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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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The Structure of Polymers
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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The Structure of Polymers
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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The Structure of Polymers
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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The Structure of Polymers
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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Addition Polymerisation
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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Addition Polymerisation
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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Addition polymerisation
C CH
HH H H H
HH H
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Addition polymerisation
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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Condensation Polymers
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
.
Condensation Polymers
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Condensation Polymers
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
Condensation Polymers
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Condensation Polymers
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