THERMOSETS & FIBRES
Brown's GCSE/IGCSE/O Level KS4 science-CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
11. Comparison of thermoplastic addition polymers, synthetic fibres from
condensation polymers and thermosets
This further page on
macromolecules-plastics describes the difference in formation of addition
polymers like poly(chloroethene)/PVC and condensation polymers like Terylene and
Nylon, all of which are thermosoftening polymers. The properties of
thermosoftening polymers (thermoplastics) are compared with thermosetting
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES - saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change-global warming :
5. Alkenes - unsaturated hydrocarbons :
6. Cracking - a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry - Why so many series of
organic compounds? : 9. Alcohols - Ethanol
- properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Condensation polymers, Nylon & Terylene,
comparing thermoplastics, fibres and thermosets
12. Natural Molecules - carbohydrates - sugars
- starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs-analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap-Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier-foundation-level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder-higher-level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word-fill worksheets
ALL my Advanced
Level Organic Chemistry revision notes
More on POLYMERS
- synthetic macromolecules
Modifying polymers, thermoplastics and
- First some
reminders from section 7. about addition polymers which were discussed
in some detail.
As an example the formation of PVC is shown below.
the long chain PVC molecules
what the molecules look like in the structure of PVC or any other
Although the PVC molecules
look straight, in reality, the long molecules will be all
twisted-jumbled up as in the thermoplastic diagram above (a bit
is a typical addition polymer (formed by simple addition of monomer
molecules), just like polythene and polystyrene etc. AND they are examples
of thermoplastics, that is they can be heated and softened, reshaped and
cooled to keep their new moulded shape.
A molecular model for a
In thermoplastics the
intermolecular forces between the polymer molecules are quite weak
compared to the strong covalent bonds (C-C) holding the chain of atoms
Because the 'intermolecular
bonding' is weak, this explains that when heated, these 'plastic'
materials will soften quite easily, which is why they are called
'thermoplastic' and have relatively low softening points and melting
Even at room temperature the
plastic is easily distorted because the polymer chains can slide over
each other i.e. the external physical force applied on bending overcomes
the intermolecular forces between the polymer molecules.
Despite their relative
weakness, on controlled heating until they are quite soft (but NOT
molten), they are readily extrusion moulded or drawn out into useful
shapes which retain their new formation on cooling.
So, overall, thermoplastics
are not that heat resistant or exceptionally rigid/strong - but their
properties do vary quite widely e.g. poly(propene) and nylon can be
drawn into strong fibres and both can be manufactured into quite strong
and rigid forms.
See nylon and terylene
- COMPARISON OF THERMOPLASTICS and THERMOSETS
and a mention of FIBRES
In thermosoftening plastics
like poly(ethene), poly(propene) or poly(chloroethene) PVC, because the
inter-molecular attractive forces between the chains are weak, the plastic softens when heated and
hardens again when cooled.
- It also means the polymer molecules can slide
over each other especially when heated to their relatively low
- This means they can be easily stretched or moulded into any
- They are examples of thermoplastics (thermosoftening
plastics), because they can be heated to make them softer - more
plastic, reshape it e.g. in an injection mould system, and on cooling the
plastic object retains its new shape - bottle, bowl, toy etc.
- However it is possible to manufacture
and process plastics in which the polymer chains are made to line up.
This greatly increases the intermolecular forces between the 'aligned'
polymer molecules and strong fibre strands of the plastic can
- Examples: The addition polymer poly(propene)
and the condensation polymers nylon and Terylene
formed you not only get polymerisation to form long molecules, you also get
chemical bonds formed between various points in one polymer chain molecule across
to another polymer molecule.
- These extra bonds are called cross-links
hold the linear polymer chains together in a much more rigid structure.
- These cross links do not
usually occur in the simpler addition polymerisations when thermoplastics
like poly(ethene) and PVC are made.
- Commercially, many thermosets consist of a
partially polymerised (but not cross-linked) resin, which contains a
cross-linking agent and a catalyst, so that when the mixture is exposed to
air or a the mixture warmed, cross-linking polymerisation occurs and the
hard thermoset is formed. This type of mixture is used to make fibre-glass
reinforced structures e.g. light car bodies or the hulls of sailing boats
- These extra cross-linking
covalent bonds formed between adjacent chains of the polymers change
the physical properties considerably and thermoset polymers have much
higher high melting points (giving greater heat resistance and thermal stability)
as well as greatly
increased strength and rigidity.
- Compared to thermosoftening plastics, thermoset
polymers do not soften or melt and only
break down at much higher temperatures compared to the softening/melting points
of thermoplastics described above.
- Thermosets are harder, more
rigid/stiffer and not as easily bent or stretched, in fact they can
be quite brittle and almost impossible to stretch (not very
- Note that thermosets type polymers can be
formed at room temperature, heating may not be required.
- Many super glues form this kind of
- However, you have to get it right first time
because thermosetting polymers cannot be softened with heat and therefore
cannot be stretched or re-shaped, but the advantage is that thermosets are
much more heat resistant than thermoplastics.
- But these cross-linked thermoset polymers
are much more rigid (e.g. can't be stretched) and stronger
material (though they can be brittle) and not as flammable as most
- On heating them strongly they do NOT melt, but
tend to char, gradually giving off gases.
A simple diagram of the
polymer molecules in the three different situation.
polymer molecules tend to be randomly jumbled up, but no cross-linking
Fibres: Fibre molecules
are thermoplastic molecules but manufactured in such a way to get the
'molecules more lined up' to increase intermolecular forces and the strength
of the fibre, but no cross-linking bonds.
Thermosets: Their great
strength and very rigid structure derives from the strong cross-links
between the polymer strands. These cross-links are full chemical covalent bonds, NOT
the much weaker intermolecular forces/bonding in thermoplastics.
In thermoplastics you have
intermolecular bonding (weak attractive forces) between polymer molecules.
In thermosets you have
intramolecular chemical bonding (very strong attractive
forces) between the adjacent polymer molecule chains.
Heat resistant polymers are
usually thermosets e.g. like melamine resin (plastic plates), but even
thermoplastics like poly(propene) can be used in hot situations e.g. plastic
(used in furniture), Bakelite
(was used for electrical fittings, a horrible brown colour but a good
insulator, not used now?), Formica (table tops) and some super
glues are examples of thermosetting polymers.
- See also ....
Other Synthetic Polymers -
SYNTHETIC FIBRES like NYLON and TERYLENE
involves linking lots of small
monomer molecules together by eliminating a small molecule. This is
often water from two different monomers, a H from one monomer, and an OH
from the other, the 'spare bonds' then link up to form the polymer
Choosing a Plastic for a
Particular Use (this section is repeated on the other
GCSE polymer notes page)
How we use polymer compositions
depends on their properties, some are quoted in the data table
So, below is a decision making
exercise on choosing a plastic for a particular job!
Note: NOT ALL the properties
are necessarily relevant to make the decision.
At the moment A to F match
questions (a) to (f) once only, but I may add further questions!
This exercise should provide a
good challenge and discussion for a class, any feedback comments
can be made
plastic could be used as for disposable tableware like plates
for hot meals or coffee cups?
plastic could be used as a moving plastic component in a
plastic could used as containers for high volume production line
of acids or alkalis?
plastic could be used as laboratory volume measuring instrument
e.g. a syringe or measuring cylinder
plastic is suitable for clothing fabrics?
plastic would be used for super-market carrier bags?
Answers near the
end of the page
Plastics are widely
used in the manufacture of cars and other road vehicles because
they are cheap to make of varied composition for a wide variety of
uses, they are light, durable and can be dyed any colour, they can
be flexible or rigid and so can be used for e.g. used for internal
fittings e.g. dashboard cover, floor covers (can be rubber too),
door coverings, transparent and coloured covers over headlights and
brake lights, and the insulating sheathing for all the electrical
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap-fill quiz worksheets
ALSO gap-fill ('word-fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap-fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
ALL my Advanced
Level Organic Chemistry revision notes
Notes information to help revise
KS4 Science Additional Science Triple Award Separate Sciences Chemistry revision
notes for GCSE/IGCSE/O level Chemistry Revision-Information Study Notes for
revising AQA GCSE Science AQA GCSE Chemistry, Edexcel
GCSE Science, Edexcel GCSE Chemistry, OCR 21st Century Science Chemistry, OCR Gateway Science
GCSE science-chemistry CCEA/CEA GCSE science-chemistry
(and courses equal to US grades 8, 9, 10)
Answers to the
Choosing a Plastic for a
Particular Use Exercise in decision making
(a) Plastic B, to be disposable it must be
cheap, chemical resistance doesn't matter (only in contact with food/drinks
once), needs to be heat resistant, transparency doesn't matter?, needs to be
(b) Plastic E, firstly, it
must be very strong to withstand the physical movement and friction in a working
machine, it withstand heat from friction, chemical resistance need not be high,
high cost acceptable for a specialised non-disposable part of a machine.
(c) Plastic F, needs to be
reasonably cheap but heat and chemical resistant.
(d) Plastic A, it needs to be
transparent to read the calibration marks accurately, it needs to be chemically
and heat resistant to safe to use in the laboratory, it needs to be rigid to
retain its accuracy, the high cost would be acceptable for a valuable measuring
instrument in the laboratory, its not disposable.
(e) Plastic C, most important
that it can be made into fibres, chemical and heat resistance is the
responsibility of the owner/wearer!, needs to opaque or it becomes a 'see
(f) Plastic D, the plastic
needs to cheap, flexible and disposable (low cost), heat and chemical resistance
are not important - responsibility of user!
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