Influence of water and degree of sulfonation on the structure and dynamics of SPEEK studied by solid-state 13C and 1H NMR

The molecular motions of sulfonated poly(ether-ether ketone) (SPEEK), synthesized by conventional method with a range of degree of sulfonation (DS) between 42 and 70%, as a function of DS and hydration were studied by 1H-13C dipolar recoupling by rotor-encoded longitudinal magnetization (RELM) and 13C spin-lattice relaxations. The proton conductivity increased linearly with increasing DS from 52% and was comparable to that of Nafion 115 measured in the same condition for DS higher than 65%. The RELM dipolar patterns analyzed by the SIMPSON simulation program indicated that the population of phenyl rings in large amplitude motions such as 180°-flips was reduced with increasing DS. On the other hand, T1ρ (13C) and T1 (13C) results suggested that the dynamic chains in both 66 kHz and 100 MHz regimes were more populated with increasing DS, possibly in small-amplitude oscillations.