Chemistry (Year 12) - Polymers, Proteins and Soaps
Polymers are big molecules, macromolecules that are made by linking up smaller repeating chemical units referred to as monomers. Monomers undergo polymerisation reactions to form polymers.
Addition Polymerisation is the joining of monomer units by breaking the carbon-to-carbon double bond in the monomer. It usually occurs between alkene monomers. For example, ethene:
Condensation Polymerisation is the joining of monomer units with reactive functional groups, releasing a small molecule like water or an alcohol in the process:
A condensation polymer can be broken up into its monomer units by splitting up the ester or amide linkages:
As the polymer chain length increases:
The number of electrons also increases. This means that there are more electrons available to form temporary dipoles. This increases the dispersion forces between the chains.
The melting point increases. This means that more energy is required to break these dispersion forces.
Polymers don’t just exist in a linear form; they can also undergo significant branching. Polymers tend to be both amorphous (irregular) and crystalline (regular) in structure. As the amorphous nature of the polymer increases:
There is a decrease in the crystallinity of the polymer.
There is a decrease in the strength of the intermolecular forces.
There is a decrease in the meltng point of the polymer.
Here are some common polymers and their corresponding monomers: