cm052391s

EpoxyResin/PolyurethaneHybridNetworksSynthesizedbyFrontal

Polymerization

SuChen,*YuanTian,LiChen,andTingHu

CollegeofChemistryandChemicalEngineeringandKeyLaboratoryofMaterial-OrientedChemicalEngineeringofJiangSuProVinceandMOE,NanjingUniVersityofTechnology,No.5XinMofanRoad,

Nanjing210009,People’sRepublicofChina

ReceiVedOctober31,2005.ReVisedManuscriptReceiVedFebruary23,2006

Wereportthefirstsynthesisoftheepoxyresin/polyurethane(EP/PU)hybridnetworksviafrontalpolymerization(FP).Inatypicalrun,theappropriateamountsofreactants(poly(propyleneoxideglycol),epoxyresindiglycidyletherofbisphenolA,2,4-toluenediisocyanate,and1,4-butanediolwithstannouscaprylate(asthecatalyst))weremixedtogetheratinitialtemperatureinthepresenceoftoluene(asthesolvent).FPwasthermallyignitedatoneendofthetubularreactor,andtheresultanthotfrontspropagatedthroughoutthereactionvessel.Onceinitiated,nofurtherenergywasrequiredforpolymerizationtooccur.Thedependenceofthefrontvelocityandfronttemperatureonthecatalystconcentrationwasthoroughlyinvestigated.ThesampleswerecharacterizedwithaFouriertransforminfraredspectrometer,thermo-gravimetricanalysis,andascanningelectronmicroscope.EP/PUhybridnetworkssynthesizedbyFPhavethesamepropertiesasthosesynthesizedbybatchpolymerization,buttheFPmethodrequiressignificantlylesstimeandlowerenergyinput.

Introduction

Interestinfrontalpolymerization(FP)hasincreasedinrecentyearssinceFPbecameapromisingnewtechniqueforsynthesizinguniformpolymersandpolymericnetworksinarapidfashion.FPisamodeofconvertingamonomerintoapolymerviaalocalizedreactionzonethatpropagatesthroughaliquidmonomer(Figure1a).Firstintroducedasawaytosynthesizepoly(methylmethacrylate)athighpressurebyChechiloetal.in1972,1thismethodwaslaterextendedbyPojmanandco-workerstoperformalargenumberofexperimentalandtheoreticalworks.2-7

Anoverwhelmingmajorityofworkhasbeenfocusedonfree-radicalpolymerizationbecauseitisusuallyhighlyexothermic,andtheheatofthereactionprovidesautoca-talysisforapolymerizationfrontpropagatingthroughaliquidmonomer.Subsequently,Pojmanandco-workershavedonealotofworkfocusingonthefeasibilityoftravelingfrontsinsolutionsofthermalfree-radicalinitiatorsinavarietyofneatmonomersatambientpressureusingliquidmonomers8,9orasolidmonomer.10,11Theavailabilityoftheirpreparation

*Towhomcorrespondenceshouldbeaddressed.E-mail:yahoo.com.cn.

prcscn@

Figure1.Schematicrepresentationof(a)FPoccurringalongatubularreactorand(b)BPoccurringinareactionkettle.

techniquesallowstravelingfrontsinsolutionsofathermalfree-radicalsystematambientpressurewithoutremovinginitiatorsfrommonomers;thus,longerpotlivescanbeachievedforthelatter.FurtherdevelopmentoftheFPawaitedthediscoveryofothersuitablemonomersthatdidnotboilatthefronttemperatureforthestablefront.Severalresearchersrecentlystudiedfrontalcopolymerization12andUV-inducedFPofmultifunctionalacrylatemonomers.13Themethodwasalsoeffectivelyappliedtoepoxyresinsandtheirinterpenetratingpolymernetworks(IPNs).14,15Pojmanetal.16reportedonepoxy-acrylatebinarysystems.Begishevet

(9)Pojman,J.A.;Craven,R.;Khan,A.;West,W.J.Phys.Chem.1992,

96,7466.

(10)Pojman,J.A.;Nagy,I.P.;Salter,C.J.Am.Chem.Soc.1993,115,

11044.

(11)Fortenberry,D.I.;Pojman,J.A.J.Polym.Sci.,PartA:Polym.Chem.

2000,38,1129.

(12)Perry,M.F.;Volpert,V.A.;Lewis,L.L.;Nichols,H.A.;Pojman,J.

A.Macromol.TheorySimul.2003,12,276.

(13)Nason,C.;Roper,T.;Hoyle,C.;Pojman,J.A.Macromolecules2005,

38,5506.

(14)Arutiunian,K.A.;Davtyan,S.P.;Rozenberg,B.A.;Enikolopyan,

N.S.Dokl.Akad.NaukSSSR1975,223,657.

(15)Chekanov,Y.;Arrington,D.;Brust,G.;Pojman,J.A.J.Appl.Polym.

Sci.1997,66,1209.

(16)Pojman,J.A.;Griffith,J.;Nichols,H.A.e-Polymers2004,13,1.

(1)Chechilo,N.M.;Khvilivitskii,R.J.;Enikolopyan,N.S.Dokl.Akad.

NaukSSSR1972,204,1180.

(2)Davtyan,S.P.;Surkov,N.F.;Rozenberg,B.A.;Enikolopyan,N.S.

Dokl.Phys.Chem.1977,232,.

(3)Davtyan,S.P.;Gel’man,E.A.;Karyan,A.A.;Tonoyan,A.O.;

Enikolopyan,N.S.Dokl.Phys.Chem.1980,253,579.

(4)Enikolopyan,N.S.;Kozhushner,M.A.;Khanukaev,B.B.Dokl.Phys.

Chem.1974,217,676.

(5)Surkov,N.F.;Davtyan,S.P.;Rozenberg,B.A.;Enikolopyan,N.S.

Dokl.Phys.Chem.1976,228,435.

(6)Pojman,J.A.;Willis,J.;Fortenberry,D.;Ilyashenko,V.;Khan,A.J.

Polym.Sci.,PartA:Polym.Chem.1995,33,3.

(7)Pojman,J.A.;Curtis,G.;Ilyashenko,V.M.J.Am.Chem.Soc.1996,

118,3783-3784.

(8)Pojman,J.A.J.Am.Chem.Soc.1991,113,6284.

10.1021/cm052391sCCC:$33.50©2006AmericanChemicalSociety

PublishedonWeb03/18/2006

2160Chem.Mater.,Vol.18,No.8,2006

Scheme1.FormationofEP/PUHybridNetworksSynthesizedbyFPorBP

Chenetal.

al.17,18studiedfrontalanionicpolymerizationofe-caprolac-tam,andFiorietal.19producedpolyacrylate-poly(dicyclo-pentadiene)networksfrontally.FPhasbeenusedtoprepareanumberofpolymermaterials.20-23Pojmanetal.24preparedthermochromiccompositeswhosecolorwastemperaturedependentviaFP.Szalayetal.25reportedconductivecompositespreparedfrontally.Vicinietal.26developedaFPmethodfortheconsolidationofstone.FioriandMariani27preparedpolyurethanes(PUs)byusing1,6-hexamethylenediisocyanateandethyleneglycolfrontallyanddemonstratedfrontalring-openingmetathesispolymerization.28Recently,Chenetal.29-31reportedthatsegmentedPUandPU-nanosilicahybridsweresynthesizedwithFP.ItprovidedafeasiblewaytouseFPtocommerciallysynthesizePUswithlessenergyandlesscostthanthoseoftraditionalbatchpolymerization(BP;seeninFigure1b).

PUsprovideawiderangeofpropertiesfromavarietyofstartingmaterials.Tailor-madepropertiesofthesematerials

(17)Begishev,V.P.;Volpert,V.A.;Davtyan,S.P.;Malkin,A.Y.Dokl.

Akad.NaukSSSR1973,208,2.

(18)Begishev,V.P.;Volpert,V.A.;Davtyan,S.P.;Malkin,A.Y.Dokl.

Phys.Chem.1985,279,1075.

(19)Fiori,S.;Mariani,A.;Ricco,L.;Russo,S.e-Polymers2002,29,1.(20)Kim,C.;Teng,H.;Tucker,C.L.;White,S.R.J.Comput.Mater.

1995,29,1222.

(21)Pojman,J.A.;Elcan,W.;Khan,A.M.;Mathias,L.J.Polym.Sci.,

PartA:Polym.Chem.1997,35,227.

(22)Chekanov,Y.A.;Pojman,J.A.J.Appl.Polym.Sci.2000,78,2398.(23)Washington,R.P.;Steinbock,O.J.Am.Chem.Soc.2001,123,7933.(24)Nagy,I.P.;Sike,L.;Pojman,J.A.J.Am.Chem.Soc.1995,117,

3611.

(25)Szalay,J.;Nagy,I.P.;Barkai,I.;Zsuga,M.Angew.Makromol.Chem.

1996,236,97.

(26)Vicini,S.;Mariani,A.;Princi,E.;Bidali,S.;Pincin,S.;Fiori,S.;

Pedemonte,E.;Brunetti,A.Polym.AdV.Technol.2005,16,293.(27)Fiori,S.;Mariani,A.Macromolecules2003,36,2674.

(28)Mariani,A.;Fiori,S.;Chekanov,Y.;Pojman,J.A.Macromolecules

2001,34,6539.

(29)Chen,S.;Sui,J.J.;Chen,L.Colloid.PolymSci.2005,283,932.(30)Chen,S.;Sui,J.J.;Chen,L.;Pojman,J.A.J.Polym.Sci.,PartA:

Polym.Chem.2005,43,1670.

(31)Chen,S.;Feng,C.;Sui,J.J.ActaPolym.Sin.2005,1,1.

canbeobtainedfromwell-designedcombinationsofmon-omericmaterials.Onamolecularbasis,PUmaybedescribedasthelinearstructureblockcopolymerofthe(AB)ntype.PartA,thehardsegment,iscomposedofoligomers,whicharepreparedbythereactionofalowmolecularweightdiolortriolchainextenderwithdiisocyanate.PartB,thesoftsegment,isnormallyapolyesterandapolyetherpolyolwithamolecularweightof1000-3000.32ToimprovetheperformancepropertiesofPUsinvariousapplications,hybridPUnanocomposites33-36andmultiphasepolymericsystemssuchasIPNs37-39havebeenextensivelyusedformorethanthreedecades.Inthispublication,wedescribehowweproducedepoxyresin/PUhybridnetworksusingFP.Inatypicalrun,theappropriateamountsofreactants(poly-(propyleneoxideglycol)(PPG),epoxyresindiglycidyletherofbisphenolA(E44),2,4-toluenediisocyanate(TDI),1,4-butanediol(BD),andstannouscaprylate(asthecatalyst))weremixedtogetherataninitialtemperatureinthepresenceoftoluene(asthesolvent).FPwasthermallyignitedatoneendofthetubularreactor,andtheresultanthotfrontspropagatedthroughoutthereactionvessel.Nofurtherenergywasrequiredforpolymerizationtooccur.Theschematicsynthesisofepoxyresin(EP)/PUhybridnetworksispresentedinScheme1.40Wedeterminedtheeffectfactorsoffrontvelocity,stannouscaprylateconcentration,and

(32)(33)(34)(35)(36)(37)(38)(39)(40)

Chen,T.K.;Tien,Y.I.;Wei,K.H.Polymer2000,41,1345.Goda,H.;Frank,C.W.Chem.Mater.2001,13,2783.Tien,Y.I.;Wei,K.H.Macromolecules2001,34,9045.

Phadtare,S.;Kumar,A.;Vinod,V.P.;Dash,C.;Palaskar,D.V.;Rao,M.;Shukla,P.G.;Sivaram,S.;Sastry,M.Chem.Mater.2003,15,1944.

Chen,S.;Sui,J.J.;Chen,L.ColloidPolym.Sci.2004,283,66.Titier,C.;Pascault,J.P.;Taha,M.;Rozenberg,B.J.Polym.Sci.,PartA:Polym.Chem.1995,33,175.

Chen,J.;Pascault,J.P.;Taha,J.J.Polym.Sci.,PartA:Polym.Chem.1996,34,28.

Chen,T.H.;Li,H.S.;Gao,Y.;Zhang,M.L.J.Appl.Polym.Sci.1998,69,887.

AnandPrabu,A.;Alagar,M.Prog.Org.Coat.2004,49,236.

EpoxyResin/PolyurethaneHybridNetworkstemperatureontheFP,alongwithcomparisonofFPwithBP.

ExperimentalSection

Materials.PPG(hydroxylnumberof56mgKOH/g,averagemoleculeweightof2000)wasacquiredfromDowCo.TheE44([epoxyvalue])0.41-0.47equiv/100g),stannouscaprylate,TDI,BD,andtolueneweresuppliedbyAldrichandusedasreceived.FP.ForthesynthesisoftheEP/PUhybridnetworksbyFP(showninFigure1a),theappropriateamountsofE44,TDI,PPG,BD,andstannouscaprylate(asthecatalyst)weremixedtogetheratambienttemperatureintolueneinaflask.AtypicalmolarcompositionwasTDI/PPG/BD)2.8:1:1mol/mol.Theflaskwasshakenvigorouslytoobtainahomogeneousmixture.Then,thesolutionwaspouredintoa10mL(D)15mm)testtube,andaK-typethermocouple,connectedtoadigitalthermometer,wasutilizedtomonitorthetemperaturechange.Thejunctionwasimmersedatabout1.0cmfromthefreesurfaceoftheliquid.Theupperlayerofthemixturewasthenheatedbyasolderingironbaruntiltheformationofahotpropagatingfront.

Thefrontvelocitiesweredeterminedbymeasuringthedistancethatthefronttraveledasafunctionoftime.WhenpureFPoccurred,aconstantvelocityfrontpropagatedwithalmostnobubbles.Temperatureprofilesandthemaximumtemperature(Tmax)ofthefrontweremeasuredbyusingaK-typethermocouplebymeasuringthetemperatureatafixedpointasafunctionoftime.Subsequently,theywereconvertedtospatialprofilesusingthefrontvelocity.BP.SeveralbatchrunshadbeenperformedtocomparetheresultantsampleswiththecorrespondingonesobtainedbyFP.Inatypicalrun,thesameamountsofeachcomponentasquotedaboveweremixedwithvigorousstirringinareactionvesselandimmersedinathermostaticoilbathsetat85°Cfor3h.Thenthemixturewascooledbacktoambienttemperatureandstirredfor1h.

Characterization.ThechemicalstructureofEP/PUhybridnetworkswasanalyzedbyFouriertransforminfrared(FT-IR)spectroscopyintherange450-4000cm-1usinganAVATAR-360(KBrdisk,scans,4cm-1resolution).TheweightlossoftheEP/PUhybridnetworksonheatingwasstudiedbythermo-gravimetricanalysis(TGA)usingathermogravimetricapparatusShimadzu-TGA50inanitrogenatmosphere.Measurementsweretakenwithaheatingrateof10°C/minfrom30to600°C.ThesurfacemorphologyofEP/PUhybridnetworkscoatedwithAuwasinvestigatedbyscanningelectronmicroscopy(SEM)usingaQUANTA200.SEMsampleswerepreparedbyapplyingdropsofhybridsontohotaluminumSEMstubs,followedbydryingatambienttemperature.

ResultsandDiscussion

PreliminaryExperiments.WehaveperformedseveralpreliminaryexperimentstofindasuitablerouteforobtainingPUbyFP.29Usually,thepotlifeisanimportantfactorforFP.Weevaluatedthepotlifeviamixingthereactants,leavingthematambienttemperature,andvisuallydetermin-ingatwhattimetheycouldspontaneouslypolymerized.Onthebasisofthispoint,weemploythesamemethodtoexaminethepotlifeinpreparingEP/PUhybridnetworksbyFP.WefoundthatasolutionofE44,PPG,BD,TDI,stannouscaprylate([NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol,[catalyst]/[TDI])1.0×10-3mol/mol),andtoluene(10wt%)exhibitedapotlifeofmorethan3hattheambienttemperature(30°C),andinstantaneousspon-taneouspolymerization(SP)doesnotoccur.Somelitera-

Chem.Mater.,Vol.18,No.8,20062161

Figure2.Frontpositionvstimefortypicalruns(a-d).(a)PurePUpreparedbyFP,[NCO]/[OH])1.4:1mol/mol;[catalyst]/TDI])1.0×10-3mol/mol;toluene)10wt%.(b)EP/PUhybridnetworkspreparedbyFP,E44)5wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(c)EP/PUhybridnetworkspreparedbyFP,E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(d)EP/PUhybridnetworkspreparedbyFP,E44)15wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.

ture27,41reportedthatanextendedpotlifeinthesynthesisofPUscanbeachievedbyaddingsuitableamountsofadditive(pyrocatechol)todepressstheactivityofdibutyltindilaurate(DBTDL,asthecatalyst)atambienttemperature.However,bypyrocatecholadditionapotlifecouldbeonlyachievedto25min.WehavefoundthatstannouscaprylatecatalystisbetterthanDBTDLforpreparingPUbyFP.Itcanbeattributedtothefactthatthecatalyst,stannouscaprylate,hastheloweractivitythanthatofDBTDL,42whichcouldobtainalongerpotlifeforFP.ThisfindingallowedustoperformpureFPrunswithoutsimultaneousoccurrenceofSP.

EffectoftheRelativeParametersRelatingtoFP.OneofthekeyfeaturesofpureFPisthatalldataonfrontvelocityversusreactiontimearewell-describedbyastraightandlinearfit.Moreover,thereisaTmaxvalueinthefunctionoffronttemperatureandfrontpositionduringtheFP.Con-versely,SPmayoccursimultaneously.

ThepositionofthethermalfrontasafunctionoftimeisgiveninFigure2for(a)purePUandEP/PUhybridnetworkswith(b)5wt%E44,(c)10wt%E44,and(d)15wt%E44.AsshowninFigure2,theexperimentaldataforallsetsofexperimentsarewell-fittedbystraightlines,meaningthatthepropagationofthepolymerizationfrontmovesataconstantvelocity.ThisisthefirststrongevidencethatpureFPisoccurring.Also,thevelocityoftheEP/PUhybridnetworksfrontdecreaseswithanincreaseoftheE44concentration.ThiscanbeexplainedbythefactthattheviscosityofhybridsincreasesasaresultofthereactionbetweentheE44andisocyanateinEP/PUhybridnetworks,whichcandecreasetheconvectionconductcausedbybuoyancy.FioriandMariani27havereportedthatdeviationsfromthelinearityaregenerallyobservedwhenasimulta-neousSPisoccurringduetoheatdispersioncausedbythemonomerfractionpolymerizedbySPandtotherelatedchangeofmediumviscosity.

(41)Dammann,L.G.;Carlson,G.M.U.S.Patent4,788,083,1988.

(42)Ocertel,G.PolyurethaneHandbook,2nded.;HanserPublishers:New

York,1993.

2162Chem.Mater.,Vol.18,No.8,2006Figure3.TypicalfronttemperatureprofileofEP/PUhybridnetworkspreparedbyFP.E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.

Figure4.FrontalvelocityofEP/PUhybridnetworkspreparedvs[catalyst]/[TDI]ratio.E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;toluene)10wt%.

FurtherevidencetosupportpureFPisthetemperatureprofile.AtypicaltemperatureprofileofEP/PUhybridnetworksisshowninFigure3.ThisexperimentwasdonewithE44)10wt%,[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol,[catalyst]/[TDI])1.0×10-3mol/mol,andtoluene)10wt%.Atemperatureincreasecanbeobservedonaccountofthehighlyexothermicreaction,andtheTmaxis94°C.Asaresultoftheconstanttemperaturevalueinzonesfarfromtheincominghotfront,thereisahorizontalpartofthecurve,meaningthatSPisnotoccurring.ThefronttemperatureprofileismoreevidencetorevealthatonlypureFPoccurs.

WestudiedthefrontvelocitydependenceonthecatalystconcentrationwithaconstantconcentrationofE44(10wt%)and[NCO]/[OH]/[epoxyvalue](1.4:1:1,mol/mol).Figure4isthecurveoffrontvelocityofEP/PUhybridnetworksversuscatalystconcentrationbyFP.Asexpected,thefrontvelocityincreaseswithhigherconcentrationsofcatalyst.FPcouldbeobservedfor[catalyst]/[TDI]between0.5×10-3and2.0×10-3mol/mol.Forlowercatalystconcentrations([catalyst]/[TDI]lessthan0.5×10-3mol/mol),nopropagat-ingfrontcouldbeachievedbecauseofheatloss.Conversely,for[catalyst]/[TDI]>2.0×10-3mol/mol,SPoccurred.Figure5isthecurveofTmaxofEP/PUhybridnetworksbyFPversuscatalystconcentrations.Anincreaseof[catalyst]/[TDI]from0.5×10-3to2.0×10-3mol/molcausedanincreaseofTmaxfrom86to105°C.Ourexperimentswereperformedundernonadiabaticconditions;forthisreason,theincreasedfrontvelocityreducedthetimeforheatloss.CharacterizationDataandComparisonbetweenSamplesPreparedbyFPandSamplesPreparedbyBP.ThepolymerstructureofEP/PUhybridnetworksisascer-tainedfromFT-IRspectra.Figure6showsFT-IRspectraof

Chenetal.

Figure5.TmaxofEP/PUhybridnetworksfrontpreparedvs[catalyst]/[TDI]ratio.E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;toluene)10wt%.

Figure6.FT-IRspectra(500-3500cm-1)ofEP/PUhybridnetworks.(a)EP/PUhybridnetworkssynthesizedbyFP,E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(b)EP/PUhybridnetworkssynthesizedbyBP,E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)70wt%.

Figure7.TGAspectraofpurePUandEP/PUhybridnetworkspreparedbyFP.(a)PurePUpreparedbyFP,[NCO]/[OH])1.4:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(b)EP/PUhybridnetworkspreparedbyFP,E44)15wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.

EP/PUhybridnetworkspreparedbyFPandBPrespectively,with[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol,E44)10wt%,and[catalyst]/[TDI])1.0×10-3mol/mol.AsisseeninFigure6,thebendingvibrationabsorptionpeaksoftheNsHgroupat1535cm-1andthestretchingvibrationabsorptionpeaksoftheCdOgroupat1730cm-1canbeobserved.However,thestretchingvibrationabsorptionpeaksoftheisocyanategroupat2356cm-1canalsobeobservedbecauseofexcessiveconcentrationofTDI.ThisallstronglyindicatesthattheproductsbyFPhavechemicalstructuressimilartothoseobtainedbyBP.40

TypicalTGAspectraforsamplesofpurePUandEP/PUhybridnetworkspreparedbyFPareshowninFigure7,eachofthemkeepingconstantaspecific[NCO]/[OH])1.4:1mol/mol,[catalyst]/[TDI])1.0×10-3mol/mol,andtoluene)10wt%.Bycomparison,inthetemperaturerangeofthefirstdegradationstep(113-270°Cataheatingrateof10

EpoxyResin/PolyurethaneHybridNetworksFigure8.TGAspectraofEP/PUhybridnetworkssynthesizedby(a)FPand(b)BP.(a)EP/PUhybridnetworkssynthesizedbyFP,E44)15wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(b)EP/PUhybridnetworkssynthesizedbyBP,E44)15wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)70wt%.

°C/min),theEP/PUhybridnetworksdegradeslightlyfasterthanpurePUbecauseofthedegradationofsomeuncon-vertedE44presentinthehybrids.Asamatteroffact,theonsettemperatureofdecomposition(113°C)ofE44wasreportedintheliterature.39ThesmallorganicmoleculestendtodegradebeforethePUpolymer,causingaslightweightlossinthehybrids.However,theEP/PUhybridnetworksshowhigherthermalresistancethanthatofpurePUinthetemperaturerangeofthedegradationstep(above270°Cataheatingrateof10°C/min),whichmightbeattributedtothepresenceofcross-linkingstructuresthroughcovalentbondsbetweenPUchainsandEPchains.ItclearlyshowsthattheEPincorporatedinthePUmatrixprovideshigherthermalstabilitiesofEP/PUhybridnetworksascribedtotheintermolecularhydrogenbondsofEP,whichimprovecohesionforceandhighregularsoftsegments.Figure8isaTGAthermogramspectracomparisonofthespectrumofEP/PUhybridnetworkspreparedbyFPcomparedwiththatofthenetworkspreparedbyBP.TheTGAspectraresultallowsustoconcludethatbothfrontandbatchsamplesshowsimilarthermalstabilities.

SEMimagesareusedtoinvestigatethesurfacemorphol-ogyofthePUandEP/PUhybridnetworksallsynthesizedbyFP.Figure9presentsthesurfacemorphologyofthePUandEP/PUhybridnetworkswithdifferentE44concentrations(5,10,and15wt%).Figure9aisthesurfaceofthepurePU.FromFigure9b-dwecanseethatboththeblackPUphaseandthewhiteEPphaseconstituteadistinct“net”structure.Theyshowisotropicandwell-pronouncedhomo-geneousnetworksoftwo-dimensionalplateletsofsimilardimensionsowingtocovalentcross-linkingbetweenEPchainsandPUchains.TheSEMmicrographsofEP/PUhybridnetworksalsorevealthatthehybriddomainsizeschangedwiththeE44concentration.Ascanbeseenfromtheimages,thedomainsizeofthesamplewith15wt%E44issmallerthanthatwith5wt%E44.Itcanbeconcludedthatthecross-linkingdensityofEP/PUhybridnetworksincreaseswiththeconcentrationofE44.ThesemicrographsprovidemoredirectevidencethattheE44uniformlydispersesinPUmatrixandformsanetworkstructureeventhoughnostirringisperformedinthiscase.

Chem.Mater.,Vol.18,No.8,20062163

Figure9.SEMimagesofthesurfacemorphorologiesofpurePUandEP/PUhybridnetworksallsynthesizedbyFP.(a)PurePUpreparedbyFP,[NCO]/[OH])1.4:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(b)EP/PUhybridnetworkspreparedbyFP,E44)5wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(c)EP/PUhybridnetworkspreparedbyFP,E44)10wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.(d)EP/PUhybridnetworkspreparedbyFP,E44)15wt%;[NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol;[catalyst]/[TDI])1.0×10-3mol/mol;toluene)10wt%.

Conclusions

ThefirstsynthesisofEP/PUhybridnetworksbyFPhasbeensuccessfullycarriedout.WehavefoundthatasolutionofE44,PPG,BD,TDI,stannouscaprylate([NCO]/[OH]/[epoxyvalue])1.4:1:1mol/mol,[catalyst]/[TDI])1.0×10-3mol/mol),andtoluene(10wt%)exhibitedapotlifeofmorethan3hattheambienttemperature(30°C),andinstantaneousSPdoesnotoccur.InagreementwithdataofotherpublishedFPsystems,theexperimentaldataforallFPexperimentsarewell-fittedbystraightlines,meaningthatthefrontspropagatewithconstantvelocities.ThefeaturesofEP/PUhybridnetworkspreparedfrontallyweresimilartothoseobtainedbyBPbutwereachievedinashorterreactiontime.FT-IRspectraofEP/PUhybridnetworksbyFPdisplaysthecharacteristicabsorptionpeaks,whicharealmostthesameasthoseofEP/PUhybridnetworksbyBP.TGAcharacterizationindicatesthatbothfrontandbatchsampleshadsimilarthermalstabilities.SEMimagesprovidedirectevidencethattheEPuniformlydispersedinthePUmatrixandformedacross-linkingnetworkstructureevenwithoutstirring.TheaboveresultsallowustoconcludethatFPcanbeexploitedasanalternativemeansforpreparationofEP/PUhybridnetworkswiththeadditionaladvantagesofhighvelocity,lowcost,andlowenergyascomparedwithtraditionalbatchmethods.

CM052391S