Polymers

1. Linear, Branched, and Cross-linked Polymers
Linearstructure–chain-likestructure
Characteristicofthermoplasticpolymers
Branchedstructure–chain-likebutwithsidebranches
Alsofoundinthermoplasticpolymers
Cross-linkedstructure
Looselycross-linked,asinanelastomer
Tightlycross-linked,asinathermoset

2. Linear structure
Structure of a thermoplastic polymer

3. Branched structure
Includes side branches along the chain

4. Loosely cross-linked
Bonding occurs between branches e.g. elastomers

5. Tightly cross-linked or network structure
Thermosetting polymers

6. Effect of Branching on Properties
Thermoplasticpolymers-
Alwayspossesslinearorbranchedstructures,oramixture
ofthetwo
Branchesincreasedisorderamongthemolecules,
whichmakesthepolymer:
Strongerinthesolidstate
Moreviscousatagiventemperatureintheplasticor
liquidstate

7. Effect of Cross-Linking on Properties
Thermosetspossessahighdegreeofcross-linking,
whileelastomerspossessalowdegreeofcross-linking
Thermosetsarehardandbrittle,whileelastomersare
elasticandresilient
Cross-linkingcausesthepolymertobecomechemically
set
Thereactioncannotbereversed
Thepolymerstructureispermanentlychanged;ifheated,it
degradesorburnsratherthanmelt

8. Mechanical Properties of Thermoplastics
Lowmodulusofelasticity(stiffness)-lowerthanmetals
andceramics
Lowtensilestrength,hardnessthanmetalsorceramics
Greaterductilityonaverage

9. Important thermoplastic resins
Commerciallyimpthermoplasticresinsincludenatural
resinsandresinsderivedfrombiopolymersand
suntheticresins
NaturalResins-resinssuchascopal,amber,rosin,
kauri,dammarandmastic,usedinvarnishes.
Whentheplantsandtreesarewoundedtheyexude
resinsknownasbalsamsasaprotectivemeasure.
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10. Naturalresinpolymersarehardwithlowthermal
conductivityandlowdielectricconstant
Theyfinduseinelectricalinsulationandbinders
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11. Cellulose derivatives
Naturallyoccurringcellulose-isapolymerof
glucose,apolyhydroxymoleculerepresentedby
generalformula(C
6H
10O
5)
n
Mostwidelyusedcellulosederivatives
Celluloseesters-cellulosenitrateandcelluloseacetate
Celluloseethers-methylcelluloseandethylcellulose
-
Thesederivativeshavefilmformingcapabilitybutthe
filmsarenotadherent.Theyalsotendtowrinkle
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12. POLY VINYL CHLORIDE (PVC)
Whenvinylchlorideisheatedinanautoclaveunder
pressinthe+nceofinitiatorlikeH
2O
2toyieldPVC
nCH
2=CH →-(-CH
2-CH-)
n-
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ClCl Cl
CCCCCC
HHH
HHHHHH
Polyvinyl chloride (PVC)
Cl Cl

13. PVCiscolorlessandodorlesspowder,
chemicallyinert,non-inflamable,exhibithigh
resistancetolight,atmosphericoxygen,acids
andalkalis
ItissolubleinchlorinatedHC(ethylchloride),
tetrahydrofuran(THF)andcyclohexanone
CommercialPVCknownunderdifferenttrade
nametygon,vinylite,velon,geonetcisahard
andstiffamorphousplasticattributedtoits
strongintermolecularforcesbutbrittle
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Pure Polyvinyl Chloride powder
POLY VINYL CHLORIDE (PVC)

14. Manufactureofpipes,tubes,tanklinings,safety
helmets,refrigeratorcomponents,lightfittings,trays,
cycleandmotorcyclemudguards
Inthemanufactureofflexiblefilmsorsheetsof
varyingthickness(0.1-8mm)requiredformaking
tableclothes,curtains,raincoats
Alsousedforwirecoatingandinsulationofeletric
cablesandmanufactureofupholstery
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POLY VINYL CHLORIDE (PVC)

15. Polytetrafluoroethylene (PTFE)
PTFEisasyntheticfluoropolymerof
tetrafluoroethylenethatfindsnumerousapplications
ThemostwellknownbrandnameofPTFEisTeflon
PTFEishydrophobic:neitherwaternorwater-
containingsubstanceswetPTFE,asfluorocarbons
demonstratemoderatedispersionforcesduetothe
highelectronegativityoffluorine.
Hasthelowestcoefficientsoffrictionagainstanysolid
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16. Teflon Monomer
C C
F
F
F
F
tetrafluoroethylene

17. Teflon Polymer
n

18. PTFE
PTFEisusedasanon-stickcoatingforpansandother
cookware.
Itisverynon-reactivebecauseofthestrengthofC–F
bonds,andsoitisoftenusedincontainersandpipework
forreactiveandcorrosivechemicals.
Itisusedaslubricant-reducesfriction,wear,andenergy
consumptionofmachinery.
Hashighresistancetowearanddeformationunderload
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19. PTFE
Alreadyhashighstrength
compressivestrengthofPTFEproductscanalsobefurther
enhancedbyadditionoffillerssuchasasbestos,glassfibers,
graphiteetc
Thispolymerhasexceptionallyhighsofteningpoint
(M.P.327°C)
Agoodelectricalinsultorusedinwires,cables,motors
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20. POLYCARBONATE
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21. PCarethermoplasticpolystershavingfunctionalgroupslinked
togetherbycarbonategroups(-O-(C=O)-O)inalongmolecular
chainandcommerciallyknownasMERLON,LEXAN.
Mostcommontypeofpolycarbonateplasticsareobtainedby
diphenylcarbonatewithbis-phenolA(2,2-bis-(4-hydroxyphenyl)-
propane)togivebisphenolAgroupslinkedbycarbonategroups
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POLYCARBONATE

22. PChavehightensileandimpactstrengthoverawide
rangeoftemperatures
Polymersarehighlytransparenttovisiblelightand
havebetterlighttransmissioncharacteristicsthanmany
typesofglasses
Theyaresolubleinorganicsolventsandalkalis
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POLYCARBONATE

23. Synthesis of Polycarbonate
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BPA-Bisphenol A Phosgene Polycarbonate
FromBPAandPHOSGENE:

24. Synthesis of Polycarbonate
Alternative Route
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FromBPAanddiphenylcarbonate:
(HOC
6H
4)
2CMe
2 + (C
6H
5O)
2CO→-[OC(OC
6H
4)
2CMe
2]-
n
Diphenyl carbonatePolycarbonate
+
Bisphenol A (BPA)
+ 2 C
6H
5OH

25. APPLICATIONS
PCareusedformakingMOULDEDdomesticwares,
housingforapparatusandelectricalinsulation
Usedinmanufactureofsunglasses/eyeglasslenses
CR-39isaspecificpolycarbonateplasticwithgoodopticaland
mechanicalproperties
CDs,DVDs,nalgenebottlesandfoodstorage
containers
Theycanbelaminatedtomakebulletproofglass
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26. PHENOLIC RESINS (PHENOPLAST)
PHENOLICRESINSarederivedfromthecondensationreaction
betweenphenolorphenolicderivatives(e.g.resorcinol)and
aldehydes(formaldehydeandfurfural)
Commerciallyimp.Aswellastheerliestphenolicresinsknownas
bakeliteisobtainedbycondensationpol.ofphenolwith
formaldehyde
Linearpoly.Aswellashighlycrosslinked3-Dnetworkstructurecan
beobtainedbyvaryingtheproportionofphenoland
formaldehydeaswellasthenatureofcatalyst
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27. Ifthephenoltoformaldehyde(P/F)ratioisgreater
than1,alinearpolymerisobtainedwithanacid
catalyst
OntheotherhandwithP/Fratiolessthan1andwitha
basiccatalysta3Dnetworkpolymerisobtained
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28. Phenolreactswithformaldehydeinitiallytoformmethylol
derivativesintheo-andp-positionswhichundergopolymerization
inthepresenceofacidcatalysttoyieldmethylenebridgedlinear
polymericresincalledNOVOLACresinwithm.w.intherangeof
about1000correspondingtoabout10phenylresidues
NOVOLACresincanundergofurtherpolymerizationtoyield3D
polymersonlywhenaccessformaldehydeisaddedandabasic
catalystisused
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29. Resoleresinisobtainedbycondensingphenolwithaccessof
formaldehyde(P/F<1)inthepresenceofbasiccatalyst
Thereactionisexothermicandhencerequirecooling
Viscosityofthemixincreasesindicatingtheformationof
polymer
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30. Condensationproductwaterisremovedbysuctiontoyielda
thermoplasticA-stageresinsolubleinorganicsolvents
A-stageresinispowderedandnecessaryfillers,colorants,
lubricantsareaddedthenadditionalamountofformaldehyde
requiredisaddedintheformofhexamethylenetetraminewhich
decomposestoformHCHOandNH3duringthefinalstep
NH3actsasacuringcatalyst
Mixtureisrolledinheatedmixingequipmentstofacilitatethe
continuationofthepolymerizationreactiontoyieldB-stageresin
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31. Resiniscooledandcutintorequiredform
B-stageresinisnearlyinsolubleinorganicsoventsbut
canbefusedwiththeapplicationofheatandpressure
B-stageresinismouldedintothefinaldesiredfinished
productandduringmouldingthehighlycrosslinkedC-
stagepolymer(bakeliteisformed)
Finishedproductisremovedfromthemouldandcant
bereshapedorreclaimedinanymannerasthe
polymerhasbeenpermanentlycuredbyheatsettings
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32. Properties and applications
Phenolic Resins have good adhesive and bonding
properties
After heat setting exhibit high resistance to heat,
flammability, abrasion, water, chemicals and
solvents
However they are susceptible to attack by alkalis
They are hard and infusible with good dielectric
properties
Fillers are used during molding of these resins to
reduce cost and also to impart specific properties
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33. Commonfillers-woodpowder,asbestos,cottonrags
etc
Phenolicresinsfinduseinthemanufactureof
electricinsulationpartssuchasswitches,plugs,switch
boards,handlesforelectricalappliances
Moldedpartsforautomobiles,PCBsandconsumer
electronicsandbearinginpropellershaftsforrolling
millsandpapermills
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