Hot SBR vs. cold SBR (styrene–butadiene rubber): identify the incorrect statement about process and properties.

Introduction / Context:
SBR can be produced by emulsion polymerisation at ~50 °C (hot SBR) or ~5 °C (cold SBR). Changes in temperature, surfactant, and initiator systems alter microstructure, branching, and molecular weight distribution, which affects performance (e.g., abrasion, tensile, resilience).

Given Data / Assumptions:

• Cold SBR: low-temperature emulsion, better wear and tensile properties.
• Hot SBR: higher temperature, more branching, different distribution.
• Emulsion pressure differences are not the defining distinction between hot and cold SBR.

Concept / Approach:
The key distinction is polymerisation temperature and recipe, not pressure. Properties indeed vary with temperature; cold SBR often exhibits improved mechanicals and lower gel. Statements tying superiority to lower pressure are misleading or incorrect because pressure conditions are comparable and not the root cause of property differences.

Step-by-Step Solution:
Validate (a): widely taught—cold SBR generally superior → correct.Validate (b): temperature strongly influences kinetics and microstructure → correct.Check (c): assertion about lower pressure is not a defining or generally correct statement → incorrect.

Verification / Alternative check:
Textbook summaries attribute improved properties to lower temperature and recipe, not to lower operating pressure.

Why Other Options Are Wrong:
(a) and (b) are valid; 'None of these' cannot be correct because (c) is wrong.

Common Pitfalls:
Overemphasising reactor pressure in emulsion SBR; mixing up cold SBR with solution SBR processes.

Final Answer:
Cold SBR production employs lower pressure than hot SBR.