The Diels-Alder reaction is one of the most studied thermoreversible equilibrium reactions. At low temperatures, the Diels-Alder cycloadduct is formed predominantly, whereas at higher temperatures the equilibrium shifts towards the reactants, which are in this study a furan and a maleimide. Their fast reaction kinetics and high conversion make them suitable candidates for self-healing networks, which can be healed at elevated temperatures due to the thermo-reversible crosslinking. In previous work, these materials have been employed in self-healing coatings [1] and self-healing soft robotic actuators [2]. In the current work, the reaction kinetics of the Diels-Alder reaction between furan and maleimide is thoroughly investigated in view of these applications.
Two stereoisomeric cycloadducts can be formed depending on the suprafacial approach between the furan and maleimide functional groups. The exo isomer (bulkier sides of the diene and dieneophile lie away from each other) is the more thermodynamically stable adduct since less steric hindrance is occurring. The endo isomer (bulkier sides lie above each other) forms faster due to a lower activation energy barrier. Although the stereochemistry is well known, its effect on the reactivity, thermal reversibility, and kinetics is often overlooked in literature. The few kinetics studies determining individual kinetics parameters for both isomers were performed in a solvent, affecting the reaction kinetics.
In this study, an amorphous, liquid bismaleimide is used, allowing a detailed calorimetric analysis of the Diels-Alder reaction kinetics between furan and maleimide, without the interference of a solvent in the reaction kinetics. For the kinetic modelling, an in-house developed Matlab software was used, which permits optimizing rate constants and activation energies to fit the isothermal (microcalorimetry) and non-isothermal (DSC) data. The kinetic model has been verified using time-resolved and temperature-controlled 1H NMR spectroscopy.

[1] J. Brancart, G. Scheltjens, T. Muselle, B. Van Mele, H. Terryn, G. Van Assche, J. Intell. Mater. Syst. Struct. 25 (2014) 40–46
[2] S. Terryn, J. Brancart, D. Lefeber, G. Van Assche, B. Vanderborght, IEEE Robot. Autom. Lett. 3 (2017) 16–21
Original languageEnglish
Publication statusPublished - 25 Aug 2018
Event12th European Symposium on Thermal Analysis and Calorimetry - Brasov, Romania
Duration: 27 Aug 201830 Aug 2018


Conference12th European Symposium on Thermal Analysis and Calorimetry
Abbreviated titleESTAC 12

ID: 39421538