Addition Polymers
Quick Notes
- Polymers are made by reacting small molecules called monomers together.
- A repeating unit is the smallest unit of a polymer that is bonded in a repeating pattern.
- Addition polymers are formed from alkenes and substituted alkenes, which act as monomers.
- IUPAC rules apply to naming polymers, using “poly(monomer name)”.
- Addition polymers are unreactive because they have only strong C–C and C–H bonds.
- Poly(chloroethene) (PVC) properties can be modified using plasticisers.
- Intermolecular forces in polyalkenes determine polymer properties.
Full Notes
What Are Addition Polymers?
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 reacting many alkene monomers together in addition polymerisation.
Monomers used must contain a C=C double bond.
Example Poly(ethene) formation
Drawing Polymer Structures
An addition polymer’s repeating unit is based on the monomer structure.
Steps to draw a repeating unit from a monomer:
- Step 1: Redraw the monomer with the C=C double bond in the middle of the structure.
- Step 2: Break the C=C double bond.
- Step 3: Extend single bonds from the two carbons to show the continuation of the polymer chain.
To find the monomer from a polymer chain:
- Step 1:Identify the repeating unit.
- Step 2: Restore the C=C double bond.
Naming Addition Polymers
IUPAC Naming Rule:
The name of the polymer is poly(monomer name).
Examples:
- Ethene → Poly(ethene)
- Propene → Poly(propene)
- Chloroethene → Poly(chloroethene) (PVC)
Why Are Addition Polymers Unreactive?
Polymers consist of strong C–C and C–H bonds, making them chemically inert.
They do not break down easily, leading to environmental concerns as they are non-biodegradable.
Intermolecular Forces in Polyalkenes
Polyalkenes have only Van der Waals forces (London Dispersion Forces) because they are non-polar.
Longer polymer chains = stronger intermolecular forces = higher melting points.
| Polymer | Intermolecular Forces | Properties |
|---|---|---|
| Poly(ethene) | Weak van der Waals | Flexible, low melting point |
| Poly(propene) | Stronger van der Waals | More rigid |
| PVC (Poly(chloroethene)) | Dipole-dipole interactions | Rigid, strong |
Plasticisers and PVC
Poly(vinylchloride), PVC, is naturally rigid due to strong dipole–dipole forces.
Plasticisers weaken these forces, making PVC flexible.
Uses:
- Rigid PVC → Pipes, window frames.
- Plasticised PVC → Electrical cable insulation, flooring.
Summary
- Addition polymers form when alkene monomers (containing C=C) link together; the smallest repeating unit comes from the monomer.
- To draw a repeating unit: center the C=C, break it, and extend bonds to show continuation; to recover the monomer, identify the unit and restore C=C.
- Name polymers using poly(monomer name), e.g., poly(ethene), poly(propene), poly(chloroethene).
- Polyalkenes are generally unreactive (only strong C–C/C–H bonds) and are non-biodegradable.
- Intermolecular forces (and chain length/branching) control physical properties; plasticisers can soften PVC.