Perfluoropolyether alkyl diesters: Structure effects of the alkyl group on the kinetics of the hydrolysis reactions

A series of perfluoropolyether bis‐carboxylic esters was synthesized and their hydrolytic stability investigated. Their formula is ROOCCF₂O(CF₂CF₂O)_p(CF₂O)_qCF₂COOR, where p/q = 1.07 and p + q = 2.94. The alkyl group, R, varied both in terms of steric hindrance and electron‐withdrawing ability. Kinetic and thermodynamic data were obtained under homogeneous conditions and compared to a fully hydrogenated ester having a closely related structure CH₃(CH₂)₃OOCCH₂O(CH₂CH₂O)_nCH₂COO(CH₂)₃CH₃, where n? = 10.6. Neutral ester hydrolysis (NEH) conditions were selected with methyl ethyl ketone as a solvent and a 3–4:1 water/ester ratio. The course of the reaction was monitored by ¹⁹F NMR or ¹H NMR (when R = CH₃CH₂? ). Results indicated that the hydrolysis of fluorinated esters, with alkyl aliphatic substituents, is governed by steric hindrance of the substituents. Two distinctive kinetic regimes were observed. The first one, at low conversion, was characterized by lower kinetic constants and related to true NEH conditions. The second regime appeared at higher conversion when acidic autocatalysis dictated the reaction behavior. This is the only observed mechanism when esters more sensitive to the hydrolysis are considered. In these cases, polar factors prevail over steric considerations. Finally, all fluorinated esters of the class (I) showed a much higher reactivity than the hydrogenated ester whose hydrolysis took place only in the presence of a strong acidic catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4266–4280, 2002