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

✍ Scribed by Xiaohong Li; Elizabeth F. McCord; Silapong Baiagern; Peter Fox; Jon L. Howell; Sangrama K. Sahoo; Peter L. Rinaldi

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 762 KB
• Volume: 49
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2763

✦ Synopsis

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. Copyright © 2011 John Wiley & Sons, Ltd.