Recyclable and Malleable Epoxy Thermoset Bearing Aromatic Imine Bonds

Thermoresponsive self-healable and recyclable polymer networks based on a dynamic quinone methide–thiol chemistry

A new type of thermoresponsive dynamic covalent polymer network was developed with excellent self-healable and recyclable properties based on a new thermoresponsive dynamic covalent chemistry between a para-quinone methide and thiol nucleophiles.

An acid-degradable biobased epoxy-imine adaptable network polymer for the fabrication of responsive structural color film

A reprocessable, acid-degradable epoxy-imine network polymer was fabricated based on an epoxide of vanillin, and it was used to prepare a composite film with structural color.

A self-healing polyurethane elastomer with excellent mechanical properties based on phase-locked dynamic imine bonds

The rigidity and the dynamic nature of the CN double bond ensure the effectiveness of the phase-locking strategy for robust self-healing materials.

Mechanically robust and reprocessable imine exchange networks from modular polyester pre-polymers

Covalent adaptable networks (CANs) containing dynamic imine cross-links impart recyclability to thermoset materials, and the distribution of these cross-links greatly affects their observed thermomechanical properties.

Synthesis and Characterization of Healable Waterborne Polyurethanes with Cystamine Chain Extenders

In this study, environmentally friendly, self-healing waterborne polyurethanes (WPUs) were prepared based on the disulfide metathesis reaction in cystamine. The cystamine acted as a chain extender in the WPU film, which showed a high mechanical strength of 19.1 MPa. The possibility of self-healing reaction was simultaneously modeled via liquid chromatography-mass spectrometry (LC-MS). WPU was confirmed to self-heal a surface crack thermally after a scratch test, and the efficiency was measured by comparing the mechanical properties before and after a cut-and-healing test. In addition, the disulfide-thiol exchange reaction was confirmed to occur in WPU with cystamine as a chain extender and 2-mercaptoethanol. Hot press tests confirmed the possibility of reprocessing the WPU. The WPU incorporating disulfide groups showed great potential as a smart self-healing material.

Thermal Healing, Reshaping and Ecofriendly Recycling of Epoxy Resin Crosslinked with Schiff Base of Vanillin and Hexane-1,6-Diamine

A bio-derived dihydroxylimine hardener, Van2HMDA, for the curing of epoxy resin was prepared from vanillin (Van) and hexamethylene-1,6-diamine (HMDA) by Schiff base formation. The epoxy resin of diglycidyl ether of bisphenol A was cured with Van2HMDA in the presence of the catalyst, 2-ethyl-4-methylimidazole (EMI). The crosslinked epoxy resin showed thermal-healing properties at elevated temperatures. Moreover, the crosslinked epoxy resin can be reshaped by heating via imine metathesis of the hardener units. The imine metathesis of Van2HMDA was confirmed experimentally. Stress-relaxation properties of the epoxy resin crosslinked with Van2HMDA were investigated, and the activation energy obtained from Arrhenius plots of the relaxation times was 44 kJ/mol. The imine bonds in the epoxy polymer matrix did not undergo hydrolysis after immersing in water at room temperature for one week. However, in the presence of acid, the crosslinked polymer was easily decomposed due to the hydrolysis of imine bonds. The hydrolysis of imine bonds was used for the ecofriendly recycling of crosslinked polymer. It is inferred that thermal-healing, reshaping, and reprocessing properties can be implemented in the various crosslinked epoxy resins with the bio-derived dihydroxylimine hardener, albeit the recycled epoxy resin is of inevitably lower quality than the original material.

A facile approach to thermomechanically enhanced fatty acid-containing bioplastics using metal–ligand coordination

Dynamic metal–ligand coordination creates physical crosslinking and thus improves chain entanglements for enhancing the thermomechanical properties of biobased polymers.