There are many ways to classify hot melt adhesives. One method is by their formulation capability. In this classification scheme hot melt adhesives are divided into two classes:
1. Those that depend on formulation with modifiers or additives for their performance and
2. Those whose performance depends primarily on the molecular design of the molecules.
In this latter class, performance does not come necessarily from formulation additives, but rather from the choice of monomers used to make the base polymer (although conventional formulations ingredients can also be used). These are sometimes referred to as"synthetically" designed hot melt adhesives.
There are two main types of synthetically designed adhesives: polyamides and polyesters. Polyamides have been used as hot melt adhesives since around 1950, and polyesters came on the scene about a decade later. A common feature of these adhesives is that they are condensation polymers formed by the reaction of two chemical species, often with the elimination of a simple by-product.