Multidimensional solution NMR ( 19 F, 1 H, and 13 C) has been used to determine chain-ends and backbone branching points and to obtain unambiguous 19 F and 1 H resonances assignments from these chain-ends and branching structures in poly(vinylidene fluoride) (PVDF). The multidimensional NMR methods employed in this study not only enabled the resonance assignments of the last monomer of the chain but also provided assignments for the last three monomer units of chain-end structures. The chain-end signals from PVDF were determined using spin−lattice relaxation measurements and 2D diffusion ordered spectroscopy (DOSY) analysis. 2D-NMR analyses were also used to assign resonances of chain branching points along the backbone of the polymer.
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 ( 19 F or 13 C 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 19 F{ 13 C} 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 19 F− 19 F gradient double quantum correlation spectroscopy (gdqCOSY), which provides 19 F− 19 F 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.
Advanced modern multidimensional solution NMR experiments have been used to deduce the sequence distribution in poly(VDF-co-HFP) copolymers. Assignment of 19 F resonances from different monomer-and regio-sequences in poly(VDF-co-HFP) copolymer were identified. In addition to corroborating some assignments reported in earlier literature, this work provides assignments of some new resonances from the spectra of poly(VDF-co-HFP) copolymer, which resulted from better dispersion of the resonances. These assignments are used for the monomer sequence analyses of two polymers using first-order Markovian statistics, and the relative reactivities of the monomers during polymerization are discussed. The results from this study provide insight into the polymerization chemistry for this fluoropolymer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.