WO2000035998A2 - Association of compounds in carbon dioxide and the gels and/or foams formed therefrom - Google Patents

Abstract

The invention relates to a method of increasing the viscosity of supercritical CO2 by combining a compound having a CO2-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution with supercritical CO2 to form a solution. The compound is then aggregated in solution to form a supramolecular network such that the viscosity of the supercritical CO2 with the supramolecular network is greater than that of the starting supercritical CO2. The invention also relates to a method of making a microcellular foam by combining a compound having a CO2-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, with supercritical CO2 to form a solution. The compound is aggregated to form a supramolecular network in solution. Then the CO2 is removed under conditions sufficient to form a microcellular foam.

Description

ASSOCIATION OF COMPOUNDS IN CARBON DIOXIDE AND THE GELS AND/OR FOAMS FORMED THEREFROM

This work was funded by the US Dept. of Energy (National Petroleum Technology Office, DOE- NPTO, contract DE-AC26-98BC15108), and the National Science Foundation (CTS-9870925, CHE-9817240).

This application claims priority to U.S. Application Ser. No. 60/112,118, filed December 15, 1998 and to U.S. Application Ser. No.60/166,164 filed November 18, 1999. Both of these applications are incoφorated herein by reference.

FIELD OF THE INVENTION

The invention pertains to a method of increasing the viscosity of supercritical CO2 and the preparation of microcellular foam materials. More specifically, the invention employs compounds having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, as gelling agents for supercritical CO₂. The invention also pertains to increased viscosity supercritical CO₂ compositions and gels as well as microcellular foams of those compounds.

BACKGROUND OF THE INVENTION

Carbon dioxide is of great interest as a solvent in chemical processing because it is nonflammable, relatively non-toxic, and naturally abundant. These "green" properties have prompted examination of a host of new applications for CO₂ such as replacing organic solvents in polymerization [1-3], as a medium for conducting hydrogenations and oxidations in the absence of transport limitations [4,5], as a solvent in biocatalysis [6], and as a raw material in synthesis [7,8]. Several of these applications were made possible by the discovery of functional groups, subsequently christened "CO₂-philic", that enable miscibility of various moieties with CO₂ at moderate pressures [9]. Development of CO₂-soluble surfactants, for example, has rendered emulsion polymerization or dry cleaning feasible, while synthesis of CO₂-philic catalysts has enabled homogeneous chemistry in carbon dioxide.

CO₂ has been extensively employed to recover oil from underground formations, as it is inexpensive, non-flammable, relatively non-toxic and remediation is not required. In enhanced oil recovery (EOR), a flooding agent is pumped into the oil-bearing formation to move the petroleum to exit wells [13]. See also U.S. Patents 4,480,696, 4,921,635 and 5,566,470. Water is most often used as the flooding agent, yet intimate contact between petroleum and water creates cross-contamination that mandates remediation of large volumes of organic-contaminated water. Indeed, a life cycle analysis of polystyrene performed during the 1980's suggested that the extraction of petroleum from the ground produces more liquid waste than any other process step over the entire cradle-to-grave lifespan of the material. Carbon dioxide would be a more sustainable flooding agent than water, but the viscosity of CO₂ is too low to efficiently recover petroleum from the formation. Rather than sweep the oil before it, carbon dioxide "fingers" its way through the petroleum and hence leaves most of the oil behind.

Researchers in the petroleum engineering field have tried for decades to design additives [14] that can raise the viscosity of carbon dioxide (at low concentration)) by the 1 to 3 orders of magnitude that would render CO₂-flooding more practical, but success has been elusive. Additives have been synthesized that enhanced the viscosity of simple hydrocarbons, yet which were not soluble in CO₂ without the use of impractically high fractions of co-solvent [15,16]. On the other hand, additives have been identified that were CO₂-soluble but which did produce any changes in the viscosity of CO₂. Improvement in the efficiency of CO₂-flooding will promote the use of CO₂ over water in EOR and thus reduce the volume of liquid waste produced during petroleum extraction. Use of CO₂ in EOR also results in its sequestration in rock formations, potentially an important part of an overall sequestration strategy [17]. Thus, what is at first glance simply a technical problem in petroleum engineering has significant environmental ramifications as well. The low viscosity of dense CO2 relative to liquid hydrocarbons at similar conditions prevents it from being effectively used as a displacing fluid in porous media. The CO2 channels through the porous media since it has a high mobility, bypassing much of the hydrocarbon phase rather than displacing it. If the CO2 mobility could be decreased to the same value as the hydrocarbons, the channeling would be inhibited and the recovery of hydrocarbons increased.

The low CO2 viscosity also inhibits its ability to transport small solid particles into formation fractures. These small particles, designed to prop up the fracture caused by the high pressure injection of CO2, must travel as far as possible into the fracture before it collapses in order to increase the permeability of the reservoir. A significant increase in CO2 viscosity would decrease the settling velocity of the particles, allowing the CO2 to transport the particles further into the fracture.

Methods of reducing the mobility of liquid or supercritical carbon dioxide in porous media include the alternate injection of water, formation of CO2 emulsions or foams and the direct thickening of carbon dioxide. The alternate injection of an aqueous phase reduces the CO2 saturation and therefore the CO2 relative permeability. Emulsions in which the liquid or supercritical CO2 where the interior CO2 phase is separated by aqueous lamallae which contain a small concentration of surfactant, can greatly diminish the CO2 mobility since the size of the pockets of CO2 are of the order of magnitude of the pores. The direct viscosity enhancement of

CO2 is a proposed method of CO2 mobility reduction in which the CO2 viscosity is greatly enhanced by the dissolution of small concentrations of a thickening agent directly into the carbon dioxide.

Alternate injection of water and gas, WAG, has been used successfully not only in the CO2 process, but also in other gas displacement processes. Klins, M., Carbon Dioxide Flooding — Basic Mechanisms and Project Design, IHRDC, Boston (1984). Stalkup, F., Miscible Displacement, SPE Monograph No. 9, SPE, New York (1983). Although the mobility ratio of CO2/water to the fluid being displaced is reduced, it usually remains unfavorable. Furthermore, the injection of water introduces several operational difficulties and increases the time required to inject the entire CO2 slug and, therefore, the duration of the oil recovery project. Slugs of carbon dioxide emulsions, sometimes referred to as foams, have displayed extremely low mobilities in lab tests, but difficulties are encountered in retaining their integrity when they contact crude oil. Stalkup, F., Miscible Displacement, SPE Monograph No. 9, SPE, New York (1983). Heller, J. and Taber, J., "Mobility Control for CO2 Floods— A Literature Survey,

Topical Report," DOE MC/10689-3 (Oct. 1980). Heller, J. and Taber, J., "Development of Mobility Control Methods to Improve Oil Recovery by CO2, Final Report," DOE/MC/10689-17

(Nov. 1983). Heller, J., Cheng, L. and Kuntamukkula, M., "Foam-Like Dispersions for Mobility Control in CO2 Floods," -SPE 11233, presented at the 57th Annual Fall Technical Conference and Exhibition of the SPE of AIME, New Orleans, LA (Sept. 26029, 1982). Bernard, G., Holm, L. and Harvey, C, "Use of Surfactant to Reduce C02 Mobility in Oil Displacement," SPEJ, Aug.

1980, pp. 282-292. Wang, G., "A Laboratory Study of CO2 Foam Properties and Displacement

Mechanism," SPE/DOE 12645, presented at the SPE/DOE Fourth Symposium on Enhanced Oil Recovery, Tulsa, OK (Apr. 15-18, 1984). These slugs have been proposed as a means of not only displacing oil, but also plugging highly permeable zones. The direct thickening of CO2 could provide a means of lowering thickening of CO2 mobility and achieving a favorable mobility ratio (less than one) without introducing large amounts of water or encountering the problems associated with the generation or propagation of a foam. Heller, J. and Taber, J., "Development of Mobility Control Methods to Improve Oil Recovery by C02, Final Report,"

DOE/MC/10689-17 (Nov. 1983).

Viscosity measurements of carbon dioxide-direct thickener mixtures were reported by Orr, F. M., Jr., J. P. Heller and J. J. Taber, "Carbon Dioxide Flooding for Enhanced Oil Recovery: Promise and Problems,: J. A. O. C. S., Vol. 59, No. 10, (Oct., 1982), p. 810A. Therein it is stated that a polymer which could dissolve at low concentrations and increase the viscosity by a factor of 20 would be needed to make the process economically feasible. However, viscosity enhancements of up to only twenty percent were found in their preliminary experiments. The atactic, straight chain polymers of relatively low molecular weight were soluble in CO2, while the higher molecular weight and isotactic ones were insoluble. The small changes in carbon dioxide's viscosity were due to several factors, the foremost being its inability to dissolve high molecular weight polymers. Plans were also mentioned of continuing the search for more effective compounds among the product lists of manufacturers, and to initiate the synthesis of new polymers may be necessary.

Heller, J. J. and J. J. Taber, "Development of Mobility Control Methods to Improve Oil Recovery by CO — Final Report," U.S. Dept. of Energy Report DOE/MC/10689-17, Nov. 1983 later reported that no CO2-thickening polymer was found among the current products of any manufacturer. However, they believed that significant progress had been made in the characteristics of polymers which enhance their solubility in CO2, perhaps enabling the synthesis of new polymers for this purpose.

In 1983, Heller, J. P., Dandge, D. K., Card, R. J. and Donarume, L. G., "Direct Thickeners for Mobility of CO2 Floods," SPE 11789, S.O.E. of A.LM.E., June 1983 further discussed the effect of polymer structure and properties on solubility in CO2. They found that halogens, aldehydes, ring systems with unsaturation in the chain backbone and aromaticity in general were not desirable for a polymer to be soluble in CO2. Similarly, insolubility was found when there was the presence of amide, ester, carbonate and hydroxyl groups in the polymer backbone. Soluble polymers generally had solubility parameters less than eight, but the authors concluded that the compounds' solubilities could not be described with this parameter alone. It was also found that higher molecular weight polymers were much more effective, on a weight concentration basis in increasing the viscosity of carbon dioxide. From this, they concluded that if higher molecular weight polymers could be synthesized which are soluble in carbon dioxide, larger viscosity increases could be achieved with smaller concentrations. The majority of soluble polymers had molecular weights under 6000.

Heller, J. P., Orr, F. M., Jr., and Watts, R. J., "Improvement of CO2 Flood Performance," U.S.

Dept. of Energy Report DOE/BCO-85/1, Dec. 1984, p. 50, have also investigated the feasibility of using tri-alkyltin fluorides to increase CO2 viscosity. This compound can form associating polymers in propane, butane and hexane which are capable of significantly increasing the fluid viscosity. These non-polar fluids do not interfere with the association between the tin and fluorine of adjacent tri-alkyltin fluoride molecules. CO2, a fluid with no dipole moment, was not able to dissolve tri-butyltin fluoride, the only commercially available tri-alkyltin fluoride, to a great enough extent to induce any notable increase in the viscosity.

Recent work by Terry, R. E., Zaip, A., Angelos, C. and Whitman, D. L., "Polymerization in Supercritical CO2 to Improve CO2 OU Mobility Ratios," SPE 16270, SPE of ADVIE, June 1983 has concentrated on synthesizing carbon dioxide soluble polymers in-situ. Using an apparatus that simulates reservoir conditions, the authors found that light olefins can be readily polymerized in such an environment using commonly available initiators. However, no apparent viscosity increases have been measured, since the solubility of the resultant polymer is low. Dandge, D. K. and Heller, J. P. "Polymers for Mobility Control in CO2 Floods," paper SPE

16271 have also reported success in synthesizing new carbon dioxide soluble polymers from high alpha-olefins, but none have yet been found which satisfactorily enhance the CO2 viscosity.

Semi-fluorinated alkanes have been shown to form gels when dissolved in alkanes such as decane and octane, probably due to resultant formation of a micro fibrillar morphology. This gel phase in decane and octane results when the mixture is heated above the melting point of the F(CF2)N(CH2)MH compound, and then cooled. Tweig, R. J., Russell, T. P., Siemens, R. and Rabolt, J. F., Observations of a Gel Phase in Binary Mixtures of Semifluorinated n- Alkanes with Hydrocarbon Liquids," Macromolecules, Vol. 18, No. 6 (1985) p. 1361.

U.S. Patent 4,921,635 to Enick, incorporated by reference in its entirety, discloses gels comprised of semi-fluorinated alkanes and liquid CO₂, useful in the tertiary recovery of hydrocarbons.

Foaming of polymers using CO₂ is generally considered a sustainable process because it promotes efficient use of raw materials, the final products are excellent thermal insulators, and because CO₂ is a more sustainable "blowing agent" than CFC's or HFC's. A one-step, CO₂-based route for generation of low bulk density, microcellular materials is of particular technical interest because these materials (organic analogs to silicate aerogels) have some intriguing applications (catalyst and separation supports, low dielectric materials, insulation, tissue engineering scaffolds) and because current routes to aerogels (organic and inorganic) involve multiple process steps and significant volumes of solvent.

Commercial foaming processes using CO₂ are by contrast "greener", but they do not generate the combination of low bulk density and sub-micron pore size. These processes either add CO₂ to a polymer melt in an extruder, or mix CO₂ with (polyurethane) precursor materials prior to polymerization. In either case, the pressure employed is relatively low (30 to 100 atm.), and thus the amount of CO₂ mixed with the polymer is usually < 5 wt. %. Foam with a very low bulk density (> 95% density reduction versus the parent polymer) is produced but with cells that can be as large as 1 mm [6]. Research conducted during the 1980s and 90s showed that high- pressure CO₂ (pressures up to 500 atm.) can be used to swell thermoplastic polymers significantly, often by 20 to 30%, and that subsequent rapid depressurization produces a microcellular foam. Such methods readily produce foams with cells < 2 im, but density reductions rarely exceed 65% [7]. There would be considerable utility in a single-step process by which one could generate organic, low density, microcellular materials with a benign foaming medium such as CO₂.

Previous work has shown that gels can be created in traditional organic solvents via hydrogen bonding [8], association between ionic groups [9], or through association between electron donating and electron accepting moieties [10]. To form foams from such gels, the supramolecular aggregates created in solution must be preserved during and after solvent removal. Research has unfortunately shown that one can design molecules that aggregate in solution through multi-point hydrogen-bond formation [11], for example, but only rarely do the aggregates form structures that can be preserved following removal of the solvent [12]. Although molecular association in CO₂ has been previously observed, the molecules in question (surfactants) were designed to form spherical micelles, whereas this invention creates supramolecular networks that will exist as stable entities in the absence of CO₂.

As can be seen from this discussion, there are at least two problems that have frustrated engineers and other workers in these areas for decades. One problem is how to raise the viscosity of CO₂ to permit its efficient use in processes such as enhanced oil recovery. Another is how to generate foam materials with a bulk density less than 10% of the parent compounds and cells smaller than 10 microns. Accordingly, there exists a need for supercritical CO₂ compositions having increased viscosities and for foam materials with improved bulk density and small cell size. This invention answers those needs.

SUMMARY OF THE INVENTION

With this invention each of these above technical problems are addressed using compounds that dissolve in carbon dioxide under relatively moderate pressures, then associate in solution to form gels. Accordingly this invention relates to compounds that are both highly CO₂ soluble and which aggregate in solution. When polymeric compounds are employed, a 1-8 order of magnitude increase in viscosity necessary to conduct CO₂ -based EOR may be achieved. When low molecular weight compounds which can exhibit multi-point bonding are employed, monolithic aggregates are formed in CO₂ which become microcellular foams when the CO₂ is removed. These microcellular foams exhibit over 90% density reduction and contain cells smaller than 10 microns.

The invention relates to a method of increasing the viscosity of supercritical CO₂ by combining a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution with supercritical CO₂ to form a solution. The compound is then aggregated in solution to form a supramolecular network such that the viscosity of the supercritical CO₂ with the supramolecular network is greater than that of the starting supercritical CO₂.

The invention also relates to a method of making a microcellular foam by combining a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, with supercritical CO₂ to form a solution. The compound is aggregated to form a supramolecular network in solution. Then the CO₂ is removed under conditions sufficient to form a microcellular foam.

DESCRIPTION OF THE FIGURES

Figure la: Scanning electron micrograph (SEM) of foam produced using compound 24 from Table 7 at 4.86 % initial composition in CO₂

Figure lb. SEM of foam produced using compound 26 from Table 7 at 4.0 % initial concentration in CO₂

Figure lc. SEM of foam produced using compound 24 from Table 7 at 2J % initial composition in CO₂

Figure Id: SEM of foam produced using compound 37 from Table 7 at 5 % initial composition in CO₂ Figure le: SEM of foam produced using compound 39 from Table 7 at A.l % initial composition in CO₂

Figure If: SEM of foam produced using compound 38 from Table 7 at 4.8 % initial composition in CO₂

Figure 2: SEM of foam produced from terpolymer of 1H, 1H, 2H, 2H perfluorodecyl acrylate (84 mole %), styrene (11 mole %) and sulfonated styrene (5 mole %) at 1.1 initial wt. % in CO₂.

Figure 3:. ΔH_m determination ofPMCH gel of 22.

Figure 4:. IR spectrum showing the carbonyl region of the PMCH gel of compound 29.

Figure 5: Plot of melting temperature versus concentration for gels of 23-26, 29 and 31. Figure 6: Plot of ln[concentration] of 25 vs 1/T.

Figure 7: DSC trace of the melting of a 4 weigth % gel of 24 in PMCH with reference PMCH DSC trace.

Figure 8: Energy minimized structure of 27 (a) top view (b) side view.

Figure 9:. Energy minimized structure of a tetramer of 24.

Figure 10: Energy minimized structure of a hexamer aggregation state of 26.

Figure 11: Solution relative viscosity of fluoroacrylate-fluorourea copolymer in carbon dioxide, P=5000psi.

Figure 12: SEM of foam produced using compound 24 from Table 7 at 4.0% initial concentration in CO₂.

Figure 13: SEM of foam produced using compound 24 from Table 7 at 2.0% initial concentration in CO₂.

Figure 14: SEM of foam produced using compound 26 from Table 7 at 4.0% initial concentration in CO₂.

DETAILED DESCRIPTION OF THE INVENTION In a first embodiment, the invention relates to a method for increasing the viscosity of supercritical CO₂ by combining a compound having a CO₂-philic functional group and an aggregating functional group with supercritical CO₂ to form a solution. The compound aggregates in solution such that a supramolecular network is formed. The supercritical CO₂ containing the supramolecular network exhibits an increased viscosity over that of the supercritical CO₂ alone. Forming a supramolecular network of these compounds within the supercritical CO₂ can also gel the supercritical CO₂.

In a second embodiment, the invention relates to a method of making a microcellular foam by combining a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, with supercritical CO₂ to form a solution. The compound is aggregated to form a supramolecular network in solution. Then the CO₂ is removed under conditions sufficient to form a freestanding microcellular foam.

Compounds Useful in the Invention

The compounds useful in the methods of the invention contain CO₂-philic and aggregating functional groups. The term "compound" refers to small molecules, monomers, oligomers and polymers. The CO₂-philic functional group enables the compound to dissolve in supercritical CO₂ and the aggregating functional group enables the compound to form a supramolecular network in solution. The term "aggregating" denotes non-covalent bonding, including, but not limited to, hydrogen bonding, dipole interactions, electrostatic interactions and van der Waals forces. The preferred aggregating functional group is a hydrogen bonding functional group such as, for example, an amide functional group, a urea functional group, a ureidopyrimidone functional group, a carboxylic acid functional group, a carbamate functional group, a sulfonamide functional group, a thiourea functional group, ureidopyridine functional group, a guanidinium carboxylate functional group, and an amino-pyridine/carboxylic acid functional group The compounds useful in the invention may also contain functionalities which permit cross- linking of the aggregated compounds. These functional groups include, for example, vinyl groups which may be crosslinked upon irradiation, hydroxyl and acid moieties to form ester cross-links, or epoxy groups.

To be useful in the invention, molecules that aggregate in supercritical CO₂ should preferably dissolve in supercritical CO₂ under accessible temperature and pressure conditions. Consequently, the compounds preferably incorporate "CO₂-philic" functional groups to allow dissolution in supercritical CO₂. "CO₂-philicity" may derive from the inclusion of functional groups that interact with the carbon atom in CO₂, and/or from weak self-interaction of the solute, or both. Effective CO₂-philes include, for example, fluorinated functional groups, siloxane functional groups, and alkylene oxide functional groups. Alkylene oxide groups which may be used include butylene oxide, isobutylene oxide, and n-butylene oxide. Preferred CO₂-philic functional groups include fluoroalkyl, fluoroether, and fluoroacrylate functional groups. Particularly preferred fluoralkyls include perflourinated alkyl groups having 1 to 15 carbon atoms. Particularly preferred fluoroethers include oligomers of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide. Preferred siloxanes include lower alkyl siloxanes such as dimethylsiloxane.

To increase the solubility of compounds possessing amides or ureas as the aggregating functional groups responsible for aggregation in fluorinated solvents and supercritical CO₂, the surface area responsible for solvation may be increased. The surface area can be changed by increasing the length of the fluorinated tail of the ester or increasing the number of fluorinated chains. Since longer perfiuorinated alcohols (greater than C_]0) may have poor solubility in standard organic solvents at room temperature, preferred compounds, as discussed below, have branched perfiuorinated systems which incorporate an additional perfiuorinated chain for each hydrogen- bonding functionality. Preferred compounds for use in the invention contain one or two urea or urethane groups (to induce aggregate formation) and fluorinated groups to promote solubility in CO₂ at moderate pressures. The use of aspartate residues in the construction of the compounds allows easy incorporation of more "CO₂-philic" functional groups (through di-ester formation) as well as generation of the urea groups needed for hydrogen bonding (through reaction with isocyanates).

Particularly preferred compounds are those which contain two or more fluorinated groups per aggregating (e.g., hydrogen bonding) functional group. Examples include fluorinated aspartate bisurethanes and fluorinated aspartate ureas and bisureas discussed below. In the formulas below, the monovalent or divalent alkyl, alkenyl, and alkynyl groups may have straight or branched chains which are unsubstituted or substituted with groups such as hydroxyl, nitro, halo, etc.

Fluorinated Bisurethanes

The preferred fluorinated bisurethanes have the following structure:

wherein: Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group, a fluoroacrylate group and a siloxane group; and R is a divalent alkyl group having from 1 to 12 carbon atoms or a divalent alkenyl, or alkynyl group having from 2 to 12 carbon atoms. Preferably, Z is a perflourinated alkyl group having 1 to 15 carbon atoms, a fluoroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, or difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. Preferably, R is a straight chain divalent alkyl, alkenyl, or alkynyl group having from 3 to 9 carbon atoms. Particularly preferred bisurethanes are those in which Z is C₈F₁₇ , and R is C₄H₈, C₆H₈ or C₈H₁₆.

Fluorinated bisurethanes may be synthesized by reacting a perfluoroalcohol with a bisisocyanate. A general synthesis scheme for these compounds is shown in Scheme 1 :

Scheme 1. Synthesis of fluorinated bisurethane compounds 1-7.

As shown in the Examples below, the synthesis of fluorinated urethane compounds was accomplished by refluxing lH,lH,2H,2H-perfluordecanol (CF) with commercially available bisisocyantes in toluene, (Scheme 1). Upon cooling to room temperature, the compounds are collected by filtration and are washed with dichlormethane/hexanes to remove unreacted starting material. Typical yields for this reaction range from 60 to 90% depending on the isocyanate employed.

Fluorinated Glycyl Triamide Compounds

The preferred fluorinated glycyl triamide compounds have the following structure:

wherein Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group ,a fluoroacrylate group and a siloxane group and R is an aromatic or 5-7 member carbocyclic group. The aromatic or carbocyclic groups may contain heteroatoms. Preferably, Z is a perflourinated alkyl group having 1 to 15 carbon atoms, a fluoroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. R is preferably a benzyl or cyclohexyl group. A synthesis protocol for the fluorinated glycyl triamides is shown below in scheme 2.

Scheme 2. Synthesis of fluorinated glycyl triamide compounds 10 and 11.

(i) EDCI, DMAP, CF (ii) TFA (iii) TEA, 1,3,5-benzene triacid chloride (iv) TEA, cis ,cis- 1,3,5-cyclohexaπe triacid chloride

Both the aryl- analog and the cyclohexyl- triamide derivatives were synthesized as (Scheme 2), by esterification of N-t-butylcarbamoyl-glycine with the perfiuorinated alcohol (CF) using (EDCI) and 4-N,N-dimethylaniline (DMAP) in dichloromethane. After aqueous workup and baseline filtration through silica the protected ester 8 is isolated as a white waxy solid in 75% yield. The amine was then deprotected with 25-50% trifluoroacetic acid (TFA) in dichloromethane. The TFA salt 9 is isolated as a white semi-crystalline solid in 87% yield after recrystalization from ethanol. Compound 9 is insoluble in dichloromethane at room temperature, however it is soluble in halogenated solvents upon addition of triethylamine (TEA). This solid was reacted with the triacid chloride of 1,3,5-benzene tricarboxylic acid in dichloromethane/tetrahydrofuran with excess triethylamine (TEA). The resulting white solid was collected by filtration and washed with aqueous 1% hydrogen chloride (HC1), water, and copious amounts of dichloromethane. After drying 10 was isolated in 77% yield after dying under vacuum for 12 hrs. Compound 11 is synthesized in the same manner by reacting cis,cis- 1,3,5-cyclohexane triacid chloride with 9 and TEA.

Fluorinated Glycyl Bisureas Compounds

The preferred fluorinated glycyl bisurea compounds have the following structure:

wherein: Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group, a fluoroacrylate group and a siloxane group; and R is a divalent alkyl group having from 1 to 12 carbon atoms, a divalent alkenyl or alkynyl group having from 2 to 12 carbon atoms, or a substituted or unsubstituted aromatic group which may contain heteroatoms. Preferably, Z is a perflourinated alkyl group having 1 to 15 carbon atoms, a fluoroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. Preferably, R is a straight chain divalent alkyl, alkenyl, or alkynyl group having from 4 to 12 carbon atoms. Scheme 3. Synthesis of glycyl bisureas 12-18.

12=R= C₄H₈

13=R= C₆H₁₂

14=R= C₈H₁₆

15=R= C₁₂H₂₄

16=R= 1,3-xylylene

17=R= 1 ,3-methylynecyclohexane

18=R= 4,4'-oxybisphenylether

The synthesis of bisureas was conducted in dichloromethane with 9 and the commercially available bis-isocyanates used previously in the formation of the urethanes (Scheme 3). Attempts to isolate the compounds via extraction led to the formation of emulsions and a sticky white solid. Isolation and purification of these compounds is achieved by addition of hexanes to the reaction mixture causing the precipitation of the bisureas and TEA hydrochloride. The compounds are isolated by filtration and washed with 1% aqueous HC1, water, and dichloromethane. Compounds 12-18 were also insoluble in neat non-halogenated solvents similar to compounds 1-7, however they have no appreciably solubility in neat halogenated solvents at room temperature either.

Aspartyl Perfluoroesters and Mosher's Amide

Preferred Aspartyl perfluoroesters useful in the invention have the generic formula:

wherein Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group, a fluoroacrylate group and a siloxane group and R' is an alkyl group having 1 to 12 carbon atoms, an aromatic group, a substituted aromatic group, or an C_\-Cn alkylene (meth)acrylate group. Preferably, Z is a perflourinated alkyl groups having 1 to 15 carbon atoms, a flouroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. More preferably, Z is C₁₀F₁₈ and R' is preferably selected from the group consisting of p-fluorophenyl, phenyl, 3,5 bis-CFs FL-., (CH₂)₅CH₃ and ethylene methacrylate. A synthetic scheme for aspartyl perfluoroesters and the corresponding Mosher's amide is shown below in Scheme 4:

Scheme 4. Synthesis of aspartyl perfluoroester 19, 20 and Mosher's amide 21.

(i) EDCI, DMAP, CF (ii) TFA (iii) TEA, MTPA chloride

The synthesis of the branched compounds 19-21 containing two perfiuorinated chains is achieved by esterification of N-t-butyl aspartic acid in dichloromethane with EDCI, DMAP and CF (Scheme 4). After the aqueous workup, the dichlormethane solution is passed through silica to remove polar organic species. Upon removal of the solvent 19 is obtained as a white greasy solid in 86% yield. In order to deprotect 19, 50% TFA CH_{2 2} is employed; after 1 hour the reaction is stopped, the solvent removed and fresh TFA/ CH_{2 2} added and the reaction is allowed to continue for an additional hour. The crude salt is recrystallized from boiling ethanol/ CH₂C1₂. Compound 20 is isolated by filtration from the supernatant liquid and the solid washed with CH₂C1₂. A second crop of crystals is obtained giving a total yield of 76%.

Aspartyl Triamide

Scheme 5. Synthesis of aspartyl triamide 22.

Preferrred aspartyl triamides which may be used in the invention have the following formula:

wherein Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group,a fluoroacrylate group and a siloxane group and R is an aromatic or 5-7 member carbocyclic group The aromatic or carbocyclic groups may contain heteroatoms. Preferably, Z is a perflourinated alkyl group having 1 to 15 carbon atoms, a fluoroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. R is preferably a benzyl or cyclohexyl group. Compound 22, below is a particularly preferred aspartyl triamide.

Scheme 5. Synthesis of aspartyl triamide 22.

22

Compound 22 is prepared by reaction of cis,cis-l,3,5-cyclohexane tricarboxylic acid chloride with 20 in CH2C12 with excess TEA, similar to the synthesis of 10 (Scheme 2). The resulting white solid formed in 88% yield is collected by filtration and washed with CH2C12, 1% HCl, water and ether. The solid is an intractable mixture of compounds that is inseparable by chromatography and is insoluble in all non acidic halogenated solvents. The white solid is approximately 90% pure by ^H NMR and was used for the gelation and solubility tests without further purification. Due to the highly hydrophobic nature of the fluorinated chains on the ester linkage and the strong hydrogen bonding seen in non-polar solvents purification of the perfiuorinated compounds is difficult.

Fluorinated Aspartate Ureas and Bisureas

Preferred flourinated aspartate ureas useful in the invention have the following structure:

wherein Z is selected from the group consisting of a fluoroalkyl group, a fluoroether group, a fluoroacrylate group and a siloxane group and R' is an alkyl group having 1 to 12 carbon atoms, an aromatic group, a substituted aromatic group, or an Cj-Cι₂ alkylene (meth)acrylate group. Preferably, Z is a perflourinated alkyl groups having 1 to 15 carbon atoms, a flouroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. More preferably, Z is C₁₀F₁₈ and R' is preferably selected from the group consisting of p-fluorophenyl, phenyl, 3,5 bis-CF₃C₆H4, (CH₂)₅CH₃ and ethylene methacrylate.

Preferred flourinated aspartate bisureas have the following structure:

wherein Z is a CO₂-philic group and R is a divalent alkyl group having from 1 to 12 carbon atoms, a divalent alkenyl, or alkynyl group having from 2 to 12 carbon atoms, a substituted or unsubstituted aromatic group, or a 5-7 member carbocyclic group which may be substituted or unsubstituted. Preferably, Z is a perflourinated alkyl group having 1 to 15 carbon atoms, a flouroether oligomer of hexafluoropropylene oxide, tetrafluoroethylene oxide, or difluormethylene oxide, or a lower alkyl siloxane such as dimethylsiloxane. Preferably, R is a straight chain divalent alkyl, alkenyl, or alkynyl group having from 4 to 12 carbon atoms or a phenylene group. Z is preferably CιoF₁₈ or hexafluoropropylene oxide oligomer.

Fluorinated aspartate ureas may be synthesized by reacting a perfluoroalcohol with a protected aspartate to form a protected fluorinated aspartate, deprotecting the fluorinated aspartate and then reacting the deprotected florinated aspartate with a isocyante. Similarly, fluorinated aspartate bisureas may be synthesized by reacting an diisocyanate with a deprotected fluorinated aspartate. This is shown in Scheme 6 below.

Scheme 6. Synthesis of fluorinated aspartate bisureas, compounds 23-29.

Bisureas containing the aspartyl moiety were prepared by reaction of 20 with bisisocyanates in CH₂C1₂ with excess TEA (Scheme 6). These compounds are collected by filtration of the reaction mixture and are washed with copious amounts of CH₂C1₂, 1% aqueous HCl, water and additional dichloromethane. All compounds were determined by H NMR to be at least 95% pure.

Another bisurea was synthesized, however the bisisocyanate is not commercially available, and was prepared in situ by a new procedure reported by Yoon [21]. In this procedure (Scheme 7) 1,4-xylenediamine was treated with 4-nitrophenylchloro formate in acetonitrile with sodium bicarbonate. The biscarbamate 30 was isolated as an off white solid in 40% yield by filtration of the reaction mixture and removal of the sodium bicarbonate by treating the solid with 1% aqueous HCl . The organic solid remaining was then dried with methanol, ether, and dichloromethane. Compound 30 was then treated with excess TEA in acetonitrile for 15 minutes to generate the bisisocyanate in situ and the solution was added to a mixture of 20 in dichlormethane and TEA, producing the bisurea 31 in 61% yield after isolation by filtration and washing of the solid.

Scheme 7. Synthesis of compound bis urea 31.

(i) 4-nitrophenyl chloroformate, NaHCO_j, acetonitrile (ii) acetonitrile, TE (iii) 20 , TEA, dichloromethane

Polymeric Compounds Having CO₂-philic and Aggregating Functional Groups

Polymeric compounds (polymers and oligomers) having a CO₂-philic functional group and an aggregating functional groups may be generated, by copolymerizing a vinyl monomer having a CO₂-philic group, such as a perflourinated alkyl, with another aggregating comonomer. Examples of the vinyl monomer having a CO₂-philic group include perflourinated alkyl (meth)acrylates, such as the highly CO₂-philic 1H, 1H, 2H, 2H perfluorodecyl acrylate. The aggregating comonomers should contain a vinyl group and an aggregating functional to promote formation of the supramolecular network. Examples of possible aggregating comonomers include, but are not limited to, styrene, α-methyl styrene, sulfonated styrene, a fluorinated alkyl aspartate alkyl (meth)acrylate urea (such as compound 39), glycidyl methacrylate, carbodiimide methacrylate, methacrylamide, acrylamide, butyl acrylamide, and ethyl acrylamide.

The polymeric compounds may also contain other vinyl comonomers known in the art. For example, suitable vinyl monomers which may be used, for example, include, but are not limited to, acrylic acid, methacrylic acid, methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; butyl acrylate; butyl methacrylate; isobutyl acrylate; isobutyl methacrylate; ethylhexyl acrylate; 2-ethylhexyl methacrylate; octyl acrylate; octyl methacrylate; iso-octyl acrylate; iso-octyl methacrylate; trimethylolpropyl triacrylate; Cj-C₁₈ alkyl crotonates; di-n-butyl maleate; di-octylmaleate; allyl methacrylate; di-allyl maleate; di-allylmalonate; methoxybutenyl methacrylate; isobornyl methacrylate; hydroxybutenyl methacrylate; hydroxyethyl (meth)acrylate; hydroxypropyl (meth)acrylate; acrylonitrile, vinyl chloride; ethylene; vinyl ethylene carbonate; epoxy butene; 3,4-dihydroxybutene; hydroxyethyl (meth)acrylate; vinyl (meth)acrylate; isopropenyl (meth)acrylate; cycloaliphaticepoxy (meth)acrylates; and ethylformamide. Such monomers are described in "The Brandon Worldwide Monomer Reference Guide and Sourcebook" Second Edition, 1992, Brandon Associates, Merrimack, New Hampshire; and in "Polymers and Monomers", the 1996-1997 Catalog from Polyscience, Inc., Warrington, Pennsylvania.

The polymeric compunds may be prepared by polymerization techniques known in the art such as, for example, solution polymerization or bulk free radical polymerization. A preferred polymer was generated, by copolymerization of the highly CO₂-philic 1H, 1H, 2H, 2H perfluorodecyl acrylate with (i) 39, and (ii) with styrene followed by partial sulfonation of the phenyl groups. Particularly preferred polymers include poly(fluorinated aspartate methacrylate urea-co-fluoroacrylate) and a terpolymer of 1H,1H,2H,2H perfluorodecyl acrylate, styrene and sulfonated styrene.

Methods For Increasing the Viscosity of Supercritical CO; and Halogenated Solvents

As discussed above, one embodiment of the invention relates to a method for increasing the viscosity of supercritical CO₂. The method combines a compound having a CO₂-philic functional group and an aggregating functional group with supercritical CO₂ to form a solution. The compound aggregates in solution such that a supramolecular network is formed. The supercritical CO₂ containing the supramolecular network exhibits an increased viscosity over that of the supercritical CO₂.alone. Forming a supramolecular network of these compounds within the supercritical CO₂ can also gel the supercritical CO_2. In a preferred method, the viscosity is sufficiently increased such that the supercritical CO₂ with the supramolecular network is a gel.

An alternative embodiment of the invention relates to a method for increasing the viscosity of halogenated solvents, preferably fluorinated solvents. The method steps are the same as those discussed for increasing the viscosity of supercritical CO₂ except that a halogenated solvent is used instead of the supercritical CO₂. For purposes of clarity the discussion below uses supercritical CO₂ as the solvent. The method combines a compound having a CO₂-phiUc functional group and an aggregating functional group with a halogenated solvent to form a solution. The compound aggregates in solution such that a supramolecular network is formed. The halogenated solvent containing the supramolecular network exhibits an increased viscosity over that of the halogenated solvents.alone. Forming a supramolecular network of these compounds within the halogenated solvent can also gel the halogenated solvent In a preferred method, the viscosity is sufficiently increased such that the halogenated solvent with the supramolecular network is a gel.

In the first step of this method, a compound having a CO₂-philic functional group and an aggregating functional group may be combined with, and preferably dissolved in, supercritical CO₂ by any means known in the art. For example, satisfactory solutions can be obtained by simple mixing at ambient temperature. Alternatively, the compound may first be combined with the CO₂ and the combination heated to dissolve the compound in the supercritical CO₂.

Once the compound is in the supercritical CO₂, the method aggregates the compound in solution. Aggregating the compound may be achieved by lowering the pressure, lowering the temperature or lowering the pressure and temperature of the solution. Lowering the pressure may be achieved by venting CO₂ vapor from the supercritical CO₂. Alternatively, the aggregating step comprises allowing the solution to stand for a time sufficient for the compound to aggregate and form a supramolecular network in solution. As aggregates form, the solution may remain clear or turn opaque.

According to this method of the invention, the viscosity of CO₂ may be enhanced by several orders of magnitude at relatively low concentration of the compound. Preferably, the viscosity shows a 1-3 order of magnitude increase. More preferably a 1-8 order of magnitude increase in the viscosity is achieved. Typically, the compound is present in an amount of less than 10 weight percent of the solution. Preferably, the compound is present in an amount ranging from about 0J to about 6 weight percent. More preferably, the compound is present in an amount less than about 1 weight %. The greater the weight percent of compound used, the higher the density of the microcellular foam formed Ideally, the amount of compound ranges from about 0J-0.5 weight percent.

Solubility and Gelation Studies

A number of solubility and gelation studies were conducted to assess the ability of the compounds discussed above to increase the viscosity of CO₂ and more preferably to gel CO₂. The variety of solvents used in these studies included chloroform, acetone, dimethylsulfoxide (DMSO), 1,2-trichlortrifluorethane (freon), perfluoromethylcyclohexane (PMCH), as well as mixtures of these solvents. While screening in organic solvents is not entirely predictive of behavior in supercritical CO₂, these studies provided insight into the solution behavior of the compounds.

Bisurethane compounds 5-7 are slightly soluble in chlorinated solvents and completely soluble, up to 50 mM, in mixtures of chlorinated solvents and acetone. Attempts to solubilize 5-7 in dichloromethane with methanol led to cloudy solutions. The solubility of these urethanes in lJJ-trichlorotrifluoroethane (freon) and in perfluoromethylcyclohexane (PMCH) was examined. These compounds are insoluble in neat fluorinated solvents at room temperature. However, when heated in a sealed NMR tube compounds 5-7 dissolved in freon. In all but one case compounds 5-7 precipitated from solution upon cooling. Once dissolved the sample was allowed to stand at room temperature for an hour before determination of gel formation by the inversion method. Compound 6 gelled freon at very high concentrations, 110 mM, compared to known gelling agents for organic liquids, which typically gel at concentrations of 3-50 mM. This gel was opaque, which is generally indicative of a suspension, however dynamic flow of the solvent was not observed when the tube was inverted or shaken. Compounds 5-7 were also dissolved in hot PMCH and allowed to cool to room temperature, however the compounds precipitated from solution with no gel formation.

Glycyl triamides 10 and 11 were insoluble in all neat solvents: chloroform, acetone, dimethylsulfoxide, freon and PMCH, both at room temperature and at the boiling point of the solvent. In PMCH the compounds form a finely divided suspension that did not settle, however no gelation was observed even at high concentration, 100 mM. These compounds are soluble in chlorinated solvents with 1% trifluoroacetic acid which disrupts intermolecular hydrogen bonding.

The solubility properties of glycyl bisureas 12-18 were poorer than those of 10 and 11. Compounds 12-18 were insoluble in all organic solvents; attempts to solubilize 1 mg of compounds 12-18 in freon and PMCH failed, even after prolonged heating. Heating 1 mg of compound in 500 μL of PMCH to the boiling point in a sealed tube resulted in the dispersion of the compound in the solvent. The solid settled to the bottom of the tube upon removal of heat. As a result no gelation was observed for these compounds. They were however soluble in TF A/chloroform mixtures similar to those of 10 and 11, however in order to generate a clear colorless solution 3% TFA was required.

Compound 22 possess interesting solubility properties which separated it from the fluorinated compounds 5-7, 10, 11, and 12-18. Compound 22 was insoluble in non-fluorinated, organic liquids. This compound is also insoluble in freon, however it was soluble in hot PMCH and in 1- 5% TFA/chloroform.

Since compound 22 was soluble in PMCH its propensity for gelation of PMCH was determined. When 23 mg of 22 was heated in 200 μL of PMCH (0.63 t.%, 3.6 mM) a stable, slightly opaque gel, as determined by inversion of a sealed test tube, was formed after setting at 22°C for 4 hours. The enthalpy of melting, ΔH_m, was determined for this gel by the dropping ball method; these data are set out in Table 1. From the plot of the log of the concentration of 22 versus the reciprocal melting temperature, the value of ΔH_m was determined (Figure 3). For compound 22 after setting for 4 hours at 22°C ΔHm was 118 ±18 kJ/mol, within the concentration range of 4.7-18.9 mM.

Table 1. Gel Melting Point Determination of 22 in PMCH.

Mass/ mg^a wt.% Con/ mM Melting Temp/ °C^b

3.10 0.86 4.79 36.5

6J6 1.69 9.52 42.0

7.24 1.99 11.2 43.5

12.24 331 18.9 45.4

(a) mass measured ±0.02 mg; (b) melting temperature measured ±0.2 °C

Attempts to gel supercritical CO2 were unsuccessful. Compound 22 was soluble in supercritical CO2 at elevated temperatures (90°C) at 6500 psi, however upon cooling to room temperature, 22 precipitated from solution. Similarly, mixed solvent systems such as acetone/CO2 or PMCH/CO2 did not result in gel formation.

Compounds 23-29 and 31 were insoluble in all neat non-halogenated solvents, and non-acidic chlorinated solvents. Additionally 23-29 and 31 were insoluble in freon, forming a fine suspension of the compound at the boiling point of the solvent. All of the compounds, except 27, were soluble in hot PMCH. These compounds are all soluble in 5% TFA in chloroform.

The gelation properties of bis-ureas 23-29 and 31 in PMCH and Supercritical CO2 were studied. With the exception of 27 and 28, these compounds form clear, colorless gels at concentrations of less than 1 wt.% after setting at 22 °C for 1 hour as determined by the inversion test described above (Table 1). The gel formed by 28 is opaque, nonuniform in density, and required approximately 16 hours to set. The gel contains suspended matter which is not eliminated upon lowering the concentration of 28. Compound 27 was insoluble in PMCH and therefore does not form a gel. The alkyl-spaced compounds 23-26 were stable at room temperature in sealed test tubes for months without the exclusion of solvent .

Table 2. Minimum Concentration for Gelation of 23-29 and 31 at 22°C for 1 hr.

Compound Minimum Concentration Minimum Concentration mM Wt.%

23 5.7 0.92

24 4.0 0.51

25 4.5 0.56

26 7.0 0.91

27 no gel No gel

28 50 5.8

29 7.0 0.83

31 7.1 0.92

Bis-urea compounds 23-26, 29 and 31 displayed a variety of physical behaviors which were concentration dependent. Once the minimum concentration for gelation was surpassed, gels formed from these bis-urea compounds set quickly upon removal of heat, typically before room temperature is reached. These gels were disrupted by mechanical action, i.e. stirring, and once disrupted the gels do not reform at room temperature. The gels do reform after reheating the sample to the boiling point of the solvent followed by cooling and the reformed gel was identical to the original gel. When the concentration of the gelling agent was greater than 2 wt.% (approximately 10 to 20 mM) solutions began to form gels within seconds upon removal of heat. At concentrations lower than the minimal gelling concentration, the solutions became inhomogeneous with portions of free flowing solvent, viscous liquid, and with small amounts of gelled solvent.

The IR spectra of gels of compounds 23-26, 29 and 31 are very similar; a typical IR spectrum is displayed in Figure 4 and the frequencies for the carbonyl and amide bands are set out in Table 3. The amide I and amide II bands of the ureas indicate that they are participating in hydrogen bonding. [18] The band for the ester carbonyl, which is found above 1730 cm- , however indicates that no hydrogen bonding is taking place with this group.

Table 3. Selected Vibrations (cm"¹) for PMCH Gels of 23-26, 29 and 31

Compound Ester Carbonyl v (CO) Urea (amide I, amide II)

23 Butyl 1744 1630, 1575

24 Hexyl 1741 1626, 1559

25 Octyl 1737 1630, 1565

26 Dodecyl 1735 1627, 1556

29 1,4-Phenylene 1746 1635, 1560

31 1,4-Xylylene 1742 1635, 1561 For compounds 23-26, 29 and 31 the melting temperature as a function of concentration was determined; this data is set out in Table 4 and shown in Figure 5. The plot of the log of concentration versus the reciprocal of the melting temperature was used to extract ΔHm; these values are given in Table 5. For gels of compounds 25 and 31 this plot is not linear (Figure 6); there appears to be a second aggregation state at higher concentrations. Therefore ΔH_m is reported for both low and high concentration ranges. After the gels were melted and removed from the hot oil bath, the gels were inverted to examine the viscosity of the hot solution; no flow was observed for any of these samples.

Table 4. Concentration and Melting Temperature for Gels Formed from 23-26, 29 and 31 in PMCH.

Compound Concentration/ mM Melting Temperature/ °C

23 Butyl* 8J2 363

12.0 47.0

17.7 59.5 19.9 60J

29.2 64.8 24 Hexyl 5.84 61 J

9.35 64.5

14.5 79.2 16.0 83.1 22.4 85.3

25 Octyl 6.90 50.8

6.94 53.5

8.46 53.8

10.3 54.1 11.0 57.0

11.8 57.5 13.8 65.2

14.6 69.1 16.6 70.1 V 0 7 0

18.8 71.5

20.8 72.0

21.0 73.8 23.8 74.5 33.7 77.1 37.3 77.2 40J 77.8

26 Dodecyl 5.47 48.5

8.21 90.0

9.38 91.0

10.7 92.0

13.0 98.0

15.3 98.0 17.6 98.0

29 1,4-Phenylene 10.4 30.3

12.4 34.0

14.5 36.0

15.0 37.1

15.9 41.0 20.3 45.0

24.1 46.0 28.1 51.5 3U 56J)

31 1,4-Xylylene 7.24 27.2

8.71 33.8

10.3 37.0

11.3 39.0 13.1 40.5

15.4 413

17.5 41.8

20.6 43.5 243 47J0

(a) data collected after setting for 1 hr. at 22°C

Table 5. ΔH_m of PMCH Gels of Compounds 23-26, 29 and 31 Set for 16 hrs. at 22°C.

Compound ΔH_m (kj/mol) ΔH_m (kJ/mol) higher concentrations

23 Butyia 35±3

24 Hexyl 46±5 25 Octyl 68±13 113±8

26 Dodecyl 249±25

29 1,4-Phenylene 37±2

31 1,4-Xylylene^c 33±5 121±18

(a) gel melted after setting for one hour at 22°C (b) Enthalpy from 0-8 mM and 8-18 mM respectively (c) Enthalpy from 0-5 mM and 5-11 mM, respectively.

Table 6. Variation of ΔH_m with Respect to Time for Gels of 24-26 in PMCH.

ΔH_m / kJ/mol dΔH_m/dt

Compound l hr. 4 hr. 16 hr. 48 hr (kJ/mol hr)

24 Hexyl 35±3 32±4 46±5 0.9±03

25 Octyl^a 48±6 51±11 113±8 164±6 2.5±0.5

26 Dodecyl ll±l 249±25 297±27 4±2

Gelation studies PMCH and supercritial CO2 were also conducted with Aspartyl Bis-urea Gelling agents 23-29 and 31. Gels formed from bis-ureas 23-29 and 31 were stable and transparent at less than 1 wt.% in PMCH and are therefore classified as super gelling agents. [19] These gels display thermoreversible behavior and are mechanically stable to shaking but are disrupted upon stirring or other vigorous agitation. The disruption severs the fibers that create the gel matrix and cannot orientate in the proper way to reform the gel. However heating the gel to the boiling point of the solvent destroys the gel and upon cooling allows the matrix to reform creating a gel that appears to be identical to the original. The bis-ureas 27 and 28 do not form transparent gels and have poor solubility in perfiuorinated solvents. One explanation for this poor solubility is the preferred orientation of the ureas, as seen in the energy minimized structures for 27, from Macromodel 5.5 using Amber* forcefield (Figure 8). [20] This structure demonstrates that the long, fluorinated tails of the aspartyl functionality prefer to come within van der Waals contact distance of each other. This orientation of the long alkyl chains presumably blocks the ureas from associating with one another through intermolecular hydrogen bonds. These form the desired rod type structure for gel formation. This model does not however rule out the possible that other aggregation states exist or possibly dominate the packing of these molecules. It is this unknown packing pattern that is responsible for the insolubility of 27, and the high concentration of 28 necessary to create an opaque gel. The time dependence seen for the formation of this gel is consistent with the need to break a kinetically preferred orientation in order to establish the more thermodynamically stable gel. In addition to the orientation of the perfluoroalkyl chains, there is an issue of isomeric purity of these compounds. Compound 28 is synthesized with the commercially-available isocyanate which is a mixture of cis and trans substituted cyclohexane. Only one component of the cis/trans urea mixture may have the capacity to aggregate into the molecular rods which are responsible for gelation behavior. The other isomer will terminate the molecular rod formation through mismatched hydrogen-bond complementarity. This change in the aggregation pattern results in a random self-association which creates domains where short rods are formed.

The monomers of 23-26, 29 and 31 cannot easily adopt a conformation where the perfiuorinated groups are close enough to associate due to the orientation imposed by the spacer. It is expected that these compounds form stacked structures. This stacked structure is also evident from the Monte Carlo conformational search of a tetramer of 24 (Figure 9). The stacks are held together by hydrogen bonding between urea groups with an average N-H— O=C distance of 2.0 A. In this aggregate structure, the alkyl groups are relatively free to move, resulting in multiple low energy conformations where the alkyl groups lie within van der Waals contact. This aggregation state is also supported by the amide I and amide II IR bands at 1660 cm"*' and 1550 cm^~l, which indicate that the ureas are involved in intermolecular hydrogen bonding, while the esters do not hydrogen bond as witnessed by the C=O vibration at 1740 cm"l.

The dimensions of the monomer comprising this aggregate are 35 A x 22 A (Figure 9(b)). From the SEM photos of a 4 wt.% gel of 24 the minimum number of molecules necessary to comprise the short fiber of 1 micrometer by 1 micrometer by 5 micrometers given the dimensions above are 300 times 300 times 10,000 molecules, a total of 9x10^ molecules.

The different morphology of the gels of 24 and 26 as seen in the SEM photos (Figure 12 and 14) is a result of the distance separating the urea groups responsible for the initial aggregation. In compound 24, the distance between the hexyl spacers is insufficient to allow the ureas to stack in a staggered conformation (crosslinking stacks) because the alkyl chains of the aspartyl group cannot move without colliding with the aspartyl group of another molecule. However the distance between the urea groups in compound 26 is 13 A, which is sufficient spacing for the ureas to crosslink between stacks without steric crowding dominating this aggregation state (Figure 10).

The change in morphology of the gels also accounts for the large increase in ΔH_m observed for the gels of 26 (249±25 kJ/mol) compared to the other bis-urea gels (30-50 kJ/mol). (The following discussion assumes that the morphology of the gel in PMCH is the same as in supercritical CO2-) This large increase in the energy necessary to melt the gels results from crosslinking caused by the urea hydrogen bonding and not the van der Waals interactions of the fluorinated aspartyl ester functionality. Since multiple forms of aggregation are available through the urea functionality (i.e. stacks and crosslinks), an amorphous network is generated which immobilizes the solvent. In order to break this amorphous network, the van der Waals interactions between stacks and the hydrogen-bonding crosslinks must be overcome. This feature explains why this gel melts at the high temperature of 96 °C at 20 mM while the other gels melt below 80 °C at this concentration.

The enthalpy of melting of compound 25 (68±13 kJ/mol) is higher than that observed for compounds 23, 24, 29, and 31. There are two possible structural motifs which account for this increase. Compound 5 could adopt a conformation which is able to crosslink through strained hydrogen bonds. The length of the octyl spacer of 5 may provide a scaffold for the packing of the ester tails, increasing the van der Waals contact between adjoining fibers. The distance between the ureas in the monomer is approximately 10 A, which is sufficient to initiate crosslinking through the hydrogen bonds, however the ester tails may be affected by steric repulsion. Since SEM measurements have not been completed on 25, it is uncertain which morphology the gel matrix exhibits.

The nonlinearity observed in ΔH_m for the gel of compound 24 is consistent with the variation in structure as seen in the SEM photos (Figures 12 and 13). At 2 wt.% the fibers which comprise the aerogel network are thin and long compared to the strands of the 4 wt.% aerogel. At higher concentrations steric crowding of the growing strands results in early termination of aggregation along the long axis, so that free molecules in solution form new strands which are incorporated into thicker fibers which support the gel network. These short fibers possess multiple contacts to adjacent strands, creating an irregular structure than is observed for the aerogel formed from 2 wt.%) . Since the fibers of the 4 wt.% aerogel are thicker than those of the 2 wt.% gel, there is a larger surface area for the contact of adjacent fibers, which results in an increased ΔH .

The time dependence observed in ΔH_m of gels of 24-26 and 31 is typical for thermoreversible gels. At the molecular level, the fibers are in dynamic motion and this motion increases the length of the junction zone; ΔH_m increases since the number of interactions per junction has increased. In hexyl 24 the time dependence of gel setting is lower (0.9±03 kJ/mol hr) than for 25 and 26 (2.5±0.5 and 4±2 kJ/mol hr, respectively) due to the fact that this compound is less viscous in hot PMCH and allows for the formation of longer, more thermodynamically stable crosslinks. The gels of 25 and 26 in PMCH are more viscous and set more quickly, generally within seconds of placing the hot solution at room temperature. Therefore, the gel network has insufficient time to form idealized crosslinks and the thermodynamically favored aggregation state.

After melting the resulting gel solutions were viscous and dynamic flow ceased within 10 seconds of the removal of the heat source. Unlike the gels of 23 which exhibit dynamic flow for several seconds, the melted gels of compounds 24-26 do not flow upon inversion. These gels either reset the gel matrix in less than 1 second at room temperature or else the gels do not completely melt at the determined melting temperature. The inability of the melted gel to flow indicates that the melting process is that of a localized disruption of the crosslinking, which allows the ball bearing to fall. The threads that comprise the network are still intact and re- crosslink once the ball bearing has passed. Additionally, the shorter and more rigid spacers in compounds 23, 28, and 31 result in lower gel melting points and lower ΔH_m. This lower melting point is a result of the inability of the aggregates to form stable crosslinks, because of the steric congestion of the aspartyl ester functionality between stacks. However, given enough time at higher concentration more thermodynamically stable crosslinking can be achieved, as seen for compound 31.

Gelation of PMCH and CO2 was acheived with small organic molecules containing two urea functionalities and four perfiuorinated tails (compounds 23-26, 29 and 31). Transparent gels which display classical thermorevesibile behavior are generated in PMCH with less than 1 wt.% (3-6mM) of these compounds, while the gels of 24 and 26 in supercritical CO2 are opaque. Compounds 5-7, and 11-18, which contain only one fluorinated group per hydrogen bonding functionality, are insoluble in PMCH and do not gel this solvent. Use of Increased Viscosity Supercritical CO? in Oil Recovery

In another embodiment of the invention, the increased viscosity CO₂ may be used in oil well fracturing and in enhanced oil recovery methods. The increased viscosity CO₂, preferably gelled CO₂, may be used in the same manner as prior liquid CO₂ formulations. The use of liquid CO₂ in such methods has been described in U.S. Patents 4,480,696, 4,921,635, and 5,566,760, which are incoφorated here by reference. The increased viscosity CO may be used in combination with other well fracturing fluids, such as water and hydrocarbons, surfactants, and proppants. Accordingly, this embodiment of the invention relates to a method for fracturing subterranean formations penetrated by a well bore. The method introduces supercritical CO₂ containing a supramolecular network of compounds having a CO2-philic functional group and an aggregating functional into the well bore at a pressure and rate of flow sufficient to fracture a subterranean formation. The method then fractures the subterranean formation.

Methods for Making a Microcellular Foam

In a second embodiment, the invention relates to a method of making a microcellular foam by dissolving a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, in supercritical CO₂ to form a solution. The compound is aggregated to form a supramolecular network in solution. Then the CO₂ is removed under conditions sufficient to form a freestanding microcellular foam. The compound is dissolved and aggregated in the supercritical CO in the same way as discussed above in the method for increasing the viscosity of supercritical CO₂.

To prepare a foam according to the invention, after the aggregating step, the CO₂ is removed under conditions sufficient to form a free-standing microcellular foam. To form foams from such gels, the supramolecular networks created in solution must be preserved during and after CO₂ removal. By changing the temperature-pressure conditions of the initial solution of the CO₂,- philic agent, a phase separation may be induced to produce an organic analog to the aerogel upon CO₂ removal, for example by depressurization. Unlike traditional aerogel generation, these microcellular foams can be formed according to the invention in a single step in CO₂ without the use of any additional solvent. Accordingly,this invention creates microcelluar foams having supramolecular networks that will exist as stable entities in the absence of CO₂.

An alternative embodiment of the invention relates to a method of making a microcellular foam with halogenated solvents, preferably fluorinated solvents. The method steps are the same as those discussed for increasing the viscosity of supercritical CO₂ except that a halogenated solvent is used instead of the supercritical CO_2. For purposes of clarity the discussion below uses supercritical CO₂ as the solvent. The method combines a compound having a CO₂-philic functional group and an aggregating functional group with a halogenated solvent to form a solution. The compound aggregates in solution such that a supramolecular network is formed. The halogenated solvent containing the supramolecular network exhibits an increased viscosity over that of the halogenated solvents.alone. Then the halogenated solvent is removed under conditions sufficient to form a free-standing microcellular foam. The compound is dissolved and aggregated in the halogenated solvent in the same way as discussed above in the method for increasing the viscosity of supercritical CO₂. The halogenated solvent may be removed by means known in the art such as evaporation, preferably under vacuum.

The invention also relates to a microcellular foam comprising a supramolecular network of compounds having a CO₂-philic functional group and an aggregating functional group. The foam is a low bulk density material composed of interlocking micro fibers and has a bulk density which is 90% less than that of the compound which forms a supramolecular network in solution. . The The microcellular foam also has a submicron pore size of less than 10 micron, preferably less than 5 micron, and more preferably less than 1 micron. As discussed above, the supramolecular network is bound together through the aggregating functional group by interactions such as hydrogen bonding, dipole interactions, electrostatic interactions or van der Waals forces. Foam Studies

The ability of several variations of the compounds according to Formulas VI and VII to form cellular materials in CO₂ (Table 7) was evaluated. First, the phase behavior was measured to determine those conditions where a single-phase solution could be produced as a function of concentration. Foams were generated from single-phase solutions in CO₂ by either (i) lowering the temperature, (ii) lowering the pressure, or (iii) lowering temperature and then pressure. When formed, aggregates were recovered after venting of the CO₂ for Scanning Electron Microscopy (SEM) analysis [14]. Behavior in CO₂ could be separated into three general types:

Type 1 : These compounds (typically powders) could dissolve in CO₂ at concentrations exceeding 5 wt % at room temperature (above a given threshold pressure that varied with molecular structure of the agent but was below 300 atm. for all cases). Measurement of the resulting viscosity of the solution showed enhancement by 3 - 5 times at < 5 wt%. Removal of the CO₂ via pressure reduction left behind a foamed material (solid at room temperature and pressure) that was stable and could easily be handled and examined via SEM.

Type 2: These compounds were < OJ wt. % soluble in CO₂ at room temperature at pressures up to the limit of the instrument (500 atm.), but would dissolve at concentrations exceeding 5 wt % at elevated temperature (typically 70 - 90C). Upon cooling at constant pressure (300 atm.), the solution would exhibit a sharp phase separation point (sudden complete opacity of the mixture). Removal of the CO₂ by gradual depressurization left behind a monolithic cellular or fibrillar material that was stable and could be handled and examined via SEM.

Type 3. These compounds, like those of type 2, were soluble in CO₂ at elevated temperature, although slow cooling of the solution led to precipitation of the material as a powder or free floating fibers, rather than as a type 2 monolithic foam.

Table 7: Solubility and foaming (type 1, 2, or 3) of Formula VI and VII compounds

Compound C0₂-phile R Group Concentration T: (Z) (wt %) Formula VII

24 (CH₂)2(CF2)₇CF3 (CH₂)₆ 2.2 - 4.9 2 26 (CH₂)₂(CF₂)₇CF3 (CH₂),2 4.0 2 29 (CH₂)2(CF2)₇CF3 1,4-phenyl 1.9 3 31 (CH₂)₂(CF₂)7CF₃ 1,4-xylyl 3.35 3 32 (CH₂)2(CF₂)7CF3 fluoroether 2.5 - 4.8 3 33 fluoroether ⁺ (CH₂)₆ 1.5 - 5.0 1

R¹ Group Formula VI

34 (CH₂)₂(CF₂)₇CF₃ p-F CfrH, 4.5 2 35 (CH₂)2(CF₂)₇CF₃ p-CF₃ C₆H₄ 2.5 3 36 (CH₂)₂(CF₂)₇CF3 3,5 bis-CF₃ C₆H₃ 6.0 1 37 (CH₂)₂(CF₂)₇CF₃ (CH₂)₅CH₃ 1.0 - 5.0 1 38 (CH₂)2(CF₂)₇CF₃ phenyl 2 - 5.1 2 39 (CH2)2(CF₂)₇CF3 ethyl methacrylate 4.7 1

— Fluorolink B, Ausimont, Mw = 3000

+ — oligomer of hexafluoropropylene oxide, Mw = 1200 (DuPont)

Small variations to the structure of the aggregating molecules can lead to large changes in their behavior in CO₂. With the exception of 33, Formula VII compounds exhibited type 2 or 3 behavior, and hence required elevated temperature to dissolve in CO₂, apparently to break the strong self-interaction between the two urea groups. Alterations to the R group of Formula VJJ compounds produce substantial changes in behavior. For example, (24) when dissolved in CO₂ at slightly less than 5 wt. %, produces a cellular material (via type 2 behavior) that exhibits a morphology (Figure la) of "stacks" of small parallelograms. Despite the dense appearance of this material, its bulk density is 97% less than that of the parent material (at 5 wt % the resulting monolith fills the entire view cell). As can be seen in Figure la, the pores (the space between the parallelograms) are sub-micron. Lengthening the R group from hexyl to dodecyl produces a foam with a more conventional porous structure, larger cells, and a slightly higher bulk density (see Figure lb).

Upon changing the concentration of the compounds in solution, dramatic changes in the morphology of the foams resulted. For example, lowering the concentration of (24) in CO₂ to < 2.5 wt. % (all other conditions the same) produces a material (Figure lc) with sub-micron pores, a fibrillar morphology, and a comparable bulk density (the monolith comprises less material but does not fill the entire volume available in the view cell) than for the material in Figure la. Some, but not all of the materials in Table 7 exhibit a morphology-concentration correlation, but it is not yet clear how the chemical structure of the agents governs this correlation.

Changing the R group from alkyl to aromatic in Formula VII compounds changes the behavior from type 2 (monolith's) to type 3 (precipitated as powders). Here, although the elevated temperature allows dissolution of these type 3 materials, the formation of large aggregates with type 2 morphology is apparently inhibited by the aromatic structures, even for (32), where the R group contains aromatic groups with a highly CO₂-philic fluoroether spacer. When fluoroether groups are used in the aspartate residue (the Z group), as in (33), type 1 foams with a more traditional cellular appearance are formed.

Reducing the number of urea groups from two to one (formula VI compounds) produces type 1 materials more readily yet still allows for types 2 and 3 to form, depending upon the structure of the R group. Somewhat surprisingly, R groups that might be suspected to be relatively CO₂- philic (p-fluoro phenyl and p-trifluoromethyl phenyl in (34) and (35)), and hence lead to solubility at room temperature, instead produced type 2 and 3 behaviors, requiring elevated temperature for dissolution. Addition of the second trifluoromethyl group (35) is needed for the molecule to dissolve at room temperature. The compounds that produced type 1 behavior generally produced foams with a traditional porous morphology, with cells larger than 1 im (see Figure Id). However, the methacrylate-functional compound (39) exhibits type 1 behavior and also produces a foam with a fibrillar structure (Figure le). The phenyl-functional material (38), exhibited type 2 behavior and produced very low density, microcellular foam monoliths that filled the view cell, like those produced from (24), with a fibrillar microstructure (Figure If).

Although the foams generated with these compounds are stable upon removal of the CO₂ (they easily support their own weight with no dimensional changes after days or weeks), they can be readily re-dissolved in CO₂. To generate foams with a greater degree of permanence, compounds such as (39) (methacrylate functional material) or an analog of (24) or (26) where a diyne functionality is included in the R group can be used. Irradiation after foam formation would polymerize these materials.

CO₂-soluble associating polymers were also generated, as discussed above, by copolymerization of the highly CO₂-philic 1H, 1H, 2H, 2H perfluorodecyl acrylate with (i) (39), and (ii) with styrene followed by partial sulfonation of the phenyl groups. Copolymers of the fluorinated acrylate and (39) dissolved readily in CO₂ at room temperature and produced stable, transparent gels at concentrations of 5 wt % and below. Unlike for the cases of type 1 structures shown in Table 7, the viscosity enhancement created by these polymers was in the 100 - 1000 range. Removal of the CO₂ produced free-standing foam monoliths with a very low bulk density (> 97%) density reduction) but larger cells (> 10 im) than those described above. Gels and foams were produced even at levels of (39) in the copolymer as low as 6 mole %. Terpolymers of the fluorinated acrylate, styrene, and sulfonated styrene also produced transparent gels in CO₂ and foam monoliths with this type of microstructure (Figure 2). Copolymers of the fluorinated acrylate with monomers that do not promote association in solution not only did not produce a large viscosity increase in CO₂, but also did not produce foam monoliths upon depressurization. Rather, the cellular materials produced from these copolymers collapsed upon removal of the CO₂.

A free standing microcellular foam is created by removing the CO2 from the gel of (24). This is the first non-covalent polymeric microcellular free-standing organic foam produced. This foam is held together by only hydrogen bonding and van der Waals interactions. The morphology of the foam is dependant on spacer length and concentration as seen for gels of (24), where at 2 wt.%) fibers are thin and infinitely long and at 4 wt.% the fibers are short and thick; The foam of (26) which collapsed upon removal of the CO2 is amorphous and sponge-like.

The microcellular foams may be used for applications such as low density structural parts, high- temperature insulation, separation media, adsorbents, and catalyst supports.

EXAMPLES

SYNTHESIS OF FLUOROALKYL ASPARTATE BISUREAS AND UREAS

Reagents:

N-t-BOC protected aspartic acid (N-t-BOC-L-Asp) and N-CBZ protected aspartic acid (N-CBZ- L-Asp) were obtained from SIGMA and stored below 0 °C in the fridge before use. lH,lH,2H,2H-Perfluorodecanol (97%) was purchased from Lancaster Synthesis. Hexafluoropropylene oxide homopolymer alcohol (MW=1200 g/mol, fluoroether monofunctional alcohol, DuPont product, brand name Krytox, 95%) was purchased from Miller- Stephenson; l-[3-(Dimethylamino)propyl]-3-ethylcarbondiimide hydrochloride (EDCI, 98+%) and 4-(Dimethylamino)pyridine (DMAP, 99+%) were both ordered from Aldrich; Palladium hydroxide, 20 wt% Pd (dry basis) on carbon (Pearhnan's catalyst) was obtained from Aldrich; Diisocyanates and isocyanates used in our synthesis were purchased from Aldrich. All other chemicals and solvents were obtained from Aldrich and used as received.

Synthesis:

The reaction routes for the synthesis of fluorinated aspartate bisureas and ureas were generalized in scheme 8 To synthesize a bisurea, a diisocyanate was reacted with the deprotected aspartate; To synthesize a urea, an isocyanate was the reactant instead.

Scheme 8. Synthetic routes for fluorinated aspartate bisureas and ureas

CF 3COOH

In our synthesis, both short chain (FW = 464g/mol) fluoroalkyl alcohol and long chain (MW = 1,200) fluoroether alcohol were used to introduce the CO₂-philic functionalities into the bisureas and ureas structures. Different diisocyanates and isocyanates were also used to give various CO₂- phobic strucutres. The synthesized bisureas were listed in Table 8. The synthesized ureas were listed in Table 9. Table 8. Fluorinated aspartate biureas synthesized; The solubility and gelling behavior at 1 wt% concentrations of theses biureas in freon 113 and PFDMCH (perfluoro-1,3 dimethyl cyclohexane) were also listed as a screemng test before evaluation in carbon dioxide.

a. Hexafluoropropylene oxide homopolymer alcohol, MW=1200 b. Fluorolink B, Ausimont, MW=3000

Table 9. Fluorinated aspartate ureas synthesized; The solubility and gelling behavior at lwt% concentrations of theses biureas in freon 113 and PFDMCH (perfluoro-1,3 dimethyl cyclohexane) were also listed as a screening test before evaluation in carbon dioxide.

a. Hexafluoropropylene oxide homopolymer alcohol, MW=1200

Procedures

(1) Synthesis of Deprotected Fluoroalkyl Aspartate Amine

Typically, in a 250ml 3-neck flask equipped with a stirring bar, charge 100ml dichloromethane. 7.88g lH,lH,2H,2H-perfluorodecanol (0.017mol) was added and the flask was cooled in an ice bath. 2g N-Boc-Asp (0.0086mol) and 3.28g (0.017mol) EDCI were subsequently charged to the reaction mixture. Start stirring until most of the reactants were dissolved. 1.05g DMAP (0.0086mol) was then introduced. The reaction mixture was kept in the ice bath for 30 min, then the ice bath was removed and reaction was kept at room temperature overnight. The reaction mixture was then diluted with 100ml chloroform and transferred to a separation funnel. The organic layer was washed with 50ml 1%HC1 twice, and 50ml brine once and dried over sodium sulfate. Solvents were later removed under vacuum to yield a pale yellow solid. The solid was then dissolved in a minimal amount of dichloromethane (Freon was added if necessary). The obtained solution was transferred to a silica column and washed with chloroform. Solvent was subsequently removed under vacuum and a white solid aspartate product was obtained with 80% yield.

The obtained aspartate diester was subject to deprotection with trifluoroacetic acid. Typically, 5g aspartate was deprotected with 10ml trifluoroaceticacid in 20ml dichloromethane for 4 hours. The solvent was removed under reduced pressure. Chloroform was added and removed under vacuum until a white solid formed. The solid was then recrystallized from 200ml ethanol and cooled to room temperature and stored in a fridge for 3 hours. The solid was collected and dried under reduced pressure. The deprotected aspartate amine was a needle-shaped white solid with 78% yield.

1H NMR spectra taken from a Bruker 300 MHz NMR showed 4.87ρρm (O=C(CH)CH₂NH in aspartate residue), 4.58ppm (O=C(CH₂)CH in aspartate residue), 4.40ppm (C₈Fι₇CH (CH₂)O in fluorodecanol residue), and 2.48ppm (C₈F₁₇(CH₂)CH in fluorodecanol residue).

(2) Synthesis of Deprotected Fluoroether Aspartate Amine

Similar to the synthesis of fluoroalkyl aspartate, fluoroether aspartate was synthesized in 100ml cooled ethyl acetate- lJJ-trichlorotrifluoroethane (called in the following Freon 113) mixture (1:1 v/v) with fluoroether alcohol and N-CBZ-Asp as the reactants. After reaction, most solvents were removed and the concentrated oil was washed with 50ml ethyl acetate twice, 50ml ethanol once, and 100ml 1% HCl twice. The residue was then diluted with 50ml freon and dried over sodium sulfate. Vacuum evaporate most freon 113 until the residue reached a volume of 20- 30ml. The yellow-colored solution was then purified over a silica column and washed down with 1:1 ethyl acetate-freon mixture. Solvents were later evaporated and yield a colorless oil. The fluoroether aspartate diester was then deprotected by hydrogenation with Pd(OH)2/C as the catalyst. Typically, 5.0g fluoroether aspartate diester was dissolved in 20ml perfluorolJ- dimethyl cyclohexane, 0J5g palladium hydroxide on carbon catalyst was added. Start stirring vigorously. N₂ was passed through the reaction flask to displace air before hydrogen was introduced. The diester was deprotected with hydrogen for 12 hours, then the catalyst was removed first by filtration (Whatman #1 filter), then the residual fine catalyst particles were removed by Millipore membrane filter (0.45μm). The solvent was removed under vacuum and residue washed with ether. Yellowish oil sample was then dried under vacuum.

1H NMR spectra showed peaks at 7J2ppm (C₆H₅CH₂ in CBZ-Asp residue), 5.99ppm (CF₂(CH₂)O from fluoroether alcohol residue), 5.00ppm (O=C(CH₂)CH in aspartate residue), 4J4ppm (O=C(CH)CH₂NH in aspartate residue), 4.69ppm (CH(NH)CO from aspartate residue), and 2.93ppm (O(CH2)C₆H₅ from CBZ-Asp residue).

(3) Synthesis of Bisureas and Ureas

The deprotected fluoroalkyl or fluoroether aspartate amines were than reacted with stoichiometric amounts of commercially available diisocyanates and isocyanates to yield biureas and ureas of different structures.

Typically, the reactions between deprotected fluoroalkyl aspartate amine and diisocyanates/isocyanates were carried out in 50ml dichloromethane with triethylamine as the catalyst. The product fluoroalkyl bisureas/ureas are white solids and collected by filtration and washed with 1% HCl and hexanes and then dried under vacuum. The fluoroether bisureas/ureas were obtained by reacting the deprotected fluoroether amine with different diisocyanates/isocyanates in 50ml freon 113, with triethylamine as the catalyst. After reactions, solvent was removed by reduced pressure and the oily product washed with 1% HCl and hexanes and dried.

The synthesized biureas/ureas were characterized by taking IR spectra on a Mattson Polaris FT- IR. Solid samples were mixed with KBr and compressed into pellets before taking the spectra. Liquid samples were prepared in the form of thin films between NaCl windows. The IR spectra for fluoroalkyl biureas/ureas are similar, showing N-H streching absorbance at 3350-3360 cm^"1, C-H stretching at 2940-2990 cm^"1, carbonyl absorbance around 1735-1745 cm^"1, N-H scissoring absorbances at 1630 and 1570 cm^"1 respectively.

The IR spectra for fluoroether bisureas/ureas usually show N-H streching absorbances at 3340- 3350 cm^"1, C-H strecthing at 2940-2980 cm^"1, carbonyl absorbance around 1760-1770 cm^"1, and two N-H scissoring absorbances at 1650 and 1570 cm^"1.

Synthesis of Random Terpolymer of Fluoroacrylate, Styrene, and Sulfonated Styrene

Reagents:

All reagents, except 95 % sulfuric acid and NaOH pellets (J. T. Baker), were purchased from

Aldrich. Monomers (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10,10-heptadecafluorodecyl acrylate and styrene) and AIBN were purified via standard procedures. 1,1,2-tτichlorotrifluoroethane

(TCTFE), Methanol (anhydrous), 1,2 dichloroethane, and acetic anhydride (99+%) were used as received.

Synthesis:

Random Copolymerization of Fluoroacrylate and Styrene:

Copolymerization was carried out by bulk free radical polymerization of fluoroacrylate and styrene in the presence of AIBN. A mixture of AIBN (approximately 0.2 mole % of monomers), styrene and fluoroacrylate was placed in an ampule. The mixture was purged with N₂, and then flame-sealed. A white waxy solid resulted after an overnight polymerization at -65-70 °C. The polymer was purified by dissolving in TCTFE and precipitating in a large excess of methanol. After vacuum drying overnight, a white polymer was obtained with 95% yield. Chemical structure and composition of the copolymer was determined by 300 MHz ^!H NMR spectroscopy as 0.16 mole% styrene-0.84 mole % fluoroacrylate.

Sulfonation of a Copolymer of Fluoroacrylate and Styrene: Sulfonation of the styrene phenyl group was performed using acetyl sulfate. The reagent was prepared according to the procedure reported in literature (1-3). For sulfonation, copolymer prepared in the previous step was dissolved in TCTFE. The solution was heated to 50-60 °C under reflux. After adjustment of the temperature, pre-determined amounts of the pre-prepared acetyl sulfate solution were added. When the acetyl sulfate was added to the polymer solution, the solution acquired a dark green/brown tint. The reaction was allowed to proceed for 2 hours at 50-60 °C and then terminated by the addition of large amount of methanol. To facilitate the complete removal of residual sulfonating agent from the functionalized polymer, the sulfonated polymer was redissolved in TCTFE and reprecipitated in methanol several times. The sample was dried in a vacuum oven overnight. The degree of sulfonation of the polymers was determined via 300 MHz 1H NMR.

Neutralization of Sulfo-functionalized Copolymer:

To the solution of the sulfonated copolymers in TCTFE was added 4-5 drops of 1 wt % phenolphthalein (indicator). The solution was then titrated with 1.0 N NaOH until the end point indicated by a change from colorless to pink. The resulting functionalized ionomer was precipitated in methanol. The polymer was purified several times by redissolution in TCTFE and reprecipitation in methanol. After drying under vacuum overnight, a slightly brown tint polymer was obtained.

Synthesis of PoIy(Fluorinated Asparate Methacrylate Urea-co- Fluoroacrylate)

Reagents:

Heptadecafluorodecyl acrylate monomer (inhibited with 100 ppm monomethyl ether hydroquinone) was purchased Aldrich. The inhibitor was removed by washing with 5% aqueous NaOH solution. The monomer was subsequently dried over MgSO₄ and stored in a fridge before polymerization. 2-Isocyanatoethyl methacrylate (inhibited with < 0.1% 2,6-di-tert-butyl-4- methylphenol) was used as received for the synthesis of fluorinated aspartate methacrylate urea monomer. 2, 2'-Azobisisobutyronitrile (AIBN) was recrystallized from methanol twice before use. Argon was ordered from Praxair and passed through a CaCl₂ drying tube before use. All other chemicals and solvents were obtained from Aldrich and used as received. Synthesis:

The fluorinated aspartate methacrylate urea was first synthesized by reacting the deprotected fluorinated aspartate salt with 2-Isocyanatoethyl methacrylate. The obtained fluorinated urea monomer was then bulk copolymerized with fluoroacrylate with different stoichiometry ratios to yield copolymers of different compositions. The monomer ratios used to synthesize copolymers of different compositions were presented in Table 10.

Table 10. Stoichiometric ratio for the synthesis of fluorinated methacrylate urea fluoroacrylate urea copolymer. N_AIBN is 0Jmol% of monomers in all three cases.

(1) Synthesis of fluorinated aspartate methacrylate urea monomer

Deprotected fluorinated aspartate were synthesized by reacting 1H, 1H, 2H, 2H- perfluorodecanol with N-BOC protected aspartic acid and the BOC group in the obtained aspartate was removed by deprotection with trifluoroacetic acid. The fluorinated aspartate trifluoroacetic acid was then reacted with 2-isocyanatoethyl methacrylate to form the urea monomer.

In a typical experiment, lg of fluorinated aspartate salt (2.48mmol) was charged into a 100ml flask equipped with a stirring bar. 50ml chloroform was added as a reaction solvent. 0.60ml triethylamine (TEA) was added through a syringe to dissolve the salt in chloroform. Start stirring until a clear solution was formed. The solution was purged with argon while 0.36ml 2- Isocyanatoethyl methacrylate (2.49mmol) was added dropwise through a syringe into the solution. The reaction mixture was allowed to react at room temperature for 4 hours. The obtained solution was diluted with 20ml chloroform and transferred to a 125ml separatory funnel. The solution was washed with 30ml 1% HCl once and 30 ml brine solution once and dried over anhydrous Νa₂SO4. The solvent was removed under vacuum. The obtained white solid was then washed with 30ml hexanes twice and dried under vacuum (30 inch Hg) overnight. 1.77g white solid product was collected, yield 66%. The collected monomer was stored in the fridge before polymerization. (2) Copolymerization of fluorinated aspartate methacrylate urea and fluorinated acrylate

The following is an example of the synthesis of a copolymer with a fluorinated acrylate to urea molar ratio of 15:1. The synthesis of copolymers with the other compositions followed the similar procedure.

Typically, 1.Og (0.93mmol) of fluorinated aspartate urea monomer was measured and added to a 50ml flask. 7Jg (14mmol) fluorinated acrylate monomer was charged to the reaction flask via a pipette. 4.9mg (0.03 mmol) of AIBN was subsequently added to the flask. The flask was then purged with argon and stirred and heated to 60°C in an oil bath until the solid urea monomer was dissolved. The reaction mixture was then kept at 60~65°C for 2 days. The obtained polymer block was cut into several pieces and dissolved in Freon 113. The resulted viscous polymer solution was precipitated into 200ml methanol three times. The polymer was dried under vacuum for two days.

The compositions of the copolymers were characterized with Bruker 300MSL NMR spectroscopy. Integration results showed the actual compositions of the copolymers, which were listed in Table 9. as R^^oy/urea-

Behavior of Fluorinated Aspartate Urea and Fluoroacrylate Copolymers in Carbon Dioxide

Experimental

A high pressure windowed cell was used to evaluate the solubility and gel forming ability of these copolymers. The solid copolymer sample was measured and charged into the sample cell.

The experiment was first done at a higher concentration (~5wt%). In the case of a single-phase swollen polymer was formed, the system was heated to 80°C while the pressure was kept above 6,000psi. The experiment was also done at lower concentrations following the same procedure. The solubility and gel formation results were presented in Table 11. Table 11

For all three copolymers, typically, at concentrations higher than 2.0wt%, the polymers formed a single-phase CO₂-swollen polymer network that filled the whole sample cell. The mixing beads could fall slowly when the high pressure cell was inverted, but the falling cylinder could not move through the swollen polymer network. Elevated temperature did not break the network structure and result in polymer solubilization in carbon dioxide. At lower concentrations (< 2wt%), however, phase separation occurred at room temperature, a swollen polymer phase and a CO₂-rich liquid phase coexisted at room temperature. Single-phase polymer in supercritical carbon dioxide solution was obtained at 90°C at the low concentration regime. For the copolymer with an acrylate to urea composition of 20:1, the single phase solution was maintained after the system was cooled to room temperature and the solution relative viscosity was measured and exhibited in Fig. 11.

PREPARATION OF FOAMS

Compound 24 from Table 7 was dissolved in supercritical CO₂ at 6500 psi and 80°C generating a 4 wt.% solution. Upon cooling to room temperature this homogeneous solution became opaque. As the CO₂ was removed slowly from the chamber no phase separation occurred, as expected for a two component system. Once at atmospheric pressure the chamber was opened to reveal a solid which filled the entire volume of the cell. This solid stood under its own weight and was amenable to handling, maintaining its shape and structure. Samples of this aerogel were examined by scanning electron microscopy (SEM); photos of this aerogel are displayed in Figure 12.

The Foam of compound 24 was redissolved in supercritical CO₂ to general a 2 wt.% solution under the same temperature and pressure conditions. Once again the solution turned opaque upon cooling. The resulting solid did not fill the entire chamber, it occupied approximately the same volume as that of the 4 wt.% aerogel. The resulting aerogel was stable to handling and was examined by SEM (Figure 13). The same sample of 24 was then redissolved in a mixed solvent system in the attempt to generate a clear gel or a viscous liquid. The resulting clear material from this experiment did not retain its shape upon removal from the chamber and was not amiable to SEM analysis.

Compound 26 was dissolved in supercritical CO₂ under the same conditions as compound 24 generating a 4 wt.% solution. This compound dissolved nicely at elevated temperatures (90° C) generating a clear, colorless solution. As the temperature was lowered an opaque solid formed in the chamber. Upon removal from the chamber the resulting solid collapsed, but maintained its shape and stood under its own weight. This structure was also examined by SEM (Figure 14).

Experimental

General Procedures

Unless indicated, reactions were carried out under typical laboratory conditions: room temperature (rt) = 293-298 K and standard pressure = 1 atm. Nitrogen (Linde Union Carbide, dry grade) was dried through two sections of Drierite (calcium sulfate) with indicator and P2O5 .

Melting points (mp) were determined on an Electrothermal capillary melting point apparatus and are uncorrected. All computer modeling studies were performed on a Silicon Graphics Indigo II workstation, using Macromodel 5.5 (Amber forcefield). Nuclear magnetic resonance (NMR) spectra were acquired using a Bruker QM, Bruker WH, IBM-Bruker AF, or a Bruker AM 500 instrument. Proton (iH) NMR were acquired at 30031 MHz or 500.51 MHz; ¹³C were recorded at either 75.46 or 125.76 MHz. Chemical shifts are expressed as parts per million

(ppm) downfield from tetramethylsilane (TMS). Fluorine (^F) NMR were recorded on an IBM-Bruker AF spectrometer at 28238 Mhz.

Mass spectra (MS) were determined by the MS Laboratory at the Department of Chemistry, University of Pittsburgh under direction of Dr. Kasi V. Somayajula or at the UIUC School of Chemical Sciences at the University of Illinois under the direction of Dr. Steven Mullen. El and FAB mass spectra were obtained using a Varian MAT CH-5 or VG 7070 mass spectrometer. All mass spectral data are expressed in units of m e.

Analytical thin layer chromatography (TLC) was conducted on precoated TLC plates: Poly Gram 0.25 mm silica gel with fluorescent indicator UV254, Poly Gram 0.2 mm aluminum oxide N with fluorescent indicator UV254 manufactured by Macherey-Nagel. Column chromatography utilized silica gel 60 (particle size 0.040-0.063 mm, 230-400 mesh ASTM) or aluminum oxide (particle size 0.063-0.200 mm, 70-230 mesh ASTM) manufactured by EM Science.

THF and diethyl ether were obtained from Fisher and distilled over Na and benzophenone under nitrogen. Dichloromethane was obtained from Fisher and distilled over CaH2 under nitrogen

Triethylamine (TEA) was distilled from KOH and stored over KOH. Toluene and acetonitrile were dried and stored over 4A sieves. Amino acids were purchased from Sigma and perfluoro alcohols from Lancaster. All other reagents, unless otherwise noted, were purchased from Aldrich as the highest grade available and used without further purification.

Identification of Gel Formation and Determination of Gel Properties

The inversion method was employed to determine if a compound formecfa gel in PMCH or freon. [19] The compound was dissolved in hot solvent, the mixture allowed to cool to room temperature and the solution allowed to set at 22°C for an appropriate amount of time. After this setting period the samples were inverted. Samples which did not move or deform were classified as gels.

The dropping ball method was performed on PMCH gels to determine the melting point of the gel. [20] A known quantity of compound was placed in a test tube with 200 mL of PMCH and a teflon stir bar. The test tube was sealed with a septum and heated with stirring until the solid dissolved. The stir bar was raised above the level of the solution by a magnet and the solution cooled to room temperature; once cooled the stir bar was removed. The test tube was then resealed and allowed to stand undisturbed at 22°C for a period of time. After the appropriate time interval the tube was opened and a 3/32" steel ball bearing was lowered gently onto the surface of the gel. The tube was resealed and placed in a Buchi 510 oil bath melting temperature apparatus modified to hold 10 samples simultaneously. The temperature of the oil bath was increased at a rate of 0J-0.5°C/min. The melting point of the gel is taken to be the temperature at which the ball bearing reaches the bottom of the test tube. The ball bearing is removed by heating the gel until a free flowing solution is formed and retrieving the ball bearing with a magnet. This gel may be used again after an appropriate time interval to reset the gel. DSC measurements were conducted on a TA Instruments DSC 2910 at a rate of 5 °C/min. Samples were placed in a Perkin Elmer volatile sample pan with cover. The instrument was calibrated using an indium standard over the temperature range of 10-110°C.

Synthetic Procedures for Compounds 5-31 N,N'-m-xylylene-bis-carbamic acid di(lH,lH,2H2H-perfluorodecyl ester (5). In 5.0 mL of toluene, lH,lH,2H,2H-perfiuorodecanol (CF, 1.00 g, 2.14 mmol) and 1,3- bis(isocyanatomethyl)benzene (162 mL, 1.03 mmol) were heated to reflux for 12 h. The solution was cooled to room temperature and the resulting white solid isolated by filtration. This solid was washed with 50 mL of 1 : 1 CH2Cl2:hexanes and dried in vacuo (-1 torr) for 6 h, yielding

0.379 g (0.339 mmol, 68% yield) of 5. m.p. 81-82 °C; ^lHNMR ((CD3)2CO/freon): 7.24-7.19 (m, 3H, ArH), 6.75 (t, J= 62 Hz, 2H, NH), 4.37 (t, J= 6.3 Hz, 4H, OCH2), 431 (d, J= 6.2 Hz,

4H, CH2Ar), 2.59 (m, 4H, CH2CF2); ¹⁹FNMR ((CD3)2CO/freon): -114.2 (s), -1223 (s), -122.5 (s) -123.0 (s), -124.2 (s), -126.7 (s); MS(EI): 1116 (M+).

{3-(lH,lH,2H2H-perfluorodecoxycarbonylamino-methyl)-cycIohexyI}-carbamic acid lH,lH,2H2H-perfluorodecyl ester (6). Compound 6 was prepared as above for 5 using CF (0.500 g, 1.07 mmol) and bis(isocyanatomethyl)cyclohexane (103 mL, 0.503 mmol) yielding

0366 g (0.326 mmol, 60 %). m.p. 73 °C; iHNMR ((CD3)2CO/freon): 4.98-4.70 (m, 2H, NH), 4.70-4.23 (m, 4H, CH2O), 3.06-2.93 (m, 4H, CH2 methylene), 2.40-230 (m, 4H, CyH), 1.71-

1.17 (m, 10H, CH2CF2 and CyH), 0.98-0.49 (m, 2H, CyH). ¹⁹FNMR ((CD3)2CO/freon): - 114.2 (s), -1223 (s), -122.5 (s), -123.0 (s), -124.2 (s), -126.7 (s); MS(EI+): 1122 (M+).

{3-(lH,lH,2H2H-perfluorodecoxycarbonyl-aminomethyI)-benzyl}-carbamic acid lH,lH,2H,2H-perfluorodecyl ester (7). Compound 7 was prepared as above for 5 using CF (0.500 g, 1.07 mmol) and 1,3-phenylenediisocyanate (0.077 g, 0.48 mmol) yielding 0.51 g (0.46 mmol, 88 %). m.p. 93-94°C; ^ΪHNMR ((CD3)2CO/freon): 8.75 (br s, 2H, NH), 7.79 (s, 1H, CHAr), 7.25 (d, J= 8.4 Hz, 2H, ArH), 7.17 (t, J= 8.4 Hz, 1H, ArH), 4.46 (t, J= 6 Hz, 4H, OCH2), 2.74-2.57 (m, 4H, CH2CF2); ¹⁹FNMR ((CD3)2CO/freon): -114.2 (s), -122.3 (s), -123.0 (s), -124.2 (s), -126.7 (s); MS (EI+): 1088 (M+).

lH,lH,2H,2H-perfluorodecyl N-(tert-butoxycarbonyl) glycinate (8). In 100 mL of dry dichloromethane, lHJHJHJH-perfluorodecanol (5.10 g, 11.0 mmol), DMAP (0.280 g, 2.28 mmol), and N-t -Boc-glycine (2.00g, 11.4 mmol) were combined. After 15 min, the reaction mixture was cooled in an ice bath to 0°C; EDCI (2.40 g, 12.5 mmol) was then added. The reaction was stirred at 0°C for 30 min. then slowly warmed to room temperature; the reaction was stirred at room temperature for 6 h. Additional dichloromethane (100 mL) was added and the reaction mixture was extracted with 1 % HCl (2 x 50 mL), water (2 x 50 mL), NaHCO3 (2 x 50 mL), and more water (2 x 50 mL). The organic layer was extracted with brine and dried over sodium sulfate. Dichloromethane was removed in vacuo yielding a pale yellow solid. The solid was taken up in a minimum of dichloromethane and passed through a plug of silica. The silica was washed with CH2CI2 (200 mL) and CHCI3 (100 mL). The solvent was removed in vacuo yielding 6J4 g of a waxy, white solid (10.0 mmol, 90 %). m.p. 56-57°C; ¹HNMR (CDCI3): 5.12 (t, J= 5.3 Hz, 1H, NH), 4.47 (t, J= 6.6 Hz, 2H, OCH2), 3.94 (d, J= 5.1 Hz, CH2NH), 2.59- 2.43 (m, 2H, CH2CF2), 1.47 (s, 9H, C(CH3)3); MS(FAB): calc'd for C12H16F17NO4 622.0884, found 622.08861.

[2-(lH,lH,2H,2H-perfluorodecyloxy)-2-oxoethyl]ammonium ,2,2-trifluoroacetate (9).

Compound 8 (4.63 g. 7.45 mmol) was added to 20 mL of 1 :1 TFA/dichloromethane and stirred under N2 for 2 h. The solvent was removed in vacuo and the residue was taken up in 10 mL of ethanol with heating. The ethanol and residue TFA were removed under vacuum and the gummy solid was dissolved in 100 mL of hot ethanol. Upon cooling to room temperature, a white, fluffy solid formed; the solid was collected by filtration and washed with ethanol and dichloromethane. Compound 36 was dried under vacuum (1 torr) for 12 h giving 4J3 g (7.91 mmol, 87 %). m.p.

110-112°C; !HNMR (DOCD3/freon): 4.58 (t, J= 6.0 Hz, 4H, NH2 and CH2O), 3.87 (s, 2H, CH2NH2), 2.75-2.63 (m, 2H, CH2CF2); MS(FAB): calc'd for C12H9F17NO2 522.03620, found 522.036184.

lH,lH,2H,2H-perfluorodecyI-2-{[(3,5-di{[2-lH,lH,2H,2H-perfluorodecoxy- 2oxoethyl)amino]carbonyl}benzoyl)amino]acetate (10). Compound 9 (1.43 g, 2.25 mmol) and TEA (0.400 mL, 2.88 mmol) were added to 10 mL of dichloromethane and the solution was cooled to 0°C. A solution of 1,3,5-benzenetricarbonyl chloride (0J0 g, 0.75 mmol) in 10 mL of THF was added dropwise over 10 min. The mixture was stirred at room temperature under N2 for 8 h. The resulting solid was collected by filtration and washed with dichloromethane, 1 % HCl, water and more dichloromethane. After drying under vacuum for 12 h at 1 torr, a white, finely divided solid was collected (1.01 g, 0.587 mmol, 77 % yield), m.p. 193°C (decomp); !HNMR (CDCI3/IO % TFA): 8.77-8.73 (m, 3H, ArH), 8.20 (br s, 3H, NH), 4.66 (m, 6H, CH2O), 4.39 (m, 6H, CH2(CO)), 2.57-2.42 (m, 6H, CH2CF2).

lH,lH,2H,2H-perfluorodecyl-2-{[(3,5-cis-cis-di{[2-lH,lH,2H,2H-perfluorodecoxy- 2oxoethyl)amino]carbonyl}cyclohexyl)amino]acetate (11). Compound 9 (1.54 g, 2.43 mmol) and TEA (0.700 mL, 5.04 mmol) were added to 50 mL of dichloromethane and the solution was cooled to 0°C. A solution of cis,cis -1,3,5-cyclohexanetriacid chloride (0.200 g, 0.736 mmol) in 10 mL of dichloromethane was added dropwise over 10 min. The mixture was stirred at room temperature under N2 for 12 h. The resulting solid was collected by filtration and washed with 200 mL of dichloromethane. The solid was dried under vacuum for 12 h yielding 0.930 g (0.539 mmol, 74 %) of white powder, m.p. 236°C (decomp); ^ΪHNMR (CDCl3/2% TFA): 7.37 (br s, 3H, NH), 4.58 (t, J= 5.1 Hz, 6H, CH2O), 4.19 (br s, 6H, CH2N), 2.61-2.48 (m, 9H, CH2CF2 and CyH), 1.79-1.52 (m, 3H, CyH). ¹⁹FNMR (CDCl3/2% TFA): -81.3 (s), -114.3 (s), -122.3 (s), -122.5 (s), -1233 (s), -124.2 (s), -126.7 (s); MS (FD) 1719.7 (M+)

lH,lH,2H,2H-perfluorodecyl 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyloxy)-2- oxoethyl]amino}carbonyl)amino]methyl}butyl} amino]acetate (12). Compound 9 (0.551 g, 0.867 mmol), TEA (0.250 mL, 1.80 mmol) and 1,4-diisocyanatobutane (50 L, 0.39 mmol) were combined in 10 mL of dichloromethane. The reaction mixture was stirred for 12 h and then 10 mL of hexanes was added. The resulting solid was isolated by filtration and washed with 50 mL each of 4:1 dichloromethane/hexanes, 1% HCl, water, and 4:1 dichloromethane/hexanes. After drying under vacuum for 16 h, 0.445 g (0376 mmol, 96 % yield) of 12 were collected, m.p.

156°C; iHNMR (CDCl3/3% TFA): 4.51 (t, J= 6.2 Hz, 4H, CH2O), 4.10 (s, 4H, CH2(CO)), 3.26

(br s, 4H, CH2CH2CH2), 2.59-2.43 (m, 4H, CH2CF2), 1.65 (br s, CH2CH2CH2); ¹⁹FNMR (CDCl3/3% TFA): -82.9 (s), -114.4 (s), -122.3 (s), -123.1 (s), -124.2 (s), -126.7 (s); MS(EI): 1182 (M+). lH,lH,2H,2H-perfluorodecyI 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyIoxy)-2- oxoethyI]amino}carbonyl)amino]hexyl}amino] acetate (13). Compound 13 was prepared analogously to 12 using 0.400g (0.629 mmol) of 9,

0J00 mL (0.720 mmol) TEA, and 53 L (0300 mmol) 1,6-diisocyanatohexane; 0.310 g (0.256 mmol, 85 % yield) of 13 were isolated.m.p. 164°C; iHNMR (CDCl3/3% TFA): 4.55 (t, J= 6.2 Hz, 4H, CH2CF2), 4.13 (s, 4H, CH2(CO)), 3.20 (br s, 4H, CH2CH2NH), 2.51-239 (m, 4H,

CH2CF2), 1.59 (br s, 4H, CH2CH2CH2), 136 (br s, 4H, CH2), NH not observed; ¹⁹FNMR (CDCl3/3% TFA): -81.5 (s), -114.4 (s), -1223 (s), -122.5 (s), -1233 (s), -124.2 (s), -126.7 (s); MS(EI): 1210 (M+).

lH,lH,2H,2H-perfluorodecyl 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyloxy)-2- oxoethyl]amino}carbonyl)amino]octyl}amino] acetate (14). Compound 14 was prepared analogously to 12 using 0.558g (0.880 mmol) of 9, 0.250 mL (1.83 mmol) TEA, and 78 L (0.400 mmol) 1,6-diisocyanatooctane; 0.426 g (0.344 mmol, 86 % yield) of 14 were isolated. m.p. 163°C; ΪHMR iHNMR (CDCl3/3% TFA): 4.57 (t, J= 6.2 Hz, 4H, CH2O), 4.17 (s, 4H, CH2(CO)), 3.21 (t, J= 7.1 Hz, 4H, CH2NH), 2.64-2.48 (m, 4H, CH2CF2), 1.61 (br s, 4H,

CH2), 1.34 (s, 8H, CH2), NH not observed; 1⁹FNMR (CDCl3/3% TFA): -81.2 (s), -114.3 (s), - 122.3 (s), -122.5 (s), -1233 (s), -124.2 (s), -126.7 (s); MS(EI): 1238 (M+).

lH,lH,2H,2H-perfluorodecyl 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyloxy)-2- oxoethyl] amino} carbonyl)amino] dodecyl} amino] acetate (15). Compound 15 was prepared analogously to 12 using 0.558g (0.880 mmol) of 9, 0.250 mL (1.83 mmol) TEA, and 108 L (0.400 mmol) lJ2-diisocyanatododecane; 0.496 g (0.383 mmol, 96 % yield) of 15 were isolated. m.p. 151°C; iHNMR (CDCl3/5% TFA): 4.58 (t, J= 6.2 Hz, 4H, CH2O), 4.17 (s, 4H, CH2(CO)), 3.21 (t, J- 7.2 Hz, 4H, CH2NH), 2.64-2.48 (m, 4H, CH2CF2), 1.61 (br s, 4H, CH2CH2NH),

134 (s, 16H, CH2), NH not observed; ¹⁹FNMR (CDCl3/5% TFA): -81.4 (s), -1143 (s), -122.3 (s), -122.5 (s), -1233 (s), -124.2 (s), -126.7 (s); MS(EI): 1294 (M+). lH,lH,2H,2H-perfluorodecyl 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyloxy)-2- oxoethyl]amino}carbonyl)amino]methyl}benzyl}amino] acetate (16). Compound 16 was prepared analogously to 12 using 0J80g (0.441 mmol) of 9, 0.070 mL (0.504 mmol) TEA, and 34 L (0.22 mmol) l,3-bis(isocyanato)methyl)benzene; 0.233 g (0J89 mmol, 85 % yield) of 16 were isolated, m.p. 188°C; ΪHNMR (CDCl3/5% TFA): 7.36-7.28 (m, 3H, ArH), 7.15 (s, 1H, ArH), 4.45 (t, 7= 6.2 Hz, 4H, CH2O), 4.39 (s, 4H, ArCH^NH), 4.14 (s, 4H, CH2(CO)), 2.54-

2.46 (m, 4H, CH2CF2), NH not observed; ¹⁹FNMR (CDCl3/5% TFA): -81.4 (s), -114.1 (s), - 122.5 (s), -123.3 (s), -124.2 (s), -126.7 (s); MS(EI): 1230 (M+).

lH,lH,2H,2H-perfluorodecyI 2-{[(3-{[{[2-(lH,lH,2H,2H-perfluorodecyloxy)-2- oxoethyl]amino}carbonyl)amino]methyl}cyclohexyI} aminojacetate (17). Compound 17 was prepared analogously to 12 using OJOOg (0.315 mmol) of 9, 0.070 mL (0.504 mmol) TEA, and 30 L (0.15 mmol) bis(isocyanatomethyl)cyclohexane; 0.170 g (0.137 mmol, 85 % yield) of 17 were isolated, m.p. 164-165°C; iHNMR (CDCl3/5% TFA): 4.26 (br s, 4H, CH2O), 4.17 (br s, 4H, CH2(CO)), 3.20-3.09 (m, 4H, CyH), 2.52-2.49 (m, 4H, CH2CF2), 1.91-1.29 (m, 8H, CyH), 0.93 (br s, 2H, CyH), NH not observed; MS(EI): 1236 (M+).

lH,lH,2H,2H-perfluorodecyl2-{[(3-{[{[2-(lH,lH,2H,2H-per fluorodecyloxy)-2- oxoethyl]amino}carbonyl]amino}anilino] acetate.(18). Compound 18 was prepared analogously to 12 using 0.280g (0.441 mmol) of 17, 0.070 mL (0.504 mmol) TEA, and 0.035 g (0.22 mmol) 1,3-phenylene diisocyanate; 0.235 g (0.195 mmol, 89 % yield) of 18 were isolated. m.p. 197°C; iHNMR (CDCl3/5% TFA): 8.22 (br s, 1H, ArH), 7.44 (t, 7= 8.0 Hz, 1H, ArH), 7.16 (d, 7= 8.0 Hz, 2H, ArH), 4.54 (t, J= 6J Hz, 4H, CH2O), 4.15 (s, 4H, CH2(CO)), 2.63-2.47

(m, 4H, CH2CF2), NH not observed; ¹⁹FNMR (CDCl3/5% TFA): -81.4 (s), -114.4 (s), -1223 (s), -122.5 (s), -123.3 (s), -124.2 (s), -126.7 (s); MS(EI): 1202 (M+).

Di(lH,lH,2H,2H-perfluorodecyl)-N-t-Boc-L-aspartate (19). DMAP (2.91 g, 23.8 mmol), CF (11.9 g, 25.0 mmol) and N-Boc-aspartic acid (3.00 g, 12.9 mmol) were combined in 200 mL of dichloromethane. The solution was cooled to 0°C and EDCI (5.407 g, 28.3 mmol) was added all at once. The solution was stirred for 30 min. at 0°C, during which time a white solid formed. The reaction was warmed to room temperature and allowed to stand for 6 h. The reaction mixture was extracted with 2x50 mL aliquots of 1 % HCl, water, NaHCO3, water, and brine. The organic layer was dried over Na2SO4, reduced in volume to ~50 mL, and passed through a plug of silica. The solvent was removed under vacuum producing 12.54 g (11.14 mmol, 89 % yield) of 26. m.p. 89°C; ΪHNMR (CDCI3): 5.48 (d, 7= 8.5 Hz, IH, NH), 4.60-4.55 (m, IH, CH), 4.53-3.48 (m, 4H, CH2CF2), 3.02 (dd, 7= 3.8 Hz, 2 = -17.4 Hz, IH, CHCH2), 2.86 (dd, 7 = 4.4 Hz, ²J= -17.4 Hz, IH, CHCH2), 2.50-235 (m, 4H, CH2CF2), 1.44 (s, 9H, C(CH3)3); MS(EI): 1024 (M-Boc)+.

Di(lH,lH,2H,2H-perfluorodecyl)-L-aspartate trifluoroacetic acid salt (20). Compound 19 was added to 20 mL of a 1 : 1 mixture of TFA/dichloromethane and stirred under N2 for lh. The solvent was removed under vacuum, another 20 mL portion of TFA/dichloromethane was added, and the reaction stirred for another hour. An off-white solid was obtained upon removal of the solvent under vacuum. The solid was dissolved in 20 mL of hot ethanol. This ethanol was removed in vacuo and the solid was recrystallized from 100 mL of hot ethanol, resulting in the formation (after drying under vacuum for 12 h) of 4.758 g (4.76 mmol, 91 % yield) of thin, white needles, m.p. 110-111°C; iHNMR (CDCI3/2O % TFA): 7.65 (br s, IH, NH), 4.72-4.68 (m, IH, α CH), 4.57-4.40 (m, 4H, CH2O), 3.35-3.11 (m, 2H, α CH2), 2.55-2.42 (m, 4H, CH2CF2); MS(FAB): calc'd for C26H14F37NO6 1026.0381, found 1026.037994.

(R)-2-(3,3,3-trifluoro-2-methoxy-2-phenyl-propionly)aspartic acid di(lH,lH,2H,2H- perfluorodecyl) ester (21). Compound 19 (0.0225 g, 0.019 mmol) and TEA (0.07 mL, 0.05 mmol) were combined in 10 mL of dry dichloromethane; R(-)-α-methoxy-α-trifluoro- methylphenyl acetic acid chloride (0.040 mL, 0.020) was added and the reaction was stirred for 4 h. The solution was diluted with 10 mL of dichloromethane and extracted with 1 % HCl (2 x 10 mL), water (2 x 10 mL) and brine (10 mL). The organic layer was dried over Na2SO4 and the solvent removed in vacuo. The solid was dissolved in a minimum amount of chloroform and placed on a silica column; the column was flushed with 100 mL of 1 :1 chloroform/freon. Removal of solvent resulted in the isolation of 20.0 mg (0.0163 mmol, 86 % yield) of 21. m.p. 101°C; iHNMR (CDCI3): 7.60 (d, 7= 8.1 Hz, IH, NH), 7.51 (br s, 2H, ArH), 738 (m, 3H, ArH), 4.91-4.88 (m, IH, αCH), 4.57-4.52 (m, IH, CH2O), 4.45-4.40 (m, IH, CH2O), 4.26-4.31

(m, IH, CH2O), 4.28-4.23 (m, IH, CH2O), 3.51 (s, 3H, OCH3), 3.06 (dd, 7- 4.85 Hz, ²7= - 17.5 Hz, IH, CH2), 2.87 (dd, 7= 4.85 Hz, ²7= -17.5 Hz, IH, αCH2), 2.51-233 (m, 4H, CH2CF2).

l,3,5- 's,c s-tri(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyl)cyclo-hexanetriamide (22).

Compound 22 was prepared analogously to 11 with compound 20 (5.43 g, 4.77 mmol), TEA (1.70 mL, 12.2 mmol), and cis.cis -cyclohexane triacid chloride (0.330 g, 1.54 mmol). After drying, 4.00 g (1.24 mmol, 88 % yield) of 22 were isolated, m.p. 285°C (decomp); iHNMR (CDCl3/5% TFA): 7.52 (d, 7= 6.9 Hz, 3H, NH), 5.01 (br s, 3H, αCH), 4.65-436 (m, 12H,

CH2O), 3.16 (dd, 7= 4.4 Hz, 27= -17.7 Hz, 3H, CHCH.2), 3.04 (dd, 7= 4.4 Hz, ²7= -17.7 Hz, 3H, CHCH_.2), 2.65-2.49 (m, 16H, CyH and CH2CF), 2.25 (d, 7= 11 Hz, 2H, CyH), 1.85-1.75 (m, 3H, CyH); MS(FD): 3237 (M+)

l,4-Bis[(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyI)carbony!amino) butane (23).

Compound 20 (0.200 g, 0.176 mmol), TEA (0.030 mL, 0.216 mmol) and 1 ,4-diisocyanatobutane (0.0106 mL, 0.084 mmol) were combined in 20 mL of dichloromethane and the solution was stirred for 12 h. The solution was filtered and the solid washed with 20 mL each of dichloromethane, 1 % HCl, water, and dichloromethane. After drying under vacuum for 12 h,

0.120 g (0.0548 mmol, 65 % yield) of a white powder were collected, m.p. 175°C; iHNMR (CDCl3/5% TFA): 4.87 (br s, 2H, αCH), 4.60-438 (m, 8H, CH2O), 3.24 (br s 2H, CH2 butyl),

3.02 (dd, 7= 4.8 Hz, ²J= -17.7 Hz, 2H, αCHCH.2), 3.02 (dd, 7= 4.4 Hz, ²J= -17.7 Hz, 2H, αCHCH2), 2.54-2.47 (m, 8H, CH2CF2), 1.62 (br s 2H, CH2 butyl); MS(FAB): 2191 (M+H)+.

l,6-Bis[(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyl)carbonylamino) hexane (24).

Compound 24 was prepared analogously to 23 using compound 20 (3.00 g, 2.66 mmol), TEA (0.500 mL, 3.60 mmol), and 1 ,8-diisocyanatohexane (0.200 mL, 1.28 mmol); 2.01 (0.905 mmol, 69 % yield) of 31 were isolated, m.p. 148 C^HNMR (CDCl3/5% TFA): 4.85 (br s, 2H, αCH), 4.61-432 (m, 8H, CH2O), 3J1-2.93 (m, 8H, αCHCH.2 and CH2 hexyl), 2.54-2.41 (m, 8H, CH2CF2), 1.56 (br s, 4H, CH2 hexyl), 1.36 (br s, 4H, CH2 hexyl); MS(FD): 2219 (M+H)+.

l,8-Bis[(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyl)carbonyIamino) octane (25).

Compound 25 was prepared analogously to 23 using compound 20 (0.500 g, 0.439 mmol), TEA (0J75 mL, 1.26 mmol), and 1,8-diisocyanatooctane (0.039 mL, 0J99 mmol); 0.330 (0J47 mmol, 74 % yield) of 25 were isolated.m.p. 136°C; iHNMR (CDCl3/5% TFA): 4.84 (br s, 2H, αCH), 4.66-4.32 (m, 8H, CH2O), 3 J 7-2.96 (m, 8H, αCHCH.2 and CH2 octyl), 2.53-2.44 (m, 8H, CH2CF2), 1.56 (br s, 4H, CH2 octyl), 136 (br s, 4H, CH2 octyl); MS(FD): 2246 (M+)

l,12-Bis[(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyI)carbonyl amino) dodecane (26).

Compound 26 was prepared analogously to 23 using compound 20 (0.500 g, 0.439 mmol), TEA (0J50 mL, 1.08 mmol), and 11,12-diisocyanatododecane (0.054 mL, 0J99 mmol); 0368 (0J47 mmol, 74 % yield) of 26 were isolated.m.p. 136 C ; iHNMR (CDCl3/5% TFA): 4.83 (br s, 2H, C H), 4.61-438 (m, 8H, CH2O), 3J6-2.94 (m, 6H, CH®2 and CH2 dodecyl), 2.97 (dd, 7= 4.5 Hz, ²7= -17.6 Hz, 2H, CH U2), 2.53-2.45 (m, 8H, CH2CF2), 1.54 (br s, 4H, CH2 dodecyl), 1.29-1.21 (m 16H, CH2 dodecyl); MS(FD): 2303 (M+).

1 ,3-Bis [(di-1 H,lH,2H,2H-perfluorodecyl-L-aspartyI)carbonyl-aminomethyl) benzene (27). Compound 27 was prepared analogously to 23 using compound 20 (1.00 g, 0.878 mmol), TEA (0J50 mL, 1.08 mmol), and l,3-bis(isocyanatomethyl)benzene (0.065 mL, 0.418 mmol); 0.767g

(0.333 mmol, 79 % yield) of 27 were isolated.m.p. 143°C; iHNMR (CDCl3/5% TFA): 7.36 (t, 7 = 6.2 Hz, IH, ArH), 7.2-7.21 (m, 3H, ArH), 4.87 (br s, 2H, αCH), 4.56-433 (m, 12H, CH2O and

ArCH2), 3.11 (dd, J= 43 Hz, ²7= -17.5 Hz, 2H, αCHCH.2), 2.97 (dd, J= 4.4 Hz, ²7=-17.5 Hz, 2H, CHCH2), 2.50-2.41 (m, 8H, CH2CF2); MS(FD): 2238.62(M+)

l,3-Bis[(di-lH,lH,2H,2H-perfluorodecyI-L-aspartyl)carbonyl-aminomethyl) cyclohexane

(28). Compound 28 was prepared analogously to 23 using compound 20 (1.00 g, 0.878 mmol), TEA (0J30 mL, 0.936 mmol), and l,3-bis(isocyanatomethyl)cyclohexane (0.073 mL, 0334 mmol); 0.742 g (0.331 mmol, 96 % yield) of 28 were isolated.m.p. 159-160°C; iHNMR (CDCl3/5% TFA): 4.85 (br s, 2H, αCH), 4.56-433 (m, 8H, CH2O), 3 J 8-2.93 (m, 4H, αCHCH2), 2.52-239- (m, 8H, CH.2CF2), 1.83-1.73 (m, 4H, CyH), 1.52-1.47(m, 2H.CyH), 0.92- 0.86 (m, 2H, CyH); MS(FD): 2245 (M+).

l,4-Bis[(di-lH,lH,2H,2H-perfluorodecyl-L-aspartyl)carbonyl-amino) benzene (29).

Compound 29 was prepared analogously to 23 using compound 20 (1.50 g, 1.32 mmol), TEA (0.380 mL, 2.74 mmol), and 1,4-phenylene diisocyanate (0.0945 g, 0.591 mmol); 130g (0.587 mmol, 94 % yield) of 29 were isolated.m.p. 233-235°C; iHNMR (CDCl3/5% TFA): 7.27 (s, 4H, ArH), 4.85 (br s, 2H, αCH), 4.57-433 (m, 12H, CH.2O and ArCH2), 3J2 (dd, 7= 4.4 Hz, ²7= - 17.6 Hz, 2H, αCHCH.2), 2.97 (dd, 7= 4.5 Hz, ²7= -17.6 Hz, 2H, αCHCH.2), 2.48-2.40- (m, 8H, CH2CF2); MS(FD): 2211(M+).

N,N'- »-xylylene-bis-carbamic acid di-4-nitrophenyl ester (30). To a well stirring suspention of 2.5 g NaHCO3 (29.4 mmol) in dry acetonitrile was added 4.44 g 4-nitrophenylchloroformate (21.9 mmol) and a freshly filtered solution of 1.10 g 1,4-xylylenediamine (735 mmol) in 20 mL of acetonitrile. The mixture was stirred for 2 h then filtered. The solid was washed with 1% HCl until foaming ceased then 100 mL of water and 100 mL of acetonitrile, and 50 mL of ether. The compound was dried on filter paper then dried in vaccuo at 1 torr for 12 h, resulting in the collection of 2.20 g (4.71 mmol, 40% yield), mp. 208-210°C; iHNMR (DMSO-d6): 8.60 (t, 7= 6.3, 2H, NH), 8.25 (d, 7= 9.1 2H ArH), 7.42 (d, 7= 9J 2H, ArH), 7.32 (s, 4H, ArH), 430 (d, 7= 63, 4H, ArCH2); ¹³CNMR (DMSO-d6): 156.2, 153.4, 144.2, 138.7, 127.3, 125.1, 122.5, 43.83.

l,4-Bis[(di-lH,lH,2H,2H-perfluorodecyI-L-aspartyI)carbonyl-aminomethyI) benzene (31).

TEA 0.612 mL (4.40 mmol) and 20 (3.00g, 2.64 mmol) were placed in 100 mL of dichloromethane and a solution of 30 (0.484 g, 2.20 mmol) and TEA (0.612 mL) in 20 mL of dry acetonitrile was prepared. The later solution was added dropwise to the first solution in 10 min. The reaction mixture was stirred for 6 h then the solvent removed in vacuo. The solid was partially dissolved in 20 mL of dichloromethane and the suspension was filtered then washed with 50 mL of dichloromethane, copious amounts of IM NaHC water, and ether. After drying in vacuo (1 torr, 12h) 3.00 g (1.33 mmol) of 31 was isolated, mp. 147-148°C; iHNMR (CDCl3/5% TFA): 7.24 (s, 4H, ArH), 4.88 (br s, 2H, αCH), 4.56-435 (m, 12H, CH2O and

ArCH2), 3.11 (dd, 7= 4.4 Hz, ²7= -17.6 Hz, 2H, αCHCH.2), 2.97 (dd, 7= 4.5 Hz, ²7= -17.6 Hz, 2H, αCHCH2), 2.52-2.43- (m, 8H, CH2CF2); MS(FAB): 2239 (M+H).

In summary, we have generated both monomeric and polymeric entities that exhibit multi-point hydrogen bonding or other association in solution to form large aggregates. These supramolecular structures become freestanding microcellular foams composed of interlocking microfibers when the CO₂ is removed, and exhibit over 95% density reduction and cells smaller thanlO microns.

Accordingly the invention advantageously relates to monomers and polymers which are"CO2- philic" and have the ability to associate in solution such that they are able to enhance the viscosity of CO2 by several orders of magnitude at relatively low concentration, and promote formation of low bulk density, microcellular materials. Thus, this invention overcomes the technical hurdles to use of CO2 in EOR or in organic aerogel formation.

In addition to their use as fracturing fluids in the tertiary recovery of petroleum from aging fields, the CO₂ gels are may be used as solvents for paints and oils, in the extraction of sludge oil from the bottom of oil wells, and in CO₂ based coating processes. The foams may be used as insulating materials and fillers.

References

The following references are cited in the specification. These and the other references discussed are incoφorated in the application.

1. J.M. DeSimone, Z. Guan, CS. Elsbernd, Science, 257, 945 (1992); C. Lepilleur, E.J. Beckman, Macromolecules 30, 745 (1997); O'Neill, M .; Yates, M.Z.; Harrison, K.L.; Johnston, K.P.; Canelas, D.A.; Betts, D.E.; DeSimone, J.M.; Wilkinson, S.P.; Macromolecules 30, 5050 (1997)

2. P.G. Jessop, T. D ariya, R. Noyori, Chem. Rev. 99, 475 (1999); D. Hancu, E.J. Beckman, indusfr. Eng. Chem. Res. 38, 2824 (1999); D. Hancu, E.J. Beckman, Indusfr. Eng. Chem. Res. (1999), 38, 2833

3. A.J. Mesiano, E.J. Beckman, A.J. Russell, Chem. Rev. (1999), 99 623

4. M. Super, E.J. Beckman, Trends in Polym. Sci. 5, 236 (1997); D.J. Darensbourg, M.W. Holtcamp, Coord. Chem. Rev. 153, 155 (1996)

5. Fulton, J.L.; Pfund, D.M.; McClain, J.B.; Romack, T.J.; Maury, E.E.; Combes, J.R.; Samulski, E.T.; DeSimone, J.M.; Capel, M.; Langmuir 11, 4241 (1995)

6. D. Klempner, K.C. Frisch, "Polymeric Foams" Carl Hanser Verlag, New York (1991)

7. S.K. Goel, E.J. Beckman, Polym. Eng. Sci., 14, 1137 (1994); S.K. Goel, E.J. Beckman, Polym. Eng. Sci., J4, 1148 (1994)

8. K. Hanabusa, K Okui, K. Karaki, T. Koyama, H. Shirai, J. Chem Soc. Chem. Comm. 1371 (1992); T. Gulik-Kryzwicki, C. Fouquey, J. Lehn, Proc. Nat. Acad. Sci. USA 163 (1993)

9. Vanhoorne, P.; Jerome, R.; Macromolecules 28, 5664 (1995); Pitsikalis, M.; Hadjichristidis, N.; Mays, J.W.; Macromolecules 29, 179 (1996)

10. The bis urea gelling agents were prepared by esterification of N-Boc-aspartic acid in dichloromethane with EDCI, DMAP and lH,lH,2H,2H-perfluorodecanol followed by deprotection with 50% TFA/CHC and reaction with the appropriate mono or bis- isocyanates in CHC with excess triethylamine. The resultant bisureas were filtered off and washed with CHC, 1% aqueous HCl, water and more CHC. All compounds gave spectroscopic characteristics consistent with their structure and were shown to be >95% pure.

11. Foam samples were fractured, sputter-coated with gold, then analyzed by SEM as described in K. Parks, E.J. Beckman, Polym. Eng. Sci. (1996), 36, 2417

12. F.I. Stalkup, "Miscible Displacement", SPE Monograph No 8., New York, NY (1983)

13. D.K. Dandge, J. heller, C. Lien, K.J. Wilson; J. Appi. Polym. Sci. (1986), 32, 5373 14. P. Gullapalli, J-S. Tsau, J.P. Heller, SPE Int. Symp. On Oilfield Chem., paper SPE 28979, Houston, TX, Feb., 1995

15. R.M. Enick, A. Iezzi, P. bendale, J. Brady, Fluid Ph. Equil. (1989), 53, Part II, 307; CA. Irani, T.V. Harris, W.R. Pretzer, U.S. patents 4,945,990 (1990); also U.S. patent 4.945,989 (1990)

16. D Reichle, et al., "Carbon Sequestration, State of the Science, a working paper for roadmapping future carbon seuqestration R&D", U.S. Dept. of Energy, Office of Sciemce, Office of Fossil Energy, February, 1999.

17. Murata, K.; Aoki, M.; Suzuki, T.; Harada, T.; Kawabata, H.; Komori, T.; Ohseto, F.; Ueda, K.; Shinkai, S.7. Am. Chem. Soc. 1994, 116, 6664-6676.

18. Aoki, M.; Nakashima, K.; Kawabata, H.; Tsutsui, S.; Shinkai, S. 7. Chem. Soc. Perkin Trans. 2 1993, 347-354.

19. Hanabusa, K.; Okui, K.; Karaki, k.; Koyama, T.; Shirai, H. 7 Chem. Soc. Chem. Comm. 1992, 1371-1372.

20. Fang, E.; Yang, J.; Geib, S. J.; Stoner, T.; Hopkins, M.; Hamilton, A. D.7. Chem. Soc. Chem. Commun. 1995, 1251-1252.

21. deLoos, M.; vanEsch, J.; Stokroos, I.; Kellogg, R. M.; Feringa, B. L. 7 Am. Chem. Soc. 1997, 119, 12675-12676.

22. Husing, N.; Schubert, U. Angew. Chem. Int. Ed. Engl. 1998, 37, 22-45.

23. Takahashi, A.; Sakai, A.; Kato, M. Polym. J. 1980, 12, 335-338.

24. Keller, A. Faraday Discuss. 1995, 101, 1-49.

25. Eldridge, J. E.; Ferry, J. D.7 Phys. Chem. 1954, 58, 992-995.

26. DeSimone, J. M.; Guan, Z.; C S, E. Science 1992, 257, 945-948.

27. Hyatt, J. A. 7 Org. Chem. 1984, 49, 5097-5101.

28. Wai, C M. Anal. Chem. 1995, 67, 919-923.

29. Hoefling, T. A.; Beitle, R. R.; Enick, R. M.; Beckman, E. J. Fluid Phase Equilib. 1993, 83, 203-12.

30. Curran, D. P. Angew. Chem. Int. Ed. Engl. 1998, 37, 1175-1196.

31. Fulton, J. L.; Pfund, D. M.; McClain, J. B.; Romack, T. J.; Maury, E. E.; Combes, J. R.; Samulski, E. T.; DeSimone, J. M.; Capel, M. Langmuir 1995, 11, 4241-4249.

32. Canelas, D. A.; DeSimone, J. M. Adv. Poly. Sci. 1997, 133, 105-140.

33. Harrison, K.; Goveas, J.; Johnson, K. P.; O'Rear, E. A. Langmuir 1994, 10, 3536-3542.

34. Johnson, J. D.; Diep, P.; Jordan, K. D.; Beckman, E. J. Abstracts of Papers, ASC 1998, 215, 183.

35. Clarke, M. J.; Harrison, K. L.; Johnson, K. P.; Howdle, S. M. 7. Am. Chem. Soc. 1997, 119, 6399-6406.

36. Garcia, T. F.; Albert, J.; Hamilton, A. D.7. Chem. Soc, Chem. Commun. 1991, 1761-1762.

37. Andreetti, G. D.; Ori, O.; Ugozzoli, F.; Alfieri, C; Pochini, A.; Ungaro, R. 7 Inclusion Phenomen. 1988, 6, 523.

38. Bollaert, V.; DeSchryver, F. C; Tackx, P.; Persoons, A.; Nusselder, J. 7. Adv. Mater 1993, 5, 268-273.

39. Dhaon, M. K.; Olsen, R. K.; Ramasamy, K. 7 Org. Chem. 1982, 47, 1962-1965.

40. Choy, N.; Moon, K. Y.; Park, C; Son, Y. C; Jung, W. H.; Choi, H.-i.; Lee, C S.; Kim, C. R.; Kim, S. C; Yoon, H. Org. Prep. Proc. Int. 1996, 28, 173-177.

41. Beckman, E. J., Personal Communication. 2. McDonald, D. Q.; Still, W. C. Tet. Lett. 1992, 33, 7743-7751.

Claims

The claimed invention is:

1. A method of making a microcellular foam comprising the steps of:

2. combining a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution with supercritical CO₂ to form a solution;

3. aggregating the compound to form a supramolecular network in solution; and removing the CO₂ under conditions sufficient to form a microcellular foam.

4. The method of claim 1, wherein the combining step (a) comprises combining the compound and the supercritical CO₂ and then heating the combination to dissolve the compound in the supercritical CO₂.

5. The method of claim 2, wherein the aggregating step (b) comprises lowering the pressure, lowering the temperature or lowering the pressure and temperature of the solution.

6. The method of claim 1, wherein the aggregating step comprises allowing the solution to stand for a time sufficient for the compound to aggregate and form a supramolecular network in solution.

7. The method of claim 1, wherein the removal step (c) comprises venting the CO₂ under conditions sufficient to maintain the supramolecular network.

8. The method of claim 1, wherein the aggregating functional group is a hydrogen-bonding functional group.

9. The method of claim 1, wherein the CO -philic functional group is a fluorinated functional group, a siloxane functional group or an alkylene oxide functional group.

10. The method of claim 6, wherein the aggregating functional group is selected from the group consisting of an amide functional group, a urea functional group, a ureidopyrimidone functional group, a carboxylic acid functional group, a carbamate functional group, a sulfonamide functional group, a thiourea functional group, ureidopyridine functional group, a guanidinium/carboxylate functional group, and an amino-pyridine/carboxylic acid functional group.

11. The method of claim 7, wherein the compound contains one or two urea or urethane groups and an aspartate residue.

12. The method of claim 7, wherein the CO₂-philic functional group is a fluoroalkyl, or a fluoroether functional group.

13. The method of claim 1, wherein the aggregating functional group is a hydrogen-bonding functional group and the CO₂-philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate, alkylene oxide or siloxane functional group.

14. The method of claim 10, wherein the compound is a fluorinated aspartate bisurea, a fluorinated aspartate urea, or a fluorinated bisurethane.

15. The method of claim 10, wherein the compound is a fluorinated bisurethane.

16. The method of claim 1, wherein the compound is a polymer prepared by copolymerizing a vinyl monomer having a CO₂-philic group, an aggregating comonomer, and a vinyl comonomer.

17. The method of claim 1, wherein the compound is a copolymer of 1H,1H,2H,2H perfluorodecyl (meth)acrylate and a comonomer having an aggregating functional group which enables the copolymer to form a supramolecular network in solution.

18. The method of claim 1, wherein the compound is present in an amount of 5 weight % or less.

19. A microcellular foam comprising a supramolecular network of compounds having a CO₂- philic functional group and an aggregating functional group wherein the foam has a bulk density which is 90% less than the compound which forms a supramolecular network in solution and a submicron pore size of less than 10 micron made by the method of claim 1.

20. A microcellular foam comprising a supramolecular network of compounds having a CO₂- philic functional group and an aggregating functional group, wherein the supramolecular network is bound together through said aggregating functional group.

21. A microcellular foam of claim 17, wherein the supramolecular network is bound together by hydrogen bonding, dipole interactions, electrostatic interactions or van der Waals forces.

22. The microcellular foam of claim 17, wherein the aggregating functional group is selected from the group consisting of an amide functional group, a urea functional group, a ureidopyrimidone functional group, a carboxylic acid functional group, a carbamate functional group, a sulfonamide functional group, a thiourea functional group, ureidopyridine functional group, a guanidinium/carboxylate functional group, and an amino- pyridine/carboxylic acid functional group.

23. The microcellular foam of claim 17, wherein the CO₂-philic functional group is selected from the group consisting of a fluorinated functional group and a siloxane functional group.

24. The microcellular foam of claim 17, wherein the compound contains one or two urea groups and an aspartate residue.

25. The microcellular foam of claim 17, wherein the CO₂-philic functional group is selected from the group consisting of a fluoroalkyl group and a fluoroether group.

26. The microcellular foam of claim 17, wherein the aggregating functional group is a hydrogen- bonding functional group and the CO₂-philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate, or siloxane functional group.

27. The microcellular foam of claim 17, wherein the compound is a fluorinated aspartate bisurea, a fluorinated aspartate urea, or a fluorinated bisurethane.

28. The microcellular foam of claim 17, wherein the compound is a polymer prepared by copolymerizing a vinyl monomer having a CO₂-philic group, an aggregating comonomer, and a vinyl comonomer.

29. The microcellular foam of claim 17, which has a pore size of less than 1 micron.

30. The microcellular foam of claim 24, which has a pore size of less than 1 micron.

31. A method for increasing the viscosity of supercritical CO₂ comprising:

32. combining a compound having a CO₂-philic functional group and an aggregating functional group which enables the compound to form a supramolecular network in solution, with supercritical CO₂ to form a solution; and

33. aggregating the compound to form a supramolecular network in solution; wherein the viscosity of the supercritical CO₂ with the supramolecular network is greater than that of the starting supercritical CO₂.

34. The method of claim 29, wherein the viscosity is sufficiently increased such that the supercritical CO₂ with the supramolecular network is a gel.

35. The method of claim 29, wherein the aggregating functional group is a hydrogen-bonding functional group.

36. The method of claim 31, wherein the hydrogen-bonding functional group is selected from the group consisting of an amide functional group, a urea functional group, a ureidopyrimidone functional group, a carboxylic acid functional group, a carbamate functional group, a sulfonamide functional group, a thiourea functional group, ureidopyridine functional group, a guanidinium carboxylate functional group, and an amino-pyridine/carboxylic acid functional group.

37. The method of claim 29, wherein the compound contains one or two urea groups and an aspartate residue.

38. The method of claim 29, wherein the CO₂-philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate, or siloxane functional group.

39. The method of claim 29, wherein the aggregating functional group is a hydrogen-bonding functional group and the CO -philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate, or siloxane functional group.

40. The method of claim 29, wherein the compound is a fluorinated aspartate bisurea, a fluorinated aspartate urea, or a fluorinated bisurethane.

41. The method of claim 29, wherein the compound is polymer prepared by copolymerizing a vinyl monomer having a CO₂-philic group, an aggregating comonomer, and a vinyl comonomer.

42. The method of claim 29, wherein the compound is present in an amount of 0J-6 weight %.

43. A supercritical CO₂ composition comprising supercritical CO₂ and a supramolecular network of compounds having a CO₂-philic functional group and an aggregating functional group, wherein the supramolecular network is bound together through said aggregating functional group.

44. The supercritical CO₂ composition of claim 39, wherein the aggregating functional group is selected from the group consisting of an amide functional group, a urea functional group, a ureidopyrimidone functional group, a carboxylic acid functional group, a carbamate functional group, a sulfonamide functional group, a thiourea functional group, ureidopyridine functional group, a guanidinium/carboxylate functional group, and an amino- pyridine/carboxylic acid functional group.

45. The supercritical CO₂ composition of claim 39, wherein the compound contains one or two urea groups and an aspartate residue.

46. The supercritical CO₂ composition of claim 39, wherein the CO₂-philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate or siloxane functional group.

47. The supercritical CO composition of claim 39, wherein the aggregating functional group is a hydrogen-bonding functional group and the CO₂-philic functional group is a fluoroalkyl, fluoroether, fluoroacrylate or siloxane functional group.

48. The supercritical CO₂ composition of claim 39, wherein the compound is a fluorinated aspartate bisurea, a fluorinated aspartate urea, or a fluorinated bisurethane.

49. The supercritical CO₂ composition of claim 39, wherein the compound is a polymer prepared by copolymerizing a vinyl monomer having a CO₂-philic group, an aggregating comonomer, and a vinyl comonomer.

50. The supercritical CO₂ composition of claim 39, wherein the supercritical CO₂ composition is a gel.

51. The supercritical CO₂ composition of claim 41, wherein the supercritical CO₂ composition is a gel.

52. The supercritical CO₂ composition of claim 43, wherein the supercritical CO₂ composition is a gel.

53. The supercritical CO₂ composition of claim 45, wherein the supercritical CO₂ composition is a gel.

54. A method for increasing the viscosity of a halogenated solvent, comprising: (a) combining a compound having a CO₂ -philic functional group and an aggregating functional group with a halogenated solvent to form a solution; and (b) aggregating the compound in solution to form a supramolecular network, wherein the halogenated solvent containing the supramolecular network exhibits an increased viscosity over that of the halogenated solven alone.

55. A method for fracturing subterranean formations penetrated by a well bore comprising: (a) introducing supercritical CO containing a supramolecular network of compounds having a CO₂ -philic functional group and an aggregating functional group into the well bore at a pressure and rate of flow sufficient to fracture a subterranean formation, and (b) fracturing the subterranean formation.