(i) Plasticizers

A plasticizer is a material, generally gaseous or liquid, which is compatible with the polymer and can be absorbed into its interstices - the space around the polymer chains. Effectively, a solvent is a plasticizer, but generally with low permanence, i.e., a solvent is generally volatile and evaporates from the polymer fairly rapidly.  A plasticizer, therefore, may be considered as a solvent with low volatility.

Plasticizers, due to their compatibility with the polymer, are able to permeate into the free volume around the polymer chains. This interaction results in a few things.  First, it reduces the effects of secondary bonding forces which tend to keep the polymer “stuck” together. Secondly, it increases intermolecular distance which results in some swelling and increased free volume. Finally, as a result of the increased free volume and decreased secondary bonding forces, the plasticizer acts as a lubricant which enhances chain mobility - the polymer molecules are more easily able to move and slip past each other in response to an applied load.