1a MPK---Structure of polymers.pdf

8/14/2019 1a MPK---Structure of polymers.pdf

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The Structure of Polymers


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What is a polymer?

made up from lots of

small moleculescalled monomers.


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All the same monomer

Monomers all sametype (A)

A + A + A + A

-A-A-A-A-

eg poly(ethene)

polychloroethene

PVC


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Copolymerisation

Copolymerisation occurs when more thanone monomeris used.

An irregular chain structure will result eg

ro ene/ethene/ ro ene/ ro ene/ethene


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Polymers are created by the chemical

These polymers are specifically made of

.

Carbon makes up the backbone of the

bonded along the carbon backbone.


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Polymers that contain primarily carbon andhydrogen are classified as organic

polymers.

Polypropylene and polystyrene are exampleso t ese.

Even though the basic makeup of many

po ymers s car on an y rogen, o erelements can also be involved.


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Oxygen, chlorine, fluorine, nitrogen, silicon,phosphorous and sulfur are other elements

that are found in the molecular makeup of

polymers. o yv ny c or e conta ns c or ne.

Nylon contains nitrogen.

Teflon contains fluorine. Polyester and polycarbonates contain

oxygen.


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There are also some polymers that,

have a silicon or phosphorous

backbone and these are consideredinorganic polymers.


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Natural Polymers

Wool, cotton, linen, hair, skin, nails,

occurring polymers

protein or cellulose


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Synthetic Polymers

Commonly referred to as plastics pliable,able to be moulded


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The bonding process:

they become flexible. There are no cross-

other.

Thermosettin ol mers do not soften

when heated because molecules are

crosslinked together and remain rigid.


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Thermoplastics

No cross links between chains.

Weak attractive forces between chains broken

by warming.

Change shape - can be remoulded.

Weak forces reform in new shape when cold.


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Thermoplastics

Thermoplastic polymers keep their plasticproperties

They soften on heating and then harden

again on cooling These polymer molecules consist of long

chains which have only weak bonds

e ween e c a ns


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Thermoplastics

The bonds between the chains are soweak that they can be broken when the

plastic is heated

The chains can then move around to forma erent s ape

The weak bonds reform when it is cooled

Thermoplastic material keeps its newshape


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Thermosets

Extensive cross-linking formed bycovalent bonds.

Bonds prevent chains moving relative to

.


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Thermosetting

Thermosetting polymers neversoften once they have been moulded.

Once set into a shape, that shape

cannot be altered These polymer molecules consist of

long chains which have many strong

c em ca on s e ween e c a ns


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Thermosetting

The bonds between the chains are so

strong that they cannot be broken when

This means that the thermosetting


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Addition Polymerisation

This bond breaks to allow the long chains

.

Modifying ethene, substituting different

produces other monomers that can be

ol merised to make ol mers with

different properties.


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Addition polymerisation

Monomers contain C=C bonds

next monomer molecule

repeated over and over.

Modern polymers also developed basedon alkynes R-C C - R


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A carbon = carbon double bond is neededin the monomer

A monomer is the small molecule that

makes up the polymer

H H H H

C CH H

n

ethene

catalyst C CH H

n

ol (ethene


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The polymer is the only product Involves the o enin out of a double bond

The conditions of the reaction can alter the

ro erties of the ol mer Reaction proceeds by a free radical

mechanism

Oxygen often used as the initiator


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C CH

HH H H H

HH H


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Conditions are high pressure and an oxygeninitiator (to provide the initial free radical).

Monomer = phenylethene

Pol mer = ol hen lethene


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Prediction the repeating unit

This is easy, basically open out thedouble bond.

H Cl H H H H

H H H HCl Cl

c oroe ene poly(chloroethene) akapolyvinylchloride (pvc)


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branches

Linear polymers are those in which themain backbone is unbranched.

The way in which side branches are

arranged on linear polymers(polypropylene) can affect the

properties of the polymer.


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branches

Isotactic Same side of the linear ol mer

Greater effect of dispersion forces

therefore hi h densit , ri id and tou hand a high softening temp.


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branches

Atactic Irre ular oints on both sides of the

linear polymer

Chains of molecules cannot get closetogether, therefore low density.

Soft, waxy little use


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Poly(propene)

This varying degree of randomness willaffect the strength and melting point of the

polymer.

The less random, the stronger the polymerand the higher the melting point

This is because in a more ordered polymer

ey c a ns can ge c oser oge er anhence the van der Waals forces will be

.


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links

Crosslinks are covalent bonds that can formbetween polymer chains.

If the number of crosslinks is small an

elastomer(vulcanised rubber) will result. If the number of crosslinks is large a hard

inflexible thermosetting polymer will be

pro uce .


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links To make a thermosetting polymer, the

linear chains are produced first

The cross linking is brought about either by

I). heat orII). adding a chemical to react between

the lateral functional groups linking the

c a ns oge er. Araldite is a good example of a two part

thermosetting polymer.


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Condensation polymerisation uses monomersthat have two functional groups per molecule.

These are said to be difunctional.

Polymerisation occurs when these monomersreact head-to-tail to form a new bond that

will eventually join the monomers together

A small molecule (often water) is eliminated


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Condensation Polymers

Suitable functional groups

-NH2 amine -OH alcohol

O O

-C carboxyl -C chloride


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Condensation Pol mers

Involves 2 monomers that have different.

They also involve the elimination of water or

another small molecule. Hence the term condensation polymer.

Monomer A + Monomer B Polymer + small

molecule (normally water).


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Condensation Pol mers

Common condensation polymers include

polyamides (the amide linkage as in

roteins . May be natural (protein, starch, cotton, wool,

silk) or synthetic (viscose, nylon, polyester)


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The OCR example here is terylene, a

polymer of benzene-1,4-dicarboxylic- - , .

HO C

O

C

O

OHn + HO CH2 CH2 OHn

heat with

an acid

catalyst

C

O

C

O

O CH2 CH2 O

poly(ethan-1,2-diyl benzene-1,4-dicarboxylate)

n


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P l mi

ese nvo ve e n age o wo monomers

through the amide linkage as in proteinse. . silk

This is an amide linkage:

OC N

H

e am e n age


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Nylon 6,6 a polyamide

H H OO2 6

H HC

OH

(CH2)4HO

C

1,6-diaminohexane hexanedioic acid

N (CH2)6 N C

O

(CH2)4 C

O

H H

part of a nylon polymer chain


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Kevlar a polyamide

CO

CH CO

HO OH

OO

N N C (CH2)4 CH H

part of the kevlar polymer chain


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Uses of polyamides

The main use of polyesters and polyamides isas fibres in clothing.

manufactured fibres woven into the natural

material (such as cotton). This gives the material more desirable

characteristics, such as stretchiness, andbetter washabilit .

Dont forget that proteins are alsopolyamides, you must know how the linkage

.


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Addition Pol mers

Ethene can be polymerised to produce both

known as polyethylene)

with high temp and high pressure long side

chains low density (eg. plastic bags)

Soft, flexible and translucent with a waxysurface that repels water.


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Addition Pol mers

High Density Polyethene (HDPE) produced with

branches dispersion forces more effective

. Rigid, stronger and more opaque than LDPE

,

water


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Addition Polymers

Rubberis an addition polymer that occurs

The monomer in natural rubber is isoprene.

. Molecular formula (C5H8)n

be attacked by oxygen and can perish (unlikeol thene

Additi P l


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Addition Pol mers

Rubber

not elastic long chains straighten out

when stretched and remain this way

uscep e o empera ure c anges

brittle when cold and sticky when hot.

Additi P l


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Addition Pol mers

Vulcanisation improved durability and

elasticity of rubber.

The linear chains are cross linked using

heat and sulfur


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Nylon

Can be extruded when molten to form

fibres or sheets of strong, durable and

e e

Its invention had a great impact on the

.



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Nylon 6 : 6

y on s a near c a n con a n ng up o

repeated units. e e y : e e e

existence of 6 carbon atoms on each of the



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PET plastic (Polyethene terephthalate).

o r n o es

An example of a polyester

Note the removal of H2O (condensation

polymer)


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Polymer Selection

Due to their versatility, polymers can beproduced for almost any imagined purpose.

A huge range of polymers exist today and are

used for many different applications. Their versatility has made them one of them

one of the most useful classes of substances

a we re y on n o ay s soc e y. This versatility can be attributed to the many

eren ways a ey can e mo e


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Recycling

Most plastics are produced from crudeoil, coal or gas.

and have become a visible part of our

environmental litter.


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Recycling

Documents

1a MPK---Structure of polymers.pdf