Vulcanization urethane elastomers

Urethanes. Urethane elastomers are prepared by the reaction of an isocyanate molecule with a high molecular weight ester or ether molecule. The result is either an elastomeric mbber form or a liquid prepolymer that can be vulcanized with an amine or a hydroxyl molecule (see Urethane... 

Thanecure . [T E] Zinc chloride/ benzothiazyl disulfide vulcanization activator for sulfiir-curable millable urethane elastomers. 

Urethane elastomers suitable for peroxide vulcanization typically are prepared from a hydroxyl-group-terminated oligomeric adipate polyester and 4,4 -methylenediphenylisocyanate (MDI). A typical structural representation is as follows ... 

Peroxide Vulcanization of Urethane Elastomers. Urethane elastomers suitable for peroxide vulcanization are typically prepared from an hydroxyl-group-terminated oligo-... 

Peroxides are vulcanizing agents for elastomers, which contain no sites for attack by other types of vulcanizing agents. They are useful for ethylene-propylene rubber (EPR), ethylene-vinyl acetate copolymers (EAM), certain millable urethane rubbers, and silicone mbbers. They generally are not useful for vulcanizing butyl rubber (poly[isobutylene-co-isoprene]) because of a tendency toward chain scission, rather than crosslinking, when the polymer is subjected to the action of peroxide. 

Until relatively recently, aU elastomers were vulcanized. However, thermoplastic elastomers were first introduced in 1954 with the introduction of urethane thermoplastic elastomers. Thus, the two major types of elastomers are vulcanizable (conventional) and thermoplastic elastomers. The conventional elastomers are frequently broadly classified as natural and synthetic rubbers. 

The first major elastomer that could be processed without vulcanization was the urethanes. The TP polyurethanes (PURs) do not have quite the heat resistance and compression-set resistance of the TS PURs, but most of their other properties are the same. The abrasion resistance among the elastomers is outstanding, their low-temperature flex is good, PURs oil resistance is excellent at 82°C (180°F), and their load-bearing capability ranks them with the best of all the elastomers. Additives can improve their dimensional stability or heat resistance, reduce friction, or increase their flame retardancy, fungus resistance, or weatherability. 

Ex. 6 Multranil 176 polyurethane elastomer is dissolved at 20% by weight in a mixture of dry ethyl acetate and acetone, and 8.3 phr of Mondur TM (XII) (for natural and synthetic rubber adhesion) or 5 phr of Mondur CB-75 (XXIX) (for non rubber adhesion) is added. These combinations are versatile adhesives for bonding vulcanized rubber (natural and synthetic) to itself, leather, urethane, PVC, cork, wood, etc. Cure occurs at room temperature, and faster at elevated temperatures. At room temperature bond strengths (peel) are (imme-diate/after 3 days) rubber-to-rubber, 5.5—9.0/ 25 rubber-to-shoe sole leather, 5.5—7.3/24 shoe sole leather-to-shoe sole leather, 7.3—9.0/ 24 rubber-to-shoe sole leather, 9.5/24 Ib/in. width. 

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