Recyclable, Malleable, and Strong Thermosets Enabled by Knoevenagel Adducts

Wang, Sheng; Feng, Hongzhi; Lim, Jason Y. C.; Li, Ke; Li, Bofan; Mah, Justin J. Q.; Xing, Zhenxiang; Zhu, Jin; Loh, Xian Jun; Li, Zibiao

doi:10.1021/jacs.4c00043

Cited by 13 publications

(3 citation statements)

References 56 publications

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“…In compound B8, an ether linkage, reflecting the chain length of A8, was introduced to increase the segmental mobility within the PCC networks. Additionally, the TCA 26 was synthesized through an esterification reaction between a cyanoacetic acid and a trimethylolethane ( Figure S23 ). Subsequently, TCA, a dialdehyde, and a catalyst TBD were mixed in THF ( Table S1 ), followed by slowly evaporating solvent at RT and precuring at 60 °C for 30 min to enhance the reaction degree and prevent side reactions of reactive groups that are likely at higher temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…Such well-conjugated systems is suitable for preparing glassy polymers with high rigidity. In addition, the highly polarized CC bond is capable of reversible formation, , or involvement in exchange reactions with active methylene compounds , or thiols, or metathesis reactions with imine bonds. , However, the direct metathesis reaction involving the Knoevenagel CC bond itself has not been previously reported.…”

Section: Introductionmentioning

confidence: 99%

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Knoevenagel C═C Metathesis Enabled Glassy Vitrimers with High Rigidity, Toughness, and Malleability

Wang,

Feng,

et al. 2024

J. Am. Chem. Soc.

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Thermosets, characterized by their permanent crosslinked networks, present significant challenges in recyclability and brittleness. In this work, we explore a polarized Knoevenagel C�C metathesis reaction for the development of rigid yet tough and malleable thermosets. Initial investigation on small molecule model reactions reveals the feasibility of conducting the base-catalyzed C� C metathesis reaction in a solvent-free environment. Subsequently, thermosetting poly(α-cyanocinnamate)s (PCCs) were synthesized via Knoevenagel condensation between a triarm cyanoacetate star and a dialdehyde. The thermal and mechanical properties of the developed PCCs can be easily modulated by altering the structure of the dialdehyde. Remarkably, the introduction of ether groups into the PCC leads to a combination of high rigidity and toughness with Young's modulus of ∼1590 MPa, an elongation at break of ∼79%, and a toughness reaching ∼30 MJ m 3 . These values are competitive to traditional thermosets, in Young's modulus but far exceed them in ductility and toughness. Moreover, the C�C metathesis facilitates stress relaxation within the bulk polymer networks, thus rendering PCCs excellent malleability and reprocessability. This work overcomes the traditional limitations of thermosets, introducing groundbreaking insights for the design of rigid yet tough and malleable thermosets, and contributing significantly to the sustainability of materials.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Knoevenagel C═C Metathesis Enabled Glassy Vitrimers with High Rigidity, Toughness, and Malleability

Wang,

Feng,

et al. 2024

J. Am. Chem. Soc.

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“…These bonds enable hydrogels to regulate dynamic behaviors rapidly and efficiently. Comparatively, spontaneous chemistries of, e.g., boronic acid/diol complexation, , Schiff-base, − and Knoevenagel condensations , ensure reversible bond formation/scission in dynamic hydrogels without any stimuli, expanding their biological applications under milder conditions. However, these spontaneous dynamic processes lack controllability and have limited reconfigurable and structural designs.…”

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confidence: 99%

Ligand Dissociation of Metal-Complex Photocatalysts toward pH-Photomanipulation in Dynamic Covalent Hydrogels for Printing Reprocessable and Recyclable Devices

Wang,

Zhu,

Liu

et al. 2024

ACS Macro Lett.

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Dynamic covalent hydrogels are gaining attention for their potential in smart materials, soft devices, electronics, and more thanks to their impressive mechanical properties, biomimetic structures, and dynamic behavior. However, a significant challenge lies in designing precise and efficient dynamic photochemistry for their preparation, allowing for complex structures and control over the dynamic process. Herein, we propose a general and straightforward orthogonal dynamic covalent photochemistry strategy for preparing high-performance printable dynamic covalent hydrogels, thereby broadening their advanced applications. This photochemical strategy uses a bifunctional photocatalyst to initiate radical polymerization and release ligands through a rapid light-mediated dissociation mechanism. This process leads to a controlled increase in system pH from mildly acidic to alkaline conditions within one hundred seconds, which in turn triggers the pH-sensitive model reactions of boronic acid/diol complexation and Knoevenagel condensation. The orthogonal photochemistry enables the formation of interpenetrated and conjoined networks, significantly enhancing the mechanical properties of the hydrogels. The reversible bonds formed during the process, i.e., boronic ester and unsaturated ketone bonds, confer excellent self-healing, reprocessable, and recyclable properties on the hydrogels through photochemical pH variations. Furthermore, this rapid, controlled fabrication process and dynamic behavior are highly compatible with printing techniques, enabling the design of adaptive and recyclable sensors with different structures. These advancements are promising for various material science, medicine, and engineering applications.

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Foam‐to‐Foam Recycling Potential of PU‐Foams by Integration of Amino Esters

Kassem,

Samat,

Imbernon

et al. 2024

Adv Funct Materials

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The increasing market demand for flexible polyurethane foams (PUFs) is prompting the academic and industrial community to seek solutions for their end‐of‐life management. In this study, this issue is addressed by incorporating β‐amino ester (BAE) moieties into the foam structure. This addition results in flexible hybrid PU‐BAE foams that can be thermally reprocessed and chemically recycled, with cell sizes ranging from 780 to 990 µm and densities between 90 and 150 kg m−3. These foams demonstrate thermomechanical reprocessability, yielding stable PU‐BAE elastomers, with glass transition temperature values ranging from 14 to 25 °C. Stress relaxation experiments reveal remarkably fast relaxation times for these hybrid elastomers (23 s at 160 °C). Furthermore, a systematic investigation of the chemical recyclability of these foams via glycosylation is conducted under mild conditions, achieving complete disintegration within 20 min at 65 °C. Finally, the chemically recycled product is converted into a foam again, achieving a closed loop foam‐to‐foam recycling process. These findings indicate that the integration of BAE into PUFs leads to an enhanced chemical recycling rate, providing a promising avenue for addressing end‐of‐life concerns in PUF‐applications.

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Recyclable, Malleable, and Strong Thermosets Enabled by Knoevenagel Adducts

Cited by 13 publications

References 56 publications

Knoevenagel C═C Metathesis Enabled Glassy Vitrimers with High Rigidity, Toughness, and Malleability

Knoevenagel C═C Metathesis Enabled Glassy Vitrimers with High Rigidity, Toughness, and Malleability

Ligand Dissociation of Metal-Complex Photocatalysts toward pH-Photomanipulation in Dynamic Covalent Hydrogels for Printing Reprocessable and Recyclable Devices

Foam‐to‐Foam Recycling Potential of PU‐Foams by Integration of Amino Esters

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