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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)

Polymers and Plastic Properties

Specification Reference S2.4.4

Quick Notes:

  • Polymers are large molecules (macromolecules) made from repeating units called monomers.
  • Addition polymers form from alkenes (e.g. polyethene), while condensation polymers release small molecules like water (e.g. proteins, nylon).
  • Common properties of plastics:
    • Lightweight
    • Moldable
    • Insulating (thermal and electrical)
    • Chemically resistant
  • Example natural polymers: proteins, DNA, starch, cellulose.
  • Example synthetic polymers: polyethene, PVC, nylon, Teflon.

Full Notes:

What Are Polymers?

Polymers are long-chain molecules made from small repeating units called monomers.

IB Chemistry schematic of a polymer showing repeating monomer units linked into a long chain macromolecule.

They form through two main types of reactions:

IB Chemistry diagram of condensation polymerization showing monomers linking while eliminating small molecules such as water.

Example Polyethene from ethene

IB Chemistry example showing ethene (C2H4) monomer forming polyethene repeating units (–CH2–CH2–)n.

Structure and Properties of Plastics

Plastics are synthetic polymers with useful and adaptable properties:

Property Reason
Lightweight Long chains of mostly C and H atoms
Moldable (malleable) Weak forces between chains (in many plastics)
Electrical insulators Electrons are localised, not free-moving
Chemically resistant Strong C–C and C–H bonds resist degradation

Natural vs Synthetic Polymers

Type Examples Monomers Polymer Type
Natural Proteins, DNA, starch, cellulose Amino acids, nucleotides, glucose Condensation
Synthetic Polyethene, PVC, nylon, polystyrene Ethene, vinyl chloride, etc. Addition or condensation

Natural polymers:

Synthetic polymers:

Linked Course Questions

Structure 3.2 – Linked Course Question

What are the structural features of some plastics that make them biodegradable?

Biodegradable plastics contain specific bonds or functional groups in their polymer chains – such as esters or amide links – that can be broken down by hydrolysis reactions, often with the help of enzymes or microorganisms. This allows the plastic to decompose naturally over time.

Summary