Characterization and kinetic study of Diels-Alder reaction: Detailed study on N-phenylmaleimide and furan based benzoxazine with potential self-healing application

Abstract

Abstract. The Diels-Alder reaction between N-phenylmaleimide and benzoxazine bearing furan group was investigated for the purpose of successful appliance of self-healing in benzoxazine polymer networks. The reaction as a function of temperature/time was performed in molten state and in a solution, where also the kinetic study was performed. The Diels-Alder reaction leads to a mixture of two diastereomers: endo presented at lower cyclo-reversion temperature and exo at higher. Therefore, the conversion rates and exo/endo ratio were studied in detail for both systems. For instance, in molten state the Diels-Alder reaction was triggered by the temperature of the melting point at 60°C with exo/endo ratio preferable to the endo adduct. The study of the kinetics in a solution revealed that the Diels-Alder reaction followed typical bimolecular reversible second-order reaction. The activation energies were close to the previous literature data; 48.4 and 51.9 kJ·mol -1 for Diels-Alder reaction, and 91.0 and 102.3 kJ·mol -1 for retro-Diels-Alder reaction, in acetonitrile and chloroform, respectively. The reaction equilibrium in a solution is much more affected by the retro-Diels-Alder reaction than in a molten state. This study shows detailed investigation of DA reaction and provides beneficial knowledge for further use in self-healing polymer networks.

Thermodynamic and Kinetic Study of Diels–Alder Reaction between Furfuryl Alcohol and N-Hydroxymaleimides—An Assessment for Materials Application

“…The activation energy value for the forward reaction (43 ± 7 kJ/mol) is lower than that of the reverse reaction (90 ± 10 kJ/mol), as expected. The calculated values of activation energy are in the range of what is generally reported for Diels-Alder and retro-Diels-Alder reactions [11,12]. The results for the reaction FAL-N2HM ( Figures S5 and S6) show only the data treatment from the NMR spectroscopy, due to the side reaction observed in the UV-Vis experiment.…”

“…That is true for the case of materials that will react in near-equimolar proportions or in which the reversibility is planned to take place in near-equilibrium conditions. Diaz et al [14], Stirn et al [12], and Koehler et al [11] modeled the kinetics of their system through different approaches, but considered an equilibrium reaction between diene, dienophile, and one adduct. Another factor to be considered in the case of evaluation of the Diels-Alder reaction and the reversibility for materials application is the ratio between the isomeric products.…”

“…However, when the reversibility of the reaction on materials application is an issue of the publication, the kinetic study becomes generally more complex and closer to the one used here. For instance, Stirn et al [12] and Koehler et al [11] used the same approach as the present work in terms of differential rate law. The difference to these works lies in the method selected for the data treatment.…”

“…The complexity of the kinetic model is increased when the reaction equilibrium and isomers are taken into account [10]. The possible application of the Diels-Alder/retro-Diels-Alder in responsive materials resulted in greater interest for the consideration of the equilibrium reaction in kinetic models for materials applications [11][12][13][14][15].…”

Polyurethanes based on thermoreversible networks designed by Diels-Alder reaction

“…For de-crosslinking of polyurethane networks, dynamic covalent chemistry is used, especially by means of the DA and retro-DA (rDA) reactions [17]. Due to its reversibility the DA reaction also represents a choice to create self-healing properties for polymer networks [18]. Concerning polyurethane, the DA reaction was employed in thermally remendable linear polymers [19][20][21][22] and thermally reversible networks [23][24][25][26][27].…”