The Structure of Polymers
What is a polymer?
made up from lots of small molecules called monomers .
What is a polymer?
made up from lots of small molecules called monomers .
All the same monomer
Monomers all same type (A) A + A + A + A
-A-A-A-A-
eg poly(ethene) polychloroethene PVC
– Copolymers
Monomers of two different types A + B A + B + A + B -A-B-A-Be. . ol amides polyesters
Copolymerisation
Copolymerisation occurs when more than one monomer is used. An irregular chain structure will result eg ro ene/ethene/ ro ene/ ro ene/ethene
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.
The Structure of Polymers
Polymers that contain primarily carbon and hydrogen are classified as organic polymers . Polypropylene and polystyrene are examples o t ese. Even though the basic makeup of many po ymers s car on an y rogen, o er elements can also be involved.
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
Nylon contains nitrogen .
Teflon contains fluorine.
or ne.
Polyester and polycarbonates contain oxygen .
The Structure of Polymers
There are also some polymers that, have a silicon or phosphorous backbone and these are considered inorganic polymers.
Natural Polymers
Wool, cotton, linen, hair, skin, nails, occurring polymers protein or cellulose
Synthetic Polymers
Commonly referred to as plastics – pliable, able to be moulded
The bonding process:
they become flexible. There are no crossother.
ol mers do not soften Thermosettin when heated because molecules are crosslinked together and remain rigid.
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.
Thermoplastics
Thermoplastic polymers keep their plastic properties 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
Thermoplastics
The bonds between the chains are so weak that they can be broken when the plastic is heated The chains can then move around to form a erent s ape The weak bonds reform when it is cooled Thermoplastic material keeps its new shape
Thermosets
Extensive cross-linking formed by covalent bonds. Bonds prevent chains moving relative to .
Thermosetting
Thermosetting polymers never soften 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
Thermosetting
The bonds between the chains are so strong that they cannot be broken when This means that the thermosetting
Addition Polymerisation
When ethene is subjected to high pressure Liquid ethene (still under high pressure) is heated in the resence of a catal st O an addition reaction takes place. For addition polymerisation to occur, the monomer must have a double C bond.
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.
Addition polymerisation
Monomers contain C=C bonds next monomer molecule
repeated over and over.
Modern polymers also developed based on alkynes R-C C - R’
Addition Polymerisation
A carbon = carbon double bond is needed in the monomer A monomer is the small molecule that makes up the polymer
H C
n
H H
H C
H
H ethene
catalyst
C
C
H H ol (ethene
n
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
Addition polymerisation H
H C
H
H
H
C H H
H
H
Addition polymerisation
Conditions are high pressure and an oxygen initiator (to provide the initial free radical).
Monomer = phenylethene
Pol mer = ol
hen lethene
Prediction the repeating unit
This is easy, basically open out the double bond.
H H
Cl H
c oroe ene
H
H
H
H
H
Cl H
Cl
poly(chloroethene) aka polyvinylchloride (pvc)
branches
Linear polymers are those in which the main backbone is unbranched. The way in which side branches are arranged on linear polymers (polypropylene) can affect the properties of the polymer.
branches
Isotactic
Same side of the linear ol mer Greater effect of dispersion forces therefore hi h densit , ri id and tou h and a high softening temp.
branches
Atactic
Irre ular oints on both sides of the linear polymer Chains of molecules cannot get close together, therefore low density. Soft, waxy – little use
Poly(propene)
This varying degree of randomness will affect the strength and melting point of the polymer. The less random, the stronger the polymer and the higher the melting point This is because in a more ordered polymer ey c a ns can ge c oser oge er an hence the van der Waal’s forces will be .
links
Crosslinks are covalent bonds that can form between 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 .
links
To make a thermosetting polymer, the linear chains are produced first The cross linking is brought about either by I). heat or II). 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.
Condensation polymerisation uses monomers that have two functional groups per molecule. These are said to be difunctional . Polymerisation occurs when these monomers react ‘head-to-tail’ to form a new bond that will eventually join the monomers together A small molecule (often water) is eliminated
Condensation Polymers
Suitable functional groups
-NH2
amine
-OH alcohol
O
-C
carboxyl
O -C
chloride
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).
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)
The ester linkage is formed between the monomers This is an ester linkage:
C O
The OCR example here is terylene, a polymer of benzene-1,4-dicarboxylic - , . n
HO
O
O
C
C
OH +
n
HO CH2 CH2 OH
heat with an acid catalyst O
O
C
C
O CH2
CH2 O n
poly(ethan-1,2- diyl benzene-1,4-dicarboxylate)
P l
mi ese nvo ve e n age o wo monomers through the amide linkage as in proteins e. . silk This is an amide linkage:
O
C
N
H e am e n age
Nylon 6,6 a polyamide H
H
O C
2 6
H
H
H
(CH2)4 C
HO
1,6-diaminohexane
N
O OH hexanedioic acid
(CH2)6
N
O
O
C
(CH2)4 C
H part of a nylon polymer chain
Kevlar a polyamide O
O C
CH
C
HO
OH
O N
N
H
H
C
O (CH2)4
part of the kevlar polymer chain
C
Uses of polyamides
The main use of polyesters and polyamides is as fibres in clothing .
manufactured fibres woven into the natural material (such as cotton). This gives the material more desirable characteristics, such as stretchiness, and better washabilit . Don’t forget that proteins are also polyamides , you must know how the linkage .
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 waxy surface that repels water.
Addition Pol mers
High Density Polyethene (HDPE) produced with – branches – dispersion forces more effective – .
Rigid, stronger and more opaque than LDPE , water
Addition Polymers
Rubber is an addition polymer that occurs
The monomer in natural rubber is isoprene. .
Molecular formula (C5H8)n be attacked by oxygen and can perish (unlike ol thene
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.
Addition Pol mers
Vulcanisation improved durability and elasticity of rubber.
The linear chains are cross linked using heat and sulfur
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
Nylon 6 : 6
y on s a near c a n con a n ng up o repeated units. e e y : ee e existence of 6 carbon atoms on each of the
Condensation Polymers
PET plastic (Polyethene terephthalate).
o
rn
o es
An example of a polyester Note the removal of H 2O (condensation polymer)
Polymer Selection
Due to their versatility, polymers can be produced 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
Recycling
Most plastics are produced from crude oil, coal or gas.
and have become a visible part of our environmental litter.
