Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Define monomer, polymer, and types of polymerisation.
• Draw and name monomers and repeating units for addition polymers.
• Draw and name monomers and repeating units for condensation polymers.
• Write balanced polymerisation equations.
• Discuss the uses, advantages, and disadvantages of polymers.

Lesson summary

Organic chemistry and macromolecules are fundamental to understanding the world around us, from the plastics we use daily to the food we eat. In South Africa, understanding these concepts is crucial for various sectors, including agriculture (fertilizers, pesticides), the petrochemical industry (Sasol), pharmaceuticals (development of new medicines), and addressing environmental challenges like plastic pollution. This week, we will focus on the structures, properties, and reactions of addition polymers and condensation polymers.

Lesson notes

2. 1.

Introduction to Polymers: Polymers are large molecules (macromolecules) composed of repeating structural units called monomers. The process by which monomers join together to form a polymer is called polymerisation. Polymers can be natural (e.g., starch, cellulose, proteins) or synthetic (e.g., polyethylene, nylon, polyester). We will focus on synthetic polymers in this lesson. 2.

2. Addition Polymerisation: Addition polymerisation involves the joining of monomers containing double or triple bonds (unsaturated monomers) without the loss of any atoms. The monomers simply add to each other to form a long chain. No other molecule is formed. A free radical initiator is usually needed to start the reaction.

Monomer: A small molecule that can bond to other identical molecules to form a polymer.

Repeating Unit: The smallest repeating section of the polymer chain.

Examples of Addition Polymers: Polyethylene (PE): Monomer: Ethene (C₂H₄)

Repeating Unit: -[CH₂-CH₂]- Equation: n CH₂=CH₂ → -[CH₂-CH₂]ₙ- Uses: Plastic bags, bottles, packaging film. It's widely used because it is cheap to produce and versatile.

Polyvinyl Chloride (PVC): Monomer: Chloroethene (Vinyl Chloride) (C₂H₃Cl)

Repeating Unit: -[CH₂-CHCl]- Equation: n CH₂=CHCl → -[CH₂-CHCl]ₙ- Uses: Pipes, window frames, flooring. PVC pipes are very common in South Africa for plumbing due to their durability and affordability.

Polytetrafluoroethylene (PTFE) (Teflon): Monomer: Tetrafluoroethene (C₂F₄)

Repeating Unit: -[CF₂-CF₂]- Equation: n CF₂=CF₂ → -[CF₂-CF₂]ₙ- Uses: Non-stick cookware, cable insulation. Mechanism of Addition Polymerisation (simplified): Initiation: A free radical initiator (e.g., a peroxide) breaks down to form free radicals. These radicals attack the double bond of the monomer, forming a new free radical.

Propagation: The newly formed free radical attacks another monomer, adding it to the chain and creating a larger free radical. This process repeats many times, leading to chain growth.

Termination: Two free radicals combine, stopping the chain growth and forming the final polymer. 2.

3. Condensation Polymerisation: Condensation polymerisation involves the joining of monomers with the elimination of a small molecule, such as water (H₂O) or methanol (CH₃OH). Each time a monomer is added, a small molecule is lost. This is important to understand as it also affects the molar mass calculation.

Examples of Condensation Polymers: Polyester (Terylene/Dacron): Monomers: Ethanediol (HOCH₂CH₂OH) and Terephthalic acid (HOOC-C₆H₄-COOH)

Repeating Unit: -[O-CH₂-CH₂-O-CO-C₆H₄-CO]- Equation: n HOCH₂CH₂OH + n HOOC-C₆H₄-COOH → -[O-CH₂-CH₂-O-CO-C₆H₄-CO]ₙ- + 2n H₂O Uses: Clothing, plastic bottles (PET). PET is widely used for water bottles in South Africa.

Polyamide (Nylon): Monomers: 1,6-Diaminohexane (H₂N(CH₂)₆NH₂) and Adipic acid (HOOC(CH₂)₄COOH)

Repeating Unit: -[NH-(CH₂)₆-NH-CO-(CH₂)₄-CO]- Equation: n H₂N(CH₂)₆NH₂ + n HOOC(CH₂)₄COOH → -[NH-(CH₂)₆-NH-CO-(CH₂)₄-CO]ₙ- + 2n H₂O Uses: Ropes, clothing, stockings. Comparison of Addition and Condensation Polymerisation: | Feature | Addition Polymerisation | Condensation Polymerisation | | ----------------- | -------------------------------------------- | --------------------------------------------- | | Monomers | Unsaturated monomers (double/triple bonds) | Monomers with two functional groups (e.g., -OH, -COOH, -NH₂) | | By-products | No by-products formed | Small molecules (e.g., H₂O) are eliminated | | Chain Growth | Rapid | Slower | | Monomer Types | Usually only one type of monomer | Usually two different types of monomers | | Polymer Structure | Usually only carbon atoms in the backbone | Other atoms (e.g., O, N) in the backbone | 2.

4. Properties and Uses of Polymers: The properties of polymers depend on factors such as the type of monomer, the length of the polymer chain (molecular weight), and the presence of branching or cross-linking. These properties determine the suitability of a polymer for a particular application.

Polyethylene: Flexible, lightweight, and inexpensive. Used for plastic bags, films, and containers.

PVC: Rigid and durable. Used for pipes, window frames, and flooring.

Teflon: Chemically inert and non-stick. Used for cookware and seals.

Polyester: Strong and resistant to stretching. Used for clothing and bottles.

Nylon: Strong, elastic, and abrasion-resistant. Used for ropes, clothing, and carpets. 2.

5. Environmental Concerns and Recycling: Plastic pollution is a significant environmental problem in South Africa. Many polymers are not biodegradable and can persist in the environment for hundreds of years. Recycling is an important strategy for reducing plastic waste. Different types of polymers require different recycling processes. Understanding the chemical structure of polymers is crucial for developing effective recycling technologies. Guided Practice (With Solutions)

Question 1: Draw the repeating unit of the polymer formed from the following monomer: CH₂=CH(CH₃) (propene).