5.5.6 Polyamides & Poly(ethenol)

Examples of polyamides

Kevlar

• Kevlar is an example of a polymer formed through condensation polymerisation
• The polymer chains are neatly arranged with many hydrogen bonds between them
• This results in a strong and flexible polymer material with fire resistance properties
• These properties also lend Kevlar to a vital application in bullet-proof vests
• The monomers used to make Kevlar are:
  • 1,4-diaminobenzene
  • Benzene-1,4-dicarboxylic acid

• As seen with Nylon, a dioyl dichloride can be used instead of the acid as well (benzene-1,4-dioyl chloride)

Kevlar is made using a diamine and dicarboxylic acid monomers

Nylon 6-6

• Nylon 6,6 is a synthetic polyamide
• Its monomers are 1,6-diaminohexane and hexane-1,6-dioic acid
  • The ‘6,6’ part of its name arises from the 6 carbon atoms in each of Nylon 6,6 monomers

Nylon 6,6 is a synthetic polyamide made using diamine and dicarboxylic acid monomers

Properties of polyamides

• Most polyamides (nylons) tend to be semi-crystalline
• They are generally very tough with good thermal and chemical resistance
• Polyamides tend to absorb moisture from their surroundings
  • This absorption increases until equilibrium is reached
• The impact resistance and flexibility of polyamides increases with water content whilst strength and stiffness decrease
• The strong bonds in polyamides make the polyamide chains strong allowing them to be made into strong fibres for clothing
  
  • E.g. Kevlar shown above
• Polyamide film (cling film) is used in food packaging due to its toughness and the fact it prevents gas molecules from passing through
• Polyamide film is also used for 'Boil in the bag' foods due to its high-temperature resistance

Poly(ethenol)

• Poly(ethenol) is another edition polymer sometimes called poly(vinyl alcohol)
• It is not made in the usual way by directly polymerising a monomer
• Instead, it is made in two stages:

Stage 1: polymerisation of ethyl ethanoate

Stage 2: poly(ethyl ethanoate) reacts with methanol forming poly(ethenol) and methyl ethanoate (this process is known as ester exchange)

• The amount of ester exchange is controlled by varying the temperature

Solubility

• Poly(ethenol) contains many OH groups
• These groups can form hydrogen bonds with water making poly(ethenol) soluble in water
• The degree of solubility depends on how many ester groups have been replaced with OH groups
  • Solubility ranges from insoluble, to soluble in warm/hot water, to soluble in cold water

Uses

• Poly(ethenol) is used to make disposable laundry bags for use in hospitals
  • These laundry bags are soluble in water
• Dirty bedding and clothing, which may be covered in microorganisms from patients, are put in the laundry bags
• The bag is then placed in the washing machine without hospital workers having to touch the dirty fabrics
• During washing the bag dissolves and the fabrics are washed clean

• Poly(ethenol) is also used to make liquid-detergent capsules that contain measured quantities of detergent for use in washing machine and dishwashers
  • The capsule dissolves during use