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.

Chemistry; Separate chemistry 2; KS4 Year 10; Polyesters: types and formation - Higher

Note: An ester has the functional group $-COO-$ 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 $C=C$ 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 (- $COOH$ ), an amino group (- $NH_2$ ) and a variable side group known as the R group.

Chemistry; Separate chemistry 2; KS4 Year 10; Polyesters: types and formation - Higher — 1. Amino group, 2. R group, 3. Carboxyl 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.

Chemistry; Separate chemistry 2; KS4 Year 10; Polyesters: types and formation - Higher — 1 and 2. Amino acids, 3. Dipeptide, 4. Forward condensation reaction, 5. Backwards hydrolysis reaction, 6. Release of a water molecule, 7. Peptide bond