Condensation polymers
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Summary
Condensation polymers
In a nutshell
Polyesters and polyamides are example of condensation polymers. They are strong due to their polar bonds. The polymers are represented using repeat units and can be determined by the monomers. Condensation polymers contain ester and/or amide links.
Condensation polymerisation
Condensation polymerisation occurs when monomers with two different functional groups are joined together by the elimination of a small molecule such as water or hydrogen chloride.
Example
Examples of condensation polymers are polyesters, polyamides, polypeptides and proteins.
Polyesters
Polyesters are formed by reacting together a hydroxyl and a carboxyl, giving rise to an ester link. Polyesters are essentially a long chain of ester molecules.
Example
Polyamides
Polyamides are formed by reacting together an amine and a carboxyl group together, giving rise to an amide link. Polyamides are essentially a long chain of amide molecules.
Example
Polypeptides and proteins
Amino acids contain both an amine and a carboxyl group. Polypeptides and proteins are formed by reacting amino acids together, giving rise to an amide link. The amide links in polypeptides and proteins are called peptide links. Proteins are the assembly of two or more polypeptides.
Repeat unit
Since polymers are (very) large molecules they are represented using repeat units in the displayed formula.
To draw a repeat unit:
PROCEDURE
| 1. | Draw the monomers near each other. |
| 2. | Draw brackets around the two monomers. |
| 3. | Remove the of the carboxyl group(s). |
| 4. | Remove one atom from the amine group(s) or the alcohol group(s). |
| 5. | If it's a polyester, join the carbon (of the carbonyl group) and the oxygen (initially part of a hydroxyl group) next each other. If it's a polyamide or polypeptide, join the carbon (of the carbonyl group) and the nitrogen (of the amine) near each other. |
| 6. | Extend the bonds at the ends of the repeat unit. Ensure they extend outside the brackets as it indicates that the chain is longer. |
| 7. | Add a subscript 'n' on the bottom right hand corner. This indicates a large number of repeat units. |
Example
Identifying the monomer
The monomers can be identified from the repeat unit.
PROCEDURE
| 1. | Find the ester/amide link in the repeat unit. |
| 2. | Break the bond of the ester/amide link. |
| 3. | Add to any carbon atoms at the end of the molecule. This will reform your carboxyl group. |
| 4. | Add a to any nitrogen or oxygen atoms at the end of the molecule. This will give you your amine or alcohol group. |
Example
The monomers for the polyamide shown to the left are -diamonopropane and heptane--dicarboxylic acid.
Condensation polymers are strong
Condensation polymers tend to be strong. This is due to the polar bonds in these polymers which give rise to hydrogen bonding and permanent dipole-dipole interactions, on top of the van der Waals forces.
Complex condensation polymers
Molecules with both an amine and an alcohol group can react with dicarboxylic acids. The polymers formed will contain amide and ester links.
Example
Molecules containing both a carboxyl group and an amine/alcohol group can undergo polymerisation with itself i.e. only one type of monomer is required for polymerisation, as the monomer contains the desired reactive functional groups.
Example
FAQs - Frequently Asked Questions
What are peptide links?
The amide links in polypeptides and proteins are called peptide links.
How are polyamides formed?
Polyamides are formed by reacting together an amine and a carboxyl group together.
What are examples of condensation polymers?
Examples of condensation polymers are polyesters, polyamides, polypeptides and proteins.