Polimerização radicalar mediada por complexos organometálicos (OMRP) de diferentes monômeros usando complexos de níquel(II) derivados de bases de Schiff

Abstract

The nickel(II) complexes of Schiff bases derived from cycloalkylamines (cycloalkyl = cyclopentyl 1a, cyclohexyl 1b, cycloheptyl 1c and cyclooctyl 1d, were synthesized: [NiII(N-salicylidene-cyclopentylamine)2] 2a, [NiII(N-salicylidene-cyclohexylamine)2] 2b, [NiII(N-salicylidene-cycloheptylamine)2] 2c and [NiII(N-salicylidene-cyclooctylamine)2] 2d. The Schiff bases 1a–d were characterized by FTIR, UV–Vis, and 1H-NMR, and complexes 2a–d were characterized by FTIR, UV–Vis, elemental analysis, cyclic voltammetry and computational methods, while complex 2b was studied in greater depth by single crystal X-ray crystallography. The X-ray structure analysis of complex 2b shows that the geometry around the metal atom is square planar, confirming the spectroscopic data. By modulating the coordination sphere of these complexes and modifying the steric and electronic effects offered by the Schiff bases, we sought to assess whether these effects can alter the controlling capacity of complexes 2a–d. The radical polymerization of vinyl acetate (VAc) or methyl methacrylate (MMA) initiated by azobisisobutyronitrile (AIBN) at 55°C was conducted. The best conversions were obtained using a ratio of [Monomer]/[AIBN]/[Ni] = 542/3/1. In both polymerizations, the linear increase of molecular weights with the conversion, polymers with low polydispersities, and the linear correlation of ln ([M]0/[M]t) over time indicated that the concentration of radicals remained constant during polymerization as mediated by 2a–d.