Cobalt(II) complexes of bidentate Schiff bases derived from cycloalkylamines as mediators in controlled radical polymerization of vinyl acetate

A series of new cobalt(II) complexes of Schiff base derived from the salicylaldehyde and different cycloalkylamines (cycloalkyl = cyclopentyl-1a, cyclohexyl-1b, and cycloheptyl-1c) was synthesized: [Co(CyPen-Salicyl)2] (2a), [Co(CyHex-Salicyl)2] (2b), and [Co(CyHep-Salicyl)2] (2c). The complexes 2a-2c were used as controlling agents for the polymerization of vinyl acetate (VAc) initiated by AIBN, according to an organometallic-mediated radical polymerization (OMRP) mechanism. The VAc polymerization mediated by complexes 2a-2c suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand. The complex 2b showed the smaller discrepancy between observed and calculated molecular weight, and narrower molecular weight distribution.The preliminary VAc polymerizations mediated by 2a-2c as a function of time ([VAc]/[AIBN]/[Co] = 542/3.25/1 at 55 °C) were first order in monomer, as assessed by the linear dependence of ln([M]0/[M]t) versus time. The VAc polymerization mediated by 2a-2c suggests that the level of control can be slightly tuned by the substitution of the cycloalkyl group on the Schiff base ligand. The difference in the reactivity of the complexes studied is directly related to the electronic characteristics of the Schiff base ligands, which are modulated by their substituents (cycloalkyl groups).