9.3 Polymers Flashcards
Polymers
Polymers are large molecules of high relative molecular mass and are made by linking together large numbers of smaller molecules called monomers.
Each monomer is a repeat unit and is connected to the adjacent units via covalent bonds.
Polymerisation reactions usually require high pressures and the use of a catalyst.
Many everyday materials such as resins, plastics, polystyrene cups, nylon etc. are polymers.
These are manufactured and are called synthetic polymers.
Nature also produces polymers which are called natural or biological polymers.
Formation of poly(ethene)
Addition polymers are formed by the joining up of many monomers and only occurs in monomers that contain C=C bonds.
One of the bonds in each C=C bond breaks and forms a bond with the adjacent monomer with the polymer being formed containing single bonds only.
Many polymers can be made by the addition of alkene monomers
Poly(ethene) is formed by the addition polymerisation of ethene monomers and is most commonly called polythene.
Other addition polymers
Other addition polymers are made from alkene monomers with different atoms attached to the monomer such as chlorine, fluorine or a methyl group.
The name of the polymer is deduced by putting the name of the monomer in brackets and adding poly- as the prefix.
For example if propene is the alkene monomer used, then the name is poly(propene).
Deducing the monomer from the polymer
Polymer molecules are very large compared with most other molecule.
Repeat units are used when displaying the formula.
To draw a repeat unit, change the double bond in the monomer to a single bond in the repeat unit.
Add a bond to each end of the repeat unit.
The bonds on either side of the polymer must extend outside the brackets (these are called extension or continuation bonds).
A small subscript n is written on the bottom right hand side to indicate a large number of repeat units.
Deducing the monomer from the polymer
Identify the repeating unit in the polymer.
Change the single bond in the repeat unit to a double bond in the monomer.
Remove the bond from each end of the repeat unit and the subscript n (which can be placed in front of the monomer).
Use of poly(ethene)
Properties - Flexible, cheap and electrically insulating..
Use - Plastic Bags (Low density polythene).
Plastic Bottles (high density polythene).
Use of poly(propene)
Properties - Flexible and strong.
Use - Food Packaging
Ropes
Carpets
Use of poly(chloroethene) (PVC)
Properties - Long-lasting, tough and cheap.
Use - Plastic Sheets
Artificial Leather
Drainpipes and Gutters
Insulation on Wires
Use of poly(tetrafluoroethene) (PTFE)
Properties - Very tough, non-stick and resistant to high temperatures.
Use - Cookware (non stick pans)
Pipework
Condensation polymers
Condensation polymers are formed when two different monomers are linked together with the removal of a small molecule, usually water.
The monomers have two functional groups present, one on each end.
The functional groups at the ends of one monomer react with the functional group on the end of the other monomer, in so doing creating long chains of alternating monomers, forming the polymer.
Polyesters are formed from two different monomers and produce water.
For every ester linkage formed in condensation polymerisation, one molecule of water is formed from the combination of a -H and an -OH group.
Condensation polymer vs addition polymer
Addition polymerisation forms the polymer molecule only.
Condensation polymerisation forms the polymer molecule and one water molecule per linkage.
Polyester
Dicarboxylic acid monomers can react with diol monomers to form ester links this is a condensation reaction. The dicarboxylic acid monomers contain two carboxylic acid groups (-COOH) and the diol monomers contain two alcohol groups (-OH).
The molecule with the ester link has a functional group at each end. These can then react in condensation reactions, making the chain longer. The series of reactions together is known as condensation polymerisation and the resultant polymer is called a polyester.
Problems with polymers
Polymers are formed by the joining up of many small molecules with strong covalent bonds.
This makes polymers unreactive and chemically inert so they don’t easily biodegrade.
Disposing polymers landfill sites
Waste polymers are disposed of in landfill sites but this takes up valuable land, as polymers are non-biodegradable so micro-organisms such as decomposers cannot break them down.
This causes sites to quickly fill up.
Disposing polymers incineration
Polymers release a lot of heat energy when they burn and produces carbon dioxide which is a greenhouse gas that contributes to climate change.
Polymers that contain chlorine such as PVC release toxic hydrogen chloride gas when burned.
If incinerated by incomplete combustion, carbon monoxide will be produced which is a toxic gas.
Disposing polymers recycling
Polymers can be recycled but different polymers must be separated from each other.
This process is difficult and expensive.
Advantages of recycling polymers
Recycling is a more economically viable process than manufacturing from scratch.
It decreases the use of crude oil which allows it to be kept for other purposes.
It is better for the environment as plastic waste is being collected and reused, hence recycling reduces the emissions of greenhouse gases and other toxic gases produced during the manufacturing process.
It also reduces the amount of landfill sites needed.
Recycling is itself an entire industry which creates employment and economic growth.
Disadvantages of recycling polymers
Sorting plastics by type of polymer is a tedious and labour intensive process which is costly.
Recycling counts on what is collected in as the raw material, therefore production of certain types of polymers may not be possible due to a lack of starting ingredients.
Melting polymers produces toxic gases that are harmful to plants and animals
Polymers can only be recycled a number of times before they lose their properties and become useless.
Recycling runs the risk of mixing different polymers together, which again will affect their properties. This is particularly risky for polymers designed for specialist use such as aircraft or automobile parts, where safety is of utmost importance.
Raw materials of polymers
Plastics are made from crude oil. Crude oil is a finite resource, eventually it will all get used up and run out. The more we use up our crude oil resources, the more expensive crude oil will become. This will then increase the price of crude oil products.
Crude oil isn’t just used to make plastics, we need it for lots of different things, such as petrol for cars and heating our homes. As resources dry up, we will face the dilemma of how to use the remaining oil. One way we can help delay this problem is by recycling our polymers.
DNA (natural polymer)
DNA (deoxyribonucleic acid) is found in every living thing and many viruses. It contains genetic instructions that allow the organism to develop and operate. It’s a large molecule that takes a double helix structure.
DNA is made of two polymer chains of four different types of monomers called ‘nucleotides’. The order of the nucleotides acts as a code for the organism’s genetic information.
Starch (natural polymer)
Carbohydrates are compounds of carbon, hydrogen and oxygen with the general formula Cx(H2O)y.
There are simple carbohydrates and complex carbohydrates.
Simple carbohydrates are called monosaccharides and are sugars such as fructose and glucose.
Complex carbohydrates are called polysaccharides such as starch
The monomers from which starch is made are sugars.
Starch is used to store energy.
Complex carbohydrates are condensation polymers formed from simple sugar monomers and, unlike proteins, are usually made up of the same monomers.
An H2O molecule is eliminated when simple sugars polymerise
The linkage formed is an -O- linkage and is called a glycosidic linkage.
Protein (natural polymer)
Proteins are condensation polymers which are formed from amino acid monomers joined together by peptide bonds.
Amino acids are small molecules containing amine (-NH2) and carboxylic acid (-COOH) functional groups.
Use of polymers
As they are poor conductors of heat and electricity, this makes polymers good thermal and electrical insulators.
These properties are extremely useful for insulating electrical wiring as they prevent electric shocks and overheating.
The low melting points and flexibility of polymers enable them to be moulded easily into an infinite variety of shapes.
Use of composites
Steel reinforced concrete has immense tensile and compressive strength allowing it to be used as columns and supporting structures in construction.
Carbon fibres composites are extremely strong and low weight, hence they are used in aviation, aeronautics and for making professional racing bicycles.
Use of glass and metals
Glass and steel are extremely useful building materials.
Apart from its transparency, the hardness and the high compressive strength of glass makes it an ideal material for making walls and windows.
Metals are used extensively in electrical cabling and in electronics due to their ability to conduct electricity.
Copper is the most frequently used as it is a good conductor and is very malleable and easy to thread into cables.
Aluminium is a very strong metal but is also very light.
This makes it ideal for use in the construction of airplanes as it has a high strength-to-weight ratio.
Physical properties of metals
Shiny, malleable and ductile so can be hammered into different shapes.
Can be mixed with other elements to form alloys, which have different properties to the elements they contain.
Corrosion resistant metals can be produced which last longer than other metals.
Good conductors of heat and electricity.
Physical properties of composites
Made from two components: reinforcement and matrix.
The matrix is what binds the reinforcement together.
Common examples include fibreglass and steel reinforced concrete.
The properties of composites depend on the reinforcement and matrix used so composites can be tailor engineered to meet specific needs.
Physical properties of polymers
Can be tailor designed to have specific properties for specific uses.
Can be made opaque or transparent.
Usually tough and flexible, some specialist polymers can be brittle.
Poor conductor of heat and electricity.
Physical properties Clay ceramics
These are hardened materials that resist compressive forces.
Clay is a soft material dug up from the earth which hardens at high temperatures and when it is fired, produces a very strong and hard material.
This allows bricks to be used to build walls which withstand the weight and pressure of the material bearing downwards on itself.
Physical Glass ceramics
Transparent and strong, glass insulates against heat.
Glass ceramics are also more durable than other materials hence they are better suited for use in windows than plastic.
Most of the glass produced is soda-lime glass which is made by heating a mixture of limestone, sand and sodium carbonate (soda) until it melts.
On cooling it solidifies to form glass.
A variation is borosilicate glass which is made using sand and boron trioxide and has a higher melting point than soda-lime glass.
Risks of nanoparticles
Nanoparticles have widespread uses and applications that can provide an immense advance in materials technology.
The use of nanoparticles in science is in its early stages so there are still a lot of unknown factors and potential risks.
In particular there is a lack of understanding on how they may affect health.
Although there haven’t been any serious short term side effects, there could be long term side effects which we haven’t detected yet as they haven’t been in use long enough.
Even a small amount of toxicity in a particular nanoparticle would be multiplied due to the high surface area to volume ratio.
This coupled with the fact that they are not easily disposed of by the body are a cause for caution in the medical application of nanoparticles.
Use of nanoparticles
The main industrial application of nanoparticles is in catalysis due to their high surface area to volume ratios.
Titanium dioxide is a good example of how the same chemical has different properties in bulk and nanoparticle form.
Titanium dioxide in nanoparticle form is used in sunscreens as it blocks UV light but leaves no white marks on the skin.
The same chemical in bulk form is used as a white pigment in paints
Fullerenes are used in the medicine and drug design as they are more easily absorbed than other particles and can deliver drugs to target areas more effectively.
Fullerenes are also used in electronic circuitry and as coatings for artificial limbs and joints.
Nanoparticles of silver are sprayed onto the fibres of medical clothing and surgical masks which gives them the flexibility of a material but with the added benefit of the antibacterial properties of silver metal.
Properties of nanoparticles
One of the most interesting features of nanoparticles is their very high surface area to volume ratio.
As particles decrease in size, their surface area increases in relation to their volume.
This is why nanoparticles may have properties different from those for the same materials in bulk.
It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes.
Fullerenes (nanoparticles made of carbon) behave very differently to larger compounds of carbon like diamond and graphite.
The surface area to volume ratio is an important feature in catalysis and surface chemistry.
The higher the ratio then the more surface area is available for reaction, hence the better the catalyst.
Nano particles
Nanoparticles are between 1 and 100 nanometres in size and usually contain only a few hundred atoms.
Atoms and simple molecules are around 100 times smaller than this.
Nanoparticles are much smaller than fine particles which have diameters of between 100 and 2500 nm.
The research into the production and application of nanoparticles is called nanoscience.
