Upcycling of atmospheric CO_2 to self-healing recyclable polymers under ambient conditions

Domain: chemistry
Published: 2026-03-02
Editorial outcome: major_revision

Abstract
The polymer industry is confronting an urgent sustainability trilemma: accelerating plastic pollution, substantial CO2 emissions from production processes, and dependence on diminishing fossil resources. Upcycling CO2 into polymers presents a promising solution to these interconnected issues; however, existing CO2-to-polymer technologies face significant challenges: dependence on concentrated CO2 sources rather than direct air capture (DAC), reliance on complex catalysts and energy-intensive conditions (elevated temperatures/pressures), and generation of polymers with limited self-healing and recyclability. Herein, we propose a catalyst-free strategy of converting atmospheric CO2 into carbonate ions (CO3 2-) as intermediates for the synthesis of dynamic covalent polymers. This approach is based on a dynamic bond system, termed the CO3 2--bridged dynamic covalent bond, enabling catalyst-free synthesis of polymers from ambient air at room temperature and pressure. The resultant polymers show excellent mechanical properties, rapid self-healing, and versatile circularity through three distinct pathways: thermal reprocessing, closed-loop chemical recycling via acid-triggered depolymerization at room temperature, and upcycling of mixed CO2-derived polymers into hybrid materials with enhanced properties. This study provides a platform for both low-energy-consuming CO2 valorization and the development of sustainable polymers.

Introduction
The global plastics industry confronts an escalating environmental pollution crisis1-3. Phasing out plastics entirely is neither feasible nor practical, as no alternatives can rival their unparalleled combination of lightweightness, durability, versatility, easy processing and affordability. This dilemma has spurred the development of innovative closed-/open-loop polymer recycling or upcycling to advance the circular economy4-15. Notably, dynamic covalent polymer, also known as covalent adaptable network (CAN), has emerged as a promising solution9-15. CAN undergoes bond exchange reactions in solid state, enabling materials to undergo thermal reprocessing similarly to thermoplastics, while retaining the advantageous properties of the thermosets16-17. This solid-state exchange reaction also endows materials with inherent self-healing capabilities18. Besides, some CANs can be depolymerized back to their precursors through the reversible dissociation of dynamic covalent bonds, thereby facilitating their closed-loop chemical recycling13-14. Pioneered by Leibler et al.9, various dynamic covalent reactions have been harnessed in CAN synthesis, such as imine exchange19, boronic ester exchange10, nucleophilic aromatic substitution14, olefin metathesis20, diketoenamine exchange21, vinylogous urethane transamination22, urethane exchange23, diselenide exchange24, oxime-ester exchange25, silyl ether exchange26 and so on. Despite these advances, current CAN systems remain challenged by harsh reprocessing conditions (elevated temperatures/pressures, catalyst dependence), limited chemical recyclability, and the persistent strength-toughness trade-off12-13, 23,27-28. These limitations highlight the urgent need for dynamic chemistries capable of simultaneously achieving superior reprocessability, chemical recyclability and balanced mechanical properties.

While recycling innovations are vital, sustainable polymer production from renewable feedstocks is also critical. Among various renewable resources, CO2 stands out as a particularly promising feedstock, offering dual benefits of mitigating carbon emissions and reducing dependence on petrochemical resources29-32. Unfortunately, the conversion of CO2 into polymers is not without challenges. Current methodologies for this C1 building block conversion rely upon concentrated pure CO2 (Supplementary Tables S1-S2). Direct air capture and utilization (DACU) represents a promising alternative pathway but remains challenging33, as it demands reaction systems with extraordinary selectivity and efficiency under ultra-dilute atmospheric CO2 conditions (∼400 ppm). Furthermore, most current synthetic pathways for CO2-derived polymers require sophisticated catalytic systems, high-energy precursors, and harsh reaction conditions (elevated pressures and temperatures) (Supplementary Tables S1-S2)27,34-36, thereby compromising economic viability and scalability. Although a few catalyst-free methods have recently emerged, significant hurdles persist in overcoming unfavorable reaction conditions and attaining excellent thermal and mechanical properties37-40. Additionally, polymers synthesized via these methods typically exhibit limited recyclability and lack inherent self-healing capacities41-42.

The fundamental challenge in converting CO2 arises from its inherent stability and inertness, yet, it also possesses a slight acidity. Previous studies have demonstrated that alkali hydroxides can efficiently (>90% yield) capture atmospheric CO2 and convert it into carbonate ions (CO3 2-)43. This inspires us to explore the feasibility of developing a catalyst-free approach to convert atmospheric CO2 into CO3 2- as intermediates for synthesizing self-healing recyclable polymers. To achieve this goal, the key is to identify an appropriate functional group capable of reversibly binding to CO3 2-. In this regard, α,α,α-trifluoroacetophenone (TFP)—a known ionophore that can form 2:1 tetrahedral adducts with CO3 2- (Fig. 1a)—emerges as a promising candidate44. Meanwhile, given its structural similarity to hemiacetal, we hypothesize that such CO3 2--bridging interactions may exhibit high plasticity, making it an attractive option for constructing recyclable polymers. Here, we show that, unlike conventional synthetic routes, this interaction—termed the CO3 2--bridged dynamic covalent bond—forms at ambient temperature through rapid, quantitative reversible reactions between CO3 2- and TFP without the need for catalysts. Furthermore, this bond not only undergoes rapid catalyst-free dynamic exchange reactions but can also be reversibly cleaved under mild acidic conditions at ambient temperature. Leveraging this chemistry platform, we synthesized a series of CANs directly using ambient air as a reactant under ambient temperature and pressure conditions, without catalysts. The resulting polymers exhibit tunable mechanical properties ranging from PDMS-like elastomers (with a Young’s modulus of 2.8 MPa and an elongation at break of 906%) to polystyrene-like rigid plastics (with a Young’s modulus of 1.6 GPa and an ultimate tensile stress of 38.6 MPa), ultrafast self-healing capabilities (98.8% efficiency in 10 minutes at 80°C), and versatile circularity through three distinct pathways: thermal reprocessing through compression molding or extrusion under mild conditions (more than five cycles without performance degradation), closed-loop chemical recycling via acid-triggered dissociation at ambient temperature (more than 95% recovery), and upcycling of mixed CO2-derived polymer networks into hybrid materials with enhanced properties (Fig. 1b). This study demonstrates an energy-efficient approach for simultaneous atmospheric CO2 valorization and sustainable polymer production.

Results
Model reactions. The nucleophilic addition reaction between CO3 2- and TFP has previously garnered attention, with successful integrations into chemical sensors and ion channels44-48. However, a comprehensive understanding of this unique reaction, its dynamic behavior, and its unexplored potential in polymer synthesis still remains elusive. To gain insights into the TFP-CO3 2- reaction, we designed tetrabutylammonium carbonate (TBAC) and TFP as the model compounds (Fig. 2a, Supplementary Fig. 1). Upon mixing them in a 2:1 molar ratio in deuterated acetonitrile (CD3CN) and allowing the reaction to proceed for 15 minutes under ambient temperature, both 1H and 19F NMR spectroscopies revealed the occurrence of a quantitative reaction with no trace of side reactions in the absence of catalysis, as evidenced by the completely upfield shifts in the proton signals of the benzene ring (Fig. 2b and Supplementary Figs. 2-3, Ha 8.08 → Ha′ 7.69 ppm, Hb + Hc 7.80 + 7.63 → Hb′ 7.33 ppm) and fluorine signals (Supplementary Fig. 4, Fa -72.27 → Fa′ -84.15 ppm). A more detailed analysis of this reaction was performed using 13C NMR spectra. As depicted in Fig. 2c, distinct shifts were observed in the carbon signals of trifluoromethyl group (quartet peak, Ca 118.01 → Ca′ 126.29 ppm) and benzene ring (Cb-d, 136.68, 130.64 and130.14 → Cb′-d’ 128.59, 128.08 and 127.86 ppm). Meanwhile, the carbonyl carbon peak of TFP at 181.11 ppm and the carbonate-related carbon peak at 160.26 ppm completely disappeared, replaced by new peaks at 93.44 ppm and 142.31 ppm, respectively, in the product spectrum. These findings suggest a nucleophilic attack by CO3 2- on the carbonyl carbon of TFP occurs, leading to the formation of anionic CO3 2--bridged adducts. This result was further confirmed by Fourier-transform infrared (FTIR) spectra and mass spectroscopy (MS) analysis (Supplementary Figs. 5-6).

To investigate the influence of counter-cations on the reaction, both organic and inorganic carbonate salts were employed. In the case of organic carbonates, including TBAC, tetrapropylammonium carbonate (TPAC), tetraethylammonium carbonate (TEAC), tetramethylammonium carbonate (TMAC) and benzyltrimethylammonium carbonate (BnMAC), all exhibited near-quantitative yields while demonstrating marked variations in reaction rates (Fig. 2d, Supplementary Figs. 7-10, 12a-e). The reaction rates decreased in the following order: BnMAC > TBAC > TPAC > TEAC > TMAC. Notably, even TMAC, which exhibited the slowest rate, reached equilibrium within 80 minutes. In contrast, inorganic carbonates displayed significantly lower conversion rates (Supplementary Fig. 11, Fig. 12f), presumably due to their poor solubility and elevated dissociation energies in organic solvents. These findings indicate the advantage of organic carbonate salts for the rapid and efficient preparation of CO3 2--bridged adducts.

The formed CO3 2--bridged bond exhibited remarkable dynamic exchange properties. When stoichiometric mixing of competitive reactant 4-fluoro-α,α,α-trifluoroacetophenone (FTFP) with CO3 2--TFP adducts (TFPCTFP) in CD3CN was followed by 10-minute incubation at ambient temperature, five expected compounds were detected via 1H, 19F NMR spectroscopy and MS (Figs. 2e-f and Supplementary Figs. 13-14). This finding confirmed the occurrence of rapid exchange reactions in the absence of catalysts. The dynamic process was further validated by analogous equilibrium in the reaction between CO3 2--FTFP adducts (FTFPCFTFP) and TFP. Beyond dynamic exchange capabilities, the CO3 2--bridged bond exhibited efficient acid-triggered cleavage under mild conditions. Upon adding aqueous H2SO4 to TFPCTFP solution in CD3CN to achieve pH 4, abundant emission of CO2 gas was detected (Supplementary Fig. 15 and Movie 1). Subsequent 1H and 19F NMR analysis of the residual solution revealed that TFPCTFP decomposed into TFP with a yield of 96.2% (Fig. 2g and Supplementary Fig. 16). Collectively, these results establish that CO3 2--bridged bonds are formed readily, undergo rapid dynamic exchanges, and can be decomposed efficiently under mild conditions.

Synthesis and Characterization of CANs
Motivated by the results of the small-molecule model reaction, we next explored the potential for developing recyclable polymers. Since CO2 can be captured from air by alkali hydroxide and converted into CO3 2- 43, our reversible chemical platform enables catalyst-free synthesis of recyclable polymers from atmospheric air via CO3 2- as intermediates. As a proof-of-concept, we synthesized the linear copolymers poly(4-vinyltrifluoroacetophenone-co-methyl acrylate) [P(VTFP-MA)-20, VTFP/MA = 1/20 mol/mol, Mn = 48.1 kDa, Đ = 1.53] via free-radical copolymerization of 4-vinyltrifluoroacetophenone (VTFP) and methyl acrylate (MA) monomers (Fig. 3a and Supplementary Figs. 17-24). The VTFP monomer was prepared in 85% isolated yield through a one-step Suzuki coupling of commercially available reagents, underscoring its potential for scalable production. Subsequently, a one-pot, two-step method was designed to synthesize polymer networks from atmospheric CO2. In the first step, ambient air from Chongqing, China (29° 49' 20.68" N, 106° 25' 23.0" E) was bubbled at ~300 mL·min-1 into an acetonitrile (CH3CN)/H2O solution of tetrabutylammonium hydroxide (TBAH) under ambient conditions, yielding TBAC (Fig. 3b and Supplementary Figs. 25-26). Monitoring the CO₂ concentration in the exhaust stream revealed that it did not rise significantly until complete conversion of TBAH to TBAC (Fig. 3c), with the endpoint determined by the solution pH reaching ~7.5 —a value corresponding to that of a pure TBAC solution at the same concentration. Quantitative analysis confirmed the TBAC purity of 94.1% (containing ~5.9% tetrabutylammonium hydrogen carbonate (TBAHC), which was verified to not affect subsequent cross-linking reaction or material properties; Supplementary Figs. 27-28) and an atmospheric CO2 capture efficiency (defined as the mass ratio of fixed CO2 to supplied CO2) of 80.0%, demonstrating the high efficacy of CO2 fixation. The cross-linked network was then prepared by adding P(VTFP-MA)-20 solution to the as-prepared TBAC solution. Upon mixing, the transparent solution transformed into a white paste within 30 seconds, and subsequently evolved into a semitransparent, free-standing gel after 40 minutes of stirring (Fig. 3d), confirming successful cross-linking. After solvent removal, the resulting CO2-derived CAN (unless otherwise specified, CO2-derived CAN is defined in this work as the network derived from P(VTFP-MA)-20, TBAH, and ambient air) was hot-pressed at 90 °C and 6 MPa for 10 minutes, producing a slightly colored, transparent CAN film exhibiting a transmittance exceeding 70% in the visible light region from 500 to 800 nm (Supplementary Fig. 29). Swelling tests confirmed the film’s insolubility in various organic solvents (e.g., tetrahydrofuran (THF), chloroform (CHCl3), toluene, n-hexane, ethyl acetate (EA)) after 12 h immersion, with gel fractions exceeding 90% in all cases, further verifying the cross-linked structure (Fig. 3e). FTIR spectroscopy confirmed the formation of CO3 2--bridged networks, as evidenced by the disappearance of detectable carbonate signals and a concurrent reduction in the benzene ring vibration of P(VTFP-MA)-20 (Fig. 3b).

Having successfully synthesized the CAN, we proceeded to investigate their thermal and mechanical properties. Differential scanning calorimetry (DSC) revealed a glass transition temperature (Tg) of 21.3 °C for the CO₂-derived CAN (Fig. 3f), which was higher than that of its linear polymer precursor. This elevated Tg was further corroborated by dynamic mechanical analysis (DMA, Fig. 3g), which showed a characteristic drop in the storage modulus (E’) at the transition. Critically, a distinct rubbery plateau in E’ above Tg was observed for the CO2-derived CAN, whereas no such plateau was evident for the for P(VTFP-MA)-20, confirming the crosslinked nature of the network49. The crosslink density (ν) was calculated to be 79.1 mol m-3 from the rubbery plateau modulus (E’r) using the equation ν = E’r/[3R(Tg+50)]. Thermogravimetric analysis (TGA) demonstrated excellent thermal stability, with a 5 % mass loss temperature (T5%) of 252 °C (Supplementary Fig. 30). To evaluate the mechanical properties, uniaxial tensile tests were conducted. The results indicated that the ultimate tensile stress, Young’s modulus, toughness, and elongation at break of the crosslinked CANs were 10.7 MPa, 84.6 MPa, 68.7 MJ·m-3, and 937%, respectively (Fig. 3h and Supplementary Fig. 31). Compared to the linear polymer P(VTFP-MA)-20, these values demonstrated respective increases of 3.45-, 32.38-, 5.81-, and 1.56-fold. This exceptional ability to simultaneously enhance strength, rigidity, toughness, and ductility is unusual, as these properties are often seen as conflicting50-51. We suspect that this paradoxical mechanical behavior may be attributed to the unique dual role of the ionic crosslinker, where CO3 2- ions function as crosslinkers, enhancing strength and stiffness, while the counter-cations serve as plasticizers, increasing toughness and ductility. The plasticizing effect of the counter-cations was initially confirmed in a control experiment, where blending tetrabutylammonium iodide (TBAI) with the linear polymer P(VTFP-MA)-20 enhanced ductility but compromised strength and stiffness compare to the pure linear polymer. To gain deeper mechanistic insights, we conducted molecular dynamics (MD) simulations using LAMMPS (Supplementary Figs. 32-33). A comparative analysis between the CO₂-derived CAN (with TBA+) and the control system (with H+ replacing TBA+) revealed key distinctions: (i) a weaker ionic association, as indicated by the significantly right-shifted first peak in the radial distribution function (RDF, g(r)) between TBA+ and the polymeric anions (Fig. 3i); (ii) significantly enhanced cation mobility, with a diffusion coefficient 2.1 times greater than that of the control group (Fig. 3j and Supplementary Fig. 34a); (iii) a considerably expanded polymer free volume fraction (FFV, Fig. 3k and Supplementary Fig. 35), which provides more space for segmental motion; and (iv) dramatically accelerated relaxation dynamics of the polymer chains, as demonstrated by a significantly increased mean-squared displacement (MSD) over time (Fig. 3l and Supplementary Fig. 34b). These findings collectively demonstrate that the bulky, flexible TBA+ cations effectively screen electrostatic interactions, enhance ion mobility, expand free volume, and lubricate polymer chains, thereby rationalizing the enhanced ductility and toughness.

This cation-mediated plasticization enables precise mechanical tailoring through cation selection. As shown in Fig. 3m, systematically shortening the alkyl chain length from TBA+ to TMA+ led to increases in Young’s modulus and ultimate tensile strength but at the expense of ductility. This trend was further accentuated with rigid aromatic counter-cations such as BnMA+, which yielded the highest Young’s modulus of 546 MPa—6.5 times that of the TBA+-based CAN—alongside a further reduced elongation at break. MD simulations attribute this systematic mechanical variation to a gradual attenuation of the cationic plasticizing effect. RDF analysis showed a progressive left-shift of the first peak for the cations-polymer interaction along the series TBA+ → TPA+ → TEA+ → TMA+ → BnMA+ (Fig. 3i), indicating a decreasing average ion-pair distance and thus stronger electrostatic interactions. This trend leads to a concomitant decrease in cation mobility and a reduction in polymer free volume (Figs. 3j-k and Supplementary Fig. 34a). As a result, segmental motion of the polymer chains becomes more restricted (Fig. 3l and Supplementary Fig. 34b), shifting the mechanical behavior from ductile to rigid and strong. To further broaden the range of accessible mechanical properties, we modulated the linear polymer backbone. By adjusting comonomer ratios and types, we synthesized a series of CANs whose mechanical properties spanned from flexible elastomers (Young’s modulus: 2.8 MPa; elongation at break: 906%) to rigid plastics (Young’s modulus: 1.6 GPa, ultimate tensile stress: 38.6 MPa), as shown in Fig. 3n and Supplementary Figs. 37-39. These results indicate the immense potential of our CANs in offering materials with customizable mechanical properties to cater to a diverse range of application requirements. Beyond tunable mechanics, the CANs exhibited exceptional durability. Taking the CO2-derived CAN (selected as the representative system for subsequent investigations unless otherwise specified) as an example, it could withstand 14-day ultraviolet (UV) exposure, high humidity (45% relative humidity), 9 thermal cycles (-20 to 110 °C), and 8-week outdoor exposure with negligible degradation in its mechanical performance, appearance, or chemical structure (Supplementary Figs. 40-43), underscoring its potential for real-world applications.

Self-healing and Reprocessing Properties
Although the CANs are crosslinked polymers with robust mechanical properties, they exhibit thermoplastic-like malleability due to catalyst-free exchange reactions. Stress relaxation measurements of CO2-derived CAN conducted at 60 °C and 1% strain (within the linear viscoelastic regime of 0.001%-10%; Supplementary Fig. 44) revealed rapid bond exchange kinetics, with a relaxation time (τ) of only 13.5 seconds (Supplementary Fig. 45). This ultrafast relaxation hindered reliable quantification at elevated temperatures via stress relaxation49; we therefore employed small-amplitude oscillatory shear (SAOS). The relaxation time τ was determined from the crossover frequency (ωc) where the storage modulus (G’) equals the loss modulus (G’’), using the equation τ = 1/ωc (Fig. 4a). Arrhenius analysis showed a linear correlation between ln(τ) and 1000/T (Fig. 4b), confirming the vitrimeric nature of the networks. The activation energy (Ea) for the solid-state bond exchange, calculated from the Arrhenius plot, was 111.9 kJ·mol-1. This value is closely consistent with the Ea derived from time-temperature superposition (TTS) analysis (Supplementary Fig. 46). Temperature-sweep rheological tests revealed a sharp, nearly three-order-of-magnitude decrease in G’, accompanied by a distinct G’/ G’’ crossover at 85 °C (Fig. 4c), consistent with a dissociative exchange mechanism in the CO2-derived networks. To further elucidate this mechanism, we performed in situ variable-temperature FTIR spectroscopy. Upon heating from 25 to 120 °C, a gradual intensification of the absorption band at 1730 cm-1 was observed, suggesting the thermally induced cleavage of CO3 2--bridged bonds to form the TFP compound (Fig. 4d). Subsequent cooling at room temperature for 24 hours restored the original CO3 2--bridged bonds, confirming the reversibility. These findings collectively demonstrate the exceptional malleability and rapid dissociative exchange reaction kinetics of the CO2-derived CAN.

Due to the rapid exchange reaction, the CANs exhibit remarkable self-healing capability after mechanical damage. As shown in Fig. 4e, two rectangular CO2-derived CAN samples (30 mm × 10 mm × 0.5 mm) were prepared, with one stained red using rhodamine B for enhanced visibility. After being cut in half, the separated samples were seamlessly reintegrated within 10 minutes at 80 °C under 0.5 MPa pressure, leaving no visible scratches. The repaired sample was capable of supporting a 1 kg object weighing over 5,000 times its own weight for at least 5 minutes at ambient temperature with negligible extension (Fig. 4f and Supplementary Movie 2). To quantify self-healing property, we compared the mechanical properties of original and repaired samples after different healing durations (Fig. 4g, Supplementary Fig. 47 and Supplementary Movie 3). After just 30 seconds of healing, the healing efficiency—defined as the ratio of the ultimate tensile stress of the repaired sample to that of the original—reached 59%. Within 10 minutes, the tensile property of the repaired sample recovered to 98.8% of its initial value. This damage-healing cycle was repeatable at least three times (Fig. 4h and Supplementary Fig. 48). Furthermore, efficient self-healing was also achieved under milder conditions, albeit with longer healing times. After 24 hours at 40 °C under 2 MPa, a healing efficiency of 98.2% was attained; even at room temperature under the same pressure, the efficiency reached 53.2% (Supplementary Fig. 49).

The rapid exchange reaction upon heating also endows CANs with exceptional reprocessability. Fragmented CO2-derived CAN can be regenerated into monolithic materials through either compression molding at 90 °C and 6 MPa for 10 minutes or injection molding at 100 °C (Fig. 4i and Supplementary Fig. 50). This demonstrates that the CANs can be reprocessed using multiple industrially relevant techniques within a short period under mild conditions. This contrasts sharply with most studied CANs, which typically require prolonged exposure to high pressure and/or temperature, often resulting in unwanted side reactions52. To further investigate their reprocessability, we conducted multiple fragment-hot pressing molding treatments. The results show that, even after five cycles, their thermal and mechanical properties, as well as chemical structure, remain virtually identical to those of the initial samples (Figs. 4j-k and Supplementary Figs. 51-52).

Closed-loop Chemical Recycling and Upcycling
After elucidating the robustness and reprocessability of the polymer networks, we embarked on an investigation into their chemical recyclability. As a demonstration, CO2-derived CAN sheets were fragmented and immersed in a 0.2 M H2SO4/ CH3CN solution at ambient temperature. After a 2.5-hour incubation period, all samples completely dissociated into soluble components (Supplementary Fig. 53a). Increasing the acid concentration to 0.5 M shortened the dissolution time to 40 minutes, yielding a transparent solution without visible residues (Supplementary Fig. 53b). Subsequent liquid-liquid extraction with ethyl acetate and water directly afforded P(VTFP-MA)-20 in ~95% yield without further purification (Fig. 5a and Supplementary Fig. 54). TBAH recovery via basic anion exchange resins achieved 97% efficiency (Supplementary Fig. 55). As expected, the recycled P(VTFP-MA)-20 and TBAH were used to resynthesize CANs. Figs. 5b-c and Supplementary Fig. 56 illustrate that the reborn CANs exhibit virtually identical chemical structures, thermal and mechanical properties to those of the original CANs after three cycles of recycling. To demonstrate the possibility of selectively recycling, two scenarios were presented: (i) a mixed plastic waste stream containing CO2-derived CAN, polyvinyl chloride, polypropylene and polyethylene (Fig. 5d); (ii) a carbon-fiber-reinforced polymer (CFRP) consisting of CO2-derived CAN and carbon fiber (CF) woven fabrics (Figs. 5e-f and Supplementary Fig. 57). The results show that our mild recycling conditions caused no degradation to non-target materials, indicating the remarkable efficiency and selectivity in degrading, separating, and recovering CANs from complex mixtures.

In addition to closed-loop chemical recycling, the recycled raw materials can also be upcycled into new CO2-derived polymers. For instance, two distinct CANs were selected—one rigid but brittle (CAN derived from P(VTFP-MA)-1.3), and the other soft yet tough (CO2-derived CAN). After individual acid-induced degradation into raw materials, they were blended and re-cross-linked via CO2 introduction, producing a hybrid network with mechanical properties surpassing both original CANs (Fig. 5g and Supplementary Fig. 58). Specifically, the hybrid exhibited 2-fold higher tensile strength and 150-fold enhanced toughness compared to original CANs. These findings demonstrate that the CO2-derived CAN exhibit both closed-loop chemical recycling and upcycling capabilities under mild conditions.

Methods
Materials
TFP, FTFP, benzyltrimethylammonium hydroxide (BnMAH, 25 wt% in water), TBAI (97%), 4-bromo-α,α,α-trifluoroacetophenone (98%), pinacol vinylboronate (97%), TBAHC(95%), cesium carbonate (Cs2CO3) were purchased from Bide Pharmatech Ltd. TBAH (40 wt% in water), tetramethylammonium hydroxide (TMAH, 25 wt% in water), tetraethylammonium hydroxide (TEAH, 25 wt% in water), tetrapropylammonium hydroxide (TPAH, 40 wt% in water), 2,2'-Azobis(2-methylpropionitrile) (AIBN, 98%), tetrakis(triphenylphosphine)palladium (Pd(PPh3)4, 99%), potassium carbonate (K2CO3, 99%), MA (99%), methyl methacrylate (MMA, 99%), ethyl methacrylate (EMA, 99%), butyl methacrylate (BuMA, 99%), 1,4-dioxane, toluene, THF, CH3CN, n-hexane were acquired from Innochem Co., Ltd. CHCl3, H2SO4, petroleum ether (PE), EA, dichloromethane, methanol (MeOH) were obtained from Chongqing Taixin Chemical Co., Ltd. All chemical reagents were used as received unless otherwise noted.

Model reaction for the catalyst-free formation of CO3 2--bridged dynamic covalent bond
The CO3 2--bridged bond formation was investigated using TFP and TBAC as model compounds. TBAC was synthesized in two steps. A TBAH aqueous solution (10 mL, 40 wt%) was saturated with CO2 (99.99%) at room temperature until the pH stabilized, yielding TBAHC. Following the addition of a stoichiometric amount of TBAH (10 mL), the mixture was stirred at ambient temperature for 30 min. The product TBAC was obtained as a white powder by freeze-drying and stored under nitrogen. 1H NMR (600 MHz, CDCl3) δ 3.31 - 3.17 (m, 8H), 1.60 (qt, J = 8.4, 6.0, 5.1 Hz, 8H), 1.40 (h, J = 7.5, 7.0 Hz, 8H), 1.00 - 0.90 (m, 12H).13C NMR (150MHz, CD3CN) δ 160.59, 59.28, 24.33, 20.30, 13.79. Elemental analysis: calcd for C33H72N2O3: C/N =14.14 (w/w), found: C/N= 14.21 (w/w).

For the model reaction, a solution was prepared by mixing TBAC (13.6 mg, 0.025 mmol, 1 equiv.) and TFP (8.7 mg, 0.05 mmol, 2 equiv.) 0.6 mL in CD3CN or CH3CN. After reacting at room temperature for 15 min, the resultant solution was directly characterized by 1H, 19F, and 13C NMR spectroscopy, IR spectroscopy, and mass spectrometry without purification.

Effect of counter-cations on the formation of CO3 2--bridged dynamic covalent bond
To investigate the influence of counter-cations, a series of carbonate salts were prepared using a method analogous to that for TBAC.
TPAC: 1H NMR (600 MHz, CD3CN) δ 3.13-3.04 (m, 8H), 1.70-1.59 (m, 8H), 0.93 (q, J = 6.7, 6.0 Hz, 12H). 13C NMR (150 MHz, CH3CN) δ 160.84, 60.88, 15.98, 10.79. Elemental analysis: calcd for C25H56N2O3: C/N =10.71 (w/w), found: C/N= 10.95 (w/w).
TEAC: 1H NMR (600 MHz, CD3CN) δ 3.22 (q, J = 7.3 Hz, 8H), 1.22 (ddt, J = 7.3, 3.8, 1.9 Hz, 12H). 13C NMR (150 MHz, CD3CN) δ 161.17, 118.26, 53.03, 53.01, 52.99, 7.67, 1.21. Elemental analysis: calcd for C17H40N2O3: C/N =7.29 (w/w), found: C/N= 7.71 (w/w).
TMAC: 1H NMR (600 MHz, D2O) δ 3.17 (s, 12H). 13C NMR (150 MHz, D2O) δ 168.27, 55.30, 55.27, 55.24. Elemental analysis: calcd for C9H24N2O3: C/N =3.86 (w/w), found: C/N= 3.85 (w/w).
BnMAC: 1H NMR (600 MHz, D2O δ 7.60 (ddt, J = 8.5, 5.7, 3.0 Hz, 1H), 7.56 (t, J = 3.5 Hz, 4H), 4.48 (d, J = 2.1 Hz, 2H), 3.09 (d, J = 2.5 Hz, 9H). 13C NMR (150 MHz, D2O) δ 165.98, 132.80, 130.83, 129.18, 127.42, 69.63, 69.61, 52.40, 52.37, 52.34. Elemental analysis: calcd for C21H32N2O3: C/N =9.00 (w/w), found: C/N= 9.24 (w/w).

The thermodynamic effect of counter-cations was assessed by 1H NMR spectroscopy. A typical sample contained TFP (2 equiv., 0.05 mmol) and the carbonate salt (1 equiv., 0.025 mmol) in 550 µL of CD3CN or a CD3CN/H2O mixture (with H2O added as needed to achieve complete dissolution). After reacting at room temperature for 2 h, the mixture was analyzed directly without purification.

The kinetic effect of counter-cations was studied by UV-Vis spectroscopy. A quartz cuvette was charged with TFP (2 equiv., 0.345 µmol) and the carbonate salt (1 equiv., 0.173 µmol) in 3 mL of CH3CN or a CH3CN/H2O mixture. The decrease in the characteristic TFP absorption at 256 nm was monitored in real time. The conversion (R%) was calculated as R% = [(A0 - At) / A0] × Yfinal, where A0 and At are the initial and time-dependent absorbance values, respectively, and Yfinal is the final yield determined from 1H NMR.

Model reaction for the catalyst-free exchange reaction
The exchange reaction was investigated using the preformed CO3 2--bridged adduct (TFPCTFP) and FTFP as model compounds. In a typical procedure, TFPCTFP (22.3 mg, 0.025 mmol, 1 equiv.) and FTFP (9.6 mg, 0.05 mmol, 2 equiv.) were dissolved in 0.6 mL CD3CN or CH3CN. After reacting at room temperature for 10 min, the mixture was directly analyzed by 1H and 19F NMR spectroscopy, as well as mass spectrometry.

Model reaction for the acid-induced dissociation of CO3 2--bridged adducts
The acid-induced dissociation was investigated using TFPCTFP as the model compound. TFPCTFP (41 mg) was dissolved in 0.5 mL CD3CN to give an 82 mg·mL-1 solution. Upon addition of aqueous H2SO4 (0.5 M, 0.5 mL) to adjust the final pH to 4 at room temperature, immediate gas evolution was observed. After stirring for 10 min, the mixture was analyzed directly by 1H and 19F NMR spectroscopy. To confirm that the evolved gas was CO2, a gas-capture setup was employed (Supplementary Fig. 15). Solid TFPCTFP (1.23 g, 1.38 mmol) in a Schlenk tube was connected to a second tube containing clear aqueous Ca(OH)2. Upon addition of aqueous H2SO4 (0.5 M, 5.0 mL), vigorous bubbling occurred in the Ca(OH)2 solution, which gradually turned opaque, confirming CO2 release.

Synthesis of monomer VTFP
A mixture containing 4-bromo-α,α,α-trifluoroacetophenone (15.18 g, 60 mmol, 1 equiv.), K2CO3 (16.70 g, 121 mmol, 2 equiv.), Pd(PPh3)4 (0.72 g, 0.62 mmol, 0.01 equiv.) and pinacol vinylboronate (11.09 g, 72 mmol, 1.2 equiv.) in dioxane/H2O (100/20 mL) was stirred under N2 at 100 °C for 24 hours. After filtration to remove insoluble solids and distillation of dioxane under reduced pressure, the residue was extracted with ethyl acetate (3×), dried over MgSO4, concentrated, and purified by flash chromatography on silica gel to afford VTFP as a colorless oil (9.60 g, 80% yield). 1H NMR (600 MHz, CDCl3) δ 8.04 (d, J = 12.6Hz, 2H), 7.56 (d, J = 12.6 Hz, 2H), 6.78 (dd, J = 16.2, 10.2Hz, 1H), 5.96 (d, J = 26.4Hz, 1H), 5.51 (d, J = 16.2 Hz, 1H). m/z calcd for C10H7F3O, 200.05 [M], Found 200.040[M].

Synthesis of P(VTFP-MA)-20
VTFP (3.00 g, 15 mmol, 1 equiv.), MA (25.80 g, 300 mmol, 20 equiv.), and AIBN (129 mg, 0.7875 mmol, 1/400 equiv.) were dissolved in 1,4-dioxane (30 mL). After degassing, the mixture was heated at 65 °C for 24 hours. Precipitation into MeOH, filtration, and drying afforded P(VTFP-MA)-20 as white solids (25.50 g, 89%). 1H NMR (600 MHz, CD3CN) δ 7.90 (d, J = 108 Hz, 2H), 7.28 (d, J = 114 Hz, 2H), 3.60 (s, 63H). Mn = 48.1 KDa, Mw = 73.7 KDa, Ð= 1.53.

Synthesis of CANs
CANs were synthesized in a one-pot, two-step procedure directly from ambient air. Taking CO2-derived CAN as an example, ambient air was bubbled at ~300 mL·min-1 into a solution of TBAH (86 mg, 0.34 mmol, 20 equiv.) in CH3CN/H2O (29:1 v/v, 3 mL) under ambient conditions until the pH reached ~7.5. Subsequently, a solution of P(VTFP-MA)-20 (800 mg, 0.0166 mmol, 0.049 equiv.) in CH3CN (1 mL) was added. Stirring the mixture at room temperature for 40 minutes afforded a cross-linked gel, which was then dried under vacuum for 12 h to yield light-yellow CAN.

Evaluation of ambient air CO2 capture performance
Ambient air (~420 ppm CO2) was bubbled at 300 mL·min-1 through a solution of TBAH (86 mg, 0.34 mmol, 1 equiv.) in CH3CN/H2O (29:1 v/v, 3 mL) at room temperature until the pH reached ~7.5—a value corresponding to that of a pure TBAC solution at the same concentration. The effluent CO2 concentration was monitored in real time using a gas detector (CMF9002, Consensic, Inc.). Gravimetric analysis showed the as-synthesized product to be 94.1% TBAC, containing ~5.9% TBAHC. The product was characterized by 1H NMR, 13C NMR, and IR spectroscopy. 1H NMR (600 MHz, D2O) δ 3.19 (m, 16H), 1.65 (p, J=7.2, 8.4Hz, 16H), 1.35 (h, J=7.2Hz, 16H), 0.95 (t, 7.2Hz, 24H). 13C NMR (150MHz, CDCl3): δ 160.3, 58.6, 23.9, 19.6, 13.7. IR (ATR): ν 2961, 1614, 1489, 1363, 966, 828, 757, 677, 468 cm-1.

Effect of trace HCO3 - on the network
To evaluate the influence of trace HCO3 - impurity, a control CAN was synthesized using purified TBAC. A solution of P(VTFP-MA)-20 (800 mg, 0.0166 mmol, 0.049 equiv.) in CH3CN (1 mL) was treated with TBAC (90.7 mg, 0.167 mmol, 10 equiv.) and stirred for 30 min at room temperature. After solvent removal, the product was then hot-pressed into rectangular specimens, followed by DSC and tensile testing of the control network against the CO2-derived CAN (Supplementary Fig. 27).

A small-molecule model reaction was further performed to probe the impact at the molecular level. A stoichiometric mixture of TFP (8.7 mg, 0.05 mmol, 1 equiv.) and TBAHC (15.2 mg, 0.05 mmol, 1 equiv.) was stirred in CD3CN (0.6 mL) at room temperature for 24 hours. The resulting mixture was directly analyzed by 1H and 19F NMR spectroscopy (Supplementary Fig. 28).

Molecular dynamics (MD) simulations
MD simulations were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package53. The General Amber Force Field (GAFF2)54 was employed to describe intramolecular interactions. For intermolecular interactions, the Lennard-Jones potential with a cutoff of 1.2 nm and Coulombic interactions with particle-particle particle-mesh (PPPM) treatment for long-range electrostatics were applied. Five systems were constructed, each containing 50 anionic polymer chains and 100 counter-cations—including TBA+, TPA+, TEA+, TMA+ and BnMA+—within a cubic simulation box of 6.8 nm under periodic boundary conditions using Packmol55. Additionally, a control system was built, in which the plasticizing TBA+ cation was replaced by H+, to elucidate the plasticizing role of the cationic structures, with charge neutrality maintained in all cases. Each system underwent energy minimization, followed by a 2 ns equilibration in the isothermal-isobaric (NPT) ensemble at 300 K and 1 atm, controlled by a Nosé-Hoover thermostat with a time step of 1 fs. After equilibration, uniaxial tensile deformation was simulated by stretching each system to 400% of its original length over a period of 10 ns at 300 K and 1 atm.

Environmental Durability Assessment
The environmental durability of the CO2-derived CAN was assessed through a series of accelerated aging tests and an outdoor exposure study. The accelerated aging tests included: (1) UV stability: samples were exposed to 365 nm UV radiation (10 W) for 5, 7, and 14 days; (2) Humidity stability: samples were conditioned at 25 °C under 15%, 30%, and 45% RH for 24 h; (3) Thermal cycling: samples underwent 3, 6, and 9 complete cycles, with each cycle consisting of 30 min at -20 °C and 30 min at 110 °C. Static outdoor exposure trials were carried out for 4, 6, and 8 weeks under ambient conditions. After each test, samples were characterized for changes in mechanical properties, appearance, and chemical structure.

Self-healing
Rectangular specimens of the CO2-derived CAN (30 mm × 10 mm × 0.5 mm) were prepared by hot pressing. For visual tracking, a trace amount of rhodamine B was doped into one set of specimens. Each sample was then cut transversely with a blade. The fractured surfaces were placed in contact and healed under controlled pressure and temperature. Standard healing was conducted at 0.5 MPa and 80°C, whereas low-temperature healing was performed at 40°C (2 MPa, 24 h) and at room temperature (25°C, 2 MPa, 24 h). The repaired samples were then evaluated by uniaxial tensile testing.

Reprocessability
The reprocessability of the CO2-derived CAN was evaluated using compression molding and injection molding. Compression molding was performed by cutting the CAN films into fragments, placing them between steel plates with PTFE films as release layers, and hot-pressing at 90 °C under 6 MPa for 10 min. Injection molding was carried out using a WZS1D micro injection molding machine (Shanghai Xinshuo Precision Machinery Co., Ltd.) at a constant temperature of 100 °C.

Chemical Recycling
CO2-derived CAN (1.00 g) was fragmented and treated with H2SO4/CH3CN solutions (0.2 M or 0.5 M) at room temperature. After complete degradation, P(VTFP-MA)-20 was recycled by liquid-liquid extraction with ethyl acetate and water, while the aqueous phase was concentrated and treated with basic anion-exchange resin to regenerate TBAH. The recycled P(VTFP-MA)-20 and TBAH were reused to synthesize CO2-derived CAN.

To assess real-world applicability, selective recyclability was demonstrated in two scenarios: (1) From mixed plastic waste: A CO2-derived CAN film (150 mg) was combined with polyvinyl chloride (130 mg), polypropylene (106 mg), and polyethylene (118 mg) in 0.5 M H2SO4/CH3CN (18 mL). After reacting for 20 min at room temperature, the CO2-derived CAN was completely degraded, while the other plastics remained intact. Following filtration, P(VTFP-MA)-20 and TBAH were recovered as described above. (2) From a carbon-fiber-reinforced polymer (CFRP) composite: A CFRP composite with the CO2-derived CAN as the matrix (364 mg) was treated with 0.5 M H2SO4/CH3CN (8 mL) at room temperature. After reacting for 30 min, the CAN matrix degraded completely, leaving the carbon-fiber fabric undamaged. After filtration, P(VTFP-MA)-20 and TBAH were similarly recovered.

Upcycling
The CO2-derived CAN and the CAN derived from P(VTFP-MA)-1.3 were individually acid-degraded to their respective linear polymers, P(VTFP-MA)-20 and P(VTFP-MA)-1.3. These polymers (P(VTFP-MA)-20: 500 mg, 0.0104 mmol, 1 equiv.; P(VTFP-MA)-1.3: 500 mg, 0.0113 mmol, 1.09 equiv.) were blended in 4 mL of CH3CN and recross-linked with atmospheric CO2-derived TBAC (406 mg, 0.745 mmol, 71.6 equiv.). After reacting for 40 min at room temperature, the resulting gel was dried under vacuum for 12 h to afford the upcycled hybrid CAN.

Characterizations
1H, 19F, and 13C spectra were acquired at 298 K on a Bruker Avance III 600 MHz spectrometer using CDCl3, CD3CN, or D2O as deuterated solvents and referenced to tetramethylsilane (TMS) or residual solvent peaks. FTIR spectra were collected on a PerkinElmer Spectrum Two spectrometer equipped with a diamond attenuated total reflectance (ATR) accessory, with background subtraction for baseline correction. For in situ variable-temperature FTIR analysis, the sample was heated from 25 to 120 °C at a constant rate of 5 °C·min-1. UV-Vis absorption spectra were recorded using an Agilent Cary 60 spectrophotometer in quartz cuvettes (0.1 cm path length) at 25 °C. GPC analysis was conducted on a Shimadzu DAWN/LC-20A system with a refractive index detector (RID), employing THF as the eluent at 1.0 mL·min-1 and calibrated against polystyrene standards. Elemental analysis was performed to confirm carbonate purity. The pH of solutions was measured using precision pH test strips. The gel fraction and swelling ratio of the CANs were determined by immersing ~230 mg of sample in 1.2 mL of solvent for 12 h at room temperature. The swelling ratio and gel fraction were then calculated as (m1- m0)/m1× 100% and m2/m0 × 100%, respectively, where m0, m1, and m2 are the initial, swollen, and dried sample masses. Tg were determined using a Netzsch DSC 214 instrument under nitrogen atmosphere with heating/cooling rates of 10 °C·min-1. Thermal stability was evaluated via TGA using a PerkinElmer TGA 8000 under air atmosphere, heating from 30 °C to 500 °C at 5 °C·min-1. Tensile testing was performed on an MTS E44 universal testing machine at room temperature using rectangular samples (30 mm × 10 mm × 0.5 mm) prepared by hot-pressing and precision cutting. At least three replicates were tested for each condition. Young’s modulus was derived from the initial linear region of stress-strain curves, and toughness was calculated as the area under the curve. DMA was carried out on a PerkinElmer DMA 8000 in tension mode at a heating rate of 2 °C·min-1 and a fixed frequency of 1 Hz. Rheological behavior was characterized using a TA Instruments DHR-1 rotary rheometer with 25 mm-diameter, 1 mm-thick compression-molded discs. Strain-sweep tests were first conducted at 1 Hz and 60 °C to determine the linear viscoelastic regime. Stress relaxation experiment were then performed at 60 °C under 1% strain. The τ was defined as the time required for G’ to decay to 1/e (~36.7%) of its initial value. SAOS tests were employed from 60 to 100 °C at a fixed strain amplitude of 1%. The master curves were constructed by applying the TTS principle to the SAOS data at a reference temperature of 60 °C. Temperature-sweep tests were conducted at a fixed strain of 1% and a frequency of 1 Hz.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript entitled \"Catalyst-Free Upcycling of Air-Captured CO₂ to Self-Healing Recyclable Polymers under Ambient Conditions\" presents a groundbreaking approach to addressing the sustainability challenges of polymer production by integrating atmospheric CO₂ valorization with dynamic covalent chemistry. The authors demonstrate a strategy for synthesizing mechanically robust, self-healing, and recyclable polymers under ambient conditions, which holds significant potential for advancing circular materials science.\nWhile the study is innovative and methodologically rigorous, I do not think the manuscript satisfy the high standard of Nature Communications in current form. Below are detailed comments and recommendations:\n1. One of the major concerns is that in the introduction part, too many selling points are presented while it is not clearly what is the major pointing of the manuscript. For example, the authors claimed that current approach overcome the high barrier of CO2 while it is mainly for the reduction of CO2 to other useful molecules instead of acid-base reaction as demonstrated in current manuscript.\n2. The authors highlight CO₂ capture as one of the central focuses of their work: (1) however, in traditional crosslinked polymer systems, the mass proportion of crosslinking agents typically remains extremely low. To establish the actual CO₂ capture performance of their system, the authors should provide detailed experimental data demonstrating the specific capacity, explicitly reporting the mass ratio of absorbed CO₂ to the unit mass of the synthesized polymer materials. (2) Environmental Impact Assessment: Quantify the carbon footprint reduction achieved by this method compared to conventional polymer production (e.g., kg CO₂ eq. per kg polymer).\n3. The authors have conducted extensive work on material recycling based on dynamic bonds; however, their presentation primarily relies on schematic diagrams of the materials and their performance depictions (Figures 4 and 5), with a notable lack of physical characterization tests to support the material analysis. It is recommended that they incorporate techniques such as DMA, advanced rheological testing (master curve), or in-situ infrared spectroscopy to validate the self-healing and reprocessing capabilities of the newly formed bonds within the polymer system.\n4. Counter-Cation Plasticization Mechanism: While the role of counter-cations in enhancing ductility is proposed, molecular dynamics simulations or variable-temperature NMR could elucidate how cation size/mobility influences chain dynamics and mechanical performance.\n5. Durability Under Real-World Conditions: Assess the long-term stability of the polymers under environmental stressors (e.g., UV exposure, humidity, thermal cycling). For instance, do the materials retain self-healing and mechanical properties after prolonged outdoor exposure?\n6. The thermogravimetric analysis (TGA) data for the linear polymer P(VTFP-MA) are lacking.\n7. Supplementary Scheme for Reaction Pathways: While Figure 1 provides a conceptual overview, a detailed reaction scheme illustrating the stepwise conversion of CO₂ to CO₃²⁻ intermediates, dynamic bond formation, and network architecture would enhance mechanistic understanding. Include molecular-level diagrams of bond exchange and acid-triggered dissociation processes.\n8. Performance Benchmarking: Include a comparative table evaluating key metrics (e.g., energy input, CO₂ conversion efficiency, mechanical properties, recyclability) against state-of-the-art CO₂-derived polymers (e.g., polycarbonates, polyurethanes) and dynamic networks (e.g., CANs). Highlight advantages such as ambient synthesis conditions and catalyst-free reprocessing.\n9. Additionally, there are a few problems that should be dealt with before published in any journal. For example:\n(1) The manuscript contains numerous figures lacking error bars, including Figure 5C and the majority of figures in SI.\n(2) The font sizes in Figure 5C are inconsistent and need to be standardized.\n(3) The manuscript contains several basic errors, such as \"Supplementary Figs. 1\" on page 2 (likely a typo where the singular \"Fig.\" is needed), the misspelled term \"waveunmber\" in Figure 3C, and \"the\" in \"the demonstrated……\" on page 4.\n(4) The layout of Figure 2 should be more neatly arranged.\n(5) The legend order in the figures should be aligned as closely as possible with the data presentation order, such as in Figure 3D.", "reviewer_2": "In this work, the authors introduced TFP, which is reactive with CO₂ and produces dynamic crosslinking agents, into a polymer. The resultant polymer was mechanically tough and thermoplastic. Due to the high reactivity of TFP, the polymer directly captured CO₂ even from air. Their findings are interesting, and the results of this work should attract the interest of many readers. I suggest the following comments to improve the results.\n1) I think that alkylammonium hydroxide is acting as a catalyst. In my opinion, “catalyst-free” is not a fact. Would you consider softening the expression in the title?\n2) As the authors stated in the Introduction, CO₂ consumption is an important target of this study. However, the amount of CO₂ consumed is not addressed. For example, it would be helpful to indicate the amount of CO₂ consumed per gram of polymer, and to compare this with other CO₂-derived polymers such as polyurethanes.\n3) P. 3, Fig. 3b: In addition to DSC measurements, I recommend performing a temperature sweep using dynamic mechanical analysis (DMA). The DMA results may exhibit a plateau above the Tg for the CO₂-derived CAN, while almost no plateau would be observed for P(VTFP-MA)-20. The storage modulus in the plateau region is related to the effective crosslinking density of the CO₂-derived CAN. It is also possible that a relaxation mode associated with network exchange might be detected above the Tg.\n4) P. 3, Fig. 3e: The CO₂-derived CAN exhibits an exceptionally high elongation at break of 958%, despite having a crosslinking density as high as 5%, assuming that all TFP sites have reacted. While the authors discuss the influence of counter cations, this reviewer believes that the high elongation may result from the breaking of CO₂-based crosslinks during sample stretching. For example, cyclic tensile testing could be employed to evaluate the plastic deformability of the network; therefore, I recommend performing such tests.\n5) P. 3, Fig. 3g: The authors indicate that the mechanical properties of the CO₂-derived CANs decrease with increasing alkyl chain length of the alkylammonium hydroxide. Please describe the cause of this result.\n6) P. 3, Fig. 3h: The authors proposed that the mechanical properties of CO₂-derived CANs are widely tunable, ranging from flexible elastomers to rigid plastics. However, this tunability is mainly due to the characteristics of the polymers used for copolymerization. Therefore, I believe that the advantage of the CO₂-derived CAN may be diminished when rigid EMA and MMA are used. Please compare the mechanical properties before and after CO₂ crosslinking for copolymers with BuMA, EMA, and MMA. If any advantages of CO₂ crosslinking are observed, they should be clearly described.\n7) P. 4, Fig. 4: Regarding the experiment shown in Fig. 4, there is no detailed description of the CO₂-derived CAN. Please include an explanation of the prepolymer. Is the prepolymer P(VTFP-MA)-20?\n8) P. 4, Fig. c and f: The authors conducted self-healing tests at 80°C; however, they also demonstrated that melt processing is possible at a slightly higher temperature of 90°C. In such a case, this reviewer believes that the observed behavior may be attributed to thermoplasticity rather than true self-healing. How would the self-healing performance be affected if the tests were conducted at a lower temperature where melt processing is not possible, such as room temperature?", "reviewer_3": "Comments for manuscript \"Catalyst-Free Upcycling of Air-Captured CO2 to Self-Healing Recyclable Polymers under Ambient Conditions\" Nature Sustainability.\nThe manuscript submitted by Prof. Liang Chen and co-workers deals with the synthesis of covalent adaptable networks using ambient CO2 as a crosslinker which enable the formation of exchangeable bonds. The manuscript is well-written, the molecular study and the effect of the counter ion on the hemiacetal-like moiety formation is highly interesting. The network characterization and material properties are well performed showing excellent mechanical properties and good (re)processability. The manuscript deserves publication after considering the following points especially further studies on rheological characterizations should be performed prior publication.\n1) Network design. Can the authors discuss the choice of (co)polymer backbone structure? Why they choose to copolymerize MMA with functionalized styrene and not a fully styrenic polymer backbone?\n2) Swelling tests in good solvents (e.g. THF or CHCl3) should be performed for each materials. My issue is that the crosslinked nature has not be evidenced either by gel content measurement or DMA.\n3) Rheology experiments to be performed. Stress relaxation experiments presented by the authored showed fast relaxation (between 10 to 100s). Small amplitude oscillatory shear experiments are generally preferred to characterize rapid relaxation (see e.g. ACS Polym. Au 2025, 5, 3, 214–240). It will also confirm the nature of the exchange mechanism (associative or dissociative) by monitoring the evolution of the storage modulus with increasing temperature. In addition, we generally performed stress relaxation experiments at T > Tg + 50°C to separate the segmental relaxation induce by the glassy to rubbery transition and the relaxation induce by the exchange reaction. Non-normalized data should be also added in the supplementary material.\n4) In addition, creep experiments especially at room temperature should be performed to determine if the material mechanical properties are stable under ambient conditions. DMA analysis to further confirm the CAN features (presence of a rubbery after Tg)."}, "author_response": "Point-by-Point Response to Reviewers' Comments\nReviewer #1:\nThe manuscript entitled \"Catalyst-Free Upcycling of Air-Captured CO to Self-Healing Recyclable\nsustainability challenges of polymer production by integrating atmospheric CO valorization with\n2\ndynamic covalent chemistry. The authors demonstrate a strategy for synthesizing mechanically\nrobust, self-healing, and recyclable polymers under ambient conditions, which holds significant\npotential for advancing circular materials science.\nWhile the study is innovative and methodologically rigorous, I do not think the manuscript satisfy\nthe high standard of Nature Communications in current form. Below are detailed comments and\nrecommendations:\nResponse: We sincerely thank you for your time and insightful feedback on our manuscript,\nespecially regarding CO capture performance assessment and the need to better articulate our core\n2\ninnovation. We have carefully considered all your comments and implemented substantive, targeted\nrevisions to address them. Detailed point-by-point responses are provided below for your review.\nComment 1： One of the major concerns is that in the introduction part, too many selling\npoints are presented while it is not clearly what is the major pointing of the manuscript. For\nexample, the authors claimed that current approach overcome the high barrier of CO while it\n2\nis mainly for the reduction of CO to other useful molecules instead of acid-base reaction as\n2\ndemonstrated in current manuscript.\nResponse: Thank you for your valuable feedback regarding the lack of focus in the original\nintroduction and the specific point concerning the claim of “overcoming the high barrier of CO ”.\nhighlighting the central innovation. The core advance of our work is the development of a novel\ndynamic covalent chemistry (DCC) enabling catalyst-free conversion of atmospheric CO into high-\n2\nperformance recyclable polymers under ambient conditions. To sharpen this focus, we have\nimplemented significant revisions: (1) Streamlined discussion of CAN limitations (Paragraph 1):\nWe now concentrate specifically on challenges most relevant to our solution—harsh reprocessing\nconditions, limited recyclability, and mechanical property trade-offs—avoiding excessive detail\nwhile clearly establishing the need for novel dynamic covalent bonds. (2) Restructured positioning\nof DACU (Paragraph 2): We explicitly position direct air capture and utilization (DACU) as the\nparamount unsolved challenge for CO -derived polymers. The revised text now highlights the\n2\nfundamental barriers our work addresses: directly converting ultradilute atmospheric CO (~400\n2\nppm) into functional polymers under ambient, catalyst-free conditions. (3) Refocused materials\nfabrication narrative: To better emphasize this central innovation, we have removed the content\nrelated to CANs derived from pure CO in the ‘Synthesis and Characterization of CANs’ section,\n2\nrefocusing all the polymer networks synthesis narrative on their direct utilization and conversion\nfrom ambient air.\nRegarding the specific point about CO activation, we appreciate this opportunity for clarification.\n2\nhowever, these predominantly target small molecule synthesis (e.g., CO -to-fuels) rather than\n2\npolymers. Well-established CO -to-polymer methodologies—such as CO /epoxide\n2 2\ncopolymerization, CO /olefin cyclization, CO /alkyne cyclization, and CO /Frustrated Lewis pairs\n2 2 2\n(FLP) coupling—all operate through non-reductive mechanisms (Chem. Soc. Rev. 2019, 48, 4466-\n4514; Cell Rep. Phys. Sci. 2022, 3, 100719). Distinct from these approaches, our work presents the\nfirst example of conversion of CO₂ into CO 2- intermediates for polymer synthesis. This strategy\n3\ndelivers three key advantages: (i) direct utilization of ultra-dilute atmospheric CO (~400 ppm),\n2\n(ii) catalyst-free operation under mild conditions (room temperature, atmospheric pressure), and (iii)\nthe generation of polymers with excellent self-healing and recyclability. We recognize that the\noriginal manuscript mention of “CO 's fully oxidized state” (Paragraph 3) could have been construed\n2\nas implying that conventional CO -to-polymer methods operate via reduction mechanisms, which\n2\nwas not our intention. To eliminate ambiguity and accurately reflect our approach, we have revised\nthe opening of Paragraph 3 to: “The fundamental challenge in converting CO arises from its\n2\ninherent stability and inertness, yet, …”.\nWe believe these revisions provide a clearer, more focused, and accurate introduction that\nproperly frames our research on atmospheric CO conversion to recyclable polymers. Thank you\n2\nagain for this helpful critique.\nComment 2： The authors highlight CO capture as one of the central focuses of their work: (1)\n2\nhowever, in traditional crosslinked polymer systems, the mass proportion of crosslinking agents\ntypically remains extremely low. To establish the actual CO capture performance of their system,\n2\nthe authors should provide detailed experimental data demonstrating the specific capacity, explicitly\nreporting the mass ratio of absorbed CO to the unit mass of the synthesized polymer materials. (2)\ncompared to conventional polymer production (e.g., kg CO eq. per kg polymer).\nin conventional polymer networks is generally low. Our initial experiments indeed explored TFP-\nbased small molecules to maximize the CO content; however, these attempts encountered synthetic\n2\nchallenges and yielded materials with unsatisfactory mechanical properties. We therefore selected\nthe linear polymer (P(VTFP-MA)-20) as our optimal strategy, as it enables both a simplified\nsynthesis and excellent material properties. While the mass of CO incorporated per unit polymer\n2\nmass is currently limited, we should note that our work establishes a distinct and valuable paradigm,\ncharacterized by: (i) direct utilization of CO from ambient air (~400 ppm), which remains\n2\\unattainable by existing CO -to-polymer methods requiring concentrated pure CO sources; (ii)\n2 2\ncatalyst-free CO fixation under exceptionally mild conditions (room temperature, atmospheric\n2\npressure), unlike literature approaches that often involve complex catalysts, high pressures, and\nelevated temperatures; and (iii) production of polymers with excellent intrinsic self-healing and\nrecyclability. Moreover, the current CO uptake has not yet reached the theoretical maximum, and\n2\nthis theoretical value can be further increased by optimizing the CO 2--bonding groups via lower-\n3\nmolecular-weight alternatives, such as trifluoromethyl alkyl ketones.\nTo address your comment directly, we have performed the following additional experiments and\nanalyses:\n(1) CO₂ Capture Capacity. To evaluate CO capture performance, we first conducted\n2\ncorresponding CO capture experiments by bubbling ambient air into an acetonitrile (CH CN)/H O\n2 3 2\nsolution of tetrabutylammonium hydroxide (TBAH) under ambient conditions. As shown in Fig.\nR1, the CO capture efficiency—defined as the mass ratio of retained CO in the system to the total\n2 2\nCO supplied from ambient air—was determined to be 80.0%, demonstrating highly efficient\n2\nfixation even under dilute CO conditions. Furthermore, the CO uptake capacity of the CANs was\n2 2\ncalculated to be 1.4-5.4 wt% (0.014-0.054 kg CO per kg polymer). This value is lower than that of\n2\nconventional CO -derived polycarbonates and polyurethanes, and is comparable to that reported for\n2\nfrustrated Lewis pair (FLP) systems (see Supplementary Tables 1-2 in the Supporting Information).\n(2) Environmental Impact Assessment. Although the mass of incorporated CO remains limited,\n2\nthe environmental carbon footprint of the production process is highly favorable. The catalyst-free\nsynthesis, which operates under ambient conditions and directly utilizes atmospheric CO ,\n2\ncircumvents the substantial energy consumption and emissions associated with conventional CO\n2\ncapture, concentration, compression, and catalytic conversion processes. Furthermore, the synthesis\nof the P(VTFP-MA)-20 precursor is straightforward, efficient, and inherently scalable. Our\npreliminary carbon footprint assessment, conducted per the ISO 14040 series using SimaPro (v9.0)\nsoftware, indicates that the net carbon footprint of our CANs is comparable to epoxy resin (EP) and\npolystyrene (PS), but lower than those of polyamide (PA), polycarbonate (PC) and polyurethane\n(PU) foam (Fig. R2a). This advantage is attributed to the direct utilization of atmospheric CO —\n2\nwhich partially displaces petroleum-based feedstocks—coupled with significantly lower energy\nconsumption during manufacturing (Fig. R2b). Moreover, the inherent reprocessability of our\nCANs further minimizes their lifetime environmental impact by extending their service life over\nmultiple cycles, thereby underscoring their environmental advantage. While the production process\nitself exhibits a favorable carbon footprint, we acknowledge that the contribution of direct air\ncapture and utilization (DACU) is still limited at the current stage. We are actively pursuing\nstrategies—including optimized network design and improved synthetic routes—to further increase\nCO uptake and enhance the thermal and mechanical properties. A comprehensive life-cycle\n2\nassessment (LCA) is also underway to more accurately quantify the full environmental benefits of\nthis approach.\nData on CO capture efficiency, along with the corresponding experimental details and discussion,\n2\nhave been incorporated into the revised manuscript (Page 3). Besides, to provide a balanced\nperspective, the Conclusions section now explicitly states the current limitation of CO uptake,\n2\npresents the quantitative data, and outlines our ongoing research direction to enhance CO uptake\n2\nand improve the thermal and mechanical properties (Page 6).\nFig. R1 (newly added Fig. 3d) | CO 2 concentration in the exhaust stream as function of time during\nthe bubbling of ambient air into the TBAH solution.\nFig. R2 | a, Greenhouse gas (GHG) emissions from the production of CANs versus conventional\npolymers. b, Main contributors to the GHG emissions from CANs production.\nComment 3： The authors have conducted extensive work on material recycling based on dynamic\nbonds; however, their presentation primarily relies on schematic diagrams of the materials and their\nperformance depictions (Figures 4 and 5), with a notable lack of physical characterization tests to\nsupport the material analysis. It is recommended that they incorporate techniques such as DMA,\nadvanced rheological testing (master curve), or in-situ infrared spectroscopy to validate the self-\nhealing and reprocessing capabilities of the newly formed bonds within the polymer system.\nResponse: We sincerely thank you for this insightful and constructive comment. In response, we\nhave conducted the following additional experiments:\n(1) Dynamic Mechanical Analysis (DMA): As shown in Fig. R3, the CO -derived CAN exhibits\n2\na distinct rubbery plateau in the storage modulus (E’) above its T , which contrasts strikingly with\ng\nthe linear polymer where E’ drops continuously with increasing temperature. This sustained\nmodulus is a key indicator of a dynamic covalent network. The crosslink density (ν) was calculated\nas 79.1 mol·m-3 using the equation ν = E’/[3R(T + 50)].\nr g\n(2) Rheological testing: The linear viscoelastic regime (LVR) was first determined through strain\nsweep tests within a strain amplitude (γ) range of 0.001%-10% (Fig. R4a). Subsequently, frequency-\nsweep small-amplitude oscillatory shear (SAOS) tests were carried out at various temperatures (Fig.\nR4b). The relaxation time (τ) was derived from the crossover frequency (ω ) where the storage\nc\nmodulus (G′) equals the loss modulus (G″), using the equation τ = 1/ω . Arrhenius analysis revealed\nc\na linear correlation between ln(τ) and 1000/T (Fig. R4c), confirming the vitrimeric nature of the\nnetworks. The activation energy (E ) for the solid-state bond exchange, calculated from the\na\nArrhenius plot, was 111.9 kJ/mol.\nFurthermore, a master curve was constructed by applying the time-temperature superposition\n(TTS) principle to the SAOS data at a reference temperature of 60 °C. The data exhibited a clear\nterminal relaxation behavior in the low-frequency region, characterized by a transition from solid-\nlike (G′ > G″) to liquid-like (G″ > G′) response (Fig. R4d). The horizontal shift factors (a ) obtained\nT\nfrom the TTS procedure were analyzed using the Arrhenius equation (Fig. R4e), yielding an\nactivation energy of 109.3 kJ/mol. This value is consistent with that obtained from the crossover\nfrequency method, thereby validating the reliability of our rheological analysis.\nTo elucidate the exchange mechanism, temperature-sweep experiments were performed. The\nresults showed a sharp, nearly three-order-of-magnitude decrease in G′, accompanied by a distinct\nG′/G″ crossover at 85 °C (Fig. R4f). This behavior is characteristic of a dissociative exchange\nmechanism, marked by a sudden loss of network integrity upon heating.\n(3) In situ variable-temperature FTIR: To further corroborate the dissociative exchange\nmechanism, we conducted in situ variable-temperature FTIR spectroscopy (Fig. R5). As the\ntemperature increased from 25 to 120 °C, a gradual intensification of the absorption band at 1730\ncm-1 was observed, indicating the thermally induced cleavage of the CO 2--bridged dynamic\n3\ncovalent bonds and regeneration of the TFP compound. Upon subsequent cooling to room\ntemperature for 24 hours, the original CO 2--bridged bonds were restored, confirming the reversible\n3\nand dissociative nature of the CAN.\nOverall, the combination of DMA, advanced rheological analyses, and in situ FTIR spectroscopy\nprovides compelling evidence for the dynamic bond exchange in our polymer system. These results\ncollectively validate the self-healing and reprocessing capabilities of the newly formed bonds within\nthe polymer system, directly addressing your insightful comment and significantly strengthening\nour manuscript. All new data and corresponding discussion have been incorporated into the revised\nmanuscript (Manuscript: Pages 4-5; Supporting Information: Pages 26-27).\nFig. R3 (newly added Fig. 3g) | DMA curves of P(VTFP-MA)-20 and CO 2 -derived CAN.\nFig. R4 (newly added Fig. 4a-c and Supplementary Figs. S42-44) | a, Strain sweep curves of\nCO -derived CAN. b, b-c, Frequency-sweep rheological measurements at various temperatures (b)\n2\nand the corresponding Arrhenius plot of relaxation time (τ) versus 1000/T (c). d-e, Master curve of\nCO -derived CAN based on TTS of SAOS experiments at a reference temperature of 60 °C (d), and\n2\nthe corresponding Arrhenius plot of horizontal shift factors (a ) versus 1000/T (e). f, Temperature-\nT\ndependent rheological behavior.\nFig. R5 (newly added Fig. 4d) | In situ variable-temperature FTIR spectra of CO 2 -derived CAN.\nComment 4： Counter-Cation Plasticization Mechanism: While the role of counter-cations in\nenhancing ductility is proposed, molecular dynamics simulations or variable-temperature NMR\ncould elucidate how cation size/mobility influences chain dynamics and mechanical performance.\nResponse: Thank you for this valuable suggestion. As recommended, we have conducted\ncomprehensive molecular dynamics (MD) simulations to elucidate the plasticization mechanism\nand to systematically investigate the influence of different counter-cations on the mechanical\nproperties.\nFirst, to directly decipher the plasticizing role of cations, we performed a comparative analysis\nbetween the CO₂-derived CAN (with TBA+) and a control system (with H+ replacing TBA+). This\ncomparison revealed key distinctions: (i) a weaker ionic association, as indicated by the significantly\nright-shifted first peak in the radial distribution function (RDF) between TBA+ and the polymeric\nanions (Fig. R6a); (ii) significantly enhanced cation mobility, with a diffusion coefficient (D) 2.1\ntimes greater than that of the control group (Fig. R6b-c); (iii) a considerably expanded polymer free\nvolume fraction (FFV, Fig. R6d-e), which provides more space for segmental motion; and (iv)\ndramatically accelerated relaxation dynamics of the polymer chains, as demonstrated by a\nsignificantly increased mean-squared displacement (MSD) over time (Fig. R6f-g). These findings\ncollectively demonstrate that the bulky, flexible TBA+ cations effectively screen electrostatic\ninteractions, enhance mobility, expand free volume, and lubricate the polymer chains, thereby\nrationalizing the enhanced ductility and toughness.\nSecond, building on this mechanistic insight, we further investigated how different counter-\ncations govern the macroscopic mechanical properties. We conducted a systematic comparison\nacross a series of cations (TBA+ → TPA+ → TEA+ → TMA+ → BnMA+), which revealed a clear\ntrend: reducing the cation size and increasing its rigidity progressively attenuates the plasticizing\neffect. This attenuation was quantitatively captured by our MD simulations, which showed a left-\nshift in the RDF peaks (Fig. R6 a), a concomitant decrease in cation mobility (Fig. R6b-c), and a\nreduction in polymer free volume (Fig. R6d-e) along the cation series. Consequently, the segmental\nmotion of the polymer chains becomes more restricted (Fig. R6f-g), shifting the macroscopic\nmechanical behavior from highly ductile to more rigid and strong. This structure-property\nrelationship provides a powerful design principle for tailoring the mechanics of our CANs.\nAll new data from these MD simulations and the corresponding discussion have been\nincorporated into the revised manuscript (Manuscript: Page 4; Supporting Information: Pages 18-\n20).\nFig. R6 (newly added Fig. 3i-l and Supplementary Figs. 32-33) | Molecular dynamics (MD)\nsimulations of the counter-cation plasticization mechanism. a, Radial distribution function (RDF)\nbetween cations and polymeric anions, indicating ionic association strength. b-c, Mean-squared\ndisplacement (MSD) of counter-cations (b) and their corresponding diffusion coefficients (c). d-e,\nPolymer free volume fraction (FFV) of the CANs. f-g, MSD of polymer backbone (f) and their\ncorresponding diffusion coefficients (g).\nComment 5： Durability Under Real-World Conditions: Assess the long-term stability of the\npolymers under environmental stressors (e.g., UV exposure, humidity, thermal cycling).\nFor instance, do the materials retain self-healing and mechanical properties after prolonged outdoor\nexposure?\nResponse: Thank you for your insightful suggestion regarding the environmental durability of our\nCO -derived CANs. In response, we have performed a series of accelerated aging tests to simulate\n2\nreal-world conditions: (1) UV resistance was evaluated by exposing samples to UV radiation (10\nW, 365 nm) for 5, 7, and 14 days; (2) Humidity stability was assessed by conditioning samples at\n25 °C under 15%, 30% and 45% relative humidity (RH) for 24 hours; (3) Thermal cycling tests were\nconducted for 3, 6, and 9 cycles (each cycle: 30 minutes at -20 °C and 30 minutes at 110 °C). The\ncomprehensive data, presented in Figs. R7-9, show that the CO₂-derived polymers retain their\nmechanical properties, appearance, and chemical structure, thereby confirming their robust stability.\nTo further evaluate practical durability, outdoor exposure trials were conducted. Results showed\nthat the networks maintained their mechanical properties, appearance and structural integrity after\n4, 6, and 8 weeks of exposure (Fig. R10a-c), underscoring their real-world application potential.\nFurthermore, self-healing experiments were conducted on the samples after 8 weeks of outdoor\nexposure. The results showed a high healing efficiency of 98.4%, with nearly complete recovery of\nmechanical properties (Fig. R10 d-f), confirming the retention of functional integrity.\nAll relevant data, experimental details, and extended discussions have been incorporated into the\nrevised manuscript (Manuscript: Page 4; Supporting Information: Pages 24-25).\nFig. R7 (newly added Supplementary Fig. 38) UV stability of the CO -derived CAN. a, Stress-\n2\nstrain curves before and after various UV exposure durations. Inset: Representative photographs of\na sample before and after 14 days of UV exposure. b, Young's modulus and toughness from (a). c,\nFTIR spectra before and after various UV exposure durations.\nFig. R8 (newly added Supplementary Fig. 39) Humidity stability of the CO -derived CAN. a,\nhours. Inset: Representative photographs of a sample before and after 24 hours of 45% RH exposure.\nb, Young's modulus and toughness from (a). c, FTIR spectra before and after conditioning at various\nRH levels for 24 hours.\nFig. R9 (newly added Supplementary Fig. 40) Thermal cycling stability of the CO -derived CAN.\n2\na, Stress-strain curves before and after various thermal cycles. Inset: Representative photographs of\na sample before and after 9 thermal cycles. b, Young's modulus and toughness from (a). c, FTIR\nspectra before and after various thermal cycles.\nFig. R10 (newly added Supplementary Fig. 41) Outdoor stability and retention of self-healing\nproperties in the CO -derived CAN. a-c, Outdoor stability assessment. a, Stress-strain curves before\n2\nand after various outdoor exposure durations. Inset: Representative photographs of a sample before\nand after 8 weeks of outdoor exposure. b, Young's moduli and toughness from (a). c, FTIR spectra\nbefore and after various outdoor exposure durations. d-f, Self-healing performance after 8 weeks of\noutdoor exposure: (d) Photographs showing the self-healing process of an 8-week outdoor-exposed\nsample; (e) Comparative stress-strain curves of the original and the healed sample; (f) Young's\nmodulus and toughness derived from (e).\nComment 6： The thermogravimetric analysis (TGA) data for the linear polymer P(VTFP-MA)\nare lacking.\nResponse: Thank you for raising this point. In response, we conducted TGA analyses on both the\nlinear polymer P(VTFP-MA)-20 and TBAC (Fig. R11). The results show that P(VTFP-MA)-20\npossesses high thermal stability, with a 5% weight loss temperature (T , ) of 315 °C, whereas\nd 5%\nTBAC decomposes at a much lower temperature of 173 °C. Although the CO -derived CAN shows\n2\nreduced thermal stability (T , =252°C) compared to linear polymer P(VTFP-MA)-20, its onset\nd 5%\ndecomposition temperature of 220 °C confirms that the formation of the network effectively\nstabilizes the thermally labile TBAC component. These new data and the corresponding discussion\nhave been added to the Supporting Information (Page 17 in the Supporting Information).\nFig. R11 (replaced with Supplementary Fig. 28) | TGA curves of CO 2 -derived CAN, linear\npolymer P(VTFP-MA) and TBAC under air atmosphere.\nComment 7： Supplementary Scheme for Reaction Pathways: While Figure 1 provides a\nconceptual overview, a detailed reaction scheme illustrating the stepwise conversion of CO to\n3\nunderstanding. Include molecular-level diagrams of bond exchange and acid-triggered dissociation\nprocesses.\nResponse: We thank the reviewer for this suggestion. As recommended, a detailed scheme\nillustrating the stepwise CO conversion, dynamic bond formation, network architecture, and\n2\nmolecular-level exchange/dissociation processes has now been added to the revised manuscript as\nFig. R12.\nFig. R12 (replaced with Fig. 1) | Methodologies for sustainable polymers. a, Reversible TFP-CO 3 2-\nreaction. b, Conversion of atmospheric CO into CO 2- as intermediates for the catalyst-free\n2 3\nsynthesis of self-healing recyclable polymers under ambient conditions.\nComment 8： Performance Benchmarking: Include a comparative table evaluating key metrics\n(e.g., energy input, CO conversion efficiency, mechanical properties, recyclability) against state-\n2\nof-the-art CO -derived polymers (e.g., polycarbonates, polyurethanes) and dynamic networks (e.g.,\nResponse: Thank you for this insightful suggestion. As suggested, we have added two comparative\ntables (Supplementary Tables 1 and 2) to the revised Supporting Information. These tables\nbenchmark our CAN against state-of-the-art CO -derived polymers and dynamic covalent networks\n2\nacross key metrics, including CO source, CO conversion rate, CO content, synthesis condition\n2 2 2\n(catalyst, temperature, and pressure), mechanical properties, recyclability (chemical recyclability,\nreprocessability), self-healing property. The comparison clearly highlights the unique advantages of\nour system, such as the direct utilization of ambient CO , catalyst-free CO fixation at room\n2 2\ntemperature and atmospheric pressure, excellent self-healing and recyclability. We are grateful for\nthis valuable input.\nComment 9： Additionally, there are a few problems that should be dealt with before published in\nany journal. For example:\n(1) The manuscript contains numerous figures lacking error bars, including Figure 5C and the\nmajority of figures in SI.\nResponse: Thank you for pointing this out. Error bars have been added to all relevant quantitative\nplots.\n(2) The font sizes in Figure 5C are inconsistent and need to be standardized.\nResponse: Font sizes in Fig. 5C have been standardized. Thank you for pointing this out.\n(3) The manuscript contains several basic errors, such as \"Supplementary Figs. 1\" on page 2 (likely\na typo where the singular \"Fig.\" is needed), the misspelled term \"waveunmber\" in Figure 3C, and\n\"the\" in \"the demonstrated……\" on page 4.\nResponse: We apologize for these oversights. All noted errors have been carefully corrected.\n(4) The layout of Figure 2 should be more neatly arranged.\nResponse: Fig. 2 has been reorganized for better visual clarity. Thank you for this valuable\nsuggestion.\n(5) The legend order in the figures should be aligned as closely as possible with the data presentation\norder, such as in Figure 3D.\nResponse: Thanks for this comment. The legend order in all figures in the revised manuscript is\nnow aligned with the data presentation.\nReviewer #2:\nIn this work, the authors introduced TFP, which is reactive with CO and produces dynamic\n2\ncrosslinking agents, into a polymer. The resultant polymer was mechanically tough and\nthermoplastic. Due to the high reactivity of TFP, the polymer directly captured CO even from air.\nI suggest the following comments to improve the results.\nResponse: We sincerely appreciate your insightful comments. We have carefully considered all of\nyour questions and have addressed them accordingly. Detailed responses are provided below.\nComment 1： I think that alkylammonium hydroxide is acting as a catalyst. In my opinion,\n“catalyst-free” is not a fact. Would you consider softening the expression in the title?\nResponse: We sincerely appreciate your insightful comment. In response, we have revised the title\nto \"Upcycling of Air-Captured CO into Self-Healing Recyclable Polymers under Ambient\nTo provide the rationale for retaining the term \"catalyst-free\" in the main text, we wish to politely\nclarify the role of alkylammonium hydroxide. According to the IUPAC definition\n(https://doi.org/10.1351/goldbook.C00876), a catalyst is a substance that “increases the rate of a\nreaction without modifying the overall standard Gibbs energy change” and is “both a reactant and\nproduct of the reaction,” meaning it is regenerated unchanged after the reaction. In our system,\nhowever, alkylammonium hydroxide is stoichiometrically and irreversibly consumed to form\ncarbonate salts, which subsequently act as crosslinkers in the polymer network formation (Fig. R13).\nSince it is not regenerated, we classify it as a reactant, not a catalyst.\nTherefore, we believe that describing the system as \"catalyst-free\" in the main text remains\nappropriate, as it correctly highlights the absence of conventional catalysts for CO activation (such\n2\nas metal complexes)—a key innovative aspect of our work. We hope this clarification addresses\nyour concern.\nThank you once again for your valuable guidance, which has certainly enhanced the clarity and\nprecision of our manuscript.\nFig. R13 | Schematic illustration of the catalyst-free conversion of CO 2 into polymer network.\nComment 2： As the authors stated in the Introduction, CO consumption is an important target of\n2\nthis study. However, the amount of CO consumed is not addressed. For example, it would be\n2\nhelpful to indicate the amount of CO consumed per gram of polymer, and to compare this with\n2\nother CO -derived polymers such as polyurethanes.\n2\ndemonstrate a CO uptake capacity of 1.4-5.4 wt% (0.014-0.054 kg CO₂ per kg polymer). This value\n2\nis lower than that of conventional CO -derived polycarbonates and polyurethanes but is comparable\n2\nto values reported for frustrated Lewis pair (FLP) systems. While the mass of CO incorporated per\n2\nunit polymer mass is currently limited, we should note that our work establishes a distinct and\nvaluable paradigm, characterized by: (i) direct utilization of CO from ambient air (~400 ppm),\n2\nwhich remains unattainable by existing CO -to-polymer methods requiring concentrated pure CO\n2 2\nsources; (ii) catalyst-free CO fixation under exceptionally mild conditions (room temperature,\n2\natmospheric pressure), unlike literature approaches that often involve complex catalysts, high\npressures, and elevated temperatures; and (iii) the generation of polymers with excellent intrinsic\nself-healing and recyclability. Moreover, the current CO uptake has not yet reached the theoretical\n2\nmaximum, and this theoretical value can be further increased by optimizing the CO 2--bonding\n3\ngroups using lower-molecular-weight alternatives, such as trifluoromethyl alkyl ketones.\nTo directly address this point, we have added two tables (Supplementary Tables 1 and 2) to the\nrevised Supporting Information (Pages 46-47), which provides a systematic comparison of key\nmetrics, including CO source, CO conversion rate, CO content, synthesis condition (catalyst,\n2 2 2\ntemperature, and pressure), mechanical properties, recyclability (chemical recyclability,\nreprocessability), self-healing property, between our work and prior CO -derived polymers.\n2\nappreciating the unique advantages of our methodology.\nFurthermore, to ensure a balanced perspective, we have revised the Conclusions section to\nexplicitly state this limitation, present the quantitative data, and outline our ongoing research\ndirection to enhance CO uptake and improve the thermal and mechanical properties of the\n2\natmospheric-CO -derived polymers (Page 6 in the revised manuscript).\ntemperature sweep using dynamic mechanical analysis (DMA). The DMA results may exhibit a\nplateau above the T for the CO -derived CAN, while almost no plateau would be observed for\ng 2\nP(VTFP-MA)-20. The storage modulus in the plateau region is related to the effective crosslinking\ndensity of the CO -derived CAN. It is also possible that a relaxation mode associated with network\n2\nexchange might be detected above the T .\ng\nResponse: Thank you for this valuable suggestion. As recommended, we performed temperature-\nsweep DMA experiments. The results provide clear evidence of a crosslinked network: the CO -\n2\nderived CAN exhibits a well-defined rubbery plateau in the storage modulus (E’) above its T ,\ng\nstarkly contrasting with the continuous modulus decline of the linear polymer precursor (Fig. R14).\nThe crosslink density (ν) was calculated as 79.1 mol m-3 from the rubbery plateau modulus (E’)\nr\nusing the equation ν = E’/[3R(T + 50)]. Furthermore, upon further heating beyond the rubbery\nr g\nplateau, a subtle but measurable gradual decrease in E’ was observed, indicative of the dissociative\nCAN.\nTo further elucidate this dissociative exchange mechanism, we conducted additional temperature-\nsweep rheological tests and in situ variable-temperature FTIR. The rheological tests revealed a sharp,\nnearly three-order-of-magnitude decrease in the storage modulus (G’) alongside a distinct G’/G’’\ncrossover at approximately 85 °C (Fig. R15a), consistent with a dissociative exchange mechanism.\nMoreover, variable-temperature FTIR spectra directly demonstrated the reversible cleavage and\nreformation of the CO 2--bridged dynamic bonds during heating and cooling process (Fig. R15b).\n(Pages 4-5 in the revised manuscript).\nFig. R14 (newly added Fig. 3f) | DMA curves of P(VTFP-MA)-20 and CO 2 -derived CAN.\nFig. R15 (newly added Fig. 4c-d) | a, Temperature-dependent rheological behavior of the CO 2 -\nderived CAN. b, In situ variable-temperature FTIR spectra of CO -derived CAN.\n2\nbreak of 958%, despite having a crosslinking density as high as 5%, assuming that all TFP sites\nhave reacted. While the authors discuss the influence of counter cations, this reviewer believes that\nthe high elongation may result from the breaking of CO -based crosslinks during sample stretching.\nnetwork; therefore, I recommend performing such tests.\nResponse: Thank you for this insightful comment on the exceptional elongation at break of our\nCO -derived CAN. The suggestion that dynamic bond breakage could contribute prompted us to\n2\nfurther investigate its origin.\nTo clarify the underlying mechanism, we considered two plausible pathways: dynamic breaking\nof CO 2- crosslinks (as suggested) and plasticization by counter-cations. To inform our investigation,\n3\nwe first surveyed the literature, which indicates that introducing dynamic covalent crosslinks\ntypically restricts chain mobility and reduces elongation at break compared to linear precursors (J.\nAm. Chem. Soc. 2019, 141, 16595-16599; Science 2017, 356, 62-65). Conversely, small-molecule\nplasticizers are known to enhance ductility in CANs by disrupting polymer-polymer interactions (J.\nAm. Chem. Soc. 2018, 140, 6217-6220; Int. J. Mol. Sci. 2024, 25, 1720). Guided by this\nunderstanding, we designed control experiments to explicitly distinguish between these two\nmechanisms. (i) Ionic Plasticization in Linear Polymer: Blending tetrabutylammonium iodide\n(TBAI) into the linear precursor P(VTFP-MA)-20 significantly increased its elongation at break\nfrom 603% to 878%, while concurrently reducing its strength and stiffness (Fig. R16a). This result\nconfirms the potent plasticizing effect of ionic species. (ii) Substitution with a Dynamic Covalent\nCrosslinker: We replaced the tetrabutylammonium carbonate (TBAC) linkages with 1,3-\ndiaminopropane crosslinks to form a dynamic network, defined as diamine-CAN (Fig. R16b). This\ndiamine-CAN exhibited a markedly lower elongation at break (331%) than its linear precursor\n(621%) (Fig. R16c). Crucially, when TBAI was added into this network, the elongation at break\nwas dramatically restored to 629% (Fig. R16c). This sequence of changes—reduced ductility upon\ncrosslinking and its recovery upon incorporating an ionic plasticizer—directly demonstrates that\nionic plasticization, rather than dynamic bond breakage, is the dominant mechanism for the high\nelongation.\nTo gain deeper mechanistic insights into this cationic plasticization, we conducted molecular\ndynamics (MD) simulations. A comparative analysis between the CO₂-derived CAN (with TBA+)\nand the control system (with H+ replacing TBA+) revealed several fundamental distinctions: (i) a\nsubstantially weakened ionic association, as evidenced by a significantly right-shifted first peak in\nthe radial distribution function (RDF) between TBA+ and the polymeric anions (Fig. R17a); (ii)\nmarkedly enhanced cation mobility, reflected in a diffusion coefficient (D) 2.1 times greater than\nthat of the control system (Fig. R17b-c); (iii) a considerably expanded polymer free volume fraction\n(FFV, Fig. R17d-e), providing more space for segmental motion; and (iv) dramatically accelerated\nrelaxation dynamics of the polymer chains, as demonstrated by a significantly increased mean-\nsquared displacement (MSD) over time (Fig. R17f-g). These findings collectively demonstrate that\nthe bulky, flexible TBA+ cations effectively screen electrostatic interactions, enhance ion mobility,\nexpand free volume, and lubricate the polymer chains, thereby establishing cationic plasticization\nas the molecular origin of the enhanced ductility and toughness.\nFollowing your recommendation, we also performed cyclic tensile tests on the CO -derived CAN,\n2\nthe diamine-crosslinked network, and the plasticized diamine network (Fig. R18). The results\nrevealed pronounced hysteresis and residual strain in all three systems. While this confirms\nsignificant plastic deformability, these data alone cannot uniquely identify the underlying molecular\nmechanism.\nIn summary, our combined experimental and simulation evidence robustly demonstrates that the\nexceptional elongation is principally governed by counter-cation plasticization, not by the breaking\nof CO 2- crosslinks during stretching. All MD simulation data and corresponding discussion have\n3\nbeen added to the revised manuscript (Manuscript: Page 4; Supporting Information: Pages 18-20).\nFig. R16 | a, Tensile stress-strain curves of P(VTFP-MA)-20 and P(VTFP-MA)-20 with TBAI\nadditive. b, Diamine-CAN were synthesized from P(VTFP-MA)-20 and 1,3-diaminopropane. c,\nTensile stress-strain curves of P(VTFP-MA)-20, diamine-CAN and diamine-CAN with TBAI\nadditive.\nFig. R17 (newly added Fig. 3i-l and Supplementary Figs. 32-33) | Molecular dynamics (MD)\nsimulations of the counter-cation plasticization mechanism. a, Radial distribution function (RDF)\nbetween cations and polymeric anions, indicating ionic association strength. b-c, Mean-squared\ndisplacement (MSD) of counter-cations (b) and their corresponding diffusion coefficients (c). d-e,\nPolymer free volume fraction (FFV) of the CANs. f-g, MSD of polymer backbone (f) and their\ncorresponding diffusion coefficients (g).\nFig. R18 | Cyclic tensile test curves of diamine-CAN (a), diamine-CAN with TBAI additive (b) and\nCO -derived CAN (c).\nthe cause of this result.\nResponse: Thank you for this valuable question. Building upon the cationic plasticization\nmechanism elucidated in our response to Comment 4, we have now provided a detailed explanation\nfor this structure-property trend in the revised manuscript, supported by molecular dynamics (MD)\nsimulations.\nOur MD simulations reveal that the systematic mechanical variation originates from a progressive\nattenuation of the cationic plasticizing effect as the alkyl chain shortens from TBA+ to TMA+ and\nfurther to the rigid BnMA+. This conclusion is supported by several key observations (Fig. R17 in\nComment 4): radial distribution function (RDF) analysis shows a progressive left-shift of the first\npeak for the cation–polymer interaction along the series TBA+ → TPA+ → TEA+ → TMA+ →\nBnMA+ (Fig. R17a), indicating a decreasing ion-pair distance and thus stronger electrostatic\ninteractions. This strengthened ionic association leads to a concomitant decrease in cation mobility\n(Fig. R17b-c) and a reduction in polymer free volume (Fig. R17d-e). As a result, the segmental\nmotion of the polymer chains becomes more restricted (Fig. R17f-g), thereby shifting the\nmacroscopic mechanical behavior from ductile to rigid and strong.\nAll relevant MD simulation data and the corresponding discussion have been incorporated into\nthe revised manuscript (Manuscript: Page 4; Supporting Information: Pages 18-20).\nComment 6： P. 3, Fig. 3h: The authors proposed that the mechanical properties of CO -derived\nis mainly due to the characteristics of the polymers used for copolymerization. Therefore, I believe\nthat the advantage of the CO -derived CAN may be diminished when rigid EMA and MMA are\n2\nused. Please compare the mechanical properties before and after CO crosslinking for copolymers\n2\nwith BuMA, EMA, and MMA. If any advantages of CO crosslinking are observed, they should be\n2\nclearly described.\nResponse: Thank you for this insightful comment. We fully agree that the intrinsic rigidity of\ncomonomers like EMA and MMA narrows the relative margin for mechanical enhancement via\nCO -derived CO 2- crosslinking, compared to flexible comonomers. Our comparative analysis\n2 3\ndemonstrates that CO 2- crosslinking imparts distinct mechanical improvements across all\n3\ncomonomer systems, even in those based on rigid monomers. For flexible comonomers like BuMA,\nCO 2- crosslinking synergistically enhances strength, stiffness, ductility, and toughness, overcoming\n3\nclassical trade-offs inherent in polymer network design, similar to the effect achieved in MA-based\nCO -derived CAN (Fig. R19a-b). For rigid comonomers (EMA, MMA), CO 2- crosslinking delivers\n2 3\na substantial boost in stiffness, with Young's modulus increasing by over 100% (Fig. R19c-d).\nAll supplementary data have been incorporated into the revised manuscript (Page 23 in the\nSupporting Information). We appreciate your valuable feedback.\nSupplementary Fig. R19 (newly added Supplementary Fig. S37) Mechanical properties of linear\nprecursor polymers and their corresponding CANs. a, Tensile stress-strain curves of P(VTFP-\nBuMA)-15 and its corresponding CANs. b, Comparison of ultimate tensile stress, Young's modulus,\ntoughness, and elongation at break for the samples in (a). c, Tensile stress-strain curves of P(VTFP-\nMMA)-15 and P(VTFP-EMA)-15, alongside their corresponding CANs. d, Comparison of Young's\nmodulus and toughness for the samples in (c).\nComment 7: P. 4, Fig. 4: Regarding the experiment shown in Fig. 4, there is no detailed description\nof the CO -derived CAN. Please include an explanation of the prepolymer. Is the prepolymer\nResponse: We sincerely thank you for this insightful comment and for pointing out the need for a\nclearer description. Yes, the prepolymer used to prepare the CO -derived CAN is indeed P(VTFP-\nTo avoid any ambiguity and to make the description more precise, we have now provided a strict\ndefinition for \"CO -derived CAN\" in the “Synthesis and Characterization of CANs” section. The\n2\nrevised text explicitly states: \"CO -derived CAN (unless otherwise specified, 'CO -derived CAN' is\n2 2\ndefined in this work as the network derived from P(VTFP-MA)-20, TBAH, and ambient air)...\" (Page\n4, Line 3). Furthermore, in the end of \" Synthesis and Characterization of CANs\" section, we have\nadded a clarification to reiterate the specific system: “Taking CO -derived CAN (selected as the\n2\nrepresentative system for subsequent investigations unless otherwise specified) as an example, …”\n(Page 4, Paragraph 3, Line 8 from the bottom).\nWe believe these revisions have clearly addressed your concern. Thank you again for helping us\nimprove the clarity of our manuscript.\nComment 8: P. 4, Fig. c and f: The authors conducted self-healing tests at 80°C; however, they also\ndemonstrated that melt processing is possible at a slightly higher temperature of 90°C. In such a\ncase, this reviewer believes that the observed behavior may be attributed to thermoplasticity rather\nthan true self-healing. How would the self-healing performance be affected if the tests were\nconducted at a lower temperature where melt processing is not possible, such as room temperature?\nResponse: We thank the reviewer for raising this important point. To directly address this concern,\nwe performed additional self-healing experiments at lower temperatures. The results demonstrate\nthat efficient healing still occurs, with healing efficiencies of 98.2% at 40 °C and 53.2% at 25 °C\n(Fig. R20). These outcomes confirm that the healing capability is intrinsic and not attributable to\nthermoplastic flow. All supplementary data and expanded discussion are now incorporated into the\nrevised manuscript (Manuscript: Page 5; Supporting Information: Page 28).\nFig. R20 (newly added Supplementary Fig. S47) | Low-temperature self-healing performance. a–\nb, Stress-strain curves of the repaired samples after different healing durations under 2 MPa at 40 °C\n(a), and the corresponding ultimate tensile stress and healing efficiencies (b). c–d, Stress-strain\ncurves of the repaired samples after different healing durations under 2 MPa at room temperature\n(c), and the corresponding ultimate tensile stress and healing efficiencies (d).\nReviewer #3:\nComments for manuscript \"Catalyst-Free Upcycling of Air-Captured CO to Self-Healing\nThe manuscript submitted by Prof. Liang Chen and co-workers deals with the synthesis of covalent\nadaptable networks using ambient CO as a crosslinker which enable the formation of exchangeable\n2\nbonds. The manuscript is well-written, the molecular study and the effect of the counter ion on the\nhemiacetal-like moiety formation is highly interesting. The network characterization and material\nproperties are well performed showing excellent mechanical properties and good (re)processability.\nThe manuscript deserves publication after considering the following points especially further studies\non rheological characterizations should be performed prior publication.\nResponse: We sincerely appreciate your positive assessment and insightful suggestions, especially\nregarding the swelling tests and rheology. All raised points have been incorporated into the revised\nmanuscript, with our detailed responses provided below.\nComment 1: Network design. Can the authors discuss the choice of (co)polymer backbone structure?\nWhy they choose to copolymerize MMA with functionalized styrene and not a fully styrenic\npolymer backbone?\nResponse: Thank you for this insightful question regarding the backbone design. Our choice to\ncopolymerize MMA with functional monomer 4-vinyltrifluoroacetophenone (VTFP), rather than\nusing a fully styrenic backbone, was primarily driven by mechanical considerations.\nOur initial attempt using a styrenic system—poly(4-vinyltrifluoroacetophenone-co-styrene)\n[P(VTFP-PS)-18, VTFP/PS = 1/18 mol/mol, M = 56.9 kDa, Đ = 1.89]—resulted in a material that\nn\nwas exceedingly brittle. Both the linear copolymer precursor and the corresponding CAN fractured\nduring hot-pressing and could not form coherent films (Fig. R21). The incorporation of MMA was\ncrucial to resolve this brittleness. The MMA segments impart enhanced ductility and film-forming\nability to the dynamic network, enabling the preparation of robust, free-standing films suitable for\nfurther characterization and application.\nFig. R21 | Photographic evidence of the mechanical brittleness in P(VTFP-PS)-18 (a) and its\ncorresponding CAN (b), as demonstrated by their fragmentation upon demolding after hot-pressing.\nComment 2: Swelling tests in good solvents (e.g. THF or CHCl ) should be performed for each\n3\nmaterials. My issue is that the crosslinked nature has not be evidenced either by gel content\nmeasurement or DMA.\nResponse: Thank you for raising this important point. In response, we have carried out\ncomprehensive swelling tests and DMA characterization, which provide clear evidence for the\ncrosslinked nature of our materials, as summarized below:\nSwelling Tests of the CO -derived CAN: Swelling experiments conducted in various solvents—\n2\nincluding tetrahydrofuran (THF), chloroform (CHCl ), toluene, n-hexane, and ethyl acetate (EA) —\n3\ndemonstrate the material's insolubility (Fig. R22), confirming its crosslinked nature. Quantitative\nanalysis revealed high gel fractions of 93.3%, 91.2%, 96.5%, 98.8%, and 92.7% in the respective\nsolvents.\nGeneralization to All CANs: These swelling studies were extended to all synthesized CANs,\nconsistently revealing excellent solvent resistance, with gel fractions in THF exceeding 90% in\nevery case (Fig. R23). These results unambiguously confirm the universal presence of a crosslinked\nnetwork across the series.\nDynamic Mechanical Analysis (DMA): Further validation comes from temperature-sweep DMA.\nAs illustrated in Fig. R24, the CO -derived CAN exhibits a distinct rubbery plateau in the storage\n2\nmodulus (E’) above its T , in striking contrast to the linear polymer, where E’ drops continuously\ng\nwith increasing temperature. This sustained modulus is a key indicator of a dynamic covalent\nnetwork. Moreover, the crosslink density (ν) was calculated as 79.1 mol·m-3 using the equation ν =\nE’/[3R(T + 50)].\nr g\nTogether, these findings conclusively verify the crosslinked structure of all CANs. All relevant\ndata and corresponding discussions have been incorporated into the revised manuscript (Manuscript:\nPages 3-4; Supporting Information: Pages 22-23). We appreciate your valuable insight.\nFig. R22 (newly added Fig. 3e) | Gel fraction and swelling ratio of the CO 2 -derived CAN in various\nsolvents.\nFig. R23 (newly added Supplementary Figs. S34a, S35a and S36a) | a, Gel fraction and swelling\nratio of the CANs with different counter-cations. b, Gel fraction and swelling ratio of the CANs\nwith different MA-to-VTFP molar ratio. c, Gel fraction and swelling ratio of the CANs with\ndifferent comonomers.\nFig. R24 (newly added Fig. 3g) | DMA curves of P(VTFP-MA)-20 and CO 2 -derived CAN.\nComment 3: Rheology experiments to be performed. Stress relaxation experiments presented by\nthe authored showed fast relaxation (between 10 to 100s). Small amplitude oscillatory shear\nexperiments are generally preferred to characterize rapid relaxation (see e.g. ACS Polym. Au 2025,\n5, 3, 214-240). It will also confirm the nature of the exchange mechanism (associative or dissociative)\nby monitoring the evolution of the storage modulus with increasing temperature. In addition, we\ngenerally performed stress relaxation experiments at T > T + 50°C to separate the segmental\ng\nrelaxation induce by the glassy to rubbery transition and the relaxation induce by the exchange\nreaction. Non-normalized data should be also added in the supplementary material.\nResponse: We sincerely appreciate your insightful suggestions. As suggested, we have performed\nthe following additional experiments:\n(1) Frequency-sweep SAOS experiments: Following your guidance, we conducted frequency-\nsweep small amplitude oscillatory shear (SAOS) at various temperatures (Fig. R25a). The relaxation\ntime (τ) was determined from the crossover frequency (ω ) where G’ = G’’ (τ = 1/ω ). An Arrhenius\nc c\nplot of ln(τ) versus 1000/T showed a linear correlation (Fig. R25b), confirming the vitrimeric nature\nof the networks. The activation energy (E ) for the bond exchange was calculated to be 111.9 kJ/mol.\na\nSubsequently, the master curve was constructed by applying the time-temperature superposition\n(TTS) principle to the SAOS data at a reference temperature of 60 °C (Fig. R25c). The horizontal\nshift factors (a ) from the TTS procedure were analyzed via the Arrhenius equation, yielding an\nT\nactivation energy of 109.3 kJ/mol (Fig. R25d). This value is consistent with that from the crossover\nfrequency method, validating the reliability of our rheological analysis.\nFig. R25 (newly added Fig. 4a-d and Supplementary Fig. 44) | a-b, Frequency-sweep SAOS\nmeasurements at various temperatures (a) and corresponding Arrhenius plot (b). c-d, Master curve\nof CO -derived CAN based on TTS of SAOS experiments at a reference temperature of 60 °C (c),\n2\nand the corresponding Arrhenius plot of horizontal shift factors (a ) versus1000/T (d). e,\nT\nTemperature-dependent rheological test of the CO -derived CAN. f, In situ variable-temperature\n2\n(2) Temperature-sweep rheological test: To confirm the nature of the exchange mechanism, we\nfirst performed temperature-sweep rheological experiments. The results show a sharp, nearly three-\norder-of-magnitude decrease in G’ accompanied by a distinct G’/G’’ crossover at approximately\n85 °C (Fig. R25e). This behavior is a hallmark of a dissociative exchange mechanism, as manifested\nby the sudden loss of network integrity upon heating.\n(3) In situ variable-temperature FTIR: To provide molecular-level validation, we conducted in\nsitu variable-temperature FTIR spectroscopy (Fig. R25f). The spectra directly demonstrate the\nthermally induced cleavage of the CO 2--bridged dynamic covalent bonds upon heating and their\n3\nsubsequent reformation upon cooling, offering unequivocal evidence for the dissociative exchange\nprocess.\nAll new data and corresponding discussion have been incorporated into the revised manuscript\n(Manuscript: Pages 4-5; Supporting Information: Pages 26-27). We are grateful for these valuable\ncomments, which have significantly strengthened our mechanistic analysis.\nComment 4: In addition, creep experiments especially at room temperature should be performed to\ndetermine if the material mechanical properties are stable under ambient conditions. DMA analysis\nto further confirm the CAN features (presence of a rubbery after T ).\ng\nResponse: Thank you for this valuable suggestion. As recommended, we conducted tensile-mode\nDMA creep tests at room temperature. The results reveal significant viscoelastic flow, with the\nresidual strain reaching 49% (Fig. R26). This pronounced creep deformation indicates the activation\nof dynamic covalent bond exchange even under ambient conditions. While this suggests that long-\nterm dimensional stability under sustained load may require further optimization, it also underscores\nthe material's potential for low-temperature self-healing applications. To validate this, we performed\nquantitative self-healing assessments at low temperatures. The network achieved excellent healing\nefficiencies of 53.2% at 25 °C and 98.2% at 40 °C within 24 hours (Fig. R27), consistent with the\nroom-temperature bond exchange dynamics observed in the creep tests.\nIn addition, as also addressed in our response to Comment 2, temperature-sweep DMA\nexperiments confirm a well-defined rubbery plateau above T , verifying the crosslinked network\ng\nstructure.\nAll relevant data, including low-temperature self-healing performance, DMA curves, and\nassociated discussions, have been incorporated into the revised manuscript (Manuscript: Page 3,\nPage 5; Supporting Information: Page 28).\nFig. R26 | Creep curves of CO 2 -derived CAN at room temperature.\nFig. R27 (newly added Supplementary Fig. S47) | Low-temperature self-healing performance. a–\nb, Stress-strain curves of the repaired samples after different healing durations under 2 MPa at 40 °C\n(a), and the corresponding ultimate tensile stress and healing efficiencies (b). c-d, Stress-strain\ncurves of the repaired samples after different healing durations under 2 MPa at room temperature\n(c), and the corresponding ultimate tensile stress and healing efficiencies (d)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The manuscript entitled \"Upcycling of Atmospheric CO2 to Self-Healing Recyclable Polymers under Ambient Conditions\" describes a strategy for producing cross-linked polymers with self-healing and closed-loop recyclability directly from atmospheric CO2 under catalyst-free conditions, presenting a valuable pathway toward green and reversible crosslinking in polymer science. This study leverages the rapid absorption of atmospheric CO2 by organic bases such as TBAC, converting it into CO32- which enable the dynamic reversible cross-linking of P(VTFP-MA)-20. The resulting covalent network exhibits excellent self-healing properties, recyclability, and favorable mechanical performance.\nOverall, the referee believes that the manuscript deserves publication in Nature Communications after the identified issues are addressed.\nHere are the minor comments the reviewer suggests:\n1. Regarding Fig. 3c, it would be more informative to plot the pH profile of the TBAH solution over time. The current format, which only labels the initial and final pH values, could be misleading to readers.\n2. While the model reactions effectively prove CO32- reacts with TFP, the study does not address whether HCO3- could also participate in or interfere with this reaction. During the cross-linking of the linear polymer, ambient air was bubbled through the TBAC solution. This process may inevitably produce HCO3-. It is important to clarify whether the presence of HCO3- competes with CO32- and adversely affects the efficiency of the cross-linking reaction.\n3. Referee believes that the statement \"the urgent need for novel catalyst-free dynamic chemistries\" in the introduction part is inaccurate, since many dynamic covalent bonds can undergo efficient exchange under thermal activation without catalyst. The reviewer recommends that the authors revise this statement to ensure accurate expression.\n4. The introduction on the up-to-date progress in CO2 utilization could be strengthened. It would be beneficial to cite recent achievements in this field (see e.g. Nat. Commun., 15, 6605 (2024)) to provide a more comprehensive background of the present work.\n5. Additionally, there are a few problems that should be dealt with before published. For example:\n(1) The letter labels (j, k, l) in the caption of Fig. 3 should be bolded and must conform to standard typesetting conventions.\n(2) In Fig. 5b, a space should be inserted between the axis label name and the following parentheses.", "reviewer_2": "The authors have conducted additional experiments and have appropriately addressed the reviewer’s questions. I recommend accepting this paper in its current version.", "reviewer_3": "The revised version of the manuscript entitled \"Upcycling of Atmospheric CO to Self-Healing Recyclable Polymers under Ambient Conditions\" includes all the suggested modifications especially about the rheological behavior of these original materials. I therefore recommend publication of this manuscript."}, "author_response": "Point-by-Point Response to Reviewers' Comments\nReviewer #1:\nThe manuscript entitled \"Upcycling of Atmospheric CO to Self-Healing Recyclable Polymers\n2\nunder Ambient Conditions\" describes a strategy for producing cross-linked polymers with self-\nhealing and closed-loop recyclability directly from atmospheric CO under catalyst-free conditions,\n2\npresenting a valuable pathway toward green and reversible crosslinking in polymer science. This\nstudy leverages the rapid absorption of atmospheric CO by organic bases such as TBAC, converting\n2\nit into CO 2- which enable the dynamic reversible cross-linking of P(VTFP-MA)-20. The resulting\n3\ncovalent network exhibits excellent self-healing properties, recyclability, and favorable mechanical\nperformance.\nOverall, the referee believes that the manuscript deserves publication in Nature Communications\nafter the identified issues are addressed.\nResponse: Thank you for your supportive feedback and insightful suggestions. All raised points are\naddressed as follows.\nHere are the minor comments the reviewer suggests:\n1. Regarding Fig. 3c, it would be more informative to plot the pH profile of the TBAH solution over\ntime. The current format, which only labels the initial and final pH values, could be misleading to\nreaders.\nResponse: Fig. 3c has been revised into a dual-y-axis plot showing both exhaust CO and TBAH\n2\npH over time, with an updated caption (please see below). We appreciate this helpful suggestion.\nFig. R1 (replaced with Fig. 3c) | CO 2 concentration in the exhaust stream and pH of the solution\nover time during the bubbling of ambient air.\n2. While the model reactions effectively prove CO 2- reacts with TFP, the study does not address\n3\nwhether HCO - could also participate in or interfere with this reaction. During the cross-linking of\n3\nthe linear polymer, ambient air was bubbled through the TBAC solution. This process may\ninevitably produce HCO -. It is important to clarify whether the presence of HCO - competes with\n3 3\nCO 2- and adversely affects the efficiency of the cross-linking reaction.\nprepared by bubbling ambient air contains ~94.1% CO 2- alongside ~5.9% HCO -. To determine\n3 3\nwhether this trace HCO - impurity interferes with the subsequent cross-linking or final network\n3\nproperties, we conducted the following two experiments.\n(1) Model Reaction Probes Chemoselectivity. To probe inherent reactivity, a stoichiometric\nmixture of the model compound α,α,α-trifluoroacetophenone (TFP) and tetrabutylammonium\nhydrogen carbonate (TBAHC) was stirred in CD CN at room temperature for 24 hours. 1H, 19F, and\n3\n13C NMR analysis of the reaction mixture showed no detectable reaction, with spectra identical to\nthose of the starting materials (Fig. R2). This stands in marked contrast to the quantitative reaction\nobserved between TFP and CO 2- under identical conditions. This confirms the high selectivity for\n3 3 3\n(2) Effect of Trace HCO - on Cross-linked Polymer Properties. To further evaluate the practical\n3\nimpact, a control network was synthesized using pure TBAC (no prior air CO exposure) and\n2\ncomprehensively compared with the CO -derived CAN. The two networks exhibited negligible\n2\ndifferences in both glass transition temperature (T ) and mechanical performance—including\ng\nYoung’s modulus, ultimate tensile stress, toughness, and elongation at break (Fig. R3).\nTogether, these results demonstrate that the trace HCO - impurity neither participates in the cross-\n3\nlinking reaction nor impairs the final thermomechanical properties of the networks. All\ncorresponding data and discussion have been incorporated into the revised manuscript (Main text:\nPage 3; SI: Pages 17-19).\nFig. R2 (newly added Supplementary Fig. 27) | Comparison of NMR spectra (in CD 3 CN) for TFP,\nTBAHC, and the reaction mixture. a, 1H NMR, b, 13C NMR, and c, 19F NMR.\nFig. R3 (newly added Supplementary Fig. 28) | Comparison of thermal and mechanical properties\nbetween the CO\n2\n-derived CAN and the network cross-linked with pure TBAC. a, DSC curves. b,\nRepresentative tensile stress-strain curves. c, Comparison of Young's modulus, ultimate tensile\nstress, toughness, and elongation at break.\n3. Referee believes that the statement \"the urgent need for novel catalyst-free dynamic chemistries\"\nin the introduction part is inaccurate, since many dynamic covalent bonds can undergo efficient\nexchange under thermal activation without catalyst. The reviewer recommends that the authors\nrevise this statement to ensure accurate expression.\nResponse: We have revised the sentence on Page 1, removing the claim regarding “catalyst-free”\nchemistry. It now reads: “…These limitations highlight the need for novel dynamic chemistries that\nsimultaneously achieve superior reprocessability, chemical recyclability, and balanced mechanical\nproperties.”\n4. The introduction on the up-to-date progress in CO utilization could be strengthened. It would be\n2\nbeneficial to cite recent achievements in this field (see e.g. Nat. Commun., 15, 6605 (2024)) to\nprovide a more comprehensive background of the present work.\nResponse: We've incorporated the suggested reference (Ref. 32) into the Introduction, enhancing\nthe background on recent CO utilization progress relevant to our study. Thank you for the helpful\n2\nsuggestion.\n5. Additionally, there are a few problems that should be dealt with before published. For example:\n(1) The letter labels (j, k, l) in the caption of Fig. 3 should be bolded and must conform to standard\ntypesetting conventions.\nResponse: The letter labels (j, k, l) in the Fig. 3 caption have been bolded and standardized. Thank\nyou for pointing this out.\n(2) In Fig. 5b, a space should be inserted between the axis label name and the following parentheses.\nResponse: Noted and corrected. We have also verified and corrected this issue in all other figures.\nReviewer #2:\nThe authors have conducted additional experiments and have appropriately addressed the reviewer’s\nquestions. I recommend accepting this paper in its current version.\nResponse: We appreciate the reviewer’s support and recommendation for publication.\nReviewer #3:\nThe revised version of the manuscript entitled \"Upcycling of Atmospheric CO to Self-Healing\nespecially about the rheological behavior of these original materials. I therefore recommend\npublication of this manuscript.\nResponse: We appreciate the reviewer’s recommendation for publication."}, {"round": 3, "reviewer_comments": {"reviewer_1": "I think the authors did a pretty good work on addressing the comments from reviewers and I would recommend the acceptance of the manuscript."}, "author_response": ""}]

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