Condensation polymers
Quick Notes
- Condensation Polymerisation
- Polyesters: formed from dicarboxylic acids and diols
- Polyamides: formed from dicarboxylic acids and diamines, or from amino acids
- Water is eliminated during the reaction
- Hydrolysis of Polymers
- Polyesters:
- Acid hydrolysis: splits ester into acid and alcohol
- Base hydrolysis: forms carboxylate salt and alcohol
- Polyamides:
- Acid hydrolysis: splits amide into dicarboxylic acid and ammonium salt
- Base hydrolysis: forms dicarboxylate salt and diamine
- Polyesters:
Full Notes
In condensation polymerisation, two different monomers react to form a polymer and a small molecule (usually water or HCl).
Formation of Polyesters
Polyesters are polymers that have an ester link joining repeating units together. They can be formed by reacting diols with dicarboxylic acids or dioyl chlorides.
Diol + Dicarboxylic Acid or Dioyl Chloride
A diol (–OH group at both ends) reacts with a dicarboxylic acid (or dioyl chloride).
Each ester bond forms with loss of H2O (or HCl if using acyl chlorides).
Polyamides
Polyamides are polymers that have an amide link (–CONH–) joining repeating units together.
They can be made by reacting a diamine (–NH2) with a dicarboxylic acid (–COOH) or dioyl chloride (–COCl).
Diamine + Dicarboxylic Acid or Dioyl Chloride
Each end of the diamine and dicarboxylic acid reacts to form an amide link and water/HCl.
Hydrolysis of Polymers
Condensation polymers are broken apart in hydrolysis reactions.
A small molecule (usually water) is added back into the polymer to break up the repeating units.
Polyester Hydrolysis
Polyesters can be broken apart using hydrolysis, with the products formed based on the conditions (acidic or basic) used.
Acid hydrolysis:
Reacts with dilute HCl or H2SO4
Breaks ester bond and forms dicarboxylic acid and dialcohol
Base hydrolysis:
Reacts with NaOH
Forms carboxylate salt and alcohol
Polyamide Hydrolysis
Polyamides can also be broken apart using hydrolysis, and again the products formed based on the conditions (acidic or basic) used.
Acid hydrolysis:
Reacts with HCl
Breaks amide bond and forms dicarboxylic acid and ammonium salt
Base hydrolysis:
Reacts with NaOH
Forms dicarboxylate salt and diamine
Summary Table
| Polymer | Link broken | Conditions | Products |
|---|---|---|---|
| Polyester | –COO– (ester) | Acid (dilute HCl/H2SO4) | Dicarboxylic acid + dialcohol |
| Polyester | –COO– (ester) | Base (NaOH) | Carboxylate salt + alcohol |
| Polyamide | –CONH– (amide) | Acid (HCl) | Dicarboxylic acid + ammonium salt |
| Polyamide | –CONH– (amide) | Base (NaOH) | Dicarboxylate salt + diamine |
Polymer Identification
You should make sure you are able to:
- Deduce the repeat unit of a polymer given its monomer(s)
- Identify bonds formed (e.g., –COO– for esters, –CONH– for amides)
- Identify monomers from a section of a polymer
- Break the polymer at ester or amide linkages
- Add OH to acid ends and H to amine/alcohol ends
- Identify type of polymerisation:
- Addition: monomer has a C=C double bond, polymer has only C–C bonds
- Condensation: involves two functional groups reacting and eliminates small molecule (e.g. H2O)
Summary
- Condensation polymers form when monomers join with loss of a small molecule such as water or HCl.
- Polyesters come from diols and dicarboxylic acids or dioyl chlorides and contain ester links.
- Polyamides come from diamines and dicarboxylic acids or dioyl chlorides and contain amide links.
- Acid and base hydrolysis break polyesters and polyamides into predictable products.
- Identify polymers by their linkages, repeat units and by reversing the linkage to find monomers.