Equilibrium melting temperature diluted systems

In order to obtain the product of the interfacial free energies for nucleation from the slopes of the straight lines in Fig. 13.31 (as well as for other systems) both the effective volume fraction and reliable equilibrium melting temperature need to be known. For these reasons values of the product OenCTun cannot be obtained in a routine manner even for crystallization from dilute solutions. Even if the proper value of aenO un could be obtained from experimental data there is a problem that has been discussed previously. It is the matter of obtaining aen- To obtain this important quantity the value of needs to be independently known. As... 

EquUibrium constants are of the order of unity for polyesters and polycarbonates, and of the order of hundreds for polyamides. In order to obtain end-group conversions above 0.99, this implies a concentration of by-product [W] below 10" times the concentration of bonds in the former two systems. The high temperature of the processes increases the vapor pressure of the by-products and their equilibrium solubility decreases, but even so partial pressures of some millibars for polyester and polycarbonate processes are required they may be obtained by using a combination of vacuum and inert stripping gas. These low partial pressures and consequently nearly infinite dilution often justify the application of Henry s law to describe the vapor-liquid equilibrium according to Eq. (24), in which Pw is the equilibrium vapor pressure of by-product W, Hw is its Henry constant for the polymer melt (in the usual range of 10-1000 bar), ww is mass fraction in the melt, is the vapor pressure of pure W, and lw is its weight fraction activity coefficient. 

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