From Slow to Fast Self-Healing at Ambient Temperature of High-Modulus Reversible Poly(methacrylate) Networks. Single- and Dual-Dynamics and the Effect of Phase Separation
Dorothee Ehrhardt, Jessica Mangialetto, Kurt Van Durme, Bruno Van Mele, Niko Van den Brande
Abstract
Reversible poly(methacrylate) networks are synthesized with tunable thermomechanical and self-healing properties. The focus is on high-modulus 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) phase-separated, 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 UV-polymerization of irreversible methacrylate-functionalized prepolymers. A tunable self-healing behavior is demonstrated. The single-dynamic 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.