Carbon dioxide is often promoted as a sustainable solvent, as CO 2 is non-flammable, exhibits a relatively low toxicity and is naturally abundant. However, injudicious use of carbon dioxide in a process or product can reduce rather than enhance overall sustainability. This review specifically examines the use of CO 2 to create greener processes and products, with a focus on research and commercialization efforts performed since 1995. The literature reveals that use of CO 2 has permeated almost all facets of the chemical industry and that careful application of CO 2 technology can result in products (and processes) that are cleaner, less expensive and of higher quality.

Supercritical and near-critical CO2 in green chemical synthesis and processing

Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials. This review focuses on recent advances in polymer synthesis and processing using liquid and supercritical CO2. The synthetic techniques discussed include homogeneous solution polymerisation, precipitation polymerisation, dispersion and emulsion polymerisation, and bulk polycondensation. The formation of porous polymers and polymer blends is also considered, and the specific advantages of CO2 in these processes are evaluated in each case. The use of CO2 as a solvent for polymer processing is reviewed from a materials perspective, with particular attention being given to the formation of polymers with well defined morphologies. The variable solvent strength associated with supercritical fluids has been utilised in areas such as polymer fractionation and polymer extraction. Plasticisation phenomena have been exploited for the impregnation and heterogeneous chemical modification of polymeric materials. The formation of microcellular polymer foams by pressure induced phase separation is considered, as is the use of CO2 for polymer particle formation, spray coating, and microlithography. The aim of the review is to highlight the wide range of opportunities available to the materials chemist through the use of carbon dioxide as an alternative solvent.

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Polymer synthesis and processing using supercritical carbon dioxide

Polymerizations in Supercritical Carbon Dioxide

Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubilit...

Improving carbon dioxide solubility in ionic liquids.

Rate coefficients of free-radical polymerization deduced from pulsed laser experiments

Cloud-point data to temperatures of 270 °C and 3000 bar are presented for CO2 with the family of poly(acrylates) including methyl, ethyl, propyl, butyl, ethylhexyl, and octadecyl, with poly(butyl methacrylate), with poly(vinyl acetate), with statistically random copolymers of poly(ethylene-co-methyl acrylate) with 41, 31, and 18 mol % acrylate, with poly(tetrafluoroethylene-co-hexafluoropropylene) and poly(vinylidene-co-hexafluoropropylene) copolymers, each with ∼20 mol % hexafluoropropylene, and with Teflon AF. Over the same range of conditions, CO2 cannot dissolve polyethylene, poly(acrylic acid), poly(methyl methacrylate), poly(ethyl methacrylate), polystyrene, poly(vinyl fluoride), or poly(vinylidene fluoride). CO2 is a weak solvent that exhibits the temperature-sensitive characteristics observed with polar solvents. The solubility of a nonpolar hydrocarbon polymer or a copolymer in CO2 can be increased by at least partially fluorinating the polymer or by incorporating some polar groups into the backb...

Solubility of Polymers and Copolymers in Supercritical CO2

The cloud-point behaviors of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-22 mol % hexafluoropropylene) (VDF–HFP22) are reported at temperatures up to 250 °C and pressures up to 3000 bar in supercritical CO2, CHF3, CH2F2, CHClF2, CClF3, CH3CHF2, CH2FCF3, CHF2CF3, and CH3CClF2. The molecular weight of PVDF has a smaller effect on the cloud point than the solvent quality. Cloud-point pressures for both fluoropolymers decrease as the solvent polarizability, polar moment per molar volume, and density increases. However, it is extremely difficult to dissolve either fluoropolymer in CClF3, which has a large polarizability and a small dipole moment. CO2 is an effective solvent because it complexes with the CF dipole at low temperatures where energetic interactions fix the phase behavior. In addition, polymer architecture has a strong impact on the cloud-point pressure. VDF–HFP22 has lower cloud-point pressures than PVDF in all solvents because it has a larger free volume that promotes facile interactions between the solvent and the polymer segments. Cloud-point data are also reported for amorphous poly(tetrafluoroethylene-co-x mol % 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole) (TFE–PDDx ; x = 65 and 85) in CO2. These data provide an interesting comparison to the PVDF–CO2 and VDF–HFP22–CO2 systems because TFE–PDD65 and TFE–PDD87 have very high glass-transition temperatures of 160 and 240 °C, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2832–2840, 2000

Solubility of vinylidene fluoride polymers in supercritical CO2 and halogenated solvents

Cloud-point data to 270 °C and 2800 bar are presented for poly(vinylidene fluoride-co-22.0 mol % hexafluoropropylene) (Fluorel) in supercritical fluid (SCF) C3F6, CClF3, CHF3, and CO2. The impact of backbone architecture on intermolecular interactions and fluorocopolymer solubility is determined by comparing the phase behavior of Fluorel to that of poly(tetrafluoroethylene-co-19.3 mol % hexafluoropropylene) (FEP19) in the same SCF solvents. Good solvents for nonpolar FEP19 (SF6 and C3F8) did not dissolve polar Fluorel even at temperatures in excess of 260 °C. Although the small dipole moments of C3F6 and CClF3 interact favorably with the polar, vinylidene fluoride segments of Fluorel, the cloud-point curves in these two solvents exhibit a sharp rise in cloud-point pressures as the temperature is decreased. Apparently, dipolar interactions between vinylidene fluoride segments are much stronger than Fluorel−C3F6 or Fluorel−CClF3 cross-interactions as the temperature is lowered. In contrast, quadrupolar CO2 ...

Impact of Backbone Architecture on the Solubility of Fluorocopolymers in Supercritical CO2 and Halogenated Supercritical Solvents: Comparison of Poly(vinylidene fluoride-co-22 mol hexafluoropropylene) and Poly(tetrafluoroethylene-co-19 mol hexafluoropropylene)

Phase behavior and small-angle neutron scattering (SANS) measurements are reported for poly(ethylene-co-1-butene) (PEB) dissolved in pentane, pentane plus ethane, and supercritical ethane to pressu...

Todd P. Dinoia

Papers

Solubility of Polymers and Copolymers in Supercritical CO2

Solubility of vinylidene fluoride polymers in supercritical CO2 and halogenated solvents

Impact of Backbone Architecture on the Solubility of Fluorocopolymers in Supercritical CO2 and Halogenated Supercritical Solvents: Comparison of Poly(vinylidene fluoride-co-22 mol hexafluoropropylene) and Poly(tetrafluoroethylene-co-19 mol hexafluoropropylene)

SANS Study of Polymer−Supercritical Fluid Solutions: Transitions from Liquid to Supercritical Fluid Solvent Quality

Solubility and phase behavior of PEP binders in supercritical carbon dioxide