Closed‐Loop Recyclable Poly(imine‐acetal)s with Dual‐Cleavable Bonds for Primary Building Block Recovery

Abstract

Chemical recycling offers a promising solution for the end‐of‐life treatment of synthetic polymers. However, the efficient recovery of well‐defined recycled building blocks continues to be a major challenge, especially for crosslinked thermosets. Here, we developed vanillin‐based polymer networks functionalized with dual‐cleavable imine and acetal bonds that facilitate chemical recycling to primary building blocks and their convenient separation at the molecular level. A library of crosslinked poly(imine‐acetal)s was synthesized by combining the in‐bulk synthesized liquid di‐vanillin acetal monomer (DVA) with commercially available liquid di‐ and triamines under solvent‐free conditions. These thermosets showed tailor‐made thermal and mechanical properties along with outstanding chemical recyclability. Under aqueous acidic conditions, poly(imine‐acetal)s selectively and completely disintegrate into small molecules. During the polymer design stage, these compounds were carefully selected to enable facile separation without tedious techniques. As a result, the primary building blocks were isolated in high yields and purity and immediately reused to produce fresh polymers with identical thermomechanical properties. Since our “design for recycling” concept aims at obtaining the primary building blocks rather than monomers after depolymerization, a plethora of possibilities are unlocked to utilize these chemical resources, including closed‐loop recycling as portrayed.

Closing the loop: polyimine thermosets from furfural derived bioresources

“…5,6 Incorporation of dynamic and cleavable imine bonds into the designed thermosets has emerged as a prospective solution for monomer recovery and thus achieving circularity as elucidated in prior studies. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Previous research endeavors have primarily focused on employing vanillin and its derivatives for the synthesis of biobased polyimine thermosets, aiming to minimize environmental impact. [18][19][20][21][22][23][24] For instance, polyimine thermosets, synthesized from a vanillin-based dialdehyde monomer and conventional amine crosslinkers (i.e., diethylenetriamine and tris (2-aminoethyl)amine), displayed tensile strength values ranging from 47 to 57 MPa, accompanied by glass-transition temperatures (T g ) approximately at 60 °C.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Previous research endeavors have primarily focused on employing vanillin and its derivatives for the synthesis of biobased polyimine thermosets, aiming to minimize environmental impact. [18][19][20][21][22][23][24] For instance, polyimine thermosets, synthesized from a vanillin-based dialdehyde monomer and conventional amine crosslinkers (i.e., diethylenetriamine and tris (2-aminoethyl)amine), displayed tensile strength values ranging from 47 to 57 MPa, accompanied by glass-transition temperatures (T g ) approximately at 60 °C. Remarkably, these thermosets exhibited notable self-healing properties and chemical recyclability in acidic conditions.…”

“…5,6 Incorporation of dynamic and cleavable imine bonds into the designed thermosets has emerged as a prospective solution for monomer recovery and thus achieving circularity as elucidated in prior studies. 7–21…”

Recent Advances in Environmentally Friendly Dual‐crosslinking Polymer Networks

“…This categorization underscores the ability of dynamic covalent bonds to provide significant mechanical properties alongside reversibility and stimulus responsiveness. Extensive research has explored a variety of dynamic covalent bonds, such as carbonate, [14] acetal, [15] disulfide, [16] ester, [17] imine bonds (Schiff‐base), [15a,18] Diels–Alder adduct, [19] diketoenamine, [20] aiming to develop polymer networks that are both recyclable and dynamically adaptable. These efforts highlight the potential of dynamic covalent bonds to revolutionize the design and functionality of polymer networks, offering a bridge between the enduring stability of covalent bonds and the flexible adaptability reversibility of non‐covalent interactions.…”

Ultrastrong, High Fire Resistance, Repairable, and Recyclable Fluorinated Biobased Polyimine Networks

“…It is a prevalent dynamic Schiff-based double-bond structure consisting of carbon and nitrogen (CN), which primarily involves reversible reactions such as condensation/hydrolysis and exchange reactions between imines . The specific reaction conditions are often influenced by external factors, including temperature, solvent, and pH value . Due to the conjugation between the imine bond and benzene ring, aromatic polyimine structures exhibit enhanced stability and higher system energy compared to polyimine in aliphatic structures.…”