Amides and polymers

Amides

Amides are made from acyl chlorides: CH3COCl + NH3 -> CH3CONH2 + HCl (ethanamide). With a primary amine an N-substituted amide forms: CH3COCl + CH3NH2 -> CH3CONHCH3 + HCl (N-methylethanamide).

Condensation polymers (spec 19.8)

Monomers with two functional groups join, losing a small molecule at each link.

• Polyesters: diol + dicarboxylic acid, losing H2O (Terylene).
• Polyamides: diamine + dicarboxylic acid (losing H2O) or diacyl dichloride (losing HCl). Nylon-6,6 from hexane-1,6-diamine, H2N(CH2)6NH2, and hexanedioic acid, HOOC(CH2)4COOH. Repeat unit: -NH(CH2)6NHCO(CH2)4CO-.
• Proteins: polyamides made from amino acids, joined by peptide (amide) links.

To draw a repeat unit, join the monomers through the link and remove the small molecule; to find monomers, break the ester or amide link and add back H2O.

Addition polymers with polar groups

• Poly(propenamide) from propenamide, CH2=CHCONH2; repeat unit -CH2-CH(CONH2)-. The amide groups hydrogen bond with water, so it absorbs water.
• Poly(ethenol), repeat unit -CH2-CH(OH)-, is soluble in water because its many -OH groups hydrogen bond with water. It is used for soluble laundry bags and detergent capsules.

Polyamides are strong, with high melting points, because hydrogen bonds form between N-H and C=O groups on neighbouring chains. Polyamides and polyesters can be hydrolysed, unlike poly(alkenes).

Worked example

Draw the repeat unit of the polymer from hexane-1,6-diamine and hexanedioyl dichloride, and name the small molecule lost.

1. Each amine N bonds to an acyl carbon, losing HCl.
2. Repeat unit: -NH-(CH2)6-NH-CO-(CH2)4-CO-

Answer: Nylon-6,6; HCl is lost at each link

Check yourself

1. What is the name of CH3CH2CONH2?
   • Propylamine
   • Ethanamide
   • Propanenitrile
   • Propanamide
   Show answer

   Propanamide. Three carbons including the C=O carbon, with -CONH2.

2. Which pair of monomers forms nylon-6,6?
   • Ethane-1,2-diol and benzene-1,4-dicarboxylic acid
   • Hexane-1,6-diamine and hexanedioic acid
   • Propenamide and ethene
   • Glycine and alanine
   Show answer

   Hexane-1,6-diamine and hexanedioic acid. Six carbons in each monomer give the name 6,6.

3. Which small molecule is eliminated when a diamine reacts with a diacyl dichloride to form a polyamide?
   • H2O
   • NH3
   • CO2
   • HCl
   Show answer

   HCl. The acyl chloride loses Cl and the amine loses H.

4. Why is poly(ethenol) soluble in water?
   • Its many -OH groups form hydrogen bonds with water molecules
   • It is ionic
   • It is hydrolysed instantly
   • It has only London forces
   Show answer

   Its many -OH groups form hydrogen bonds with water molecules. Hydrogen bonding between polymer and water.

5. Why do polyamide chains attract each other strongly?
   • The chains are covalently cross-linked
   • They contain ionic bonds
   • Hydrogen bonds form between N-H groups on one chain and C=O groups on another
   • They have no polar groups
   Show answer

   Hydrogen bonds form between N-H groups on one chain and C=O groups on another. Interchain hydrogen bonds give strength and high melting points.

6. What is the repeat unit of poly(propenamide)?
   • -CH2-CH(CONH2)-
   • -CH2-CH(NH2)-
   • -NH-CH2-CO-
   • -CH2-CH(OH)-
   Show answer

   -CH2-CH(CONH2)-. Addition polymer: the C=C opens and CONH2 is the side group.

7. How many carbon atoms are in one repeat unit of nylon-6,6?
   Show answer

   12. Six from the diamine plus six from the diacid.

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Sources

• Pearson Edexcel IAL Chemistry (2018) specification
• Pearson Edexcel IAL Chemistry (2018) scheme of work

Last updated 7 November 2026. Spotted a mistake? Tell us.