Polymers and polymer chemistry

7/23/2019 Polymers and polymer chemistry

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PolymersLarry Scheffler

Version 1.0


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Defnitions

Polymer:a long chain molecule made

up of many small identical units.

Monomer:the smallest repeating unit of

a polymer (propene in polypropylene).

.


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IUPAC Defnition A polymer is a substance composed of

molecules characterized by the multiple

repetition of one or more species of

atoms or groups of atoms (constitutional

repeating units) lined to each other inamounts sufficient to pro!ide a set of

properties that do not !ary maredly

"ith the addition of one or a fe" of theconstitutional repeating units.#


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Common Polymers

$olymers are common in nature. %ood&

rubber& cotton& sil& proteins& enzymes&

and cellulose are all e'amples of polymers

A "ide !ariety of synthetic polymers ha!e

been produced& largely from petroleum

based ra" materials. hese include

polyurethane& teflon& polyethylene&polystyrene& and nylon.


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Common Polymers


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Polymer Recycling Codes

ommon household polymers


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Polymers

he number code indicates the polymer type


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Polymers

ypes of synthetic and natural polymers.


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Addition Polymers

Addition polymerization* a reaction in "hichunsaturated monomers combine "ith each other to forma polymer

+'ample* etrafluoroethene can be polymerized to form

polytetrafluoroethene& commonly no"n as eflon


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Addition Polymers

Some common addition polymers

,any plastics areaddition polymersmade from

hydrocarbonsources.

he hydrocarbonmust beunsaturated in orderto polymerize


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Addition Polymers

$oly!inyl chloride

$oly!inyl chloride or

$V is "ide used

for pipes and other

structural materials Vinyl chloride is also

no"n as

chloroethene


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Condensation Polymers

ondensation polymers form from

condensation reactions.

-n a condensation polymer a smaller

molecule such as "ater is eliminated

-n order to form a condensation polymer

the monomer must ha!e t"o functional

groups


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Example o a CondensationPolymer

ylon // is a condensation polymer

-t is also a copolymer since it is made from

t"o different monomers


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Example o a CondensationPolymer 2

acron is also a condensation polymer

-t is also a copolymer since it is made from t"o

different monomers

Ethylene Glycol (1,2ethanediol) para Terephthalic acid

Dacron is an example o a polyester


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Co-polymers

o polymers are made from than onemonomer

,any natural polymers are copolymers.

2or e'ample& proteins are condensationpolymers formed by 3oining as many as 40

different amino acids


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Polymer Structure

Molec!lar Mass:5 $olymers are high molecular mass structures

5 +'tremely large molecular "eights are to be found in

polymers "ith !ery long chains.

Molec!lar "hape:5 $olymer chain molecules are usually straight chains

5 hese chains may bend& coil and in& leading to

e'tensi!e intert"ining and entanglement of neighboring

chain molecules.

5 hese random coils and molecular entanglements are

responsible for many of the important characteristics of

polymers.


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!e Polymer StructureDetermines its C!aracteristics

he physical properties of a polymer& such as its strengthand fle'ibility depend on:

#hain len$th -n general& the longer the chains thestronger the polymer6

"ide $ro!ps $olar side groups gi!e stronger attractionbet"een polymer chains& maing the polymer stronger6 %ranchin$ Straight& unbranched chains can pac

together more closely than highly branched chains. hesepolymers are more crystalline and therefore stronger6

#ross&lin'in$ -f polymer chains are lined togethere'tensi!ely by co!alent bonds& the polymer is harder andmore difficult to melt.


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Structure" #inear Polymers

5Linear $olymers ha!e monomerunits that are 3oined together end toend in single fle'ible chain.

5Linear polymers ha!e e'tensi!e !ander %aals attractions bet"een thechains.

5+'amples* polyethylene& poly!inylchloride& polystyrene& and nylon


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Structure" $ranc!ed Polymers

5 7ranched $olymers ha!e side or branchchains are connected to the main ones.

5 he branches& considered to be the part

of the mainchain molecules& result fromside reactions that occur during thesynthesis of the polymer.

5 he pacing efficiency is reduced "ith

the formation of side branches& "hichresults in a lo"ering of the polymerdensity


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Structure" Cross-#in%ed Polymers

5Ad3acent linear chains are 3oined one toanother at !arious positions by co!alentbonds.

5 he process of cross lining is achie!ed eitherduring synthesis or by a nonre!ersiblechemical reaction that is usually carried out atan ele!ated temperature.

5 his cross lining is accomplished by additi!eatoms or molecules that are co!alently bonded

to the chains.5 ,any of the rubber elastic materials are cross

lined. -n case of rubbers& it is called!ulcanization


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Structure" &et'or% Polymers

5 et"or $olymers ha!e trifunctionalmonomer units&

5 8a!ing three acti!e co!alent bonds allo"

these polymers to form threedimensionalnet"ors instead of the linear chainframe"or

5 et"or polymers ha!e distincti!emechanical and thermal properties.

5 +'amples include epo'ies and otheradhesi!es.


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Polymer Properties

Stretch

Linear Polymer

The chains can be stretched, which causes

them to flow past each other. When released,the polymer will not return to its original form.

Stretch

Cross-Linked Polymer

The cross-links hold the chains together.When released, the polymer will return to it'soriginal form.

Relax


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Polymer Microstructure$olyolefins "ith side chains ha!e stereocenters on e!ery other

carbonCH3

n

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:All stereocenters have same orientation

Syndiotactic:Alternating stereochemistry


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Microstructure andProperties

acticity affects the physical properties5Atactic polymers "ill generally be amorphous& soft&

fle'ible materials5 -sotactic and syndiotactic polymers "ill be more

crystalline& thus harder and less fle'ible.

$olypropylene ($$) is a good e'ample5Atactic polypropylene is a lo" melting& gooey material

5 -soatactic polypropylene is is high melting (19/:)&crystalline& tough material that is industrially useful5 Syndiotactic polypropylene is has similar properties&

but is !ery clear. -t is harder to synthesize

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Polymers and polymer chemistry