Thermal properties of poly(ethylene oxide) complexed with sodium thiocyanate and potassium thiocyanate

Abstract

The melting behavior of series of solvent-cast mixtures of a low molecular weight (a,, = 4 Y . lo3) poly(ethy1ene oxide) (PEO) with NaSCN and KSCN has been studied by DSC and optical microscopy.The results show great similarities between the two systems. Their common characteristics are f i t the formation of a single solid compound, P(E03.NaSCN) and P(EO,,.KSCN), that melts incongruently to yield the solid salt and a peritectic liquid and second a liquid-liquid miscibility gap occurring at the melting point of the pure salt. Both systems exhibit a nearly vertical salt liquidus curve, indicating that complex formation also takes place in the liquid phase. The stoichiometry of the solvate is close to 4/1 for NaSCN and 5/1 for KSCN. The mixtures with NaSCN were highly crystalline over the whole composition range while those with KSCN showed either partial crystallinity or the absence of crystallinity at PEO contents above that of the solid compound. Because of the peritectic reaction, in either system the solid compound cannot participate in the formation of a eutectic mixture with the solid salt. In turn, it can form a eutectic mixture with solid PEO. In the case of the PEO-NaSCN system for which the construction of a complete phase diagram was possible, the eutectic composition is close to 93% by weight in PEO with a corresponding tie line located 4 "C below the melting point of pure PEO. The analysis of the P(E03-NaSCN) liquidus curve in terms of the Flory-Huggins thermodynamic concepts indicates the presence of a strong exothermic interaction (x = -1.2), associated with the solvation of P(E03.NaSCN) by PEO yielding the solvate P(EO,.NaSCN). For either system, the reverse path of the peritectic reaction is not quantitative for a mixture having the composition of the solid compound. In either case, melt recrystallization yields a material that contains the solid salt in addition to the solid compound.ABSTRACT: 2,2'-Azobis([ 2-13C]propionitrile) (1) was prepared in 35% overall yield starting from [ 1-'3C]-acetaldehyde (99 atom 7%). Quantitative I3C NMR analysis of end groups in styrene-acrylonitrile copolymers prepared with 1 as initiator allows determination of the relative rates of addition of these olefins to the 1-cyanoethyl radical. We have found k A / k s = 0.12 f 0.03, a result conistent with the penultimate model treatment of this copolymerization system by Hill, O'Donnell, and O'Sullivan.

Electrospinning as a New Method for Preparing Pure Polymer Complexes

“…12 Robitaille et al showed that the pure complex can be prepared by solvent-casting when using low molecular weight (4000 g/mol) PEO but that the entanglement network prevents it for high molecular weight PEO such as the one used in this work. 7 For instance, highly heterogeneous films with a low degree of crystallinity were obtained by Lee and Crist when using 600 000 g/mol PEO, leading to an erroneous determination of the complex stoichiometry. 7,13 Pure complex could not be obtained by melt-cooling a stoichiometric blend since large crystals of NaSCN form during the first peritectic melt of the blends.…”

“…These crystals are subsequently encapsulated in the complex and cannot participate in the formation of further complex. 7 A partial degradation is also observed when heating at temperatures close to or above the NaSCN melting point, further limiting the potential of this method.…”

“…In both cases, pure samples could not be obtained by melt-cooling, cocrystallization, or solvent casting but were readily prepared by electrospinning. 7,10 Experimental Section Sample Preparation. PEO with an average molecular weight of 400 000 g/mol (Scientific Polymer Products) and NaSCN (Fisher Scientific) were used as received and stored under vacuum.…”

Phase behaviors of polymer blend(PEO–PPO) electrolyte/LiCF3SO3 systems in lithium battery

“…In fact, the objective of several studies has been to determine domain existence as a function of salt concentration and temperature. 8 For example, Prud'homme and coworkers 9,10 reported on complete phase diagrams for PEO-NaSCN and PEO-KSCN systems. Lee and Crist 11 also reported on the phase behavior for PEO-NaSCN mixtures, which show eutectic points containing important physical meanings in SPE-salt systems.…”

Electrochemical Properties for Solid Polymer Electrolyte/Salt Systems in Lithium Secondary Batteries

“…1 Phase diagram studies of PEO-based electrolyte systems were initiated mainly as a consequence of previous ionic conductivity studies which showed significant variations of the ionic conductivity as a function of different experimental parameters, thermal history being one of the most important. Robitaille et al 2 and Bésner and Prud'homme 3 reported complete phase diagrams for PEO/NaSCN and PEO/KSCN. Stainer et al 4 constructed the phase diagram for PEO/NH 4 SCN.…”