Polymer Bulletin, Vol.74, No.4, 931-948, 2017
2,6-Bis-benzimidazolylpyridines as new catalyst in copper-based ATRP
The ligands, 2,6-bis(NH-benzimidazol-2-yl)pyridine (L1) and 2,6-bis(N-methyl-benzimidazol-2-yl)pyridine (L2), were synthesized by a one-step reaction of 2,6-pyridinedicarboxylic acid with a diamine (o-phenylenediamine or N-methyl-1,2-phenylenediamine), respectively, in syrupy phosphoric acid at ca. 200 A degrees C. Their efficiency as a catalyst in Cu-based atom transfer radical polymerizations (ATRP) of methylmethacrylate (MMA) was investigated. The linear first-order kinetic plots were observed; indicating that the number of active species is constant during the polymerization and termination reactions are limited. The apparent rate constant values of ATRP of MMA with CuCl/L1 catalyst system at 90 A degrees C in acetonitrile were found to be between 3.83 x 10(-5) and 1.33 x 10(-4) s(-1), while they were between 1.86 x 10(-4) and 4.40 x 10(-4) s(-1) in the case of CuCl/L2 catalyst, indicating the presence of lower radical concentration throughout the polymerization of MMA using CuCl/L1 catalyst system. In both the cases, low apparent rate constant values are obtained. This indicates that ATRP proceeded at reasonable rates and a good control over ATRP in general. Apparent rate constant vs [ligand]/[catalyst] ratio plots showed a maximum at the [ligand]/[catalyst] ratio of two. M (n,GPC) values increased slightly linearly with conversion and molecular weight values were closer to M (n,th) in the case of ATRP of MMA using CuCl/L2 catalyst complex. Cyclic voltammetry measurements confirmed that CuCl/L1 and CuCl/L2 complexes in acetonitrile give reversible redox couples and copper(I) centers in CuCl/L1 and CuCl/L2 catalyst complexes that are readily oxidized and they potentially suit to facile ATRP.
Keywords:2,6-BisNH-benzimidazol-2-yl)pyridine;2,6-BisN-methyl-benzimidazol-2-yl)pyridine;Cu-based atom transfer radical polymerization;Cyclic voltametry measurements