POLYMERISATION OF ALKENES Process during polymerisation, an alkene undergoes an addition reaction...

POLYMERISATION OF ALKENES

Process • during polymerisation, an alkene undergoes an addition reaction with itself

• all the atoms in the original alkenes are used to form the polymer

• long hydrocarbon chains are formed

ADDITION POLYMERISATION

the equation shows the original monomer and the repeating unit in the polymer

ethene poly(ethene)

MONOMER POLYMER

n represents a large number

Industrial Polymerisation

• Radical Polymerisation– 200°C and high pressure– Leads to branching of the polymer chain and

polymer mixtures– Poly(phenylethene), poly(styrene) and branched

Poly(ethene)

Industrial Polymerisation

• Ziegler-Natta process– Specialist catalysts: TiCl3 and Al(C2H5)2Cl at 60°C– Alkene is passed over the catalyst– Conversion is low and any unreacted alkene is

recycled and passed over the catalyst repeatidly– Most common method for the manufacture of

non-branched poly(ethene)

Questions

• State one key advantage of the Ziegler-Natta process over that of radical polymerisation– Greater control over the product formed leads to

more straight chain polymers• Draw a section of a polymer made from three

molecules of ethene

Addition Polymerisation

• Drawing a polymer from a monomer– Draw the four groups at right angles– Replace the double bond with a single bond– Draw side links

POLYMERISATION OF ALKENES

ETHENE

EXAMPLES OF ADDITION POLYMERISATION

PROPENE

TETRAFLUOROETHENE

CHLOROETHENE

POLY(ETHENE)

POLY(PROPENE)

POLY(CHLOROETHENE)

POLYVINYLCHLORIDE PVC

POLY(TETRAFLUOROETHENE)

PTFE “Teflon”

Poly(propene)polypropylene

Poly(phenylethene) polystyrene

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

POLYMERISATION OF ALKENES

SPOTTING THE MONOMER

Questions

• Draw a section of the polymer that can be made from 1-chloropropene, showing two repeat units.

• The polymer on the right is poly(vinyl alcohol), PVA.– Identify the repeat unit– Draw the structure of the

monomer that forms PVA

O

“Plastic” wallets and carrier bags are often made from PVC PVC as a leather substitute

Some uses of PTFE

Non-stick coating for pans

Low friction coating for surgical sutures

Insulating tapes

Items made from polymers have recycling symbols moulded into them. High-density poly(ethene) HDPE and poly(propene) PP are particularly suitabel for recycling.

Task• Working in pairs research how different types

of polymers are recycled.– Group 1 - PETE– Group 2 - HDPE– Group 3 - V– Group 4 – LDPE– Group 5 - PP– Group 6 - PS– Group 7 – Other

• Report back to the class

POLYMERISATION OF ALKENES

PROBLEMS WITH POLYMERS

• Although polymers derived from alkenes are invaluable to modern society, their disposal creates widespread problems.

– they are unreactive to most chemicals and bacteria (non-biodegradable)

– if they are just discarded they add to the landfill problem

• recycling high cost of collection and re-processing

• burn waste saves on landfill sites and produces energy

• toxic fumes (HCl) can be removed from burning chlorinated polymers

• feedstock use the waste for the production of useful organic compounds• new technology can convert waste into hydrocarbons

• hydrocarbons can then be turned back into polymers.

Questions

• Give two uses of polystyrene– Foam packaging, insulation, model making, food

retail trade• What do you understand by the term non-

biodegradable?– A non-biodegradable material does not break

down naturally or safely in the environment by biological means.

Questions

• Why is it important to replace polystyrene as a packaging material?– The non-biodegradability of polystyrene means

that waste polystyrene ends up in landfill sites, which are rapidly running out of space.

• When PVC is burned poisonous gases may be released. Suggest two such gasses. – HCl and CO

A summary of how poly(propene) can be recycled.

Lactic acid is now used to make compostable polymers

© Pearson Education Ltd 2008This document may have been altered from the original

Summary

• Addition polymer – very long molecular chain, formed by repeated addition reactions of many unsaturated alkene monomers

• Repeat unit – specific arrangement of atoms that occurs in the structure over and over again

• Describe uses of certain polymers• Outline how waste polymers are recycled,

separated and processed• Revise section 2.1.20 other uses of polymer waste