Supercritical polymer fractionation

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

Puskas, J.E., Pattern, W.E., Wetmore, P.M., and Krukonis, A. Synthesis and characterization of novel six-arm star polyisobutylene-polystyrene block copolymers. Rubber Chem. TechnoL, 72, 559-568, 1999. Puskas, J.E., Wetmore, P.M., and Krukonis, A. Supercritical fluid fractionation of polyisobutylene-polystyrene block copolymers, Polym. Prepr., 40, 1037-1038, 1999. 

In most enzymatic syntheses of polyesters, the polymerization was carried out in organic solvents or bulk. Using supercritical fluoroform as solvent, the polymerization of bis(2,2,2-trichloroethyl) adipate and 1,4-butanediol was demonstrated [60]. The molecular weight increased as a function of the pressure. By changing the pressure, the low-dispersity polymer fractions were separated. 

Another important aspect of supercritical fluids application is in polymer fractionation, in order to obtain mono-dispersed molecular weights. The simulation of the fractionation of polyethylene from ethylene and hexane solutions into fractions of different molecular weights was proposed by Chen et al. [7]. 

Lopes JA, Gourgouillon D, Pereira PJ et al (2000) On the effect of polymer fractionation on phase equilibrium in C02 + poly(ethylene glycol)s systems. J Supercrit Fluids 16(3) 261-267... 

Supercritical carbon dioxide has been industrially used in a variety of processes, including coffee decaffeination, tea decaffeination, and extraction of fatty acids from spent barley, pyrethrum, hops, spices, flavors, fragrances, com oil, and color from red peppers. Other applications include polymerization, polymer fractionation, particle formation for pharmaceutical and military use, textile dyeing, and cleaning of machine and electronic parts. 

Although the density of the supercritical extractant is typically lower than that of the polymer, the column could as easily operate upside down, that is, if the density of the supercritical extractant was higher than that of the feed oil, the inlet positions of the respective streams shown in figure 9.2 would be reversed. Later in this chapter some phase and fractionation studies on an acrylate-ethylene copolymer with supercritical chlorodifluoromethane are presented. Over much of its active P-T range, supercritical chlorodifluoromethane is more dense than some of the polymers. Therefore, if that system were to be scaled to continuous operation at the commercial level, the liquid or melted polymer would be fed to the bottom of the extractor and chlorodifluoromethane to the top the subsequent fractions would be removed from the top of each separation vessel instead of from the bottom, as shown in the figure. In the polymers patent section of this book, we describe a process for polymer fractionation via stepwise pressure reduction exactly analogous to the process shown schematically in figure 9.2—the Hunter and Richards 1945 patent. 

Because the interfering amine functionality was replaced with an imine, it was possible to analyze each fraction for molecular weight distribution by GPC using either polystyrene or specially synthesized polydimethylsiloxane calibration standards. The low molecular weight cyclic content of the early fractions was determined by HPLC and the higher cyclics (Dg, D7, Dg) were identified by GC-MS. The absence of amine functionality in the early fractions, which is indicative of the presence of cyclics, was also confirmed by FT-IR. It is apparent, then, that complete characterization of the fractionated polymer was no small task, especially in light of the fact that even though supercritical fluid fractionation can process initial sample sizes of 20-25 g, some of the fractions were only 0.5-1.0g in size, and therefore the workup required substantial effort and care. 

Krukonis (1982a) also found that in some cases supercritical fluid fractionation can concentrate polymer species that escape detection during conventional analysis of the parent polymer. Consider, for example, figure... 

Figure 9.40 GC-MS chromatogram of fraction 3 of the chlorotrifluoroethylene polymer fractionated with supercritical ethylene.

In the first edition of this book a report of the results completed under the National Science Foundation funding was given of the supercritical fluid fractionation of a number of liquid crystal and photoresist polymers (Krukonis, 1984b). Table 9.31 gives the structures of several polymers that were tested on the program. Results with three of these polymers are presented in order to illustrate the extent of separation that can be achieved by supercritical fluid fractionation. 

As the next step in the evaluation of supercritical fluid fractionation of the polysiloxane polymers, fractions are being converted into block copolymers for the purpose of determining the properties that derive from the narrow molecular weight fractions. 

Figure 9.47 GPC chromatograms of the fractions of the low-molecular-weight cyclohexyl-substituted polysilane polymer fractionated with supercritical propane. (A, B, and C are sequential fractions.)...

Reference to parts of this patent was made in Chapter 9. There are actually two processes described that are carried out with supercritical fluids fractionation of solid polymers and comminudon of solid polymers that are normally difficult to obtain in the form of fine granules or powders. In the examples given, a number of polymers, operating condidons, and observadons are presented. C)ne of the examples is presented here for its informadonal value. 

Supercritical fluid fractionation of polymers fundamental and practical... 

PRA Pratt, J.A., Lee, S.-H., and McHugh, M.A., Supercritical flirid fractionation of copolymers based on chemical composition and molecular weight, J. Appl. Polym. Sci., 49, 953, 1993. 

The Borstar process involves the use of two cascaded reactors. In the first stage, ethylene is polymerized in supercritical propane by the addition of a transition metal catalyst in a loop reactor, which leads to low-molecular-weight polyethylene. The reaction mixture is then transferred into a gas-phase reactor in which high-molecular-weight polymers are formed. The direct result of this two-stage process is an intimate mixing of the two polymer fractions, which differ in their molar masses. 

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