Lesson Outcomes Polymers All must Describe LD and HD polythene and production Describe thermosoftening and thermosetting polymers Most Should Explain properties in terms of bonding between polymer chains.

Polymers Describe LD and HD polythene and production from monomers. Describe thermosoftening and thermosetting polymers (D-C) State advantages and disadvantages of using polymers. Explain properties in terms of bonding between polymer chains. (B-A*)

Polymers CHEMISTRY 2 GCSE Additional Science Chapter 9

Properties of Polymers Poly(ethene) and other polymers are simple molecular structures with covalent bonds within the molecule but only weak forces of attraction between the molecules. This gives them the typical properties of simple molecular structures. In poly(ethene), the long molecules lie side by side. These can uncoil and slide past each other, making the material flexible. Long polymer chains have stronger forces of attraction than shorter ones. By making the chains of a polymer longer, a stronger and less flexible material is produced.

Low Density Polythene Low-density polyethene The side branches stop the polymer molecules from lining up regularly. Its structure is not crystalline. This means that: the material has a lower density than HDPE the forces of attraction between polymer molecules are weakened the material is less strong, and has a lower melting point, than HDPE Made using high pressure ( up to 3000 atmospheres) and moderate temperature ( about 300oC)

High Density Polythene The polymer molecules line up regularly to give a crystalline structure. This means that: the material has a higher density than LDPE the forces of attraction between polymer molecules are strong the material is stronger, and has a higher melting point, than LDPE . Made using a catalyst, 100 oC and normal atmospheric pressure

Thermoplastics and thermosets Thermoplastics is the name given to plastics that melt when heated. Can be melted and reshaped many times. They are used to make bowls, buckets and clingfilm. Thermosets is the name given to plastics that do not soften when heated so can be moulded only once. They are used to make saucepan handles and electrical fittings. The difference:- Thermoplastics Thermosets GCSE Additional Science Chapter 9 Thermoplastics are long chains with weak forces between them. These chains slip easily over each other, so they are flexible. They melt when heated gently because the weak forces need little energy to break. The chains are connected by cross-links within a thermoset. They do not slip over each other easily so are more rigid than thermoplastics. A lot of heat energy is needed to break the cross-links, so they do not soften (melt) when heated.

Advantages and Disadvantages of Polymers Cheap Advantages Made from a non-renewable resource Disadvantages Traps and kills Animals when it’s litter Do not corrode Light Use less energy to make than traditional materials Easy to mould into different shapes Many are non-biodegradable Polymers Creates rubbish and pollution GCSE Additional Science Water doesn’t affect them Strong for their weight Chapter 9 Must recycle them to maintain clean environment Suitable for a wide variety of uses