Polymer Chemistry: Monomers, Polymers & Polymerization
Explore the basics of polymer chemistry, including addition and condensation polymerization, strengthening techniques, and real-world examples like Kevlar.
Section 2.2 | Pages 116–121
POLYMER CHEMISTRY
Monomers, Polymers & Polymerization
20-Minute Lesson | High School Chemistry
What We'll Cover Today
Section 2.2
Key Definitions
— Plastic, Monomer, Polymer, Polymerization
Addition Polymerization
— Polyethylene synthesis
Polyacrylamide Gel
— Synthesis, notation & uses
Strengthening Polymers
Why Polymers Are Flexible & Stretchable
Kevlar
— Strength & Applications
Condensation Polymerization
— How to identify it
Key Definitions
PLASTIC
A synthetic or semi-synthetic material made from polymers that can be molded into shape.
MONOMER
A small, simple molecule that can bond with other monomers to form a polymer. (e.g. ethylene, CH₂=CH₂)
POLYMER
A large molecule (macromolecule) made up of many repeating monomer units bonded together in a long chain.
POLYMERIZATION
The chemical process by which monomers are joined together to form a polymer.
Addition Polymerization: Polyethylene
The Reaction
n CH₂=CH₂ → —[CH₂—CH₂]ₙ—
Monomer: Ethylene
Polymer: Polyethylene
Key Requirement
⚡ A C=C double bond (alkene) is REQUIRED for addition polymerization. The double bond breaks open and allows monomers to link together into a chain.
No atoms are lost in addition polymerization — all monomer atoms become part of the polymer chain.
Polyacrylamide Gel
THE REACTION
n CH₂=CH—C(=O)—NH₂
➔
—[CH₂—CH(CONH₂)]ₙ—
Monomer: Acrylamide
Polymer: Polyacrylamide
SHORTHAND NOTATION
—(CH₂—CH—CONH₂)ₙ—
Monomer:
Acrylamide (CH₂=CHCONH₂)
Polymer:
Polyacrylamide
Uses of Polyacrylamide Gel:
Gel electrophoresis (separating DNA/proteins in labs)
Water treatment (flocculant)
Soil conditioning in agriculture
Soft contact lenses
Pharmaceutical drug delivery
How Can a Polymer Be Strengthened?
🔗
Cross-Linking
Adding chemical bonds between polymer chains (cross-links) restricts movement and makes the material harder and more rigid. Example: Vulcanization of rubber.
🧬
Increasing Chain Length
Longer polymer chains have more intermolecular forces between them, increasing strength and toughness.
🛡️
Adding Fillers/Reinforcers
Mixing in materials like carbon fiber, glass fiber, or nanoparticles adds mechanical strength. Example: Carbon-reinforced polymers.
💎
Crystallinity
Increasing the ordered (crystalline) regions in a polymer improves strength. More ordered chains pack tightly and resist deformation.
Why Are Polymers Flexible & Stretchable?
Long, Tangled Chains
Polymer chains are very long and become tangled or coiled. Under stress, these chains can uncoil and straighten out — this allows the material to stretch without breaking.
Weak Intermolecular Forces
The forces between polymer chains (van der Waals forces) are relatively weak, allowing chains to slide past each other. This gives polymers their flexibility.
Amorphous Regions
Disordered (amorphous) regions in a polymer have chains arranged randomly — like a ball of yarn. These regions allow bending and flexing without snapping.
Flexibility comes from the ability of long chains to move, bend, and slide relative to each other.
Kevlar: Exceptionally Strong
What Makes Kevlar Strong?
Uses of Kevlar
Kevlar is a para-aramid synthetic fiber — its molecular structure is what makes it one of the strongest materials on Earth.
Condensation Polymerization
How to Identify It
Small Molecule Is Released
A small molecule (usually water H₂O, or sometimes HCl or methanol) is released as a by-product during the reaction. This is the key sign of condensation polymerization.
Two Functional Groups Required
The monomers must have two reactive functional groups (e.g. —COOH and —NH₂, or —COOH and —OH). These react at BOTH ends, releasing a small molecule.
Atoms Are LOST
Unlike addition polymerization, atoms are removed from the monomers. The polymer has fewer atoms than the sum of all monomers.
Feature
Addition Polymerization
Condensation Polymerization
Bond Required
C=C double bond
Two functional groups
By-product
None
Water (or HCl, etc.)
Atom count
All atoms kept
Atoms lost
Example
Polyethylene
Nylon, Kevlar, Polyester
Lesson Summary
Definitions
Addition Polymerization
Requires C=C double bond. Ethylene → Polyethylene. No atoms lost.
Polyacrylamide Gel
Acrylamide monomer → Polyacrylamide. Used in gel electrophoresis, water treatment, and more.
Strengthening Polymers
Cross-linking, longer chains, fillers, increased crystallinity.
Flexibility & Stretch
Long coiled chains uncoil under stress. Weak IMFs allow sliding. Amorphous regions allow bending.
Kevlar
Para-aramid fiber. Rigid aromatic rings + hydrogen bonding = extraordinary strength. Used in armor, aerospace, tires.
Condensation Polymerization
Small molecule (H₂O) released. Two functional groups needed. Atoms are LOST. Examples: Nylon, Polyester.
Section 2.2 | Pages 116–121
End of Lesson
- chemistry
- polymers
- monomers
- polymerization
- polyethylene
- kevlar
- high-school-science
- material-science