posted on 2012-12-21, 00:00authored byLinlin Li, Eric B. Twum, Xiaohong Li, Elizabeth F. McCord, Peter A. Fox, Donald F. Lyons, Peter L. Rinaldi
NMR is a powerful tool to study the microstructures of
poly(vinylidene
fluoride-co-tetrafluoroethylene), poly(VDF-co-TFE). This study shows that the microstructures in this
copolymer can be established completely on the basis of 2D-NMR, in
which improved dispersion is achieved by the second dimension (19F or 13C chemical shifts). 2D-NMR has been proven
to be extremely effective for identifying the carbon sequence distributions
in the polymer main chain. For lower level sequences (3- or 5-carbon
sequences), resonance assignments on the basis of one- and two-bond 19F{13C} gradient heteronuclear single quantum coherence
(gHSQC) experiments are in good agreement with assignments obtained
by traditional methods. Higher level sequences (7- or 9-carbon sequences),
which can not be assigned unambiguously by traditional methods, were
determined by 19F–19F gradient double
quantum correlation spectroscopy (gdqCOSY), which provides 19F–19F correlations over 3–5 bonds. A quantitative
study was also conducted on the composition of this copolymer. Three
different approaches were used to calculate the fraction of TFE and
the inversion ratio of VDF units.