Chemistry – Organic chemistry - Polymers | e-Consult

Addition Polymerisation:

In addition polymerisation, small molecules called monomers combine to form a large chain called a polymer. This process typically involves unsaturated monomers, meaning they contain double or triple bonds. The double or triple bonds in the monomers are broken, and the monomers add to each other in a chain reaction. No atoms are lost in the process; only bonds are broken and formed. Therefore, the molar mass of the polymer is approximately the same as the average molar mass of the monomer. A common by-product is none.

Starting Materials: Unsaturated monomers (e.g., ethylene, propylene, vinyl chloride).

Products: Polymers with no repeating units of the original monomer (e.g., polyethylene, polypropylene, PVC).

By-products: None (ideally). However, impurities can sometimes lead to the formation of small amounts of other compounds.

Examples: Polyethylene (plastic bags), Polypropylene (containers), Polyvinyl Chloride (PVC - pipes).

Condensation Polymerisation:

In condensation polymerisation, monomers combine to form a polymer, and a small molecule, such as water, is removed as a by-product. This process typically involves monomers containing functional groups like carboxyl (-COOH) and amine (-NH2) groups. The monomers react with each other, and the removal of the small molecule (e.g., water) links them together to form the polymer chain. The molar mass of the polymer is less than the sum of the molar masses of the monomers because of the loss of the small molecule.

Starting Materials: Monomers with functional groups (e.g., amino acids, esters, carboxylic acids).

Products: Polymers with repeating units of the original monomer (e.g., nylon, polyester, protein).

By-products: Small molecules like water, methanol, or hydrochloric acid.

Examples: Nylon (clothing), Polyester (clothing, bottles), Protein (muscle, hair), Starch (energy storage in plants).

Here's a table summarizing the key differences: