Organic peroxides, vulcanization

For organic peroxide vulcanization, a variety of organic peroxides have been shown to be effective [7]. Such peroxides would include di-t-butyl peroxide dicumyl peroxide t-butyl cumyl peroxide l,l-di(t-butylperoxy)-3,3,5-trimeihyl cyclohexane 2,5-dimethyl-2,5-di(r-butylperoxy)hexane 2,5-dimethyl-2,5-di(r-butylper-oxy)hexyne-3 a,a-bis(t-butylperoxy)diisopropylbenzene t-butyl perbenzoate and t-butylperoxy isopropylcarbonate. In contrast to NBR elastomers where 1-3 phr of peroxide is effective, HNBRs generally require peroxide levels of 5-8 phr for effective vulcanization. As discussed earher, this is due to the very low levels of unsaturation present in the HNBR polymers. The specific peroxide chosen will depend on the process safety desired and the vulcanization temperature to be used. Generally, the most common organic peroxides used in HNBR elastomers are Dicumyl peroxide, such as Varox Dicup 40C from R.T. Vanderbilt, on an inert carrier for vulcanization below 177°C and a,a-bis(t-butylperoxy)diisopropylbenzene, such as Varox VC40KE from Vanderbilt, on an inert carrier for vulcanization above 150°C. 

The effectiveness of organic peroxide vulcanization can be enhanced by coagents. The most common coagents used are N-AT-m-phenylenedimaleimide (Vanax... 

Peroxides. See also Inorganic peroxides Organic peroxides acid hydrolysis of, 23 459 diacyl, 24 282-284 explosive, 20 569-573 formation of, 20 577 as free-radical initiators, 24 279-293 organomercury-containing, 23 445 potassium salts of, 18 478 silylation and, 22 703 stereoisomers of, 28 459 as vulcanizing agents, 22 795 ... 

The saturated rubbers such as butyl or EPDM cannot be cross linked by sulphur and accelerators. Organic peroxides are necessary for the vulcanization of these rubbers. When the peroxides decompose, free radicals are formed on the polymer chains and these chains can then combine to form cross links of the type where only carbon-carbon bonds are formed, unlike in sulphur vulcanization. These carbon-carbon bonds are quite stable ones. Such bonds are also formed by vulcanization using gamma or x-ray radiation of compounded rubbers. Some rubbers can be vulcanized by the use of certain bisfunctional compounds which form bridge type cross... 

The EPM rubbers, being completely saturated, require organic peroxides or radiation for vulcanization. The EPDM terpolymers can be vulcanized with peroxides, radiation, or sulfur. 

The production volume of hydrogen peroxide is in hundreds of thousands of tons. It is one of the most widespread and valuable products in modem chemistry. All over the world hydrogen peroxide is widely applied in epoxidation and hydroxylation processes, for example, in glycerol production from allyl alcohol or organic peroxides, which are polymerization and vulcanization initiators. 

Organic peroxides are another type of cross-linking agents. Vulcanization by means of peroxides is a free radical process that leads to the formation of carbon-carbon covalent bonds between chains. Below we show a diagram of the process ... 

As EPR and EPDM elastomers, the vulcanization process is carried out using organic peroxides because the polymer chains do not contain unsaturated bonds. If the polydimethylsiloxane chains are modified by introducing a small quantity of vinyl groups, the vulcanization is carried out using cumyl peroxide. 

The PFAP(I) selected for this study is an amorphous fluoroelastomer that consists of pendant trifluoroethoxy and octafluoropentoxy groups (II). A small quantity of cross-link site was incorporated also to facilitate vulcanization via conventional methods, i.e., organic peroxides, sulfur-accelerator, and radiation (high-energy electrons). 

Cross-linking essentially forms a chemically bonded network matrix of one giant molecule. Organic peroxides are also used as vulcanization catalysts. 

Silicone, natural, and synthetic rubbers have been used for the fabrication of implants. Natural rubber is made mostly from the latex of the Hevea brasiliensis tree and the chemical formula is the same as that of cw-1,4 polyisoprene. Natural rubber was found to be compatible with blood in its pure form. Also, cross-linking by x-ray and organic peroxides produces rubber with superior blood compatibility compared with rubbers made by the conventional sulfur vulcanization. 

Figure 15.7 Results demonstrating that much more polymeric material can be extract by suitable organic solvents bom vulcanizates derived from polystyrene-polybutadie blends than from vulcanizates from styrene-butadiene copolymers (Shundo et al. [19 ( ) peroxide-vulcanized copolymers (O) sulfur-vulcanized copolymers (O) radi don-vulcanized copolymers (A) peroxide-vulcanized latex blends (A) sulfiir-vulcaniz< latex blends (A) radiation-vulcanized latex blends ( ) peroxide-vulcanized roll blenr ( ) sulfur-vulcanized roll blends (Qf) radiation-vulcanized roll blends. The compoun for peroxide vulcanizates and sulfur vulcanizates were as given in the cation Figure 15.6. The compound for radiation vulcanization was (parts by mass) polymer 10 calcium caibonate ICIO. Roll blending was done at 110°C. Peroxide and sulfur vulca-izatkxis were carried out at 150°C. Radiation vulcanization was achieved using 10 n from a cobaIt-60 source in air at normal ambient temperature...

The accelerated-sulfur vulcanization of these rubbers along with the vulcanization of other rubbers, which are vulcanized by closely related technology, comprises more than 90% of all vulcanization. These rubbers include ethylene-propylene-diene-monomer rubber (EPDM), butyl rubber (HR), halobutyl rubbers, and nitrile rubber (NBR). Nevertheless, we give some consideration to vulcanization by the action of other vulcanization agents such as organic peroxides, phenolic curatives, and quinoid curatives. 

The following is a partial list of organic peroxides that are key vulcanizing agents ... 

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