Polymers IGCSE

🧪 POLYMERS - Complete Notes

Cambridge IGCSE Chemistry | Chapter 19

1️⃣ What are Polymers?

POLYMER = A very large molecule made from many small repeating units called monomers

MONOMER = A small molecule that joins to other monomers to form a polymer

POLYMERISATION = The process of joining monomers to form a polymer

📊 Types of Polymers

Natural Polymers	Synthetic Polymers
✓ Proteins (meat, eggs)	✓ Poly(ethene) (plastic bags)
✓ Starch (rice, bread)	✓ Poly(propene) (ropes)
✓ Natural rubber	✓ PVC (pipes)
✓ Silk	✓ Nylon (clothing)
✓ Cellulose	✓ PET (bottles)

2️⃣ Addition Polymerisation

Addition polymerisation occurs when unsaturated monomers (with C=C double bonds) join together to form a polymer as the only product.

⚠️ Key Requirements:
• Monomer must be unsaturated (contain C=C)
• Monomer must be an alkene
• NO by-products formed

🔬 Example: Poly(ethene) from Ethene

Monomer: Ethene

      H   H

      |   |

      C = C

      |   |

      H   H

POLYMERISATION ↓ (high temp, pressure, catalyst) Polymer: Poly(ethene)

      H   H   H   H   H   H

      |   |   |   |   |   |

  ----C — C — C — C — C — C----

      |   |   |   |   |   |

      H   H   H   H   H   H

Chemical Equation:

         H   H                         [ H   H ]

         |   |                         [ |   |  ]

    n   C = C    ──────────→    ----[ C — C  ]----

         |   |    catalyst            [ |   |  ]n

         H   H                         [ H   H ]

Where n = 10,000 to 30,000

📦 Uses of Poly(ethene):
• LDPE (Low Density): plastic bags, cling film, squeeze bottles
• HDPE (High Density): water pipes, bottles, containers, bins

📚 Other Addition Polymers

Monomer	Polymer	Uses
Propene (C₃H₆)	Poly(propene)	Ropes, carpets, containers
Chloroethene	PVC (Polyvinyl chloride)	Pipes, window frames, wire coating
Styrene	Polystyrene	Cups, packaging, insulation
Tetrafluoroethene	Teflon (PTFE)	Non-stick pans, coatings

3️⃣ Condensation Polymerisation

Condensation polymerisation occurs when monomers join with the elimination of small molecules such as water (H₂O), ammonia (NH₃), or hydrogen chloride (HCl).

⚠️ Key Requirements:
• Usually TWO different monomers
• Each monomer has TWO functional groups
• Products: Polymer + Small molecule (by-product)

🧵 NYLON - A Polyamide

Monomers:

1. DICARBOXYLIC ACID (two —COOH groups)

     O          O

     ║          ║

 H—O—C—[XXXX]—C—O—H

2. DIAMINE (two —NH₂ groups)

     H   H

     |   |

 H—N—[YYYY]—N—H

REACTION:

     O          O         H   H

     ║          ║         |   |

 H—O—C—[XX]—C—O—H + H—N—[YY]—N—H

         ↓                 ↓

    removes OH        removes H

         ↓_________________↓

              H₂O (water)

            ↓ FORMS ↓

     O          O     H       H

     ║          ║     |       |

  —C—[XXXX]—C—N—[YY]—N—

              ↑_______↑

           AMIDE LINKAGE

            (—CO—NH—)

📌 Properties of Nylon:
✓ Strong and durable
✓ Can be drawn into fibres
✓ Resistant to wear

Uses: Clothing, fishing lines, ropes, parachutes, toothbrush bristles

🍾 PET - A Polyester

Monomers:

1. DICARBOXYLIC ACID (two —COOH groups)

     O          O

     ║          ║

 H—O—C—[XXXX]—C—O—H

2. DIOL (two —OH groups, an alcohol)

 

 H—O—[YYYY]—O—H

REACTION:

     O          O              

     ║          ║              

 H—O—C—[XX]—C—O—H + H—O—[YY]—O—H

         ↓                 ↓

    removes OH        removes H

         ↓_________________↓

              H₂O (water)

            ↓ FORMS ↓

     O          O          

     ║          ║          

  —C—[XXXX]—C—O—[YY]—O—

              ↑_______↑

           ESTER LINKAGE

            (—CO—O—)

📌 Properties of PET:
✓ Strong and lightweight
✓ Water-resistant
✓ Transparent when thin
✓ Recyclable!

Uses: Drink bottles, food containers, clothing fibres, carpets

♻️ PET Recycling:
PET → Heat (no air) → Breaks into monomers → Separated → New PET products
Recycled PET used for: carpets, fleece jackets, new bottles

⚖️ Comparison: Addition vs Condensation

Feature	Addition	Condensation
Monomers	ONE type (alkene)	TWO types
Requirement	Must have C=C	Must have 2 functional groups each
Products	Polymer ONLY	Polymer + small molecule
By-products	None	H₂O, HCl, or NH₃
Formula pattern	Exact multiple of monomer	NOT exact multiple
Examples	Poly(ethene), PVC	Nylon, PET, Proteins

4️⃣ Plastics and Pollution

PLASTICS = Materials made from synthetic polymers

🔥 Types of Plastics

Thermoplastics	Thermosetting Plastics
✓ Soften when heated	✗ Do NOT soften when heated
✓ Can be reshaped	✗ Harden permanently
✓ Recyclable	✗ Decompose if overheated
Ex: Poly(ethene), PVC	Ex: Bakelite, epoxy resin

🌍 Environmental Problems

⚠️ THE BIG PROBLEM: Most plastics are NON-BIODEGRADABLE

This means:
• Bacteria cannot break them down
• Plastic waste stays for 100s of years
• Accumulates in environment

Timeline:
🍌 Banana peel: 1 month
📄 Paper: 6 months
🍾 Plastic bottle: 450 years!
🛍️ Plastic bag: 1000 years!

🗑️ Disposal Methods

Method	✓ Advantages	✗ Disadvantages
Recycling	Saves resources, reduces waste	Expensive, needs sorting
Cracking	Recovers chemicals	High cost, high temperature
Landfill	Cheap and easy	Wastes space, lasts forever
Incineration	Produces energy, reduces volume	Toxic gases, air pollution

♻️ THE 3 Rs SOLUTION:
1. REDUCE → Use less plastic
2. REUSE → Use items many times
3. RECYCLE → Turn old plastic into new products

5️⃣ Natural Polymers - PROTEINS

PROTEINS = Natural polyamides made from amino acid monomers

Found in: muscles, skin, hair, nails, enzymes, antibodies

🧬 Amino Acids - The Building Blocks

General Structure of Amino Acid:

        H   O

        |   ║

    H—N—C—C—O—H

        |

        R

Where:

• —NH₂ = amino group

• —COOH = carboxylic acid group

• R = side chain (different for each amino acid)

• H = hydrogen on central carbon

Examples of Amino Acids:

GLYCINE (simplest): R = H
Formula: H₂N—CH₂—COOH

ALANINE: R = CH₃
Formula: H₂N—CH(CH₃)—COOH

CYSTEINE: R = CH₂SH (contains sulfur)
Found in hair and skin proteins

📊 Important Facts:
• About 20 different amino acids exist
• All proteins contain: C, H, O, N
• Some also contain: S, P
• Proteins have hundreds to thousands of amino acids

🔗 How Proteins Form

Condensation Polymerisation:

AMINO ACID 1  +  AMINO ACID 2

     ↓                ↓

  H   O            H   O

  |   ║            |   ║

H-N-□-C-O-H  +  H-N-△-C-O-H

      ↓                ↓

  removes OH      removes H

      ↓________________↓

           H₂O (water)

         ↓ FORMS ↓

  H   O      H   O

  |   ║      |   ║

H-N-□-C-N-△-C-O-H

        ↑

   PEPTIDE LINKAGE

   (amide linkage)

    —CO—NH—

🔬 Proteins vs Nylon

Feature	PROTEINS	NYLON
Type	Natural polyamide	Synthetic polyamide
Linkage	Peptide (—CO—NH—)	Amide (—CO—NH—)
Formation	Condensation	Condensation
Monomers	Amino acids	Dicarboxylic acid + diamine
By-product	Water (H₂O)	Water (H₂O)
Found in	Living organisms	Factories/labs

📝 Quick Summary

🎯 KEY FORMULAS & LINKAGES:

1. Addition Polymerisation:
n(monomer with C=C) → Polymer
Example: n(C₂H₄) → [—CH₂—CH₂—]ₙ

2. Amide Linkage (Nylon & Proteins):

     O   H

     ║   |

  —C—N—

Written as: —CO—NH— or —CONH—

3. Ester Linkage (PET):

     O   

     ║   

  —C—O—

Written as: —CO—O— or —COO—

4. Peptide Linkage (Proteins):
Same as amide: —CO—NH—

✅ REMEMBER:
• Addition = One monomer type, C=C needed, NO by-products
• Condensation = Two monomer types, two functional groups each, produces small molecules
• Proteins = Natural polyamides from amino acids
• Plastics = Non-biodegradable, environmental problem
• Recycling = Important solution (especially PET)

🎓 Study Complete!

Cambridge IGCSE Chemistry - Chapter 19: Polymers

Always remember: Reduce, Reuse, Recycle! 🌍♻️