Part 2. Quantitative interpretation of model compound sulfonation

The mechanism and kinetics of sulfonation of two PEEK model compounds in concentrated sulfuric acid were studied. The first model compound (monomer) is representative of a PEEK repeat unit. The second one is a PEEK dimer. Because both model compounds are fluoroarylketone-ended, the sulfonation reactions were followed by F-19 NMR. The sulfonation reactions were treated following a first-order kinetics with respect to the unsulfonated PEEK repeat unit. The comparison between the monomer and dimer results showed two different types of sulfonation behaviour. If only one apparent kinetic constant is considered for monomer sulfonation, two kinetic constants were taken into account to describe the dimer sulfonation process. This is due to a rate slowing effect of a sulfonic acid group on the sulfonation of the adjacent PEEK repeat unit. Furthermore, the results also confirm the rate slowing effect of the fluorine atom on the sulfonation of the neighbouring PEEK repeat unit. (C) 2001 Society of Chemical Industry.