Q.Explain the difference between Buna-N and Buna-S.

Both Buna-N and Buna-S are synthetic elastomers formed by copolymerisation of buta-1,3-diene ($CH_2=CH-CH=CH_2$) with a different second monomer, giving them different properties.

Buna-N: copolymer of buta-1,3-diene and acrylonitrile ($CH_2=CH-CN$).

The polar $-CN$ group gives Buna-N good resistance to petrol, oil and organic solvents, so it is used to make oil-seals, tank linings and fuel hoses.

Buna-S: copolymer of buta-1,3-diene and styrene ($C_6H_5-CH=CH_2$).

$n\,CH_2=CH-CH=CH_2 + n\,C_6H_5-CH=CH_2 \longrightarrow \text{Buna-S}$ …

Identify the common monomer (buta-1,3-diene) shared by both, then contrast the second comonomer (acrylonitrile vs styrene) and the resulting p …

• Forgetting that both share buta-1,3-diene as one monomer — treating them as unrelated rubbers. …