week 8 © pearson education ltd 2009 this document may have been altered from the original describe...

Week 8

© Pearson Education Ltd 2009This document may have been altered from the original

• Describe condensation polymerisation forming polyesters and polyamides, such as Terylene and poly(lactic acid).

• State the use of polyamides as fibres in clothing.

Polymers• Long chain molecule made up of many small

monomer units joined together.• Addition polymers:• Monomer units alkenes• e.g. ethene → poly(ethene)• One type of monomer only.• 100% atom economy.• Designed with specific properties.• Can identify monomer from repeat unit which has

no obvious functional groups in skeleton of chain.• Repeat unit – specific arrangement of atoms that

occurs in the structure over and over again. Repeat units are included in brackets, outside which is a letter n.

Week 8


Addition polymerisation of an alkene

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Propene monomers forming poly(propene)

Polymers

• Condensation polymers:• Made by reactions where small molecules e.g.

water or HCl are eliminated.• Chemical reactions between monomer units with

different (reactive) functional groups.• Either 1 monomer with 2 different functional

groups ( i.e. bifunctional monomers) or 2 different monomers, each with 2 identical functional groups but the functional groups are different on each monomer.

• Condensation is a reaction in which 2 small molecules react together to form a larger molecule, with the elimination of a small molecule such as water.

Esters

• Made by reaction of a carboxylic acid and an alcohol.

• E.g. propanoic acid + methanol → methyl propanoate + water

How must this be modified to make a POLYester?

Polyesters

• Monomers are joined by ester linkages with the loss of water.

• Monomers must be single bifunctional molecules or 2 monomers, one a carboxylic acid and the other an alcohol.

• The repeat units reflect the monomers used to make them.

• If bifunctional single monomer then there is ONE REPEAT unit with a bridging oxygen at one end and a carbonyl group at the other.

• If 2 monomers are used the repeat unit has 2 adjacent bridging oxygen atoms and 2 adjacent carbonyl groups.

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Formation of polyesters from two types of monomer (left) and from one type of monomer (right)

Condensation Polymerisation

• Polyesters must have monomers containing at least one carboxylic acid group and one alcohol group.

• Terylene has 2 monomer units,1 a dicarboxylic acid (terepthalic acid – benzene-1,4-dicarboxylic acid).

• And a diol, ethan-1,2-diol.• Used to manufacture fibres. E.g. carpets, sports clothing,

shirts, bedding. Fibres are elastic and good for clothing because multiple dipole-dipole attractions can break and reform making it good for clothing.

• Polylactic acid has one single monomer- 2-hydroxypropanoic acid.

• It is both photodegradable and biodegradable.• It is used for waste sacks, food and drinks packaging. In

each case an ester linkage is formed between the OH and the carboxyl groups and water is eliminated.

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Formation of Terylene, a polyester

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Condensation polymerisation of lactic acid

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• Describe condensation polymerisation to form the polyamides nylon-6,6 and Kevlar.

• State the use of polyamides as fibres in clothing.

Polyamides

Polyamides contain this functional group.

Found in protein (polypeptide) chains – which are natural polyamides.

As before either 1 bifunctional monomer (e.g. amino acids) or 2 monomers, each with the same functional group at both ends but the functional groups are different on each monomer.

Structure of the Skeleton

• As before:• Monomers must have at least one amino

group and one carboylic acid group which react together with the loss of a water molecule.

• If bifunctional single monomer then there is ONE REPEAT unit with an NH at one end and a carbonyl group at the other.

• If 2 monomers are used the repeat unit has 2 adjacent N-H groups and 2 adjacent carbonyl groups.

Week 8


Formation of polyamides from two types of monomer (left) and from one type of monomer (right)

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Formation of the polyamide nylon-6,6

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Formation of the polyamide Kevlar

Uses of Polyamides

• Fibres in clothing.• Nylon:• Strong, stretchy fibres used in underwear,

upholstery, carpets, tents, ropes etc.• Nylon is ideal for making fibres because• i) the amide links in the backbone are themselves

strong.• ii) the chains are aligned along the length of the

fibre. Hydrogen bonds form between the chains and when the fibre is stretched and then released these bonds re-form to bring the nylon molecules back to their original position, making the nylon elastic. Good for tights!

Uses of Polyamides

• Kevlar:• High tensile strength. Used as lightweight

replacement for steel (5 times stronger). Body armour. Immense strength from H- bonding between amide groups and very flat planar structure means close packing and strong attractions between stacked rings.

Kevlar showing close packing

Week 8


• Compare condensation polymerisation with addition polymerisation.

• Suggest the type of polymerisation from a given monomer or pair of monomers, or a given section of a polymer molecule.

• Identify the monomer(s) required to form a given section of a polymer (and vice versa).

Addition or Condensation Polymers?

• Work through examples on p. 58 in text book – supplied in the short term.

POLYMERISATION OF ALKENESPOLYMERISATION OF ALKENES

SPOTTING THE MONOMER

Week 9


• Describe the acid and base hydrolysis of polyesters and polyamides.

• Outline the role of chemists in the development of degradable polymers.

• Explain that condensation polymers may be photodegradable and may be hydrolysed.

Break down of condensation polymers

• All readily hydrolysed.• All react with hot, aqueous acid or alkali.• Acid hydrolysis of polyester:• The parent monomer units are made.• Alkaline hydrolysis:• The sodium salt and the diol are made.• Acid hydrolysis of polyamide:• The dicarboxylic acid and the ammonium salt of

the amine.• Alkaline hydrolysis:• Sodium salt of dicarboxylic acid and diamine

formed.

Week 9


Acid and base hydrolysis of the polyester Terylene

Week 9


Acid and base hydrolysis of the polyamide nylon-6,6

Degradable Polymers

• Degradable polymer – breaks down into smaller fragments when exposed to light, heat or moisture.

• Biodegradable polymer – breaks down completely into carbon dioxide and water.

• E.g. Poly(lactic acid) derived from cornstarch

• Poly(glycolic acid) from sugar cane and unripe grapes.

• These are polyesters.

Biodegradable Polymers

• PLA- compost bags, food packaging, disposable table ware.

• PGA- surgery for stiches.• Cellulose and potato starch used to make

biopolymers- used in thermoformed trays for fresh veg and meat etc.

• Also in disposable crockery.• Carrier bags from tapioca starch.

Photodegradable polymers

• Become weak and brittle when exposed to sunlight.

• Made by blending the polymer with light sensitive additives which catalyse the breakdown of the polymer in uv light.

• OR can be made including C=O bonds which can absorb light energy and break.

• A waxy substance forms first and then eventually bacteria convert it to carbon dioxide and water only.

week 8 © pearson education ltd 2009 this document may have been altered from the original describe...

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