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HSC Chemistry

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  1. Module 5: Equilibrium and Acid Reactions
    5.1 Static and Dynamic Equilibrium
    5 Topics
  2. 5.2 Factors that Affect Equilibrium
    2 Topics
  3. 5.3 Calculating the Equilibrium Constant
    2 Topics
  4. 5.4 Solution Equilibria
  5. Module 6: Acid/Base Reactions
    6.1 Properties of Acids and Bases
    7 Topics
  6. 6.2 Using Brønsted–Lowry Theory
    2 Topics
  7. 6.3 Quantitative Analysis
    1 Topic
  8. Module 7: Organic Chemistry
    7.1 Nomenclature
    2 Topics
  9. 7.2 Hydrocarbons
    2 Topics
  10. 7.3 Products of Reactions Involving Hydrocarbons
  11. 7.4 Alcohols
    1 Topic
  12. 7.5 Reactions of Organic Acids and Bases
  13. 7.6 Polymers
    2 Topics
  14. Module 8: Applying Chemical Ideas
    8.1 Analysis of Inorganic Substances
    3 Topics
  15. 8.2 Analysis of Organic Substances
  16. 8.3 Chemical Synthesis and Design
  17. Working Scientifically
    Working Scientifically Overview
    1 Topic

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Lesson 13, Topic 2
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Addition Polymers

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Addition polymers are synthetically produced by adding together unsaturated monomers without the elimination of any atoms.

Addition Polymerisation

  1. Initiator molecule breaks C=C in alkenes (addition reaction). The new substance is a monomer radical, i.e. has one free electron.
  2. The monomer radical breaks the C=C in another monomer and bonds to it. This, in turn, creates leaves an un-bonded electron across the broken double-bond.
  3. The polymer propagates in this repeating fashion until an inhibitor molecule bonds to the end of a chain, de-radicalising the polymer and preventing it from further elongating.

Structure of Polymers

MonomersPolymer Structure

Ethylene

Polyethylene (PE)

Vinyl chloride (chloroethene)

Polyvinyl chloride (PVC)

Styrene (ethenylbenzene)

Polystyrene (PS)

Tetrafluoroethylene (tetrafluoroethene)

Polytetrafluroethylene (PTFE)

Uses of Additional Polymers

PolymerPropertiesUses
Polyethylene

Low Density – Branched chains; cannot pack closely together.
Thermoplastic
Flexible
Low melting point (~80 °C)
Lightweight
Waterproof
Plastic bags
Squeezy sauce bottles
Vacuum cleaner tube
Water bottles
Prosthetics
Polyethylene

High Density – Unbranched, linear chains; packs tightly.
Thermoplastic
Harder/more rigide than LDPE; less flexible
Freezer bags
Cutting boards
Garbage bins and buckets
Polyvinyl chloride

Standard
Thermoplastic
Very hard
Rigid
Brittle
Piping, sliding, gutters
Credit cards
Waste water pipes
Polyvinyl chloride

Flexible
Flexible
Flame retardant
Resistant to chemical corrosion
Raincoats
Shower curtains
Electrical wire insulation
PolystyreneStiff
Brittle
Transparent
Can be expanded to form styrofoam (low density insulator)
CD and packaging
Plastic wine glasses
Floatation devices
Shock-absorbent packaging
Foam coffee cups
PolytetrafluoroethyleneHard
Rigid
High melting point (327 °C)
High chemical resistance
Low coefficient of friction
Non-stick coating for cooking pans
Anti-corrision container, pipe and medical coatings
Sliding applications, e.g. bearings.

Explanation of Properties

PolymerProperties
PolyethyleneLDPE has a high degree of branching, which means is has a low degree of crystallinity and relatively weak dispersion forces. It therefore has a low melting point, is low density and flexible.

HDPE has a low degree of branching, so a high degree of crystallinity and stronger dispersion forces. This gives it a high melting point, high density and rigidity.
Polyvinyl chlorideThe bulky chlorine side group increases dispersion forces and physical flexibility, resulting in hardness and rigidity.

Plasticisers may be added along with PVC chains to increase flexibility by weakening the dispersion forces.
PolystyreneBulky benzene substituent increases physical rigidity and strength due to increased dispersion forces.
PolytetrafluoroethyleneFluorine side groups repel, locking the polymer into a linear, elongated helix. Chains align closely to form a crystalline structure, making PTFE hard and rigid due to dispersion forces.