Polymer00019 - to steam, hot water, and aqueous acids over...

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8 1.4.2 Curing of Fluoroelastomers There are usually there types of curing agents for fluoroelastomer vulcanization, peroxide, diamine and bisphenol, with various curing mechanisms, respectively. Different from peroxide curing with free radicals, diamine curing is based on the addition of diamine to the polymer chain after the VDP type fluoroelastomer is subjected to dehydrofluorination in the presence of basic media which can extract hydrofluoride from the elastomer (Salamone 1999). Another curing agent for fluoroelastomer is bisphenol, and the crosslinking mechanism mainly includes three steps, i.e. dehydrofluorination by hydroxide ions, substitution of fluorine atoms by bisphenol and elimination of HF (Taguet, et al. 2005). Fluoroelastomers cured with peroxides, or free radicals, exhibit improved resistance
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Unformatted text preview: to steam, hot water, and aqueous acids over those cured with bisphenols. Peroxide-cured compounds generally do not contain much inorganic bases, so they are less susceptible to attack by aqueous fluids. On the other hand, the curing of fluoroelastomers using peroxide requires crosslinking agents (radical traps), and the resulting compounds give lower thermal stability than that cured with bisphenols. For peroxide curing, fluoroelastomers must contain sites reactive toward free radicals, usually bromine or iodine introduced within chains by incorporation of cure-site monomers or at chain ends by chain-transfer agents. In the late 1970s, DuPont offered the first commercial peroxide-curable fluoroelastomers which had a bromine-containing cure-site monomers (i.e., 4-P* + P* P-P (crosslink)...
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