J.R. MacCallum

An investigation of the conducting species in polymer electrolytes

Abstract The conductances of LiClO 4 and LiCF 3 SO 3 solutions in a low mol. wt polyether have been measured as a function of salt concentration. The results have been interpreted in terms of ion pair and triplet formation. It is concluded that, at the electrolyte concentrations normally used to form “polymer electrolytes”, most of the salt is present as ion pairs and that the conducting species are likely to be triplets and higher charged aggregates rather than single ions.

The effects of radiation-induced crosslinking on the conductance of LiClO4·PEO electrolytes

The conductance/temperature behaviour of poly(ethylene oxide)/LiClO4 electrolyte prepared under anhydrous conditions has been studied. Amorphous electrolyte samples have been crosslinked using γ-radiation from a Co-60 source. It is shown that light crosslinking cause a small reduction in the conductivity, probably due to restricted backbone segmental motion; however the tendency of electrolyte, treated in this way, to transform to a mixed crystalline/amorphous state of much lower conductivity, seems to have been comletely eliminated.

Preparation and characterization of a lithium ion conducting electrolyte based on poly(trimethylene carbonate)

Abstract In this paper, the results of preliminary studies of two new solvent-free polymer electrolytes based on poly(trimethylene carbonate), p(TMC), with lithium trifluoromethanesulphonate, (triflate), and lithium perchlorate are described. Thin films of these electrolytes were obtained by evaporation of solvent from homogeneous mixtures of known masses of host polymer and salt. Electrolytes with compositions of n between 1.5 and 85, where n represents the molar ratio of (OCOCH2CH2CH2O) units per lithium ion, have been prepared. These solvent-free electrolytes were characterized by measurements of total ionic conductivity, differential scanning calorimetry (DSC) and thermogravimetry (TGA). As expected from previous studies with these salts in poly(ethylene oxide), PEO, the triflate-based system showed superior thermal stability but with a lower total ionic conductivity than that of the perchlorate-containing electrolyte. The highest conductivity (approximately 3×10−4 Ω−1 cm−1) was found at 95°C with the electrolyte composition of (TMC)2LiClO4.

Synthesis and characterization of ABA block copolymer-based polymer electrolytes

Abstract The synthesis and some of the properties of a novel ion-conducting polymer are described. The polymer, based on a styrene-butadiene-styrene ABA triblock copolymer has pendant, short-chain poly(ethylene oxide) (PEO) grafted onto the B block. The concentration of PEO in the polymer can be controlled by varying either the number of pendant groups per molecule or the molecular weight of the PEO chain. The polymers were combined with LiCF 3 SO 3 to form ion-conducting phases. The conductivities of films of these materials were found to be sensitive to preparation technique, and especially to casting solvent. The best conductivities, typically 10 −5 S cm −1 at ambient temperatures, were obtained using solvents that were likely to induce microphase separation (with concomitant improvement in the mechanical properties of the system). The temperature dependence of the conductivity suggested that the materials were essentially amorphous over the range studied.

Poly(ethylene oxide) - LiCF3SO3 - polystyrene electrolyte systems

Abstract Polymer electrolytes based on poly(ethylene oxide), polystyrene and LicF 3 SO 3 have been prepared. Thin films formed by a hot-pressing technique had superior conductivities to solvent cast systems. The inclusion of the polystyrene support polymer at concentrations up to 60% by volume, improve the physical strength of the electrolytes without seriously impairing the conductivity at temperatures above 60 °C.

A novel technique for measuring TH diffusion constant of oxygen in polymer films

Abstract A simple technique has been developed facilitating measurement of the diffusion constant for O 2 in polymeric glasses. The method used is such that measurements can be made over a wide range of temperatures. Measured values for the diffusion constant for O 2 in poly(styrene) and poly(methyl methacrylate) are reported.

Hindered Amine Light Stabilizers: A proposed photo-stabilization mechanism

Abstract Hindered amines are known to act as good photo-oxidative stabilizers for polymers, but controversy still surrounds the mechanism whereby this is achieved. The significance of complex formation between hindered amines and hydroperoxide groups in the mechanism is questioned, and the inability of hindered amines, or their nitroxide derivatives, to act as excited state quenchers is demonstrated. A mechanism involving complexation of trace transition metal impurities is proposed to account for the photo-stabilizing ability of these compounds.

Conductivity of poly(ethylene oxide)/silica composite films containing lithium trifluorosulphonate

Conductivity of lithium triflate dissolved in silica/PEO composites is reported. The amount of silica added to the films varies between 7% and 24%, high and low molar mass PEO samples are used as co-composite materials. Measurements indicate good conductivity coupled with good physical properties over a range of temperatures.

The photodegradation of poly(vinyl chloride)—V The effect of wavelength of irradiation on the dehydrochlorination reaction

Abstract For a purified sample of poly(vinyl chloride), it is found that radiation of wavelength less than 300 nm causes dehydrochlorination. It appears that polychromatic radiation yields a constant ratio of concentrations of polyenes, even from the very early stages of reaction. It is proposed that energy transfer is an important step in the photodecomposition of poly(vinyl chloride).

The kinetic compensation effect for the thermal decomposition of some polymers

Abstract The kinetic compensation effect was investigated for a great variety of polymers, showing its existence for a homogeneous solid state decomposition.