Mass spectrometry insight into the electro-copolymerization mechanism of aniline with o-phenylenediamine

It has been a challenge to accurately characterize the chain growth mechanism during copolymerization. Herein, an electrochemistry-microtube-mass spectrometry (EC-mTube-MS) was developed for on-line monitoring of aniline (ANI) electro-copolymerized with o-phenylenediamine (oPD). Short-lived intermediates and co-oligomers belonging to polyANI-oPD were structural identified with tandem MS method for the first time. The free binding between ANI and oPD monomers determined the presence of more species for a given co- n -mer. Chain growth was found to compete with 2H + , 2e − intramolecular oxidation of co-oligomers, resulting in the units with quinone or phenazine structures. MS signals for polyANI and polyoPD were observed as well, indicating that the homopolymerization occurred simultaneously with the copolymerization, which may affect the formation efficiency even performance of the final copolymer. Investigations on the monomer feed ratio and solution pH provided data support for improving the copolymerization efficiency, and the recommended parameters are c ANI : c oPD  ≥ 10:1 and pH = 7.