Which one of the following statements is not true ?

Options

A. Buna-S is a copolymer of butadiene and styrene
B. Natural rubber is a 1, 4-polymer of isoprene
C. In vulcanization, the formation of sulphur bridges between different chains make rubber harder and stronger
D. Natural rubber has the trans-configuration at every double bond

Explanation

To solve the question, we need to evaluate each of the provided statements about polymers and rubber. We will analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: Buna-S is a copolymer of butadiene and styrene.**
- Buna-S, also known as styrene-butadiene rubber (SBR), is indeed a copolymer made from the monomers butadiene and styrene. This statement is true.

2. **Option B: Natural rubber is a 1,4 polymer of isoprene.**
- Natural rubber is derived from the polymerization of isoprene (2-methyl-1,3-butadiene) and is primarily in the 1,4 configuration. This statement is true.

3. **Option C: In vulcanization, the formation of sulfur bridges between different chains makes rubber harder and stronger.**
- Vulcanization is a chemical process that involves the addition of sulfur to rubber, creating cross-links (bridges) between polymer chains. This process enhances the strength and durability of rubber. This statement is true.

4. **Option D: Natural rubber has the trans configuration at every double bond.**
- This statement is incorrect. Natural rubber is primarily composed of cis-polyisoprene, where the double bonds have a cis configuration, not trans. Therefore, this statement is not true.

### Conclusion:
The statement that is not true is **Option D: Natural rubber has the trans configuration at every double bond.**

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