POLYMERISATION OF ALKENES Process during polymerisation, an alkene undergoes an addition reaction with itself all the atoms in the original alkenes are

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


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


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


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

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POLYMERISATION OF ALKENES Process during polymerisation, an alkene undergoes an addition reaction with itself all the atoms in the original alkenes are