Recyclable Thermosets Based on Dynamic Amidation and Aza-Michael Addition Chemistry

Abstract

Utilizing the dynamic amidation and aza-Michael addition chemistry, a set of high strength, recyclable, and self-healable covalent adaptable networks (CANs) are synthesized by reacting the precursor and commercial oligoamine cross-linkers under mild temperature (25–50 °C) and solvent-free conditions. The amide linkages present in these CANs are readily hydrolyzable under mild acidic (pH = 5.3) conditions, whereas the aza-Michael adducts with secondary amines are thermally reversible. Utilizing the above, these CANs are depolymerized under ambient conditions in mild acidic solution and recycled with retention of original mechanical properties. The crack on the material surface is self-healed at 50 °C. The precursor, a Knoevenagel condensation product of terephthalaldehyde and diethyl malonate, is easily synthesized in a large scale. Suitable model compounds are synthesized and studied to further understand the transformations involved in the polymerization–depolymerization of these networks. These networks exhibit adequate tensile properties (ultimate tensile strength ≤35 MPa and Young’s modulus ≤3 GPa), and the properties can be tuned further by suitably changing the oligoamine cross-linker. The simplicity of synthesis, cost effectiveness, adequate mechanical property, stability in aqueous and organic media, and recyclability along with self-healability render these CANs suitable for a range of applications.

Multistimuli, Multiresponsive Fully Supramolecular Orthogonally Bound Polymer Networks

“…The DSC spectrum of the covalent reference network also displays an endothermic transition at 190 °C, which is attributed to the decomposition of the network via a retro aza-Michael addition (Supporting Figure S5). 24 The traces of the neat M1 and The mechanical properties of the various materials were further probed by tensile tests that were conducted at room temperature ( Figure 4, Table 1). The reference polymer C1 shows the typical stress-strain curve of a weakly cross- networks, which, as also reflected by the DMA data, is more pronounced in the metallosupramolecular polymer.…”

Structural effects on the reprocessability and stress relaxation of crosslinked polyhydroxyurethanes

“…However, these desirable properties are no longer advantageous once thermosets are damaged or discarded, since their inability to dissolve or melt precludes reshaping or repair. The incorporation of covalent bonds capable of dynamic exchange into crosslinked polymers imparts self‐healing to elastomeric materials and reprocessability to thermoset‐like materials, yet compromises their toughness if not carefully controlled . Polymer networks termed vitrimers are a subset of repairable crosslinked polymers with outstanding mechanical properties that rely on associative, rather than dissociative, exchange reactions to relax stress and undergo repair .…”

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

“…Such recycling features of strong and rigid polymers are superior as compared to similar recycling ways in literature. 2,13,[60][61][62][63][64] PETMP 80-20 -Zn can also be used as binders to prepare recyclable Carbon-fiber (CF) composites. Carbon-fiber (CF) composites have undergone rapid development in recent years for a wide range of industrial applications, such as aerospace, wind power, and sporting goods.…”