Q.Define the term plasticizers.

Plasticizers

Plasticizers are additives blended into a polymer to increase its flexibility, softness and processability. Many useful polymers are rigid and brittle in the pure state because their long chains are held together by strong intermolecular (van der Waals) forces and can pack closely. A plasticizer is a small, relatively non-volatile molecule that inserts itself between the polymer chains, pushing them apart and reducing the intermolecular forces between them. This lowers the glass-transition temperature ($T_g$), lets the chains slide past one another more easily, and turns a hard material into a soft, pliable one.

The most familiar example is poly(vinyl chloride), PVC. Rigid, un-plasticized PVC is used for drainpipes and window frames; when a plasticizer such as di-octyl phthalate (DOP) or dibutyl phthalate is added, the same PVC becomes soft and is used for raincoats, cable insulation, garden hoses, artificial leather and flexible tubing. The more plasticizer added, the softer and more rubber-like the product. …