Using Alkenes to make Polymers L.O: To know that alkenes can undergo polymerisation reactions to form polymers, and to know how to show the formation of polymers from monomers. To know some of the main uses of polymers. Wednesday, 07 November 2018Wednesday, 07 November 2018

1 2 Starter What are the properties of alkanes and alkenes? Come up with at least 3 properties for each and number them 1-6+. If both alkanes and alkenes share a property, just put ‘both…’ – don’t write it twice with different numbers Then make a Venn diagram (like the one below) using the numbers from each property and putting those that are shared in the centre. 2 e.g. 1. Both contain carbon and hydrogen atoms. 2. Alkenes have carbon-carbon double bonds 1

Polymerisation The most useful thing you can do with alkenes is probably polymerisation. This means joining together lots of small alkene molecules (monomers) to form very large molecules — these long-chain molecules are called polymers.

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Poly(ethene) Many ethene molecules can be joined up to produce poly(ethene) or “polythene”.

Poly(ethene) This reaction can be shown like this: …where n is a very large number of monomers

Polymers For the exam you need to know the structures of poly(ethene) and one other polymer, called poly(propene). Poly(propene) is made when lots of propene monomers join together.

Polymers – Match them up! Match the names with the pictures. 1. Many ethene monomers 2. A section of poly(ethene) 3. Many single ethenes 4. Poly(ethene) 5. Many single propenes 6. Poly(propene)

Polymers – Matched Up 1. Many ethene monomers 2. A section of poly(ethene) Make sure that they are all matched up like this… 3. Many single ethenes 4. Poly(ethene) 5. Many single propenes 6. Poly(propene)

EASY! Finding monomers In the exam, you might be given a polymer and asked to draw the monomer that makes it. All you have to do is take the bit of the polymer that repeats, remove the bonds from either side and add a double bond into it. For example… The monomer that makes this polymer is...

EASY! Naming Polymers You could also be asked to name a polymer that you haven't come across before. Naming polymers is easy. All you have to do is put ‘poly' in front of the name of the monomer. For Example… The polymer that is formed from but-2-ene is called poly(but-2-ene). : If a polymer that is formed from bromoethene, what is it’s name? : poly(bromoethene)

Properties & Uses of Polymers The physical properties of a polymer depend on what it's made from. Polyamides are usually stronger than poly(ethene), for example. A polymer's physical properties are also affected by the temperature and pressure of polymerisation. Poly(ethene) made at 2000 atmospheres pressure and 200 °C is flexible, and has low density. But poly(ethene) made at 60 °C and a few atmospheres pressure with a catalyst is rigid and dense. The fact that different polymers have different properties means they are useful for different things.

Examples… Uses of polymers

Light, stretchable polymers such as low density poly(ethene) are used to make plastic bags.

Tights Elastic polymer fibres are used to make super-stretchy LYCRA® fibre for tights.

Uses of Polymers New uses for polymers are developed all the time. Some waterproof coatings for fabrics are made of polymers, and so are many new packaging materials. Dental polymers are used in resin tooth fillings. Polymer hydrogel wound dressings keep wounds moist. Memory foam is an example of a smart material. It's a polymer that gets softer as it gets warmer. Mattresses can be made of memory foam — they mould to your body shape when you lie on them.

Waterproofing Some waterproof coatings for fabrics are made of polymers

Packaging Materials Many new packaging materials are made of polymers.

Dental polymers are used in resin tooth fillings.

Wound Dressings Polymer hydrogel wound dressings keep wounds moist.

The properties of smart materials can change in response to external stimuli, like heat or pressure. Memory foam is an example of a smart material. It's a polymer that gets softer as it gets warmer. Mattresses can be made of memory foam — they mould to your body shape when you lie on them. Mattresses

Problems with using polymers Most polymers aren't “biodegradable” — they're not broken down by microorganisms, so they don't rot. This means it's difficult to get rid of them — if you bury them in a landfill site, they'll still be there years later. The best thing is to reuse them as many times as possible and then recycle them if you can.

Biodegradable Packaging However, new biodegradable packaging materials are being developed. Plastic bags and other biodegradable plastics made from polymers and corn starch are being produced. Here is a VIDEO showing how potato starch can be made into plastic in the same way corn starch is made into plastic.

Crude oil Things made from polymers are usually cheaper than things made from metal. However, as crude oil resources get used up, the price of crude oil will rise. Crude oil products like polymers will get dearer. It may be that one day there won't be enough oil for fuel and plastics and all the other uses. Choosing how to use the oil that's left means weighing up advantages and disadvantages on all sides.

Fact Recall Describe what happens during a polymerisation reaction. Give two factors that affect the physical properties of a polymer. What property of memory foam makes it a good material to make mattresses out of? What does the term biodegradable mean? Are most polymers biodegradable or non-biodegradable? Explain why the cost of making things from polymers is likely to rise in the future. 4.

Application What is the name of the polymer that is formed from chloroethene? Draw the monomers that each of these polymers are made from: b) Draw the polymer that would be formed from each of these monomers:

Answers (fact recall) Many small alkene monomers are joined together to form long-chain polymers. E.g. the monomers that the polymer is made from and the conditions (temperature and pressure) of the polymerisation reaction. It gets softer as it gets warmer, so a memory foam mattress will mould to your body shape when you lie on it. Biodegradable means the material can be broken down by microorganisms. Non‑biodegradable Polymers are made from crude oil. Crude oil is non‑renewable so the price of crude oil, and therefore the price of polymers, will increase when the crude oil reserves start to run out. 4.

Answers (application) Poly(chloroethene) a) b)