Classify polymers based on their intermolecular forces and structure:
- Fibres (Nylon, Polyester): Strong H-bonds or dipole-dipole forces, crystalline nature.
- Elastomers (Rubbers): Weak van der Waals forces, coiled chains, elastic.
- Thermoplastics (PVC, Polythene): Intermediate forces, linear chains, soften on heating.
- Thermosetting (Bakelite, Urea-formaldehyde): Extensive cross-linking on heating, become hard and infusible.
Let's identify each polymer structure and match it to its type.
Structure I: $(-\text{CH}_2-\text{CH(Cl)}-)_n$
This is the repeating unit of Polyvinyl chloride (PVC). PVC is a classic example of a thermoplastic polymer. It softens on heating and can be remolded.
So, D $\rightarrow$ I.
Structure II: $[-\text{NH}-(\text{CH}_2)_6-\text{NH}-\text{CO}-(\text{CH}_2)_4-\text{CO}-]_n$
This is the structure of Nylon 6,6. Nylons are polyamides characterized by strong intermolecular forces (hydrogen bonds), which lead to close packing of chains. This makes them strong and crystalline, a characteristic of fibres.
So, A $\rightarrow$ II.
Structure III: $[-\text{CH}_2-\text{C(Cl)}=\text{CH}-\text{CH}_2-]_n$
This is the structure of Neoprene (polychloroprene), a synthetic rubber. Rubbers are characterized by weak intermolecular forces and coiled polymer chains, allowing them to stretch and return to their original shape. They are elastomers.
So, B $\rightarrow$ III.
Structure IV: The image shows a highly cross-linked structure derived from urea and formaldehyde. The repeating unit $(-\text{NH}-\text{CO}-\text{NH}-\text{CH}_2-)_n$ is that of Urea-formaldehyde resin. This resin forms an extensive 3D network of covalent bonds upon heating, which sets into a hard, infusible solid. It cannot be remolded. This is the definition of a thermosetting polymer.
So, C $\rightarrow$ IV.
Matching the pairs:
A $\rightarrow$ II
B $\rightarrow$ III
C $\rightarrow$ IV
D $\rightarrow$ I
This corresponds to option (B).
