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1、POLYMERSCIENCEFUNDAMENTALSOFPOLYMERSCIENCEThermalTransitionsinPolymersProf.PremamoyGhoshPolymerStudyCentre“Arghya”3,kabiMohitlalRoadP.P.Haltu,Kolkata-700078(21.09.2006)CONTENTSIntroductionGlasstransitionandMeltingTransitionMeltingPointorFirstOrderTransiti
2、onGlassTransitionorSecondOrderTransitionBrittlePointDevelopmentofCrystallinityinPolymersCrystalllizationofRubberonCoolingMechanismofCrystallizationStress-inducedCrystallizationofRubberMeltingofRubberPolymerSingleCrystalsStructureofBulkPolymersSpherulitesT
3、hermalAnalysisKeyWordsMorphology,crystallization,crystallinity,crystallinezones,crystallizability,glassystate,rubberystate,glasstransition,melting,firstordertransition,secondordertransition,brittlepoint,volumechange,specificvolume,polymersinglecrystals,sp
4、herulites,thermalanalysis,dilatometer,foldedchaintheory,stress-inducedcrystallization.Introduction:PolymerMorphologyTwodifferentstatesorformscanbeidentifiedinwhichapolymercandisplaythemechanicalorthermomechanicalpropertiesthatcanbeassociatedwithsolids,viz
5、.,theformofacrystalortheformofaglass.Itisnotreallythecasethatallpolymersareabletocrystallize.Asamatteroffact,ahighdegreeofmolecularsymmetryandmicrostructuralregularitywithinthepolymerchainsareaprerequisiteforcrystallizationtooccur.Eveninthosepolymers,whic
6、hdocrystallizeinanyrate,theultimatedegreeofcrystallinitydevelopedismostlylessthan100%.Studiesofphysicalform,arrangementandstructureofthemoleculesorthemolecularaggregatesofamaterialsystemrelatestowhatisknownasitsmorphology.Polymermorpho-logycoversthestudyo
7、fthearrangementofmacromoleculesoverthecrystalline,amorphousandtheoverlappingregionsandtheoverallphysicalclusteringofthemolecularaggregates.Whencooledfrom,themoltenstates,differentpolymersexhibitdifferenttendenciestocrystallizeatdifferentratesdependingonma
8、nyfactorsincludingprevailingphysicalconditions,chemicalnatureoftherepeatunitsandofthepolymerasawhole,theirmolecularorsegmentalsymmetryandstructuralregularityorirregularity,asreferredtoabove.Bulkypendentgroupsorchain
