-Fractions from crude oil can be broken down by thermal decomposition in a catalytic cracker,
-The fraction is vapourised and passed over a hot catalyst which causes the molecules to split apart and make smaller molecules,
-One of these molecules will be an alkene or an unsaturated hydrocarbon!
-An alkene's general formula is CnHzn,
-Alkenes are more reactive because of the carbon to carbon double bond, (C=C)!
Making polymers from alkenes!
-Polymers are larger versions of monomers (which join together to make the polymers,)
-Lots of alkene molecules can join together to create polymers by additional polymerisation because they are alkenes, e.g. ethene into poly(ethene) or polythene, This reaction is called additional polymerisation, because the molecules simply add together under pressure and the polymer is produced,
-We can react other alkenes together in a similar way to form polymers such as poly(propene). For example, plastic bags, bottles, containers and toys are made from alkenes,
In additional polymerisation (with alkenes) there is only one product because the reactants add together!
Double bonds in the monomer become single bonds in the polymer!
The properties of plastics!
-Polymers have very long molecules that form a tangled mass, rather like spaghetti. This means that they are strong whilst being flexible,
-Using different monomers (e.g Ethene, methene) to create a polymer gives it different properties,
-Thermosoftening polymers have weak intermolecular forces between their molecules, therefore, when heated they soften and when they cool down, the harden again, this means that they can be heated to mould them into a shape more than once!
-When thermosetting polymers are heated for the first time, chemical bonds form between the polymer molecules, they link together in a giant network and they can NOT be remoulded again... but they set hard!
-Polymers have very long molecules with strong bonds holding the atoms together within the molecules,
Chemical bonds= stronger, make new compounds. Intermolecular forces= weaker, non permanent bonds.