Ethylene-Propene Elastomers

Copolymers and terpolymers of ethylene and propene, commonly known as EPM and EPDM polymers, respectively, are useful elastomers [Ver Strate, 1986], EPM and EPDM are acronyms for ethylene-propene monomers and ethylene-propene-diene monomers, respectively. The terpolymers contain up to about 4 mol% of a diene such as 5-ethylidene-2-norbomene, dicyclopentadiene, or 1,4-hexadiene. A wide range of products are available, containing 40-90 mol% ethylene. The diene, reacting through one of its double bonds, imparts a pendant double bond to the terpolymer for purposes of subsequent crosslinking (Sec. 9-2b). 

More than 800 million pounds of EPM and EPDM polymers were produced in the United States in 2001. Their volume ranks these materials fourth behind styrene-1,3-butadiene copolymers, poly( 1,4-butadiene), and butyl rubber as synthetic rubbers. EPM and EPDM polymers have good chemical resistance, especially toward ozone. They are very cost-effective products since physical properties are retained when blended with large amounts of fillers and oil. Applications include automobile radiator hose, weather stripping, and roofing membrane. 

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A comonomer for the synthesis of ethylene/propene elastomers - 2-ethylidene-norbomene (7) - is synthesised via a Diels-Alder cycloaddition of cyclopenta-diene and butadiene followed by an isomerization with titanium-based catalysts of the intermediate 2-vinyl derivative 6 in excellent yield (98 %) (eq. (12)) [22]. 

It is necessary for the dispersed rubbery substance to have a Tg value lower than the temperature at which the high-impact material is to be used. Many elastomers will satisfy this condition they are butyl rubber, polybutadiene, SBR, BAN, ethylene-propene elastomer, polychloroprene, EVA, polyisoprene, polyacrylates, PIB, and chlorinated polyethylene (CPE) elastomers. However, they are not all useful for specific blends such as PVC-based blends because they do not fulfill the other necessary properties. 

Homogeneous vanadium-based catalysts formed by the reaction of vanadium compounds and reducing agents such as organoaluminum compounds [10-12] are used industrially for the production of elastomers by ethylene/propene copolymerization (EP rubber) and ethylene/propene/diene terpolymerization (EPDM rubber). The dienes are usually derivatives of cyclopentadiene such as ethylidene norbomene or dicyclopentadiene. Examples of catalysts are Structures 1-4. Third components such as anisole or halocarbons are used to prevent a decrease in catalyst activity with time which is observed in the simple systems. 

During World War II a shortage of natural rubber in the United States prompted an intensive program to produce synthetic rubber. Most synthetic rubbers (called elastomers) are made from petroleum products such as ethylene, propene, and butadiene. For example, chloroprene molecules polymerize readily to form polychloroprene, commonly known as neoprene, which has properties that are comparable or even superior to those of natural rubber ... 

When comonomers are introduced, this destroys chemical regularity of chain units. It thereby reduces or even eliminates crystallinity, depending on the comonomer content. An illustration which is also important in applications is provided by ethylene copolymers. If propene is introduced into polyethylene, the level of crystallinity is reduced (therefore also diminishing its modulus and density). This is because it limits the possibilities for a crystalline structure to those sequences made up of (CH2)i units. A whole family of new compounds, called Low Density Linear PolyEthylenes (LDLPE), was developed during the 1980s. Ethylene/propene (50/50) copolymers form amorphous compounds which are used as elastomers (EPDM). 

Propylene oxide is produced from the chlorohydrination of propene similar to the process used to make ethylene oxide (see Ethene). A major use of propylene oxide involves hydrating propylene oxide to produces propylene glycol, propylene polyglycols, and other polyether polyols. These products are used to produce both rigid and flexible polyurethane foams, but they are also used to produce polyurethane elastomers, sealants, and adhesives. 

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