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Whatarepolymerblends?Itis"multicomponentpolymer".Sincemostofthemulticomponentpolymersareofmultiplephases,Itisalsocalled"multiphasepolymer".Toemphasistheimportancethechemicaland/orphysicalinteractionsofthepolymerchainsatamolecularlevel,itisalsobeenreferredtoas"polymeralloy".Acommonpolymerblendinvolvestwoormorehomopolymersmixedtogether.However,someblockcopolymersalsoshowphaseseparationbehaviorjustlikepolymerblenddoes.Toobtainoptimumpropertyofpolymers,ablendshouldhaveasynergisticpropertyenhancementfromallcomponentpolymers.Forexample,highimpactpolystyrene(HIPS)ispolystyrenetoughenedwithSBR(styrene-butadienerubber).Withtheuseofspecialtechniques,therubberparticlescanbetotallydispersedinPSmatrix.Also,therearePSchainsinfusedinrubberparticlesforming"cellularstructure".Withthisphasestructure,asatisfiedtougheningeffectisachievedwithadditionofonly5-10%rubber.AnotherexampleoftougheningPSistoblendstyrene-acrylonitrilerandomcopolymerandpolystyrene-graftedrubber.ThisproductiscalledABS.Clearly,thereistremendouschangeinproductproperties,asbeingshowedintheplot(aplotcomparingthetensilepropertiesofPS,HIPSandABS):Thattellsuswhytheresearchonpolymerblendsiscatchingsomuchattentioninacademicsaswellasinindustry.YoumaybeimpressedmorebylookingatHYPERLINK"http://www.pslc.ws/macrog/mpm/blends/links1.htm"areviewonthisresearcharea(seehowpolymerscientistsgetexcitedaboutit).ThephasemorphologyofpolymerblendsdeterminestheirpropertiesanditcanbeevaluatedbymanyHYPERLINK"http://www.pslc.ws/macrog/mpm/blends/chara.htm"characterizationtechniques.Thephasestructureinformationalsoincludestheinterfaceofphases.Tounderstandthemechanismforformingthesestructures,wehavetolearnalittleaboutHYPERLINK"http://www.psrc.usm.edu/macrog/blend.htm"\l"not"thethermaldynamicsofpolymerblends.Whichhasbeenthesubjectofintereststothepolymerphysicistsforalongtime.ThefirstsystematicdescriptionofpolymersystemsaremadebyP.J.Flory.Inhisbiblebook"PrinciplesofPolymerChemistry",hestatesthattwohighpolymersaremutuallycompatiblewith
