Copolymer identification: in a copolymer, the repeating chain contains two different monomer units. Which of the following is a copolymer used widely in tyres?

Introduction / Context:
Classifying polymers as homopolymers or copolymers is foundational to predicting performance. Copolymers combine two (or more) different monomers to tailor elasticity, glass transition temperature, strength, and chemical resistance. The tyre industry especially relies on specific copolymers for abrasion resistance and grip.

Given Data / Assumptions:

• Buna-S is styrene-butadiene rubber, commonly called SBR.
• PTFE is polytetrafluoroethylene from tetrafluoroethylene (one monomer).
• PMMA is polymethyl methacrylate from methyl methacrylate (one monomer).
• Polycaprolactam is nylon-6 from caprolactam (ring-opening of one monomer).

Concept / Approach:
Copolymer definition: polymer chains built from at least two distinct monomer species. SBR fits precisely: chains incorporate styrene units and butadiene units, giving a rubber with improved processability and balanced properties for treads and general-purpose elastomer uses.

Step-by-Step Solution:
Evaluate each choice: identify number of monomers.Recognise SBR (Buna-S) = styrene + butadiene → copolymer.Eliminate PTFE, PMMA, and nylon-6 as homopolymer/ring-opening cases.

Verification / Alternative check:
Materials references list SBR as the predominant tyre copolymer blended with natural rubber and other additives for performance.

Why Other Options Are Wrong:
PTFE, PMMA, Nylon-6: each derived from a single monomer → not copolymers.

Common Pitfalls:
Assuming “nylon” implies two monomers; nylon-6 forms from one lactam via ring opening, not a diacid/diamine pair like nylon-6,6.

Final Answer:
Buna-S