Tacticity has an enormous influence on the physical and chemical properties of polymers. There is considerable work using 1D-NMR and empirical rules to study the stereo-sequences in polymers. This work suggests that 1H/13C/19F 3D-NMR experiments can provide superior resolution and atomic connectivity information, so that unambiguous resonance assignment can be made for poly(vinyl fluoride) (PVF). Compared to prior work on 3D-NMR studies of stereosequence effects in fluoropolymers, the 3D-NMR pulse sequence used in this work is based on single quantum coherence transfer, which eliminates the complicated splitting patterns resulting from evolution of multi-quantum coherence. In addition, selective excitation of the 19F nuclei of interest significantly reduces the folding of peaks from other spectral regions. This greatly simplifies the spectra and makes the assignment of resonances much easier. Based on our results, it is possible to assign the 19F resonance to the pentad level. For example, consider the resonances of mm-centered sequences, which are not well resolved in 19F-19F COSY 2D-NMR spectrum, 1H/13C/19F 3D-NMR data provide clear evidences for all of the three pentad structures: mmmm, mmmr and rmmr. Examples showing the resonance assignments of head-to-tail and head-to-head sequences will be presented.

Characterization of stereo-sequences in poly(vinyl fluoride) by 1H/13C/19F 3D-NMR

245th National Meeting (2013)

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