Reversible redox behaviour of two electroactive polymethacrylates

Summary

The radical melt polymerization of 2-[4-(6-methacryloyloxyhexa-1,6-diyloxy)phenylazo]-anthraquinone is described yielding the homopolymer p _m with the number average molecular weight (M _n ) of M _n =74kg/mol determined by gel permeation chromatography (GPC) using polystyrene (PS) calibration. The redox properties of a thin film of p _m were investigated by cyclic voltammetry. Two reversible redox waves were found at all applied sweep rates indicating two reversible electron (E) transfer processes of the anthraquinone units according the EE-mechanism. A thin film of the randomlike copolymethacrylate cp _r with the molar mass of M _n =73kg/mol was investigated, too. The sidegroups of cp _r are substituted by 77mol% with benzyl, by 22mol% with phenylazoanthraquinone and by 1mol% with COOH groups. The redox properties of cp _r depend on the timescale of the cyclovoltammetric experiment. At high sweep rates two reversible redox waves are observable corresponding to the EE-mechanism. At low sweep rates an additional reversible redox wave appears, which is essentially smaller than the other two. The third wave is explained to be a result of hydrogen bonding between the COOH groups and anthraquinone mono- and dianions. The most anthraquinone units are reduced according the EE-mechanism without hydrogen bonding due to statistical reasons. The reversible redox properties of p _m and cp _r are closely connected to their molar masses (M _n ≈75kg/mol), because both polymers have been previously obtained by radical solution polymerization yielding low molecular products with molar masses of M _n ≈10kg/mol. The low molecular polymers have shown an irreversible redox behaviour. Therefore, it could be demonstrated that the molar mass of an electroactive polymer significantly affects its redox properties.