Polymerisation & Plastics 10.05 p176-177. Learning objective Can explain the difference between monomers & polymers. Can explain how polymers are formed.

From Alkanes to Alkenes Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient. They do not flow easily and are difficult to ignite. Crude oil often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules. We can make hydrocarbons more useful by cracking. These molecules are cracked into smaller molecules by heating.

Cracking Ethane to make Ethene Some of the smaller molecules formed by cracking are used as fuels, and some of them are used to make polymers in the manufacture of plastics. Ethane is a small molecule (C2H6) By cracking Ethane at a high temperature it can form Ethene + hydrogen. C2H6 + Heat C2H4 + H2

Alkenes The double bond makes them reactive. You can make the alkene polymerise (break the double bond) by heating. The double bond breaks and many small alkenes become a long chain.

What are polymers? Polymers are large molecules made when lots of small molecules called monomers join together. This process is called polymerisation. You get the monomers from the cracking of hydrocarbons.

Polymers Each polymer molecule is made from a repeating monomer (Greek) poly = “many” meros = “part” Each polymer molecule is made from a repeating monomer Monomers are small molecules (not single atoms). polymerisation monomers Single polymer chain

Monomers + heat = Polymer Monomers - Ethene (C2H4) Polymer - Poly(ethene) (generally shortened to polythene)

Ethene Ethene is another name for polythene. Polythene is used to produce plastic bags, cling film and bottles. Ethene can react with other chemicals to produce other plastics like polyphenylethene (frigolit), drain pipes, toothbrushes, fast food boxes, plastic cups and many more.

Properties of plastics They do not conduct electricity and are poor conductors of heat. They are non-reactive, not affected by air, water or many chemicals. They are strong because their long molecules are attracted to each other so hard to tear apart by intermolecular forces.

Intermolecular Forces Most molecules have weak bonds between them. Strong bonds hold the molecules together but there is some attraction between molecules. Van der Waals forces are the strong attractions between the polymer chains so the plastic is stronger and has a higher melting point.

Task What is the difference between a monomer and a polymer? Explain how polymers are formed? Why is it important to know about how plastics are made?

Polyphenylethene (Polystyrene or Frigolit) Polystyrene is made up of many monomers to form large chains. Why is polystyrene useful? Can polystyrene break down? Can we recycle polystyrene?