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Structure, production & uses of addition polymers-plastics

Addition polymers - properties and uses of plastic materials


 Doc Brown's chemistry revision notes: GCSE chemistry, IGCSE  chemistry, O level & ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old students of chemistry AND Doc Brown's Advanced A Level Organic Chemistry Revision Notes - Help in Revising Advanced Organic Chemistry

7. Making Polymers - plastics and their uses

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Sub-index for this page

(Sub-links also used for Advanced Level Organic Chemistry Part 2 Alkenes including notes on polymers)

7A. Structure Introduction to the formation and structure of addition polymers from alkenes

7B. Examples of poly(alkene) polymer molecules e.g. manufacture of poly(ethene) to start with

7C. Summary of the properties and uses of poly(ethene)

7D. Poly(propene) - formation, structure, properties and uses

7E. Poly(chloroethene) - formation, structure, properties and uses

7F. Polystyrene - formation, structure, properties and uses

7G. Poly(tetrafluoroethene) or PTFE - formation, structure, properties and uses

7H to 7N are now on a separate page with a sub-index at the top

7H More general comments on the uses of polymer plastics

7I Problems with using polymer plastics: methods of recycling, disposing, pollution e.g. PET, PVC etc.

7J Highlighting three specific problems associated with using and disposing of polymers or plastic materials

7K Biodegradable and compostable polymers - these should break down due to bacterial activity

7L The recycling case of PET/PVC and other plastics - examples of reclamation

7M Summary of advantages and disadvantages of recycling plastic polymers - the 'pros and cons'!

7N Logistic exercise - choosing a plastic for a particular use

All My synthetic polymer-plastics revision notes pages

Introduction to addition polymers: poly(ethene), poly(propene), polystyrene, PVC, PTFE - structure, uses

More on the uses of plastics, issues with using plastics, solutions and recycling methods

Introducing condensation polymers: Nylon, Terylene/PET, comparing thermoplastics, fibres, thermosets

Extra notes for more advanced level organic chemistry students

Polymerisation of alkenes to addition polymers - structure, properties, uses of poly(alkene) polymers

The manufacture, molecular structure, properties and uses of polyesters

Amides chemistry - a mention of polyamides

The structure, properties and uses of polyesters and polyamides involving aromatic monomers

The chemistry of amides including Nylon formation, structure, properties and uses

Stereoregular polymers -  isotactic/atactic/syndiotactic poly(propene) - use of Ziegler-Natta catalysts

TOP OF PAGE and sub-index

doc b oil notes7. Introducing polymerisation, polymers and plastics

7A. The structure and formation of POLYMERS

Reactions of alkenes (4) polymerisation/polymerization

Polymerisation means joining lots of small molecules (called monomers) into very large long molecules (called polymers).

The average molecular mass of polymer is very large e.g. 10,000 to 50,000

Polymers are long chain molecules formed from lots of repeating units joined together by strong covalent bonds, often, but not always, single C-C covalent bonds for carbon based polymers.

This page describes the formation of big polymer molecules called polyalkenes from small molecules called alkenes and relates their structure to their physical properties and uses.

A comparative intermolecular forces note:

These are the relative weak forces between whole molecules.

They are not as strong as the covalent bonds between the atoms in a molecule.

The intermolecular forces between polymer molecules are bigger than those between small molecules like water and great enough to ensure plastic polymers like poly(ethene) and PVC are solid at room temperature.

The greater the intermolecular forces the greater the energy needed to overcome them and melt a material.

These intermolecular forces are much weaker than ionic or covalent bonds so the melting points of polymers are still much less than those of giant covalent structures like diamond or silica or ionic compounds like sodium chloride.

The polymerisation equation for alkenes

Alkenes are made by cracking some of the fractions obtained by the fractional distillation of crude oil

The diagram below shows the general equation for the formation of a plastic polymer from alkenes.

diagram equation for the polymerisation of alkenes to make an addition polymer plastic doc b oil notes

This is a general equation for the addition polymerisation of ANY alkene.

The 'starter' molecule is called the monomer.

The name of the polymer is quite simply derived from the monomer name in () preceded by poly

i.e. poly(alkene monomer name)

There are many different alkenes, so there are many different polymers with a range of physical properties and uses.

  • When catalysed and heated under pressure, unsaturated alkenes link together when 'half' of the double bond opens.

    • The spare bond on each carbon atom of the double bond are used to join up the molecules.

    • To form an addition polymer, the monomer molecule must have a double bond.

    • The general equation for polyalkene formation is shown in the diagram above and it is the presence of the carbon = carbon (C=C) double bond in the alkene molecule that enables the molecules to join together to form a long chain.

    • In terms of the 'backbone' of carbon atoms, the essential molecular linking is equivalent to ...

      • ... C=C + C=C + C=C ... etc.  ===>  ... -C-C-C-C-C-C- ... etc. (hydrogen and other atoms ignored)

      • .... to give a long polymer chain molecules, hundreds-thousands of carbon atoms long!

      • ... and the whole chain of atoms is held together by strong carbon-carbon covalent bonds.

      • This process is called addition polymerisation, the monomer molecules all add together, with no other product formed other than the long polymer molecule.

        • Note!

        • Full equations showing all the atoms involved are given in the next section 7b.

        • The attractive forces between the molecules, the so-called 'intermolecular forces' or 'intermolecular bonding' are much weaker than the chemical bonds between the atoms, but they are most important in determining the properties of the polymer AND as you will read on later, they can be changed to change the physical properties of a polymer.

    • Think of the process as springing open half of the C=C double covalent bond of an alkene and using the 'spare bonds' to link across from one alkene molecule to another.

      • This can only happen if the hydrocarbon molecule is unsaturated, like alkenes (with a C=C double bond).

      • You cannot polymerise saturated hydrocarbon molecules like alkanes (all C-C single bonds).

  • Most polymers (plastics) are made from alkene compounds containing the -C=C- bond by addition polymerisation.

  • The general reaction is small monomer molecule ==> long polymer molecule as the small molecules link together to form a long chain with no other molecules formed.

  • The original small molecule is called the monomer and the long molecule is called the polymer, which is the sort of molecule most plastic materials consist of.

    • The polymer is now a saturated molecule but has the same C:H ratio as the original alkene.

  • So lots of small molecules join up to form a big long molecule in a process called addition polymerisation and the polymers are named as poly(name of original alkene), i.e. poly(alkene)

    • Several examples are shown and their formation and structure described below, namely for poly(ethene), poly(propene), poly(chloroethene) PVC, polystyrene.

    • Their properties and uses of these thermoplastic materials are also described and explained.

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7B. Examples of poly(alkene) polymer molecules e.g. poly(ethene) to start with ...

its formation, structure and uses of it and other plastic materials

  • The polymers described on this page are typical addition polymers (formed by simple addition of monomer molecules), just like polythene and polystyrene etc.

    • The starting small molecule is called the monomer.

    • In addition polymerisation there is no other product except the polymer itself because all the molecules are used up to form longer and longer polymer chains (very long molecules) with the same repeating unit based on the original monomer (see the first example below).

    • AND they are all examples of thermoplastic polymers (thermoplastics), that is, the polymer can be heated and softened, reshaped and cooled to keep their new moulded shape.

    • The monomers a polymer is made from determine the type and strength of intermolecular bonds between the polymer chains, hence they determine the physical properties of the polymer e.g. strength - rigidity, softening - melting point.

    • See examples below of addition polymers AND

    • Comparing addition polymers & condensation polymers - thermosoftening and thermosetting polymers

    • -

  • The structure and formation of Poly(ethene)

  • The equation for the formation of the polymer poly(ethene) from the monomer ethene is shown below.

    • It is often commercially called 'polythene' or written incorrectly as polyethene or polyethylene.

    • The equation for the polymerisation of ethene is shown in several ways below using displayed formulae.

diagram equation for making poly(ethene) polythene from the alkene ethene doc b oil notes

above is the (repeating unit) of poly(ethene)

The repeating unit is shown in brackets e.g. for poly(ethene) it is CH2-CH2

To indicate the repeating nature of the molecule, bond dashes go through the brackets giving the 'shorthand' or 'abbreviated' representation of the structure of poly(ethene)   -(-CH2-CH2-)n-   where n is the very large number, and can represent hundreds or even thousands of repeating units in one polymer molecule, in this case poly(ethene).

Above is show the displayed formula style equation for poly(ethene) formation, or a simpler molecular formula style equation below.

n CH2=CH2 ===> -(-CH2-CH2-)n-

The repeating unit shown in brackets for poly(ethene) is (CH2-CH2)  and n is a very large number, and can represent hundreds or thousands of repeating units in one molecule.

-(-CH2-CH2-)n-  is a sensible way of writing these huge molecules!

You need to be able to work backwards from a polymer formula to work out the original small monomer molecule.

 In other words, from the diagram below, work out WY>C=C<XZ from -(WY>C-C<XZ)n-

alkenes structure and naming (c) doc b

General equation for polymerising an alkene

  • The molecular structure of poly(ethene)

  • diagarm of the molecular structure of poly(ethene) polythene plastic

  • A 'picture' of a section of a very long chain poly(ethene) polymer molecule, essentially consisting of hundreds or thousands of -CH2-CH2- ethene units all joined together.

  • Above is a 'space-filling' model 'ball and below a 'stick' type of model.

  • Although the poly(ethene) molecules look straight, in reality, the long molecule will be all twisted, jumbled and tangled up as in the thermoplastic diagram on the right.

    • A pile of spaghetti isn't a bad analogy here!

    • However in addition polymers, each molecule does consist of a regular repeating unit based on the original monomer eg -CH2-CH2- in poly(ethene)

    • These are typical thermosoftening polymers consisting of individual, tangled polymer chains and melt relatively easily when they are heated.

  • Using these models' to explain the general physical properties of a thermoplastic polymer.

    • The bonds in these polymer molecules are covalent and very strong, but the intermolecular forces are much less strong BUT greater than in small molecules like water or pentane so polymers are solid at room temperature.

      • Generally speaking, the bigger the molecule the bigger the intermolecular forces, the higher the melting point, because more energy is needed to weaken the intermolecular forces.

      • The higher the temperature, the greater the kinetic energy of the particles to overcome the molecular attractive forces.

    • Because polymer molecules are very big, compared to small covalent molecules like water or ethanol, the intermolecular forces (intermolecular bonding) are much greater and so polymers-plastics like poly(ethene), PVC poly(chloroethene), polystyrene or poly(propene) are all solid at room temperature.

    • BUT, the intermolecular forces (electrical attractive forces) between the polymer molecules are still quite weak compared to the strong covalent bonds (C-C) holding the chain of atoms together.

      • In general, intermolecular bonding forces are much weaker than covalent or ionic bonds.

    • Because this 'intermolecular bonding' is weaker, when heated, these 'plastic' materials will soften/melt quite easily (hence easily remoulded) at relatively low temperatures (e.g. for poly(ethene) 110-150oC), without breaking any covalent bonds in polymer molecule, which is why they are called 'thermoplastic' and have relatively low softening/melting points.

    • Even when 'cold' and apparently solid, the plastic is easily distorted (easily bent when stressed) 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 (even fibres) which retain their new formation on cooling.

    • Also, the flexibility and sometimes stretchability is actually very useful - think of plastic 'polythene' bags and PVC coated electrical cables.

  • How is poly(ethene) manufactured? e.g. for commercially available plastics like 'polythene'

    • What reaction conditions are used in the manufacture of polymers?

    • Does changing the reaction conditions have any effect on the physical properties of the polymer?

    • Can we make different forms of the same polymer for different uses?

    • The properties of polymers - plastics depend on what monomers they are made from and the reaction conditions under which they are made. For example, low density polyethene (LD, LDP) and high density poly(ethene) (HD, DDP) are produced from ethene using different catalysts and different reaction conditions.

    • All polymers have their own characteristic physical properties depending on their specific molecular structure.

      • The strength of the intermolecular forces (intermolecular bonding) between the polymer molecules is crucial to how strong, rigid, flexible etc. the manufacture plastic material is.

      • If the molecules can be made more 'lined up way' and more 'densely' packed, the intermolecular forces (intermolecular bonding) increases, the physical properties change e.g. the polymer density and rigidity increases, so it is stronger and less flexible.

      • It is possible to achieve variations in the physical properties of plastics like 'polythene' by varying the manufacturing conditions to give subtle differences in the molecular structure and composition of the polymer-plastic produced..

      • Two different types of poly(ethene) and their molecular structure and physical properties are described with reference to their different uses.

    • Making polymers - typical reaction conditions:

      • Polymers like poly(ethene) are usually produced under conditions of relatively high pressure, elevated temperature and a catalyst.

      • An initiator is sometimes used to get the reaction going e.g. a highly reactive peroxide molecule - this get's used up, so its NOT a catalyst

    • However, by changing and selecting the reaction conditions e.g. pressure, temperature or catalyst, you can make subtle changes to the physical properties of the polymer obtained from the polymerisation process e.g. changing temperature, pressure or catalyst. This allows the manufacture of a weaker more flexible lower density poly(ethene) referred to as LDPE (LD poly(ethene), and a stronger less flexible higher density form of poly(ethene), HDPE (high density poly(ethene).

      • LDPE In the original high pressure process developed in the 1930s, poly(ethene) was made at a moderate temperature of 80oC to 300oC and a very high pressure of 1000 atm to 3000 atm. pressure (1 atm = normal atmospheric pressure at sea level), the poly(ethene) product has a lower density and very flexible. Small controlled traces of oxygen (< 10 ppm) or organic peroxides are used to initiate the polymerisation process.

        • The polymer chains are quite jumbled up and the polymer chains also have many branches (NOT cross-links), and the intermolecular forces between molecules are weaker, so the plastic is less strong and less rigid, more flexible than HDPE poly(ethene).

        • This lower density weaker form of poly(ethene) melts at around 115oC, but softens well before that temperature, so don't have very hot drinks from an LDPE polythene cup!

          • LDPE poly(ethene) density ranges from 0.91 - 0.94 g/cm3.

          • LDPE poly(ethene) has about half the strength of HDPE poly(ethene).

        • This 'low density poly(ethene)' is known by the acronym LDPE and is used for plastic bags, plastic bottles, cling film wrap, laminating paper, car covers, squeezy bottles, liners for tanks and ponds, moisture barriers in construction.

        • Low density poly(ethene) is not very heat resistant and softens easily if heated, so it can't be used for any application where temperatures well above room temperature will be encountered!

      • HDPE However in the 1950s, it became possible to make poly(ethene) in a low pressure process at around a lower temperature, maybe as low as 50oC, and using a much lower pressure of a 2 atm to 80 atm.,  AND a different catalyst, the polymer product is more dense and less flexible.

        • Here the polymer chains are much more aligned with each other, maximising the intermolecular forces/bonding between the molecules, so the plastic is stronger and more rigid and less flexible than LDPE poly(ethene).

        • The polymer molecules are longer with far fewer branches in the chains and this allows the poly(ethene) molecules to get closer together (just compare the two diagrams above-right).

        • This is a more heat resistant higher density stronger form of poly(ethene) melting at around 135oC and can withstand contact with hot water without distortion!

          • HDPE poly(ethene) density ranges from 0.95 - 0.97 g/cm3.

          • HDPE has about double the strength of LDPE poly(ethene).

        • This 'high density poly(ethene)' is known by the acronym HDPE, it is tougher, stronger and more hard wearing than LDPE. HDPE poly(ethene) is used for:

        • freezer bags, water pipes, wire and cable insulation - these three need to be a bit flexible but quite strong

        • or more rigid uses like drainpipes, water tanks, buckets, washing-up bowls, plastic milk bottles, strong plastic crates, extrusion coating.

    • In general, in terms of how the polymer molecules are packed ...

      • the closer the polymer chains are packed together, the stronger the intermolecular forces/bonding, the density increases and the strength of the polymer increases (this tends to increase the hardness and crystallinity of the plastic),

      • the more jumbled or 'spread out', the polymer chains are, the weaker the intermolecular forces/bonding, the polymer material is less dense and weaker e.g. more flexible.

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7C. Summary of the properties and uses of poly(ethene)

  • (Old or commercial names: polyethylene, polythene)

  • First and foremost poly(ethene) from ethene is a cheap, if not very strong, useful plastic.

  • Poly(ethene) on heating is readily moulded into any shape e.g. 'plastic' bottles.

  • This is because poly(ethene) is an example of a thermoplastic - it can be heated to soften it, reshape it e.g. in an injection mould system, and on cooling retains its new shape - bottle, bowl, toy etc.

  • Lower density poly(ethene) is light and flexible and used for plastic bags, detergent/shampoo bottles, plastic piping, laminating paper and acts as a very good electrical insulator - its not just PVC that has been used for insulating electrical cable wires..

  • Higher density poly(ethene) is used where a less flexible/stretchy more rigid and stronger form is needed e.g. drainpipes, milk crates - where a much tougher plastic is needed.

  • A general important point to make here is that the use of a polymer doesn't just depend on its chemical composition and molecular structure, but mainly on its physical properties (which of course are derived from the polymers structure).

  • These differences become accentuated when comparing thermosoftening plastics and thermosetting plastics which also includes a discussion on modifying polymers to change their properties, hence varying their uses.

  • What happens if you strongly heat plastics like poly(ethene)?

    • You can thermally degrade poly(ethene) in a sort of 'cracking experiment' illustrated below.

    • Thermally degrading poly(ethene)

    • When you strongly heat a plastic-polymer you break some of the carbon-carbon bonds (C-C) in the polymer chains to produce much smaller and volatile molecules.

    • Some of the molecules will be liquid or gaseous alkenes which you can collect as shown above.

    • You can test the organic liquid in the bottle or the gases collected in the inverted test tube initially filled with water.

    • The collected hydrocarbons should include alkenes (including the original ethene) which you can test for with bromine water - which turns from orange to colourless (see chemistry of alkenes for details of alkene test).

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7D. Poly(propene) - formation, structure, properties and uses

  • (Old or commercial names: polypropylene, polyprene and polypropene).

  • The polymerisation of the monomer propene and the molecular structure of the polymer formed, poly(propene), is shown below.

diagram equation for making poly(propene) from propene doc b oil notes

  • Above is the (repeating unit)

  • displayed formula style equation for poly(propene) formation, or simpler molecular formula style equation below.

  • n CH2=CH-CH3 ===> -[-CH2-CH(CH3)-]n-

  • The properties and uses of Poly(propene), incorrectly but in industry called 'polypropene'

    • Poly(propene) is made from propene and is stronger, more rigid and hard wearing than polythene but still flexible.

    • Poly(propene) is also a thermoplastic and can be moulded into many useful objects.

    • It is used in food packaging, containers that are dishwasher safe, laboratory equipment and  containers holding chemicals because of poly(propene)'s resistance to chemical attack..

    • Poly(propene) can be drawn out into strong fibres (just like nylon and Terylene).

    • Poly(propene) is used for making strong containers like milk crates and plastic furniture - examples of thermoplastic moulding and pipes and containers that can withstand boiling water.

    • Poly(propene) is used for carpet fibres, thermal underwear and synthetic ropes - these last three are examples of using poly(propene) fibres.

    • -

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7E.  Poly(chloroethene) - formation, structure, properties and uses

  • Poly(chloroethene), PVC

  • The old name for poly(chloroethene) was polyvinyl chloride, hence the use of the commercial name PVC, and is made from polymerising the monomer chloroethene, CH2=CHCl, (old name vinyl chloride).

    • PVC formation and molecular structure is shown in the diagrams below

    • The equation for the polymerisation of the monomer chloroethene to form poly(chloroethene) is shown in different ways.

diagram equation for making PVC plasic poly(chloroethene) from the alkene chloroethene doc b oil notes

  • Diagrams of the (repeating unit) of poly(chloroethene), PVC

    • displayed formula style equation for poly(chloroethene) formation, or simpler molecular formula style equation below.

    • n CH2=CHCl ===> -(-CH2-CHCl-)n-

    • The repeating unit shown in brackets for poly(chloroethene) is -(CH2-CHCl)-

  • The molecular structure of PVC poly(chloroethene)

  • diagarm of the molecular structure of poly(chlorothene) PVC plastic

  • Above is a 'picture' of a section of a very long chain poly(chloroethene) polymer molecule (PVC), essentially consisting of hundreds or thousands of -CH2-CHCl- chloroethene units all joined together.

  • The above diagram is that of a 'ball and stick' type of model and although it looks straight, in reality, the long molecule will be all twisted-jumbled up like in the diagram on the right.

  • The chlorine atoms are shown as a regular arrangement, but they will be more randomly distributed down the ...-C-C-C-... chain depending on which way round the chloroethene molecule added.

  • The properties and uses of PVC poly(chloroethene)

    • Poly(chloroethene), another thermoplastic, is much tougher than poly(ethene), very hard wearing with good heat stability, and is an excellent electrical insulator, so is used for covering insulation electrical wiring and plugs.

      • Note that most plastics are poor conductors of electricity and so act as good electrical insulation materials.

    • PVC is also replacing metals for use as gas pipes and water drain pipes and guttering because it is strong and durable.

    • PVC can be manufactured to be quite rigid or quite flexible depending on its intended use, and, you can vary the composition so that rigidity or flexibility to suit a particular use.

    • More flexible poly(chloroethene) has found a use in the clothing industry e.g. as artificial leather and is readily dyed with bright colours!

    • Rigid PVC is replacing wood for e.g. window frames, metals for guttering and piping because it is tough and hard wearing (durable) with excellent weather proofing properties.

      • PVC can be coloured to suite aesthetic taste and unlike wood, it doesn't rot and it doesn't have to be painted, so saving time as well as money!, but PVC windows are not as aesthetically pleasing as nicely painted wooden windows (I have to say this, because living with persistently rotting windows in an old grade II listed Victorian schoolhouse, I'm not allowed to use PVC windows!).

    • More general points - ways of modifying the properties of a particular polymer-plastic composition.

      • If you increase the chain length of the polymer molecules you increase the intermolecular forces between the chains so it is stronger and less flexible and has a higher softening/melting point.

      • If you shorten the average chain length the polymer has lower softening/melting and is easier to shape, and the plastic is more flexible.

      • If you can reduce the branches in a polymer chain, the molecules can pack closer together (rather like in a fibre), this increases the intermolecular forces giving a more dense, stronger and more crystalline polymer with a higher softening/melting point.

      • Another way of changing the physical properties of a polymer is to add a plasticiser.

        • A plasticiser additive is a relatively large non-volatile molecule (but much smaller than a polymer molecule) that 'pushes' the polymer chain apart a little.

        • This reduces the intermolecular forces, making the plastic more softer, flexible and easier to shape.

        • By this means you can make a rather more 'stretchy' PVC for use as synthetic leather.

        • Plasticisers (e.g. PCBs) are used in PVC to make it more flexible e.g. when it is used for electrical insulation cable.

        • Pollution note: Plasticisers known as PCBs are toxic and can leach out into the environment, and, just like pesticides contaminating water, they can build up in food chains to potentially poison fish and humans, so there use is strictly controlled.

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7F. Polystyrene - formation, structure, properties and uses

  • Polystyrene

    • Polystyrene is a polymer made from the monomer 'styrene* (another alkene monomer)

    • Polystyrene's new modern systematic name is poly(phenylethene), a polymer made from polymerising phenylethene monomer (shown below).

    • (c) doc b phenylethene, old name 'styrene', hence the common name 'old name' of 'polystyrene'

      • You can tell that this molecule can theoretically act as a monomer, that is it can be polymerised to a polymer, because it is an alkene with the characteristic C=C carbon-carbon double bond which can partially open up to form linking -C-C-C-C- bonds.

      • Phenylethene (styrene) is like ethene, but one of the hydrogens is replaced with a phenyl group derived from a benzene ring (a -C6H5 group actually, but don't worry about this at GCSE level).

    • diagram equation for formation of polystyrene from styrene phenylethene to poly(phenylethene)

      • A molecular formula equation for the formation of poly(phenylethene), aka polystyrene!

    • You can make polystyrene in the school laboratory quite easily.

      • You mix styrene, a colourless flammable 'smelly' liquid, with some peroxide initiator in a test tube.

      • Cover the test tube top with a cotton wool plug to minimise fumes escaping.

      • Since the styrene is both volatile and flammable, you heat the mixture gently in a warm water bath - do not heat in a bunsen flame!

      • Gradually, the 'runny' liquid starts to thicken and become viscous as monomer upon monomer add together.

      • You are observing the molecules getting longer and longer and the corresponding intermolecular attractive forces getting stronger making the viscosity increase of the polymer.

      • Eventually the mixture sets hard to give a clear mass of polystyrene, and a completely useless test tube!

    • Properties and uses of polystyrene

    • Expanded polystyrene (EPS), with its trapped gas (from the 'blowing agent' e.g. CO2) gives the material excellent heat insulation properties (thermal insulation material, due to the trapped gas - poor conductor of heat).

      • It can be made into disposable cups for hot drinks like tea, coffee and soup. It can be used as a thermal insulator in other situations BUT bear in mind that it is a highly flammable material and on strong heating gives off flammable gases! So, remember, its a very flammable material and there have been tragic accidents when used as ceiling insulation in homes. I hope/presume this building practice is banned?

    • Polystyrene is also used in a gas expanded form for packaging and insulation - 'polystyrene foam' or 'expanded polystyrene'. This is light and useful for packing breakable objects and valuable items like computers!

    • Polystyrene is chemically very stable and a potential pollutant, so, hopefully, food packaging will be minimised and polystyrene packaging replaced with biodegradable materials - maybe a return to paper and cardboard!

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7G. Poly(tetrafluoroethene) or PTFE - formation, structure, properties and uses

  • Poly(tetrafluoroethene) or PTFE

    • PTFE a short acronym! and it's commercial name is TEFLON

    • Poly(tetrafluoroethene) is made by polymerising tetrafluoroethene (its like ethene except all the H atoms are F atoms!)

    • n CF2=CF2 ===> -(-CF2-CF2-)n-

diagram equation for making PTFE from tetrafluoroethene

  • Above is the (repeating unit) of poly(tetrafluoroethene)

  • PTFE is one of the most hard wearing of commonly used thermoplastics.

  • PTFE is chemically a very unreactive plastic and, unlike poly(ethene) and poly(propene), it doesn't burn easily, so has good flame resistant properties.

    • Advanced level note of PTFE properties:

    • The bonds between the carbon and fluorine atoms are very strong and not easily broken by a chemical reagents, hence its very useful chemical inertness.

    • Average bond enthalpies/kJmol-1: C-C  348, C-H  412, C-F 484, C-Cl 338.

    • The greater the bond enthalpy, the higher the activation energies for any chemical attack on the PTFE polymer chain.

  • PTFE with its excellent heat resistance, can with stand quite high temperatures.

  • PTFE's remarkable 'non-stick' properties, combined with its thermal stability and flame resistance has made it an excellent coating for 'non-stick' cooking pans i.e. you coat the metal surface of a cooking pan with PTFE.

    • It is the only known surface a gecko can't stick to! tough on the gecko!

  • PTFE has very low coefficient of friction and can be moulded into moving parts in machines (sliding/rotating surfaces etc.) and is used for taps in burettes.

  • Like most plastics, it is a poor electrical conductor - so a very good electrical insulator, it is strong and flexible and used for electrical insulation.

  • The use of PTFE in 'breathable' fabrics like GORE-TEX are described and discussed on the smart materials page 6. Gore-Tex and Thinsulate etc

Some extra notes about addition polymers: structure, properties & uses notes for advanced level students only

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7H. More on the USES OF POLYMERS - Plastics

Now on separate page (c) doc b More on the uses of plastics, problems with plastics and recycling

7I. Problems with using polymer plastics: recycling, disposing and pollution

Now on separate page (c) doc b More on the uses of plastics, problems with plastics and recycling

Summary of advantages and disadvantages of recycling plastic polymers - the 'pros and cons'!

The recycling case of PET plastics

Now on separate page (c) doc b More on the uses of plastics, problems with plastics and recycling

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7J. Choosing a Plastic for a Particular Use

Now on separate page (c) doc b More on the uses of plastics, problems with plastics and recycling

Multiple Choice Quizzes and Worksheets

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (easier-foundation-level)

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (harder-higher-level)

KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry

and (c) doc b 3 linked easy Oil Products gap-fill quiz worksheets

ALSO gap-fill ('word-fill') exercises originally written for ...

... AQA GCSE Science (c) doc b Useful products from crude oil AND (c) doc b Oil, Hydrocarbons & Cracking etc.

... OCR 21st C GCSE Science (c) doc b Worksheet gap-fill C1.1c Air pollutants etc ...

... Edexcel GCSE Science Crude Oil and its Fractional distillation etc ...

... each set are interlinked, so clicking on one of the above leads to a sequence of several quizzes

14-16 gcse organic chemistry keywords and phrases: revision study notes for 14-16 school chemistry AQA Edexcel OCR IGCSE/GCSE 9-1 chemistry science topics modules for studying how to make poly(ethene) its properties and uses of poly(propene), uses and properties of poly(chloroethene), properties and uses of PVC, properties and uses of  PTFE, examples of addition polymers, equations for addition polymerisation

Website content Dr Phil Brown 2000+.

All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted.

Exam revision summaries & references to science course specifications are unofficial.

Doc Brown's revision notes on organic chemistry for UK GCSE level and US grade 9 and grade 10 examinations

INDEX of GCSE level notes on Organic Chemistry

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