High-molar-mass polymer systems

Figure 15. The LCT configurational entropy s T (normalized as in Fig. 11) as a function of the reduced specific volume 8v = [v T) — v(T = To)]/v(T), which is a measure of the excess free volume in the polymer system. Different curves refer to the F-F and F-S polymer fluids and to low and high molar mass polymer chains.

The parameter K was assumed to be independent of the concentration but dependent of the molar mass. The determination of K was carried out with a single viscosity measurement. In reality the Fikentscher K depends on the concentration and shows only small changes with the molar mass for high molar mass polymers [44]. It should be used only in a small and known concentration and molar mass range, for which the K value was determined. In all other cases, the intrinsic viscosity should be used as a characteristic value for polymer solvent systems. 

Additives such as pyridine, tertiary amines, or acetylacetone have been used to modulate the metal acidity and improve the sdectivity toward high-molar-mass polymers. As an example, the addition of acetylacetone as chdating agent to AIR3/H2O or Z-nRojH O systems permits, by limiting the cationic process, to... 

The preceding sections highlight the many constraints upon the formation of high molar mass polymers by linear step polymerization. Special polymerization systems often have to be developed to overcome these constraints and are exemplified here by systems developed for the preparation of polyesters and polyamides. 

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