POLYMERS

C₁₀H₂₂ is called decane and is produced from the naptha fraction. A refinery may have plenty of naptha and might want to break it down into smaller more valuable molecules. This is where cracking comes in. For example at 800°C in the presence of a catalyst :-

decane(C10H22)

octane(C8H18) +

(ethene)

Octane is very valuable hydrocarbon because it's ideal for petrol. When any alkane is cracked you always get smaller alkanes plus some alkenes. The alkenes are very important chemicals because the double bonds can open up to form POLYMERS. Lots of ethene molecules can, under certain conditions, join together to form a polymer called polyethene. We call the individual molecules MONOMERS.

It's very simple, lots of monomers open up their double bonds and join up to form a polymer:-

n is the number of ethene molecules (monomers) that go into making the polymer chain. n can be well over 100,000. Polythene is very cheap and strong, it comes in two varieties (high density and low density). It's used to make:

• Plastic bags (bin liners, carrier bags etc.)
• Bottles
• Buckets and bowls

This molecule is called propene, notice that it has three carbons in the chain. Propene polymerises to give polypropene. Polypropene can be moulded or spun into strong fibres.  It is used to make:

• Ropes
• Packing crates and containers
• Carpets

Look at how propene can polymerise:

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