Starter – what links these?

Learning objectives Outline the use of alkenes in the manufacture of margarine by catalytic hydrogenation of unsaturated vegetable oils. Outline the use of alkenes in the formation of a range of polymers using unsaturated monomer units. Describe the addition polymerisation of alkenes. Deduce the repeat unit of an addition polymer obtained from a given monomer. Identify the monomer that would produce a given section of an addition polymer.

Super ethene Unsaturated compounds are important starting materials for many common industrial processes e.g. 1,2-dichloroethane – a degreaser and paint remover Ethane-1,2-diol – antifreeze or for making polyester Ethanoic acid – used as vinegar and in organic synthesis

Hydrogenation Margarine is a butter substitute Why do we use margarine? Write yourself some brief notes on how hydrogenation occurs and what the products are.

Polymers What are polymers made of? How do they join together? What is this process called? Can you make a polymer?

Polymers and industry Huge industry Two key processes: Radical polymerisation Temperatures of 200˚C and very high pressures Leads to branching of the polymer chain and production of polymer mixtures Typical products are poly(phenylethene), poly(styrene) and branched poly(ethene)

Polymers and industry Huge industry Two key processes: The Ziegler-Natta process Uses specialist catalysts such as TiCl 3 and Al(C 2 H 5 ) 2 Cl at 60˚C Karl Ziegler discovered the titanium based catalyst and it was improved by Giulio Natta to increase control of the polymer formed The alkene is passed over the catalyst, the conversion is low and so the catalyst is passed over the catalyst repeatedly Most common method for producing unbranched catalysts

Addition polymerisation Different alkene monomers can join together to form polymers with different properties Polymers are formed from thousands of monomer units so it isn’t possible to draw the full structural formula, instead to represent polymers, we use repeating units

General equation addition polymerisation A repeat unit is a specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets and, outside of which is the symbol n.

Common polymers What’s the link between the monomer unit and the polymer? Monomers are unsaturated with a C=C double bond Polymers are saturated with single bonds only n monomer molecules  one polymer molecule with n repeat units

Teflon Read page 137 on the discovery of Teflon – make some notes

Identify the monomer This is the molecule Orlon. It is used as a synthetic fibre. It is resistant to sunlight and atmospheric gases so it is used as tent material and sunshades. The repeating unit has been shaded in and the monomer drawn – it just needs the double bond adding.

Examiner tip Make sure you can draw the polymer from the monomer All you need to do is replace the double bond with a single bond, draw side links and put brackets around the outside!

Plenary Complete questions on page 135 and 137 Question 15 on page 143

Homework Exam questions on the wiki