- In 1933, Gibson and Fawcett carried out a reaction between ethene and benzaldehyde at a pressure of 2000 atmospheres.
- The apparatus leaked and they accidentally obtained a white waxy substance which had an empirical formula of CH2.
- Polythene was born.
- Michael Perrin later joined them and discovered that the polymerisation reaction would not occur if there wasn’t enough oxygen. The leak in the original apparatus lead to oxygen getting into the mixture.
- Perrin also showed that benzaldehyde could be removed from the mixture and the polymer would still be formed.
- The amount of oxygen in the manufacturing process had to be just right, too little and polymerisation would not occur, too much and the process would run out of control.
- Polythene is tough, durable and has excellent electrical insulating properties.
- Polythene replaced rubber insulating on wires, as it had no adverse effects when left out in the weather.
- Polythene also has almost no tendency to absorb electrical signals and so it was useful for insulating telephone cables.
- This property also made it the perfect substance to use in the development of RADAR during World War Two.
- Polythene eventually began to replace many naturally occurring substances; however polythene was overexploited; it was used for a variety of novelties as a cheap substitute for many substances.
- This gave plastic a bad name.
Different kinds of polythene
- The polymer created by Gibson and Fawcett was a low density poly(ethene) (LDPE). The chains are not well organised and so the density and strength are lowered.
- Karl Zeiger developed a high density poly(ethene) (HDPE), by passing ethene through a small amount of TiCl4 and (C2H5)3Al in a liquid alkane.
- The discovery was prompted by the accidental formation of HDPE in apparatus that had nickel left over as impurities.
- HDPE chains are well organized, and so give the polythene extra strength.
Useful books for revision:
Revise AS Chemistry for Salters (Written by experienced examiners and teachers of Salter's chemistry)
Revise AS Chemistry for Salters (OCR) (Salters Advanced Chemistry)