Combined Reprocessability and Self-Healing in Fluorinated Acrylic-Based Covalent Adaptable Networks (CANs)

Abstract

Combining reprocessing and self-healing in one material provides an opportunity for the development of sustainable materials with enhanced mechanical properties. We developed fluorinated acrylic-based covalent adaptable networks (CANs) capable of self-healing and reprocessing by copolymerizing (2-acetoacetoxy)ethyl methacrylate (AAEMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), and n-butyl acrylate (nBA), followed by cross-linking with tris(2-aminoethyl) amine (TREN). These materials exhibit the maximum stress at break of about 16 MPa and the storage modulus of ∼2.6 GPa in the −60 to 25 °C range. Capable of complete recovery of mechanical properties, these materials are reprocessable by compression molding at 120 °C. The recovery of physical and chemical properties involves the exchange reactions between vinylogous urethane linkages and primary amines. Upon multicycle reprocessing, junction densities and stored entropic energy are also recovered and preserved. These CANs self-heal under ambient conditions. Upon damage, initially C═O groups of vinylogous urethanes respond to perturbation by conformational changes, followed by the (E) → (Z) isomerization of C═C bonds accompanied by the conformational rearrangements of the CF3 and CH2 moieties. This reversible process leads to the recovery of dipolar interactions that facilitates self-healing under ambient conditions. The concept of equipping materials with dynamic cross-linking and self-healing attributes can be extended to other systems.