Magic angle spinning (MAS) nuclear magnetic resonance (NMR) for ¹⁹F and ¹H nuclei was used how exposure to high-pressure (70 MPa) H₂ gas affected an O-ring material. ¹⁹F MAS NMR revealed that poly(vinylidenefluoride- co-hexafluoroprophylene) in VDF/HFP = 76.1/23.9 mol % (FKM type 1) was involved in the O-ring material. This copolymer may undergo main-chain scission and termination to -CF₂H end groups during
depressurization of high-pressure H₂ . Evidence for formation of additional -CF₂H end group includes a small increase in the ¹⁹F MAS NMR signal at -96 ppm, and a corresponding ¹H MAS NMR signal at 7.1 ppm in comparison with those in the material that had not been exposed to high-pressure H₂. Neither the ¹⁹F nor the 1H MAS NMR showed chemical shift after exposure to H₂ ; this absence of response means that exposure to H₂ did not affect the structure of the polymer.