Ethylene-propylene copolymers peroxide-curing

While the first vulcanization involved heating the elastomer with sulfur, it has since been recognized that neither heat nor sulfur is imperative for the vulcanization process. Vulcanization or cure can be effected by nonsulfur-containing compounds, including peroxides, nitro compounds, quinones, or azo compounds. Polyethylene, ethylene-propylene copolymers, and polysiloxanes are cross-linked by compounding them... 

Uncured ethylene-propylene copolymers are soluble in hydrocarbons and have rather poor physical properties useful technological properties are developed only on vulcanization. As mentioned above, the saturated copolymers are vulcanized by heating with peroxides whilst the terpolymers are vulcanized by conventional sulphur systems. The peroxide-cured rubbers have somewhat better heat aging characteristics and resistance to compression set but sulphur-cured rubbers are more convenient to process and allow greater compounding freedom. 

Until they are vulcanized, elastic, amorphous ethylene-olefinic copolymers have very little possible utility except as components of caulks or sealants. However, grafting MA on the copolymers, using peroxide initiators, and compounding the modified materials with zinc oxide provides improved rubbers. A typical recipe would consist of 100 parts ethylene-propylene copolymer, 20 parts zinc oxide, 7 parts MA, and 2 parts BPO. Curing is carried out at 160°C for 30-45 min. Previously grafted copolymers, containing 2-5 MA residues, can also be cured with N-phenyl-B-naphthylamine initiator, steric acid modifier, and zinc oxide crosslinker. 

The failure of rubber parts used in domestic water applications has been reported flem several US states. The complaints involved swelling and cracking and are related to nitrile and ethylene-propylene copolymer type compoimds. The failure of the rabber parts coincides with the implementation and use of chloramines as a method of water purification. This investigation was designed to determine if EPDM composition variables influenced resistance to chloramines. Also evaluated were peroxide vs sulphur cure systems, the effect of antioxidants and whether practical compoimds can be developed for water systems. 5 refs. 

The unmodified PGV and modified MMTs were used as a fillers in ethylene-propylene copolymer EPR and hydrogenated butadiene-acrylonitrile rubber HNBR. The elastomers were cured using dicumyl peroxide DCP. 

Ethylene propylene copolymers (EPM) are made by Ziegler-Natta and metallocene polymerization and are the commercial mbbers with the lowest density. EPM cannot be vulcanized and thus is not reactive to peroxide curing. To introduce an unsaturated site suitable for crosslinking, a non-conjugated diene termonomer such as ethylidene norbomene, 1,4 hexaadiene or dicyclo-pentadiene, is employed to produce the mbber known as EPDM. Ethylene propylene diene mbber has small number of double bonds, external to the backbone, introduced in this way. In EPDM, the E stands for ethylene, the P for propylene, the D for diene and the M indicates that the mbber has saturated chain of the polymethylene type, properties of EPM and EPDM are ... 

Ethylene/propylene products reign supreme among the copolymers. They are elastomers. Plastics containing about 20% or more propylene perform like natural rubber and can be cured by peroxide cross-linking. They are faster to chemical and to ageing than other types of natural rubber. 

Like the butyls, there are basically two types of ethylene propylene. One is a fully saturated chemically inert copolymer of ethylene and propylene (EPR). The other, called EPDM, has the ethylene and the propylene, plus diene monomer. EPDM is chemically reactive and capable of sulfur vulcanization. The copolymer, EPR, is cured with a peroxide catalyst. 

The copolymer ethylene propylene rubber (EPM) is manufactured directly from only the two monomers, ethylene and propylene. Since this polymer contains no unsaturation, it must be cured with a peroxide vulcanizing agent. 

The blends of EPDM terpolymers and isotactic PP with curing agents, such as peroxide, phenol resins, and sulfur, are termed as thermoplastic vulcanized elastomer (TPV) since the rubber domains are vulcanized. Polyolefin copolymers, such as random copolymer of propylene with ethylene, copolymers of other olefins, elastomeric PP, and elastomeric PE, are developed with recent advances of... 

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