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4.8.3Electrochemistry

Condensation Polymers — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 17 of 20 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Condensation Polymerisation

Definition
  • Definition Condensation polymers form when two different monomers link together with the loss of a small molecule, usually water.
Functional groups
  • Functional groups Each monomer has a functional group at each end, and these groups react with one another to form a chain.
Polyester
  • Polyester A polyester is made from a dicarboxylic acid and a diol, linked by ester groups.
Water
  • Water One molecule of water is formed for every ester link, using an H from the alcohol and an OH from the acid.
Comparison
  • Comparison Unlike addition polymerisation, condensation polymerisation produces a small molecule as a by-product.

Part 2 of 5Forming Terylene

1
Terylene is formed from a dicarboxylic acid, benzene-1,4-dicarboxylic acid, which has a –COOH group at each end.
2
It is combined with a diol, ethane-1,2-diol, which has an –OH group at each end.
3
Each –COOH group reacts with an –OH group on another monomer, forming an ester link and releasing one molecule of water.
4
Repeated ester links build up a long polyester chain in which the two monomers alternate.

Part 3 of 5Deducing Monomers from a Polyester

Deducing Monomers from a Polyester
Find the links
  • Find the links Identify each –COO– ester link in the polyester chain.
Break the link
  • Break the link Split the C–O bond of each ester group, which separates the chain into two halves.
Add water
  • Add water Hydrolysis adds water across the ester link, giving –OH to the carbon of the C=O and H to the oxygen.
Result
  • Result The two monomers are a dicarboxylic acid and a diol, as in polybutylene terephthalate, PBT, made from terephthalic acid and butane-1,4-diol.
Biopolyesters
  • Biopolyesters Biopolyesters are made by micro-organisms from sugars and plant oils, and they biodegrade naturally in the environment.

Part 4 of 5Worked Example

Question

  • A polyester is formed from ethane-1,2-diol (C₂H₆O₂) and benzene-1,4-dicarboxylic acid (C₈H₆O₄).
  • Find the molecular formula of the repeat unit formed when one water molecule is lost at each ester link, with two links per repeat unit.

  1. Add the monomer formulaeC₂H₆O₂ + C₈H₆O₄ = C₁₀H₁₂O₆
  2. Each repeat unit has two ester links, so two water molecules (H₄O₂) are removed
  3. C₁₀H₁₂O₆ − H₄O₂ = C₁₀H₈O₄

Answer C₁₀H₈O₄

Part 5 of 5Exam Checklist & Tips

4.8.3 – Key Points for the Exam

  • Condensation polymerisation Polymer formation in which a small molecule, usually water, is lost at each link.
  • Dicarboxylic acid A molecule with two –COOH groups, one at each end.
  • Diol A molecule with two –OH groups, one at each end.
  • Ester link The –COO– group formed between an acid and an alcohol group in a polyester.
  • Hydrolysis The breaking of a bond by reaction with water, here reversing the formation of an ester link.
  • Biopolyester A polyester made by micro-organisms that can biodegrade.

Common Mistakes

  • Forgetting to state that condensation polymerisation forms a small molecule, usually water, as a by-product.
  • Giving addition-type answers for condensation polymers, which always form a by-product.
  • Adding the OH and H to the wrong atoms when deducing monomers: the C=O carbon gets OH and the oxygen gets H.
  • Confusing biopolyesters, which are made by micro-organisms and can biodegrade, with other polyesters that may not.

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