Glass Transitions in Ionic Polymers

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  

Since a variation of the counterion implies a corresponding variation in interchain attraction, can the glass transition be correlated with various parameters of the counterion by simple electrostatic considerations  

To what extent do the cations act as crosslinks in the classical sense in parallel with their effect on the glass transition  

With regard to the network poljuners specifically, is there a uniform and predictable way in which the introduction of purely ionic forces (in the form of network modifiers) affects the glass transition or do the effects depend much more on the nature of the network  

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L. Holliday, in Ionic Polymers, edited by L. Holliday, John Wiley Sons, New York (1975), 1-68. The glass transition in ionic polymers is discussed on pages 35-46. 

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. 

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... 

It is evident that under these conditions a significant increase in the glass transition of the polymer backbone over that of PS is observed, but more importantly, a substantial rubbery plateau is observed which extends to temperatures above 250°C. Clearly this rubbery plateau can be attributed exclusively to ionic assoociation. The magnitude of the increase in glass transition and the actual modulus of the plateau depends on the level of metal sulfonate groups incorporated in the PS chain. 

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. 

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. 

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