalyst don't promote copolymerization at all.
The controlled synthesis of gold nanoparticles (AuNPs), incarcerated in a semicrystalline nanoporous polymer matrix that consisted of a syndiotactic polystyrene-co-cis-1,4-polybutadiene multi-block copolymer is described. This catalyst was successfully tested in the oxidation of primary and secondary alcohols, in which we used dioxygen as the oxidant under mild conditions. Accordingly, (±)-1-phenylethanol was oxidised to acetophenone in high yields (96%) in 1 h, at 35 °C, whereas benzyl alcohol was quantitatively oxidised to benzaldehyde with a selectivity of 96% in 6 h. The specific rate constants calculated from the corresponding kinetic plots were among the highest found for polymer-incarcerated AuNPs. Similar values in terms of reactivity and selectivity were found in the oxidation of primary alcohols, such as cinnamyl alcohol and 2-thiophenemethanol, and secondary alcohols, such as indanol and α-tetralol. The remarkable catalytic properties of this system were attributed to the formation, under these reaction conditions, of the nanoporous ε crystalline form of syndiotactic polystyrene, which ensures facile and selective accessibility for the substrates to the gold catalyst incarcerated in the polymer matrix. Moreover, the polymeric crystalline domains produced reversible physical cross-links that resulted in reduced gold leaching and also allowed the recovery and reuse of the catalyst. A comparison of catalytic performance between AuNPs and annealed AuNPs suggested that multiple twinned defective nanoparticles of about 9 nm in diameter constituted the active catalyst in these oxidation reactions.
Re-cycling carbon dioxide with iron". The synthesis of cyclic organic carbonates in high yield, stereo- and chemo-selectivity was accomplished through the coupling of carbon dioxide and epoxides, catalysed by a novel air-stable and easy-to-handle thioether-triphenolate iron(iii) complex
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