2D‐NMR studies of a model for Krytox^® fluoropolymers

Abstract

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.

Characterization and quantification of microstructures of a fluorinated terpolymer by both homonuclear and heteronuclear two‐dimensional NMR spectroscopy

“…The advantages of using 2D NMR for studying the backbone microstructures of fluoropolymers such as poly (VDF‐co‐TFE) and Krytox® perfluoro(polyalkyl ether) have been shown . However, there is a limited number of reports on detailed microstructural analysis of THV.…”

“…Determining these sequence orders provide valuable information about polymerization conditions and structure‐property relationships. In this regard, advanced NMR techniques such as selective COSY are versatile methods for identification and analysis of polymer microstructures . For this purpose, both gCOSY and gHSQC were applied to figure out sequence orders of THV.…”

Advanced Solution 2D-NMR of Fluoropolymers

“…Figure 3 shows the modified version of the HSQC pulse sequence used to study the fluoropolymers which are the subject of this work. Details regarding the implementation of this experiment can be found in reference (23), however, there are several unique and noteworthy features. 1 H decoupling is performed on a third rf channel throughout the experiment, especially with materials such as PVDF, which have high hydrogen content.…”

“…Solvents were purchased from Aldrich Chemical Co and Cambridge Isotope Laboratories and used as received; THFPO was purchased as the acid fluoride from Alfa Aesar and converted to the carboxylic acid as previously described (23). PVDF was provided by E. I. Dupont de Nemours and Co.…”

“…An additional delay was required at the end of the evolution period to allow creation of the antiphase magnetization from coupling between the nuclei creating the cross-peaks. The original paper should be consulted for details (23).…”