Unlocking Dual Recycling in Photo‐Curable Polycyanurate Thermosets Derived from Bio‐Resources

Abstract

Polycyanurate thermosets are extensively utilized in high‐performance applications due to their exceptional thermal and mechanical properties. However, their inherently crosslinked nature has traditionally rendered them nonrecyclable, limiting their sustainability. Recent studies have demonstrated that these networks can undergo dynamic rearrangement under specific conditions, enabling reversibility. In this study, a bio‐derived cyanurate monomer from eugenol was synthesized and polymerized via thiol‐ene photopolymerization, yielding recyclable polycyanurate thermosets with robust material properties. The dynamic character of these networks was leveraged through nucleophilic aromatic substitution (S_NAr) chemistry, unlocking two distinct recycling pathways: i) selective monomer recovery and ii) closed‐loop polymer regeneration. Depolymerization in the presence of eugenol enabled the selective recovery of well‐defined monomeric components, while phenol‐mediated cleavage facilitated polymer breakdown into chemically recyclable intermediates, which were directly reassembled into reformed thermosets. Both recycling pathways resulted in regenerated polymers that retained their original thermal, mechanical, and thermomechanical properties, demonstrating the efficiency and robustness of this approach. By establishing a controlled depolymerization and reassembly framework, this study introduces a sustainable design strategy for achieving closed‐loop recycling in high‐performance thermosets, providing a scalable pathway toward circular polymer materials.

A dual‐pathway recycling strategy for polycyanurate thermosets is presented. The thermosets are prepared by curing a bio‐derived eugenol‐based triazine monomer with various dithiols via thiol‐ene photopolymerization. Recyclability is enabled through two distinct S_NAr‐based depolymerization approaches: selective monomer recovery and closed‐loop polymer regeneration. The recycled materials retain their original performance.

Introduction

Thermoset polymers are indispensable in modern industry, serving as the backbone of structural composites, aerospace components, automotive parts, and high‐performance coatings.^{[ 1} , ^{2 ]} Their exceptional thermal stability, mechanical strength, and chemical resistance make them irreplaceable in applications requiring durability in demanding environments. As a result, thermosets account for approximately 65 million tons of the over 400 million metric tons of plastics produced annually.^{[ 3} , ⁴ , ^{5 ]} However, their characteristic property—the formation of permanent, covalent crosslinked networks—renders them intrinsically nonrecyclable.^{[ 6} , ⁷ , ^{8 ]} This structural rigidity, while ensuring performance, prevents reprocessing, leading to end‐of‐life disposal via landfilling or incineration, posing severe environmental and economic challenges.^{[ 9 ]}

The growing demand for sustainable polymer solutions, driven by legislative action and global environmental goals, has underscored the urgent need for recyclable thermosetting materials that can maintain their structural and functional integrity over repeated use cycles.^{[ 3} , ¹⁰ , ¹¹ , ¹² , ^{13 ]} Unlike thermoplastics, which can be reprocessed through remelting or dissolution processes, recycling thermosets requires selective cleavage of crosslinked polymers to oligomers and monomers—a task that remains one of the foremost challenges in polymer chemistry.^{[ 12} , ^{13 ]}

To address this challenge, significant efforts have been directed toward developing strategies that enable thermoset recyclability while maintaining their high‐performance properties.^{[ 14 ]} A widely explored approach involves the integration of dynamic covalent bonds into polymer networks, allowing for bond exchange and reprocessing under controlled conditions.^{[ 15 ]} Another effective method relies on chemical depolymerization, where crosslinked materials are selectively cleaved into their original monomers.^{[ 12} , ¹⁴ , ¹⁶ , ^{17 ]} This approach enables the regeneration of new polymers with properties identical to the pristine material, effectively closing the recycling loop while preserving material performance.^{[ 12} , ¹⁶ , ^{17 ]} Chemical depolymerization presents a promising pathway toward polymer circularity by conserving raw materials and reducing waste accumulation. To facilitate this process, various cleavable linkages, including imine,^{[ 16} , ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ , ^{21 ]} acetal,^{[ 22} , ²³ , ²⁴ , ²⁵ , ^{26 ]} boronic ester,^{[ 27} , ²⁸ , ²⁹ , ³⁰ , ^{31 ]} and hexahydrotriazine,^{[ 32} , ³³ , ³⁴ , ^{35 ]} have been incorporated into thermosetting networks. These functional groups allow for selective degradation under specific chemical environments, providing a tunable approach to designing recyclable thermosets while ensuring stability during use.

As a promising class of high‐performance thermosets, cyanate ester‐based polycyanurate networks (PCNs) have recently gained significant attention as potential candidates to address the challenges associated with thermoset recycling. PCNs exhibit outstanding thermal resistance, mechanical strength, and chemical stability, making them well‐suited for high‐performance applications such as aerospace, structural composites, and advanced coatings.^{[ 36 ]} Traditionally regarded as nonrecyclable, groundbreaking studies have revealed that PCNs can undergo selective depolymerization via nucleophilic aromatic substitution (S_NAr) reactions, enabling chemical recycling under mild conditions.^{[ 37} , ³⁸ , ³⁹ , ⁴⁰ , ^{41 ]} Zhang and coworkers demonstrated that aliphatic cyanurate esters could be selectively cleaved through base‐catalyzed S_NAr reactions with aliphatic alcohols, providing an efficient route for polymer degradation and monomer recovery.^{[ 39} , ^{40 ]} Furthermore, transitions from aromatic to aliphatic esters were shown to be feasible, broadening the scope of potential nucleophiles. However, the reverse transformation—from aliphatic to aromatic systems—remained unachievable,^{[ 39 ]} likely due to the lower electrophilicity of aliphatic cyanurates and the reduced nucleophilicity of aromatic alcohols, which limit efficient substitution under mild conditions, posing a major challenge for recycling rigid aromatic PCNs. Although aromatic‐to‐aromatic exchange has been demonstrated,^{[ 37 ]} and similar strategies have been applied in the synthesis of COF materials,^{[ 38 ]} the recyclability of such rigid networks based on these motifs remains unexplored. These findings expand the scope of recyclable high‐performance thermosets, demonstrating the feasibility of polycyanurate depolymerization while underscoring the ongoing challenge of achieving closed‐loop recycling in rigid aromatic PCNs.

Parallel to recycling efforts, the transition toward bio‐derived polymers has gained increasing attention, driven by the urgent need to reduce reliance on finite petroleum resources and mitigate the environmental impact associated with conventional polymer production.^{[ 6} , ²⁰ , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ^{49 ]} Phenolic compounds sourced from lignin and other biomass have demonstrated potential as renewable monomers.^{[ 49} , ⁵⁰ , ⁵¹ , ^{52 ]} Among these, eugenol, a bio‐derived phenol from clove oil, offers aromatic rigidity and reactive alkene functionality, making it a valuable building block for polymer synthesis.^{[ 31} , ⁴⁶ , ⁵³ , ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ , ^{58 ]} Eugenol‐based monomers are particularly well‐suited to thiol‐ene photopolymerization, a fast, efficient, and energy‐saving curing method that enables the synthesis of polythioether‐based thermosetting networks under ambient conditions, combining chemical resistance and flexibility with robust mechanical performance.^{[ 59} , ⁶⁰ , ⁶¹ , ^{62 ]}

Combining advances in chemical recycling strategies with the integration of renewable feedstocks represents a powerful approach to address both the recyclability and sustainability challenges associated with thermosets. Here, bio‐derived eugenol was incorporated into the design of aromatic PCNs to construct photocurable, high‐performance thermosets. The latent reversible nature of the aromatic PCNs was subsequently exploited through S_NAr chemistry to unlock their recyclability, enabling dual recycling pathways: i) selective monomer recovery and ii) closed‐loop polymer regeneration. This approach delivers robust thermosetting materials that retain their high‐performance properties across multiple lifecycles, offering a viable solution aligned with the principles of circular polymer design (Figure 1).

Figure 1.

Schematic illustration of the dual recycling pathways for PCNs via dynamic S_NAr chemistry: monomer recovery and closed‐loop chemical recycling.

Results and Discussion

Monomer Synthesis and Characterization

The bio‐derived cyanurate monomer functionalized with terminal alkene groups (M1) was synthesized via a nucleophilic substitution reaction of cyanuric chloride with eugenol in anhydrous CHCl₃ under inert conditions (Figure 2a; see Supporting Information for details). The crude product was readily purified through extraction and washing steps, affording the target compound as a white solid in quantitative yield. Comprehensive structural characterization was performed using ¹H, ¹³C, and 2D NMR techniques (HSQC and HMBC) and LC‐MS. The absence of the hydroxyl proton in the ¹H NMR spectrum, along with the aromatic proton signal adjacent to the oxygen appearing at 7.00 ppm and the methoxy group signal at 3.70 ppm, confirmed the successful substitution (Figure S1). In the ¹³C NMR spectrum, the formation of the cyanurate core was evidenced by the appearance of a characteristic signal at 173.69 ppm, which was absent in the eugenol precursor (Figure S2). Correlation assignments obtained from HSQC and HMBC experiments further validated the structural integrity of M1 (Figures S3 and S4). LC‐MS analysis confirmed the molecular formula and high purity of the monomer (Figure S5).

Figure 2.

Synthesis and characterization of monomer M1 and polycyanurate thermosets P1 and P2. a) Synthesis of M1 and photopolymerization scheme; b) and e) TGA curves; c) and f) DMA results; d) and g) tensile stress–strain curves.

Polymer Synthesis and Characterization

To investigate the structure–property relationship and demonstrate the tunability of the polycyanurate networks, M1 was polymerized with two structurally distinct thiols: 1,4‐benzenedimethanethiol (T1) and 2,2′‐(ethylenedioxy)diethanethiol (T2) (Figure 2a). These thiols were selected to introduce contrasting rigidity and flexibility into the resulting polymer networks (P1 and P2). Stoichiometric ratios were carefully maintained to ensure balanced thiol‐ene click addition, with each alkene functionality paired with a thiol group. Photopolymerization was carried out in CH₂Cl₂ under 365 nm UV light in the presence of the photoinitiator 2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone (Irgacure 2959) for 2 h under an inert atmosphere. Transparent off‐white polymer films were obtained in both cases. Successful polymer network formation was confirmed by FTIR spectroscopy, where the disappearance of the characteristic C═C stretching vibration at approximately 1645 cm⁻¹ indicated complete alkene conversion (Figures S6 and S7). The biobased content of the obtained thermosets was calculated to be approximately 59.5% for P1 and 58.2% for P2, based on the weight contribution of the eugenol segments to the total polymer formulations.

The thermal stability, thermomechanical behavior, and mechanical performance of P1 and P2 were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile testing. TGA revealed decomposition temperatures at 5% weight loss (T _d5%) of 338 °C for P1 and 349 °C for P2, reflecting the excellent thermal stability of both networks (Figure 2b,e). Char yields at 800 °C were 22.5% for P1 and 12.7% for P2, highlighting the thermal robustness of the cyanurate core.^{[ 41 ]} The higher aromatic content in P1, originating from the thiol component, contributes to its increased char residue compared to the aliphatic thiol‐based P2.^{[ 63 ]} DSC measurements indicated that the glass transition temperature (T _g) varied with thiol selection: P1, based on the rigid aromatic T1, exhibited a T _g of 75.5 °C, while P2, prepared using the flexible aliphatic T2, had a lower T _g of 43.9 °C (Figures S8 and S9). DMA analysis corroborated these findings, with T _g values, determined from the peak of tan(δ) measured as 98.1 °C for P1 and 54.4 °C for P2 (Figure 2c,f). Mechanical testing further demonstrated the influence of thiol selection on network stiffness and strength. P1, containing rigid aromatic moieties, exhibited a Young's modulus of 2.22 GPa and a tensile strength of 76.9 MPa, values comparable to those of high‐performance thermosets used in structural applications (Figure 2d,g). In contrast, the more flexible P2 network exhibited a lower Young's modulus of 1.38 GPa and a tensile strength of 41.0 MPa, accompanied by a substantially higher elongation at break of 26.0%, compared to 9.3% for P1 (Table 1). Additionally, toughness values were calculated as 5.39 MJ m⁻³ for P1 and 5.80 MJ m⁻³ for P2. These performance values place the synthesized networks within the competitive range of common commercial and literature‐reported thermosets. P1 exhibits strength and stiffness comparable to vinyl ester, unsaturated polyester, and rigid polyurethane systems, and falls within the range of several epoxy and cyanate ester resins.^{[ 39} , ⁴⁰ , ⁶⁴ , ⁶⁵ , ⁶⁶ , ⁶⁷ , ⁶⁸ , ⁶⁹ , ⁷⁰ , ^{71 ]} In contrast, P2 demonstrates lower stiffness and strength but greater flexibility, broadening its suitability for applications where mechanical adaptability is essential (Figure S10). Altogether, these results underline the versatility of the photopolymerization approach in tailoring the mechanical and thermomechanical performance of polycyanurate thermosets by simply varying the thiol component, providing access to a broad range of properties suitable for different applications.

Table 1.

Thermal and thermomechanical properties of the pristine and recycled polymers.

Polymer	T d5% (°C)	T d30% (°C)	T g (°C)	E 30 ′ (GPa)	Young's modulus (GPa)	Tensile strength (MPa)	Elongation at break (%)
P1	338	358	75.5 a) /98.1 b)	1.68	2.22 ± 0.11	76.9 ± 0.1	9.3 ± 0.9
P1R	331	351	80.6 a) /93.1 b)	1.48	2.11 ± 0.01	75.2 ± 0.9	6.4 ± 1.0
P2	349	370	43.9 a) /54.4 b)	1.74	1.38 ± 0.02	41.0 ± 0.6	20.2 ± 1.1
P2R	330	369	37.6 a) /54.6 b)	1.77	1.39 ± 0.03	38.1 ± 0.6	25.1 ± 4.9

^a) Obtained from DSC analysis.

^b) Obtained from DMA analysis based on the peak of tan (δ).

The swelling behavior of P1 and P2 was assessed in a series of protic and aprotic solvents with varying polarities, including CH₂Cl₂, THF, acetonitrile, ethyl acetate, DMF, DMSO, ethanol, water, 1 M HCl, and 1 M NaOH. Polymer samples with comparable dimensions were immersed in 2 mL of each solvent at room temperature for 2 days. After this period, the samples were removed, blotted dry with a tissue, and weighed. Subsequently, the samples were dried under vacuum at 100 °C for 2 days to determine their gel fractions. The highest swelling ratio was observed in CH₂Cl₂, reaching 190%, while the gel fractions remained consistently high, ranging from 96.2% to 100%, indicating the formation of robust crosslinked networks resistant to solvent‐induced degradation. Furthermore, the polymers exhibited stability under both acidic and basic conditions, as evidenced by preserving their mass in 1 M HCl and 1 M NaOH solutions (Figures S11 and S12). Solvent resistance was further evaluated by subjecting the cured P2 samples to swelling in THF for 24 h, followed by drying and conditioning at 100 °C for 2 days. Tensile tests performed after this treatment showed nearly identical mechanical performance, confirming the robustness of the network under solvent exposure (Figure S13).

Selective Monomer Recovery and Recycling

While dynamic S_NAr reactions have previously enabled the synthesis and recycling of aliphatic alcohol‐based PCN networks, extending this approach to aromatic systems has remained challenging. Although phenol‐based cyanate esters have been employed to construct aromatic PCNs with promising properties,^{[ 39 ]} their recyclability remains unexplored. In this work, the dynamic nature of aromatic alcohol‐based PCNs was utilized to achieve selective monomer recovery through base‐catalyzed S_NAr reaction (Figure 3a).

Figure 3.

Dual recycling concept; a) selective monomer recovery pathway for P1 and closed‐loop recycling pathway for P2; b) ¹H NMR spectra of recovered monomers M1R, M2, D1, and D2.

Depolymerization of the P1 network was performed in excess eugenol at 80 °C in the presence of K₂CO₃ for 16 h. Following the reaction, the mixture was neutralized with 1 M HCl and extracted with CHCl₃ and water. Eugenol, serving both as a reactant and a solvent, was successfully recovered via vacuum distillation at 80 °C with a yield of 93.2%. Its chemical purity was confirmed by ¹H NMR analysis (Figure S14). The remaining organic phase was purified via column chromatography using a cyclohexane/ethyl acetate gradient, affording the M1R monomer in 73% yield and the D1 diol in 78% yield (Figure 3a). The recovered M1R monomer was characterized using ¹H NMR, ¹³C NMR, and mass spectrometry, confirming structural consistency to the virgin M1 monomer (Figures S15–S17). Detailed structural analysis of D1 was performed using ¹H NMR, ¹³C NMR, HSQC, HMBC, and LC‐MS, confirming the formation of a single well‐defined product (Figures S18–S21). In the ¹H NMR spectrum, the singlet at 7.20 ppm was attributed to the aromatic unit of T1, while peaks at 6.82 and 6.65 ppm were assigned to the eugenol moiety. A shift in the methoxy proton signal from 3.70 to 3.86 ppm, alongside the disappearance of alkene signals at 5.99 and 5.12 ppm and the emergence of methylene protons adjacent to sulfur atom at 2.62–2.40 ppm, confirmed successful thiol‐ene addition. D1, as an aromatic polyol, is a potentially valuable building block for polyurethane synthesis, underlining the broader chemical utility of the recovered intermediates.^{[ 72 ]}

To evaluate the recyclability and reusability of the recovered monomers, M1R was subjected to photopolymerization under conditions identical to the original P1 synthesis. The recovered M1R was reacted with fresh T1 in CH₂Cl₂ in the presence of Irgacure 2959 under 365 nm UV light for 2 h under an Ar atmosphere (Figure 4a,b). The resulting polymer, denoted as P1R, was obtained as an off‐white transparent film. FTIR analysis confirmed structural equivalence with the original P1 thermoset (Figure S22). The thermal and mechanical properties of P1R were compared to those of the virgin P1 network to assess potential property degradation after recycling. TGA analysis revealed that the T _d5% of P1R was 331 °C, closely aligning with the 338 °C of P1, indicating preserved thermal stability (Figure 4c). DSC measurements showed a T _g of 80.6 °C for P1R, comparable to 75.5 °C for P1 (Figure 4d). T _g values determined from tan(δ) peaks in DMA were 93.1 °C for P1R and 98.1 °C for P1, verifying that the viscoelastic behavior and network integrity were retained after recycling (Figures 4e and S23). Mechanical testing further confirmed the structural resilience of the recycled network. P1R exhibited a Young's modulus of 2.11 GPa and a tensile strength of 75.2 MPa, closely matching those of P1 (2.22 GPa and 76.9 MPa, respectively), validating the robustness of the recovered material (Figure 4f and Table 1).

Figure 4.

Selective monomer recovery and repolymerization of P1: a) schematic illustration of depolymerization and photo‐induced repolymerization; b) photographs of P1, recovered monomers (M1R and D1), and repolymerized P1R; c)–f) overlaid TGA, DSC, DMA, and tensile data of P1 and P1R.

Collectively, these results demonstrate that the recovered M1R monomer can be efficiently repolymerized into high‐performance thermosetting materials, while the structural integrity, thermal stability, and mechanical properties of the recycled polymer network are effectively retained across the depolymerization and repolymerization cycles.

Closed‐Loop Recycling of PCN Networks

Beyond selective monomer recovery, achieving polymer network reformation without requiring additional feedstock represents a complementary and equally valuable approach to sustain material circularity. While PCNs are susceptible to depolymerization via S_NAr reactions, realizing closed‐loop recycling in aromatic cyanate ester systems requires careful molecular design. To this end, we employed a monomer designed to interact with a low‐boiling‐point aromatic alcohol (phenol) during both depolymerization and reassembly. During depolymerization, phenol acts as a nucleophile, cleaving the polymer network and yielding the M2 monomer. Upon repolymerization, phenol moiety functions as a leaving group, enabling cyanurate network reformation through S_NAr substitution with diols. Building on this strategy, the closed‐loop recycling of the P2 network was explored via an aromatic alcohol‐mediated pathway (Figure 3a).

The P2 thermoset was reacted with excess phenol at 80 °C under an argon atmosphere in the presence of K₂CO₃ for 16 h. After neutralization with 1 M HCl, the mixture was sequentially washed with water and methanol, affording the M2 monomer in 84% yield, as confirmed by NMR and mass spectrometry (Figures 3b and S24–S28). The ¹H NMR spectrum exhibited aromatic proton signals at 7.36, 7.23, and 7.14 ppm, indicating the incorporation of phenol into the monomer structure (Figure S24). Additionally, ¹³C NMR analysis revealed a characteristic peak at 173.67 ppm, corresponding to the cyanurate core (Figure S25). The remaining portion was purified by gradient column chromatography (cyclohexane/ethyl acetate), yielding the D2 diol in 76% yield. The chemical structure of D2 was confirmed through comprehensive NMR and mass spectrometry analyses, with characteristic CH ₂ proton signals appearing at 3.64, 2.72–2.52, and 1.90 ppm (Figures S29–S33). Additionally, phenol was recovered in 68% yield from the aqueous phase by extraction, highlighting the potential for its reuse in subsequent depolymerization processes as part of a closed‐loop system (Figure S34).

For closed‐loop network reformation, recovered monomers M2 and D2 were placed in a Teflon mold, dispersed in THF, and reacted in the presence of TBD at 65 °C under nitrogen for 16 h. The polymer was post‐cured under vacuum at 110 °C for 18 h, followed by an additional curing step at 160 °C for 5 h to enhance the crosslinking density and ensure the complete removal of residual phenol. After solvent evaporation, the polymer was compression‐molded at 180 °C under 10 MPa pressure for 1 h, yielding P2R, a transparent, defect‐free, off‐white thermoset (Figure 5a,b).

Figure 5.

Closed‐loop recycling of P2: a) schematic representation of depolymerization with phenol and repolymerization via S_NAr reaction; b) photographs of P2, recovered monomers (M2 and D2), and repolymerized P2R; c)–f) overlaid TGA, DSC, DMA, and tensile data of P2 and P2R.

Characterization of P2R revealed thermal and mechanical properties nearly identical to those of P2, validating the efficiency of the closed‐loop recycling process (Figure 5c–f). FTIR analysis exhibited indistinguishable spectra for P2R and P2, confirming that the chemical structure of the network was fully retained after recycling (Figure S35). TGA analysis indicated a T _d5% of 330 °C for P2R, consistent with P2, highlighting the preservation of thermal stability. Overlaid TGA profiles further corroborated this observation (Figure 5c). DSC analysis revealed a T _g of 37.6 °C for P2R, closely aligning with 43.9 °C for P2 (Figure 5d). DMA analysis yielded T _g values from tan(δ) peaks of 54.2 °C for P2R and 54.4 °C for P2, confirming the retention of viscoelastic behavior and crosslinking density (Figures 5e and S36). Mechanical testing further supported these findings, with P2R exhibiting a Young's modulus of 1.39 GPa and a tensile strength of 38.1 MPa, both closely matching those of P2 (1.38 GPa and 41.0 MPa, respectively; Figure 5f and Table 1).

P2R exhibited thermal and mechanical properties comparable to virgin P2, confirming that the closed‐loop recycling process enabled efficient network reformation while preserving polymer performance. At the same time, the selective monomer recovery pathway provides access to the D1 diol, which could similarly be utilized in closed‐loop recycling, demonstrating the potential to reconstruct P1R with properties equivalent to its original material. These results establish aromatic alcohol‐mediated S_NAr chemistry as a robust platform for circular polycyanurate systems, offering a blueprint for designing recyclable high‐performance thermosetting materials.

Conclusion

This study introduces a bio‐derived polycyanurate thermoset platform that seamlessly integrates photochemical curing, high‐performance properties, and dual chemical recycling pathways, offering a scalable solution for thermoset recyclability. The incorporation of thiol‐ene photopolymerization enables an energy‐efficient curing approach, while thiol‐based flexibility allows for precise tuning of the inherently rigid cyanurate backbone, expanding its applicability in coatings, sealants, and other mechanically demanding applications.

A key advancement of this work lies in the demonstration of two complementary depolymerization strategies, establishing a versatile and controllable recycling framework suited for industrial implementation. Eugenol‐triggered depolymerization enables selective monomer recovery, allowing for repolymerization with different thiols. This adaptability enables precise control over the mechanical properties of the material in each recycling step, ensuring its suitability for diverse applications. Meanwhile, phenol‐triggered depolymerization enables closed‐loop polymer reassembly, allowing polymer regeneration without additional feedstock, significantly enhancing resource efficiency. Importantly, the polymer network remains stable under ambient conditions, ensuring long‐term material integrity, while depolymerization is selectively induced under basic catalysis with specific nucleophiles, offering precise control over recycling. While the current approach involves column chromatography and extended reaction conditions that are more suited to laboratory‐scale demonstrations, these steps could be optimized depending on specific application needs and processing conditions.

Beyond recyclability, this study successfully demonstrates aromatic‐to‐aromatic exchange in PCN recycling—unlocking the potential of lignin‐based phenols and providing a strong alternative to existing strategies for rigid high‐performance thermosets, while increasing the biobased content of the final material. By integrating bio‐derived monomers, light‐driven polymerization, and chemically controlled reversibility, this study redefines the design paradigm for recyclable thermosets, establishing a foundation for next‐generation circular polymer systems.

Conflict of Interests

The authors declare no conflict of interest.

Supporting information

Supporting Information

Dedicated to Prof. E. W. “Bert” Meijer on the occasion of his 70th birthday

Dağlar Ö., Chen Y.‐R., Tomović Ž., Angew. Chem. Int. Ed. 2025, 64, e202507567. 10.1002/anie.202507567

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.