If no elastomer proves to be acceptable a non-elastomer seal may be your only answer. Keep in mind that this O-ring selection chart is only a guide to help you in selecting the correct elastomer for your mechanical seal application. It was created from published information, various industry guide lines and many years of practical experience by field sales and engineering people. Most mechanical seals use at least one dynamic elastomer, so even small amounts of swelling or chemical attack is almost always un-acceptable. If the elastomer is located close to the seal face it will see the additional heat that is being generated by rubbing friction.
Elastomers are poor conductors of heat.
Cooling one side of the O-ring does not always allow the coolant to conduct to the hot side. Oxidizers spontaneously emit oxygen at either room temperature or under slight heating. The oxygen can then combine with the carbon in mechanical seal faces or the carbon black used to color O-rings, causing chemical attack. The largest group of oxidizing materials is comprised of peroxides. Hydrogen peroxide and benzoyl peroxide are typical.