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

Abstract

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 n̄ = 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

Unexpected effect of alkoxides on the reactivity of sodium borohydrid in the reduction of perfluoropolyether carboxylic esters

“…However, minor changes in the mechanism, or in the relative rate of the different steps here described, could be observed if fluorinated esters having different molecular weight are considered. Moreover, the presence of bulky fluorinated groups close to the reactive centre, or bulky alcoholic residue (compared to the ethyl group here described) [15], could significantly modify the substrate reactivity. These topics will be the subject of further study, together with a deeper investigation of the hydrolysis sensitivity of the molecule during reduction.…”

“…The hydrolysis of the ester group leads to the formation of the corresponding carboxylic acid [15], or salt, that are both not reduced by sodium borohydride. Consequently, the choice of proper experimental conditions, both in terms of thermal and humidity control, is mandatory in order to get a high selective process.…”

Fluorinated Polymer Films from Acylation of ATRP Surface-Initiated Poly(hydroxyethyl methacrylate)

“…In this work, the acylation reaction results in a fluorinated ester linkage on the polymer side chains. Esters having fluorocarbon constituency next to the carbonyl moiety are known to be susceptible to degradation upon exposure to heat 25,26 or base . While gaining the surface properties of fluorinated polymers is directly advantageous for our method of surface-initiated polymerization and modification, the ability to simply and effectively cleave the fluorocarbon side chains could have a broad impact on the preparation of temporary resists or patterned films and surfaces .…”

“…Esters having fluorocarbon constituency next to the carbonyl moiety are known to be susceptible to degradation upon exposure to heat 25,26 or base. 48 While gaining the surface properties of fluorinated polymers is directly advantageous for our method of surfaceinitiated polymerization and modification, the ability to simply and effectively cleave the fluorocarbon side chains could have a broad impact on the preparation of temporary resists or patterned films and surfaces. 25 The stability of PHEMA-based polymer films against hydrolysis was evaluated by placing samples of PHEMA, C3F7-PHEMA, C7F15-PHEMA, and C6F5-PHEMA in deionized water or a 0.5 M KOH solution in ethanol for various amounts of time, rinsing with deionized water, drying with nitrogen, and then examining their IR spectra.…”

New hydrofluoropolyethers

“…Water can be present as impurity (humidity) or generated by some of the described reaction pathways. The hydrated intermediate [RfCH(OH) 2 ], analogously to other OH containing intermediates reported in the reaction scheme, could react with the starting acyl chloride forming the corresponding esters (reaction h), which in principle could undergo hydrogenolysis to alcohol (carboxylic acid as side product), or to aldehyde and its hydrated form (reactions i and l, respectively) [32]. However, the strong hydrolysis sensitivity of these fluorinated esters makes these reactions highly improbable and for this reason they have been shown as dotted lines.…”