Why is neoprene relatively non-inflammable compared to many hydrocarbon rubbers?

Introduction / Context:
Neoprene (polychloroprene) is a synthetic rubber valued for oil resistance, weathering, and relatively low flammability. Understanding the chemical reason for its flame resistance is helpful in materials selection for hoses, belts, and gaskets in demanding environments.

Given Data / Assumptions:

• Neoprene is derived from chloroprene monomer (2-chloro-1,3-butadiene).
• Comparison is with hydrocarbon rubbers lacking halogens.
• No special flame retardants are assumed beyond inherent chemistry.

Concept / Approach:
Halogens (e.g., chlorine) in polymer chains inhibit flame propagation by releasing HCl and interfering with radical chain reactions in the flame zone. This lowers heat release and slows combustion compared to purely hydrocarbon backbones.

Step-by-Step Solution:
Identify neoprene structure: polymer of a chlorinated diene.Relate halogen content to flame inhibition mechanisms.Conclude that chlorine presence reduces flammability.

Verification / Alternative check:
Halogenated polymers like PVC and neoprene exhibit higher limiting oxygen index (LOI) values than comparable hydrocarbon polymers, corroborating reduced flammability.

Why Other Options Are Wrong:
Cross-link density affects softening and char but is not the primary reason for inherent flame resistance.Linear structure does not inherently reduce flammability.Absence of chlorine is the opposite of the correct reasoning.Fillers may influence fire behavior but are not the intrinsic cause.

Common Pitfalls:
Confusing vulcanisation effects with chemistry of the backbone; assuming any cross-linked rubber is non-flammable.

Final Answer:
Because chlorine atoms in the monomer reduce flammability