Supercritical fluid fractionation of copolymers based on chemical composition and molecular weight

Abstract

SYNOPSISPoly(ethy1ene-co-methyl acrylate) copolymers of 30, 40, 60, and 70 wt % acrylate in the backbone have been fractionated with supercritical ( SCF ) propane, propylene, butane, 1-butene, and chlorodifluoromethane. The fractionations were performed isothermaIIy using an increasing pressure profile that provided gram-sized fractions with molecular weight distributions of -1.2 to 2.2 as compared to those of the parent copolymers, which were -2.6 to 3.

Supercritical devolatilization of polymers

“…Recently, the use of supercritical fluids in the processing of polymers has received much attention. Applications include fractionation of polymers (Yilgor and McGrath, 1984;Kumar et al, 1986b;Scholsky et al, 1987;Elsbernd et al, 1990;Meilchen et al, 1990;Pratt et al, 1993;Saltzman et al, 1993) with respect to molecular weight, chemical composition and backbone structure, modification of synthetic polymers by using supercritical fluids as a solvent medium (Trivedi et al, 1994;Watkins and McCarthy, 1996), dissolution and precipitation of polymers using a supercritical solvent (Kumar et al, 1986a), separating polymcr solutions with supercritical fluids by inducing a phase split (McHugh and Guckes, 1985), generation of microcellular polymeric foams using supercritical carbon dioxide (Goel and Beckman, 19921, impregnation of polymers (Sand, 1986;Berens et al, 1992), and the utilization of supercritical fluids to extract impurities from polymers (Copelin, 1981;Yilgor and McGrath, 1984;Krukonis, 1985;Scholosky, 1987;Jarzebski et al, 1990;Venema et al, 1993). The removal of volatile impurities such as monomers, Correspondence concerning this article should be addressed to J. I.. Duda solvents, condensation by products, catalysts, and side-reaction products from polymers represent an important step in polymer processing.…”

Fractionation of poly(ethylene-co-vinyl acetate) in supercritical propylene: Towards a molecular understanding of a complex macromolecule

“…The column contains a dense knitted stainless steel mesh packing (Goodloe᭨), which row MWD fractions of increasing MW but of the same vinyl acetate (VA) content. Pratt et al 4 and serves as a high surface area support for the molten polymer. Pressure is controlled to within {5 McHugh 5 also used that technique to fractionate a series of poly(ethylene-co-methyl acrylate) bar, and the flow rate controlled via a pressurereduction valve.…”

“…Fractionation by Size: Isothermal Increasing choice of this particular SCF solvent follows from Pressure Profiling the recommendations made by Pratt et al 4 to match the physical properties of the SCF solvent Isothermal increasing pressure profiling is a wellknown technique using SCFs to fractionate polymers with those of the polymer to insure a finite solute solubility at the conditions of the fractionation.…”

“…the SCF solvent based on the CPP data reported 4 for a propylene solution containing Ç 5 wt % In principle, the MWD of the fractions can be made as narrow as desired based upon the number of frac-EMA, a LDPE copolymer structurally and chemically similar to the parent EVA used in this work; tions (pressure levels) collected. Point A is a triple point where three phases, solidfluid-liquid (SFL), coexist.…”

High Molecular Weight Poly(L‐lactide) and its Microsphere Synthesized in the Supercritical Dimethyl Ether

“…Interest stems primarily from the ability to change the bulk properties of supercritical fluids (e.g., density and solubility) dramatically with small variations in temperature and pressure such that supercritical fluids have liquidlike dissolving power while exhibiting the transport properties of a gas. [1][2][3][4][5] For example, the use of supercritical carbon dioxide (scCO 2 ) as a solvent for polymerization is attractive because of its low toxicity and cost. Also, scCO 2 is a viable 'green' alternative and can be removed without trace.…”