Polymers Revision Notes

Monomers are small, simple molecules that can join together chemically to form larger molecules. Each monomer acts as a building block. For example, ethene (C2H4) is a monomer used to make poly(ethene). Monomers typically have reactive sites, such as double bonds, that allow them to link with other monomers.

Monomers are usually small organic molecules with low molecular mass. Their ability to bond repeatedly is essential for forming polymers.

• Monomers are small molecules that can join together.
• They have reactive sites like double bonds.
• Example: Ethene is a monomer for poly(ethene).

Polymers are very large molecules made by joining many monomers in a repeating pattern. The word 'polymer' means 'many parts'. These extensive molecules can be linear chains, branched chains, or cross-linked networks depending on the monomers and polymerisation process.

Because polymers consist of many repeated units, their molecular mass is much greater than that of monomers. This large size gives polymers unique physical properties such as strength, flexibility, and melting points different from their monomers.

• Polymers are large molecules made of many monomers.
• They have repeating units linked chemically.
• Their size leads to unique physical properties.

Polymerisation is the chemical process where monomers link together to form polymers. This involves breaking certain bonds in the monomers (such as double bonds) and forming new bonds between monomers.

For example, in addition polymerisation, the double bonds in alkene monomers open up and join end-to-end, creating a long chain polymer. Each monomer adds to the chain, repeating the same unit many times.

The process can be represented as: n (monomer) → (polymer)n, where n is the number of monomers joined.

• Polymerisation links monomers into polymers.
• It involves breaking and forming chemical bonds.
• Addition polymerisation opens double bonds to form chains.

A common example is poly(ethene), formed from ethene monomers. Ethene molecules (C2H4) have a double bond between carbon atoms. During polymerisation, this double bond breaks, and monomers link to form a long chain:

Monomer: CH2=CH2 (ethene) Polymer repeat unit: –CH2–CH2–

Other polymers include poly(propene) from propene monomers and poly(vinyl chloride) from vinyl chloride monomers. Each polymer’s properties depend on the monomer’s structure and how they link.

• Poly(ethene) is made from ethene monomers.
• Ethene’s double bond breaks to form polymer chains.
• Different monomers produce polymers with different properties.

The arrangement and type of monomers in a polymer affect its properties. For example, linear polymers may be flexible, while cross-linked polymers are rigid.

The length of the polymer chain (number of monomers) influences melting point and strength. Longer chains generally increase these properties.

Understanding that polymers are large molecules made from many monomers helps explain why plastics and other materials behave differently from small molecules.

• Polymer structure affects physical properties.
• Chain length influences melting point and strength.
• Polymers differ significantly from their monomers in behaviour.

Ethene is a simple hydrocarbon with the formula C2H4. It belongs to the alkene family, characterised by the presence of a carbon-carbon double bond (C=C). This double bond is reactive and allows ethene molecules to link together during polymerisation.

The double bond in ethene is key to its ability to form polymers because it can open up to form single bonds with other ethene molecules, creating long chains.

• Ethene formula: C2H4
• Contains a carbon-carbon double bond (alkene)
• Double bond is reactive and essential for polymerisation

Addition polymerisation is a chemical reaction where many small alkene molecules (monomers) join together without the loss of any atoms, forming a large molecule called a polymer.

In this process, the double bonds in the monomers break, and the molecules link end-to-end, creating a long chain. This contrasts with condensation polymerisation, where small molecules like water are lost.

For poly(ethene), the ethene monomers open their double bonds and connect to form a polymer chain with the repeating unit –CH2–CH2–.

• Monomers are alkenes with double bonds
• Double bonds break to form single bonds linking monomers
• No atoms are lost during addition polymerisation
• Polymer chains consist of repeating units derived from monomers

During the polymerisation of ethene, the double bonds between carbon atoms break, allowing each carbon to form new single bonds with neighbouring monomers.

This process results in a long chain polymer called poly(ethene), which has the general formula (C2H4)n, where n represents the number of repeating units.

The polymerisation is typically initiated by heat, pressure, or catalysts that help break the double bonds and start the chain reaction.

• Double bonds in ethene break to form single bonds
• Ethene molecules link to form long chains (polymer)
• Poly(ethene) formula: (C2H4)n
• Conditions: heat, pressure, or catalysts initiate polymerisation

Poly(ethene) is a versatile plastic used widely in packaging, containers, and plastic bags due to its flexibility, durability, and resistance to chemicals.

Its properties depend on the polymer chain length and branching, which are controlled during polymerisation.

Understanding the formation of poly(ethene) helps explain why it is lightweight and mouldable, making it suitable for many everyday products.

• Common plastic material
• Flexible, durable, chemically resistant
• Used in packaging, bags, containers
• Properties depend on polymer structure