ASTM D 1418 Designation: IIR

ASTM D 2000, SAE J200 Type / Class: AA, BA

STANDARD COLOR: Black

TRADE NAMES:
• Exxon Butyl® (Exxon Chemicals)
• Polysar® (Bayer Corp.)

RELATIVE COST: Medium

GENERAL TEMPERATURE RANGE: -50° to +250° F

An unsaturated copolymer of isobutylene and isoprene (thus the designation IIR), butyl rubber has two defining traits: (1) it is composed entirely of petroleum, limiting its usefulness around hydrocarbons (since “likes dissolve likes”); and (2) it offers excellent resistance to gas permeation, making it ideal for vacuum seals. Though ethylene propylene is now used rather than butyl for a number of applications, butyl is still used in some aircraft hydraulic systems. Butyl offers stronger resistance to sunlight and ozone than isoprene alone; presence of the saturated isobutylene in the polymer chain makes this possible (see Figure 32). Butyl also resists heat, chemicals, and abrasion.

IIR PERFORMS WELL IN:
• Hot water & steam (up to 250° F, 121° C)
• Phosphate ester type hydraulic fluids (e.g. Skydrol®, Fyrquel®, Pydraul®)
• Silicone fluids & greases

IIR DOES NOT PERFORM WELL IN:
• Mineral oil & grease
• Hydrocarbon oil & fuel