Supercritical fluid fractionation

Purification of poloxamers has been extensively investigated due to their use in medical applications, the intention often being to remove potentially toxic components. Supercritical fluid fractionation and liquid fractionation have been used successfully to remove low-molecular weight impurities and antioxidants from poloxamers. Gel filtration, high-performance liquid chromatography (HPLC), and ultrafiltration through membranes are among the other techniques examined [5]. 

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. 

SCCO2 fractionation of fish oil ethyl esters was employed to prepare ethyl esters of two omega-3 fatty acids. The triacylglycerol products were isolated using supercritical fluid fractionation (Nilsson et al., 1989). 

Daneshvar M, Gulari E (1992) Supercritical-fluid fractionation of poly(ethylene glycols). J Supercrit Fluids 5(2) 143-150... 

USAF (United States Air Force). 1991. Supercritical Fluid Fractionation of JP-8. Final report for period August 1990-June 1991. Aero Propulsion and Power Directorate, Wright Research Development Center, Air Force Systems Command, Wright-Patterson Air Force Base, OH. NTIS Publ. No. AD-A247-835. 

Figure 1. Setup for supercritical fluid fractionation. Abbreviations are as follows TC, temperature controller T, thermocouple PC, pressure controller and P, pressure gauge. The experimental conditions were as follows supercritical solvent, ethane pressure profiling, 800-4000 psi (1 psi = 6895 Pa) and temperature, 80 °C.

Supercritical Fluid Fractionation. In general, the methods previously reported (9, 13) were used. The setup is shown in Figure 1. 

Supercritical-fluid-fractionation techniques have been explored to separate the aminopropyl-terminated oligomers into fractions of narrow poly-dispersity. The fractions have been fully characterized in terms of their structure, molecular weight, molecular weight distribution, and functionality. The results of selected studies are presented in this section. 

Figure 9. A typical supercritical fluid fractional separation system.

The TG products were isolated using supercritical fluid fractionation employing pressure programming at 60 with pure CO2 and CO2 plus 4 wt% ethanol. Analyses of the isolated EE and TG indicated that reactant EE are incorporated into the TG with little or no selectivity regardless of chain length or degree of unsaturation. 

Figure 8 Thermal gradient supercritical fluid fractionation column.

The properties of siloxane-containing block copolymers prepared from the functionally terminated siloxanes are influenced by the molecular weight distribution of the material which is typically Gaussian. The range of potential applications of the block copolymers can be extended if the molecular weight distributions of the siloxane blocks can be minimized. Thus, the impetus for evaluating supercritical fluid fractionation, aside from its utility as a characterization tool, as a means of improving end product performance is established. 

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... 

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. 

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. 

Barry, E. F., P. Ferioli, and J. A. Hubball. 1983. Purification of OV-17 by supercritical fluid fractionation for fused silica capillary gas chromatography. J. High Resolut. Chromatogr. Chromatogr. Commun. 6 172. 

Ellis, S. R. M. 1971. Vapor phase extraction process. Br. Chem. Eng. 16 358. Elsbernd, C. S. 1988. Synthesis, kinetics, and supercritical fluid fractionation studies of functional organosiloxanes and their incorporation into segmented copolymers. Ph.D. diss., Virginia Polytechnic Institute and State University. 

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