5.21 understamd that condensation polymerisation produces a small molecule, such as water, as well as the polymer

When condensation polymerisation occurs, a small molecule (such as water) is produces, as well as the monomer.

5.20 understand that some polymers, such as nylon, form by a different process called condensation poymerisation

Most often, condensation polymerisation involves two different types of monomer. These monomers react together forming bonds between them, making polymer chains. However, for each new bond that forms, a molecule (e.g. water) is lost.

5.19 explain that addition polymers are hard to dispose of as their inertness means that they do not easily biodegrade

Most addition polymers are inert. All this means is that they do not react easily (due to the fact that the carbon bonds are very strong and hard to break). This means that it takes a really long time for addition polymers to biodegrade. Furthermore, burning plastics releases toxic chemicals so that's not a good idea either. Because of this, it is hard to dispose of polymers (that's why we recycle them).

5.18 describe some uses for polymers, including poly(ethene), poly(propene) and poly(chloroethene)

Polyethene is light and stretchy making it ideal for packaging such as plastic bags, water bottles/food containers and carpets.

Polypropene is a tough polymer but is quite flexible and heat resistant too, this makes it ideal for making things like crates

Polychloroethene is used to make clothes, drainpipes and insulating cables

5.17 deduce the structure of a monomer from the repeat unit of an addition polymer

To find the structure of a monomer, take the repeat unit of an addition polymer and add a double bond between the two carbons.

5.16 draw the repeat unit of addition polymers, including poly(ethene), poly(propene) and poly(chloroethene)

To find the repeating unit, just find the section of the polymer that is repeated and draw it out, writing the number of monomers there are next to it (if you don't know how many monomers there are, you must put an 'n')...

Polyethene


Polypropene

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Polychloroethene

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5.15 understand that an addition polymer is formed by joining up many small molecules called monomers

A polymer is just a very long saturated chain (saturated as it has no carbon double bonds). Small molecules called monomers join together to make polymers. One type of polymer is an addition polymer. The monomers that make up addition polymers are alkenes as they have a carbon-carbon double bond. If alkenes are put under a high pressure with a catalyst, they will break their carbon-carbon double  bond and polymerise (join together), forming a polymer.