1H NMR study of the kinetics of substituted aniline polymerization. I. Homopolymerization of 2‐methoxyaniline |
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Authors: | Ida Mav Majda
igon |
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Institution: | Ida Mav,Majda Žigon |
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Abstract: | We studied the kinetics of the oxidative chemical homopolymerization of 2‐methoxyaniline (OMA) in aqueous acid solutions by monitoring OMA depletion with 1H 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 pKa 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 polymerization 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 |
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Keywords: | aniline derivative 2‐methoxyaniline chemical polymerization reaction conditions kinetics 1H NMR |
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