Styrene–butadiene rubber (SBR) made by emulsion polymerization maintains approximately what weight ratio of styrene to butadiene for general-purpose tyre applications?

Introduction / Context:
SBR is the workhorse synthetic rubber in tyres and many general applications. Its properties depend on the styrene:butadiene ratio (S:B) and polymerization technique (hot vs. cold emulsion), influencing glass transition, abrasion, and dynamic behavior.

Given Data / Assumptions:

• Emulsion polymerization route (hot or cold), typical for SBR production.
• General-purpose grade used widely in tyres.
• Need to recall the conventional S:B ratio by weight for balanced properties.

Concept / Approach:

Conventional general-purpose SBRs commonly use about 23–25% styrene and 75–77% butadiene by weight, giving a nominal weight ratio S:B close to 1:3. This balance provides abrasion resistance, good processability, and suitable viscoelastic response for tyre treads and other applications.

Step-by-Step Solution:

Verification / Alternative check:

Polymer datasheets and handbooks list SBR 1500-series formulations around 23.5% styrene (≈1:3 S:B by weight), confirming the canonical ratio.

Why Other Options Are Wrong:

3:1, 2:1, 1:2: These imply far higher styrene content, stiffening the rubber excessively and deviating from standard tyre-grade SBR proportions.

Common Pitfalls:

Confusing block copolymers or impact modifiers (higher styrene) with elastomeric SBR ratios; mixing up weight and mole ratios.

Final Answer:

1:3