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Organic Chemistry Revision Notes - Help in Revising Advanced Organic Chemistry
All My synthetic
polymer-plastics revision notes pages
to addition polymers: poly(ethene), poly(propene), polystyrene, PVC, PTFE -
More on the
uses of plastics, issues with using plastics, solutions and recycling
condensation polymers: Nylon, Terylene/PET, comparing
thermoplastics, fibres, thermosets
notes for more advanced level organic chemistry students
Polymerisation of alkenes to addition polymers - structure, properties, uses of
The manufacture, molecular structure, properties and uses of
chemistry - a mention of
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
general points on the USES OF
POLYMERS - Plastics
Polymers have many useful applications and new
uses and new polymers are being developed all the time
There are lots of examples!
- some described in
section 7B and more listed below (and described above) are on many
A wide range of
polymers are available for use in an even wider range of
applications, it seems endless these days from when I was a
chemistry student in the 1960s when some of the properties of these
new polymers were unthinkable! e.g. electrical conducting, light
Its important to realise
that polymer plastics are alternatives to traditional materials like
wood and metals and in many cases, if not completely, replacing them
on a large scale e.g. water pipes, window frames.
properties can range from being very rigid or
flexible-stretchy-elastic, very strong, easily moulded if gently
heated and pressed (thermoplastic) or set hard after moulding
and very heat resistant (thermoset).
considerably in strength e.g. polyamides or nylons are much stronger
than poly(ethene) and can even be manufactured to provide a variety
of strengths and flexibilities (see example of
LDPE and HDPE commercial products of
Many metals have become
quite expensive so things made from plastics derived from oil and
quite cheap at the moment, but prices will rise as cheap oil gets
packaging materials which are light and stretchable.
Waterproof coatings for fabrics
Dental polymers for
Wound dressings made
from hydrogels - polymers that hold water and keep wounds moist.
materials (including shape memory polymers)
eg 'memory foam' is a polymer that gets softer when it gets warmer
so you can make a mattress which adopts your body shape for
Elastic fibres that are
very stretchable to make tight fitting clothing eg Lycra fibres for
tights and sports clothing.
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 electric kettles.
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
to redo photo
Plastics can be coated with all sorts of materials. This plastic
knife and fork are coated with a material that gives the impression
of being a silvery metal and is as bright and shiny as the brass case of the
old metal pocket watch.
Some polymer materials are
relatively soft and 'springy', these are called elastomers
e.g. rubber which can be stretched and deformed, but on release of
the tension, the material goes back to its original shape.
7I. Problems with using
polymer plastics: methods of recycling, disposing and pollution
7J Highlighting three
with using and disposing of
polymers or plastic
Polymers or plastics cannot be easily broken down by
i.e. most, at the moment, most are NOT biodegradable
which leads to
waste disposal and other environmental problems eg
'Non-rotting' litter around the environment.
Land-fill sites are getting full
and recycling isn't as easy as it may seem. (see point 3.below)
using waste plastic as fuel must be very efficient to avoid any other
pollution problem. (see point 2.)
Even our lakes, seas and
oceans are carrying waste plastic materials causing harmful effects on
Can we burn waste plastic?
When plastic materials burn they can
produce highly toxic gases such as carbon monoxide, hydrogen cyanide and
hydrogen chloride - particularly from PVC and other plastics containing
chlorine and nitrogen.
Combustion of waste plastics
contributes to global warming since carbon dioxide produced.
In a recycling-disposal
centre, you need very high
tech incinerators with sophisticated facilities to remove any
harmful gases or particles, plus monitoring technology - and then you
can release the smoke into the environment.
I've visited such a
recycling plant near Harrogate in North Yorkshire, England.
Its an impressive operation
and the 'organic' waste that cannot be recycled is burnt to provide
energy to generate electricity.
The plant generates 30MW of
electricity, the recycling centre runs off 5MW of electricity, so 25 MW
of power is put into the National Grid electricity supply.
Nothing is wasted, all
residues are found some use for!
The burning of plastic waste as a
fuel is sometimes referred to as 'energy recovery' and is appropriate if
you can do nothing else with combustible waste!
The toxic fumes from plastic
materials cause deaths in house fires and controversial problems with alleged inefficient waste incinerators as they will
definitely cause environmental problems if burned on waste tips!
can we recycle plastics? What ways are used to recycle plastics? issues?
It is highly desirable to
recycle plastics for several reasons
Less environmental impact
i.e. less unsightly pollution, reduction of volume of waste in land-fill
It conserves valuable oil
based resources, especially as oil is becoming increasingly expensive.
to recycle plastics because of separation into the different types of plastics and their different physical properties.
BUT this should not prevent us from trying
and it would be beneficial to prolong the life of the finite crude
oil reserves AND reduce pollution and space in land-fill sites.
Research is ongoing to devise methods
of recycling plastics as 'new' chemical feedstock from which to
make useful organic chemical products.
There are problems in trying
to sort out the different plastics into useful categories, they are not
easy separate, you can't just use any old mixture of polymers.
At the moment, a lot may
have to be sorted by hand - lack of automation makes the sorting more
You also have the cost
of collecting domestic rubbish or industrial waste, transporting it
and sorting it all out, all of which costs money.
Manual sorting of plastic waste
is inefficient and labour intensive, but methods of sorting are
improving including optical scanning techniques to separate the
different types of plastic waster e.g. PET from HDPE and other
technologies can separate PVC from other plastics
people are coming up with ideas. A company in Scarborough, England, is
collecting waste plastic. This is shredded and compressed into porous
pads and used for good 'underground' drainage layers for footpaths, golf
greens and sand bunkers etc. and has a good working life because the
material isn't biodegradable!
Clear soft drink bottles are
made from PET (polyethene/polyethylene terephthalate) which can be
recycled as fibre-fill for pillows and carpets.
This save 90% of the energy
costs compared to the original manufacturing process.
Energy costs are a big
economic recycling factor, its not just about making naturally occurring
resources like oil last longer.
However, it takes about
20,000 drinks bottles to make a tonne of recycled PET.
In 1988 Australia issued
bank notes made from recycled poly(propene). These plastic notes
apparently have the advantage of being more difficult to forge and they
Other ideas include making
more durable plastic bags that can be used many times for shopping.
Ideally some recycled
thermoplastics and scrap material from a plastic product manufacturing
process, can be heated and remoulded in the same process or another
You can also manufacture
plastics whose break down is initiated by exposure to sunlight. This is
particularly useful in agriculture where plastic bags of fertiliser are
in common use.
7K Biodegradable and compostable polymers -
these should break down due to bacterial activity
Degradable polymers will break
down in the environment from the effects of weathering or light
(particularly uv radiation), but very slowly due to their great
Biodegradable polymers can be
broken down by the enzymes in microorganisms.
They often based on a polyester
structure (but NOT PET/Terylene) and are relatively easily hydrolysed
and broken down by the metabolic chemistry of microorganisms.
are being developed which are
or can be recycled, so will the
paper bag and cardboard package make a comeback? (in Ireland you have to
bring your own bag or buy one, and not necessarily a plastic one!), this
isn't a recycling process BUT it does reduce environmental pollution.
Hydrocarbon polymers like poly(ethene) or
poly(propene) containers have strong C-H and C-C bonds are strong and
non-polar so these polymers are not susceptible to chemical attack.
The same argument applies to PTFE with
its strong C-C and C-F bonds.
In fact the vast majority of synthetic
polymers are NOT biodegradable, because enzymes have not yet evolved in
microorganisms to break them down.
Polymers can be made more degradable by
including an additive that promotes breakdown by oxidation - makes the 'oxo-biodegradable'.
As well as this additive, thin films of
poly(ethene) and poly(propene) polymer formulations also include a
controlled amount of antioxidant that prevents the plastic breaking down too
soon! Once the antioxidant is used up, the polymer molecules will begin to
break down. This non-oxidation lifetime can be designed to be months or
years followed by the oxidative degradation in contact with the oxygen in
air, which itself may take months or years.
Where possible, these plastics are made
from renewable raw materials such as cellulose (from wood), lactic acid and
Bioplastics are manufactured by
non-hazardous methods and so better for the environment.
Waste bioplastic materials should
naturally degrade in the environment to water and carbon dioxide from
bacterial activity and not cause pollution and damage to the environment
e.g. avoiding unsightly litter and dangers to animals.
Compostable plastics have to meet strict
criteria and must break down to water, carbon dioxide, harmless
inorganic compounds and biomass residue i.e. degrade in the same way as any
other organic material added to a compost heap!
You can mix starch granules (very biodegradable) with plastics like poly(ethene) which enables
microorganisms to grow and feed in the plastic and may eventually help
biodegrade the plastic itself?
By breaking down the starch e.g. by
microorganisms also break down the poly(ethene) into tiny particles
making less conspicuous litter, BUT, there is growing concern about the
effects of micro plastic particles on organisms in the environment.
You can make biobags and cutlery from
renewable and biodegradable cornstarch to replace non-biodegradable polythene bags. Many supermarket
bags are made from plant starch and since they are compostable, they can be
used as bin liners for collecting food waste - so they both compost
Similarly, tableware such as plates, cups and food
bags can be manufactured from sugar cane fibre (a biodegradable natural polymer) replacing
non-biodegradable plastics like polystyrene.
Polylactic acid is biodegradable, can
be used for cold drink cups and biodegrades in 180 days.
acid is also biodegradable, it is quite easily broken down by hydrolysis
and decomposes in less than a month on a compost heap.
Extra advanced level note
These are synthetic polymers
specially designed to become weak and brittle when exposed to sunlight
for a long time - uv light of higher energy photons, has more effect
than visible light photons.
This can be facilitated by
incorporating light sensitive additives into the polymer formulation
that catalyse the breakdown of the polymer on absorption of uv
Another way to achieve this effect is
to incorporate carbonyl bonds (>C=O) into the polymer chain structure.
The carbonyl groups in the
polymer chain absorb uv photons and break the polymer chain at that
The initial product from
photodegradable polymers exposed to uv light, is a waxy mixture
which ultimately breaks down into carbon dioxide and water by
So the photodegradable polymer is
converted to biodegradable products!
7L The recycling case of PET/PVC and
other plastics - examples of reclamation
Recycling PET ('poly(ethylene
PET is a polyester used for
making plastic drinking bottles and made from the non-renewable resource
of crude oil.
If it can be recycled, you
save lots of energy and uses less of a valuable resource of organic
chemicals (oil) than if you were making a new quantity of PET.
To make PET, you have to
extract oil, fractionally distil it, chemically modify fractions to
produce molecules from which you can then make the monomers to
polymerise to make PET.
PET bottles can be recycled to make
other products including packaging materials, carpets and new bottles
The PET objects must be
sorted out from other plastic waste.
They can then be shredded
and melted down to be moulded into other useful objects.
If PET wasn't recycled, it
would end up in a polluting space occupying land-fill site.
PET bottles can be recycled
e.g. in poorer countries, they can be filled with water unfit for
cooking and drinking, left out in bright sunlight. PET lets uv radiation
through which sterilises the heated water - the heat and uv radiation
kills many pathogens (bacteria, viruses, protozoa and worms).
Recycling PVC poly(chloroethene),
The recycling of PVC is
particularly awkward problem because its high content of chlorine in
the polymer structure and the process is uneconomic i.e. it costs
more to recycle than making 'new' PVC from the petrochemical
To avoid a build-up of PVC in
landfill sites, it has been incinerated, but this produces harmful
fumes that may enter the air environment e.g. fumes of highly acidic
fumes from hydrogen chloride, which are costly to remove from the
waste combustion gases.
However, there is a method being
developed that involves dissolving and separating PVC using a
solvent. High quality PVC is precipitated from the solvent for reuse
and the used solvent is recovered and recycled to be reused to
extract more PVC from waste.
Recycling Poly(ethene), 'polythene'
HDPE can be re-used to make hard
wearing tough plastic materials like waste bins, water butts and
LDPE waste is recycled to make
plastic refuse sacks.
Recycling Poly(propene), 'polypropylene'
Poly(propene) can be recycled
by mechanical means. It can be sorted from other types of waste
plastic by hand - but, unfortunately, this is inefficient in
time/cosy and labour intensive.
However, the sorting can be done
automatically using infrared spectroscopy or flotation - the latter
uses the different densities of plastics to sort them.
After the separation, the
poly(propene) is shredded into flakes and processed into granules
which can be melted down and moulded into new items.
This process can be repeated
several times with significant degradation to the polymer structure
e.g. no loss of strength.
It is possible, in the absence of
air (oxygen), to thermally degrade waste poly(propene) at ~500oC
to produce a chemical feedstock similar to naphtha from the
fractional distillation of crude oil,
A nice example of recycling, a door
mat made from recycled plastic-rubber flip-flops, a present from a
friend who runs an outlet for the FAIRTRADE retail organisation.
11. for the chemistry of making polyesters
Summary of advantages and disadvantages of recycling plastic polymers - the
'pros and cons'!
Reduces the quantity of oil needed - a finite resource
not easy, and expensive, to separate the different types of polymer
in a recycling centre - prior to be reformed in some way to make a
Reduces the quantity of non-biodegradable waste in land-fill sites
Mixing recycled plastics together reduces the quality of the plastic
Reduces emissions of greenhouse gases if burned
Unlike with metals, its difficult to keep on recycling the same
polymer material e.g. the structure gets weaker
Recycling usually reduces the energy and resources needed to
replaced redundant materials
Processing waste plastic can produce obnoxious harmful gases - not
good for us or the environment - surely we have all smelt overheated
or burned plastic!
Recycling reduces costs, because of 4. above.
due to carbon monoxide etc.
Logistic exercise - choosing a plastic for a particular use
(this section is repeated
on the other GCSE
condensation polymer notes page)
How we use polymer compositions depends on
their properties, some are quoted in the data table below
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 appreciated.
made into fibres?
(a) Which plastic could
be used as for disposable tableware like plates for hot meals or coffee
(b) Which plastic could
be used as a moving plastic component in a machine?
(c) Which plastic could
used as containers for high volume production line of acids or alkalis?
(d) Which plastic could
be used as laboratory volume measuring instrument e.g. a syringe or
(e) Which plastic is
suitable for clothing fabrics?
(f) Which plastic would
be used for super-market carrier bags?
Answers near the end of the
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