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CHAPTER 13
INTRODUCTION TO POLYMER
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At the end of this lecture,students should be able to:
Determine types of polymer Determine physical properties ofpolymer
Determine types of polymerization
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Introduction
Polymer is a macro moleculecomprised of repeating structuralunits joined by covalent bonds.
◦
Greek word: “ poly ”= many , “ mer ”= parts he repeating unit is a !roup ofatoms covalently bonded to!etherin a speci"c spatial arran!ement.
◦ Monomer : the building block or structuralunit of the polymer.
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Types o Polymers
PolymerInorganic Organic
Natural Synthetic Natural Synthetic
• clays (bricks,cement, pottery)
• sands (glass)
• fibres • polysaccharides(starch, cellulose)
• proteins(collagen, lignins)
• polyisoprene(rubbers)
• adhesives
• fibres•
coatings• plastics• rubber
s• resinsClassi!cation "ased on #ource
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Types o Polymers
T&ermoplastics T&ermosets
'i!h molar mass molecules (ow molar mass molecules
)o crosslinkin! *rosslinked
+often upon heatin! ecompose chemicallyupon heatin!
*an be remelted *annot remelt
-ecyclable )on recyclable
Classi!cation "ased on P&ysical
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Types o Polymers
here are three di erent types based on the structureof the polymers.
◦ Linear polymers on #tructure
◦ "ranc&ed c&ain polymers
◦ Cross lin'ed or Net$or' polymers
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Types o Polymers
POLYMER N(ME
#/* #oly$vinyl chloride%
#+ #oly$styrene%
+0- +tyrene1butadiene1rubber
#2 #oly$ethylene terephthalate%
#/Ac #oly$vinyl acetate%
#/A #oly$vinyl alcohol%
#A) #oly$acrylonitrile%
+A) +tyrene1acrylonitrile copolymer
A0+ Acrylonitrile1butadiene1styreneterpolymer
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Classi!cation o Polymers
#olymers can be classi"ed as:◦ Addition polymers◦ *ondensation polymers
)o$ever* some polymers are neit&ercondensation nor addition polymers .
herefore, polymers are classi"ed based onthe polymerisation mechanism:
◦ *hain reaction◦ +tep reaction
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Classi!cation o Polymers
)omopolymers 1 consist of chainswith identical bondin% lin'a%es toeach monomer unit.
his usually implies that the polymeris made from all identical monomermolecules .
hese may be represented as : 13A1A1A1
A1A1A41
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Mode o Polymerisation
(ddition polymerisation :◦ se,uential addition of one bifunctional5
polyfunctional monomer to !rowin! polymerchains $it&out t&e elimination of any
part of the monomer molecule.# n 6 7 → # n68
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(ddition Polymerisation
( simple representation is -.(-(-(-(--
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Mode o Polymerisation
Condensation polymerisation :◦ polymers formed from bifunctional
monomers with the elimination o a smallmolecule species $w%. he reaction can
occur between any two !rowin! polymermolecules.P m 1 P n P m1n 1 $
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Condensation Polymerisation
( simple representation is -.(-"-(-"-- -
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Types o Polymeri2ationReactions
C&ain reaction :◦ polymerisation process by repeated
addition of monomer molecules to!rowin! polymer chain without theelimination of low molar mass molecules.
9 → 91*' ; 1*'- →
91*' ; 1*'-1*' ; 1*'- etc.
where 9 is an initiator
*' ; =*'- 33
*' ; =*'-
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4ree Radical Mec&anism
Initiation : *l ; → ; *lPropa%ation : *l 6 *' > → '*l 6 *' ?*' ? 6 *l ; → *' ? *l 6 *lTermination $? types%
$i%dimerisation :*' ? 6 *' ? → *' ? 1*' ? $ii%disproportionation :
*' ? 1*' ; *' ; 6 *' ? $*' ; %; *' ; → *' ? *' = *' ; 6 *' ? $*' ; %; *' ?
$iii%c&ain trans er : a chain transfer a!entdeposits a hydro!en with one electron on theradical of a !rowin! polymer chain and thisprocess initiate another polymerisation process.
uv
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Molecular 5ei%&t Control
@n polymerisation process, the aim isto control the molecular wei!ht.
he followin! variables in uence themolecular wei!ht:
◦ Temperature : the hi!her $optimum% thetemperature, the shorter the time re
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Molecular 5ei%&t Control
◦ Concentration o initiator : Dor additionpolymerisation, hi!her concentration ofinitiator will result in lower molecularwei!ht polymer.
◦ Concentration o monomer :
◦ Type o initiator : the initiator forms
radicals by decomposition reaction whichhas a half life which is dependent ontemperature and type of initiator.
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Cationic Polymerisation
Monomer (pplication
@sobutylene *' ; =*$*' ? %; 2lastomer, adhesives
/inylethers *' ; =*'F-Adhesives, te&tileaids, platiciBers
Dormaldehyde *' ; =F 2n!ineerin! plastics
2thyleneimine *yclo1$)'*' ; *' ; %#aper additive,
occulant
etrahydrofuran *yclo1$F$*' ; %>%+oft se!ment forpolyurethanes
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Cationic Polymerisation
Initiators : "ronsted acids $ perchloric acid,trichloroacetic acid, tri uoromethanesulfonic acid,etc. %CLe$is acids $ AlCl 3 , TiCl 4 , etc. %Coinitiators : water, carbenium salts $ acetyl
perchlorate %
he !rowin! polymer chain is positivelyc&ar%ed which stabilise itself by addition ofnucleophilic species.
/ery few monomers are polymerisedcationically on an industrial scale.
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Cationic Polymerisation
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(nionic Polymerisation
Anionic polymerisation are initiated bybases or Le$is bases such as alkalimetals, alko&ides, amines, phosphines,Gri!nard compounds and sodium
naphthalene. he type and proportion of the initiatin!species stron!ly a ect the polymerisationrates and the tacticity o t&e polymers$tacticity: refers to how the pendant groups arearranged in a polymeric strand isotactic,sindiotactic, atactic %
Tacticity $from Greek taktikos : of or relatin! to arran!ement or
order% is the relative stereochemistry of adjacent chiral centerswithin a macromolecule
http://en.wikipedia.org/wiki/Stereochemistryhttp://en.wikipedia.org/wiki/Chirality_(chemistry)http://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Chirality_(chemistry)http://en.wikipedia.org/wiki/Stereochemistry
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Tacticity o t&e polymers
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(nionic Polymerisation
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(nionic Polymerisation
Narro$ molar mass distribution
2mployed for the production ot&ermoplastics especially blockcopolymers $syrene1butadiene1styrene type%
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P&ysical Properties
he physical properties of polymermaterial are lar!ely determined by:
◦ Molecular $ei%&t◦ #tren%t& o intermolecular orces◦ Re%ularity o t&e polymer structure◦ 4le9ibility o t&e polymer molecule
he physical properties includemeltin% point , %lass transitiontemperature , solubility , meltviscosity , tensile stren%t& .
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P&ysical Properties
Meltin% point :◦ a temperature ran!e in which the viscosity of the
polymer chan!es from a solid to a li
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P&ysical Properties
Tensile stren%t& :◦ measures how diHcult it is to break a substance
when stress is applied to pull it apart.◦ ensile stren!th !enerally increases with molecular
wei!ht.
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T)E END
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