Chapter 23
Addition polymers
23.1 What are synthetic polymers?
23.2 Addition polymerization and addition
polymers
23.3 Structures, properties and uses of some
addition polymers
Key terms
Progress check
Summary
Concept map
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23.1 What are synthetic polymers?
(a)
(b)
(e)
(d)
(c)
(f)
(g)
Figure 23.1 Some plastic articles (a) water bottle (b) shopping bag (c)
containers (d) cutlery (e) drawers (f) footwear and (g) toy.
Think about
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Plastics are polymers which are made up of very
large molecules.
At some stage during processing, they can be
turned into any desired shape.
Learning tip
The shape fixing processes of plastic articles are
called moulding.
23.1 What are synthetic polymers?
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Polymers, polymerization and monomers
Polymer: a compound which consists of very
large molecules formed by joining many small
molecules together repeatedly
Polymerization: the process of joining many
small molecules together repeatedly to form very
large molecules
Monomers: the compounds whose molecules join
together repeatedly in polymerization
23.1 What are synthetic polymers?
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small monomer molecules
a part of a very large polymer molecule
Figure 23.2 In polymerization, many monomer molecules join together to
form a polymer molecule.
23.1 What are synthetic polymers?
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Natural and man-made polymers
Polymers can be natural or man-made.
Natural polymers occur naturally.
Man-made polymers include:
regenerated polymers
synthetic polymers
made artificially from the corresponding
monomers
There are two types: addition polymers
and condensation polymers
23.1 What are synthetic polymers?
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cotton
natural
polymers
carbohydrates (e.g.
cellulose, starch)
proteins (e.g. wool,
silk, meat)
POLYMERS
latex
man-made
polymers
natural rubber
quartz
inorganic polymers
(e.g. silicon dioxide)
23.1 What are synthetic polymers?
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natural
polymers
regenerated
polymers
(e.g. rayon)
synthetic polymers
POLYMERS
man-made
polymers
Figure 23.3 Classification of
polymers into natural polymers
and man-made polymers.
addition polymers
(e.g. polyethene)
condensation
polymers
(e.g. nylon)
23.1 What are synthetic polymers?
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Learning tip
We should note that all plastics are polymers, but not
all polymers are plastics.
Key point
A polymer is a compound which consists of
very large molecules formed by joining many
small monomer molecules together repeatedly.
Polymerization is the process of joining many
small molecules together repeatedly to form
very large molecules.
Class practice 23.1
23.1 What are synthetic polymers?
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23.2 Addition polymerization and addition
polymers
Unsaturated hydrocarbons such as alkenes can be
obtained by cracking of petroleum fractions.
Alkenes and unsaturated compounds can undergo
addition reactions.
Alkenes and unsaturated compounds can form
polymers by a special type of addition reaction
known as addition polymerization.
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What is addition polymerization?
Addition polymerization is a reaction in which
monomer molecules join together repeatedly to
form polymer molecules, without the elimination
of small molecules (such as H2O or HCl).
Monomer molecules involved must contain
carbon-carbon double bonds.
They undergo addition reactions among
themselves to form an addition polymer.
23.2 Addition polymerization and addition polymers
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The monomers can be represented by a general
formula:
where –X stands for an atom or a group of
atoms such as –H, –CH3,
, –Cl and so on.
By breaking open the carbon-carbon double bond, a
monomer molecule will have two ‘free’ electrons
which can join to other molecules:
‘free’ electrons that can
join to other molecules
23.2 Addition polymerization and addition polymers
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Learning tip
stands for a phenyl group (C6H5–). It is derived
from a benzene molecule by removing one hydrogen
atom. A phenyl group contains carbon-carbon double
bonds as shown below:
By repeating this addition process many times,
long polymer chains form.
23.2 Addition polymerization and addition polymers
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Each polymer chain is a macromolecule.
a section of a polymer chain
Polymer molecules do not have the same size.
For example, polyethene may be represented
as -[CH2 – CH2]-n , where n usually varies from
about 1000 to 30 000.
23.2 Addition polymerization and addition polymers
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Repeating unit
Repeating unit: the group of atoms in a polymer
molecule coming from a monomer (or a set of
monomers), which repeats to give the whole
polymer structure.
The repeating unit is
, which is derived
from one monomer molecule.
23.2 Addition polymerization and addition polymers
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The general equation for addition polymerization
is:
n molecules
of monomer
a long polymer chain consisting
of n repeating units (n usually
varies from 1000 to 30 000)
Figure 23.4 Paper clip chains
represent polymer molecules.
Each clip represents a
monomer molecule.
23.2 Addition polymerization and addition polymers
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Key point
Addition polymerization is a reaction in
which monomer molecules join together
repeatedly to form polymer molecules, without
the elimination of small molecules (such as
H2O or HCl).
Skill corner 23.1
Example 23.1
Example 23.2
Class practice 23.2
23.2 Addition polymerization and addition polymers
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23.3 Structures, properties and uses of
some addition polymers
Polyethene [polythene]
Polyethene (PE) is made by addition polymerization
of ethene.
The equation for the polymerization is:
ethene
polyethene or polythene
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Two types of polyethene:
low-density polyethene (LDPE)
high-density polyethene (HDPE)
23.3 Structures, properties and uses of some addition polymers
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Properties and uses
Polyethene is light (less dense than water) and
has a low melting point.
1. Low-density polyethene
It has a melting point of about 105°C and
softens in boiling water.
It is flexible.
2. High-density polyethene
It has a higher melting point of about 135°C.
It is quite rigid.
23.3 Structures, properties and uses of some addition polymers
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Figure 23.5 (left) These products are made of low-density polyethene.
Figure 23.6 (right) The bottles of these chemicals are made of highdensity polyethene.
As polyethene is cheap, it is the most widely used
plastic today.
Example 23.3
23.3 Structures, properties and uses of some addition polymers
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Polypropene [polypropylene]
Polypropene (PP) is made by addition
polymerization of propene (CH3–CH=CH2).
The equation for the polymerization is:
propene
polypropene
23.3 Structures, properties and uses of some addition polymers
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Properties and uses
Polypropene has a melting point of about 165°C.
Its density falls between low-density polyethene
and high-density polyethene.
It is resistant to many chemical solvents, acids and
alkalis.
23.3 Structures, properties and uses of some addition polymers
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It is used to make many different products, such as
ropes, fibres, baskets, boxes, luggage cases, food
containers and packaging film.
Figure 23.7 These products
are made of polypropene.
23.3 Structures, properties and uses of some addition polymers
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Polyvinyl chloride
Polyvinyl chloride (PVC) is made by addition
polymerization of chloroethene.
The equation for the polymerization is:
common name: vinyl chloride
polyvinyl chloride
systematic name: chloroethene
polychloroethene
23.3 Structures, properties and uses of some addition polymers
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Properties and uses
PVC is stiff and brittle.
It becomes more flexible when mixed with a
plasticizer.
Learning tip
Plasticizer is a substance added to a plastic to make
it softer and more flexible.
23.3 Structures, properties and uses of some addition polymers
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PVC with little or no plasticizer added is quite
rigid, and is thus used in making floor tiles and
pipes.
Figure 23.8 PVC pipes.
When suitably plasticized, PVC becomes soft and
flexible.
It is water resistant and is a good insulator of
electricity.
23.3 Structures, properties and uses of some addition polymers
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It can be used to make shower curtains,
tablecloths, raincoats and artificial leather.
It is also commonly used to make insulating
coverings for electric wires.
Figure 23.9 These products
are made of PVC.
PVC is not used to make food containers
because it is poisonous.
Class practice 23.3
23.3 Structures, properties and uses of some addition polymers
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Polystyrene
Polystyrene (PS) is made by addition
polymerization of styrene.
The equation for the polymerization is:
styrene or
phenylethene
polystyrene or
polyphenylethene
23.3 Structures, properties and uses of some addition polymers
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Properties and uses
1. Polystyrene
It is transparent, hard but brittle.
It is commonly used to make transparent
containers such as sample bottles, cups,
measuring cups and compact disc cases.
Figure 23.11 These products
are made of polystyrene.
23.3 Structures, properties and uses of some addition polymers
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2. Expanded polystyrene
It is a white solid foam.
It has very low density but is still quite rigid.
It is an excellent heat insulator and a good
shock-absorbent.
It is non-toxic.
23.3 Structures, properties and uses of some addition polymers
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It is widely used as packaging materials.
It is sometimes used as lightweight ceiling tiles
in buildings.
It is also used to make disposable foam cups
and food boxes.
(b)
(a)
Figure 23.12 (a) Ceiling tiles made of expanded polystyrene (b)
foam cups and food boxes.
23.3 Structures, properties and uses of some addition polymers
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Perspex (or polymethyl methacrylate or acrylic)
Perspex is made by addition polymerization of
methyl 2-methylpropenoate.
The equation for the polymerization is:
methyl
2-methylpropenoate
Perspex or
polymethyl 2-methylpropenoate
23.3 Structures, properties and uses of some addition polymers
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Properties and uses
Perspex is hard, tough and rigid.
It is highly transparent but quite easily scratched.
It is usually used as a substitute for glass.
It is used for making aeroplane windows,
advertising sign boxes, safety spectacles,
illuminated signs and plastic optical fibres.
23.3 Structures, properties and uses of some addition polymers
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Figure 23.13 This aquarium
is made of Perspex.
Experiment 23.1
Figure 23.14 Lenses of the exterior
lights of automobiles are made of
Perspex.
Example 23.4
23.3 Structures, properties and uses of some addition polymers
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Addition polymer
Polyethene (PE)
Properties
Uses
LDPE
• low density
• softens in boiling
water
• flexible
• plastic bags
• wrapping film for
food
• flexible cold water
pipes
HDPE
• low density (but
higher density than
LDPE)
• quite rigid
• higher melting
point than LDPE
• bottles for certain
chemicals
• buckets
• boxes
23.3 Structures, properties and uses of some addition polymers
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Examples
Addition polymer
Properties
Uses
Polypropene (PP)
• low density
• high melting
point
• resistant to
many chemicals
• ropes and fibres
• baskets and
boxes
• luggage cases
• food containers
• packaging film
Polystyrene (PS)
• transparent
• hard but brittle
• easily scratched
• transparent
containers
• compact disc
cases
23.3 Structures, properties and uses of some addition polymers
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Examples
Addition polymer
Polystyrene (PS)
Properties
Uses
Expanded
polystyrene
• very low density
• quite rigid
• excellent heat
insulator
• shock-absorbent
• non-toxic
• packaging
materials
• lightweight ceiling
tiles
• disposable foam
cups and food
boxes
Polyvinyl chloride • stiff but can be
(PVC)
made flexible
• brittle
• water resistant
• good electrical
insulator
• poisonous
• floor tiles
• pipes
• shower curtains
• tablecloths
• raincoats
• artificial leather
• insulating
coverings for
electric wires
23.3 Structures, properties and uses of some addition polymers
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Examples
Addition polymer
Perspex
Properties
Uses
• hard
• tough
• rigid
• not easily
scratched
• highly transparent
• aeroplane
windows
• advertising sign
boxes
• safety spectacles
• illuminated signs
• plastic optical
fibre
Table 23.1 Properties and uses of some addition polymers.
Class practice 23.4
Experiment 23.2
Reading to learn
Activity 23.1
Experiment 23.2
23.3 Structures, properties and uses of some addition polymers
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Examples
Key terms
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
addition polymer 加成聚合物
addition polymerization 加成聚合作用
high-density polyethene 高密度聚乙烯
low-density polyethene 低密度聚乙烯
macromolecule 巨大分子
man-made polymer 人造聚合物
monomer 單體
natural polymer 天然聚合物
polymer 聚合物
polymerization 聚合作用
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11.
12.
13.
regenerated polymer 再造聚合物
repeating unit 重複單位
synthetic polymer 合成聚合物
Key terms
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Progress check
1. What are synthetic polymers?
2. What is addition polymerization?
3. Why can alkenes and unsaturated compounds
undergo addition polymerization?
4. What is a repeating unit?
5. How can we describe an addition polymerization
using chemical equations?
6. How can we deduce the repeating unit of an
addition polymer obtained from a given monomer?
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Summary
23.1 What are synthetic polymers?
1.
2.
3.
Plastics are polymers which are made up of
very large molecules. At some stage during
their processing, they can be turned into any
desired shape.
Polymerization is the process of joining many
small molecules together repeatedly to form
very large molecules.
The compounds whose molecules join together
repeatedly in polymerization are called
monomers.
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23.2 Addition polymerization
4.
5.
Addition polymerization is a reaction in which
monomer molecules join together repeatedly to
form polymer molecules, without the elimination
of small molecules (such as H2O or HCl).
A repeating unit is the group of atoms in a
polymer molecule coming from a monomer (or
set of monomers), which repeats to give the
whole polymer structure.
Summary
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23.3 Structures, properties and uses of some
addition polymers
6.
Table 23.1 on p.17–18 summarizes the
properties and uses of some common addition
polymers including polyethene (PE),
polypropene (PP), polyvinyl chloride (PVC),
polystyrene (PS) and Perspex.
Summary
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Concept map
Alkenes
____________
and unsaturated compounds
addition polymerization
ADDITION POLYMERS
a type of
Synthetic polymers
examples
Polyethene Polypropene
monomer
Ethene
Polyvinyl
chloride
monomer
Propene
Polystyrene
monomer
Vinyl chloride
monomer
Styrene
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Perspex
monomer
Methyl 2methylpropenoate