Conformation analysis and molecular mobility of ethylene and tetrafluoroethylene copolymer using solid‐state ¹⁹F MAS and ¹H → ¹⁹F CP/MAS NMR spectroscopy

Abstract

The changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable-temperature (VT) solid-state 19F magic angle spinning (MAS) and 1H --> 19F cross-polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T1rho(F) values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 degrees C. Quantum chemical calculations of magnetic shielding constants showed that the high-frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH2-CF2 linkage in the E-TFE unit. Although the 19F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 degrees C), they were successfully distinguished by using the dipolar filter and spin-lock pulse sequences at 145 degrees C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the 1H --> 19F CP curve, showed a significant decrease with increasing temperature from 42 to 145 degrees C. This is due to the averaging of 1H-19F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T1rho(F) and 1H --> 19F CP measurements in the phase transition temperature range.

Emulating Natural Product Conformation by Cooperative, Non‐Covalent Fluorine Interactions

“…Solid‐state NMR analysis : In an attempt to reconcile the solution‐phase NMR analysis with the crystallographic data, a solid‐state NMR analysis was performed to compare candidate 3 c with 3 d as a control. From previous studies on fluorinated and perfluorinated polymers, including polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PTFCE), and polyvinylidene fluoride (PVDF), a correlation between the isotropic 19 F chemical shift and the specific polymer chain conformation has been established . This conformational effect, referred to as the γ‐ gauche effect, was shown to be ≈10–15 ppm when comparing the various crystalline forms of PVDF, whereas molecular packing effects are ≈3–8 ppm .…”

Improved efficacy of α‐particle–targeted radiation therapy

“…7). 25–30 Those lines are marked with dotted lines in the Figure 7. Several Lorentzian lines were used to fit the spectra perfectly.…”

Solid‐state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)

“…Fluorine chemical shifts are referenced to hexafluorobenzene, which is assigned a value of 163.6 ppm with respect to CFCl 3 with 100 kHz of proton decoupling field to correct the Bloch-Siegert effect. 23 The sample whose dimensions were 3.0 mm in width by 40 mm in length was rolled in the direction of the length and was packed at the center of the rotor. Spin-lattice relaxation times in the laboratory frame for fluorine (T 1 F ) were measured by an inversion recovery technique.…”