Free volume effect weight

McMaster " demonstrated that LOST behavior arises from free volume effects. In particular, if the pure component thermal expansion coefficients are sufficiently different, LCST behavior becomes more likely. It should be noted again that the normal entropic effects are very small. By using Flory s equation-of-state thermodynamics, it can be demonstrated that LCST behavior should generally be expected for high-molecular-weight mixtures. Although the detailed thermodynamic arguments are beyond the scope of this chapter, the theory has been reviewed recently. " ... 

Free volume effects have been considered in studies done on polyisoprene and polybutadiene. It has been shown that the inclusion of corrections for changes in free volume with molecular weight in calculating diffusion coefficients brings closer agreement between theory and experiments. 

Fig. 17a-c. Effective proton transverse relaxation time T2=(l/T2,j) (see Eq. 160) in different linear polymers of different molecular masses measured at 90 MHz as a function of the reciprocal temperature [33]. A characteristic temperature Tchar shows up for MyJ>Mc in the form of a relatively sharp bend in the temperature dependence. This bend disappears when approaching the critical molecular weight from above. For M additional molecular weight dependence reveals itself as a consequence of the chain length dependent free-volume effects, a Polyisobutylene. Symbols for the data points have been plotted for three different molecular weights only, while the data for all other molecular weights are represented by polygonal lines for the sake of clearness. From the top to the bottom, the lines refer to data for M = 1,600 5,800 15,800 34,000 55,000 80,600 122,000 182,000 393,000 610,000 830,000 1,100,000. The critical molecular... 

Experimental data of the effective transverse relaxation time are plotted in Fig. 17 as a function of the reciprocal temperature for different polymers. The molecular weight dependence for M free-volume effects. We will come back to this sort of molecular weight effect later in the review. 

The viscous shear properties at any given shear rate are primarily determined by two factors, the free volume within the molten polymer mass and the amount of entanglement between the molecules. An increase in the former decreases the viscosity whilst an increase in the latter, i.e. the entanglement, increases viscosity. The effects of temperature, pressure, average molecular weight, branching and so on can largely be explained in the these terms. 

The reactivity of macromonomers in copolymerizalion is strongly dependent on the particular comonomer-macromonomer pair. Solvent effects and the viscosity of the polymerization medium can also be important. Propagation may become diffusion controlled such that the propagation rate constant and reactivity ratios depend on the molecular weight of the macromonomer and the viscosity or, more accurately, the free volume of the medium. 

It was suggested in a previous publication (9) that flocculation at the UCFT can be ascribed to the free volume dissimilarity between the polymer stabilizing the particle and the low molecular weight dispersion medium. Incorporating this idea in a quantitative way into the theory of steric stabilization allowed for a qualitative interpretation of the experimental data. This idea is further extended to include the effect of pressure on the critical flocculation conditions. 

The equivalent weight increased from 210 for UPE A to 316 for UPE E with one third of the maleic anhydride was replaced with succinic anhydride and 634 for UPE F with two thirds of the maleic anhydride is replaced with succinic anhydride. This change will effectively decrease the crosslink density of the final cured film. The Brookfield viscosities of the two new polyesters (E and F) are less than those from the first series. Since the molecular weights should be about the same (1760), it is not surprising that the Brookfield viscosities were relatively constant for all three unsaturated polyesters. The slight decreasing trend in viscosity with increasing succinic anhydride in the unsaturated polyester may be due to the increased free volume obtained when succinic anhydride is substituted for maleic anhydride. 

A comprehensive model which is based on the free-volume theory and which accounts for the effect of molecular weight and solvent on chain entanglements and glassy-state transition has been recently developed by Marten and Hamielec (7 ). This model accounts for diffusion-controlled termination and propagation... 

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