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 K(4), containing four Krytox(®) fluoropolymer repeat units, was analyzed to interpret the multiplet patterns in the NMR spectra from the polymer model. (19)F {(13)C}-Heteronuclear single-quantum correlation experiments, performed with delays optimized for (1)J(CF) and (2)J(CF), provided spectra that permitted identification of resonances from individual monomer units. Selective, (19)F-(19)F COSY 2D-NMR experiments were performed with different excitation regions; these experiments were combined with selective inversion pulses to remove (19)F-(19)F J couplings in the f(1) dimension. The resulting COSY spectra were greatly simplified compared with standard (19)F-(19)F 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.

No abstract

Perfluoropolyalkylethers (PFPAEs) are a class of fluorinated polymers having −OCF2–, −OCF2CF2–, and −OCF2CF­(CF3)– as common chain units. The ether linkages distinguish them from other famous fluorinated polymers such as poly­(tetrafluoro­ethylene). Their higher mobility highlighted by below zero glass transition temperatures permit them to be noncrystalline, which makes them easy to use for many applications. They possess interesting tribological properties, combined with an excellent thermal and chemical stability, make them very useful as lubricants. However, after chemical modifications, they also demonstrated to be very useful in numerous applications as surfactants, electrolytes, high performance coatings, vitrimers, or microfluidic devices, to give a few examples. This Perspective aims to summarize all the chemical modifications reported on these PFPAEs to provide a new insight into their potential utility in emerging fields. Indeed, the end group can modulate the properties of PFPAE-based materials such as lubricity, superhydrophobicity, biofouling, antibacterial activity, amphiphilicity, and the ability to react further with comonomers under photochemical and thermal processes. It can also modulate their intrinsic properties such as viscosity and solubility in common organic solvents. The chemical modifications are sorted in five main parts: the condensation reactions, the nucleophilic reactions, the click chemistry reactions, the radical reactions, and finally reactions going through other mechanisms or requiring a multistep process. They can be employed as such or for further polymerization processes depending on the targeted application. Examples of applications are thoroughly described to demonstrate their current usefulness and to help provide direction for their future use.

No abstract