NMR Study of the Chain End and Branching Units in Poly(vinylidene fluoride-co-tetrafluoroethylene)

Abstract

2D-NMR techniques were used to identify the detailed structures of chain end and branching units in poly(vinylidene fluoride-co-tetrafluoroethylene), poly(VDF-co-TFE). Atomic connectivity information was provided by selective 19 F− 19 F COSY (correlation spectroscopy), 19 F{ 1 H} gHETCOR (gradient heteronuclear correlated), and 1 H{ 13 C} HSQC (heteronuclear single quantum correlation) experiments. Diffusion ordered spectroscopy (DOSY) and spin− lattice relaxation (T 1 ) data permitted distinction of backbone, short chain branch, and chain end resonances from one another. Quantitative data on these structures are reported; quantitation also supported assignments through the consistent relative intensities of resonances from the same structures. Possible reactions during the polymerization which could lead to these structures are discussed.

Characterization and quantification of microstructures of a fluorinated terpolymer by both homonuclear and heteronuclear two‐dimensional NMR spectroscopy

“…On the other hand, selective COSY experiments provide better digital resolution and sensitivity. This results in less time and stronger cross‐peaks because anti‐phase cross‐peak components are well resolved . It has been already shown that 19 F– 19 F gCOSY can provide valuable information about microstructural assignments in the polymer main chains .…”

“…It has been already shown that 19 F– 19 F gCOSY can provide valuable information about microstructural assignments in the polymer main chains . The experiment gCOSY was also employed for chain end analysis of a fluorinated polymer . For example, the cross‐peak between CF 2 of HFP at −103.98 ppm and CF 3 of HFP at −71.35 ppm are important examples of the weakest through‐bond correlations by gCOSY.…”

“…The advantages of using 2D NMR for studying the backbone microstructures of fluoropolymers such as poly (VDF‐co‐TFE) and Krytox® perfluoro(polyalkyl ether) have been shown . However, there is a limited number of reports on detailed microstructural analysis of THV.…”

19F DOSY diffusion‐NMR spectroscopy of fluoropolymers

“…Recently, it has been shown that 19 F detected DOSY experiments could be used to distinguish between the resonances of polymer chain-ends and other branching structures in a series of fluoropolymers. [40][41][42] Generally, the performance of 19 F NMR experiments on fluoropolymers creates some unique complications that often interfere with detection of important signals. [39] These factors include: (1) the presence of many scalar couplings among 1 H, 19 F and 13 C; (2) the large magnitudes of many 19 F homonuclear couplings (especially 2 J FF ); (3) the large 19 F chemical shift range; and (4) the low solubility of these materials (which requires that experiments be performed at high temperatures).…”

“…[41] These spectra were devoid of the aforementioned problems because the resonances were dispersed over the relatively narrow (50 ppm) CF 2 region of the 19 F chemical shift range, and almost all of the CF 2 fluorines were chemically equivalent. However, problems were encountered in later attempts to study copolymers and terpolymers of VDF containing hexafluoropropylene (HFP).…”