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4.8.6Unit 4. Rates, Equilibria and Further Organic Chemistry

Forming Polyesters — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 4 parts Lesson 50 of 56 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 4Condensation Polymers

Polyesters are condensation polymers joined by ester links.

Condensation
  • Condensation Each time two monomers join, a small molecule such as water or HCl is lost.
Two monomers
  • Two monomers A dicarboxylic acid (or diacyl chloride) reacts with a diol, each having a functional group at both ends.
One monomer
  • One monomer A hydroxycarboxylic acid contains both an OH group and a COOH group, so it can polymerise on its own.
Ester link
  • Ester link The linkage –COO– joins each monomer unit, repeated thousands of times along the chain.
Hydrolysis weak point
  • Hydrolysis weak point The carbonyl carbon of each ester link is open to attack by water,
    • which is why strong acid or alkali slowly degrades polyesters.

Part 2 of 4Examples

Examples
PET
  • PET Benzene-1,4-dicarboxylic acid and ethane-1,2-diol form poly(ethylene terephthalate), used in bottles and fibres.
Repeat unit
  • Repeat unit The repeat unit of PET is –OC–C₆H₄–COO–CH₂CH₂–O–, enclosed in brackets with extension bonds.
Polylactic acid
  • Polylactic acid 2-hydroxypropanoic acid polymerises to give a biodegradable polyester used in packaging and surgical stitches.
Acyl chloride route
  • Acyl chloride route Using a diacyl chloride is faster and gives HCl instead of water as the small molecule lost.

Part 3 of 4Properties and Breakdown

1
The ester links in polyesters can be hydrolysed by acid or alkali, so the polymers are not as chemically inert as poly(alkenes).
2
This means polyesters can be broken down to their monomers, allowing chemical recycling.
3
Poly(alkenes) have unreactive C–C backbones, which resist hydrolysis and so are not biodegradable.
4
Polyesters have polar ester groups, giving permanent dipole attractions between chains that make fibres strong.

Part 4 of 4Exam Checklist & Tips

4.8.6 – Key Points for the Exam

  • Condensation polymerisation Joining monomers with loss of a small molecule.
  • Monomer Small molecule that joins to form a polymer.
  • Repeat unit The part of a polymer chain that repeats.
  • Diol Compound containing two OH groups.

Common Mistakes

  • Drawing the repeat unit with the end bonds missing.
  • Saying addition polymers lose water as they form.
  • Forgetting that one monomer is a diacid and the other a diol.
  • Claiming polyesters are completely unreactive.

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