Which one of the following is NOT a copolymer?

We need to identify which polymer is not a copolymer among the given options. A copolymer is formed by polymerization of two or more different types of monomers, whereas a homopolymer is formed from only one type of monomer.

Option A: Neoprene is obtained by polymerization of chloroprene (2-chloro-1,3-butadiene) only:

$$nCH_2=CCl-CH=CH_2 \xrightarrow{polymerization} (-CH_2-CCl=CH-CH_2-)_n$$

Since it is formed from only one monomer (chloroprene), neoprene is a homopolymer, not a copolymer.

Option B: PHBV (Poly-$$\beta$$-hydroxybutyrate-co-$$\beta$$-hydroxyvalerate) is a copolymer of 3-hydroxybutyric acid and 3-hydroxypentanoic acid.

Option C: Buna-S is a copolymer of 1,3-butadiene and styrene.

Option D: Butadiene-styrene is the same as Buna-S—a copolymer of butadiene and styrene.

The correct answer is Option A: Neoprene.