What is the significance of water in condensation polymerisation?

Water is significant in condensation polymerisation as it's often produced as a by-product during the reaction.

Condensation polymerisation is a type of polymerisation in which monomers or reactants, with two functional groups, react to form a polymer and a small molecule such as water, which is eliminated during the process. This is why water is significant in this type of reaction.

The process begins with the reaction between two different bi-functional or tri-functional monomer units. Each monomer has two reactive sites, which can bind to either end of another monomer. As the reaction proceeds, these monomers start to link up, losing small molecules in the process. The most common type of condensation polymerisation is the reaction between a dicarboxylic acid and a diol, which produces a polyester and water.

The water molecule is formed by the elimination of a hydrogen atom from one reactive site and a hydroxyl group from the other. This is why it's called 'condensation' polymerisation, as the reaction involves the condensation, or removal, of a water molecule.

The production of water also helps to drive the reaction to completion. In a closed system, the reaction would reach equilibrium, with both the forward (polymerisation) and reverse (depolymerisation) reactions occurring at the same rate. However, the continual removal of water, a product of the reaction, shifts the equilibrium towards the polymerisation direction according to Le Chatelier's principle. This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. Therefore, the production and removal of water is crucial in ensuring the reaction continues until the monomers are all used up.

In summary, water plays a pivotal role in condensation polymerisation, not only as a by-product but also as a driving force for the reaction to proceed.