Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP

[Display omitted] ► Iron complexes as mediators in normal and reverse ATRP of MMA in DMF. ► Electrochemical and polymerization properties are investigated. ► Strong indications of different iron species in normal and reverse ATRP. ► The nature of the ligand is not crucial for the polymerization outcome. In an attempt to correlate the ATRP kinetics and the redox properties of the mediator, eight iron complexes with nitrogen, phosphorous and carboxylic acid containing ligands were investigated by electrochemical measurements and by using them as mediators in normal and reverse ATRP of MMA in DMF. The redox properties of the iron complexes in DMF, measured by cyclic voltammetry, did not differ significantly, which was reflected in the ATRP kinetics as the apparent rate constants were practically the same with all the complexing ligands. The degree of control over the polymerization was, however, much improved in reverse ATRP as compared to normal ATRP. In this ATRP system, the ligand type is not crucial for the redox or polymerization properties. Several observations indicate that the iron species in the two systems were not the same, the Fe(III) species resulting from oxidation of Fe(II) in normal ATRP is different from the starting Fe(III) species in reverse ATRP.