Polyamides & Poly(ethenol) (Edexcel International A Level Chemistry)

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Polyamides - Physical Properties

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 addition 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:

preparation-of-polyethenol-stage-1

Stage 1: polymerisation of ethenyl ethanoate

preparation-of-polyethenol-stage-2

Stage 2: poly(ethenyl 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

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.