Tubeless automobile tyres are commonly manufactured from which rubber type formed by copolymerizing isobutylene with a small percentage of isoprene for vulcanization sites?

Introduction / Context:
Tubeless tyre technology relies on innerliner air-retention and chemical resistance. The choice of rubber strongly affects gas permeability, ageing, and road performance. Knowing which rubber underpins tubeless tyres is foundational in polymer engineering and automotive materials selection.

Given Data / Assumptions:

• Copolymer system: predominantly isobutylene with a minor fraction of isoprene.
• Key requirement: very low air permeability, good heat/oxidation resistance.
• Application: tyre innerliner and sometimes entire tubeless tyre components.

Concept / Approach:

Butyl rubber (IIR) is a copolymer of isobutylene with a small amount of isoprene. The isoprene introduces unsaturation sites for vulcanization, while the highly saturated backbone from isobutylene confers exceptionally low gas permeability, making it ideal for tubeless tyres and innerliners. Other rubbers either permeate gases faster or target different performance attributes (oil resistance, flame resistance, etc.).

Step-by-Step Solution:

Verification / Alternative check:

Standard tyre construction references specify butyl/IIR (and halobutyl variants) for innerliners due to superior air retention compared to SBR or natural rubber.

Why Other Options Are Wrong:

Nitrile (NBR): Oil/fuel resistant, not optimal for air impermeability. Silicone: Excellent thermal stability but high gas permeability. Neoprene: Polychloroprene; used in hoses, belts, not the low-permeability leader in tyres.

Common Pitfalls:

Assuming oil/fuel resistance (NBR) equals suitability for innerliners; overlooking gas permeability as the critical driver.

Final Answer:

Butyl rubber