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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.4 - From models to materials

2.4.1 The Bonding Continuum 2.4.2 Using the Bonding Triangle 2.4.3 Alloys 2.4.4 Polymer and Plastic Properties 2.4.5 Addition Polymerization 2.4.6 Condensation Polymerization (AHL)

Addition Polymerization

Specification Reference S2.4.5

Quick Notes:

  • Addition polymers form when alkene monomers undergo polymerization by breaking their double bonds and joining together.
  • The C=C double bond in each monomer opens up and links to neighbouring monomers, forming long chains.
  • The repeating unit is the smallest segment that repeats throughout the polymer.
  • You must be able to:
    • Deduce the repeating unit from a given monomer
    • Deduce the monomer from a given polymer structure
  • Only alkenes and simple derivatives are considered here.

Full Notes:

Addition polymers are (very) large molecules made up of repeating units, bonded together over and over again. Repeating units are formed from small molecules called monomers.

Addition polymers are formed by joining many alkene monomers in an addition reaction.

Monomers must contain a C=C double bond.

Example Poly(ethene) formation

IB Chemistry schematic showing ethene monomers with C=C bonds polymerizing into a long-chain poly(ethene) via opening of the double bond.

Ethene (CH2=CH2) → Poly(ethene)

Deducing the Repeat Unit from a Monomer

An addition polymer’s repeating unit is based on the monomer structure.

Steps to draw a repeating unit from a monomer: example of PVC (polyvinylchloride)

IB Chemistry worked steps showing how the vinyl chloride monomer is redrawn, the C=C broken, and the repeat unit of poly(chloroethene) formed with extension bonds.
  1. Redraw the monomer with the C=C double bond in the middle of the structure.
  2. Break the C=C double bond.
  3. Extend single bonds from the two carbons to show the continuation of the polymer chain.

Identifying the Monomer from a Polymer

To find the monomer from a polymer chain:

IB Chemistry example illustrating how to identify a repeating unit in a polymer chain and then restore the C=C double bond to obtain the monomer.
  1. Identify the repeating unit.
  2. Restore the C=C double bond.

Properties of Addition Polymers

Addition polymers are chemically inert: Strong C–C and C–H bonds make addition polymers very unreactive.

They are also non-biodegradable: These materials are not broken down naturally, causing long-term environmental issues.

Explanation: The strength and stability of the carbon chain makes these materials resistant to biological and chemical degradation.

Common Examples of Addition Polymers

Monomer Polymer Name Repeating Unit Structure Uses
Ethene (CH₂=CH₂) Polyethene (PE) –CH₂–CH₂– Bags, bottles
Propene (CH₂=CHCH₃) Polypropene (PP) –CH₂–CH(CH₃)– Crates, ropes
Chloroethene (CH₂=CHCl) Polyvinyl chloride (PVC) –CH₂–CHCl– Pipes, insulation
Tetrafluoroethene (CF₂=CF₂) Polytetrafluoroethene (PTFE) –CF₂–CF₂– Non-stick coatings (Teflon)
Phenylethene (CH₂=CHC₆H₅) Polystyrene –CH₂–CH(C₆H₅)– Packaging, containers

Linked Course Questions

Structure 3.2 – Linked Course Question

What functional groups in molecules can enable them to act as monomers for addition reactions?

Molecules that act as monomers in addition reactions must contain carbon–carbon double bonds (C=C) — also known as alkene functional groups. These double bonds are reactive sites where the π bond can break, allowing the monomers to join together and form long polymer chains without eliminating any atoms.


Reactivity 2.1 – Linked Course Question

Why is the atom economy 100% for an addition polymerization reaction?

In addition polymerisation, the entire monomer molecule is used to form the polymer — no atoms are lost or wasted in the process. Since no by-products are formed, all the atoms from the reactants end up in the final product, giving the reaction an atom economy of 100%.

Summary