FabricationandCharacterizationofOrtho-HydroxylCopolyimide-basedMicroporousMembranesforGasSeparations

Abstract

Inthisthesis,adetailedunderstandingofthegasseparationperformancebasedonmolecularstructures,multicomponentsystemofgasseparationmembraneswasdiscussedandefficientwaytopreparethesegasseparationmembraneswassuggestedandinvestigated. InChapter1,theroleoffluorinatedcontentsinTRpolymersfortheirmicroporousstructuresandgasseparationperformancewasinvestigatedbycontrollingfluorinecontentsviaeithercopolymerizationorpolymerblendingapproach.AseriesofTRcopolymersandTRpolyblendsweresuccessfullypreparedviapost-fabricationontheirprecursorofcopolyimidesandpolyimideblends,respectively.Alloftheprecursorpolyimidesexhibitedimide-to-benzoxazolethermalcyclizationreactionaround400oCregardlessofthefluorinatedunitcontentsandpolymerpreparationmethods.MicroporosityandgaspermeabilityofthepolymerswereenhancedbyTRconversionandthepresenceofbulkyhexafluoroisopropylidenemoieties.Furthermore,TRpolymerblendsexhibiteddistinctivethermo-mechanicalpropertieswithtwoseparatedglasstransitiontemperaturesandimprovedgastransportbehaviorscomparedtothecorrespondingTRcopolymerssynthesizedfromthesamestartingmonomers.Inthisstudy,TRpolymerblendscontaining90%fluorinateddiamine,TR-Blend-AH91,showedthehighestgaspermeability(P(CO2)=603Barrer)amongtheTRpolymersinthiswork. InChapter2,anewefficientmethodwasemployedandpracticallyrealizedtopreparemicroporousmembranessuchasthermallyrearranged(TR)andcarbonmolecularsieve(CMS)inawayusinginfrared(IR)irradiation.TheeffectsoftheIRtreatmentconditionsuchastemperature,time,andenvironmentonthethermalconversionofTRandCMSmembraneswereinvestigatedforthefirsttime.ThemembranessubjectedtotheIRfurnaceexhibitedthesamechangesofthechemicalstructureandcomparablegastransportbehaviorsasthemembranestreatedintheelectricfurnace.Surprisingly,thetreatingtemperatureandprocessingtimeofmembraneswerereducedby~100◦Candafactorof~20,respectively,intheIRfurnaceresultfromtheenergy-intensiveradiationandcontrolofinstanttemperature.ByreplacingtheelectricfurnacewiththeIRfurnace,energysavingsbyafactorof~10wereobtainedatthesamethermalconversionrateandconsequently,theoverallproductivitywasimprovedbymorethanafactorof100.TheapplicabilityandadvantagesofefficientIRirradiationonTRandCMSmembranefabricationwereconfirmedinthisstudy.ThisresearchwaspublishedinJournalofMembraneScience613(2020)118477 Lastly,inChapter3aboveresearchesaresummarizedandsuggestionsforthefutureworksregardingmembraneresearchwillbediscussedbasedonmaterialchemistryandposttreatmentsofmembranethatcanimprovemicroporosityandgastransportperformance.