Polyesters: types and formation - Higher
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Summary
Polyesters: types and formation
In a nutshell
Polyesters are formed when monomers with two different functional groups are joined together by the elimination of a small molecule such as water or hydrogen chloride. They are essentially a long chain of ester molecules.
Formation of a polyester
Polyesters can be made from dicarboxylic acid and diol monomers via a condensation polymerisation reaction. The monomers alternate along the chain. This is shown below.
Note: An ester has the functional group and they are formed from an alcohol and a carboxylic acid.
Addition vs. condensation polymerisation
| | Addition Polymerisation | condensation polymerisation |
| Monomers | One type | Condensation polymerisation can occur between two different monomers with different functional groups or one type of monomer with two different functional groups. |
| Products | One product formed which is the poly(alkene) | A polymer and a small molecule are produced |
| Functional groups | The monomer contains a group | Each monomer has two reactive functional groups |
Biological polymers
Biological polymers are examples of condensation polymers. Some of these are described below.
biological polymer | essential information |
| DNA | DNA stores genetic material and is made up of monomers called nucleotides. These are adenine (A), thymine (T), guanine (G) and cytosine (C). The nucleotides form polymers which then join together through hydrogen bonding to form a double helix structure. |
| Starch | Starch is how plants store their energy. It is a polymer of glucose. |
| Cellulose | Cellulose is the main component of plant cell walls and it is formed by a condensation reaction with glucose molecules. |
| Protein | Proteins are polypeptides. They are formed from monomers called amino acids that have joined together through condensation reactions. Different proteins will be formed from different amino acid sequences and they will all have different functions as a result. |
Proteins
Proteins are formed from amino acids. All amino acids have the same general structure. They each have a carboxyl group (-), an amino group (-) and a variable side group known as the R group.
Condensation reactions
Polypeptides are formed when amino acids join together via a peptide bond. This releases a molecule of water. The reverse is known as hydrolysis, which happens when a polypeptide is broken down and requires a molecule of water.
FAQs - Frequently Asked Questions
How are polyesters made?
Polyesters are formed when monomers with two different functional groups are joined together by the elimination of a small molecule such as water.
Which monomers are required for polyesters to form?
Polyesters can be made from dicarboxylic acid and diol monomers via a condensation polymerisation reaction.
What are proteins?
Proteins are polypeptides. They are formed from monomers called amino acids that have joined together through condensation reactions.