Weakest Intermolecular Force of Attraction Among Polymers

To determine the polymer with the weakest intermolecular forces of attraction, we classify the given polymers based on the nature of their intermolecular forces:

1. Elastomers: In elastomers, the polymer chains are held together by the weakest intermolecular forces (primarily weak van der Waals forces). This allows the polymer to stretch under stress and return to its original shape.

   • Natural rubber (cis-1,4-polyisoprene) is an elastomer and possesses the weakest intermolecular forces among the given choices.

2. Thermoplastics: These polymers have intermediate intermolecular forces that are stronger than those in elastomers but weaker than those in fibres.

   • Poly(vinyl chloride) (PVC) has polar $\text{C}-\text{Cl}$ bonds, leading to moderate dipole-dipole attractions between the chains.

3. Fibres: These polymers possess strong intermolecular forces such as hydrogen bonding or strong dipole-dipole interactions, which give them high tensile strength and crystalline structure.

   • Nylon (e.g., Nylon-6,6) is a polyamide containing strong intermolecular hydrogen bonding between the carbonyl oxygen and the amide hydrogen ($>\text{C}=\text{O}\cdots\text{H}-\text{N}<$).
   • Cellulose is a polysaccharide containing numerous $-\text{OH}$ groups that form extensive networks of strong intermolecular hydrogen bonds.

Comparing the relative strength of intermolecular forces:
$\text{Natural rubber (Elastomer)} < \text{Poly(vinyl chloride) (Thermoplastic)} < \text{Nylon, Cellulose (Fibres)}$

Hence, the intermolecular force of attraction is the weakest in natural rubber.

Correct Answer: D