No abstract

No abstract

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.

No abstract