Comparative study of the catalytic activity of the complexes Cp*RuCl(PAr3)2 [Ar = -C6H5 and 4-CF3-C6H4] in the ATRP of styrene

Styrene polymerization by ATRP was conducted independently using the complexes Cp*RuCl(PPh3)2, and Cp*RuCl[P(4-CF3-C6H4)3]2 as catalysts, in order to evaluate the influence of the electronic properties of the phosphine ligands on the rate and control of the polymerization. The kinetic data for polymerizations carried out with Cp*RuCl(PPh3)2, show that molecular weights increase linearly with conversion with an average initiation efficiency of 0.77. The molecular weights obtained in the kinetic study with Cp*RuCl[P(4-CF3-C6H4)3]2 also increase with conversion but show a marked deviation below the theoretical molecular weights. This behavior was explained by the gradual, irreversible, oxidation of catalyst Cp*RuCl[P(4-CF3-C6H4)3]2 as confirmed by 31P-NMR spectroscopy. Catalyst Cp*RuCl(PPh3)2 promotes the polymerization with a rate of polymerization higher than that obtained using Cp*RuCl[P(4-CF3-C6H4)3]2; this is consistent with the better electron donating properties of PPh3 versus P(4-CF3-C6H4)3. Preliminary studies of styrene polymerization by ATRP in supercritical CO2, shows that only catalyst Cp*RuCl[P(4-CF3-C6H4)3]2, with fluorinated ligands, was active. (author)