Ethylene-propylene-diene , sulfur

Ethylene-propylene-diene rubber is polymerized from 60 parts ethylene, 40 parts propylene, and a small amount of nonconjugated diene. The nonconjugated diene permits sulfur vulcanization of the polymer instead of using peroxide. 

Dithiophosphates. These compounds (13) are made by reaction of an alcohol with phosphoms pentasulfide, then neutralization of the dithiophosphoric acid with a metal oxide. Like xanthates, dithiophosphates contain no nitrogen and do not generate nitrosamines during vulcanization. Dithiophosphates find use as high temperature accelerators for the sulfur vulcanization of ethylene—propylene—diene (EPDM) terpolymers. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Ethylene—Propylene (Diene) Rubber. The age-resistant elastomers are based on polymer chains having a very low unsaturation, sufficient for sulfur vulcanization but low enough to reduce oxidative degradation. EPDM can be depicted by the following chain stmcture ... 

The accelerated sulfur vulcanization of general-purpose diene rubbers (e.g., NR, styrene-butadiene rubber [SBR], and butadiene rubber [BR]) by sulfur in the presence of organic accelerators and other rubbers, which are vulcanized by closely related technology (e.g., ethylene-propylene-diene monomer [EPDM] mbber, butyl rubber [HR], halobutyl mbber [XIIR], nitrile rubber [NBR]) comprises more than 90% of all vulcanizations. 

Comparison of Properties of Sulfur- and Peroxide-Cured Ethylene-Propylene-Diene Rubber (EPDM)... 

FIGURE 20.6 Phase images of ethylene-propylene-diene terpol3mier (EPDM) samples at different scales. Images of the unvulcanized sample are shown in (a, d) and images of samples, which were cross-linked with different amount of sulfur curative—1 phr—in (b, e) and 2 phr—in (c, f). White arrows in (f) most likely indicate locations with small sulfur crystals. 

FIGURE 20.7 Phase images of ethylene-propylene-diene terpolymer (EPDM) samples loaded with oil (50 wt%). Image in (a) was obtained on the unvulcanized sample and images in (b,c,d) on samples cross-linked with different amounts of sulfur curative 0.5, 1.0, 1.5 phr, respectively. 

FIGURE 20.8 Load-versus-penetration LvP) curves obtained during nanoindentation of ethylene-propylene-diene terpol3nner (EPDM) samples. Approach curves are shown as solid line and retract curves as broken lines. The curves in (a, b) were obtained respectively on the unvulcanized and cross-linked (amount of sulfur curative was 1.0 phr) samples of neat EPDM. The curves in (c, d) were obtained respectively on the unvulcanized and cross-linked (amount of sulfur curative was 1.0 phr) samples of EPDM loaded with oil (50 wt%). 

Sulfur-containing spiro orthocarbonates, cationic polymerization of, 23 729 Sulfur-cured EPDM, 21 8041. See also Ethylene- propylene-diene monomer (EPDM) rubber Sulfur deposits... 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

The elastomeric sealing components of the metering valve are particularly critical. In those valves used with CFC propellants, the elastomeric seals have typically been formed from an acrylonitrile/butadiene rubber, which has been cured with sulfur. These rubber seals may not be fully compatible with HFA propellants hence, alternative elastomeric materials have been used. These materials include peroxide-cured acrylonitrile/ butadiene, ethylene-propylene diene monomer (EPDM), and chloroprene and thermoplastic elastomers (TPE). The elastomeric materials used to form the dynamic seals around the stem and the static gasket seal between the can and valve may differ based on the required properties of the rubber for the specific function of the seal. The most important characteristics of the elastomeric seals... 

These polyolefin rubbers are produced in two main types the saturated co-polymers, ethylene propylene rubber (EPM), and the unsaturated ethylene-propylene diene terpolymer (EPDM). The monomers are co-polymerised in ziegler natta type catalysts. The EPDM types are capable of sulfur vulcanisation as they contain, in addition to olefins, a non coagulated diene as the third monomer. 

All solvents were purified according to the literature methods (6). Sulfur monochloride (Aldrich Chemical Co.) was used as received. Ethylene-propylene-diene terpolymers (Epcar 346 ... 

We will now report the results of autohesion for homogeneous, symmetric joints of polyisoprene rubber (IR) and styrene-butadiene copolymer (SBR) both vulcanized by a sulfur-based system (Section 24.2.1), and of ethylene-propylene diene terpolymer (EPDM) crossHnked by an electron beam (Section 24.2.2). 

Over the years, much of the research on accelerated-sulfur vulcanization was done by using natural rubber as a model substrate. Natural rubber was the first elastomer and therefore the search for the understanding of vulcanization originated with work on natural rubber. Most of the work cited in the previous sections is related to natural rubber. However, some rather early studies have been directed to the vulcanization of butadiene 1,4-polymers (Skinner and Watson, 1969 Wolfe et al, 1329 Gregg and Katrenick, 1970). More recent is the work of Pellicioli and coworkers. Early basic work on the vulcanization of ethylene-propylene-diene-monomer rubber (EPDM) has been carried out (van den Berg et al., 1984a,b). Recently, Kuno and coworkers did basic work on EPDM networks. They found that, essentially, the vulcanizate properties depend only on the crosslink density, not on the type of curing system (Dijkhuis et al., 2009). 

Copolymerization of ethylene and propylene produces an elastomeric polymer that is virtually inert because of the absence of carbon-carbon double bonds (EPM). Such polymers thus tend to be crossUnked with peroxides or by radiation. To improve the reactivity of ethylene-propylene copolymers, 1-10% of a third monomer can be added to give a terpolymer or ethylene-propylene-diene monomer (EPDM). The primary diene monomers used in EPDM are 1,4-hexadiene, dicyclopentadiene, and ethyUdene norbomene. Introduction of an unsaturated monomer such as ethylidene norbomene will enable use of sulfur-based crosslinking systems. 

Ethylene-propylene rubber is a synthetic hydrocarbon-based rubber made either from ethylene-propylene diene monomer or ethylene-propylene terpolymer. These monomers are combined in such a manner as to produce an elastomer with a completely saturated backbone and pendant unsaturation for sulfur vulcanization. As a result of this configuration, vulcanizates of EPDM elastomers are extremely resistant to attack by ozone, oxygen, and weather. 

Accelerated-sulfur vulcanization is the most widely used method. For many applications, it is the only rapid crossUnking technique that can, in a practical manner, give the delayed action required for processing, shaping, and forming before the formation of the intractable vulcanized network. It is used to vulcanize natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (HR), chlorobutyl rubber (ClIR), bromobutyl rubber (BUR), and ethylene-propylene-diene-monomer rubber (EPDM). The reactive moiety for all of these elastomers can be represented by... 

TPO materials are defined as compounds (mixtures) of various polyolefin polymers, semicrystalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene—propylene rubber (EPR) [2]. A common rubber of this type is called ethylene propylene diene monomer rubber (EPDM), which has a small amount of a third monomer, a diene (two carbon-carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements, lubricants, heat stabilizers, antioxidants, UV stabilizers, colorants, and processing aids. They are characterized by high impact strength, low density, and good chemical resistance they are used when durability and reliability are primary concerns. 

Since EPR rubber molecules do not contain unsaturation, they can be vulcanized only by organic peroxide curing systems. If a third monomer is added during the polymerization, i.e., a diene monomer (wherein only one of the two double bonds takes part in the polymerization), unsaturation can be introduced into the molecule, and it can then be vulcanized by accelerated sulfur curing systems. A chemical structure for ethylene-propylene-diene-monomer (EPDM) rubbers can be expressed as follows ... 

A.S.Z. Naseri, A. JalaU-Arani, A comparison between the effects of gamma radiation and sulfur cure system on the microstructiire and crosslink network of (styrene butadiene rubber/ethylene propylene diene monomer) blends in presence of nanoclay. Radiation Physics and Chemistry, ISSN 0969-806X 115 (October 2015) 68-74. http //dx.doi. org/10.1016/jjadphyschem.2015.05.037. 

Uses vulcanizing accelerator sulfur dyes pharmaceuticals floatation agent acid inhibitor intermediate for organic synthesis accelerator and activator for chloroprene rubber and ethylene-propylene-diene terpolymers as heat stabilizer in PVC adhesive-tape backing A... 

Ethylene propylene diene polymers (EPDM) are basic elastomers with double bonds in the side chain. They are generated by adding small amounts of diene mmiomers in the copolymerisation of ethylene and propylene. Due to the presence of this unsaturated bond in the basic elastomer both vulcanisation with peroxides and vulcanisation with sulfur are possible. Vulcanisation with peroxides is usually chosen. This generates a product that is relatively inert and weU resistant to ageing. 

An ethylene propylene diene monomer/poly (ethylene-co-vinyl acetate) (EPDM/ EVAc) blend has also been proven to exhibit the above observations in systems with benzene, toluene and xylene as probe molecules [64]. The reduction in solvent uptake was prominent when the EVAc content was increased, and the compositions became less rubbery or more plastic-like due to the semicrystalline nature of EVAc. The liquid sorption characteristics of sulfur- and peroxide-cross-linked 40/60 EPDM/EVAc blends can be explained by the nature of the S—S and C—C chemical bonds. 

Ethylene-propylene diene rubber exhibits very good hot-air resistance. If the temperature peaks do not exceed 135 °C, a sulfur/acceleration system can be used in most cases. Above 135 °C, peroxide crosslinking is required. The relatively best hot-air resistance is achieved by using a low-molecular type (so that no or very little free oil has to be added) and by using high ethylene content [697]. 

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