Synthesis and Reactions of Viton® Model Compounds

Abstract

Viton® gaskets and O-ring seals are common components of engines and other industrial systems due to their high thermal and chemical resistances. However, degradation of Viton® seals has been observed when they are exposed to oils containing basic or nucleophilic petroleum additives. These processes are difficult to follow by standard analytical techniques due to Viton® being a high molecular weight polymer. In this project, a series of compounds that model the structural features of Viton® elastomers were synthesised by reaction of perfluoroalkyl iodides with vinylidene fluoride and subsequent capping with antimony pentafluoride.

These Viton® model compounds were subsequently reacted with a range of bases and nucleophiles and the products characterised by NMR spectroscopy and mass spectrometry. The analysis confirmed that exposure of vinylidene fluoride (VDF) containing Viton® model compounds to basic species (pKa > 10) under relatively mild conditions (temperature ≤ 120 ⁰C, atmospheric pressure) causes dehydrofluorination, synthesising alkenes that can subsequently react with certain nucleophiles such as KOMe and water.

These results indicate that Viton® elastomers are vulnerable to dehydrofluorination on exposure to basic petroleum additives, and to subsequent nucleophilic attack that can lead to unwanted crosslinking of the polymer chains and degradation of seals.