A 19F NMR signal assignment and a detailed structural study of alternating tetrafluoroethylene-propylene copolymer by high resolution 19f nmr spectroscopy and computational chemistry

Abstract

19F NMR spectra of Tetrafluoroethylene-propylene(TFE-P) alternating copolymers are very complicated mainly due to 2J f-f couplings and an accurate signal assignment is very difficult. In the present work, simplified 19F NMR spectra of TFE-P alternating copolymers are measured in solution by J-resolved and COSY techniques. Thus geminal fluorine nuclei on the carbon atom adjacent to CH2 groups and those on the carbon atom adjacent to CHCH3 groups are assigned accurately. Also the two CF2-CF2 pairs of connection are found and these two pairs are assigned to meso or racemic configurations, respectively. Further, the conformational exchange of TFE-P copolymers in solution is discussed in a wide temperature range on the basis of experimentally obtained 19F NMR chemical shifts and theoretically calculated 19F nuclear magnetic shieldings. © 2009 The Society of Polymer Science.