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

Abstract

Differential scanning calorimetry (d.s.c.) and electrical conductivity measurements of poly(propylene oxide), PPO, complexed with the salts NaI and KSCN are reported. In addition, 23Na n.m.r. measurements on PPO‐NaI (x = 8), both at ambient and elevated pressure (2 kbar), have been performed. The d.s.c. data clearly indicate that the salt precipitates out of the complexes at about 85°C for NaI and 60°C for KSCN. These effects are manifested by a dramatic departure of the conductivity from Vogel‐Tammann‐Fulcher (VTF) behaviour, and a relatively sharp drop in mobile Na+ concentration, as deduced from n.m.r. measurements, above about 80°C. High pressure n.m.r. linewidth measurements are consistent with a pressure‐induced increase in glass transition temperature.

Systematics of salt precipitation in complexes of polyethylene oxide and alkali metal iodides

“…Two studies deal with SP in the PPO-KSCN system [10,11]. Teeters et al [11] investigated SP as a function of salt concentration in PPO complexed with NaSCN or KSCN and found a monotonic decrease of the SP onset temperature with increasing cation-to-oxygen ratio.…”

“…Most early reports on SP in polymer electrolytes concern PPO that was complexed with sodium salts to a fixed O/Na ratio of (or close to) 8, including NaClO 4 [6], NaI [7,10], and NaSCN [7,8,11]. Two studies deal with SP in the PPO-KSCN system [10,11].…”

“…Furthermore, the tendency for SP appears to be more prominent at elevated temperatures, which are less interesting for most practical applications. However, only few workers in the field seem to have recognized that SP is a basic phenomenon whose understanding may lead to deeper insight into the salt-polymer interaction [10,11].…”

“…This is particularly true for salts consisting of large polarizable anions and small cations such as Li and Na, which are of technological relevance [3,4]. The frequent use of such well-behaved systems in basic and applied research on polymer electrolytes may explain why salt precipitation (SP) has been observed rather as a side effect in only a few cases [5][6][7][8][9] and why SP has been made to the object of study even more rarely [10,11]. Furthermore, the tendency for SP appears to be more prominent at elevated temperatures, which are less interesting for most practical applications.…”

Raman spectroscopic study of ion–ion interaction and its temperature dependence in a poly(propylene-oxide)-based NaCF3SO3 –polymer electrolyte

“…5 ,7,8 In fact, it has been found that in some complexes (PPO-NaI and PPO-KSCN) the electrical conductivity, instead of increasing, begins to drop above some critical temperature if the samples are equilibrate long enough. 8 The equilibrium time was then attributed to the time needed for the salt to precipitate at a certain temperature. In the case of sodium salts it has been shown that the precipitation temperature increases as the concentration decreases and as the melting point of the dopant salt decreases.…”