STUDY OF SELF-HEALING FULLY REVERSIBLE DIELS-ALDER THERMOSETTING SYSTEMS

An efficient mechanism of an intrinsic self-healing polymer network is based on dynamic covalent bonding by the introduction of thermoreversible Diels-Alder (DA) cycloadditions. The cycloadduct single bonds are preferentially broken in case of material damage, but also reversibly reform, leading to a repeatable healing cycle and an increased lifetime for many applications, such as sustainable coatings [1-3]. However, for coating applications sufficient thermo-mechanical stability is required for surface protection, requiring a network material exhibiting a high glass transition (Tg). As such, these materials are usually used in their vitrified state. The potential self-healing reactions will thus occur under diffusion-controlled instead of kinetically controlled conditions. Little information can be found in literature regarding the study of diffusion-controlled reversible network formation, as opposed to their irreversible analogues.

This work focuses on the effect of vitrification on Diels-Alder reaction kinetics, using model systems formed by furan-functionalized Jeffamines and bismaleimides. These fully reversible systems exhibit a Tg high enough to efficiently study the vitrification effect at low temperatures. Using (MT)DSC measurements, vitrification is followed through isothermal and non-isothermal measurements based on the evolution of the heat capacity, while isothermal measurements from microcalorimetry give information on the heat flow evolution.

These results are compared to a kinetic model, taking into account the stereochemistry of the system based on literature values [4]. In addition, rheology complements these measurements, allowing the construction of a time-temperature-transformation (TTT) diagram.

This work is the first systematic study of diffusion-controlled reversible Diels-Alder network formation in the perspective of self-healing applications. The Diels-Alder reaction is proven to proceed both under kinetically and diffusion-controlled conditions, allowing self-healing of the material even in mobility-restricted conditions. The self-healing ability of the vitrified Diels-Alder model networks is demonstrated.