1 H NMR Study of the Kinetics of Substituted Aniline Polymerization. I. Homopolymerization of 2-Methoxyaniline IDA MAV, MAJDA Z ˇ IGON National Institute of Chemistry, Laboratory for Polymer Chemistry and Technology, Hajdrihova 19, POB 3430, 1000 Ljubljana, Slovenia Received 2 January 2001; accepted 30 April 2001 Published online 00 Month 2001 ABSTRACT: We studied the kinetics of the oxidative chemical homopolymerization of 2-methoxyaniline (OMA) in aqueous acid solutions by monitoring OMA depletion with 1 H NMR spectroscopy. We used the same semiempirical kinetic model used for aniline (ANI) homopolymerization to evaluate the experimental data. The reaction kinetics of OMA homopolymerization was similar to that of ANI, although we obtained longer induction and propagation times for OMA. This was attributed to steric hindrance of the bulky methoxy substituent during the coupling reaction. Furthermore, it was suggested that a lower OMA polymerization rate could also be related to a lower concentration of nonprotonated OMA molecules in the reaction solution due to a higher pK a value for OMA than for ANI. This may also explain the lower OMA end conversion (90%) compared with that of ANI (96%). The OMA end conversion was not influenced substantially by reaction conditions; it was lower than 90% only when high acid or low oxidant (oxidant-deficient oxidant/OMA ratio) concentrations were applied. Because the oxidant took an active part in polymerization, it markedly influenced the polymer- ization rate, especially the initiation rate. The OMA initiation and propagation rates increased with increasing oxidant and initial monomer concentrations and with the reaction temperature, but there was no uniform trend in the correlation between the homopolymerization rate and acid concentration. The activation energies of the OMA initiation and propagation were 57 and 10 kJ/mol, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2471–2481, 2001 Keywords: aniline derivative; 2-methoxyaniline; chemical polymerization; reaction conditions; kinetics; 1 H NMR INTRODUCTION The polymerization mechanisms of aniline (ANI) and its derivatives are very complex and have been studied intensively by many groups. The polymerization mechanisms and reaction kinetics have been investigated mostly by electrochemical polymerization, that is, by cyclic voltammetry in aqueous solutions. 1–5 It is generally agreed that the initiation reaction (induction period) involves the oxidation of neutral (nonprotonated) ANI monomers to radical cations, whose radical cou- pling leads to the formation of dimeric species: p-aminodiphenylamine, N-phenyl-p-phenylenedi- amine, or benzidine. The oxidation of dimeric spe- cies, as well as subsequently formed oligomers and polymers, all with lower oxidation potentials than ANI, occurs immediately after their forma- tion. An electrophilic attack on the ANI monomer by oxidized species would accomplish a growth Correspondence to: I. Mav (E-mail: ida.mav@ki.si) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 39, 2471–2481 (2001) © 2001 John Wiley & Sons, Inc. 2471