Polymers, ionic glass transition

Before treatment with alcohol, the ionic conductivity of lithium borate polymers was 6.23 X 10-5 to 2.07 X 10-7 Scm-1 at 50°C. The maximum ionic conductivity was observed for the polymer with a PE040o spacer unit. After the polymer reaction with alcohols, glass-transition temperatures of these polymers were found to be -52 to 39°C, which was higher than that of poly(lithium mesitylhydroborate) ( 69°C). 

Table 6 Glass Transition Temperature, Ionic Conductivity and VFT Parameters For Polymer/Salt Hybrids 10...

The mobility of the ions in polymer electrolytes is linked to the local segmental mobility of the polymer chains. Significant ionic conductivity in these systems will occur only above the glass transition temperature of the amorphous phase, Tg. Therefore, one of the reqnirements for the polymeric solvent is a low glass-transition temperature for example, Tg = —67°C for PEO. 

Bamford, D., Dlubek, G., Reiche, A., Alam, M.A., Meyer, W., Galvosas, P., Rittig, F. (2001) The local free volume, glass transition, and ionic con-ductivity in a polymer electrolyte a positron lifetime study . J. Chem. Phys. 115, 7260. 

When the polymer film is heated up to its glass transition temperature, the material conductivity facilitates the breakdown risk, and the sample surface may be seriously damaged. Moreover, the conductivity of a polymer film containing ionic chromophores diminishes the amplitude of the applied electric field. 

In dealing with the glass transitions of ionic inorganic polymers, several factors need to be considered these are ... 

To what extent do linear ionic polymers differ from thdr non-ionic counterparts Specifically are tte theories developed for organic polymers with regard to, for instance, the molecular weight dependence of the glass transition applicable also to ionic systems, and if not are the ionic systems qualitatively different from their non ionic counterparts or is the difference merely quantitative, implying only a higher d ree of intermolecular attraction ... 

The implications of the drastic difference in the Tg vs. relation for the two types of polymers described here will be discussed more fully in Section II-D however, one can safely say that the difference between ionic and non-ionic polymers with regard to their glass transition behavior is quantitative rather than qualitative, provided that the number of ions per repeat unit is the same for the terminal groups as for the middle groups. The ions, most reasonably, act to increase the inter-molecular forces and thus raise the glass transition, just as hydrogen bonds or strong dipoles would be expected to do. 

The observed leveling-off of the qja vs. Tg plot after calcium might be an experimental error. However, it is believed to be real, for the following reason. Experience with the ionic phosphate polymers 19, 21, 22) (see also the description of the NaPOg-PgOg system below) indicates that the microscopic mechanism of the glass transition in some cases... 

This paper has reviewed several studies, particularly those performed on the phosphate polymers, in which ionic forces were imjx>rtant in determining the properties or behavior of the material. Only very few properties were investigate among these were 1) the glass transitions as a function of the molecular we ht, the nature of the terminal group, and the nature of the counterion, 2) the viscoelastic properties as a function of the counterion and 3) the viscoelastic relaxation mechanism, with specific emphasis on the separation of the a and mechanisms. In this treatment, a deliberate attempt was made to present pertinent theories, insofar as they exist, but it seems evident that here as much work remains to be done as on the experimental level, if not more. 

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