Polymers

Página 1

Making plastics

Polymer: A substance which has very long molecules made up of many small molecules joined together

Plastic: Any synthetic or semi-synthetic organic polymer. There are two types of plastic:

Thermoplastics:

Plastics that soften when heated

Used in bowls, buckets, packaging

Made up of polymer chains that are not linked up and so can slide over each other

Thermosets:

Resistant to heat and do not soften when heated

Used in electric light fittings, saucepan handles

Strong cross linkages hold the structure together and makes them resistant to heat

Made in a liquid form, then placed in a mould and allowed to set

Página 2

Polymerisation

Monomers: The small molecules used to form polymers

Addition polymers: Made from only one type of monomer

Condensation polymers: Made from two or more different types of polymer

Polyethene is made by heating ethene under pressure. It is very strong and is commonly used in plastic carrier bags

The properties of polymers depend on what they are made from and the conditions under which they are made. For example, low density

(LD) and high density (HD) poly(ethene) are produced using different catalysts and reaction conditions.

Página 3

Different types of polymers

Nylon is tough, lightweight, keeps water out and keeps UV light out but does not let water vapour through it which means that sweat condenses on the inside of clothes made out of nylon.

GORE-TEX material is made by coating nylon with a PFTE membrane. The holes in membrane are too small for water to

pass through but are big enough for water vapour to pass through. Therefore, GORE-TEX materials have all the positives of nylon but they are also breathable.

Factors that affect polymer properties:

1. Chain length: Longer chains get tangled with and stick to each other, making them harder to separate. This means polymers with longer chains have a higher melting point, strength and toughness

2. Cross-linking: Cross linking permanently attaches the chains to each other, increasing the rigidity, strength and hardness

3. Plasticizers: Plasticizers block the formation of intermolecular bonds by sitting between chains. This leads to the formation of a weak but flexible polymer.

4. Crystallinity: When a polymer is crystalline, it will be tightly packed with the chains parallel to each other. This leads to strong intermolecular forces between the chians, causing increases in strength and melting point.

Página 4

Plastics and the environment

Nearly all plastics are nonbiodegradable (do not rot)

Because they do not rot away, plastics fill up landfill sites meaning new landfill sites need to be found

Advantages of recycling waste plastic:

Current landfill sites can be used for longer

Less oil used for plastic production

Less energy consumed

Página 5

Biological polymers

DNA is a polymer made from four different monomers called nucleotides

Starch is a polymer based on sugars

Proteins are polymers based on amino acids

Polyesters

Some polymers are made via condensation reactions.

Each time a condensation reaction occurs, a molecule of water is formed.

Polyester is formed in this way when a molecule containing two alcohol groups and a molecule containing two carboxylic acids combine.