Synthesis, characterization, and gelation and development of liquid crystalline order during isothermal cure of rigid rod epoxy

121 Pages·2002·4.6 MB·English

by  Cho, Seunghyun, 1965-

SYNTHESIS,CHARACTERIZATION,ANDGELATIONANDDEVELOPMENTOF
LIQUIDCRYSTALLINEORDERDURINGISOTHERMALCUREOFRIGIDROD
EPOXY
By
SEUNGHYUNCHO
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
2002
Thisworkisdedicatedtomyfamily:mymother,fatherandsisterfortheirlove,support
andtrustinme;myhusband,Dr.BongsooLee;andmychildren,ChungwonandSuyeon
fortheirloveandpatience.Withouttheirendlesscaringandsupport,thisworkwouldnot
havebeenpossible.
u
ACKNOWLEDGMENTS
I would first like to acknowledge my advisor, Dr. Elliot P. Douglas, for his
support,encouragement,knowledgeandguidance.Ialsoappreciatethemembersofmy
supervisorycommittee:Dr.RonaldBaney,Dr.RandolphDuran,Dr.LaurieGowerand
Dr.WolfgangSigmundfortheirvaluableadviceandguidance.
Iwouldliketoextendmygratitudetomycolleagues:Dr.ArthurGavrinforhis
helpfulknowledgeandsupportinsynthesis,Dr.JianxunFengandDongsikKimfortheir
kindandfriendlyadviceandencouragement.Ialsothankallofmygroupmembersand
friends who gave support, collaboration and encouragement: Yi-yeoun Kim, Tonya
Bervaldi, Wei-ling Jia, Susan Leander, Stephanie DiFrancesco, Elizabeth Oborn, Dr.
Han-yingZhaoandDerekLincoln.
I greatly appreciate the provider of funding for this project: the U.S. Army
Research Office (under Grant DAAG55-98-1-0114 to Dr. Elliot P. Douglas as a
PresidentialEarlyCareerAwardforScientistsandEngineers).
iii
TABLEOFCONTENTS
£age
ACKNOWLEDGMENTS
ii
LISTOFTABLES vi
LISTOFFIGURES vii
ABSTRACT
ix
CHAPTER
REVIEWOFLITERATURE
1 1
1.1 LiquidCrystals 1
1.1.1 LiquidCrystallinePolymers(LCPs) 3
1.1.2 LiquidCrystallineThermosets(LCTs) 4
1.1.3 Applications 6
1.2 ThermalStability 8
1.3 TheTransitionDiagrams 9
1.3.1 GelationandVitrificationTimes 9
1.3.2 MeasurementsofTransitions 10
1.3.3 TransitionDiagrams 11
1.4 CuringKinetics 13
1.5 GoalsofThisStudy 15
2 SYNTHESISANDCHARACTERIZATIONOFLIQUIDCRYSTALLINE
EPOXYMONOMERS
17
2.1 Introduction 17
2.2 ExperimentalSection 18
2.2.1 Synthesisof4,4’-diglycidyloxy-a-methylstilbene(DOMS) 18
2.2.2 SynthesisofD2A1 22
2.2.3 ThermogravimetricAnalysis(TGA) 24
2.2.4 ResultsandDiscussion 24
2.2.5 SynthesisofDOMS 24
2.2.6 SynthesisofD2A1 37
2.2.7 ThermalAnalysis 43
2.3 OtherSyntheses 58
IV
1.1.1 SynthesisofCompoundIIwithHydroquinoneStartedfrom
AllylBromide 58
1.1.2 CompoundIIIwithMethoxyHydroquinone 61
1.1.3 CompoundIVwithBiphenol .62
1.1.4 SynthesisofCompoundVIwithHydroquinoneStartedfrom
8-Bromo-l-Octene 63
1.1.5 SynthesisofCompoundVII .64
1.1.6 SynthesisofCompoundVIIIwithAcetoxyBenzoicAcid. 65
1.2 Conclusions 67
2 GELATIONANDDEVELOPMENTOFLIQUIDCRYSTALLINEORDER
DURINGISOTHERMALCUREOFRIGIDRODEPOXY.
2.1 Introduction
.69
2.2 ExperimentalSection .70
2.2.1 MaterialsandSamplePreparation .70
2.2.2 ParallelPlateRheology .71
2.32.2.R3esultDsifafnedreDntiisaclusSsciaonnningCalorimetry(DSC) .7721
2.3.1 TransitionDiagrams .72
2.3.2 GelPointsvs.Conversion .82
2.3.3 PhaseTransitionvs.Conversion 88
2.4 Conclusions
.93
3 CONCLUSIONSANDFUTUREWORK
REFERENCES
102
BIOGRAPHICALSKETCH
109
LISTOFTABLES
Table page
2-1ElementalAnalysisresultsfordiol 19
2-2ElementalAnalysisresultsforDOMS 20
2-3ElementalAnalysisresultsforD2A1 23
2-4TransitiontemperaturesofDOMS 31
2-5TransitiontemperaturesofD2A1 38
2-6Gelationtimesforvariouscuringagents 43
2-7ThermogravimetricAnalysisdatacomparisonforDOMSandDGEBA 50
22--8ElementalAnalysisresultsofCompound1 60
3-
2-9ElementalAnalysisresultsofCompoundII 60
2-10Transitiontemperatures(10°C/minrate) 61
2-11ElementalAnalysisresultsofCompoundIII 62
2-12ElementalAnalysisresultsofCompoundIV 62
2-13Transitiontemperatures(10°C/minrate)ofCompound IV 62
2-14ElementalAnalysisresultsofCompoundV 63
15ElementalAnalysisresultsofCompoundVI 64
1TmiamxeismoufmlioqfuidDcSrCyst(taplelaikn)ephaseappearancebyPOM(t|C)andsecondpeak 78
3-2Geltimesandconversionatgelpoints 88
3-3Timesofliquidcrystallinephaseappearance(t|c)andconversion
atphasetransition(aic) 91
vi
LISTOFFIGURES
1-
2F-igure page
1-1 Liquidcrystallinemesophases 2
2TypicalLCTmonomers 7
1SynthesisschemeforDiol 26
2-2SynthesisschemeforDOMS 27
2-3SynthesismechanismforDiol 29
2-4SynthesisstepsofDOMSfromdiolandepichlorohydrin 30
2-5DSCthermographsforDOMS(10°C/min,N2) 32
2-6SchemeofDOMSandsulfanilamide 34
2-7Curingmechanism 35
2-8SynthesisschemeforD2A1 39
2-9PolarizedopticalmicroscopyofD2A1 40
2-10Curingagents 44
2-11Gelpointandvitrificationpointdetermination 45
2-12ThermogravimetricAnalysisscanofDOMS-SAAsystem
(heatingrate10°C/min,underN2) 46
2-14ChemicalstructureofDGEBA 48
2-15ThermogravimetricAnalysisscanofDOMSandDGEBA
(heatingrate10°C/min,underN2) 48
2-16ThermogravimetricAnalysisscanofD2Al-2.0wt%MIsystem 49
2-17Flynn-WallplotofDOMS-SAAsystem 53
2-18PlotofInqvs.1/Tforoc=0.40forcalculationofEd 54
2-19ActivationenergiesfordecompositionofDOMS-SAAsystem 55
2-20ActivationenergiesfordecompositionofD2Al-2.0wt%MIsystem 56
2-21Synthesisscheme 59
22--22MolecularstructureofCompoundIII 61
32--23MolecularstructureofCompoundIV 62
2-24MolecularstructureofCompoundVI 64
2-25Synthesisscheme 65
26Synthesisscheme 66
1oLfiqDuOidMSCr-ySstAalAlinseysPtheamseTimeTemperatureTransformationdiagram 75
3-2IsothermalscandiagramofDSCat150°C 77
3-3TimeTemperatureTransformationdiagramofD2A1-1.5wt%MIsystem 79
3-4LiquidCrystallinePhaseTimeTemperatureTransformationdiagram
ofD2Al-2.0wt%MIsystem 80
3-5TimeTemperatureTransformationdiagramofD2A1-2.5wt%MIsystem 81
3-6Cureexothermofuncuredandpartiallycuredsample 84
3-7ConversionatgelationforDOMS-SAAsystem 87
3-8ArrheniusplotofIn(tgei)vs.1/T 89
3-9Plotofphasetransitiontemperatureandgelpointsvs.conversion 90
3-10Idealizedplotforcuretemperaturevs.timeorconversion 100
viii
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
SYNTHESIS,CHARACTERIZATION,ANDGELATIONANDDEVELOPMENTOF
LIQUIDCRYSTALLINEORDERDURINGISOTHERMALCUREOFRIGIDROD
EPOXY
By
SeunghyunCho
August2002
Chairman:ElliotP.Douglas
MajorDepartment:MaterialsScienceandEngineering
Theliquidcrystallinethermosetmonomers4,4’-diglycidyloxy-a-methylstilbene
(DOMS) and D2A1 that resulted from reaction between DOMS and aniline were
synthesized.Themonomerswerecharacterizedwithcross-polarizedopticalmicroscopy,
differentialscanningcalorimetry(DSC)anddynamicthermogravimetricanalysis(TGA).
DOMS showed monotropic liquid crystalline mesophase and D2A1 showed smectic
phaseevenatroomtemperatureandturnedintonematicthencleareduponheating.
DOMSwascuredwithsulfanilamide(SAA)andD2A1 wascuredwithcatalytic
curingagent,1-methylimidazole(MI).ThermalstabilitytestsofDOMS-SAA,D2A1-MI
andcommercialnonliquidcrystallineepoxy,diglycidyletherofbisphenolA(DGEBA)
SAA system via dynamic TGA shows that the factor that most influences thermal
stability is the molecular structure ofthe material itselfrather than liquidcrystalline
phases.The%conversiondataweredeterminedfromdynamicDSCscantoexaminethe
IX
applicabilityofFlory’sgelationtheory.Theresultsrevealthateventhoughtheamountof
reaction that occurs in the liquid crystalline phase is different at different cure
temperatures, the isoconversion theory ofgelation fits quite well. The actual average
value ofthe conversion at the gel point is 0.677, which is slightly higher than the
calculatedtheoretical valueof0.577becauseofthe failedassumptionsofthis theory.
Thatis,theremightbereactivitydifferencesamongthesametypesoffunctionalgroups
andintramolecularconnectionsarepossible.
Thephasetransitionsdonotshowisoconversionbehaviorincontrasttogelation.
Instead,theconversionwherephasechangesfromisotropictoaliquidcrystallinephase
tendstoincreasewithtemperaturebecausethecriticallengthofthemoleculesneededfor
theliquidcrystallinityincreaseswithtemperature.
x