Polymer ppt and classification of polyme

polymer

1. Polymers
Syntheticresinsandplastics,classificationofpolymers,generalpropertiesofpolymers,structure
ofPE,PP,PVC,PS,Nylon6,Nylon66,PTFE,PETandtheiruses;frommonomertoplastic,
polymerrequirementsforpolymerformation;biodegradablepolymers.

2. •Theword‘polymer’iscoinedfromtwoGreekwords:polymeansmany
andmermeansunitorpart.
•Thetermpolymerisdefinedasverylargemoleculeshavinghigh
molecularmass.Thesearealsoreferredtoasmacromolecules,whichare
formedbyjoiningofrepeatingstructuralunitsonalargescale.
•Therepeatingstructuralunitsarederivedfromsomesimpleandreactive
moleculesknownasmonomersandarelinkedtoeachotherbycovalent
bonds.Thisprocessofformationofpolymersfromrespectivemonomers
iscalledpolymerisation.

3. •Thedegreeofpolymerization(DP)isdefinedasthenumberofmonomerunitsinthepolymer.Itis
calculatedastheratioofmolecularweightofapolymerandmolecularweightoftherepeatunit.
DP=
molecular weight of a polymer
molecular weight of the repeat unit
Classificationofpolymers
Thereareseveralwaysofclassificationofpolymersbasedonsomespecialconsiderations.The
followingaresomeofthecommonclassificationsofpolymers:
ClassificationBasedonSource
Underthistypeofclassification,therearethreesubcategories.
1.Naturalpolymers
Thesepolymersarefoundinplantsandanimals.Examplesareproteins,cellulose,starch,resinsand
rubber.
2.Semi-syntheticpolymers
Cellulosederivativesascelluloseacetate(rayon)andcellulosenitrate,etc.aretheusualexamplesofthis
subcategory.
3.Syntheticpolymers
Avarietyofsyntheticpolymersasplastic(polythene),syntheticfibres(nylon6,6)andsyntheticrubbers
(Buna-S)areexamplesofmanmadepolymersextensivelyusedindailylifeaswellasinindustry.

4. ClassificationBasedonStructureofPolymers
Therearethreedifferenttypesbasedonthestructureofthepolymers.
1.Linearpolymers
Thesepolymersconsistoflongandstraightchains.Theexamplesarehighdensitypolythene,
polyvinylchloride,etc.Thesearerepresentedas:
2. Branched chain polymers
These polymers contain linear chains having some branches, e.g., low density polythene.
These are depicted as follows:
3. Cross linked or Network polymers
These are usually formed from bi-functional and tri-functional monomers and contain strong
covalent bonds between various linear polymer chains, e.g. bakelite, melamine, etc. These
polymers are depicted as follows:

5. ClassificationBasedonmodeofpolymerisation
Polymerscanalsobeclassifiedonthebasisofmodeofpolymerizationintotwosubgroups.
1.Additionpolymers
Theadditionpolymersareformedbytherepeatedadditionofmonomermoleculespossessingdoubleortriple
bonds,e.g.,theformationofpolythenefrometheneandpolypropenefrompropene.However,theaddition
polymersformedbythepolymerisationofasinglemonomericspeciesareknownas homopolymers,e.g.,
polythene.
Thepolymersmadebyadditionpolymerisationfromtwodifferentmonomersaretermedas copolymers,e.g.,
Buna-S,Buna-N,etc.

6. 2.Condensationpolymers
Thecondensationpolymersareformedbyrepeatedcondensationreactionbetweentwodifferent
bi-functionalortri-functionalmonomericunits.Inthesepolymerisationreactions,the
eliminationofsmallmoleculessuchaswater,alcohol,hydrogenchloride,etc.takeplace.The
examplesareterylene(dacron),nylon6,6,nylon6,etc.Forexample,nylon6,6isformedby
thecondensationofhexamethylenediaminewithadipicacid.

7. ClassificationBasedonMolecularForces
Alargenumberofpolymerapplicationsindifferentfieldsdependontheiruniquemechanical
propertiesliketensilestrength,elasticity,toughness,etc.Thesemechanicalpropertiesare
governedbyintermolecularforces,e.g.,vanderWaalsforcesandhydrogenbonds,presentinthe
polymer.Theseforcesalsobindthepolymerchains.
1.Elastomers
Thesearerubber–likesolidswithelasticproperties.Intheseelastomericpolymers,thepolymer
chainsareheldtogetherbytheweakestintermolecularforces.Theseweakbindingforcespermit
thepolymertobestretched.Afew‘crosslinks’areintroducedinbetweenthechains,whichhelp
thepolymertoretracttoitsoriginalpositionaftertheforceisreleasedasinvulcanisedrubber.The
examplesarebuna-S,buna-N,neoprene,etc.

8. 2.Fibres
Fibresarethethreadformingsolidswhichpossesshightensilestrengthandhigh
modulus.Thesecharacteristicscanbeattributedtothestrongintermolecularforceslike
hydrogenbonding.Thesestrongforcesalsoleadtoclosepackingofchainsandthus
impartcrystallinenature.Theexamplesarepolyamides(nylon6,6),polyesters
(terylene),etc.

9. ClassificationBasedoneffectofheatonthem
1.Thermoplasticpolymers
Thesearethelinearorslightlybranchedlongchainmoleculescapableof
repeatedlysofteningonheatingandhardeningoncooling.Thesepolymerspossess
intermolecularforcesofattractionintermediatebetweenelastomersandfibres.
Somecommonthermoplasticsarepolythene,polystyrene,polyvinyls,etc.
2.Thermosettingpolymers
Thesepolymersarecrosslinkedorheavilybranchedmolecules,whichonheating
undergoextensivecrosslinkinginmouldsandagainbecomeinfusible.These
cannotbereused.Somecommonexamplesarebakelite,urea-formaldelyderesins,
etc.

10. ClassificationBasedonGrowthPolymerisation
Theadditionandcondensationpolymersarenowadaysalsoreferredaschaingrowthpolymers
andstepgrowthpolymersdependingonthetypeofpolymerisationmechanismtheyundergo
duringtheirformation.
Addition Polymerisation
Inthistypeofpolymerisation,themoleculesofthesamemonomerordifferentmonomersadd
togetheronalargescaletoformapolymer.Themonomersusedareunsaturatedcompounds,e.g.,
alkenes,alkadienesandtheirderivatives.Thismodeofpolymerisationleadingtoanincreasein
chainlengthorchaingrowthcantakeplacethroughtheformationofeitherfreeradicalsorionic
species.However,thefreeradicalgovernedadditionorchaingrowthpolymerisationisthemost
commonmode.

11. Condensation Polymerisation
Thistypeofpolymerisationgenerallyinvolvesarepetitivecondensationreactionbetweentwo
bi-functionalmonomers.Thesepolycondensationreactionsmayresultinthelossofsome
simplemoleculesaswater,alcohol,etc.,andleadtotheformationofhighmolecularmass
condensationpolymers.
Inthesereactions,theproductofeachstepisagainabi-functionalspeciesandthesequenceof
condensationgoeson.Since,eachstepproducesadistinctfunctionalisedspeciesandis
independentofeachother,thisprocessisalsocalledasstepgrowthpolymerisation.

14. Someimportantadditionpolymers
(a)Polythene
Therearetwotypesofpolytheneasgivenbelow:
(i)Lowdensitypolythene:Itisobtainedbythepolymerizationofetheneunderhighpressureof1000to
2000atmospheresatatemperatureof350Kto570Kinthepresenceoftracesofdioxygenoraperoxide
initiator(catalyst).Thelowdensitypolythene(LDP)obtainedthroughthefreeradicaladditionandH-atom
abstractionhashighlybranchedstructure.
Lowdensitypolytheneischemicallyinertandtoughbutflexibleandapoorconductorofelectricity.
Hence,itisusedintheinsulationofelectricitycarryingwiresandmanufactureofsqueezebottles,toys
andflexiblepipes.
(ii)Highdensitypolythene:Itisformedwhenadditionpolymerisationofethenetakesplaceina
hydrocarbonsolventinthepresenceofacatalystsuchastriethylaluminiumandtitaniumtetrachloride
(Ziegler-Nattacatalyst)atatemperatureof333Kto343Kandunderapressureof6-7atmospheres.
Highdensitypolythene(HDP)thusproduced,consistsoflinearmoleculesandhasahighdensitydueto
closepacking.Itisalsochemicallyinertandmoretougherandharder.Itisusedformanufacturing
buckets,dustbins,bottles,pipes,etc.

16. (b)Polytetrafluoroethene(Teflon)(PTFE)
Teflonismanufacturedbyheatingtetrafluoroethenewithafreeradicalorpersulphate
catalystathighpressures.Itischemicallyinertandresistanttoattackbycorrosive
reagents.Itisusedinmakingoilsealsandgasketsandalsousedfornon–sticksurface
coatedutensils.

17. (PP)
(PS)

18. CondensationPolymerisation
Polyamides
Thesepolymerspossessingamidelinkagesareimportantexamplesofsyntheticfibresandaretermed
asnylons.Thegeneralmethodofpreparationconsistsofthecondensationpolymerisationof
diamineswithdicarboxylicacidsandalsoofaminoacidsandtheirlactams.
(i)Nylon6,6:Itispreparedbythecondensationpolymerizationofhexamethylenediaminewith
adipicacidunderhighpressureandathightemperature.
Nylon6,6isusedinmakingsheets,bristlesforbrushesandintextileindustry.
(ii)Nylon6:Itisobtainedbyheatingcaprolactumwithwateratahightemperature.
Nylon6isusedforthemanufactureoftyrecords,fabricsandropes.

19. Polyesters
•Thesearethepolycondensationproductsofdicarboxylicacidsanddiols.
Dacron(PET)
•Dacronorteryleneisthebestknownexampleofpolyesters.
•Itismanufacturedbyheatingamixtureofethyleneglycolandterephthalicacidat
420to460Kinthepresenceofzincacetate-antimonytrioxidecatalyst.
•Dacronfibre(terylene)iscreaseresistantandisusedinblendingwithcottonand
woolfibresandalsoasglassreinforcingmaterialsinsafetyhelmets,etc.
•Theformationofteryleneordacronbytheinteractionofethyleneglycoland
terephthalicacidisanexampleofthistypeofpolymerisation.
Polyethylene terephthalate (PET)

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