Polymers - C5 Flashcards
Polythene can reach a strain of … % when it is extended e….y. It is s….g but flexible.
1, elastically, strong.
What is the structure of polythene and why does this make it strong and flexible?
Tightly packed chains make up polythene. These chains can unfold and rotate, increasing the length of the polymer while also preventing cracks from propagating. Chains can slide over each other. The chains absorb energy when unfolding, so they are tough.
Cross links can be added to polymers by c….y joining two chains together through c….. bonds.
chemically, covalent.
What can be done to natural rubber to increase stiffness?
If rubber is heated with sulphur, the sulphur atoms can be covalently bonded with the rubber, forming cross-links and preventing chains from sliding to increase stiffness and reduce flexibility. This is vulcanisation.
What can rubber be used for?
Shock absorbers and tyres.
What happens when rubber is stretched?
The chains rotate to form straighter paths. When the force is removed, they contract.
What sort of bonds do polymers have and how does this affect conductivity?
Polymers have strong covalent bonds making them strong. As there are no free electrons, they are electrical and thermal insulators.
Why is polystyrene stiff and brittle?
Benzene rings stop rotation, and do not allow chains to slide past each other. It is rigid.
Why is bakelite stiff and brittle?
Cross-links stop chains from unfolding or sliding.
Bonds in polymers are d…..k so polymers can sometimes be brittle.
Directional
Polymers have strong c….t bonds and weak i…..r forces.
covalent, intermolecular.
Describe polythene’s unusual semi-crystalline structure.
In some regions it is amorphous with tangled chains, reducing flexibility, increasing stiffness, and making it more brittle, as well as less strong. In others it is crystalline, with a regular structure and higher strength. When polythene is stretched this increases the size of crystalline regions, and the material can neck in these regions.
