Buna-S is a homopolymer or copolymer.

Explanation

To determine whether Buna-S is a homopolymer or a copolymer, we can follow these steps:

### Step 1: Understand the Definitions
- **Homopolymer**: A polymer that is made from only one type of monomer. The repeating units in the polymer chain are identical.
- **Copolymers**: A polymer that is made from two or more different types of monomers. The repeating units in the polymer chain are different.

### Step 2: Identify the Monomers in Buna-S
Buna-S is synthesized from two different monomers:
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