NMR, DSC, DMA, and High Pressure Electrical Conductivity Studies in PPO Complexed with Sodium Perchlorate

Abstract

Audio frequency electrical conductivity, DSC, DMA, and 23Na NMR measurements have been carried out on Parel 58 elastomer complexed with sodium perchlorate. [As Parel 58 is primarily po]y(propylene oxide), itwill be referred to as PPO.] The DSC and DMA measurements yield similar values for T~ which are about 72~ higher than the "central" T~ for uncomplexed PPO. In addition, the DSC studies show that the sodium perchlorate is insoluble above about 140~ The conductivity measurements have been carried out in vacuum over the temperature range 290-380 K and at pressures up to 0.65 GPa from 315-370 K. From a VTF analysis Ea is found to be about 0.09 eV, and To is found to be about 45~ below the "central" glass transition temperature which is the same behavior observed previously for PPO complexed with lithium salts and for the ~ relaxation in uncomplexed material. In addition, it is found that the vacuum activation volumes for the electrical conductivity and the a relaxation are approximately the same when compared relative to To. The 23Na NMR measurements reveal the presence of both bound and mobile sodium species, where the bound species constitutes only about 20% of the total sodium at temperatures below %, and is no longer observable above about 80~ In addition the mobile 23Na resonance becomes motionally narrowed above T~. The NMR results combined with conductivity data imply that ion motion is controlled by large scale segmental motions of the polymer chains.In recent papers, results for the temperature and pressure variation of electrical conductivity in PPO complexed with lithium salts along with the temperature and pressure variation of the a relaxation have been presented (1, 2). The most important result of that work is that it was shown that to within experimental uncertainty, the temperature and pressure variation of the electrical conductivity was found to be the same as the temperatfire and pressure variation of the electrical relaxation time for the ~ relaxation. This provides quantitative evidence that, for PPO, ionic conductivity is controlled by large-scale segmental motions [conformational rearrangements of the polymer chain backbone (3)] characteristic of the glass-rubber transition. "Such rearrangements occur by a mechanism of hindered rotation around main chain bonds and involve cooperative thermal motions of individual chain segments. The hindrance to these "miero-Brownian" motions can be described in terms of viscous or frictional forces which result from interactions of the moving segment with neighboring molecules or with segments within the same chain (3)." However, in the earlier paper (2), it was emphasized that the conductivity results alone could not be used to elucidate the transport mechanism as the shift in carrier concentration with temperature was unknown. In the present paper both electrical conductivity and nuclear magnetic resonance (NMR) measurements are * Electrochemical Society Active Member.carried out on PPO complexed with sodium perchlorate. The combination of the r...

D.s.c., electrical conductivity, and n.m.r. studies of salt precipitation effects in PPO complexes

“…Poly(propylene oxide) (PPO) is known to form amorphous ion conducting complexes with alkali metal salts. [1][2][3] Previous studies of PPQ complexed with LiClO 4 2 and NaClO 4 3 have shown that large scale segmental motion of the polymer chains is principally responsible for ionic transport, in general agreement with the results of a wide array of recent investigations. The studies in our laboratories 2 ,3 can be summarized briefly as follows.…”

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Low-viscosity ionic liquid–doped solid polymer electrolytes

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