In addition polymerization, the molecules of the same or different monomers simply add on to one another leading to the formation of a macromolecules without elimination of small molecules like \(\mathrm{H}_2 \mathrm{O}, \mathrm{NH}_3\) etc. Addition polymerization generally occurs among molecules containing double and triple bonds. For example, formation of polythene from ethene and neoprene from chloroprene, etc.
In condensation polymerisation, two or more bifunctional trifunctional molecules undergo a series of independent condensation reactions usually with the elimination of simple molecules like water, alcohol, ammonia, carbon dioxide and hydrogen chloride to form a macromolecule. For example, nylon-6, 6 is a condensation polymer of hexamethylenediamine and adipic acid formed by elimination of water molecules.