The intermolecular force of attraction refers to the force that holds the molecules of a substance together. It is responsible for the physical properties of the material, such as its strength, flexibility, and melting point. In the case of polymers, which are large molecules made up of repeating units, the intermolecular forces play a crucial role in determining their properties.

Among the given polymers - cellulose, poly(vinyl chloride) (PVC), nylon, and natural rubber - the one with the weakest intermolecular force of attraction is natural rubber.

Natural rubber is a polymer made from the monomer isoprene. It has a highly flexible and elastic structure due to the presence of many double bonds in its polymer chain. These double bonds give natural rubber its unique ability to stretch and return to its original shape. However, they also weaken the intermolecular forces between the polymer chains.

1. Intermolecular Forces in Cellulose:
Cellulose is a linear polymer made up of glucose units. It has a strong intermolecular force of attraction due to the presence of hydrogen bonds between the hydroxyl groups of adjacent polymer chains. These hydrogen bonds contribute to the high strength and rigidity of cellulose fibers.

2. Intermolecular Forces in Poly(vinyl chloride) (PVC):
PVC is a polymer made from the monomer vinyl chloride. It has a relatively weak intermolecular force of attraction due to van der Waals forces between the polymer chains. These forces are weaker than hydrogen bonds but still contribute to the overall strength and rigidity of PVC.

3. Intermolecular Forces in Nylon:
Nylon is a synthetic polymer made from the monomers adipic acid and hexamethylene diamine. It has a strong intermolecular force of attraction due to hydrogen bonding between the amide groups of adjacent polymer chains. This hydrogen bonding gives nylon its high strength and thermal stability.

4. Intermolecular Forces in Natural Rubber:
Natural rubber is a polymer made from the monomer isoprene. It has the weakest intermolecular force of attraction among the given polymers. The presence of double bonds in the polymer chain disrupts the formation of strong intermolecular forces such as hydrogen bonding. As a result, natural rubber exhibits high elasticity and flexibility.

In conclusion, among cellulose, poly(vinyl chloride), nylon, and natural rubber, the polymer with the weakest intermolecular force of attraction is natural rubber.