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Bernhard Wunderlich Thermal Analysis of Polymeric Materials Bernhard Wunderlich Thermal Analysis of Polymeric Materials With 974 Figures 123 Prof. Dr. Bernhard Wunderlich 200 Baltusrol Road Knoxville, TN 37922-3707 USA [email protected] Library of Congress Controll Number: 2004114977 ISBN 3-540-23629-5 Springer Berlin Heidelberg New York This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on micro- film or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springeronline.com © Springer-Verlag Berlin Heidelberg 2005 Printed in The Netherlands The use of general descriptive names, registred names, trademarks etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design: KünkelLopka, Heidelberg Production: LE-TeX Jelonek, Schmidt & Vöckler GbR, Leipzig Typesetting by the author Printed on acid-free paper 2/3130/yl – 543210 __________________________________________________________________ Preface Thermalanalysisisanoldtechnique. Ithasbeenneglectedtosomedegreebecause developmentsofconvenientmethodsofmeasurementhavebeenslowandteaching of the understanding of the basics of thermal analysis is often wanting. Flexible, linearmacromolecules,alsonotasaccuratelysimplycalledpolymers,makeupthe final, third, class ofmolecules which only was identified in 1920. Polymers have neverbeenfullyintegratedintothedisciplinesofscienceandengineering. Thisbook isdesignedtoteachthermalanalysisandtheunderstandingofallmaterials,flexible macromolecules,aswellasthoseofthesmallmoleculesandrigidmacromolecules. The macroscopic tool of inquiry is thermal analysis, and the results are linked to microscopicmolecularstructureandmotion. Measurementsofheatandmassarethetworootsofquantitativescience. The macroscopic heat is connected to the microscopic atomic motion, while the macroscopicmassislinkedtothemicroscopicatomicstructure. Themacroscopic unitsofmeasurementofheatandmassarethejouleandthegram,chosentobeeasily discernablebythehumansenses. Themicroscopicunitsofmotionandstructureare the picosecond (10(cid:1)12 seconds) and the ångstrom (10(cid:1)10 meters), chosen to fit the atomic scales. One notes a factor of 10,000 between the two atomic units when expressed in “human” units, second and gram—with one grambeing equalto one cubiccentimeterwhenconsidering water. Perhapsthisisthereasonforthemuch betterunderstandingandgreaterinterestinthestructureofmaterials,beingcloserto humanexperiencewhencomparedtomolecularmotion. Inthe19thcenturythedescriptionofmaterialscouldbebasedforthefirsttimeon an experiment-based atomic theory. This permitted an easy recognition of the differencesbetweenphasesandmolecules. Phasesaremacroscopic,homogeneous volumes of matter, separated from other phases by well-defined boundaries, and moleculesaretheconstituentsmallestparticlesthatmakeupthephases. Asresearch progressed, microphases were discovered, initially in the form of colloidal dispersions. Morerecently,itwasrecognizedthatphase-areasmaybeofnanometer dimensions (nanophases). On the other hand, flexible macromolecules have micrometerlengthsorlarger. Particularlythenanophasesmaythenhavestructures withinterfacesthatfrequentlyintersectmacromolecules,givingthematerialsunique properties. Finally,theclassicalphases,gases,liquids,andsolids,werefoundtobeinneed ofexpansiontoincludemesophasesandplasmas. Thediscussionofhistoryinthe firstlectureshowsthetortuouspathscientificdiscoverytakestoreachthepresent-day knowledge. Easier ways can be suggested in hindsight and it is vital to find such simpler approaches so to help the novice in learning. In this book on “Thermal AnalysisofPolymericMaterials”aneffortismadetodiscoversuchaneasyroadto understandthelarge,flexiblemoleculesandthesmallphases,andtoconnectthem tothesmallmoleculesandmacroscopicphaseswhichareknownformuchlonger. V__I___________________________________________________________P_r_ef_a_c_e Sincethegoalofthisbookistoconnectthenewknowledgeaboutmaterialstothe classicaltopics,butitssizeshouldberestrictedtotwotothreesemesters’worthof learning,severalofthestandardclassicaltextsweresurveyedbytheauthor. Only whenatopicneededspecialtreatmentfortheinclusionofthermalanalysisormacro- molecules,wasthistopicselectedforamoredetaileddiscussioninthisbook. The knowledgeinpolymerscience,inturn,oftenimprovestheunderstandingoftheother types of molecules. A typical example is discussed in the first lecture when describingtheclassification-schemeofmolecules. Withthisapproach,thelearning ofmaterialsscience,asawhole,maybelessconfusing. Aseriesofsixadditional examplesofsuchimprovementoftheunderstandingisgivenonpg.VII. The study of “Thermal Analysis of Polymeric Materials” is designed to accomplishtwogoals: First,thelearningofthenewsubjectmatter,andsecond,to stimulateareviewoftheclassicaltopics. Naturally,onehopesthatinthefutureall topics are included in the main educational track. This joining of the physics, chemistry,andengineeringofsmallandlargemoleculeswiththermalanalysisisof urgencysincemoststudentsmustintheircareerhandlepolymericmaterialsanddeal withtheapplicationofsometypeofthermalanalysis. Alistofshortsummariesof thesevenchaptersofthebookisgivenbelowforageneralorientationandtoallow forreading,startingatdifferententrypoints: Chapter1 Atoms,Small,andLargeMoleculesisdesignedtoenhancetheunderstanding andhistoryofthedevelopmentofknowledgeaboutsmallandlargemolecules. Furthermore, thenomenclature,description,andcharacterizationoflinearmacromoleculesbybasictheory andexperimentaresummarized. Chapter 2 Basics of Thermal Analysis contains definitions of systems, flux, and production and the following thermodynamic functions of state which are needed for the descriptionofthermalanalysisresults: heatcapacity,enthalpy,entropy,andfreeenthalpy. Chapter3 DynamicsofChemicalandPhaseChangesisasummaryofthesynthesesby matrix, stepwise, step, and chain reactions. It also contains information on emulsion polymerizations,cross-linking,gelation,copolymerization,anddecomposition. Kineticsof nucleation,crystallization,andmelting,aswellasglasstransitionsarechosenasrepresentative ofthedynamicsofphasechanges. Chapter 4 Thermal Analysis Tools contains a detailed description of thermometry, calorimetry, temperature-modulated calorimetry (TMC), dilatometry, thermomechanical analysis(TMA),dynamicmechanicalanalysis(DMA),andthermogravimetry(TGA). Chapter 5 Structure and Properties of Materials covers the solid states (glasses and crystals),mesophases(liquid,plastic,andcondiscrystals),andliquids. Alsotreatedaremulti- phasematerials,macroconformations,morphologies,defectsandthepredictionofmechanical andthermalproperties. Chapter6 SingleComponentMaterialsprovidesdetaileddescriptionsofphasediagrams withmelting,disordering,andglasstransitions. Inaddition,theeffectsofsize,defects,strain ontransitionsandpropertiesofrigidamorphousandotherintermediatephasesaretreatedin thelightofthermalandmechanicalhistories. Chapter 7 Multiple Component Materials, finally covers our limited knowledge of chemicalpotentialsofblends,solutions,andcopolymers. TheFlory-Hugginsequation,phase diagrams, solvent, solute, and copolymer effects on the glass, melting, and mesophase transitionsarethemajortopics. This book grew out of the two three-credit courses “Physical Chemistry of Polymers” and “Thermal Analysis” at The University of Tennessee, Knoxville (UTK). First, the lectures were illustrated with overhead foils, generated by computer, so that printouts could be provided as study material. In 1990 these P_r_e_f_ac_e___________________________________________________________V__II overheads were changed to computer-projected slides and the textbook “Thermal Analysis”waspublished(AcademicPress,Boston). In1994,acondensedtextwas added to the slides as lecture notes. A much expanded computer-assisted course “Thermal Analysis of Materials” was then first offered in 1998 and is a further development,enablingself-study. Thecomputer-assistedcourseisstillavailablevia theinternetfromourATHASwebsite(web.utk.edu/~athas)andseesperiodicupdates. It is the basis for the present book. A short version of the ATHAS Data Bank, a collection of thermal data, is included as Appendix 1. A treatise of the theory of “Thermophysics of Polymers” was written by Prof. Dr. Herbert Baur in 1999 (Springer,Berlin)andcanserveasacompanionbookforthetheoreticalbasisofthe experimentalresultsof“ThermalAnalysisofPolymericMaterials.” Thebookcontains,asshownabove,acriticallyselected,limitedseriesoftopics. Thefieldofflexiblemacromoleculesisemphasized,andthetopicsdealingwithsmall molecules and rigid macromolecules, as well as the treatment of mechanical properties, are handled on a more elementary level to serve as a tie to the widely available,generalscienceandengineeringtexts. TopicsthatareDifferentforPolymersandSmallMolecules The structure of a macromolecular substance is characterized by a diversity of molecularshapesandsizes,asisdiscussedinChap.1. Theseareitemsunimportant forsmallmolecules. Chemicallypure,smallmoleculescanbeeasilyobtained,are ofconstantsizeandoftenarerigid(i.e.,theyalsoareofconstantshape). Classically, one treats phases of two components as ideal, regular, or real solutions. Usually, however, one concentrates for the non-ideal case only on solutionsofsaltsbydiscussingtheDebye-Hückeltheory. Polymerscience,inturn, adds the effect of different molecular sizes with the Flory-Huggins equation as of basic importance (Chap. 7). Considerable differences in size may, however, also occur in small molecules and their effects are hidden falsely in the activity coefficientsofthegeneraldescription. Thecomparisonoftheentropyofrubbercontractiontothatofthegasexpansion, on one hand, and to energy elasticity of solids, on the other, helps the general understandingofentropy(seeChap.5). Certainly,theremustbeabasicdifference ifoneclassofcondensedmaterialscanbedeformedelasticallyonlytolessthan1% andtheotherbyupto1,000%. Thekineticsofchainreactionsofsmallmoleculesismuchhardertofollow(and prove)thanchain-reactionpolymerization. Oncethereactionisover,thestructure oftheproducedmacromoleculecanbestudiedaspermanentdocumentationofthe reaction(seeChaps.1and3). The notoriously poor polymer crystals described in Chap. 5 and their typical microphaseandnanophaseseparationsinpolymersystemshaveforcedarethinking of the application of thermodynamics of phases. Equilibrium thermodynamics remains important for the description of the limiting (but for polymers often not attainable) equilibrium states. Thermal analysis, with its methods described in Chap.4,isquiteoftenneglectedinphysicalchemistry,butunitesthermodynamics withirreversiblethermodynamicsandkineticsasintroducedinChap.2,andusedas animportanttoolindescriptionofpolymericmaterialsinChaps.6and7. The solid state, finally, has gained by the understanding of macromolecular crystalswithhelicalmolecules,theirdefectproperties,mesophases,smallcrystalsize, glasstransitions,andrigid-amorphousfractions(Chaps.5and6). V__I_II__________________________________________________________P_r_ef_a_c_e GeneralReferences The general referencesshould be used for consultation throughout your study of Thermal AnalysisofPolymericMaterials.Youmaywanttohavethetextbooksathandwhichyouown, andlocatetheotherreferencebooksinthelibraryforquickaccess. Frequentexcursionstothe literatureareabasisforsuccessinlearningthematerialofthiscourse. Typicalbooksonpolymerscienceare(chemistry,physics,orengineering): 1. RodriguezF,CohenC,OberCK,ArcherL(2003)PrinciplesofPolymerSystems,5thed. Taylor&Francis,NewYork. 2. StevensMP(1989)PolymerChemistry,2nded. OxfordUniversityPress,NewYork. 3. Billmeyer,Jr.FW(1989)TextbookofPolymerScience,3rded. Wiley &Sons,New York. Typicalphysicalchemistrytextsare: 4. AtkinsPW(1998)PhysicalChemistry,6thed. OxfordUniversityPress,Oxford. 5. MortimerRG(1993)PhysicalChemistry. Benjamin/Cummings,RedwoodCity,CA. 6. MooreWG(1972)PhysicalChemistry,4thed.PrenticeHall,EnglewoodCliffs,NJ. Asmentionedabove,thecompanionbooktreatingthetheoryofthesubjectis: 7. BaurH(1999)ThermophysicsofPolymers. Springer,Berlin. Referencebooksfornumericaldataonpolymersandgeneralmaterialsare: 8. BrandrupJ,ImmergutEH,GrulkeEA,eds(1999)PolymerHandbook.Wiley,NewYork, 4thedn. 9. LideDR,ed(2002/3)HandbookofChemistryandPhysics,83rd ed. CRCPress,Boca Raton,FL.(Annualnewedns.) Fordetailedbackgroundinformationonanytypeofpolymerlookup: 10. MarkHF,GaylordNG,BikalesNM(1985–89)EncyclopediaofPolymerScienceand Engineering,2nded; KroschwitzJIed (2004) 3rded. Wiley,NewYork. Alsoavailable withcontinuousupdatesviatheinternet: www.mrw.interscience.wiley.com/epst Formoreadvancedtreatisesonphysicalchemistry,youmaywanttoexplore: 11. EyringH,HendersonD,JostW(1971–75)PhysicalChemistry,AnAdvancedTreatise. AcademicPress,NewYork. 12. Partington JR (1949–54) An Advanced Treatise on Physical Chemistry. Longmans, London. Acknowledgments Thisbookhasgrownthroughmanystagesofdevelopment. Ateverystagethebook wasshapedandimprovedbymanyparticipatingstudentsandnumerousreviewers. Research from the ATHAS Laboratory described in the book was generously supportedovermanyyearsbythePolymersProgramoftheMaterialsDivisionofthe National Science Foundation, present Grant DMR-0312233. Several of the instrument companies have helped by supplying information, and also supported acquisitionsofequipment. Since1988theATHASeffortwasalsosupportedbythe DivisionofMaterialsSciencesandEngineering,OfficeofBasicEnergySciences, U.S.DepartmentofEnergyatOakRidgeNationalLaboratory,managedandoperated by UT-Battelle, LLC, for the U.S. Department of Energy, under contract number DOE-AC05-00OR22725. Allfigureswereoriginallynewlydevelopedanddrawnfor thecomputercourse“ThermalAnalysisofMaterials”andhavebeenadaptedorwere newlygeneratedforthepresentbook. Knoxville,TN,January2005 BernhardWunderlich __________________________________________________________________ Contents Preface................................................................................................... V TopicsthatareDifferentforPolymersandSmallMolecules ................ VII GeneralReferences .............................................................................. VIII Acknowledgments ............................................................................... VIII 1 Atoms,Small,andLargeMolecules 1.1 MicroscopicDescriptionofMatterandHistoryofPolymerScience 1.1.1 History ...................................................................................................... 1 1.1.2 MolecularStructureandBonding ............................................................. 3 1.1.3 ClassificationSchemeforMolecules ....................................................... 6 1.1.4 TheHistoryofCovalentStructures .......................................................... 9 1.1.5 TheHistoryofNaturalPolymers .............................................................. 9 1.1.6 TheHistoryofSyntheticPolymers ......................................................... 11 1.2 Nomenclature 1.2.1 Source-andStructure-basedNames ....................................................... 13 1.2.2 CopolymersandIsomers ........................................................................ 22 1.2.3 Branched,Ladder,andNetworkPolymers ............................................. 24 1.2.4 FunnyPolymers ...................................................................................... 25 1.3 ChainStatisticsofMacromolecules 1.3.1 MolecularMassDistribution .................................................................. 27 1.3.2 RandomFlight ........................................................................................ 31 1.3.3 MeanSquareDistancefromtheCenterofGravity................................. 32 1.3.4 DistributionFunctions ............................................................................ 33 1.3.5 StericHindranceandRotationalIsomers ............................................... 37 1.3.6 MonteCarloSimulations ........................................................................ 40 1.3.7 MolecularMechanicsCalculations......................................................... 41 1.3.8 MolecularDynamicsSimulations ........................................................... 43 1.3.9 EquivalentFreelyJointedChain ............................................................. 47 1.3.10 StiffChainMacromolecules ................................................................... 47 1.4 SizeandShapeMeasurement 1.4.1 Introduction ............................................................................................ 50 1.4.2 LightScattering ...................................................................................... 50 1.4.3 FreezingPointLoweringandBoilingPointElevation ........................... 58 1.4.4 Size-exclusionChromatography ............................................................. 62 1.4.5 SolutionViscosity .................................................................................. 63 1.4.6 MembraneOsmometry ........................................................................... 65 1.4.7 OtherCharacterizationTechniques ........................................................ 66 References........................................................................................... 68 X____________________________________________________________C_o_n_t_en_t_s 2 BasicsofThermalAnalysis 2.1 Heat,Temperature,andThermalAnalysis 2.1.1 History .................................................................................................... 71 2.1.2 TheVariablesofState ............................................................................ 75 2.1.3 TheTechniquesofThermalAnalysis ..................................................... 76 2.1.4 Temperature ............................................................................................ 79 2.1.5 Heat(TheFirstLawofThermodynamics).............................................. 81 2.1.6 TheFutureofThermalAnalysis ............................................................. 84 2.2 TheLawsofThermodynamics 2.2.1 DescriptionofSystems ........................................................................... 88 2.2.2 TheFirstLawofThermodynamics ......................................................... 90 2.2.3 TheSecondLawofThermodynamics .................................................... 91 2.2.4 TheThirdLawofThermodynamics ....................................................... 94 2.2.5 Multi-componentSystems ...................................................................... 96 2.2.6 Multi-phaseSystems ............................................................................... 98 2.3 HeatCapacity 2.3.1 MeasurementofHeatCapacity............................................................. 101 2.3.2 ThermodynamicTheory........................................................................ 104 2.3.3 QuantumMechanicalDescriptions ....................................................... 106 2.3.4 TheHeatCapacityofSolids ................................................................. 111 2.3.5 ComplexHeatCapacity ........................................................................ 117 2.3.6 TheCrystallinityDependenceofHeatCapacities ................................ 118 2.3.7 ATHAS ................................................................................................. 121 2.3.8 PolyoxideHeatCapacities .................................................................. 128 2.3.9 HeatCapacitiesofLiquids.................................................................... 131 2.3.10 ExamplesoftheApplicationofATHAS .............................................. 134 Polytetrafluoroethylene ..................................................................... 134 Poly(oxybenzoate-co-oxynaphthoate) ............................................... 134 Large-amplitudemotionsofpolyethylene ......................................... 136 Polymethionine ................................................................................. 136 MBPE-9 ............................................................................................ 137 Liquidselenium................................................................................. 138 Poly(styrene-co-1,4-butadiene) ......................................................... 139 Hypotheticalentropyoftheliquid atabsolutezerooftemperature ......................................................... 140 Starchandwater ................................................................................ 142 Conclusions ....................................................................................... 144 2.4 NonequilibriumThermodynamics 2.4.1 FluxandProduction.............................................................................. 147 2.4.2 MeltingofLamellarCrystals ................................................................ 148 2.4.3 ExperimentalData ................................................................................ 154 2.4.4 InternalVariables.................................................................................. 155 2.4.5 TransportandRelaxation ...................................................................... 158 2.4.6 RelaxationTimes .................................................................................. 159 2.5 PhasesandTheirTransitions 2.5.1 DescriptionofPhases ........................................................................... 162 C__o_n_te_n_t_s__________________________________________________________X_I 2.5.2 PhasesofDifferentSizes ...................................................................... 167 2.5.3 Mesophases .......................................................................................... 169 2.5.4 MesophaseGlasses ............................................................................... 175 2.5.5 ThermodynamicsandMotion ............................................................... 176 2.5.6 GlassTransitions .................................................................................. 178 2.5.7 First-orderTransitions .......................................................................... 181 References......................................................................................... 184 3 DynamicsofChemicalandPhaseChanges 3.1 StepwiseandStepReactions 3.1.1 StepwiseReactions ............................................................................... 189 3.1.2 MechanismofStepReactions .............................................................. 193 3.1.3 Examples .............................................................................................. 196 3.1.4 Conditions ............................................................................................ 198 3.1.5 ReactionRates ...................................................................................... 200 3.1.6 LithiumPhosphatePolymerization ....................................................... 201 3.2 ChainandMatrixReactions 3.2.1 MechanismofChainReactions ............................................................ 206 3.2.2 Kinetics................................................................................................. 212 3.2.3 Equilibrium ........................................................................................... 214 3.2.4 ChainReactionswithoutTermination .................................................. 215 3.2.5 EmulsionPolymerization...................................................................... 217 3.2.6 MatrixReaction .................................................................................... 218 3.3 MolecularMassDistributions 3.3.1 NumberandMassFractions,StepReactions ....................................... 219 3.3.2 NumberandMassFractions,ChainReactions ..................................... 221 3.3.3 StepReactionAverages ........................................................................ 224 3.3.4 ChainReactionAverages ..................................................................... 225 3.4 CopolymerizationandReactionsofPolymers 3.4.1 ChainReactionCopolymers ................................................................. 227 3.4.2 StepReactionCopolymers ................................................................... 229 3.4.3 Gelation ................................................................................................ 230 3.4.4 Decomposition ...................................................................................... 231 3.4.5 PolymerReactions ................................................................................ 233 3.5 CrystalandMolecularNucleationKinetics 3.5.1 ObservationofNucleationandCrystalGrowth.................................... 238 3.5.2 EvaluationofNucleationRates ............................................................ 240 3.5.3 MathematicalDescriptionofPrimaryNucleation ................................ 242 3.5.4 HeterogeneousNucleation .................................................................... 246 3.5.5 SecondaryNucleation ........................................................................... 249 3.5.6 MolecularNucleation ........................................................................... 253 3.6 CrystallizationandMeltingKinetics 3.6.1 LinearMeltingandCrystallizationRates ............................................. 255 3.6.2 DirectionalDependenceofCrystallization ........................................... 256 3.6.3 DiffusionControlofCrystallization ..................................................... 257