Natural rubber chemistry: the main constituent (polymer backbone) of natural rubber is which polymer?

Introduction / Context:
Natural rubber, harvested as latex from Hevea brasiliensis, is a cornerstone elastomer in tyres and engineering goods. Identifying its chemical backbone is essential in understanding its properties and cure behaviour.

Given Data / Assumptions:

• We focus on the repeat unit of natural rubber.
• Isomers and microstructure (cis vs trans) matter for properties.
• Compare with common synthetic elastomers.

Concept / Approach:
Natural rubber is predominantly cis-1,4-polyisoprene. This cis configuration yields high extensibility, resilience, and strain crystallisation, contributing to strength in tyres. Polybutadiene is a synthetic diene rubber; polychloroprene is neoprene (synthetic); polystyrene is a rigid thermoplastic—none match natural rubber’s composition.

Step-by-Step Solution:
Identify “natural rubber” → latex polymer.Recall: backbone = cis-1,4-polyisoprene.Eliminate alternative elastomers and thermoplastics.

Verification / Alternative check:
Rubber handbooks specify natural rubber as cis-1,4-polyisoprene with minor non-rubber constituents (proteins, lipids, inorganic).

Why Other Options Are Wrong:
Polybutadiene: different monomer, synthetic.Polychloroprene: chlorinated diene (neoprene), synthetic.Polystyrene: unrelated thermoplastic.

Common Pitfalls:
Confusing “rubber-like” behaviour with identical chemistry; several elastomers share properties but differ in monomer.

Final Answer:
Polyisoprene (cis-1,4-)