Chapter 1 Intro Polymers

8/19/2019 Chapter 1 Intro Polymers

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Introduction

to PolymersChapter 1


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Polymers: Introduction

• Polymer: High molecular weight molecule made up of a

small repeat unit (monomer).

– A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A

• onomer: !ow molecular weight compound that can "e

connected together to gi#e a poymer

• $ligomer: %hort polymer chain• Copolymer: polymer made up of & or more monomers

– 'andom copolymer: A---A-A--A--A----A-A-

– Alternating copolymer: A--A--A--A--A--A--A-

– loc copolymer: A-A-A-A-A-A-A-A--------


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3

Polymer

Poly mer many repeat unit (building blocks)

C C C C C C

HHHHHH

HHHHHH

Polyethylene (PE)

ClCl Cl

C C C C C C

HHH

HHHHHH

Poly(vinyl chloride) (PVC)

HH

HHH H

Polypropylene (PP)

C C C C C C

CH3

HH

CH3CH3 H

repeat

unit

repeat

unit

repeat

unit

Carbon chain backbone


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• hat are the general structural and chemical

characteristics o! polymer molecules"

• hat are some o! the common polymeric

materials# and ho$ do they di!!er chemically"

• Ho$ is the crystalline state in polymers

di!!erent !rom that in metals and ceramics "

P$!*+' %,'C,'+%


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%

Chemistry and %tructure of Polyethylene

•Polyethylene is a long&chain hydrocarbon'•op !igure sho$s repeat unit and chain structures'•ther !igure sho$s *ig*ag backbone structure'

Tetrahedral

arrangement

of C-H


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+ncient Polymers

• ,aturally occurring polymers (those derived!rom plants and animals) have been used !or

centuries'

– ood – -ubber

– Cotton – ool

– .eather – /ilk

• ldest kno$n uses

– -ubber balls used by 0ncas


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Cellulose

• Cellulose is a highly abundant organic compound'E1tensive hydrogen bonding bet$een the chains causesnative celluose to be roughly 24 crystalline' 0t alsoraises the melting point (5678C) to above itscombustion temperature'

• Cellulose serves as the principal structural component o!green plants and $ood'

• Cotton is one o! the purest !orms o! cellulose and hasbeen cultivated since ancient times'

• Cotton also serves (along $ith treated $ood pulp) as thesource the industrial production o! cellulose&derivedmaterials $hich $ere the !irst 9plastic9 materials o!commercial importance'

http://en.wikipedia.org/wiki/Cottonhttp://en.wikipedia.org/wiki/Cottonhttp://en.wikipedia.org/wiki/Cotton


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-ubber

• + variety o! plants produce a sap consisting o! a colloidaldispersion o! cis&polyisoprene' his milky !luid is especiallyabundant in the rubber tree (Hevea): it drips $hen the bark is$ounded'

• +!ter collection# the late1 is coagulated to obtain the solidrubber' ,atural rubber is thermoplastic# $ith a glass transition

temperature o! –28C'• -a$ natural rubber tends to be sticky $hen $arm and brittle

$hen cold# so it $as little more than a novelty material $hen !irstintroduced in Europe around ;22'

• 0t did not become generally use!ul until the mid&nineteenthcentury $hen Charles


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Common Polyolefinsonomer Polymer

Ethylene

H3C CH3n-epeat unit

Polyethylene

CH3CH3

n

CH3 CH3 CH3 CH3 CH3 CH3CH3Propylene

Polypropylene

PhCH3

n

Ph Ph Ph Ph Ph PhPh/tyrene

Polystyrene

ClCH3

nCl Cl Cl Cl Cl ClCl

Vinyl ChloridePoly(vinyl chloride)

>6C C>6

etra!luoroethylene

>3C

>6C

C>6

>6C

C>6

>6C

C>6

>6C

C>6

>6C

C>6

>6C

C>6

C>3n

Poly(tetra!luoroethylene)? e!lon


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Polyesters Amides and

rethanesonomer Polymer

C)6HH)6CH)

)H) )

H) )H6C

H6C )

nerephthalic

acid

Ethyleneglycol

Poly(ethylene terephthalate

H

Ester

H H

@ H6, ,H6@ +dipic +cid ;#A&Biaminohe1ane ,ylon A#A

H ,H

,H

H

@ @n

C6HH6C

erephthalic

acid

,H6H6,

;#@&Biamino

ben*ene

evlar

H

H,

H, H

n

+mide

H))H

Ethyleneglycol

H6C)C, ,C)

@#@&diisocyantophenylmethane /pande1

H6

C

H

,

H

,

)

H)

)

)

H6

C

H6

C ) Hn

Drethane linkage


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/atural Polymersonomer Polymer

0soprenen

Polyisoprene?,atural rubber

H

H

H

H

H

HHH

H

H

Poly(&B&glycoside)?cellulose

H

H

H

H

HHH

H

H

H

n

&B&glucose

H3,

)

)

-

Polyamino acid?protein

H3,

)H,

-;

)H,

-nF;

)

)H

-nF6n

+mino +cid

Gase

H

P

oligonucleic acidB,+

,ucleotideGase C#


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0hat aes Polymers niue2

• 'eally "ig molecules (macromolecules) lie

polymers ha#e #ery different properties than

small molecules–Chain entanglement: Longpolymer chains get entangled with

each other.

•When the polymer is melted, thechains can flow past each other.

•Below the melting point, the chains

can move, but only slowly. Thus theplastic is flexible, but cannot be easilystretched.

•Below the glass transition point, thechains become locked and the

polymer is rigid


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Physical Properties

/tretch

!inear Polymer

he chains can be stretched# $hich causesthem to !lo$ past each other' hen released#the polymer $ill not return to its original !orm'

/tretch

Cross-!ined Polymer

he cross&links hold the chains together'hen released# the polymer $ill return to itIsoriginal !orm'

-ela1


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Polymer icrostructure

Polyolefins with side chains have stereocenters on every other carbo

CH3n

CH3 CH3 CH3 CH3 CH3 CH3CH3

With so many stereocenters, the stereochemistry can be complex. There

are three main stereochemical classifications for polymers.

Atactic: random orientation

Isotactic: +ll stereocenters have same orientation

%yndiotactic: +lternating stereochemistry


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How to 3etermine icrostructure213C NMR is a very powerful way to determine the

microstructure of a polymer.

;3

C ,J- shi!t is sensitive to the t$ostereocenters on either side on sptectrometers

5 3 JH*' his is called pentad resolution'

r mm r mr

mmrm pentad

m meso (same orientation)r racemic (opposite orientation)

;6 ; 6

13C NMR spectrum of CH3

region of atactic


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0hy is this important2

• ,acticity affects the physical properties

– Atactic polymers will generally "e amorphous

soft fle4i"le materials

– Isotactic and syndiotactic polymers will "e

more crystalline thus harder and less fle4i"le• Polypropylene (PP) is a good e4ample

– Atactic PP is a low melting gooey material

– Isoatactic PP is high melting (1567) crystalline

tough material that is industrially useful – %yndiotactic PP has similar properties "ut is

#ery clear. It is harder to synthesi8e


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Hydrocarbon Jolecules

• Jany organic materials are

hydrocarbons (composed o! hydrogenand carbon)'

• Jost polymers are made up o! H and C'

• he bonds bet$een the hydrocarbonmolecules are covalent'

• Each carbon atom has @ electrons that

may be covalently bonded# the hydrogen

atom has ; electron !or bonding'

• + single covalent bond e1ists $hen each

o! the 6 bonding atoms contributes one

electron (e1? methane# CH@)'


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/aturated Hydrocarbons

Each carbon has a

single bond to @ otheratoms: the @ valence

electrons are bonded#

the molecule is stable'

E1amples are seen inthe table'

he covalent bonds in

each molecule are

strong# but only $eakhydrogen and van der

aals bonds e1ist

bet$een the

molecules'

Jost o! these hydrocarbons have relativelylo$ melting and boiling points'

Ho$ever# boiling temperatures rise $ithincreasing molecular $eight'


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Dnsaturated Hydrocarbons

•Bouble K triple bonds are some$hat unstable –involve sharing 6 or 3 pairs o! electrons#respectively' hey can also !orm ne$ bonds – Bouble bond !ound in ethylene & C6H@

– riple bond !ound in acetylene & C6H6

C CH

H

H

H

C C HH


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0somerism

• $o compounds $ith same chemical !ormula canhave di!!erent structures (atomic arrangements)'

!or e1ample? C7H;7• normal&octane

• 6#@&dimethylhe1ane

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H3C CH6 CH6 CH6 CH6 CH6 CH6 CH3

H3C CH

CH3

CH6 CH

CH6

CH3

CH3

H3C CH6 CH3( )A


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Jonomer

.ong chain polymer

Synthesis/ polymerization

The natureof the

catalyst

used

The way thechain grow

the final

product


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The important of polymerization

-Affect the structure- hence properties-Sometimes can convert

monomers directly to finish

product


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Three- Stage Process for Chain Growth Polymerization


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%tep-9rowth Polymeri8ation

/tage ;

Consumptiono! monomer

n n

/tage 6

Combinationo! small !ragments

/tage 3

-eaction o!oligomers to givehigh molecular$eight polymer


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@3@3

+ddition (Chain) Polymeri*ation

– Initiation

– Propagation

– ,ermination


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@@@@

Condensation (/tep) Polymeri*ation


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Polymeri*ation

• >ree radical polymeri*ation? ethylene gas reacts $ith

the initiator (catalyst)' (M-'N is the unpaired electron)

C C

H H

HH

monomer (ethylene)

- F

!ree radical

- C C

H

H

H

H

initiation

- C C

H

H

H

H

C C

H H

HH

F - C C

H

H

H

H

C C

H H

H H

propagation

dimer

Jonomer re!ers to the small molecule !rom $hich apolymer is synthesi*ed'


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/ome Common +ddition Polymers


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/ome Condensation Polymers


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J.ECD.+- E0


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olecular 0eight of PolymersUnlike small molecules, polymers are typically a mixture of

differently sized molecules. Only an average molecular weight

can be defined.

•Measuring molecular weight

•Size exclusion chromatography

•Viscosity

•Measurements of average molecularweight (M.W.)

•Number average M.W. (Mn): Total

weight of all chains divided by # ofchains

•Weight average M.W. (Mw):

Weighted average. Always largerthan Mn

•Viscosity average M.W. (Mv):

Average determined by viscosity

O o! molecules

Jn

J$

increasing molecular $eight

Jv


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0hat the 0eights eanMn: This gives you the true average weight

Let's say you had the following polymer sample:2 chains: 1,000,000 Dalton 2,000,000

5 chains: 700,000 Dalton 3,500,000

10 chains: 400,000 Dalton 4,000,000

4 chains: 100,000 Dalton 400,000

2 chains: 50,000 Dalton 100,00010,000,000

10,000,000/23 = 435,000 Dalton

1 Dalton = 1 g/mole


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0eight A#erage olecular 0eight

Mw: Since most of the polymer mass is in the heavier

fractions, this gives the average molecular weight of the most

abundant polymer fraction by mass.6##

;##= '6×;## = 6#

3#%#

;## = '3%× 2# = 6@%#

@##

;##= '@× @# = ;A#

@#

;##

= '@ ×;# = @#

;#

;##= ';× %# = %

otal = A#%


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Begree o! Polymeri*ation# DP

DP average number o! repeat units per chain

weightmolecularunitrepeatwhere =m

m

M DP

n

=

E1' problem @';b#

!or PVC? m 6(carbon) F 3(hydrogen) F ;(Clorine)

(!rom !ront o! book) 6(;6';;) F 3(;'7) F ;(3%'@%)

A6'@A gQmol

BP 6;#;% Q A6'@A 337'@6


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Polymer Chain .engths

• Jany polymer properties are a!!ected by the

length o! the polymer chains' >or e1ample# themelting temperature increases $ith increasing

molecular $eight'

• +t room temp# polymers $ith very short chains

(roughly ; gQmol) $ill e1ist as liLuids'

• hose $ith $eights o! ; gQmol are typically

$a1y solids and so!t resins'

• /olid polymers range bet$een ;# and severalmillion gQmol'

• he molecular $eight a!!ects the polymerRs

properties (e1amples? elastic modulus K strength)'

Polymers Jolecular /hape


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Polymers – Jolecular /hape

• /traight (b) and t$isted (c) chain segments are

generated $hen the backbone carbon atoms (darkcircles) are oriented as in the !igure above'

• Chain bending and t$isting are possible by rotation o!

carbon atoms around their chain bonds'

• /ome o! the polymer mechanical and thermal

characteristics are a !unction o! the chain segment

rotation in response to applied stresses or thermal

vibrations'


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Jolecular /tructures !or Polymers

• he physical characteristics o! a polymer dependalso on di!!erences in the structure o! the

molecular chains (other variables are shape and

$eight)'

• .inear polymers have repeat units Soined end toend in single chains' here may be e1tensive van

der aals and hydrogen bonding bet$een the

chains' E1amples? polyethylene# PVC# nylon'

Granched Cross&.inked ,et$ork.inear

secondarybonding


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Jolecular /tructures& Granched

• here side&branch chains have connected to main chains#

these are termed branched polymers' .inear structures

may have side&branching'

• HBPE – high density polyethylene is primarily a linear

polymer $ith minor branching# $hile .BPE – lo$ density

polyethylene contains numerous short chain branches'

•


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Jolecular /tructures

Cross&linked# ,et$ork

• 0n cross&linked polymers# adSacent linear chainsare Soined to one another at various positions by

covalent bonding o! atoms' E1amples are the

rubber elastic materials'

• /mall molecules that !orm 3 or more activecovalent bonds create structures called net$ork

polymers' E1amples are the epo1ies and

polyurethanes'

Granched Cross&.inked ,et$ork.inear

secondarybonding


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hermoplastics and hermosets• he response o! a polymer to mechanical !orces at elevated

temperature is related to its dominant molecular structure'• ne classi!ication o! polymers is according to its behavior

and rising temperature' hermoplastics and hermosets are

the 6 categories'

• + thermoplastic is a polymer that turns to a liLuid $henheated and !ree*es to a very glassy state $hen cooled

su!!iciently'

• Jost thermoplastics are high&molecular&$eight polymers

$hose chains associate through $eak Van der aals !orces

(polyethylene): stronger dipole&dipole interactions and

hydrogen bonding (nylon)'


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• hermoplastic polymers di!!er !rom thermosetting

polymers (Gakelite# vulcani*ed rubber ) since

thermoplastics can be remelted and remolded'

• hermosetting plastics $hen heated# $ill

chemically decompose# so they can not berecycled' Tet# once a thermoset is cured it tends to

be stronger than a thermoplastic'

• ypically# linear polymers $ith minor branched

structures (and !le1ible chains) are thermoplastics'he net$orked structures are thermosets'

hermoplastics and hermosets

E l ! h l i


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E1amples o! hermoplastics


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Jore E1amples o! hermoplastics

http://www2.dupont.com/Teflon/en_US/index.html

http://en.wikipedia.org/wiki/Teflon

Polymer

/peci!ic hermoplastic Properties

http://www2.dupont.com/Teflon/en_US/index.htmlhttp://en.wikipedia.org/wiki/Teflonhttp://www2.dupont.com/Teflon/en_US/index.htmlhttp://en.wikipedia.org/wiki/Teflonhttp://www2.dupont.com/Teflon/en_US/index.html


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/peci!ic hermoplastic Properties

hermoset data


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hermoset data


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hermoset Properties

/peci!ic Elastomeric Properties


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/peci!ic Elastomeric Properties

Elastomers# o!ten re!erred to as rubber# can be a thermoplastic or a thermosetdepending on the structure' hey are e1cellent !or parts reLuiring !le1iblity#strength and durability? such as automotive and industrial seals# gaskets andmolded goods# roo!ing and belting# aircra!t and chemical processing seals#!ood# pharmaceutical and semiconductor seals# and $ire and cable coatings'

h l ti h t


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3

• hermoplastics? &&little cross linking &&ductile

&&so!ten $ith heating

&&polyethylene

polypropylene

polycarbonate polystyrene

• hermosets?

&&large cross linking (; to %4 o! mers)

&&hard and brittle

&&do , so!ten $ith heating

&&vulcani*ed rubber# epo1ies#

polyester resin# phenolic resin

Callister,Fig. 16.9

T

Molecular weight

Tg

Tmmobileliquid

viscousliquid

rubber

toughplastic

partiallycrystalliesolid

crystalliesolid

hermoplastic vs hermoset

C t lli it i P l


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Crystallinity in Polymers

• he crystalline state may

e1ist in polymeric materials'• Ho$ever# since it involves

molecules instead o! Sustatoms or ions# as $ith metals

or ceramics# the atomicarrangement $ill be morecomple1 !or polymers'

• here are ordered atomicarrangements involving

molecular chains'• E1ample sho$n is a

polyethylene unit cell (orthorhom"ic).

C t l /t t


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Crystal /tructures

>e3C – iron carbide –

orthorhombic crystal

structure

The effect of temperature on the structure and


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©

2 0 0 3 B r o o k s / C o l e , a d i i s i o n o f T h o m s o n ! e a r n i n g , " n c # T h o m s o n ! e a r n i n g $ i s a t r a d e m a r k u s e d h e r e i n u n d e r l i c e n s e #

The effect of temperature on the structure andbehavior of thermoplastics.

Pol mer Cr stallinit


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Polymer Crystallinity

Polymers are rarely ;4 crystalline

• Bi!!icult !or all regions o! all chains tobecome aligned

• Begree o! crystallinity

e1pressed as 4 crystallinity' && /ome physical propertiesdepend on 4 crystallinity'

&& Heat treating causes

crystalline regions to gro$

and 4 crystallinity to

increase'

crystallineregion

amorphousregion

,ypes of Polymers


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,ypes of Polymers

• Polymer Classifications

– ,hermoset: cross-lined polymer that cannot "emelted (tires ru""er "ands)

– ,hermoplastic: elta"le plastic

– +lastomers: Polymers that stretch and then return to

their original form: often thermoset polymers – ,hermoplastic elastomers: +lastic polymers that can

"e melted (soles of tennis shoes)

• Polymer amilies

– Polyolefins: made from olefin (alene) monomers

– Polyesters Amides rethanes etc.: monomers lined

"y ester amide urethane or other functional groups

– /atural Polymers: Polysaccharides 3/A proteins

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Chapter 1 Intro Polymers

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