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

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.