Condensation Polymers

This is part of the HSC Chemistry course under the topic Polymers. There are two types of polymers: addition and condensation polymers.

HSC Chemistry Syllabus

• model and compare the structure, properties and uses of condensation polymers of ethylene and related monomers, for example: – polyesters – polyamides (nylon) (ACSCH136)

Condensation Polymers: Polyesters and Polyamides (Nylon)

This video introduces the concept of condensation polymers. This video discusses the structure, properties and uses of polyesters and polyamides (nylon).

 

Condensation Polymers

In contrast to addition polymers:

• Condensation polymers are formed through condensation reactions through which a small molecule e.g. H₂O is also formed.

• Condensation polymerisation usually involves more than one monomer type.

• Condensation polymers are usually thermoplastics, meaning they can be melted for reshaping and recycling.

 

Two types of condensation reactions used to produce polymers: Esterification: reaction between alcohol and carboxylic acid to form an ester. Amidation: reaction between amine and carboxylic acid to form an amide. (extension)   In general, the number of water molecules produced (eliminated) from a polymerisation reaction is always one less than the number of monomers in the final polymer. For example, if a polymer has 10 monomers, then 9 H2O molecules would have been produced.

Figure: Condensation reaction between methanol and butanoic acid.

Polyesters

• Structure: monomers are joined together via esterification i.e. reaction between an alcohol and a carboxylic acid functional group.
• A water molecule is eliminated every time two monomers are joined.
• A polyester can be produced by reacting dicarboxylic acids and dialcohols.

• A polyester can be produced by using a monomer that contains both carboxylic acid and alcohol functional groups.

 

• Polyethylene terephthalate (PET) is the specific polyester used in textiles. It is produced using two monomers: a dicarboxylic acid and a dialcohol.

 

Properties of Polyesters	Uses
High tensile strength Can be drawn into fibres  Abrasion-resistant Heat-resistant Crease/wrinkle-resistant UV-resistant Thermoplastic Hydrophobic; greater moisture resistance	Clothing Carpets and other textiles Fruit containers Single-use plastic bottles Toasters  Shower headers

 

• Naturally found polyesters are biodegradable but most synthetic polyesters are not. However, polyesters can be recycled and re-processed because their inter-chain linkages are easy to overcome without distorting the polymer backbone.

Polyamides

• Structure: monomers are joined together via amidation, that is a reaction between a carboxylic acid and an amine functional group. A water molecule is eliminated every time a dicarboxylic and a diamine molecule join together.

• In addition to dispersion and dipole-dipole forces, hydrogen bonds are also formed between polyamide chains. This is because polyamide molecules contain hydrogen atoms bound to nitrogen atoms, which allows them to donate hydrogen bonds to oxygen atoms in nearby polyamide chains.

 

Diagram shows hydrogen bonds formed between adjacent polyamide chains

 

• Nylon 6 is a common polyamide produced from 6-aminohexanoic acid (monomer)

  

• Nylon 66 is another common polyamide produced from two monomers: hexandioic acid (adipic acid) and hexan-1,6-diamine.

 

Properties of Nylon	Uses of Nylon
High tensile strength  Can be drawn into fibres Abrasion-resistant Elastic  Thermoplastic Absorbs moisture	Clothing: Lingerie, tights, raincoats and swimwear Carpets, drapes and bedding Seat belts Ropes, nets, sleeping bags, tents

Polyesters vs Polyamides

 

Property	Polyamide (nylon)	Polyester (PET)
Structure	Both are condensation polymers. Both uses carboxylic acid functional group in monomer(s).  Production of polyamides and polyesters produce water as byproducts  Unlike polyesters, hydrogen bonds are formed between polyamide chains.
Properties	Similarities High tensile strength Both can be drawn into fibres: good for textile use Abrasion-resistant Thermoplastic: can be re-shaped and recycled via melting   Differences Polyesters are more heat resistant Polyamides have greater tensile strength than polyesters  Nylon can absorb moisture whereas polyesters are more hydrophobic so they are less able to do so.
Uses	Similarities Both are useful in textiles e.g. clothing and carpets due to their high tensile strength, ability to be drawn into fibres and recyclable nature (thermoplastic)   Differences Polyesters are more heat resistant, so they are found in appliances that are exposed to high temperatures such as toasters. Polyesters are found in plastic containers for fruits and plastic bottles. Nylon is also found in fishing nets and ropes, applications that require greater tensile strength.

Addition Polymers vs Condensation Polymers

Similarities

• Both types of polymers are produced from organic monomers which consist of carbon atoms as the backbone.
• Relatively low cost compared to alternatives
• Most are thermoplastics
• Strong and light weight
• Non-biodegradable (environmental implications)

 

Differences

• Water is also produced during condensation polymerization.
• Different properties that determine polymers’ uses.
• Condensation polymers can be drawn into fibres (good for textile).
• Condensation polymers are more easily recycled.

 

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