Broadening polymer fractionation

The nonuniform displacement can occur in the injection of the polymer solution and in the injection of the solvent. The former will be manifested in early fractions. The latter will be seen in the broadening of the distribution in late fractions and in the prolonged time necessary to wash the column. 

The micro-mixed reactor with dead-polymer model was developed to account for the large values of the polydispersity index observed experimentally. The effect of increasing the fraction of dead-polymer in the reactor feed while maintaining the same monomer conversion is to broaden the product polymer distribution and therefore to increase the polydispersity index. As illustrated in Table V, this model, with its adjustable parameter, can exactly match experiment average molecular weights and easily account for values of the polydispersity index significantly greater than 2. 

Apart from the data of thermonephelometry and HS-DSC,1H NMR studies have also revealed [27] some properties that allowed the attribution of such s-type copolymers to the protein-like ones. A marked broadening of the water proton signal was observed caused by the decreased mobility of bound water just in the vicinity of the temperature of HS-DSC peak. These data indicated the heat-induced compaction of the interior of the polymer coils, as would occur with protein-like macromolecules. Figure 5 demonstrates the experimental data, viz., the temperature dependences of signal width at half-height for the peaks of water protons recorded in D2 O-solutions of p- and s-fractions of the copolymer synthesized from the feed with an initial comonomer ratio of 85 15 (mole/mole). 

It will be seen later that it is very important to use a good value for Dg in order to obtain agreement between the model predictions cuid experimental chromatogrcuns. The parauneter Dg is not only responsible for the fractionation of the polymer but also in determining the extent of broadening. 

These equations are general and apply equally for multifunctional reactions such as that of Af with B, or that of Ay with A—A and B B. Depending on which of these reactant combinations is involved, the value of a will be appropriately determined by the parameters r,f, p, and p. For convenience the size distributions in the reaction of equivalent amounts of trifunctional reactants alone, that is, where a p, will be considered. A comparison of Eqs. 2-89 and 2-166 shows that the weight distribution of branched polymers is broader than that of linear polymers at equivalent extents of reaction. Furthermore, the distribution for the branched polymers becomes increasingly broader as the functionality of the multifunctional reactant increases. The distributions also broaden with increasing values of a. This is seen in Fig. 2-17, which shows the weight fraction of x-mers as a function of a for the polymerization involving only trifunctional reactants. 

When analyzing the deviations of phase equilibrium for real polymeric systems forming a mesophase from the theoretically calculated phase diagram, we must pay attention to one more circumstance, namely, polydisperse nature of real polymers. In all the cases the transition from an isotropic solution to anisotropic one is a result of superposition of equilibria typical of individual fractions of a polymer, which differ in molecular mass. As was shown by Flory this must result in a broadening... 

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