Jon Lee Howell

2D-NMR studies of a model for Krytox® fluoropolymers

Multiple two‐dimensional nuclear magnetic resonance (2D‐NMR) techniques have been used to study the structures of Krytox® perfluoro(polyalkyl ether) and its mechanism of polymerization. Model compound K4, containing four Krytox® fluoropolymer repeat units, was analyzed to interpret the multiplet patterns in the NMR spectra from the polymer model. 19F {13C}‐Heteronuclear single‐quantum correlation experiments, performed with delays optimized for 1JCF and 2JCF, provided spectra that permitted identification of resonances from individual monomer units. Selective, 19F‐19F COSY 2D‐NMR experiments were performed with different excitation regions; these experiments were combined with selective inversion pulses to remove 19F‐19F J couplings in the f1 dimension. The resulting COSY spectra were greatly simplified compared with standard 19F‐19F COSY spectra, which are too complicated to interpret. They give information regarding the attachments of monomer units and also provide insights into the nature of the stereoisomers that might be present in the polymer. Both infrared and NMR spectra show peaks identifying chain end structures. With the help of these studies, resonances can be assigned, and the average number of repeat units in the polymer chain can be calculated based on the assignments obtained. Copyright

Reactions of poly-hexafluoropropylene oxide acids and their corresponding salts

Abstract Investigation of the decomposition or fluorination of poly-hexafluoropropylene oxide (poly-HFPO) carboxylic acids and their salts reveals a new type of product from the decarboxylation of poly-HFPO and proposes an explanation for its formation.

On the preparation of 1H-perfluoroalkanes and a mechanism for the reduction of perfluoroalkyl iodides

Abstract 1 H -Perfluoroalkanes are prepared by sodium methoxide reduction of 1-iodoperfluoroalkanes. The experimental evidence indicates that the reaction proceeds either through a radical or a thermal mechanism. We have found that a high yield of 1 H -perfluoroalkanes at complete conversion can be accomplished at atmospheric pressure using this technology.

A Convenient Route to Tetraalkylammonium Perfluoroalkoxides from Hydrofluoroethers

Hydrofluoroethers are shown to alkylate tertiary amines readily under solvent-free conditions, affording valuable tetraalkylammonium perfluoroalkoxides bearing α-fluorines. The reaction of R(F)CF2-OCH3 (R(F)=CF2CF3, CF2CF2CF3, and CF(CF3)2) with NR(1)R(2)R(3) produces twenty new α-perfluoroalkoxides, [(CH3)NR(1)R(2)R(3)][R(F)CF2O] under mild conditions. These α-perfluoroalkoxides are easy to handle, thermally stable, and can be used for the perfluoroalkoxylation of benzyl bromides.

2-D NMR Studies of Chain-End Structures in Poly(Hexafluoropropylene Oxide) Fluoropolymers

2-D NMR techniques were used to study the structures of poly (hexafluoropropylene oxide) (PHFPO) and its mechanism of polymerization. Model compounds K4, containing four hexafluorpropylene oxide repeat units, and E4 and E2, containing four and two ether oxygens respectively, were analyzed to interpret the resonance patterns in the NMR spectra from the polymers. Selective 19 F- 13 C gradient HSQC experiments provided information about the C-F attachments within monomer units of the backbone and chain ends. A series of 19 F- 19 F selective COSY 2-D NMR experiments were performed to determine the connections and arrangements of each hexafluoropropylene oxide unit. When selective experiments were combined with selective inversion pulses to remove most of the JFF couplings in the f1 dimension, greatly simplified 19 F- 19 F COSY 2-D NMR spectra were obtained. This made it possible to resolve signals from various stereo sequences and monomer inversions. Resonance chain-end structures detected in the polymer have been identified and attributed to the various mechanisms for initiation and termination of polymerization. Unambiguous evidence of inverse addition and isopropyl end-group structures was obtained.

Perfluoroalkyl iodide coupling in aqueous media

Abstract A careful review of the literature would lead one to believe that coupling reactions between perfluoroalkyl iodides would not occur in aqueous media. Indeed, reduction to the hydroperfluorocarbon is expected. We have found that addition of linear perfluoroalkyl iodides to aqueous suspensions of zinc metal lead to the formation of pure linear perfluoroalkanes. Easily prepared are n-perfluorooctane from C 4 F 9 I, n-C 12 F 26 from C 6 F 13 I, and n-C 16 F 34 from C 8 F 17 I. Mixed materials could be separated easily by physical means. The scope of the reaction as a function of acid strength and concentration, different fluorinated iodoalkanes, different metals, and metal R f I ratio will be reported.