Macromolecules

Macromolecules

1. Macromolecules
B.Sc. SEM-V
Paper-II (Physical Chemistry)
Dr. N. G. Telkapalliwar
Associate Professor
Department of Chemistry
Dr. Ambedkar College, Nagpur

2. •Macromoleculesarecollectionoflargenumberofunitmolecules
linkedtogetherusuallybyacovalentbond.
•Manynaturalsubstanceslikeproteins,rubber,diamond,chlorophyll
andhemoglobinetc.arethesubstancehavinglargenumberofsimple
moleculeslinkedthroughcovalentbond.
•Simplemoleculesusuallycalledasmonomerformsmacromolecules
throughtheprocessofpolymerization.
•Dimersareformedoncombiningtwomonomers,trimerson
combiningthree,tetramersoncombiningfourandsoon.
•Insomecases,theserepetitionsarelinearandhencechainisbuilt
whereasinsomecasestheserepetitionsarebranchedandhencethree
dimensionalstructureisbuildup.
Macromolecules

3. Polymerization
Monomer
Vinyl chloride
Polyvinyl chloride

5. Monomer Structure

6. Polymercanhavedifferentchemicalstructures,physicalproperties,
mechanicalbehaviour,thermalcharacteristicsetc.andcanbeclassifiedin
differentways.
Natural and synthetic polymer.
Organic and inorganic polymer.
Thermoplastic and thermosetting polymers.
Classification Based on the structure of the polymers.
Addition and condensation polymers.
Homopolymersand copolymers.
Fibres, plastics and elastomers.
Linear branched and cross-linked polymers.
Classification of Polymers

7. Natural and synthetic polymer
i) Natural polymers are isolated from the natural materials.
Ex: Cotton, Silk, Wool, Natural Rubber, Proteins, Gums, etc.
ii) Synthetic polymers are derived from low molecular weight compound.
Ex: Ethylene to Polyethylene, Styrene to Polystyrene, etc.
Organic and inorganic polymer
i) Organic polymers generally made up of carbon atoms or hydrocarbons with
oxygen and nitrogen. Synthetic polymers are derived from organic polymers.
ii) Non-carbon polymers are referred to as Inorganic polymers. Glass and
silicon rubbers are the examples of inorganic polymers.
Classification of Polymers

8. Classification of Polymers
Thermoplastic and Thermosetting polymers
i)Certain polymers are heated and molded in a desired shape which can be
retained even after cooling. The process is usually repeated to heat, mold and
cool to desired shape. Polymer which gets soften on heating and stiff on
cooling are known as Thermoplastic polymers.
ii) There are certain polymers, that undergoes chemical transformation on
heating such as infusion like rice after cooking. Such polymers, that sets into
an infusible and insoluble mass after heating are called as Thermosetting
polymers.
Ex: Rice after cooking

9. Classification of Polymers
Plastics
Whenever,polymersareusedforhardandtoughutilityarticlesby
applicationofheatandpressure,theyarecalledasPlastics.
Examples:Polystyrene,PVC,,Polymethylmethacrylate,etc.
Elastomers
Whenpolymersaredesignedandpreparedforelasticnatureapplication,
theyareknownasElastomers.
Examples:Naturalrubber,Siliconrubber,etc.
Fibers
Whenpolymersaredrawnforlonglength,usuallymorethan100timesits
diameter,theyarecalledasfibers.
Example:NylonandTerylene,etc.
LiquidResins
Whenever,polymersaredesignedforsealants,adhesivesoranyotherliquid
formapplication,whichondryingbecomehardandstrongareknownas
LiquidResins.
Example:Polymerpaints,adhesives

10. Classification of Polymers
Polymersarefurtherclassifiedbaseduponhowthemonomerunitsarelinked
together.Polymericmaterialscouldbelinear,branched,orcross-linked
subjectedtotheintermolecularlinkagesbetweentheindividualchains.
Linear, Branched and Cross-linked Polymers

11. Linear Polymers
•Inlinearpolymerstherepeatingunitsarejoinedtogetherendtoendina
singleflexiblechain.
•Thepolymericchainsarekepttogetherthroughphysicalattractions.
ThesepolymershaveextensiveVanderWaalsattractionskeepingthe
chainstogether.
•Typicallylinearpolymersaremadefrommonomerswithsingleend
group.
•Linearpolymerscontainingsidegroupsaspartofmonomerstructuredo
notqualifyasbranchedpolymers.
•Someofthecommonexamplesoflinearpolymersarepolyethylene,PVC,
polystyrene,andpolyamides.
•Linearpolymersaregenerallymorerigid.

12. Branched Polymers
•Branchedpolymershavesidechainsorbranchesgrowingoutfromthe
mainchain.
•Thesidechainsorbranchesaremadeofthesamerepeatingunitsasthe
mainpolymerchains.
•Thebranchesresultfromsidereactionsduringpolymerization.
•Monomerswithtwoormoreendgroupsarelikelytosupportbranching.
•Forapolymertoclassifyasbranchedpolymerthesidechainsorbranches
shouldcompriseofaminimumofonecompletemonomerunit.
•Oneofthemostcommonexampleislow-densitypolyethylene(LDPE)and
hasapplicationsrangingfromplasticbags,containers,textiles,and
electricalinsulation,tocoatingsforpackagingmaterials.
•Thelengthofthesidechainsorbranchesdifferentiatesbetweenlong-or
short-branchedpolymers.

13. Cross-linked Polymers
•Cross-linkedpolymers,asthenamesuggest,arepolymersinwhichthe
adjacentpolymerchainsareconnectedinathree-dimensionalnetwork
structure.
•Theconnectionsarealsoknownascross-links.
•Thecross-linkscouldbeaconsequenceofcovalentbondingbetweenthe
chainsorbranches.
•Cross-linkstendtobepermanentinnature.
•Oncethecross-linksbetweenthechainsdevelopthepolymerthenbecomes
thermoset.
•Suchpolymersarecharacterizedbytheircrosslinkdensityordegreeof
crosslinkwhichistheindicationofnumberofjunctionpointsperunitvolume.
•Commonexamplesincludeepoxies,bulkmoldingcompounds,rubber,and
variousadhesives.

14. Isotactic , Syndiotactic, Atactic in Polymers
What is Isotactic Polymer?
Anisotacticpolymerisapolymerwhichhasthesubstituentsonthesameside
ofthecarbonchain.Thatmeans;allthesubstituentsofthepolymermaterial
arelocatedonthesamesideofthebackboneofthepolymer.
Theconfigurationinwhichallthe‘R’groupslieonthesamesideoftheplan
formedbytheextended-chainbackboneoralltheasymmetriccarbonatoms
havethesameconfigurationi.e.either‘d’or‘l’aretermedasIsotactic
polymers.
Forexample,industriallypreparedpolypropyleneisisotactic.Itsproduction
methodisZiegler-Nattacatalysis.Usually,thesepolymersaresemi-crystalline.
Theyshowahelixconfiguration.
Isotactic

15. What is Syndiotactic Polymers
Syndiotacticpolymersarepolymermaterialswhichhavethesubstituentsin
analternatingpattern.Therefore,substituentgroupshavealternatepositions
alongthebackboneofthepolymer.
Thepolymersinwhichasymmetriccarbonatomshavealternate‘d’or‘l’
configurationsi.e.thesubstituentgroups‘R’liesalternateaboveandbelowor
oneandothersideofthebackbonechainarecalledasSyndiotacticpolymers.
Forexamples,Ifweproducepolystyreneviametallocenecatalysis
polymerization,itgivesasyndiotacticpolystyrenematerialanditisa
crystallinematerial.Thepolymercontains100%racemodiads(thediad
containstwounitsorientedinopposition).
Syndiotactic

16. Anatacticpolymerisapolymermaterialwherethesubstituentsina
carbonchainarearrangedinarandommanner.Usually,polymersthatform
viafreeradicalpolymerizationhasthisstructure;forexample,polyvinyl
chloride.Atacticpolymershaveanamorphousstructureduetotherandom
arrangementofsubstituentgroups.
Polymerswithnoregulararrangementsof‘d’or‘l’configurationsofthe
asymmetriccarbonatomsorrandomarrangementsof‘R’groupsoneitherside
ofbackbonechainareknownasAtacticPolymers.
Atactic
What is Atactic Polymers

18. Isotactic
Syndiotactic
Atactic

19. Isotactic
Syndiotactic
Atactic

20. Addition and Condensation Polymers
Theprocessofcombiningalargenumberofsmallmoleculestoformasingle
macromoleculeisknownaspolymerization.
Thesmallmoleculesthatactasthebuildingblocksofpolymersarecalled
monomers.
Basedonthekindsofreactionsinvolved,polymerizationisdividedintotwo
groupsknownasadditionpolymerizationandcondensationpolymerization.
Additionpolymerizationistheprocessofrepeatedadditionofmonomersthat
possessdoubleortriplebondstoformpolymers.
Condensationpolymerizationisaprocessthatinvolvesrepeatedcondensation
reactionsbetweentwodifferentbi-functionalortri-functionalmonomers.
Themaindifferencebetweenadditionandcondensationpolymerizationisthatin
additionpolymerizationthepolymersareformedbytheadditionofmonomers
withnoby-productswhereasincondensationpolymerization,thepolymersare
formedduetothecondensationmorethanonedifferentmonomersresultinginthe
formationofsmallmoleculessuchasHCl,water,ammonia,etc.,asby-products.

21. Condensation polymerization
Addition polymerization
1.
2.
1. 2.

22. Addition Polymerization Condensation Polymerization
Monomers must have either a double
bond or triple bond
Monomers must have two similar or
different functional groups
Produces no by-products By-products such as ammonia, water
and HCl are produced
Addition of monomers results in
polymers
Condensation of monomers result in
polymers
The molecular weight of the resultant
polymers is a multiple of monomer’s
molecular weight
The molecular weight of the resultant
polymer is not a multiple of
monomer’s molecular weight
Lewis acids or bases, radical initiators
are catalysts in addition
polymerization
The catalysts in condensation
polymerization are catalysts in
condensation polymerization.
Common examples of addition
polymerization are PVC, polyethene,
Teflon etc.
Common examples of condensation
polymerization are nylon, bakelite,
silicon, etc.
Difference between
Addition and Condensation polymerization.

23. Addition polymerization
Condensation polymerization

24. Apolymersmolecularweightisthesumoftheatomicweightsofthe
individualatomsthatcompriseamolecule.Itindicates
theaveragelengthofthebulkresin’spolymerchains.
Onecannotsurelyguessabouttheexactdegreeofpolymerization.
Undersuchcondition,molecularweightofpolymercanbeviewed
statisticallyandexpressedassomeaverageofthemolecularweights
contributedbytheindividualmoleculesthatbuiltthepolymer.
Thetwomostcommonandsimplemethodsare
1)Number-averagemolecularweightorNumberaveragemolarmass
1)MassaveragemolecularweightorWeightaveragemolarmass
Molar masses of polymers

25. Number-averagemolecularweightorNumberaveragemolarmass
Thenumberaveragemolecularweightisdefinedasthetotalweight
ofpolymerdividedbythetotalnumberofmolecules
Themassaveragemolecularweightisdefinedasthesumofproducts
ofmolecularmassesofgroupsofmoleculeswiththeirrespective
molecularmassesandthensumisdividedbythetotalmass.
MassaveragemolecularweightorWeightaveragemolarmass

26. Determination of Molecular weight ofpolymers
Viscometry:Themolecularweightobtainedbythistechniqueistheviscosityaverage
molecularweight,Mv..Theviscosityofapolymersolutionisconsiderablehighas
comparedtothatofpuresolvent.Theincreaseinviscositybythemacromoleculesina
solutionisadirectfunctionofthehydrodynamicvolumeandhencethemolecular
weightofthemacromolecules.
Therelationshipbetweenviscosityofapolymersolutionandmolecularweightis
givenbyMark-Houwinkequation-
[η] =KM
a
Where[η]istheintrinsicviscosity,M-molecularweightandaandKareconstantfora
particularpolymer/solvent/temperaturesystem.ValuesofKandaareavailableformay
knownpolymers.
ForapolymertypeofknownKandavalueswhatisrequiredisthedeterminationof
theintrinsicviscosityusingtheaboveequation.
Forunknownpolymersystems,theKandavaluesaregeneratedbyfractionatingthe
polymersampleintoseveralfractionsandforeachfractionthemolecularweightis
determinedbyOsmometryorlightscatteringmethodandcorrespondingintrinsic
viscosityismeasured.
Viscometryor Viscosity method

27. Determination of Molecular weight ofpolymers
Viscometry:Aplotoflog[η]againstlogMgivesastraightline.
Fromthegraph,thevalueofKandacanbedeterminedfrom
theirordinateinterceptandslopeoftheline.
[η] =KM
a
log [η] = log K + alogM
Now,letusseehowtheintrinsicviscositycanbemeasures.Assumethataliquidis
flowingthroughacapillarytube.ThetimerequiredfortheliquidofvolumeVtopass
throughthecapillaryofradiusrandlengthlisrelatedtoitsabsoluteviscosityby
the
Poiseuille Equation- η=
3.14??????�
4
�
8 ????????????
8????????????η
t =
3.14??????�
4
Where P is the pressure head under which the liquid flow takesplace.
If η and η
o are the absolute viscosities of a solution and the pure
solventrespectively and t and to are their corresponding time flow,
then
�η
η
�=
�
=
η
��
η/ η
o is known as the relative viscosity, η
r orη
rel
Viscometryor Viscosity method

28. Determination of Molecular weight ofpolymers
Commonly used terms inviscometry:
IntrinsicviscosityisalsoknownasStaudingerindex
orlimitingviscosityindex(dimensionisreciprocalof
concentration).Forcalculatingtheintrinsicviscosity
ofapolymersampleinsolution,weneednotknow
theabsoluteviscositiesofsolventandsolution,but
onlytheflowtimeofconstantvolumeofsolventand
thesolutionthroughaparticulartube.Thisprinciple
isusedintheviscometrictechniqueofmolecular
weightdetermination.Theterm[η]hasrelatedto
thetwoviscosityfunctionsthroughhefollowing
twoequationsbyHugginsandKraemerequations.
K”&k”areconstantsforagiven
polymersolvent/temperaturesystem
Viscometryor Viscosity method

29. Determination of Molecular weight ofpolymers
Problem:Calculatetherelativeviscosity,specificviscosity,andreducedviscosityofa
0.5%(madebydissolving0.25gofpolymerin50mLofsolvent)solutionwherethe
timeforsolventflowbetweenthetwoappropriatemarkswas60sandthetimeof
flowforthesolutionwas80s.
Relative viscosity ??????
�= 80 s/60 s =1.3
The specific viscosity η
��is determined by using therelation,
Specific viscosity, ??????
�??????= 1.3-1 =0.3
The reduced viscosity is η
red is given by therelation-
The most widely employed concentrations in viscosity determinations are g/mL (g/cc)
and g/dL or %. The units g/cc are recommended by IUPAC, while the units of % or g/dL
are the most commonly usedunits.
The reduced viscosity, η
redis-
�
Solution:Using the relationoftimeofflowwithrelative viscosity, �η
η
�=
�
=
η
�
η
�
η
��=
η
−1
���
η
��
η=
�
Viscometryor Viscosity method

30. Determination of Molecular weight ofpolymers
Problem: Determine the molecular weight of a polystyrene sample which has an a value
of 0.60, a K value of 1.6 104 dL/g, and a limiting viscosity number or intrinsic viscosityof
0.04 dL/g.
Solution: The molecular weight can be found by therelationship:
Hence, the molecular weight of the polymer is 1 x10
4
Viscometryor Viscosity method

31. Determination of Molecular weight ofpolymers
Osmometryor Osmotic pressureMethod
Osmometry:MembraneosmometryisabsolutetechniquetodetermineM
n.The
solventisseparatedfromthepolymersolutionwithsemipermeablemembranethatis
stronglyheldbetweenthetwochambers.Onechamberissealedbyavalvewitha
transducerattachedtoathinstainlesssteeldiaphragmwhichpermitsthe
measurementofpressureinthechambercontinuously.Membraneosmometryis
usefultodetermineM
nabout20,000-30,000g/molandlessthan500,000g/mol.
WhenM
nofpolymersamplemorethan500,000g/mol,theosmoticpressureof
polymersolutionbecomesverysmalltomeasureabsolutenumberaverageof
molecularweight.Inthistechnique,thereareproblemswithmembraneleakageand
symmetry.Theadvantagesofthistechniqueisthatitdoesn’trequirecalibrationandit
givesanabsolutevalueofM
nforpolymersamples.
Sinceosmoticpressureisdependentoncolligativeproperties,i.e.,thenumberof
particlespresent,themeasurementofthispressure(osmometry)maybeappliedto
thedeterminationoftheosmoticpressureofsolventsvs.polymersolutions.

32. Determination of Molecular weight ofpolymers
Osmoticpressure
The reciprocalofthe numberaveragemolecularweight (Mn )isthe interceptwhen
data forπ /RTC vs. C are extrapolated to zeroconcentration.
Thedifferenceinheight(h)oftheliquidsinthecolumnsmaybe
convertedtoosmoticpressure(π)bymultiplyingthegravity(g)
andthedensityofthesolution(p),i.e.,π=hpg.
Inanautomaticmembraneosmometer,theunrestricted
capillaryriseinadilutesolutionismeasuredin
accordancewiththemodifiedvan’tHoffequation:

33. Determination of Molecular weight ofpolymers
LightScatteringMethod:Lightscatteringmethodstodeterminationofweightaverage
molecularweight,Mw.Whenpolarizableparticlesareplacedintheoscillatingelectric
fieldofabeamoflight,thelightscatteringoccurs.Lightscatteringmethoddependson
thelight,whenthelightispassingthroughpolymersolution,itismeasurebyloses
energybecauseofabsorption,conversiontoheatandscattering.Theintensityof
scatteredlightreliesontheconcentration,sizeandpolarizabilitythatisproportionality
constantwhichdependsonthemolecularweight.
Figure: Modes of scattering of light in solution. Figure: Schematic representation of lightscattering.
Forlightscatteringmeasurements,thetotalamountofthescatteredlightisdeduced
fromthedecreaseinintensityoftheincidentbeam,I0,asitpassesthroughapolymer
sample.ThiscanbedescribedintermsofBeer’slawfortheabsorptionoflight.

34. Determination of Molecular weight ofpolymers
Lightscattering
TheBeer’slawfortheabsorptionoflightasfollows:
whereisthemeasureofthedecreaseoftheincidentbeamintensity
perunitlength1ofagivensolutionandiscalledtheturbidity.
Theintensityofscatteredlightorturbidity(τ)isproportionaltothesquareofthe
differencebetweentheindexofrefraction(n)ofthepolymersolutionandofthe
solventn
0,tothemolecularweightofthepolymer(M),andtotheinversefourthpower
ofthewavelengthoflightused(λ).Thus,
wheretheexpressionfortheconstantHis
wheren
0indexofrefractionofthesolvent,nindexofrefractionofthesolution,cconcentration,the
virialconstantsB,C,etc.,arerelatedtotheinteractionofthesolvent,Pistheparticlescattering
factor,andNisAvogadro’snumber.Theexpressiondn/dcisthespecificrefractiveincrementandis
determinedbytakingtheslopeoftherefractiveindexreadingsasafunctionofpolymer
concentration.

35. Determination of Molecular weight ofpolymers
Lightscattering
Inthedeterminationoftheweight-averagemolecularweightofpolymermoleculesin
dust-freesolutions,onemeasurestheintensityofscatteredlightfromamercuryarc
lamporlaseratdifferentconcentrationsandatdifferentangles(θ),typically0,90,45,
and135.Theincidentlightsendsoutascatteringenvelopethathasfourequivalent
quadrants.Theratioofscatteringat45
o
comparedwiththatfor135
o
iscalledthe
dissymmetryfactorordissymmetryratioZ.ThereduceddissymmetryfactorZ0isthe
interceptoftheplotofZasafunctionofconcentrationextrapolatedtozero
concentration
Light-scatteringenvelopes.Distancefromthescatteringparticletotheboundariesof
theenveloperepresentsthemagnitudeofscatteredlightasafunctionofangle.
Scatteringparticle
IncidentLight
Scatteringparticle

36. Determination of Molecular weight ofpolymers
Lightscattering
Severalexpressionsaregenerallyusedindescribingtherelationshipbetweenvalues
measuredbylightscatteringphotometryandmolecularweight
Atlowconcentrationsofpolymerinsolution,theaboveequationreducestoan
equationofastraightline(y=b+mx):
Whentheratiooftheconcentrationctothe
turbidity(relatedtotheintensityofscatteringat0
and90)multipliedbytheconstantHisplotted
againstconcentration,theinterceptofthe
extrapolatedcurve,isthereciprocalofMwandthe
slopecontainsthevirialconstantB,asshownin
Figure. Typicalplotusedtodetermine
Mw
-1
fromlightscatteringdata

37. Kinetics of Polymerization
Thepolymerizationofalkenesoccursinaverydifferentwaythanmonomersthat
undergocondensationreactions.Whetheritoccursthroughananionic,cationic,or
radicalmechanism,polymerizationofalkenesinvolvesachainreaction.
Atypicalradicalpolymerizationstartswiththethermaldecompositionofaradical
initiatortoprovidetworadicals.Therateofdecompositiondependsonlyonthe
decompositionrateconstantandtheconcentrationoftheinitiator.

38. Oncetheradicalshavebeengenerated,theyareabletoundergoradicaladditionto
amonomerdoublebond.Althoughthisisformallyaradicalpropagationstep,in
polymerchemistryitistermedtheinitiationstep,becauseitisthefirsttimea
monomerhasundergoneradicaladdition.Thisstepconsumesthefirstmonomer
andproducesanewradicalspecieswhichwillbecomethegrowingradicalchain.It
requiresacollisionbetweentheradicalandamonomer,sotherateofinitiation
dependsonthosetwoconcentrationsandthechaininitiationrateconstant,k
i.

39. Thatratelawdependsonareactiveintermediate.It'snotaveryhelpfulratelaw,
becausethereactiveintermediateisn'tsomethingthatwehavedirectlymeasuredout
andaddedtothereaction,anditmightnotevenoccurathighenoughlevelsthatwe
canmeasureitsconcentrationasthereactionprogresses.
Weusuallylookforwaystoexpresstheratelawinwaysthatdonotincludereactive
intermediates.Inthisparticularsituation,thewayofgettingaroundthissituationisto
assumethatthedecompositionoftheinitiatoristheratedeterminingstep.
Makingtheradicalsinthefirstplaceisprobablytheslowpartbecauseitisheavily
dependentonbondbreaking,whichisenergyintensive.Oncewehaveradical,it
probablyundergoesadditiontoamonomerfairlyquickly,initiatingchaingrowth.If
that'strue,wecanassumethatthechaininitiationstepproceedsveryquickly
afterward,sothattheratereallydependsonlyontherateofthedecompositionstep.

40. Inpractice,polymerchemistsaddanotherfactortotheratelaw.Thisfactor,f,takesinto
accountthefactthatonlysomeoftheradicalsfromtheinitiatoractuallyreactwith
monomerstoinitiategrowingchains.Therestdecaythroughsomeothersidereactions.
Usually,fisassumedtobearound0.5.
Oncethefirstmonomerhasbeeninitiatedintoaradical,itcanreactwithanother
monomertoenchainitandmakeanewradical.Thisistheprincipalpropagationstepof
thechainreaction.Thatstepwillkeeprepeating,addingmoremonomersintothe
chain.Therateconstantforthisstep,k
propork
p,isidenticalnomatterhowmany
monomershavebeenenchained,butisdistinctfromk
ibecauseofthedifferentnature
oftheradicalintermediatesinthetwodifferentsteps.

41. Thereisonelastprocess,orgroupofprocesses,tocompletethechainreactioncycle.
Intermination,tworadicalscombineinsomewaytoformclosed-shellproducts.
Thereareavarietyofwaysthatcanhappeninaradicalpolymerization.Thesimplest
eventconceptuallyiscoupling,inwhichtworadicalchainscometogetherandforma
bond.Thatstepisshownbelow.

42. Onceagain,theselasttworates--ofpropagationandoftermination--dependon
concentrationsofreactiveintermediates,whichwedonottypicallyknow.Thistime
wewilluseaverystandardassumption,whichisthattheconcentrationofthis
reactivespeciesremainsconstant,beingconsumedassoonasitisgenerated.The
usualwaythatweapplythesteadystateapproximationistoassumezerochangein
concentrationofthereactiveintermediate.Thatmeansthatthesumofalltherates
forprocessesgeneratingtheintermediateequalthesumofalltheratesconsuming
theintermediate.Inpolymerchemistry,wetakeaslightshortcut,andjustassume
thattherateofappearanceoftheradicalinthefirstplaceequalsitsrateof
disappearance.Wealreadyhaveexpressionsforbothofthoserates.
Byrearranging,wecangetanexpressionforthe
reactivechainendconcentration.Thenwecanjust
substitutetheresultintoourexpressionfor
propagationrate:
Theresultsumsupthefactorsthatcontrolthegrowth
rateforthepolymer.Thegrowthrateincreaseslinearly
withtheconcentrationofmonomer,andasthesquare
rootoftheinitiatorconcentration.Therestofthe
factorsarejustconstants,sowecanthinkoftherate
lawasonecombinedconstantandthosetwo
concentrationdependences.

43. Electronically conducting polymers
Electronicallyconductingpolymersaremacromoleculeswithgreaterelectrical
andelectronicconductivity.
Conductingpolymersareconjugatedpolymers,namelyorganiccompoundsthat
haveanextendedp-orbitalsystem,throughwhichelectronscanmovefromone
endofthepolymertotheother.
Likeinmetalsorsemiconductors,electronicallyconductingpolymersalso
resemblewiththeelectricalconductionbutwiththehelpofconjugated
delocalizeddoublebond.
Theessentialstructuralcharacteristicofallconductivityconjugatedpolymersis
theirquasi-infiniteπsystemextendingoveralargenumberofrecurringmonomer
units.Thisfeatureresultsinmaterialswithdirectionalconductivity.Theextended
πsystemofconjugatedpolymerarehighlysusceptibletochemicalorelectrical
oxidationorreduction.Thesealtertheelectricalandopticalpropertiesofthe
polymer,andbycontrollingthisoxidationandreduction,itispossibleto
systematicallycontroltheelectricalandopticalpropertieswithagreatdealof
precision.

44. 1)Poly-acetylene
2)Poly-sulphurnitride
3)Poly-para-phenylene
4)Poly-aniline
Electronically conducting polymers

45. Polyacetylene(IUPACname:polyethyne)usuallyreferstoanorganicpolymerwiththe
repeatingunit(C
2H
2)
n.Thenamereferstoitsconceptualconstruction
frompolymerizationofacetylenetogiveachainwithrepeatingolefingroups.This
compoundisconceptuallyimportant,asthediscoveryofpolyacetyleneandits
highconductivityupondopinghelpedtolaunchthefieldoforganicconductive
polymers.
Polyacetylene
Polyacetyleneconsistsofalongchainofcarbonatomswithalternatingsingle
anddoublebondsbetweenthem,eachwithonehydrogenatom.Thedoublebonds
canhaveeithercisortransgeometry.Thecontrolledsynthesisofeachisomerofthe
polymer,cis-polyacetyleneortrans-polyacetylene,canbeachievedbychangingthe
temperatureatwhichthereactionisconducted.Thecisformofthepolymeris
thermodynamicallylessstablethanthetransisomer.Despitetheconjugatednatureof
thepolyacetylenebackbone,notallofthecarbon–carbonbondsinthematerialare
equal:adistinctsingle/doublealternationexists.Eachhydrogenatomcanbereplaced
byafunctionalgroup.Substitutedpolyacetylenestendtobemorerigidthansaturated
polymers.Furthermore,placingdifferentfunctionalgroupsassubstituent'sonthe
polymerbackboneleadstoatwistedconformationofthepolymerchaintointerrupt
theconjugation.

46. Synthesis:
Avarietyofmethodshavebeendevelopedtosynthesizepolyacetylene,from
pureacetyleneandothermonomers.Oneofthemostcommonmethods
usesaZiegler–Nattacatalyst,suchasTi(OiPr)
4
/Al(C
2
H
5
)
3
,withgaseous
acetylene.Thismethodallowscontroloverthestructureandpropertiesofthe
finalpolymerbyvaryingtemperatureandcatalystloading.Mechanistic
studiessuggestthatthispolymerizationinvolvesmetalinsertionintothetriple
bondofthemonomer.
Structure:
Polyacetyleneisoneofthemostpromisingmaterialsforapplicationsin
optoelectronics.

47. Poly-sulphurnitride orPolythiazyl(SN)
x
Polythiazyl(polysulfurnitride),(SN)
x,isanelectricallyconductive,gold-orbronze-
coloredpolymerwithmetallicluster.Itwasthefirstconductiveinorganic
polymerdiscoveredandwasalsofoundtobeasuperconductoratverylow
temperatures(below0.26K).Itisafibroussolid,describedas"lustrousgoldenonthe
facesanddarkblue-black",dependingontheorientationofthesample.Itisairstable
andinsolubleinallsolvents.
Structureandbonding:
ThestructureofthecrystallinecompoundwasresolvedbyX-raydiffraction.This
showedalternatingSNbondlengthsof159pmand163pmandSNSbondanglesof120
°CandNSNbondanglesof106°C

48. Properties
Polythiazylisametallic-goldenandshiny,crystallinebutfibrousmaterial.Thepolymer
ismostlyinerttooxygenandwater,butdecomposesinairtoagreypowder.At
temperaturesabove240°Cexplosivedecompositioncanoccur.Thecompoundalso
explodesonimpact.Polythiazylshowsananisotropicelectricalconductivity.Alongthe
fibresorSNchains,thebondiselectricallyconductive,perpendiculartoitactsasan
insulator.Theone-dimensionalconductivityisbasedonthebondingconditionsinthe
S-Nchain,whereeachsulfuratomprovidestwoπelectronsandeachnitrogenatom
providesoneπelectrontoformtwo-center3πelectronbondingunits.
Synthesis
Polythiazylissynthesizedbythepolymerizationofthedimerdisulfurdinitride(S
2
N
2
),
whichisinturnsynthesizedfromthecyclicalternatingtetramertetrasulfur
tetranitride(S
4
N
4
).Conversionfromcyclictetramertodimeriscatalysedwith
hotsilverwool.
i) S
4
N
4
+ 8 Ag → 4 Ag
2
S + 2 N
2
ii) S
4
N
4
(w/ Ag
2
S catalyst) → 2 S
2
N
2
(w/ 77K cold finger) → S
2
N
2
iii) S
2
N
2
(@ 0°C, sublimes to surface) → thermal polymerization → (SN)
x
Uses
Duetoitselectricalandelectronicalconductivity,polythiazylisused
inLEDs,transistors,batterycathodes,andsolarcells.

49. Poly-para-phenylene
PROPERTIES
Poly-para-phenylene(PPP),alsocalledself-reinforcedpolyphenylene(SRP),isone
ofthestiffestandstrongestmelt-processableengineeringthermoplasticsonthe
market.Duetoitsinherentrigidrod-likestructure,itpossessesoutstanding
mechanicalpropertiesoverawidetemperaturerangeincludinghighstrengthand
modulusandmoderatehighimpactstrength.Italsopossessesahighglass
transitiontemperature(155°C)andaheatdistortiontemperatureintherangeof
150-160°C(300-325°F).Unlikemostotherhigh-performancethermoplasts,ithas
excellentmechanicalpropertiesatverylowtemperatureswithoutfiber
reinforcement.Inaddition,itpossessesexceptionalabrasionandsolvent
resistance,outstandingthermal-oxidativestability,andinherentflameresistance.
Synthesis of
Poly-para-phynylene

50. Important performance properties of Poly-para-phenylene:
•Very high mechanical strength and stiffness
•High compression strength and high pressure resistance
•Excellent resistance to wear and scratching
•Good cold temperature properties (stable to about -270°C
1
)
•High glass transition temperature of about 155°C
•Outstanding dimensional stability before and after processing
•Low thermal expansion coefficient (low thermal shrinkage)
•Outstanding acid and base resistance
•Good solvent and hot steam resistance (but lower than PEEK
1
)
•Good processability(can be extruded and injection molded)
APPLICATIONS:
Itsexceptionalmechanical,chemical,thermalandelectricalpropertiesmakeSRP
anexcellentchoiceformanyverydemandingapplicationsincludingsemiconductor
components,highperformancebushings,bearings,valves,valveseats,andaircraft
substructures.Duetoitshighspecificstrength,SRPisanexcellentcandidatefor
light-weighthigh-performanceapplications.Electricalconductivepolyphenylene
(p-orn-doped)isusedasanantistaticcoatingtoprotectintegratedcircuitsfrom
staticcharges,humidity,andcorrosion.

51. Poly-aniline
PolyanilinePANIisanintrinsicallyconductivepolymer.Thediscoveryofelectrically
conductivepolymercompositionsbasedonpolyanilineprovidesconductivematerials,
whicharesolubleinselectedorganicsolvents.Thesematerialsarewhicharemelt
processableandexhibitgoodambientstabilitycharacteristics.
Somepolyanilinebasedmaterialsaresolutionandmeltprocessable.Theyofferclear
benefitsovertraditionalplasticsmadeconductivebytheadditionoffillers(carbon
blacks,metalparticlesandflakes,metalfibres,carbonfibres,andothers).Theyprovide
preciselycontrolledelectricalconductivityoverawiderange,improvephase
compatibilityandthusblendabilitywithbulkpolymers,provideeasiermeansof
processingandformingconductiveproductsandprovidelowcostsolutionsforthe
productionoftransparentandcolouredthinfilmsandcoatings.
Synthesis of Polyaniline

52. Properties and advantages of Polyaniline
Theelectricalconductivityofpolyanilinebasedcompositionscanbeclosely
controlledoverawiderange.
Polyanilinebasedcompositionscanbeprocessedusingconventionaltechniques
suchasblowandinjectionmoulding,extrusion,calendering,filmcasting,and
fibrespinning.
Electricallyconductivepolyanilinebasedblendswithcommoditypolymerscan
beproducedbyusingcommonsolutionandmeltprocessingtechniques.
Plasticisedpolyanilinecompositionsimprovemeltprocessingperformanceby
loweringthemelt-viscosity,loweringtheprocessingtemperatureandshortening
theprocessingtime.
Electricallyconductive,colouredandtransparentthinfilmsandcoatings,which
wouldotherwisebedifficulttoachievewithconventionalfilledmaterials,canbe
madeusingpolyanilinebasedcompositions.

53. Applications of Poly-aniline
•Neatmaterials,blends,compoundsandsolutions
Polyanilinebasedconductivepolymerscanbeusedneat,orasblendsand
compoundswithcommoditypolymers.
•Electrostaticdischarge(ESD)protectionmaterials
Onetargetapplicationofthesematerialsistheprotectionfromelectrostatic
discharge(ESD).
•Intermsofyarnandfiber,PolyanilinePANIcanbeappliedforconductivetextiles,
antistaticfloors,automotiveindustry,etc.