The Polymer Revolution

The Polymer Revolution

1. Addition Reactions of Alkenes

   • Adding hydrogen to C=C bonds produces alkanes.
     • e.g. Ethene will react with hydrogen gas to produce ethene but only with a nickel catalyst, 150 degrees and high pressure/platinum catalyst at room temp and pressure.
     • The C=C bond opens up and hydrogen atoms join on to give an alkane.
   • Bromine water can be used to test for C=C bonds.
     • When you shake an alkane with bromine water it decolourises - becomes colourless - and forms a dibromoalkane.
     • Adding bromine is the test for unsaturation. Saturated compounds don't react.
   • Electrophilic Addition
     • The bromine is an example of electrophilic addition.
       • During electrophilic addition reactions, the double bonds open up and atoms are added to the carbons.
       • They happen because the bond has got plenty of electrons and is easily attacked by electrophiles.
         • Electrophiles are electron-pair acceptors - they usually don't have enough electrons so they're are attracted to areas where there's a lot of them about.
         • The double bond is nucleophilic - it's attracted to places that don't have enough electrons.
     • Hydrogen Halides
       • Alkenes also undergo addition reactions with hydrogen bromide - to form bromoalkanes.
       • If the HBr adds to an unsymmetrical alkene, like propene, there are two possible products.
     • Reacting Alkenes with Water and an H2SO4 Catalyst Makes Alcohols
       • • H2C=CH2 + H2SO4 --> CH3CH2OSO2OH
         • Ethene + Sulphuric Acid --> Ethyl H Sulfate
   • Ethanol is manufactured by steam hydration.
     • It is hydrated by steam at 300 degrees and a pressure of 60atm. This reaction is reversible and the reaction yield is low but the unreacted ethene gas is recyclable.

2. Alcohols and Other Organic Compounds

   • Alcohols
     • The alcohol homologous series has the general formula CnH2n+1OH.
     • In a primary alcohol, the carbon with the -OH is attached to one other carbon.
     • In a secondary alcohol, the carbon with the -OH is attached to 2 other carbons.
     • In a tertiary alcohol, the carbon with the -OH is attached to three other carbons.
     • They can be dehydrated to form alkenes. C2H5OH --> CH2=CH3 + H2O
       • Ethanol vapour can be passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3.
       • It can also be heated by reflux with excess concentrated sulfuric acid at 170 degrees. The ethene produced is then collected over water.
         • In this method, the sulfuric acid acts as the dehydrating agent in the elimination reaction.
     • Alcohols can be Oxidised
       • Using an Oxidising Agent
         • Complete oxidation forms carbon dioxide and water. This is a combustion reaction.
       • By Burning Them
         • Primary alcohols are oxidised to aldehydes then carboxylic acid.
         • Secondary alcohols are oxidised to ketones only
       • Whether a primary alcohol is oxidised into a aldehyde or a carboxylic acid depends on the reaction conditions.
         • Gently heating ethanol with potassium dichromate(VI) solution and sulfuric acid in a test tube produces apple smelling ethanal (aldehyde). However it usually oxidises to form vinegar smelling ethanoic acid.
           • To just get an aldehyde it needs to be taken out of the oxidising solution as soon as it's formed.
         • To produce a carboxylic acid, the alcohol has to be vigorously oxidised. The alcohol is mixed with excess oxidising agent and heated under reflux.
   • Aldehydes and Ketones
     • Their general formula is CnH2nO
     • Aldehydes have their carbonyl group at the END of the carbon chain.
     • Ketones have their carbonyl group anywhere in the MIDDLE of the carbon chain.
     • They both contain a double-bonded oxygen.
   • Carboxylic Acids
     • They contain a -COOH functional group.

3. Hydrogen Bonding

   • Hydrogen bonding is the strongest intermolecular force.
     • It only occurs when hydrogen is covalently bonded to fluorine, nitrogen or oxygen because they are very electronegative so they draw the bonding electrons away from the hydrogen atom.
       • Water and ammonia both have hydrogen bonding.
   • Density of Water and Ice
     • There is the max no. of hydrogen bonds in ice which forms a lattice structure. As the ice melts some of the hydrogen bonds break and the lattice breaks down which allows molecules to fill the spaces.
   • Boiling Points
     • Hydrogen bonding is quite a strong intermolecular force, so it has a lot of effect on the properties of substances.
       • Substances that form hydrogen bonds have higher boiling points and melting points because they require extra energy to break the bonds.
         • This is the case with water and ammonia.
   • Polymers Can Dissolve
     • Polymers have incredibly long chains so ones with -OH groups can form hydrogen bonds with water molecules, allowing it to dissolve.
     • Polymer molecules can also bond to each other by hydrogen bonds.
       • If the polymer has loads of -OH groups, the hydrogen bonding will be very strong.
       • If the polymer has very few -OH groups, there won't be many hydrogen bonds formed with water molecules and the polymer will be insoluble.
       • If the polymer has not too many hydrogen bonds and not too few then it'll be soluble.

4. Polymers

   • Addition Polymers
     • The double bonds in alkenes can open up and join together to make long chains called polymers.
       • This is called addition polymerisation.
         • For example, poly(ethene) is made by the addition polymerisation of ethene.
     • Copolymers are made from more than one type of monomer, they join in a random order.
       • For example, ethene can be combined with propene to produce a polymer with different properties from either poly(ethene) or poly(propene).
   • Monomers
     • To find the monomer used to form an addition polymer, take the repeated unit and add a double bond.
     • Because of the loss of the double bond, poly(alkenes) are unreactive.
   • Cross-Linking
     • Thermoplastic Polymers
       • They don't have cross-linking between chains, it's only weak intermolecular forces that hold the chains together.
       • These forces are easy to overcome so it's super easy to melt the plastic. They can be melted and remoulded.
     • Thermosetting Polymers
       • e.g. Bakelite
       • They have covalent cross links which hold the chains together in a 3D giant covalent structure.
       • The polymer doesn't soften when it's heated, though, heated too much it can char. They are strong, hard and insoluble.
   • Properties and Uses
     • Poly(chloroethene) is durable and flexible so it can be used for water pipes, insulation and building material.
     • Poly(tetrafluorioethene) is chemically inert and has non-stick properties. This makes it ideal for coating frying pans.
     • Polystyrene is cheap and can be made into expanded polystyrene which is a good, light insulator.
     • Perspex is transparent and pretty strong so it can be used in place of glass for certain things.

5. E/Z Isomerism

   • Rotation
     • Single bond allow atoms to rotate freely.
     • Atoms can't rotate around C=C bonds and this is what causes E/Z isomerisation.
   • Stereoisomerism
     • Stereoisomers have the same structural formula but a different spacial arrangement.
     • This happens when the 2 double bonded carbon atoms each have different atoms or groups attached to them.
     • When the same groups are across the double bond then it's the E-isomer.
     • When the same groups are both above or both below the double bond then it's the Z-isomer.
   • Cis-Trans Isomers

6. Infrared Spectroscopy

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