A systematic study of diffusion-controlled reversible Diels−Alder (DA) network formation is performed under both isothermal and nonisothermal reaction conditions based on two amorphous furan−maleimide thermoset model systems. The experimental evolution of the glass-transition temperature, T g , with the predicted DA conversion, x, simulated by a two-equilibrium kinetic model for endo and exocycloadducts leads to the T g −x relationship of these model systems. The heat capacity, c p , from modulated temperature differential scanning calorimetry enables the characterization of (partial) vitrification along the reaction path. In isothermal DA reactions at T cure , a stepwise negative drop in Δc p at the onset of vitrification is observed, followed by a diffusion-controlled reaction at a reduced rate. T g can exceed T cure by at least 15 °C. In nonisothermal DA cure at a sufficiently low heating rate, (partial) vitrification is also possible (negative Δc p step), followed by diffusion-controlled cure until devitrification occurs again (positive Δc p ). Gelation along the reaction path is proven by dynamic rheometry, and gelled glasses can always be obtained under ambient conditions. This information is of importance in the damage management of reversible thermosets by self-repair of microcracks in bulk, as evidenced by dynamic mechanical analysis of a compressed powder after healing below T g .

Time-Temperature-Transformation (TTT), Temperature-conversion-Transformation (TxT), and Continuous-Heating-Transformation (CHT) diagrams are studied for a set of reversible 0.0 0.2 2 elastomeric and thermosetting covalent networks, based on Diels-Alder (DA) furan-maleimide cycloaddition reactions, using different concentrations of furan and maleimide functional groups.Microcalorimetry, modulated temperature differential scanning calorimetry and dynamic rheometry are used as experimental tools in combination with kinetic modelling. The DA kinetics, based on two parallel equilibrium reactions for endo and exo cycloadducts, are optimized for the set of reversible networks cured between 20 °C and 90 °C. Each simulated iso-conversion line in TTT and CHT, in contrast with irreversible networks, shows a totally different shape with a horizontal asymptotic limit at the high temperature side, Tcure, corresponding to the DA equilibrium conversion xeq at Tcure. It is also proven that all gelation lines are iso-conversion lines, and that each gel conversion can be predicted by the Flory-Stockmayer equation. Moreover, the slight differences in the endo-exo kinetics and equilibrium constants lead to a predicted superposition and a double asymptotic behavior of the iso-conversion lines in TTT and CHT. As a consequence, two subsequent gelation/de-gelation events can occur during non-isothermal cure, as shown in the CHT diagram. These phenomena are experimentally confirmed for one of the reversible covalent networks.

While thermally reversible polymer network coatings based on the Diels-Alder reaction are widely studied, the mechanisms responsible for the heating-mediated healing of damage is still not well understood. The combination of microscopic evaluation techniques and fundamental insights for the thermoreversible network formation in the bulk and coating shed light on the mechanisms behind the damage healing events. The thermomechanical properties of thermoset and elastomer coatings, crosslinked by the furan-maleimide Diels-Alder cycloaddition reaction, were studied in bulk and compared to the thermal behaviour applied as coatings onto aluminium substrates. The damage sealing of thermoset (Tg = 79 °C) and elastomer (Tg = −49 °C) coatings were studied using nano-lithography and atomic force microscopy (AFM). The sealing event is studied and modelled at multiple temperatures and correlated to the changes in the network structure and corresponding thermomechanical properties.

Two reversible polymer networks, based on Diels–Alder cycloadditions, are selected to discuss the opportunities of mobility-controlled self-healing in ambient conditions for which information is lacking in literature. The main methods for this study are (modulated temperature) differential scanning calorimetry, microcalorimetry, dynamic rheometry, dynamic mechanical analysis, and kinetic simulations. The reversible network 3M-3F630 is chosen to study the conceptual aspects of diffusion-controlled Diels–Alder reactions from 20 to 65 °C. Network formation by gelation is proven and above 30 °C gelled glasses are formed, while cure below 30 °C gives ungelled glasses. The slow progress of Diels–Alder reactions in mobility-restricted conditions is proven by the further increase of the system’s glass transition temperature by 24 °C beyond the cure temperature of 20 °C. These findings are employed in the reversible network 3M-F375PMA, which is UV-polymerized, starting from a Diels–Alder methacrylate pre-polymer. Self-healing of microcracks in diffusion-controlled conditions is demonstrated at 20 °C. De-gelation measurements show the structural integrity of both networks up to at least 150 °C. Moreover, mechanical robustness in 3M-F375PMA is maintained by the poly(methacrylate) chains to at least 120 °C. The self-healing capacity is simulated in an ambient temperature window between −40 and 85 °C, supporting its applicability as self-healing encapsulant in photovoltaics.

Reversible poly(methacrylate) networks are synthesized with tunable thermomechanical and self-healing properties. The focus is on highmodulus networks (guide value of around 500 MPa at 25 °C) in combination with fast self-healing for applications as coatings at ambient temperature. In case of a broad temperature window for outdoor applications, mechanical robustness up to 120 °C is aimed for. Methacrylate-functionalized Diels− Alder prepolymers containing furan−maleimide reversible covalent bonds are first synthesized at 25 °C. The prepolymers act as reversible crosslinkers in the subsequent UV-polymerization at 60 °C. Reaction-induced phase separation is achieved by changing the balance between soft and hard blocks, leading to homogeneous and (partially) phaseseparated, fully reversible poly(methacrylate) networks. The incorporation of urethane bonds introduces hydrogen bonding capacity. For comparison, irreversible poly(methacrylate) networks, that is, without reversible Diels−Alder bonds, are synthesized via UVpolymerization of irreversible methacrylate-functionalized prepolymers. A tunable self-healing behavior is demonstrated. The singledynamic high-modulus poly(methacrylate) networks, purely based on reversible Diels−Alder bonds, show the slowest self-healing, for example, for 7 days under ambient conditions. The dual-dynamic high-modulus poly(methacrylate) networks, based on covalent Diels−Alder bonding and supramolecular hydrogen bonding, show the fastest self-healing, for example, for 10 min under ambient conditions if hydrogen bonding is combined with intrinsic local network mobility in case of a (partially) phase-separated network morphology.