Important Elastomers

We will finish this chapter with the following sections that give many of the details for elastomers including chemical structure, manufacturing process, some properties, and main uses. Some familiarity with these elastomers is essential. 

Radial tires, favoring natural rubber, gave good growth since 1980. Will slow now that radial tires no longer increasing No production in U.S. 

2- and 1,4-Butadiene units mixed Properties, see Table 18.2 Uses 

Tires and tire products, including tread rubber, 77% mechanical goods, 15% automotive, 5% miscellaneous, 3% 

Change to radial tires, favoring natural rubber, now complete Replacement automotive parts a growing use 1990-2000 Annual change of 1.0% 

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Elastomers. Elastomers are polymers or copolymers of hydrocarbons (see Elastomers, synthetic Rubber, natural). Natural mbber is essentially polyisoprene, whereas the most common synthetic mbber is a styrene—butadiene copolymer. Moreover, nearly all synthetic mbber is reinforced with carbon black, itself produced by partial oxidation of heavy hydrocarbons. Table 10 gives U.S. elastomer production for 1991. The two most important elastomers, styrene—butadiene mbber (qv) and polybutadiene mbber, are used primarily in automobile tires. 

Polysiloxanes (silicons) form another group of important elastomers. Again, processing typically does not involve either carbon black or sulfur. 

This table contains only a selection of the most important elastomers. Their structure is shown in the unvuloanized state. 

Elastomers are elastic materials that stretch to high extensions and rapidly recover their original dimensions once the applied stress is released. They are formed by a loose network. Styrene-butadiene rubber (SBR) and ethylene-propylene-diene monomer (EPDM) are examples of important elastomers. 

It was my privilege to know Paul when he was at Cincinnati and I was at Akron. I envied his university association and was surprised when he left Cincinnati to join Standard Oil at Linden, NJ in 1940. Our paths crossed again when I served as a consultant for Rubber Reserve Corp. on the butyl rubber program. However, to my knowledge, Paul did not attempt to correct tlie difficulties experienced by Standard Oil when its attempts to produce this elastomer at Baton Rouge, LA were unsuccessful. Of course, it is a pleasure for me to report that Dr. John Durland and I were able to solve the production problem and make possible the commercial products of this important elastomer. 

Ethylene/propylene copolymerization is of significant commercial importance. Elastomers formed from random ethylene/propylene copolymers (EP) possess a number of valuable properties including a high plateau modulus ( 1.6 MPa), which permits a higher filler loading and more cost-effective compounding. Furthermore, of the major hydrocarbon-based rubbers, EP is by far the least reactive with oxygen and ozone. 

Copolymerization has practical utility for changing the properties of a homopolymer in a desired direction. A number of commercially-important elastomers are copolymers. Butyl rubber is a copolymer of isobutylene with ]-Z% isoprene. The isoprene units in the copolymer allow it to be crosslinked. Although polystyrene is far too rigid to be elastomeric, styrene-1,3-butadiene copolymers (SBR) are useful as elastomers. Polyethylene is a semi-crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and a diene (e.g.. 

In the case of important elastomers formed by polymerisation of conjugated dienes, addition across one double bond can, by electron migration, cause movement of the second double bond. This results in either 1,2 or 1,4 addition across the four-carbon monomer (Figure 2.4). 

Figure 4. Carbon Is photoelectron spectrum for the commercially important elastomer hexafluoropropylene vinylidene fluoride.

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