Polymer fractionation

Procedures for separating high polymers into fractions of restricted molecular weight range vary, but all of them depend on the very small decrease in solubility with increase in molecular weight in a given poly- 

The theory of fractionation will be discussed in Chapter XIII. It is sufficient to observe here that polymer fractionation depends on the tenuous differentiation indicated above. In order to make the most of it, the ratio of the volumes of the supernatant and precipitated phases should be as large as possible the ratio should be at least ten and 

The successive fractions may be obtained by lowering the temperature in suitable increments rather than by varying the solvent composition isothermally. If a poor solvent is found from which the polymer precipitates in a convenient temperature range, it may be used alone without addition of another component. 

Fractional extraction occasionally is employed. The polymers of lowest molecular weight are extracted first from the sample, which is 

Probable errors in assigning the integral distribution curve, as indicated by scatter of the points in Fig. 57, are magnified in the process of taking the slope for the deduction of the differential distribution. Only the approximate location of the maximum and breadth of the latter are experimentally significant. 

---

If the poorer solvent is added incrementally to a system which is poly-disperse with respect to molecular weight, the phase separation affects molecules of larger n, while shorter chains are more uniformly distributed. These ideas constitute the basis for one method of polymer fractionation. We shall develop this topic in more detail in the next section. 

From plots of n/c2 versus C2, evaluate M for each of the four polymer fractions. Do the data collected from the two different solvents conform to expectations with respect to slope and intercept values ... 

Both preparative and analytical GPC were employed to analyze a standard (NBS 706) polystyrene sample. Fractions were collected from the preparative column, the solvent was evaporated away, and the weight of each polymer fraction was obtained. The molecular weights of each fraction were obtained usmg an analytical gel permeation chromatograph calibrated in terms of both and M. The following data were obtained ... 

Data relating to polymer fractions insoluble in / -heptane. 

Montedison and Mitsui Petrochemical iatroduced MgCl2-supported high yield catalysts ia 1975 (7). These third-generation catalyst systems reduced the level of corrosive catalyst residues to the extent that neutralization or removal from the polymer was not required. Stereospecificity, however, was iasufficient to eliminate the requirement for removal of the atactic polymer fraction. These catalysts are used ia the Montedison high yield slurry process (Fig. 9), which demonstrates the process simplification achieved when the sections for polymer de-ashing and separation and purification of the hydrocarbon diluent and alcohol are eliminated (121). These catalysts have also been used ia retrofitted RexaH (El Paso) Hquid monomer processes, eliminating the de-ashing sections of the plant (Fig. 10) (129). 

Currently, there is continuing work on an iadustry standard method for the direct determination of monomer, dimer, and trimer acids. Urea adduction (of the methyl esters) has been suggested as a means of determining monomer ia distilled dimer (74). The method is tedious and the nonadductiag branched-chain monomer is recovered with the polymeric fraction. A micro sublimation procedure was developed as an improvement on urea adduction for estimation of the polymer fraction. Incomplete removal of monomer esters or loss of dimer duriag distillation can lead to error (75). 

Residuum oil supercritical extraction-petroleum deasphalting Polymer fractionation Edible oils fractionation Analytical SGF extraction and chromatography Reactive separations... 

A typical balance of processability and end use performance is the general requirement of polymeric resins. The studies on the different polymer fractions have provided a great support in tailoring the MW and MWD in order to achieve the required properties and eliminating the unwanted molecular species. The increase in low-... 

Koningsveld, R. Preparative and Analytical Aspects of Polymer Fractionation. Vol. 7. 

For the purpose of illustration, let us consider the degradation behavior of a hypothetical monodisperse polymer fraction flowing along the central streamline. 

The calculations are applied to a polymer sample following a Schulz-Zimm distribution with Mw = 1.03 x 10s and Mw/N4n = 1.017. These values are representative for the polymer fractions used in most of the experiments in transient elongational flow [147, 155], To visualize the evolution of the degradation, it is convenient to make a distinction between the polymer fraction N from the starting material which remains intact and the fraction Nf newly formed following the degradation process... 

Fig. 45. Radial strain rate distribution function and its influence on the degradation yield O (r0 orifice radius, r axial distance from the orifice center) C(r2/r0) variation of the strain rate as a function of (r/r0)2 obtained from the reciprocal of the degradation yield curve of a monodisperse polymer fraction (see Fig. 46) C(r/r0) radial distribution of the strain rate in the plane of the orifice, calculated from the function C(r2/rg)...

Fig. 46. Dependence of the degradation yield on strain rate e(0), and on ratio of weight- to number-average molecular weight (Mw/M ) of polymer as indicated at curves. The dotted line is extrapolated for a monodisperse polymer fraction...

Table 1. Principal characteristics of the polymer fractions used...

The syrup discharging from the tower enters an enclosure where it is subjected to milling under vacuum and/or an inert atmosphere. Vacuum as high as 29.8 in. Hg is suggested. The action in this chamber accomplishes three purposes a) blends the polymer melt, b) removes most of the unreacted volatile materials in the melt, and c) degrades the higher molecular weight polymer fraction = 150,000) without... 

There Is a large body of experimental literature relating to polymer fractionation In liquid-liquid equilibria. In addition, numerous authors have analyzed polymer fractionation using Flory-Huggins theory. We have considered use of the corresponding states theory to model polymer fractionation for the ethylene/ polyethylene system at reactor conditions (18). Results of the... 

Segregated CFSTR Micro-mixed CFSTR With Dead Polymer Fraction D D /D D D /D... 

Autocatalytic rate constant for initiation Fraction active polymer in CFSTR with dead polymer Fraction by-pass in by-pass CFSTR... 

NMR data were obtained for individual fractions. Whenever detailed data are available for polymer fractions, we can use the approach outlined above to advantage. We shall show the analysis of the data for Sample I in their paper. For convenience, the NMR intensities are given in Table I. 

In this case, the intensities corresponding to the various tacticity sequences are directly analyzed. The information content, however, is somewhat lower than in the case where the NMR data of pairs of polymer fractions are analyzed simultaneously. Nevertheless, useful information is available. 

In order to test higher-order or multi-site models, it is preferable to study HMR data of polymer fractions. In this work, we shall use the pairwise HMR/fractions data to fit to multi-site models. This Is carried out in the same way as in the pairwise fraction on the tactlcity data. We can either use the two-state B/B model, or even three-state B/B/B model If applicable. The comonomer sequence intensity data for the two fractions are entered Into the computer. A total of 12 entries are Involved (6 for each fraction). The equations for the three-state copolymer... 

---