Solid-state 1H-static, 1H-MAS, and 1H→19F/19F→1H CP/MAS NMR study of poly(vinyl fluoride)

Solid-state 1H→19F-CP/MAS, 19F→1H CP/MAS, and 1H fast MAS NMR spectra have been investigated for a semicrystalline polymer, namely poly(vinyl fluoride) (PVF), together with its solution-state 19F spectrum and static solid-state 1H pulsed and broad line NMR measurements. The static 1H pulsed NMR measurements of T1ρH and T2H showed the two-phase (immobile and mobile) nature, and the Goldman–Shen type phase selection at 130°C indicated that a measure for the lamellar size yields about 4.2 nm. Although the solid-state 19F-CP/MAS spectrum shows a featureless lineshape, the mobile region was selectively observed by a newly developed DIVAM pulse sequence. Solid-state spin-lock experiments showed significant differences in T1ρF and T1ρH between the immobile and mobile regions, and the effective time constants, THF∗ and T1ρ∗, which were estimated from the 1H→19F CP curves, also clarify the difference in the strengths of dipolar interactions. Furthermore, the 1H→19F inversion recovery CP (IRCP) experiment was more advantageous in observing the relatively weak dipolar interactions in the mobile region. The inverse 19F→1H CP/MAS and 1H→19F CP-drain MAS experiments gave complementary information to the 1H→19F CP/MAS spectra, although spinning at 35 kHz is necessary to separate the signals between CHF and CH2 protons in the 1H spectra. The hetero-nuclear dipolar oscillation behaviours and the effective time constants, THF∗, TFH∗, and T1ρ∗ determined from the 1H→19F CP/MAS, CP-drain MAS, and 19F→1H CP/MAS experiments are consistent with each other. In addition, the value of NF/NH (N is a spin density) estimated from the CP-drain curve is equivalent to that calculated from the chemical structure.