Which of the following polymers does not involve cross-linkages ?

Options

A. Vulcanised rubber
B. Bakelite
C. Melamine
D. Teflon

Explanation

To determine which of the following polymers does not involve cross-linkages, we will analyze each option provided:

1. **Vulcanized Rubber**:
- Vulcanized rubber is derived from natural rubber, which is a polymer of isoprene.
- During the vulcanization process, sulfur is added to create cross-linkages between the polymer chains, enhancing its strength and elasticity.
- Therefore, vulcanized rubber **does involve cross-linkages**.

2. **Bakelite**:
- Bakelite is a thermosetting polymer formed from the polymerization of phenol and formaldehyde.
- It is characterized by its strong cross-linking structure, which makes it heat resistant and durable.
- Hence, Bakelite **also involves cross-linkages**.

3. **Melamine**:
- Melamine is another thermosetting polymer formed from melamine and formaldehyde.
- Similar to Bakelite, it has a highly cross-linked structure that provides heat resistance and strength.
- Consequently, melamine **does involve cross-linkages**.

4. **Teflon**:
- Teflon, or polytetrafluoroethylene (PTFE), is formed from the polymerization of tetrafluoroethylene (CF2=CF2).
- It is an addition polymer and does not have cross-linkages in its structure.
- Therefore, Teflon **does not involve cross-linkages**.

Based on the analysis above, the polymer that does not involve cross-linkages is **Teflon**.

### Final Answer:
**Teflon**