Intra-polymer electron-transfer reaction between partially quaternized poly(1-vinylimidazole) and a cobalt(II) Schiff-base complex: effect of alkyl chain length

Abstract

A macromolecule–metal complex having redox centres on the polymer backbone of partially quaternized poly(1-vinylimidazole)(QPVIm) has been designed. This complex consisted of a divalent Co(tfacacen) complex [tfacacen =N,N′-ethylenebis (1,1,1-trifluoro-4-iminopentan-2-one)] coordinated to imidazolyl residues on QPVIm and also of quaternized imidazolium residues linked covalently to the same polymer backbone. The Co(tfacacen) and the quaternized imidazolium residues act as reducing and oxidizing agents, respectively. The intra-polymer electron-transfer reaction between Co(tfacacen) and the quaternized imidazolium residue has been investigated in connection with alkyl chain length in the quaternized imidazolium residue. The order of increasing reaction rate was ethyl < n-butyl < n-hexyl regarding alkyl chains in the quaternized imidazolium residues. Further, the reaction rate dramatically increased by addition of water. The facts suggest that Co(tfacacen) solvophobically interacts with the alkyl chains in the quaternized imidazolium residues. Viscosity measurements showed that the volume of the polymer domain of QPVIm, which was the reaction site, increased with increasing alkyl chain length, degree of quaternization, and amount of water added to DMF. This was attributed to a decrease in electrostatic attraction between the imidazolyl and quaternized imidazolium residues. Therefore, these results suggested that an increase of alkyl chain length and addition of water results in the enhancement of reaction rate.