IB MYP 4-5 Chemistry -Polymers- Study Notes - New Syllabus

Polymers (Addition and Condensation Polymers)

A polymer is a very large molecule made by joining together many small repeating units called monomers. The process of forming polymers from monomers is called polymerization.

Monomer → small molecule
Polymer → giant molecule made from many monomers linked in a chain

Key Terms

• Monomer: A small, reactive molecule that can join to other similar molecules to form a polymer. Example: Ethene (\( \mathrm{C_2H_4} \))
• Polymer: A long-chain molecule made of many repeating units. Example: Poly(ethene)
• Repeat unit: The specific arrangement of atoms that repeats again and again along the polymer chain.

Types of Polymerization

• Addition polymerization – Monomers add together with no small molecule produced.
  Usually involves alkenes (C=C double bond).
• Condensation polymerization – Monomers join together and small molecules such as water (H₂O) or HCl are released.
  Usually involves monomers with two functional groups (e.g., –COOH, –OH, –NH₂).

Addition Polymers

In addition polymerization, many monomers with double bonds (usually alkenes) join together to form a long chain. The double bond in each monomer opens up and links with others.

General form: \( \mathrm{n\ CH_2=CHR \ \longrightarrow\ [-CH_2-CHR-]_n} \)

Example: Ethene → Poly(ethene)

\( \mathrm{n\ CH_2=CH_2 \ \longrightarrow\ [-CH_2-CH_2-]_n} \)

• Monomer: Ethene (\( \mathrm{CH_2=CH_2} \))
• Polymer: Poly(ethene) (also called polythene or polyethylene)
• Uses: Plastic bags, bottles, toys

Example: Chloroethene → PVC

\( \mathrm{n\ CH_2=CHCl \ \longrightarrow\ [-CH_2-CHCl-]_n} \)

• Monomer: Chloroethene (vinyl chloride)
• Polymer: PVC (polyvinyl chloride)
• Uses: Pipes, window frames, insulation

Properties of Addition Polymers:

• Usually non-biodegradable (they do not break down easily in nature).
• Often strong, flexible, waterproof.
• Poor conductors of electricity (good electrical insulators).

Condensation Polymers

In condensation polymerization, monomers with two functional groups react together to form long chains, and a small molecule like water or HCl is eliminated each time a link is formed.

Important: Each step forms a link AND releases a small molecule.

Example: Formation of a Polyester

React a diol (a molecule with two –OH groups) and a dicarboxylic acid (a molecule with two –COOH groups).

Diol: \( \mathrm{HO{-}R{-}OH} \)

Dicarboxylic acid: \( \mathrm{HOOC{-}R'{-}COOH} \)

They join by forming an ester link (-COO-) and release water.

\( \mathrm{-HO{-}R{-}OH + HOOC{-}R'{-}COOH- \rightarrow -[{-}R{-}OOC{-}R'{-}COO{-}]_n + H_2O} \)

• Polymer formed: Polyester
• Linkage type: Ester linkage (–COO–)
• Uses: Clothing fibres (e.g. PET), bottles, textiles

Example: Formation of a Polyamide (like Nylon)

React a diamine (two –NH₂ groups) with a dicarboxylic acid (two –COOH groups).

Diamine: \( \mathrm{H_2N{-}R{-}NH_2} \)

Dicarboxylic acid: \( \mathrm{HOOC{-}R'{-}COOH} \)

They join by forming an amide link (–CONH–) and release water.

\( \mathrm{-H_2N{-}R{-}NH_2 + HOOC{-}R'{-}COOH- \rightarrow -[{-}R{-}NHCO{-}R'{-}CONH{-}]_n + H_2O} \)

• Polymer formed: Polyamide (e.g. Nylon)
• Linkage type: Amide link (–CONH–)
• Uses: Ropes, fishing line, parachutes, engineering plastics

Addition vs. Condensation Polymers — Summary Table

 Environmental Impact of Polymers

• Non-biodegradability: Many addition polymers (like poly(ethene)) do not break down easily. They persist in landfills and oceans for many years.
• Microplastics: Plastics can break into tiny particles that enter food chains and harm wildlife.
• Recycling: Some plastics can be melted and reshaped (thermoplastics). Others are harder to recycle.
• Incineration issues: Burning plastics can release toxic gases, e.g. burning PVC can release hydrogen chloride gas (\( \mathrm{HCl} \)).
• Bioplastics and biodegradable polymers: Research is moving toward polymers that can break down naturally to reduce pollution.

Everyday Uses of Important Polymers