IGCSE CHEMISTRY
POLYMERS
Content
Polymers
Polymers
Core
• Define polymers as large molecules built up
from small units (monomers)
Supplement
• Understand that different polymers have
different units and/or different linkages
Lesson 3
c) Synthetic
polymers
c) Synthetic polymers
5.15 understand that an addition polymer is formed by
joining up many small molecules called monomers
5.16 draw the repeat unit of addition polymers, including
poly(ethene), poly(propene) and poly(chloroethene)
5.17 deduce the structure of a monomer from the repeat
unit of an addition polymer
5.18 describe some uses for polymers, including
poly(ethene), poly(propene) and poly(chloroethene)
5.19 explain that addition polymers are hard to dispose of
as their inertness means that they do not easily
biodegrade
5.20 understand that some polymers, such as nylon,
form by a different process called condensation
polymerisation
5.21 understand that condensation polymerisation
produces a small molecule, such as water, as well as the
polymer.
The Monomer
Do you
remember
ethene?
The Monomer
Do you
remember
ethene?
Alkene
C2H4
The Monomer
Do you
remember
ethene?
Alkene
C2H4
Unsaturated hydrocarbon
because it has a double bond
The Monomer
Can be
produced by
the
cracking of
crude oil
products
Do you
remember
ethene?
Alkene
C2H4
Unsaturated hydrocarbon
because it has a double bond
The Monomer
Can be
produced by
the
cracking of
crude oil
products
Do you
remember
ethene?
Alkene
C2H4
Unsaturated hydrocarbon
because it has a double bond
Polymerization
Polymers are large molecules built by linking 50
or more smaller molecules called monomers
Each repeat unit is connected to the adjacent
units via covalent bonds
Some polymers called homopolymers contain just
one type of unit, Examples include polythene and
polychloroethene, commonly known as PVC
If same monomers of alkene join together to
form a polymer, it is called addition
polymerization.
Polymerization
The process of joining single
monomers together to form
longer chain polymers is
known as polymerization.
Polymerization
The process of joining single
monomers together to form
longer chain polymers is
known as polymerization.
Pressure
+
Catalyst
Polymerization
The process of joining single
monomers together to form
longer chain polymers is
known as polymerization.
Pressure
+
Catalyst
Polymerization
The process of joining single
monomers together to form
longer chain polymers is
known as polymerization.
Pressure
+
Catalyst
Polyethene molecule
(or “polythene”)
Single ethene molecules
Polymerization
The process of joining single
monomers together to form
longer chain polymers is
known as polymerization.
Pressure
+
Catalyst
Polyethene molecule
(or “polythene”)
Single ethene molecules
Polymerization
This process is known as addition polymerization
because the polymer has the same basic formula
as the monomer.
Polymerization
This process is known as addition polymerization
because the polymer has the same basic formula
as the monomer.
Polyethene is one of a large group of synthetic
substances that we refer to as PLASTICS.
PLASTICS - advantages
PLASTICS - advantages
Easily shaped and
moulded, and can be
extruded, injection
moulded and vacuum
formed
PLASTICS - advantages
Easily shaped and
moulded, and can be
extruded, injection
moulded and vacuum
formed
They are relatively
inexpensive, being
produced as a byproduct of oil
refining.
PLASTICS - advantages
Easily shaped and
moulded, and can be
extruded, injection
moulded and vacuum
formed
They are durable, and
do not rust, corrode
or decay.
They are relatively
inexpensive, being
produced as a byproduct of oil
refining.
PLASTICS - advantages
Easily shaped and
moulded, and can be
extruded, injection
moulded and vacuum
formed
They are durable, and
do not rust, corrode
or decay.
They are relatively
inexpensive, being
produced as a byproduct of oil
refining.
They are lighter than
steel, wood or stone.
PLASTICS - advantages
Easily shaped and
moulded, and can be
extruded, injection
moulded and vacuum
formed
They are durable, and
do not rust, corrode
or decay.
They are relatively
inexpensive, being
produced as a byproduct of oil
refining.
They are lighter than
steel, wood or stone.
They are thermal and
electrical insulators.
PLASTICS - disadvantages
PLASTICS - disadvantages
They are not
biodegradable. This
means that they do not
decay naturally
PLASTICS - disadvantages
They are not
biodegradable. This
means that they do not
decap naturally
Many plastics produce
poisonous fumes when
they burn.
Other examples of addition polymers
Other examples of addition polymers
Propene
C3H6
Polypropene
or polypropylene
Use: washing-up
bowls
Other examples of addition polymers
Chloroethene
(Vinyl chloride)
C2H3Cl
Polychloroethene
or PVC
Use: waterproof
material
Uses for Polymers
POLYMER
Properties
Uses
Uses for Polymers
POLYMER
Properties
Uses
Polythene
Very cheap
and strong.
Easily moulded.
Plastic bags,
bottles,
buckets
Uses for Polymers
POLYMER
Properties
Uses
Polythene
Very cheap
and strong.
Easily moulded.
Plastic bags,
bottles,
buckets
Polyvinyl
chloride
(PVC)
Forms strong
waterproof
sheets. Hard but
flexible.
Electric wire
insulation,
plastic sheets
Uses for Polymers
POLYMER
Properties
Uses
Polythene
Very cheap
and strong.
Easily moulded.
Plastic bags,
bottles,
buckets
Polyvinyl
chloride
(PVC)
Forms strong
waterproof
sheets. Hard but
flexible.
Electric wire
insulation,
plastic sheets
Polystyrene
Cheap, easily
moulded. Can be
expanded into
foam
Packaging, radio
outer cases
Uses for Polymers
POLYMER
Properties
Uses
Polythene
Very cheap
and strong.
Easily moulded.
Plastic bags,
bottles,
buckets
Polyvinyl
chloride
(PVC)
Forms strong
waterproof
sheets. Hard but
flexible.
Electric wire
insulation,
plastic sheets
Polystyrene
Cheap, easily
moulded. Can be
expanded into
foam
Packaging, radio
outer cases
Polypropene
Resistant to
high
temperatures
Trays, sinks,
bottles, funnels
C = C
CH3
So that was
H
addition
polymerization.
What’s all this I
hear about
condensation
polymerization?
C = C
CH3
So that was
H
addition
polymerization.
What’s all this I
hear about
condensation
polymerization?
What’s a
condensation
reaction?
Condensation Reaction:
“Two molecules combine
with the loss of a smaller
molecule, which may be
water”.
Condensation Reaction:
“Two molecules combine
with the loss of a smaller
molecule, which may be
water”.
The polymer does not have the same
empirical formula as the monomers.
Condensation Polymerisation
Formation of Nylon
Formation of Terylene
Nylon is made by condensation
polymerization.
Nylon is a polyamide made from dicarboxylic acid
monomers (a carboxylic with a -COOH group at
either end) and diamines (an amine with an -NH2
group at either end)
Each -COOH group reacts with another -NH2 group
on another monomer
An amide linkage is formed with the subsequent
loss of one water molecule per link
For example, nylon is made by condensation
polymerization.
Nylon is a polyamide made from dicarboxylic acid
monomers (a carboxylic with a -COOH group at
either end) and diamines (an amine with an -NH2
group at either end)
Each -COOH group reacts with another -NH2 group
on another monomer
An amide linkage is formed with the subsequent
loss of one water molecule per link
Practice the structural formula of Nylon
Terylene (polyester)
Terylene is made by condensation
polymerization.
Terylene is a polyester made from dicarboxylic
acid monomers (a carboxylic with a -COOH group at
either end) and diols (an alcohol with an -OH group
at either end)
Each -COOH group reacts with another -OH group
on another monomer
An ester linkage is formed with the subsequent
loss of one water molecule per link
Terylene is made by condensation
polymerization.
Terylene is a polyester made from dicarboxylic
acid monomers (a carboxylic with a -COOH group at
either end) and diols (an alcohol with an -OH group
at either end)
Each -COOH group reacts with another -OH group
on another monomer
An ester linkage is formed with the subsequent
loss of one water molecule per link
Terylene
Terylene clothing is generally softer than that
made from nylon but both are hard wearing.
Because an ester link is formed during the
polymerisation, Terylene is known as a polyester.
Nylon
Nylon is made by reacting two different chemicals
together.
The starting molecules for nylon are more
complicated than those for poly(ethene) and are
called 1,6-diaminohexane and hexanedioic acid.
Nylon
Nylon is made by reacting two different chemicals
together.
The starting molecules for nylon are more
complicated than those for poly(ethene) and are
called 1,6-diaminohexane and hexanedioic acid.
Nylon
Each -COOH group reacts with another –NH2 group
on another monomer.
An amide linkage is formed with the subsequent
loss of one water molecule per link
The structure of polyamide:
Nylon
Biopolymers
Carbohydrates
Starch is a biopolymer or natural polymer. It is a
condensation polymer of glucose, a type of sugar. It
is often produced as a way of storing energy and is
formed as a result of photosynthesis in green
plants.
A H2O molecule is eliminated when simple sugars
polymerise. The linkage formed is an -O- linkage
called a glycosidic linkage
Biopolymers
Carbohydrates
Starch belongs to the more complicated group of
carbohydrates known as polysaccharides. Starch
does not form a true solution and it does not have a
sweet taste.
With iodine it gives an intense blue colour (nearly
black), which is used as a test for starch or iodine
itself.
Biopolymers
Hydrolysis of Carbohydrates
The complex carbohydrates also undergo hydrolysis
and produce the simple sugar monomers from which
they were made.
This can be done by refluxing with more moderately
concentrated HCl.
Biopolymers
Hydrolysis of Carbohydrates
If starch is mixed with saliva and left to stand for
a few minutes, it will break down to maltose, a
disaccharide (that is two joined monosaccharides).
The enzyme present in the saliva, called amylase,
catalyses this hydrolysis reaction.
Biopolymers
Summary of Hydrolysis of Carbohydrates
Biopolymers
Proteins
Amino acids are the building blocks of proteins.
Similar to nylon proteins are polyamides, as they
contain the –CONH– group, which is called the
amide or, in the case of proteins, the peptide link.
Proteins
are
formed
by
condensation
polymerisation.
Amino acids are small molecules containing NH2 and
COOH functional groups
Biopolymers
Proteins
Biopolymers
Proteins
General structure of Protein
Biopolymers
Hydrolysis of proteins
Proteins can be hydrolysed by the addition of
water in acidic or alkaline conditions
• Heat and concentrated acid (usually 6 mol/dm3
HCl) are used with a reflux condenser to prevent
the acidic vapours from escaping the reaction
vessel
• Aqueous ammonia is added after completion to
neutralise the excess acid
• Enzymes can also be used to hydrolyse some
proteins at room temperature, mimicking natural
bodily processes
Biopolymers
Biuret test.
A mixture of dilute sodium hydroxide and 1%
copper(ii) sulfate solution is shaken with a sample
of the material under test. If a protein is present,
a purple colour appears after about three minutes
Reaction conditions in Polymerization
Polymer
Temp oC
Pressure atm
Catalysts
Polyethene (LDPE)
80 to
300
1000 to 3000
Organic
peroxide
Polyethene (HDPE)
50
2 to 80
Different type
Nylon
280
High pressure
Acid
Terylene
150
High pressure
Zinc acetate
End of lesson