Advancing aerogel recyclability through polyhexahydrotriazine reactivity

Domain: physics
Published: 2025-12-05
Editorial outcome: major_revision

Abstract
Organicaerogelshaveemergedaspromisingmaterialsforadvancedthermal insulation.However,theirchemicallyrobustcovalentnetworksposeamajor barrierforeffectiverecycling.Introducingspecificchemicalbondsintothe aerogelscaffoldthatenableon-demandreversibilityoffersaviablepathwayto enhancerecyclabilityandpromotethesustainableuseofthesematerials.In thiswork,wedemonstratethathexahydrotriazine(HT)unitsundergo nucleophilicattackbyaminesandengageinmetathesisreactions,funda- mentallyredefiningtheirreactivebehaviors.Basedonthis,weintroducea waste-minimized,closed-loopchemicalrecyclingprocessforhighlyporous, thermallysuperinsulatingorganicaerogels.Thesematerialsarepartially depolymerizedintosolubleoligomersuponexposuretoprimaryaminesand canbereassembledintofreshpolymernetworksondemand.Additionally,by varyingtheaminefeedstocksduringdepolymerization,wetailorkeyaerogel properties,suchasthermalconductivityandflameresistance,beyondtheir initialsynthesis.Underheatandpressure,HTbondexchangeenablesaerogels totransformintohigh-performancethermoset-likefilms,whichcansubse- quentlyreverttoaerogels.ThisbreakthroughinHTchemistrysetsabench- markforatom-efficientrecycling,reprogramming,andreprocessingofHT- basedmaterials,providingatransformativefoundationforacircularmaterials platformwithbroadimpact.

Introduction
Aerogels,identified by IUPACasone of the top ten emerging tech- nologies in chemistry, present a promising material for energy conservation1.Thesematerialsexhibitultralowthermalconductivity, reaching values lower than0.020Wm⁻¹K⁻¹,farsurpassing the insu- lating performance of conventional materials, such as polystyrene foams, polyurethane foams, and glass wool2,3. Organic aerogels, in particular,haveshowngreatpromiseforreducingenergyconsump- tionandgreenhousegasemissionsduetotheirultralowdensity,great mechanicalproperties,andexceptionalthermalperformance3,4.While addressingthesekeychallengesinsustainabledevelopmentisessen- tial,ensuringtherecyclabilityoforganicaerogelsisequallyimportant toestablishthemastrulysustainablematerials.However,thehighly crosslinked and robust molecular structures of traditional organic aerogelsrenderthemnon-recyclable.Toaddressthislimitation,itis imperativetointegraterecyclabilityasacorecriterioninthedesignof neworganicaerogelmaterials,allwhilemaintainingtheirexceptional high-performanceproperties,anambitiousyetcriticalscientificchal- lenge.Onepromisingapproachinvolvesusingcrosslinkednetworks with reversible chemical linkages, such as imines and hexahydro- triazines (HT), to achieve closed-loop recycling under mild conditions5–7. In these systems, straightforward hydrolysis reactions enableselectiveandefficientdepolymerization,revertingthemateri- alstotheiroriginalmonomericbuildingblocks.Thesemonomerscan beisolatedwithhighpurityandreuseddirectlytosynthesizethesame organicaerogelmaterials,ensuringacircularrecyclingprocess.Yet, isolatingmonomersafterdepolymerizationinvolveswaste-generating purification steps. To eliminate these labor-intensive processes and preventthelossofvaluablechemicalresources,suchasmonomers, acids,bases,andsolvents,werecentlyintroducedanunprecedented recyclingstrategyfororganicaerogels,termedtheaerogel-to-sol-to- aerogel(ASA)process8.Insteadofcapitalizingonreversiblechemical bonds, this method relies on reshuffling and reorganizing covalent bondsintegratedinorganicaerogelnetworks.Usingaminolysiswith additionalamines,wedemonstratedthatfullycrosslinkedpolyimine aerogelscanbeefficientlybrokendownintosolubleoligomers,which canthenberepolymerizedbyintroducinganappropriateamountof suitable aldehydes. This unique foam-to-foam recycling approach utilizes 100% of the originally building blocks and avoids external purification steps, representing a significant advancement in the environmentallyfriendlyandresource-efficientmanagementofther- mallyinsulatingmaterials.

In our efforts to adapt the ASA process to different types of aerogel networks, we made an unexpected discovery: HT moieties, formed through the condensation of formaldehyde and primary amines9, display reactivity through aminolysis with other primary amines,showcasingtheirabilitytoundergonucleophilicattacksunder mildconditions,andmetathesiswithotherHTgroups.Traditionally, HTgroupsareknowntoundergonucleophilicattacksonlywiththiols andphosphinesunderharshconditions,makingthemunsuitablefor chemicalrecyclingstrategiesthroughtheASAprocess10,11.Buildingon this groundbreaking discovery, we developed fully recyclable poly- hexahydrotriazine (PHT) aerogels (Fig. 1a). The aminolysis reaction betweenHTgroupsandaromaticprimaryaminesenablesthecleavage ofcrosslinkedPHTnetworksintosolubleaminaloligomermixtures.

Results
Synthesisandclosed-looprecyclingofPHTaerogels
ToapplythereactivityofHTmoietiesfororganicaerogelrecycling,we synthesizedaPHTaerogelthroughthepolycondensationof2,2-bis[4- (4-aminophenoxy)phenyl]propane (BAPP) and PFA (Fig. 1b)7. To ensure the exclusive formation of HT structures and prevent the generation of unwanted hemiaminal intermediates—which could compromisethethermalstabilityandmechanicalperformanceofthe final materials—it is essential to react an equimolar amount of repeatingunitsinPFAandamine7,12,13.Thetwoprecursorsweremixed inN-methylpyrrolidone(NMP)at100°Cfor8h,resultinginthefor- mationofastableorganogel,whichwasfurthercuredatroomtem- peraturefor24h(Fig.1b).Afterbeingsolventexchangedtoethanol, theorganogelwasdriedusingsupercriticalCO ,preservingtheporous 2 structureoftheaerogelnetwork.Toenhancethesustainabilityofthe PHT synthesis, all solvents used were recovered through stepwise distillation with high purity and good to high recovery yields (Sup- plementaryFig.S6andSupplementaryTableS1).TheresultingPHT aerogel(PHT-pristine)exhibitslowbulkdensity(0.15gcm−3)andhigh porosity(88%),keyfeaturesoflightweightmacro-mesoporousmate- rials.PHT-pristinealsoshowsalargespecificsurfaceareaof129m2g−1, a total pore volume of 6.08cm3g−1, and a mesopore volume of 0.25cm3g−1,indicativeforitshighlyporousarchitecture.Itisnotedthat PHT-pristine possesses a predominantly macroporous architecture withamesoporousfractionasmeasuredbynitrogensorption(Sup- plementary Fig. S7a). Importantly, PHT-pristine exhibits an ultralow total thermal conductivity of 18.8mWm−1K−1 (Supplementary TableS2).ApplyingtheKnudsenmodelshowsthatthegaseouscon- tribution to the total conductivity is 9.3mWm−1K−1, which is sig- nificantly lower than that of open still air, while the remaining 9.5mWm−1K−1originatesfromthesolidphase14.Theseresultsindicate that the excellent thermal insulation performance of PHT-pristine arisesfromtheinterplayofKnudsen-inducedreductioningas-phase conduction and inherently low solid-phase conductivity. Given its exceptionalmaterialperformanceasathermalinsulatingunit,PHT- pristineservesasapromisingstartingpointforthedevelopmentofa sustainable aerogel system. Building on the results of the model reactions,weexploredwhetherPHT-pristineaerogelundergoesami- nolysisinthepresenceofprimaryamines.Thisprocesswouldresultin partial depolymerization into soluble oligomeric structures and a drasticreductionincrosslinkdensity(Fig.1a).Toinitiatetheaerogel depolymerizationprocess,PHT-pristinefragmentsweretreatedwith a 14wt% BAPP solution in NMP, using an amount equivalent to 1.5 times the BAPP content present in the aerogel. This amount was foundtobetheminimumquantityofBAPPnecessaryfordissolution ofthePHTaerogel(SupplementaryFig.S8).After4hofultrasonica- tion, a clear red solution containing soluble oligomeric structures was obtained. The mixture was firstly analyzed by NMR spectroscopy. In the 1H NMR spectrum, characteristic signals for aminalstructuresweredetectedat4.5and6.3ppm(Supplementary Fig.S9a).The1HCOSYNMRspectrumfurtherrevealsthatthesetwo signalsarecoupled,providingfurtherconfirmationoftheembedded aminal structure (Supplementary Fig. S9b). Moreover, the DEPT 13C NMR spectrum shows a methylene carbon signal at 54 ppm, corre- sponding to the aminal groups and aligning with similar aminal- containing structures reported in the literature (Supplementary Fig.S9c)15.Similarly,theaminalstructurewasalsoidentifiedbyMALDI- TOFanalysis,wheretheaminalgroupispresentedasaBAPPdimer (Supplementary Fig. S10). To confirm the presence of the formed oligomers,1HDOSYNMRexperimentswereconducted.Thespectra revealed that the oligomeric structures exhibiting the characteristic aminalsignalsarelargerinsizethantheoneofBAPPamine(Supple- mentary Fig. S11a). In addition, this oligomer mixture was analyzed usingGelPermeationChromatography(GPC)inN,N-dimethylforma- mide (DMF), which showed a broad molecular weight distributionrangingfrom400to7000Da(SupplementaryFig.S11b). Overall, these findings align with our model reaction, strongly indicating that nucleophilic attacks occur within the polymer system.Moreover,theyconfirmthatthePHTnetworkcanbepartially depolymerized into soluble oligomer structures through aminolysis withadditionalamines.

To complete the recycling loop, the PHT solution in NMP was directlyutilizedtoprepareafreshPHTaerogel.Thiswasachievedby introducinganequivalentamountofrepeatingunitsinPFA,relativeto theadditionalaminefunctionalgroups,asa1.6wt%solutioninNMP. Asaresult,astableorganogelwasfirstformedandconvertedintoan aerogelbyfollowingthestandardaerogelpreparationsteps,including solvent exchange with ethanol and drying with supercritical CO 2 (Fig.2a,b).Duringtherecyclingprocedure,100%oftheinitialche- mical resources were utilized in the material preparation, and no purificationstepswererequired.ThepotentialoftheASArecycling processwasdemonstratedbysuccessfullycompletingthreerecycling cycles.ThereconstitutedaerogelsweredesignatedasPHT-A1,PHT-A2, and PHT-A3,corresponding to their respective recycling generation (SupplementaryTableS3).ThesuccessfulformationofPHTforeach recycling iteration was confirmed by 13C MAS NMR spectroscopy, wherthechemicalshiftaround70ppmvalidatestheHTstructure within PHT-pristine and PHT-As (Fig. 2c)7. Furthermore, the results demonstratetheabsenceofPHTdegradationorsidereactionsduring theASAprocesses.ItisevidentthatthesoleformationofHTstructures could be achieved without the presence of unwanted hemiaminal structures, which could lower the thermal stability and mechanical performanceofthefinalmaterials7,13.Regardingtheaerogel-specific properties,PHT-Asexhibitvirtuallyidenticalpropertiescomparedto PHT-pristine,thusdemonstratinggreatreproducibility(Fig.2d,eand SupplementaryTableS3−7).Accordingtothenitrogenphysisorption isotherms,PHT-AsexhibitsimilarhysteresistoPHT-pristine,suggest- ingcomparablemesoporousstructures(SupplementaryFig.S7a).This resemblanceisalsoreflectedintheirnanoscalemorphologies,where both PHT-pristine and PHT-As consist of a branch-like skeleton topology (Fig. 2f). Importantly, PHT-As achieve a thermally super- insulating performance with a low thermal conductivity of approxi- mately 19mWm−1K−1. To further evaluate the thermal insulation performanceofPHT-As,weemployedtheKnudsenmodeltoseparate thetotalmeasuredthermalconductivityintogaseousandsolidcon- tributions (Supplementary Table S5)16. The gaseous conductivity values across different generations remained stable at around 9.0mWm⁻1K⁻1,whilethesolidcontributionwasconsistentlycloseto 9.5mWm⁻1K⁻1. The reproducible solid thermal conductivity can be attributedtotheidenticalchemicalcompositionofPHT-Asacrossthe recyclingcycles,asconfirmedby13CMASNMRresults(Fig.2c).Like- wise,theircomparablemorphologicalcharacteristics,revealedbySEM andBETanalyses,accountfortheconsistentgaseousconductivity.In addition,thethermalandmechanicalperformanceofPHT-Asarealso in line with PHT-pristine, asdemonstrated by similarthermalgravi- metricanalysis(TGA)anduniaxialcompressiontestingresults(Sup- plementaryFig.S7b−candSupplementaryTableS7).Overall,ourPHT aerogels show efficient closed-loop recycling under a waste-mini- mized,resource-conserving,andreproduciblefashionbyfullyutilizing thereactivityofHTmoieties.

ReprogrammingofPHTaerogels
Thematerialpropertiesofapolymerareprimarilydeterminedbyits chemicalcomposition,buttailoringthesecharacteristicsaftersynth- esisremainsasignificantchallenge.Incontrast,theASAprocessoffers auniqueopportunityforon-demandreprogrammingofaerogelfea- turesaftertheirinitialfabrication.Thisreprogrammingprocessclosely resemblestherecyclingprotocol,withthekeydistinctionbeingthe introductionofdifferentaromaticaminesduringtheASAprocessthat induceanalterationofmaterialproperties(Fig.3a).Toexplorethis approach, we selected three distinct aromatic amines: 9,9-bis(4- aminophenyl)fluorene(FDA),N,N-bis(4-aminobenzyl)terephthalamide (BAPTPA), and hexa(aminophenyl)-cyclotriphosphazene (HAPP), to modulatetheaerogel-specificproperties.Forexample,FDAwasused in a NMP solution to partially depolymerize the PHT network by applying 1.5 equivalents of amine functional groups relative to the embedded amine groups. After complete dissolution, an equivalent amount of repeating units in PFA relative to the additional amine functionalgroupswasaddedasa1.6wt%NMPsolution,andthemix- turewasheatedto100°Cfor2.5htoformanorganogel.Theresulting organogelwassolvent-exchangedtoethanolanddriedusingsuper- criticalCO toyieldPHT-B. Following the same procedure,BAPTPA 2 andHAPPwereincorporatedintoPHTaerogelstosynthesizePHT-C andPHT-D,respectively(Fig.3a,bandSupplementaryTableS8).
Compared to PHT-pristine, reprogrammed PHT-B exhibits superior characteristics, such as lower bulk density (<0.13 gcm−3), higher porosity (>90%), larger specific surface area (≈256 m2g−1), larger mesopore volume (0.61cm3g−1), and intrinsic hydrophobicity (Fig. 3c−d, Supplementary Fig. S12a−c, and Supplementary TableS3−6).Bycalculatingtheaverageporediameter,PHT-Bexhibits a much lower average pore diameter (112nm) compared to PHT- pristine(188nm,SupplementaryTableS4).Itsmoreintricatetopology canalsobefoundfromSEM,wheresolidsphericalorhemispherical particles embedded within a necklace-like skeleton were observed (Fig.3e).Notably,PHT-Bachievesasignificantlylowerthermalcon- ductivity(15.9mWm−1K−1)comparedtoPHT-pristine,thusimproving itsthermalinsulationperformance14.Toprobethiseffect,weevaluated boththegaseousandsolidconductivityofPHT-BusingtheKnudsen model(SupplementaryTableS5)16.PHT-Bexhibitsmarkedlyreduced gas-phaseconductivity,arisingfromitssmalleraverageporesizethat amplifies the Knudsen effect, as well as slightly lower solid-phase conductivity. The pore-size reduction stems from the molecular architecture of FDA, whose spiro-carbon moiety disrupts efficient packingduringpolymerization,producingafinelystructuredmicro- porousnetwork17.Inaddition,theincorporationofrigid,non-coplanar spirounitscreatesextrafreevolumeandamoretortuousporenet- work.Thesestructuralfeatureshinderheattransportwithinthesolid framework,furthersuppressingheatconduction18.
AsforPHT-C,weselectedBAPTPAastheaminefeedstock,which was derived from commercial polyethylene terephthalate (PET) bottles19. This amide-containing linker canengage inintermolecular hydrogen bonding within the polymer network, thereby enhancing crosslinkdensityandyieldingamechanicallymorerobuststructure than PHT-pristine20. As anticipated, PHT-C demonstrates a higher compressivemodulus(1.86MPa)andgreatercompressivestrengthat a10%deformationratio(669kPa,SupplementaryFig.S12candSup- plementaryTableS7).Inaddition,PHT-Cretainsitslightweightand highlyporouscharacteristicsalongwithitshighspecificsurfacearea (Fig.3d,SupplementaryFig.S12aandSupplementaryTableS4).PHT-C alsoachieveslowerthermalconductivitycomparedtoPHT-pristine, makingitamoreefficientthermallysuperinsulatingmaterial.
Lastly, HAPP was specifically designed to enhance the thermal stabilityandflameresistanceoftheaerogelPHT-D.Itsstructurefea- tureshexafunctionalaromaticaminemoietiesthatincreasecrosslink density,whilethephosphazeneringservesasanacidandgassource forintumescentflameretardant5,21.AccordingtoTGA,thefabricated PHT-Dshowsasimilardecompositiontemperatureat5%weightloss compared to PHT-pristine and other reprogrammed aerogels, con- firmingtheformationofPHT(SupplementaryFig.S12dandSupple- mentaryTableS7).Ontopofthat,thecharyieldat793°CforPHT-Dis found to be around 40%, surpassing other PHT aerogels, which is contributedbyhighcrosslinkdensityandflameretardantphospha- zenecontent.TofurtherinvestigatetheflameresistanceofPHT-D,we conductedinitialburningtestsbyexposingPHT-Dsampletoanopen flamefor10s(SupplementaryFig.S12eandSupplementaryMovieS1). Duringtheexperiment,therewasnoignitionobservedonPHT-D,and thecombustionofPHT-Dstoppedalmostimmediatelyafterremoving the sample from the fire. After the burning test, PHT-D shows the formation of a char layer on the surface, which inhibited further burningofitsinterior(SupplementaryFig.S12f).Thisvalidatesthatthe introduction of HAPP enhances both thermal stability and flame resistance. Besides, PHT-D exhibits a higher bulk density and lower porosity than PHT-pristine, which contributes to a higher thermal conductivity value of 19.7mWm−1K−1 (Fig. 3d and Supplementary TableS5).WhilethisvalueishighercomparedtootherPHTaerogels, PHT-D still outperforms commercially available thermally insulating materials2,4.Overall,this reprogramming strategy,enabled byrever- siblechemistry,marksasignificantadvancementfororganicaerogels inparticular,andforthebroaderrealmofreconfigurablematerialsin general22,23.

ReprocessingofPHTaerogels
To demonstrate the metathesis of HT moieties within the aerogel network, PHT-pristine was reprocessed by compression molding underthesameconditionsappliedinthemodelreaction.Theuseof heat and pressure facilitated the reshuffling of the covalent bonds, resultingintheformationofanintact,yellow,transparentthermoset- like polymeric film, labeled PHT-E1 (Fig. 4a). Furthermore, we suc- cessfullyrecycledPHT-E1followingourclosed-looprecyclingproto- col,resultinginthecreationofanewaerogelgeneration,labeledPHT- F1(Fig.4b).Todemonstratetheversatilityandreproducibilityofthis process, we fabricated another polymeric film (PHT-E2) and a sub- sequent aerogel generation (PHT-F2) from PHT-F1 using the same procedures(Fig.4c−dandSupplementaryTableS9).
TheformationofPHTwasdeterminedby13CMASNMRspectro- scopy,wherethechemicalshiftsofPHT-E1andPHT-E2areinlinewith thoseofthePHT-pristine(SupplementaryFig.S13a).Itconfirmsthat thechemicalstructureofPHTisfullyretainedandnosignificantside productsareformedduringreprocessingunderheatandpressure.To investigatethemechanicalpropertiesofthecompactthermoset-like films,tensiletestingmeasurementswereconducted(Fig.5aandSup- plementaryTableS10).ItwasobservedthatbothgenerationsofPHT- Essharegreatmechanicalperformancewithtensilestrengthof68MPa andelongationatbreakwithapproximately3.0%.PHT-Esalsoshow hightensilemodulusupto2.2GPa,inlinewithreportedPHT-based cross-linked polymers9,24. Moreover, we performed stress-relaxation experimentsusingarheometertogetfurtherinsightsintothedynamic behavior ofHTmoieties(Fig.5band SupplementaryFig.S13b).The activationenergy(E)fortheHTbondexchangereactionswascalcu- a lated using the Arrhenius equation (Fig. 5c and Supplementary Fig.S13c).Thevalueswerefoundtobe312and263kJ/molforPHT-E1 andPHT-E2,respectively,whicharesignificantlyhigherthanthosefor otherdynamiccovalentbonds25–29.
ThethermalpropertiesofPHT-EsandPHT-Fswereinvestigated using differential scanning calorimetry (DSC), dynamic mechanical thermalanalysis(DMTA),andTGA.ByDSCmeasurements,itisfound that all the generations of thermoset-like films and aerogels share similar glass transition temperature (T ) in the range of 150–160°C g (Fig.5d).ThesevaluesalignwiththeDMTAdata,whichshowthatthe T valuesofPHT-Esfallbetween160–170°C(Fig.5e,Supplementary g Fig.S13d, and Supplementary Table S11). This consistency suggests thatthereprocessingandrecyclingofthermoset-likefilmsandaero- gelsweresuccessfullyperformedwithoutcompromisingthethermal and mechanical properties of the polymer network. TGA measure- mentsalsoshowedsimilardecompositionprofilesfortheaerogelPHT- FsandfilmPHT-Es(Fig.5f).Thedecompositiontemperaturesat5% weight loss indicate the presenceofHT structures in the materials, ratherthanpotentialhemiaminalbyproductswithlowerdecomposi- tiontemperature.ToevaluatetheresistanceofPHT-E1invarioussol- vent media, solvent stability tests wereconducted using a range of proticandaproticsolvents,includingchloroform,n-hexane,acetone, water,ethanol,methanol,acetonitrile,DMF,andDMSO(Supplemen- taryFig.S14).Afterfivedays,thespecimenswereweighed,andthe masschangeswererecorded.Allsamplesdemonstratedexceptional stability in the tested solvents. Notably, the highest swelling ratio (228%)wasobservedinchloroform,indicatingstronginteractionswith thePHTpolymer.Inaddition,thegelfractionsofallspecimenswere calculatedtobeabove91%,confirmingthepolymerstabilityofPHT-E1 (SupplmentaryTableS12).
Theaerogel-specificpropertiesofthereprocessedaerogels,PHT- F1 and PHT-F2, were investigated using various measurements and comparedwithPHT-pristine.AsshownintheradialgraphinFig.5g,all aerogelproperties,includingbulkdensity,porosity,andspecificsur- face area, show similarity across all aerogel specimens. The water contactangleimagesalsoindicatethattheintrinsichydrophobicityis well-preservedthroughouttheprocess(SupplementaryFig.S15).More importantly, the thermal conductivity values of PHT-F1 and PHT-F2 align with those of PHT-pristine, achieving the same standard as thermally superinsulating units. PHT-Fs exhibit similar surface area values, which is further reflected in their nanoscale morphology (Fig. 5h and Supplementary Fig. S13e). In addition, the mechanical propertiesofPHT-FsarecomparabletoPHT-pristine,asindicatedby thesimilarstress-deformationcurves(SupplementaryTableS13and SupplementaryFig.S13f).Thissuggeststhatthepolymerstructureof PHT-Fsremainsmechanicallyrobustevenafterundergoingheatand pressuretreatmentduringhot-pressingexperiments.Overall,wehave successfullydemonstratedthereprocessingofthesehigh- performance PHT aerogels into mechanically robust thermoset-like films, which can readily be converted back into thermally super- insulatingmaterialsasneeded.

Methods
Materials
Hexachlorocyclotriphosphazene,4-acetamidophenol,potassiumcar- bonate, PFA, triazabicyclodecene (TBD), and sodium hydroxide (NaOH)werepurchasedfromMercklifescienceB.V.p-Anisidineandp- phenetidine were purchased from TCI Europe B.V. BAPP, FDA, and 4-aminobenzylamine were purchased from BLD Pharmatech Ltd. Ethanol absolute (EtOH), chloroform, isopropanol, acetone, tetra- hydrofuran (THF), toluene and DMF were purchased from Biosolve B.V.NMPwaspurchasedfromVivochemB.V.DMSO-d 6(99.9%D)and CDCl (99.9% D) were purchased from Cambridge Isotope Labora- 3 tories, Inc. Liquid CO dip tube grade 2.7, nitrogen grade 5.0, and 2 helium grade 4.6 were purchased by Linde Gas Nederland B.V. Amberlyst15hydrogenformwaspurchasedfromSigmaAldrichLtd andusedafterwashedwithdistilledwater.PETbottlewasteisused afterbeingwashedwithisopropanol.

Instrumentation
Nuclear magnetic resonance (NMR) Spectroscopy. The chemical structuresofallchemicalswereidentifiedbyNMRspectroscopyusing aBrukerUltraShieldspectrometer(400MHzfor1HNMR,100MHzfor 13CNMR,161.9MHzfor31PNMR)at25°CusingDMSO-d 6orCDCl 3 as solvent.AllNMRDOSYexperimentswereperformedusingaBruker UltraShield spectrometer (400MHz) at25°Cusing DMSO-d 6 as sol- vent.Typically,avalueof2mswasusedforthegradientduration(δ), 60ms for the diffusion time (Δ), and the gradient strength (g) was variedfrom0.95Gcm−1to46.55Gcm−1in16steps.Eachparameterwas chosen to obtain 95% signal attenuation for the slowest diffusion species at the last step experiment. The pulse repetition delay (including acquisition time) between each scan was larger than 2s. DataacquisitionandanalysiswereperformedusingMestReNova.The T1/T2analysismoduleofTopspinwasusedtocalculatethediffusion coefficientsandtocreatetwo-dimensionalspectrawithNMRchemical shiftsalongonedimensionandthecalculateddiffusioncoefficients alongtheother.Themodelreactionsonthebondexchangereaction of hexahydrotriazine were identified by NMR spectroscopy using a BrukerUltraShieldspectrometer(500MHzfor1HNMR,125MHzfor 13CNMR)at25,65,or100°CusingDMSO-d assolvent.
6

Magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Solid-stateMASNMRspectraweremeasuredusingan 11.7T Bruker NMR spectrometer operating at 125MHz for 13C NMR spectra,respectively.13CMASNMRexperimentswereperformedusing aBrukertriplechannel4mmMASprobeheadspinningat13kHz.13C MASNMRspectrawererecordedusinga13C{1H}crosspolarization (CP) pulse sequence with a ramped contact pulse of 1ms and an interscandelayof3s.NMRchemicalshiftcalibrationsof1Hand13C NMRspectraweredoneusingtetramethylsilane(TMS)andsolidada- mantane,respectively.

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). MALDI-TOF MS of OMeHT and OEtHT were recorded on autoflex® maX, Bruker-MALDI-TOF Mass Spectrometer equipped with a 355nm Nd:YAG smartbeam laser. α- Cyano-4-hydrocycinnamic acid (CHCA) and 2-[(2E)−3-(4-tert-butyl- phenyl)−2-methylprop2-enylidene]malononitrile(DCTB)wereusedas matrices.ThesamplewassolubilizedinTHFofchloroformwithcon- centrationof2mgmL−1.

Gelpermeationchromatography(GPC).GPCmeasurementsofPHT aerogels of dissolution were performed on LC-250C (Shimazu) equippedwithtwoPSSGRAMliner10μmcolumnsandarefractive index(RI)detector.Theaerogelswerefirstlydispersedin0.1MLiBr/ DMF solution at10wt%. After ultrasonicallytreating the solution at 65°Cfor4h,aclearsolutioncanbeobtained.Thesolutionwasthen dilutedinto2mg/mLsolutionby0.1MLiBr/DMFsolution.Later,the solutionwasfilteredwith0.2μmPTFEfilterbeforeanalysis.DMFwas usedastheeluentwithaflowrateof1mL/min,andtheGPCtraceswere calibrated with a PMMA as a standard to calculate the molecular weight.

Scanning electron microscopy (SEM). The morphology of PHT aerogelswerecharacterizedbySEM(FEIQuanta2003D)ataccelera- tionvoltageof10kV.Theaerogelsamplesweresputteredwithgoldfor 40sbeforetesting.PHTaerogelswithsampledimensionsof60mm diameterand5mmthicknesswereused.

Nitrogen physisorption porosimetry. The specific surfacearea and pore size distribution of the aerogels were analyzed by a Brunauer–Emmett–Teller(BET)analyzer(TriStarIIPlus).Beforemea- surement,thesampleswereoutgassedat80 Cfor2hundervacuum conditions.Nitrogengrade5.0andHeliumgrade4.6werechosento measure the physisorption isotherm. PHT aerogels with sample dimensionsof60mmdiameterand5mmthicknesswereused.

Heliumpycnometry.Theporosityandskeletaldensityoftheaerogels were measured by gas pycnometer (AccuPyc II 1345) using Helium grade4.6.10datapointsweretakenwith10equilibriumcycles.PHT aerogels with sample dimensions of 60mm diameter and 5mm thicknesswereused.

Thermogravimetric analysis (TGA). The thermalproperties of PHT aerogelsweremeasuredbyTGA550(TAInstruments)underanitro- genatmosphereattheheatingrateof10°C/minfrom40to793°C. PHTaerogelswithsampledimensionsof60mmdiameterand5mm thicknesswereused.

Differential scanning calorimetry (DSC). DSC measurements were performedonTAQ2000.3–5mgofsampleswereusedinahermenic Tzeropan.Theexperimentswerecarriedoutfrom–50to200°Cata rateof10°C/minunderargonatmosphere.Glasstransitiontempera- tures(Tg)weredeterminedbytakingthemidpointofthereversible endothermofthe2ndheating.

Dynamic mechanical analysis (DMA). The dynamic mechanical measurements were performed on a TA Instruments DMA850. The experimentswerecarriedoutfrom40to200°Cataheatingrateof 3°C/minunderanoscillatorystrainof0.01%andafrequencyof1Hz. Theglasstransitiontemperature(T )wasrecordedasthemaximum g valueoftanδ.

Stress-relaxationanalysis.Stress-relaxationanalysiswasperformed onaTAInstrumentsHR20.Therelaxationmodulus(G(t))wasfollowed overdifferenttimeperiodsforaconstantappliedstrainof1%atthe constanttemperature(from190to170°C).Therelaxationmodulus (G)wasnormalizedbytheinitialvalue(G ). 0.1s
The activation energy (E) of the bond exchange reaction was a furthercalculatedusingtheArrheniusequation:
τ*ðTÞ=τ oexpðE a =RTÞ ð1Þ
whereτ*istherelaxationtimedeterminedviamodulusrelaxationto1/ e;τ isthecharacteristicrelaxationtimeatinfinitetemperature;E is 0 a the experimental activation energy (kJ/mol); R is the universal gas constant(8.314JK–1mol–1);andTistheabsolutetemperature(K).

Thermalconductivitytest.Thethermalconductivitywasmeasured by heatflow meter (Thermtest Inc., HFM-25) at 20°C and 20−30% humidityaccordingtoASTMC518internationalstandard.PHTaero- gelswithsampledimensionsof60mmdiameterand5mmthickness wereused.Priortothemeasurement,themachinewascalibratedwith EPS1450Easreferencematerial.

Wateruptaketest.Priortotesting,PHTaerogelspecimenswith15mm thicknessand25mmdiameterwereplacedin80°Cvacuumovenfor 2h.Themassofasamplewasdeterminedbeforeandaftersubmerging it completely under distilled water for 24h. The water uptake was calculatedaccordinglyinrelationtotheweightofthesample.

Contactangletest.Thehydrophobicityoftheaerogelswasstudiedby acontactangleanalyzer(Data-PhysicsOCA30)atrelativehumidityof 40%.PHTaerogelswithsampledimensionsof60mmdiameterand 5mmthicknesswereused.

Uniaxialcompressiontest.Uniaxialcompressiontestwasconducted by compression testing machine (ZwickRoell Materials Testing Machine, Zwicki Z2.5/TN). PHT aerogels with sample dimensions of 25mmdiameterand15mmthicknesswereused.

Solventresistance measurements. Solvent resistanceand gel con- tentofPHTfilmswereinvestigated.Priortothemeasurements,the specimensweredriedinavacuumovenat80°Cfor2h.Thesamples with5mmthicknessand30mgweightwerecutandweighed(m ).The 0 sampleswerethenplacedintovialscontainingdifferentorganicsol- vents,including,chloroform,n-hexane,acetone,distilledwater,etha- nol, methanol, acetonitrile, dimethylformamide, and dimethylsulfoxide.Thesolutionswerekeptatroomtemperature.The appearancesofthesolutionswererecordedbydigitalcameraafter24, 48,and120h.After120h,thesamplesweretakenoutfromvials,and theresidualsolventontheirsurfacewaswipedoffbeforeweighing (m)thesamples.Finally,thesamplesweredriedinavacuumovenat s 80°Covernight,andthemassofthedriedsampleswasweighed(m ). d Theswellingratioandgelcontentwerecalculatedasfollowingequa- tions:
Swellingratio=ðm s (cid:2)m o Þ=m o×100% ð2Þ
Gelcontent=m d =m o ×100% ð3Þ

InvestigationofbondexchangereactionbetweenOMeHTandp- anisidineusing1HNMRspectroscopy
OMeHT(10.0mg,0.025mmol)andp-anisidine(13.7mg,0.111mmol, 4.5eq.)weredissolvedin1.0mLofDMSO-d .Thesolutionwasthen 6 transferredintoanNMRtubeandsealedwithaseptumcap.Subse- quently,theNMRtubewasplaceddirectlyintotheNMRmachine,and measurementswereinitiatedpromptly.1HNMRspectrawereacquired at 65°C, with readings taken at 20-minute intervals, employing 32scanspertimepoint.Atotalof13spectraweretakenatareaction time of 4h (Supplementary Fig. S1b). After the first reaction was completed,thetemperaturewasraisedto100°C.Asolutionofpar- aformaldehyde(3.35mg,0.111mmol)in0.1mLofDMSO-d wasadded 6 to the same NMR tube. The 1H NMR measurements were started promptly at 100°C for 4hours, with readings taken at 20-minute intervals,employing32scanspertimepoint(SupplementaryFig.S1c). After24hoftheendofthereaction,the1Hand13CNMRmeasurements weredoneat25°C(SupplementaryFig.S3).

Pristinepolyhexahydrotriazineaerogelsynthesis(PHT-pristine)
The PHT organogel was prepared by mixing components A and B. ComponentAconsistsof2.29gBAPPdissolvedin11.3gNMP,while component B consists of 0.34g PFA dissolved in 11.2g NMP. Both componentswerepreparedinaPPvialbydissolvingtheminNMPat 100°C.Thegellingwasinitiatedbymixingthetwocomponentsinto one vial at 100°C. The mixture was shaken until a homogeneous solution was obtained. The solution was poured into a PP vial with 70mm diameter, and was then placed in an oven at 100°C until gelationwascompleted.Afterwards,theorganogelwassealedandlet agingfor24hunderambientcondition.Afteraging,theorganogelwas placedinasolventbath(300mL)forsolventexchange.Theoriginal solventwaswashedoutbyexchangingthesolventtwice,24heach time,with0.1Msodiumhydroxide,distilledwater,andethanol.The ethanol-saturatedgelwasthentransferredtoanautoclave,submerged inethanol,andsealedinasupercriticalfluid-extractionautoclave.The pressurewasmaintained at 100bar and the temperature was main- tainedabove60°CwiththeconstantinflowofCO 2 .Themixtureof solvent and CO 2 was vented out multiple times during the drying processwhilewithstandingthepressureandtemperature.Theaerogel wasthenstoredinanitrogenovenat80°Cfor2htoensurecomplete removalofthesolvent.Thedriedsamplewasstoredinadesiccator chamberwithrelativehumidityof30%topreventpossiblemoisture uptake.

RecoveryofthesolventusedduringPHT-pristinesynthesis
The solvents used during the solvent exchange step of the PHT- pristine synthesis were collected and processed for recovery. The combinedsolventmixturewasfirstsubjectedtodistillationat80°Cto recoverethanol.Followingethanolseparation,theremainingmixture wasneutralizedusinganion-exchangeresin(Amberlyst15)toremove residual sodium ions. After neutralization, the solvent mixture was distilledat110°CtosequentiallyseparatewaterandNMP.Therecov- eredfractionsofethanol,water,andNMPwerecollectedforfurther characterization, and the recovery yields were calculated (Supple- mentaryFig.S6andSupplementaryTableS1).

InvestigationofPHT-pristinedepolymerizationprocess
PHT-pristinewasgrindedandkeptinthedesiccatorbeforeuse.DMF was selected as the solvent for PHT depolymerization due to its compatibilitywithMALDI-TOFandGPCmeasurements,asitdoesnot interferewithmassspectrometryanalysisandservesasaneffective eluentinGPC.Firstly,1.05gofPHT-pristinewasaddedtoavialanda BAPP(1.48g)solutioninDMF(9g)wasaddedtotheaerogelpowder. Thevialwassealedwithparafilmandultrasonicatedat65°Cfor4h untilfullissolution.ForNMRmeasurement,0.1mLoftheclear solution was taken out, and 0.4mL of DMSO-d 6 was added to the solution.ThesolutionwasanalyzedwithseveralNMRmeasurements, including1H,1HCOSY,13CDEPT,and1HDOSYNMR(Supplementary Figs.S9–11).

PHTaerogelclosed-looprecycling
The protocol is divided into two parts: depolymerization and re- gelation.

Depolymerization.PHT-pristineorPHT-A1weregrindedandkeptin the desiccator before use. Certain amount of aerogel powders was addedtothevial(thedetailedformulationisshowninSupplementary TableS3).ThePHTaerogelpowderswerepartiallydepolymerizedby addinga14wt%BAPPsolutioninNMP,equivalentto1.5timestheBAPP content in the aerogel. After the addition, the vial was sealed with parafilmandultrasonicatedfor4huntilfulldissolution.

Re-gelation. After full dissolution of the mixture is achieved, the solutionwasplacedin100°CovenalongwithPFAdissolvedinNMP solution.Thegellingwasinitiatedbymixingthetwocomponentsinto onevial.Themixturewasshakenuntilahomogeneoussolutionwas obtained.ThesolutionwaspouredintoeitheraPPmoldwitha70mm diameteroraPPcontainerwitha26mmdiameterandwasplacedin the100°Covenfor4huntilgelation.Afterwards,theorganogelwas sealed and aged for 24h under ambient condition. After aging, the organogelwasplacedinasolventbath(300mL)forsolventexchange. Theoriginalsolventwaswashedoutbyexchangingthesolventtwice, 24h each time, with 0.1M sodium hydroxide, distilled water, and ethanol.The ethanol-saturated gel wasthen transferred to anauto- clave, submerged in ethanol, and sealed in a supercritical fluid- extractionautoclave.Thepressurewasmaintainedat100barandthe temperaturewasmaintainedabove60°Cwiththeconstantinflowof CO .ThemixtureofsolventandCO wereventedoutmultipletimes 2 2 duringthedryingwhilewithstandingthepressureandtemperature. Theaerogelwasthenstoredinanitrogenovenat80°Cfor24hto ensurecompleteremovalofthesolvent.Thedriedsamplewasstored in a desiccator chamber with relative humidity of 30% to prevent possiblemoistureuptake.ThedetailedformulationisshowninSup- plementaryTableS3.

PHTaerogelsreprogramming
The protocol is divided into two parts: depolymerization and re- gelation.

Depolymerization.PHTaerogelsweregrindedandkeptinthedesic- catorbeforeuse.Certainamountofaerogelpowderwasaddedtothe vial(thedetailedformulationsareshowninSupplementaryTableS8). ThePHTaerogelpowderswerepartiallydepolymerizedbyaddingthe respectiveaminesolutionsinNMP(themolarcontentofaminefunc- tionalitiesinthesesolutionsisequivalentto1.5timesthemolarcon- tent of amine groups of BAPP embedded in the aerogel). After the addition,thevialwassealedwithparafilmandultrasonicatedfor4–8h untilfulldissolution.

Re-gelation. After full dissolution of the mixture was achieved, thesolutionwasplacedin100°CovenalongwiththePFAsolution in NMP. The gelling was initiated by mixing the two components into one vial. The mixture was shaken until a homogeneous solutionwasobtained.ThesolutionwaspouredintoeitherPPmold witha70mmdiameterorPPcontainerwith26mmdiameter,andwas placed in the 100°C oven for 0.5 to 4h untilgelation. The formed organogelwassealedandletagedfor24hunderambientcondition. After aging,theoriginalsolventwaswashed outbyexchangingthe solventtwice,24heachtime,with0.1Msodiumhydroxide,distilled water,andethanol.Theethanol-saturatedgelswerethentransferred to an autoclave, submerged in ethanol and sealed ina supercritical fluid-extraction autoclave. The pressure was maintained at 100bar, andthetemperaturewasmaintainedabove60°Cwiththeconstant inflowofCO .ThemixtureofsolventandCO wereventedoutmul- 2 2 tiple times during the drying while withstanding the pressure and temperature.Theaerogelwasthenstoredinanitrogenovenat80°C for24htoensurecompleteremovalofthesolvent.Thedriedsample wasstoredinadesiccatorchamberwitharelativehumidityof30%to preventpossiblemoistureuptake.Thedetailedformulationisshown inSupplementaryTableS8.

InvestigationofbondexchangereactionbetweenOMeHTand OEtHTviahot-pressingexperiment
OMeHT(10mg,4.06mmol,1eq.)andOEtHT(9mg,4.06mmol,1eq.) weremixedandplacedbetweentwoaluminumplates.Theexperiment was performed by hot-pressing the aluminum plates with a 12MPa pressure at 180°C for 0.5h, followed by an increasing pressure of 40MPaat180°Cfor0.5h.Thelightyellowpastewasobtainedand usedforfurthercharacterizations.

PHTaerogelsreprocessing
ThePHT-pristineorPHT-F1werechoppedintosmallpieces.Repro- cessing was performed by hot-pressing the chopped pieces with a 12MPapressureat180°Cfor0.5h,followedbyincreasingpressureof 40MPa at 180°C for 0.5h. A compression mold with dimension of 5×5cm wasused. The yielding polymer film (PHT-Es)was used for further characterizations. The protocolof PHT-Fs synthesis was fol- lowedbytheprocedureofPHTaerogelclosed-looprecycling.Instead ofusingPHT-pristineorPHT-A1asstartingmaterials,choppedpieces ofPHT-E1orPHT-F1wereutilized.Thedetailedformulationisshownin SupplementaryTableS9.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript presents a concept of utilizing hexahydrotriazine (HT) structures in recyclable and reprogrammable aerogels and thermosets. However, there are areas where the novelty and scientific impact can be improved. Although the manuscript claims that the HT structure represents a breakthrough in the field of polymer recycling. However, numerous studies have already reported the use of azines as a dynamic covalent functional group. The protocol for preparing dynamic aerogels described in this manuscript may not meet this journal's novelty requirements.\n(1) The manuscript only provides qualitative observational data (e.g., NMR spectra) but lacks quantitative evaluation of the dynamic bond exchange process efficiency. It is recommended to introduce more rigorous quantitative analytical methods for assessing the efficiency of dynamic exchange processes. Specific approaches may include: monitoring the depolymerization degree over time, calculating the yield of soluble oligomers, and measuring the repolymerization efficiency to ensure the majority of the original material is retained.\n(2) The testing section describes the dynamic exchange reactions but does not sufficiently explore the kinetic characteristics of these reactions. The authors are advised to incorporate a discussion on the kinetics of HT bond exchange reactions, with particular attention to key factors such as exchange rates under varying conditions (e.g., temperature, pressure, or amine concentration). This would contribute to a more in-depth understanding of the reaction speed and its controllability.\n(3) The manuscript demonstrates the successful recycling performance of PHT aerogel over two cycles, but it does not address potential performance variations or limitations after multiple cycles. It is recommended to supplement the discussion with test results from a broader range of cycles (e.g., 5–10 cycles) to evaluate the long-term reproducibility and stability of the dynamic exchange reaction.\n(4) Although the manuscript hints at the potential applications of HAT chemistry in self-healing materials and vitrimer networks, it lacks sufficient detail or experimental data to substantiate these claims. Additional experimental validation of HAT structures in application scenarios such as self-healing materials and vitreous networks should be provided, or such speculative statements should be removed. If the intention is to propose future research directions, their prospective nature should be explicitly indicated and supported by relevant literature citations.", "reviewer_2": "My report is attached in MSWord and PDF.", "reviewer_3": "The manuscript presents an innovative and potentially impactful study on the dynamic covalent behavior of hexahydrotriazine (HT) and its application in fully recyclable aerogels and thermosets. The discovery that HT units can undergo transamination and metathesis reactions under mild conditions opens up new avenues for designing circular polymeric materials. The proposed aerogel-to-sol-to-aerogel (ASA) strategy is compelling and aligns well with the current demand for sustainable materials. However, while the manuscript demonstrates a high level of technical rigor and novelty, several key aspects require clarification, additional data, and better articulation before it can be considered for publication. I recommend major revision.\n1. The manuscript claims unprecedented dynamicity of HT structures, but lacks detailed mechanistic discussion. The authors should provide deeper insights—ideally supported by theoretical calculations (e.g., DFT)—into the activation energy, reaction pathway, and reversibility under realistic conditions.\n2. Only two ASA recycling cycles are presented. For a truly circular material platform, a more extensive demonstration (e.g., ≥10 cycles) is necessary to validate long-term recyclability and performance retention.\n3. Although the authors claim \"waste-free\" and \"100% of the initial chemical resources remained,\" no quantitative mass balance or recovery yield data are provided. Please include such data to support this strong claim\n4. Although the complex reaction between HTs is considered to be reversible, are there irreversible structures such as secondary condensation and cross-linking densification (e.g., C-C bonding or excessive cross-linking) under hot-pressing conditions, and can these structures be recovered by ASA? Can the authors further confirm this by techniques such as FTIR and XPS?\n5. What are the influence patterns of other types of amine substances on the efficiency of ASA and product performance? Can it replace the above-mentioned aniline raw materials?\n6. The SEM image only shows the local morphology. It is recommended to add TEM or gas pore size distribution map (such as BJH method) to describe the microstructure of the above sample more comprehensively.\n7. NMP is a known hazardous solvent, and its reuse has raised concerns about sustainability. Please discuss potential alternatives or provide reasons for choosing NMP in the context of green chemistry.\n8. Many material property data (for example, surface area, thermal conductivity) have no error lines or statistical significance. Please add the standard deviation and repeat the measurement where applicable.\n9. Although the thermal conductivity of aerogel is low, does its performance decline in a humid environment? Its long-term stability under humidity, mechanical cycling or ultraviolet radiation should be evaluated. At least the moisture resistance after multiple cycles should be tested and reported.\n10. The article points out that the thermal conductivity and mechanical strength can be adjusted by different aromatic amines, but the correlation between the microscopic pore structure and the molecular structure has not been established in detail. Why can the spiro structure of the FDA increase the specific surface area? Can the structural differences of pores at different scales be verified through PALS, BET or SAXS systems?\n11. At present, new materials are synthesized only based on different amines, but do different crosslinking degree networks have an inhibitory effect on the reactivity of ASA? A denser network may lead to difficulties in disaggregation."}, "author_response": "We would like to express our sincere gratitude to you and the reviewers for their time and effort in evaluating our manuscript. We greatly appreciate the insightful comments and suggestions provided. After carefully reviewing the feedback, we have revised the manuscript accordingly to enhance its quality and align it with the expectations of the readership of Nature Communications. We have addressed all the reviewers’ comments in a point-by-point reply, performed several additional experiments as requested, and made corresponding changes to the manuscript and the Supporting Information. These revisions are highlighted in yellow in the revised manuscript for your convenience.\nDuring the revision process, we also recognized that some terminology in our original submission required clarification. In particular, the terms “dynamic covalent chemistry” and “dynamicity” were not always used with complete accuracy. Since dynamic covalent chemistry applies only to the metathesis reactions of hexahydrotriazine (HT) structures, but not to the irreversible reactions with amines, we now limit the use of this term exclusively to metathesis processes. Accordingly, we have revised the title and relevant sections of the manuscript to avoid the term “dynamicity”. Furthermore, we determined that “aminolysis” more accurately describes the reaction with amines than “transamination”, and we have updated the manuscript accordingly. These terminology changes are highlighted in blue. We went carefully through the Reviewer 1’s comments and addressed them point-by-point.\n[... Author response continues for all reviewers ...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised manuscript have been much improved and I recommend it for publication in Nature Communications.", "reviewer_2": "Please see attachment entitled: Leventis Second Review of the Tomovic manuscript.docx", "reviewer_3": "The revised manuscript can be accepted."}, "author_response": "We would like to express our sincere gratitude to the editorial team and reviewers for their time and effort in evaluating our manuscript. We greatly appreciate the thoughtful feedback and insightful suggestions provided throughout the review process.\nIn response to the editorial guidance and the final reviewer comments, we have carefully revised the manuscript to align with the standards and expectations of Nature Communications. Specifically, we have addressed the editorial requests outlined in the Author Checklist and incorporated the final recommendation regarding the use of the term “thermoset.” As suggested, we have revised the language to describe our materials as “thermoset-like films” or “cross-linked polymeric film”.\nWe have also updated the manuscript accordingly, with all changes highlighted in yellow for ease of review. We believe these final revisions fully address the remaining concerns and further strengthen the clarity and impact of our work. We hope the revised version meets the journal’s requirements and will be of broad interest to the Nature Communications readership."}]

Decision letter