Among common plastics, which one is a true copolymer (composed of two different monomer species in the chain)?

Introduction / Context:
Copolymers combine properties of two monomers and are engineered for specific applications like tyres, impact modification, and adhesives. Distinguishing them from homopolymers helps predict behaviour under load, temperature, and chemical exposure.

Given Data / Assumptions:

• SBR is polymerised from styrene and butadiene.
• Polystyrene, PTFE, and polypropylene are homopolymers of styrene, tetrafluoroethylene, and propylene respectively.

Concept / Approach:
Only SBR fits the definition of a random (or controlled) copolymer in the list, delivering a balance of resilience and processability widely used in tyre treads and general rubber goods.

Step-by-Step Solution:
Identify number of monomers: SBR uses two; others use one.Therefore SBR is the copolymer.

Verification / Alternative check:
Polymer handbooks classify SBR as a key copolymer in elastomer technology.

Why Other Options Are Wrong:
PS, PTFE, PP are homopolymers.

Common Pitfalls:
Assuming blends (physical mixtures) are copolymers; chemical copolymerisation is different from blending.

Final Answer:
SBR (styrene-butadiene rubber)