Chemistry · Grade 12 · Organic Chemistry · Term 3

Polymers and Polymerization

Learn how small organic molecules, called monomers, link together to form large macromolecules, or polymers, and explore their diverse applications in modern life.

TL;DR:Dive into the world of macromolecules by exploring how tiny building blocks link up to create the plastics, fabrics, and even biological molecules that define our world.

• Ontario Curriculum Expectations
• Ontario Curriculum: SCH4U, Strand B - Organic Chemistry, B1: Analyse the origins and the properties of a variety of organic compounds that are used in diverse applications.

About This Topic

This topic, Polymers and Polymerization, is a cornerstone of the Grade 12 Chemistry curriculum, typically situated within the organic chemistry unit. It provides a tangible and highly relevant application of fundamental organic principles, such as functional groups, bonding, and reaction mechanisms. For Canadian students, this topic offers a direct link to major national industries, including petrochemicals in Alberta and advanced materials manufacturing in Ontario and Quebec. It also connects directly to pressing environmental issues that resonate across Canada, such as microplastic pollution in the Great Lakes and Arctic, and the challenges of municipal recycling programs. By exploring both the synthesis and the societal impact of polymers, this unit encourages students to think critically about the materials that shape their world.

The curriculum requires students to move beyond simple memorization of polymer types. They must grasp the mechanistic differences between addition and condensation polymerization, linking the structure of monomers to the macroscopic properties of the resulting polymer. This involves a sophisticated understanding of intermolecular forces, chain entanglement, and cross-linking. The topic culminates in an evaluation of the lifecycle of synthetic polymers, from production to disposal. This aligns with cross-curricular priorities focused on environmental stewardship and scientific literacy, empowering students to engage in informed discussions about sustainability, material science innovation, and public policy regarding plastics.

Key Questions

1. Compare the processes of addition polymerization and condensation polymerization.
2. Explain how the properties of a polymer are related to the structure of its monomer and the bonds between chains.
3. Evaluate the societal and environmental impact of the production and disposal of synthetic polymers.

Learning Objectives

• Differentiate between addition and condensation polymerization by identifying monomers and drawing reaction mechanisms.
• Predict the physical properties of a polymer (e.g., rigidity, melting point) based on its chemical structure, including monomer type and intermolecular forces.
• Illustrate the formation of common synthetic polymers such as polyethylene, PVC, and nylon.
• Analyse the societal benefits and environmental drawbacks of using synthetic polymers.
• Classify common materials as natural or synthetic polymers and describe their uses.

Key Vocabulary

Monomer	A small molecule that can be bonded to other identical molecules to form a polymer.
Polymer	A large molecule, or macromolecule, composed of many repeating subunits (monomers).
Polymerization	A chemical process that combines several monomers to form a polymer or polymeric compound.
Addition Polymerization	A process where monomer units add to one another in such a way that the polymer contains all the atoms of the monomer unit, typically involving the breaking of a double or triple bond.
Condensation Polymerization	A process where monomers join together with the loss of a small molecule, such as water. The monomers must each have at least two functional groups.
Cross-linking	The formation of covalent bonds that link one polymer chain to another, resulting in a more rigid material.

Watch Out for These Misconceptions

Common Misconception

All plastics are the same and have the same properties.

What to Teach Instead

Plastics are a diverse group of polymers. Their properties, such as strength, flexibility, and melting point, vary significantly based on the monomer used, chain length, branching, and the presence of additives.

Common Misconception

Polymers are always man-made, artificial materials.

What to Teach Instead

Many essential biological molecules are natural polymers. Examples include DNA and RNA (polynucleotides), proteins (polypeptides), and starch and cellulose (polysaccharides).

Common Misconception

If a plastic has a recycling symbol on it, it is always recycled.

What to Teach Instead

The number inside the chasing arrows symbol is a resin identification code, not a guarantee of recyclability. The ability to recycle a plastic depends on the local municipal facilities' capacity to collect, sort, and process that specific type of material.

Active Learning Ideas

Socio-Scientific Issues

Nylon Rope Trick Demonstration

In a fume hood, carefully pour a solution of adipoyl chloride in cyclohexane on top of an aqueous solution of hexamethylenediamine. Students can use forceps to gently pull the polymer film that forms at the interface, creating a continuous strand of nylon.

20 min·Whole Class

Socio-Scientific Issues

Polymer Properties Investigation

Provide students with numbered samples of different polymers (e.g., LDPE, HDPE, PET, PVC). They will perform a series of tests for density (sink/float), flexibility, and heat resistance to identify the materials and relate their properties to their known structures.

45 min·Small Groups

Socio-Scientific Issues

Bioplastic Synthesis Lab

Students follow a procedure to create a simple bioplastic from corn starch, water, vinegar, and glycerol. They can then pour the mixture into a mould and let it dry, observing the properties of the resulting material over a few days.

50 min·Pairs

Real-World Connections

• Development of biodegradable and compostable plastics from sources like corn starch (PLA) to address waste management challenges.
• Use of specialized polymers like Kevlar in bulletproof vests and high-performance sporting equipment, demonstrating the link between structure and strength.
• Application of biocompatible polymers in medical implants, drug delivery systems, and tissue engineering.
• The role of polymers like nylon, polyester, and Gore-Tex in the textile industry for clothing, from everyday wear to high-tech outdoor gear.
• The use of various polymers in food packaging to extend shelf life, ensure safety, and reduce food waste.

Assessment Ideas

Exit Ticket

Use an exit ticket where students must draw the repeating unit of a polymer given its monomer, or vice versa, for a simple addition polymer like polypropylene.

Peer Assessment

A research project and presentation where students analyse a specific polymer. They must cover its synthesis, properties, applications, and a full lifecycle analysis of its environmental impact.

Quick Check

A unit test question that requires students to compare and contrast addition and condensation polymerization, including balanced chemical equations for a specific example of each.

Frequently Asked Questions

What is the difference between a polymer and a plastic?

A polymer is a large macromolecule made of repeating monomer subunits. A plastic is a material made from a polymer, but it often contains other additives like colourants, plasticizers, or stabilizers to enhance its properties for a specific use.

Why is a small molecule like water often produced during condensation polymerization but not addition polymerization?

In condensation polymerization, monomers with two functional groups react to join together, and a small molecule, often water, is eliminated in the process of forming the new bond. In addition polymerization, the double or triple bond within a monomer breaks, allowing the monomers to add directly to one another without the loss of any atoms.

What is the difference between a thermoplastic and a thermosetting polymer?

Thermoplastics, like polyethylene, consist of long chains with weak intermolecular forces between them. They can be melted and reshaped multiple times. Thermosetting polymers, like Bakelite, have strong covalent cross-links between their chains, forming a rigid 3D network. Once set, they cannot be remelted.