Polystyrene-Toluene

Styronc, O Toluene,Polystyrene DVB Divinyl Benzene, crosslinker for Network II... 

Figure 5-3 Test of predictive capabilities of proposed free-volume model using data for the toluene polystyrene system. Only data points represented by solid symbols were used to obtain free-volume parameters (73).

Lundberg. Bull s data at T = 298.15 K have been used for the activity of water in this system." Starkweather has determined the activity of water in the concentration range 0 volume fraction as ai = 12 1, the expression that was used in our calculations. The molecular weight and the partial specific volume of collagen were taken from ref 41. The results of the calculations are presented in Figures IB, 2B, and 3B. In contrast to the toluene + polystyrene mixture, the solvent (water) is in deficit around a central water molecule but in excess around a protein molecule. 

Figure 4. The contribution to ISnn due to different volumes of solvent and solute (A) toluene + polystyrene, (B) water + collagen, (C) water...

Let us emphasize the physical significance of the obtained results regarding the excesses (deficits). A n > 0 means preferential hydration (or solvation in the case of toluene + polystyrene mixture) of the solvent molecules, and A i2 > 0 means that the polymer (protein) molecules are preferentially hydrated (or solvated for the toluene + polystyrene mixture). 

In contrast to Ann, Ann 0 for all mixtures investigated, and hence, the polymers or proteins are preferentially hydrated (solvated in the case of toluene + polystyrene mixture). Let us examine separately the contributions to Ann provided by the entropic and enthalpic factors. The contribution to Ann provided by the different sizes of the solvent and polymer (protein) molecules will be evaluated from the excess in an ideal... 

Figure 4.4.15. Experimental data of the system toluene + polystyrene, = 1380 g/mol, at 323.15K, isopiestic vapor pressure/sorption measurement (fiill circles), VPO at higher concentrations (gray circles), data from authors own work.

Fig. 13. Concentration dependence of the self-diffusion coefficient and the thermodynamic factor Q for the toluene-polystyrene system at 110°C and for the o-xylene-polyethylene system at 150°C. Q = (l a>A)(d In a /d In coa- From Ref. 45.

Except for supercritical extraction conditions, hydrostatic pressure effects are typically of negligible importance for simple solvent vapors diffusing in polymers, since the saturation vapor pressure is low, <101.3 kPa (1 atm), in most applications. The predictive power of the approach is indicated by the results for the mutual diffusion coefficient of toluene in a toluene-polystyrene system (Fig. 14) (35). 

Fig. 14. Dependence of diffusivity on mass fraction for the toluene-polystyrene system.

Even in the case of toluene-polystyrene solutions, xi2 is in the range 0.3-0.4. Thus a positive enthalpy of mixing tends to oppose the polymer dissolution in a solvent (AG > 0). In the Flory-Huggins model, two components can mix with each other only if the positive enthalpy term is compensated by the entropy term (-TA.S), which is always negative. 

It can be seen that a filament is formed during the start of the formation of the toluene/polystyrene droplet. This behavior has been observed by several researchers for polymer solutions and is explained as being due to the stretching of the polymer and the non-Newtonian behavior of the... 

Solution We approximate the styrene-polystyrene system by using a toluene-polystyrene system. For this, the viseosity ean be estimated by... 

This process has been illustrated by Duda et al. for a variety of polymers [59] and Figine 13.12 shows the predictive abilities of their theory for the toluene-polystyrene system. Parameter values used are listed in Table 13.1. The results obtained are excellent. These authors also note that the diffusion coefficient given by Eq. (13.6.11) is insensitive to polymer molecular weight, and there is, therefore, no influence of polydispersity. Furthermore, for semicrystalline polymers above the glass transition temperature, the polymer may be considered to be made up of two phases—one of which has a zero diffusivity [51]. Thus, if the volume fiaction of the crystalline phase is 4>, the effective diffusivity of the polymer is D(j). Finally, Kulkami and Mashelkar [63] have proposed an altered fi-ee-volume-state model that seeks to provide a unified... 

Figure 13.12 Test of predictive capabilities of free-volume theory using data for the toluene-polystyrene system. Only data points represented by solid symbols were used to obtain free-volume parameters. (From Duda, J. L., J. S. Vrentas, S. T. Ju, and H. T. Liu Prediction of Diffusion Coefficients for Polymer-Solvent Systems, AIChE J., vol. 28, pp. 279-285. Reproduced with the permission of the American Institute of Chemical Engineers Cop3right 1982 AIChE. All rights reserved.)...

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