Lesson 7　Isobutylene-Based
Elastomer (IIR)

New Words

Notes

[1] Sulfur-cured butyl rubber has relatively poor thermal stability, softening with prolonged exposure at temperatures above 150℃ because the low unsaturation prevents oxidative crosslinking. 硫黃硫化的丁基橡膠熱穩定性相對要差一些，若在超過150℃條件下長期使用會變軟，這是因為它的低不飽和結構阻止了氧化交聯。

[2] Curing with phenol-formaldehyde resins instead of sulfur, however, provides products with very high heat resistance, the property responsible for a large market in tire-curing bladders. 如果不用硫黃硫化，而用酚醛樹脂硫化，丁基橡膠制品會得到更好的耐熱性，這正是它能作為輪胎硫化膠囊而大范圍使用的重要原因。

[3] The molecular structure of the polyisobutylene chain provides less flexibility and greater delayed elastic response to deformation than most elastomers. 聚異戊二烯結構中的大分子結構使丁基橡膠的彈性降低，而且其滯后現象比大多數彈性體要嚴重。

Exercises

1. Translate the first and second paragraphs of the text into Chinese.

2. Put the following words into English.

陽離子溶液聚合　　丁基橡膠　　　飽和的　　　　溶脹　　　　輪胎硫化膠囊

氣密性　　　　　　極性的　　　　絕緣電纜

Halobutyl Rubbers

Halobutyl rubbers are produced by the controlled chlorination (chlorobutyl; CIIR) or bromination (bromobutyl; BIIR) of butyl rubber. Halogenation produces an allylic chlorine or bromine adjacent to the double bond of the isoprene unit. The halogenated butyl rubbers share many of the attributes of their butyl rubber parent: superior air impermeability, resistance to chemicals, moisture, and ozone, and vibration damping. The presence of halogen provides new crosslinking chemistry and the ability for adhesion to and vulcanization with general purpose, highly unsaturated elastomers. Bromobutyl is generally faster curing than chlorobutyl and somewhat more versatile in the curing systems that can be used to tailor product properties. Halobutyl rubbers typically use a zinc oxide-based cure, but bromobutyl can be vulcanized with peroxide or magnesium oxide as well.

The primary application for halobutyl rubber is in tires. The combination of low gas and moisture permeability, high heat and flex resistance, and ability to covulcanize with highly chemically unsaturated rubber has secured the use of these rubbers in the inner liners of tubeless tires. Passenger tires use chlorobutyl alone or in a blend with 20% to 40% natural rubber. High-service steel-belted truck tires use 100% bromobutyl inner liner compounds. Chlorobutyl is also used for truck inner tubes for its superior heat resistance compared to butyl rubber. Halobutyl rubbers are added to sidewall compounds for improved ozone and flex resistance, and to certain tread compounds for improved wet skid resistance and traction.

Halobutyl rubbers are also used in vibration damping mounts and pads, steam and automatic dishwasher hoses, chemical-resistant tank linings, and heat-resistant conveyor belts. They are also widely used in pharmaceutical closures because of their low gas and moisture permeability, resistance to aging and weathering, chemical and biological inertness, low extractables (with metal oxide cures), and good self-sealing and low fragmentation during needle penetration.

Words and Expressions