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Send EmailButyl Rubber, Isobutylene Isoprene Rubber, IIR, 9010-85-9
Butyl Rubber (IIR)
1. Chemical Structure & Production
Definition: Butyl rubber (IIR) is a synthetic elastomer produced by cationic copolymerization of isobutylene (~98%) and a small amount of isoprene (~2%). Isoprene introduces a limited number of double bonds into the polymer chain, enabling vulcanization (crosslinking) with sulfur or other agents.
Correct Chemical Formula:
−[CH₂–C(CH₃)₂]ₘ−[CH₂–C(CH₃)=CH–CH₂]ₙ−
Poly(isobutylene‑co‑isoprene). Note: isoprene is C₅H₈, not C₄H₈.
CAS Number: 9010-85-9 (correct).
Distinction from Polyisobutylene (PIB): PIB is fully saturated (no isoprene) and cannot be vulcanized. Butyl rubber contains isoprene for crosslinking.
2. Physical & Chemical Properties (Detailed)
| Property | Typical Value / Behavior | Remarks & Corrections |
|---|---|---|
| Appearance | Solid (high MW) or viscous liquid (low MW) | Correct |
| Density | 0.91–0.93 g/cm³ | ~0.92 g/cm³ |
| Service temperature range | –50°C to +120°C | T_g ≈ –65°C; above 120°C degrades rapidly |
| Solubility | Soluble in aliphatic/aromatic hydrocarbons (hexane, toluene, gasoline); insoluble in oils, alcohols, acetone, water | Correction: “Soluble in oils” is wrong. Butyl rubber swells in oils but does not dissolve; its oil resistance is poor. |
| Gas permeability | Extremely low (≈1/10 of natural rubber) | Key property: Outstanding air, O₂, N₂ barrier |
| Abrasion resistance | Moderate to low | Correction: Not “excellent”. Inferior to NR and SBR – reason butyl is used in inner liners, not treads |
| Weathering & ozone resistance | Excellent | Far better than natural rubber |
| Flame behavior | Combustible; incompatible with strong oxidizers | Correct |
3. Alternative Names & Clarifications
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IIR – Isobutylene Isoprene Rubber (standard abbreviation)
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Halogenated butyl rubber – Bromobutyl (BIIR) or Chlorobutyl (CIIR) – faster vulcanization, better adhesion to other elastomers.
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Polyisobutylene (PIB) – different material (no unsaturation), used in adhesives, sealants, grease thickeners.
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“Synthetic rubber” – overly broad term; butyl is one specific type.
4. Detailed Applications
| Industry | Application | Reason / Mechanism |
|---|---|---|
| Automotive | Inner tubes, tire inner liners (halogenated butyl) | Extremely low gas permeability maintains tire pressure |
| Pharmaceutical | Stoppers for vials, syringe plungers, dropper bulbs | High purity, low toxicity, autoclavable, chemical resistance |
| Industrial | Chemical hoses, vacuum seals, vibration dampers | High damping coefficient, ozone resistance |
| Construction | Roofing membranes, waterproofing tapes, window seals | UV & weather resistance, low water vapor permeability |
| Adhesives & Sealants | Pressure-sensitive adhesives (PSA), HVAC sealing tapes | Tackiness, flexibility, permanent plasticity (often PIB-based) |
Additional uses: Chewing gum base (low MW PIB), neutron shielding (high hydrogen content), explosive binders.
5. Advantages & Limitations
| Advantages | Limitations |
|---|---|
| Lowest gas permeability of any rubber | Poor oil, fuel, and solvent resistance (swelling) |
| Excellent ozone, UV, and chemical resistance | Low abrasion resistance |
| Wide temperature range (–50 to +120°C) | Slow vulcanization (halogenated types improve this) |
| High damping (vibration & sound absorption) | Higher cost than NR or SBR |
| Low toxicity (medical grade) | Poor adhesion to other elastomers unless halogenated |
6. Safety & Handling
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Fire hazard: Combustible; dense black smoke. Use water spray, CO₂, or dry chemical.
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Incompatibility: Strong oxidizers (nitric acid, peroxides), concentrated chlorine/fluorine.
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Thermal decomposition: Above 200°C releases isobutylene monomer and toxic gases (CO, hydrocarbons).
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Health: Solid form is inert. Avoid inhalation of dust or fumes (respiratory irritation).
Summary
Butyl rubber’s unique combination of extremely low gas permeability, high damping, and excellent weather/ozone resistance makes it irreplaceable for tire inner liners, pharmaceutical stoppers, and vibration isolators. However, its poor oil resistance and low abrasion resistance limit its use in dynamic or oil-contact applications. Halogenated versions (bromobutyl, chlorobutyl) overcome some of these drawbacks.
