What are Condensation Polymers?
Condensation polymers form when monomer functional groups react and release a small byproduct—typically water. Nylon, polyester, and polyurethane are everyday examples.
In condensation polymerization, two monomer molecules bond together and release H₂O (or HCl, NH₃, etc.). The repeating pattern is (unit − byproduct release − unit − …). Every ester or amide bond releases water.
- 1↓Monomer 1: DiolExample: ethylene glycol HO−CH₂−CH₂−OH
- 2↓Monomer 2: Dicarboxylic AcidExample: terephthalic acid HOOC−C₆H₄−COOH
- 3↓Ester bond formsOH (from diol) + COOH (from acid) → CO−O− + H₂O
- 4↓Water releasedEach reaction releases one H₂O molecule (hence 'condensation').
- 5Polyester chain growsRepeat: free −OH and −COOH groups continue reacting until one runs out.
Step-by-step worked examples
In polyester synthesis, 100 diol molecules and 100 dicarboxylic acid molecules react completely. How many water molecules are released?
Each ester linkage forms between one −OH and one −COOH, releasing one H₂O. 100 diols + 100 acids → 100 ester bonds (approx.) ≈ 100 H₂O molecules released. (The final molecule has 100 monomers, so ~99 internal water releases, plus end caps.)
Nylon-66 is made from hexamethylene diamine (6 carbons) and adipic acid (6 carbons). Write the repeat unit.
Hexamethylene diamine: H₂N−(CH₂)₆−NH₂ Adipic acid: HOOC−(CH₂)₄−COOH Amide bond: −NH−CO−(CH₂)₄−CO−NH−(CH₂)₆− Repeat unit: −[NH−(CH₂)₆−NH−CO−(CH₂)₄−CO]− Water released at each amide linkage.
Polyurethane forms from a diol and a diisocyanate. Does it release water like polyester?
Diol (−OH −OH) + Diisocyanate (−N=C=O −N=C=O) A urethane bond forms: −NH−CO−O− (no byproduct released). This is NOT typical condensation—no water released. (Some urethane syntheses use water in a separate step, but the chain growth doesn't release it.)
Flashcards
Quick quiz
Q1.A polyester made from ethylene glycol and terephthalic acid releases H₂O at each…
Q2.How many functional groups does a monomer in condensation polymerization need?
Q3.If a reaction releases H₂O (or HCl or NH₃), it is ___ polymerization.
Q4.Nylon is an example of a ___ polymer.
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Common mistakes
Condensation polymers contain water trapped inside. — Correct: Water is expelled as a byproduct—it is NOT chemically bonded to the polymer.
All condensation polymers are strong and rigid. — Correct: Strength depends on chain structure, cross-linking, and hydrogen bonding—not just the condensation mechanism.
You need only one type of monomer for condensation polymerization. — Correct: Typically two different monomers (diol + dicarboxylic acid, or diamine + dicarboxylic acid) are required.
Polyester is the only common condensation polymer. — Correct: Polyester, nylon, polyamide, polyurethane, and polycarbonate are all major condensation polymers.
FAQ
Why is water released in condensation reactions?
When −OH and −COOH (or −NH₂ and −COOH) react, they must lose a water molecule to form a new covalent bond (C−O or C−N).
Can condensation polymers be recycled?
Yes! Heat or chemical treatment can break ester/amide bonds by hydrolysis—adding water back—to recover monomers.
What is the most common polyester?
PET (polyethylene terephthalate), made from ethylene glycol + terephthalic acid. Used in plastic bottles and polyester fiber.
Is polyurethane a true condensation polymer?
Debated: it doesn't always release a small molecule during synthesis, but it forms from diols and diisocyanates in a condensation-like reaction.