Polymers
Properties of polymers
Further information on how A large molecule formed from many identical smaller molecules known as monomers. are made from Small molecule, usually containing a C=C bond, that can join end to end with other monomers to form a polymer molecule. can be found in More organic chemistry.
Different polymers have different The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point., depending on the monomers they are made from and the conditions under which these monomers were joined together. This means that different polymers have different uses. For example, poly(ethene) can be made in low A measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3). and high density forms.
| Polymer | Properties | Uses |
| Low density poly(ethene), LDPE | Flexible, unreactive, can be made into films | Most carrier bags, bubble wrap |
| High density poly(ethene), HDPE | Strong, flexible, resists shattering, resists chemical attack | Plastic bottles, pipes, buckets |
| Polymer | Low density poly(ethene), LDPE |
|---|---|
| Properties | Flexible, unreactive, can be made into films |
| Uses | Most carrier bags, bubble wrap |
| Polymer | High density poly(ethene), HDPE |
|---|---|
| Properties | Strong, flexible, resists shattering, resists chemical attack |
| Uses | Plastic bottles, pipes, buckets |
Low density poly(ethene) has a structure where the polymer chains are branched and this means that the A collection of two or more atoms held together by chemical bonds. are arranged randomly. High density poly(ethene) has less branching of the polymer chains, so the molecules line up much more closely.
Thermosoftening and thermosetting plastics
Plastics can be put into one of two categories, depending on how they respond when heated.
Thermosoftening plastics melt when they are heated. Most plastics that we come across in everyday life are thermosoftening plastics. This means that they can be Used materials that have been reprocessed to make new materials., which involves melting them before making a new product.
Thermosoftening plastics do not have A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. between neighbouring polymer molecules, so the molecules can move over each other when heated and the plastic melts.
Thermosetting plastics do not melt when heated. They tend to char and burn when heated, but they are resistant to much higher temperatures than thermosoftening plastics. They are used to make electrical plugs, which must not melt, even if there is a malfunction and the wiring inside gets hot.