BACKGROUND INFORMATION This invention relates to a process of making (thio)urethanes under superatmospheric conditions. An isocyanate group-containing compound and a compound that includes a hydroxyl or thiol group are combined in a fluid under superatmospheric pressure and allowed to react.

Over the past two to three decades, interest in supercritical fluids (SCFs) as reaction solvents has grown due to a variety of factors including their low cost and their environmental friendliness. Carbon dioxide (CO ) has been of special interest.

Much ofthe work relating to reactions in SCFs has involved addition reactions where at least one ofthe reactants is unsaturated. See, e.g., U.S. Patent No. 3,522,228; DeSimone et al., Science, 257, 945-47 (1992); and Kumar et al., Poly. Preprints, 27(2), 224 (1986) and 28(2), 286 (1987).

Some condensation reactions in SCFs have been described previously, but most have involved biochemical systems such as enzymatic ester synthesis (e.g., Ikushima et al., Chem. Letters, 109-12 (1993)) or peptide synthesis (e.g., U.S. Patent Nos. 5,241,048 and 5,001,224). Non-biochemical esterification of oleic acid using a significant excess of methanol has been described by Vieville et al., Ind. Eng. Chem. Res., 32, 2065-68 (1993). Conversely, supercritical CO ₂ has been described as an inhibitor to the reaction of isocyanates with hydroxyl group- containing compounds (e.g., European Patent document 0 506 041 A2). Reactions involving isocyanates have been of significant industrial importance over the past several decades. Urethanes often are made by reacting an isocyanate with an alcohol. These reactions are properly classified as condensation reactions even though no small molecule is created as a byproduct. Polymerization reactions involving polyisocyanates and polyols are known to proceed by a step-growth polymerization mechanism.

Most urethane syntheses require a catalyst. Catalysts typically add to the cost of a product in which they are used. A reaction medium that acts as a

catalyst or in which reactions proceed at a faster rate than in typical organic solvents would be advantageous.

Many urethane syntheses require an inert organic solvent as a reaction medium. The use of organic solvents, also known as volatile organic compounds (VOCs), has come under increased scrutiny because ofthe potential hazards they pose to human health and the environment. The need for a non- VOC reaction medium for urethane and polyurethane syntheses is becoming increasingly apparent.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a process for making a (thio)urethane that includes the steps of (a) introducing into a pressure vessel a mixture including (1) a fluid which is a gas at standard temperature and pressure (STP) but which is held at a pressure greater than atmospheric pressure such that it is a liquid or a SCF and (2) a compound that includes an isocyanate group, and (3) a compound including a hydroxyl or thiol group, then (b) allowing the compounds to react to form a (thio)urethane. At least one ofthe compounds is at least partially soluble in the fluid; more preferably both ofthe compounds are at least partially soluble in the fluid. In another aspect, the present invention provides a mixture including (1) the above-described fluid, (2) a compound comprising an isocyanate group, (3) a compound comprising a hydroxyl or thiol group, and (4) the reaction product of compounds (2) and (3). This mixture can be prepared according to the above- described process. Optionally, the mixture can include one or more cosolvents and/or a catalyst system.

Also described is the reaction product of (2) and (3) in the above- described fluid.

Unless a contrary intention is expressly indicated, the following definitions apply herein throughout:

"(thio)urethane" means either a urethane or a thiourethane; "group" or "compound" or "monomer" or "polymer" means a chemical species that can be substituted by conventional substituents that do not interfere with the desired product (e.g., alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.); and

"hydrofluorocarbon" means a gas ofthe general formula C,HbF _c (where b+c = 2a+2) that can be easily liquified under pressure. Many fluids that are gases at STP but that become a liquid or a SCF when subjected to a pressure greater than atmospheric pressure provide convenient and relatively clean solvents for organic reactions. By "clean" is meant that the solvent can be recycled or vented directly to the atmosphere. Of particular interest as an SCF is CO ₂ , which provides a non- VOC reaction medium and which, in certain instances, has been found to allow for reaction rates for

(thio)urethane condensation reactions that exceed reaction rates in currently used solvents.

Also, the products of reactions performed in such fluids can be separated and/or isolated in a relatively easy manner. Small molecule and polymeric urethanes and thiourethanes (i.e., (thio)urethanes) are widely used throughout various industries, especially in rubber, adhesive, and sealant formulations. Of particular interest are those (thio)urethanes in which a significant number of hydrogen atoms have been replaced by fluorine atoms. Such compounds can impart protection against water, soil, grease, oil and/or other stains.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The (thio)urethane synthesis ofthe present invention is carried out in fluids that are gases at STP but that become liquids or SCFs when subjected to superatmospheric pressure. Preferably, the reactions are carried out in an SCF. Any material that is a gas at STP but that can be transformed to a liquid or an SCF under increased (i.e., superatmospheric) pressure can be used as the

reaction fluid in the method ofthe present invention. The reaction fluid preferably is one that is not harmful to the environment and is non-toxic towards humans, animals, and plants when vented or released. Preferred fluids include CO ₂ , hydrofluorocarbons (HFCs), hydrofluorocarbon ethers such as 1,1,1,2,2-pentafluoroethyl methyl ether, and perfluorocarbons (e.g., perfluoropropane, perfluorocyclobutane) that are gases at STP, hydrocarbons that are gases at STP, polyatomic gases (e.g., SF ₆ , NH ₃ , N ₂ O, and CO), noble gases, and mixtures thereof. Most preferred reaction fluids include CO ₂ , HFCs, perfluorocarbons, and mixtures thereof. Examples of useful HFCs include those that are known to be good solvents for many small organic compounds, especially those HFCs that comprise from 1 to 5 carbon atoms. Specific examples include 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane, trifluoromethane, and 1,1,1,2,3,3,3-heptafluoropropane.

Reaction conditions can vary widely. Reaction temperatures can range from -78° to 250°C, preferably from 15° to 200°C. Pressures typically range from 0.1 to 690 MPa, preferably 0.1 to 400 MPa, more preferably 0.1 to 140 MPa, most preferably 0.8 to 100 MPa. Particular ranges within these broad ranges are effective for various reaction media and reactants. Varying temperature and/or pressure affects the reaction rate, and those skilled in the art can recognize how to optimize conditions for a given system.

Many ofthe above-described reaction conditions can be quite extreme. Therefore, the reaction is normally carried out in a high pressure reactor (although other devices can prove useful depending on a particular set of reaction conditions). Often used is a stainless steel reactor, which optionally can be equipped with high pressure (e.g. sapphire) windows for observation of cell contents and/or an additional pressure handling system for the addition of various materials under supercritical conditions. Such a reactor can be run in batch or continuous mode.

The reactor can be equipped with heating and/or cooling elements as well as some type of stirring apparatus. If desired, the reaction temperature can be monitored by a thermocouple type device that can be connected to a temperature

controller, which optionally can be microprocessor controlled. The reactor can also be fitted with a microprocessor process control unit. The reactor can be equipped with a venting mechanism to release pressure.

As mentioned previously, (thio)urethane synthesis involves one or more compounds that comprise at least one isocyanate group and one or more compounds that comprise at least one functional group that is coreactive with an isocyanate group, such as a hydroxyl or a thiol group. These reactants can be added in approximately stoichiometric amounts. For instance, where one mole of a triisocyanate is used, approximately three moles of a compound comprising a single hydroxyl group can be used to make a urethane. Alternatively, prepolymers that are, or that comprise, the reaction product of an isocyanate and a polyol or polythiol where either the isocyanate or the polyol/thiol is added in excess also can be prepared by the method ofthe present invention. (Thio)urethane prepolymer synthesis involving an excess of one ofthe two components is known in the relevant art and is not discussed in detail here.

The isocyanate and coreactant preferably are at least somewhat soluble in the fluid reaction medium; nevertheless, even if only one is somewhat soluble, the other can be essentially insoluble (although such insoluble materials are preferably ground into coarse granular form before being introduced into the pressure vessel). By "somewhat soluble" is meant that the reactant, if solid at STP, is at least swellable in the fluid. If both reactants are solids, at least one is preferably more than merely swellable, i.e., preferably at least 5 to 10% soluble in the fluid. Most preferably, both reactants are mostly or completely soluble in the fluid. Nevertheless, even slightly soluble reactants can be useful in the process ofthe present invention.

Isocyanates that can be used in the reaction ofthe present invention include mono- and polyisocyanates. Useful monoisocyanates include octadecyl isocyanate, butyl isocyanate, hexyl isocyanate, phenyl isocyanate, benzyl isocyanate, naphthyl isocyanate, and the like. Useful diisocyanates include 1,6- hexamethylene diisocyanate (HMDI), 1,4-tetramethylene diisocyanate, 2,4- and 2,6-toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI),

cyclohexane 1,3- and 1,4-diisocyanate, isophorone diisocyanate (IPDI), 1,5- and 1,4-naphthalene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and the like. Useful tri- and polyisocyanates include monomers such as 4,4',4"- triphenylmethane triisocyanate and the Desmodur™ series of polyisocyanates (Bayer Chemicals; Philadelphia, PA), as well as polymers such as Vornate™ M220 polymeric polyisocyanate (Dow Chemical Co.; Midland, MI), polymethylene poly(phenylisocyanate) (PMDI), as well as combinations ofthe foregoing. Those skilled in the art will readily recognize other useful compounds that comprise one or more isocyanate groups. Also included in the reaction mixture ofthe present invention is at least one compound that comprises an -OH or -SH functional group. The hydroxyl- or thiol-functional component can be present as a mixture or blend of materials which can include materials that contain mono- and polyhydroxyl (or mono- and polythiol) groups where the hydroxyl (or thiol) hydrogen is sterically and electronically available to the coreactive isocyanate.

Useful hydroxyl-functional materials include aliphatic, cycloaliphatic, or alkanol-substituted arene mono- or polyalcohols having from one to about 18 carbon atoms and one to five hydroxyl groups, preferably one to four hydroxyl groups, or combinations thereof. Useful monools include methanol, ethanol, 1- propanol, 2-propanol, 2-methyl-2-propanol, 1 -butanol, 2-butanol, 1-pentanol, neopentyl alcohol, 3-pentanol, 1-hexanol, 1-heptanol, 1-octanol, pentaerythritol, 2-phenoxyethanol, cyclopentanol, cyclohexanol, cyclohexylmethanol, 3- cyclohexyl-1 -propanol, 2-norbornanemethanol, and tetrahydrofurfuryl alcohol. This list is not meant to be exhaustive; rather, it is merely illustrative. Polyols useful in the present invention include aliphatic, cycloaliphatic, alkanol-substituted arene polyols, or combinations thereof having from about two to about 18 carbon atoms and two to five hydroxyl groups, preferably two to four hydroxyl groups. Examples of useful polyols include 1,2-ethanediol, 1,2- propanediol, 1,3 -propanediol, 1,4-butanediol, 1,3-butanediol, 2-methyl-l,3- propanediol, 2,2-dimethyl-l,3-propanediol, 2-ethyl-l,6-hexanediol, 1,5- pentanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, glycerol,

trimethylolpropane, 1,2,6-hexanetriol, trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerine, 2-ethyl-2-(hydroxymethyl)- 1 ,3-propanediol, 2-ethyl- 1 ,3-pentanediol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, and polyalkoxylated bisphenol A derivatives. Examples of other useful polyols are disclosed in U.S. Patent No. 4,503,211. This list also is not intended to be exhaustive.

Useful higher molecular weight polyols include the polyethylene and polypropylene oxide polymers having a number average molecular weight (M„) in the range of 200 to 20,000, such as the Carbowax™ polyethyleneoxide materials (Union Carbide Corp.; Danbury, CT); caprolactone polyols with a M _n in the range of 200 to 5,000, such as the Tone™ polyol materials (Union Carbide); polytetra- methylene ether glycol with a M„ in the range of 200 to 4,000, such as the Terathane™ materials (DuPont; Wilmington, DE); hydroxyl-terminated polybutadiene resins, such as the Poly bd™ materials (Elf Atochem; Philadelphia, PA); phenoxy resins, such as those commercially available from Phenoxy Associates (Rock Hill, SC); poly(vinyl alcohol) or copolymers thereof (e.g., copolymers of vinyl alcohol and either vinyl acetate or ethylene), or similar materials supplied by other manufacturers.

Useful thiols include aliphatic, aromatic, and alicyclic thiols where the thiol hydrogen is sterically and electronically available. Included are polymeric or oligomeric polythiols reported as useful in the cure of epoxy resins, such as Capcure™ 3-800 (Henkel Corp.; LaGrange, IL), and the polysulfide polyols commercially available as LP-3™, LP-8™, LP-12™, etc. (Morton International, Inc.; Chicago, IL). Also useful are ethylene bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), and pentaerythritol tetra(3- mercaptoproprionate) (Evans Chemetics; Lexington, MA). Again, this list is not meant to be exhaustive.

Fluorinated urethanes have been shown to be useful as stain or moisture repellents. Such materials can be prepared by reacting a fluorinated alcohol with an isocyanate. Fluorinated alcohols useful in the present invention are

(1) those having the general formula Rf(CH ₂ ) _n CH ₂ OH wherein n is a whole number from 0 to about 20 (inclusive), preferably from 0 to about 12 (inclusive), more preferably from zero to four (inclusive), most preferably zero or one, (2) those having the general formula (CF ₂ ) _m (CH ₂ OH) ₂ where m is an integer from 1 to 20 inclusive, preferably 1 to 12 inclusive, more preferably 2 to 4 inclusive,

(3) those having the general formula wherein R ¹ is a monovalent, straight chain or branched alkyl, cycloalkyl, or aryl radical comprising from 1 to about 12 carbon atoms, preferably from 1 to about 8 carbon atoms, more preferably from one to four carbon atoms, and

(4) those having the general formula R _f SO ₂ N(C ₂ H ₄ OH) ₂ , in which Rf is a monovalent, fluorinated, saturated aliphatic radical comprising from 1 to about 20 carbon atoms, preferably one to twelve carbon atoms, more preferably from three to twelve carbon atoms, most preferably about eight carbon atoms. The aliphatic radical can be straight, branched, or cyclic. Heteroatoms (or radicals), such as divalent oxygen, trivalent nitrogen, and hexavalent sulfur can interrupt the alkyl chain. Preferably, where heteroatoms are present, the aliphatic radical contains at least two carbon atoms for each heteroatom. Non-skeletal valence bonds ofthe aliphatic radical are preferably carbon-to-fluorine bonds, i.e., the radical is preferably perfluorinated. Where Rf contains a cyclic structure, such structure preferably has 5 or 6 ring atoms, one or two of which can be heteroatoms. Preferably, R is free of ethylenic or other carbon-carbon unsaturation, i.e., R _f is a saturated aliphatic, cycloaliphatic or heterocyclic radical. Examples of R _f radicals are fluorinated alkyl (e.g., — CF ₃ ) and alkyloxyalkyl (e.g. , — CF ₂ OCF ₃ ). R _f preferably is a perfluorinated, straight-chain aliphatic radical consisting only of carbon and fluorine atoms.

Examples of preferred fluorinated alcohols useful in the preparation of fluorinated urethanes include 1,1-dihydroperfluorooctanol, 1,1,2,2-tetrahydro- perfluorooctanol, 1,1,2,2,3,3-hexahydroperfluorodecanol, 2-N-ethyl perfluoro- octanesulfonamido ethanol (EtFOSE), 2-N-methyl perfluorooctanesulfonamido

ethanol (MeFOSE), 2-N-ethyl perfluorobutanesulfonamido ethanol, 2-N-methyl perfluorobutanesulfonamido ethanol, 2-N-n-propyl perfluorodecanesulfonamido ethanol, N-ethyl-N-(2-hydroxyethyl) perfluoroheptanamide, Zonyl BA™ fluorochemical telomer alcohol (DuPont Chemicals; Wilmington, DE), and the like. With the possible exception of MeFOSE, which can be made according to the process described in U.S. Patent No. 3,734,962, such fluoroalcohols are available from a variety of manufacturers and retailers (e.g., PCR Inc.; Gainesville, FL). Useful fluorinated polyols include N,N-bis(2-hydroxyethyl) perfluorooctane- sulfonamide (FOSEE diol) as well as linear and branched fluorinated polyether polyols such as, for example, the Fomblin-Z-Dol™ and Fluorolink™ series of polyols (Ausimont; Morristown, NJ). ϊ desireci, fluorinated urethanes can also be made by reacting a fluorinated isocyanate witn a hydrocarbon alcohol. Additionally, a highly fluorinated urethane can be iade by reacting a fluorinated isocyanate with a fluorinated alcohol. Regardless of identity, the coreactive compounds preferably are added to the pressure vessel prior to introduction ofthe fluid. This simplifies the type of equipment needed as well as the number and type of preparation steps.

A catalyst or catalyst system can optionally be included in the reaction mixture. The identity and amount ofthe catalyst used depends on the particular reactants in a given reaction (i.e., whether an alcohol or thiol is being reacted with the isocyanate). Typical catalysts include tin-containing compounds such as dibutyltin dilaurate and stannous octoate. Surprisingly, however, certain condensation reactions that normally require catalysts when performed in typical organic solvents can be performed according to the process ofthe present invention in the absence of a catalyst. Whether or not the solvating fluid is in some way activating or complexing one or both ofthe reactants is unknown. Increased pressure can also affect the reaction rate.

If desired, a cosolvent can also be included in the reaction mixture to aid in the solubilization of one or more components in the initial reaction mixture. Any common solvent that is soluble in the reaction mixture can act as a cosolvent in the method ofthe present invention. Typical examples include tetrahydrofuran,

liquid alkanes (or a mixture of liquid alkanes), toluene, ketones (e.g., acetone or 3- pentanone), and esters (e.g., ethyl acetate). When a cosolvent is used, it preferably is present in an amount less than about 20% (by vol.), preferably less than 10% (by vol.), ofthe total reaction mixture. The product ofthe process ofthe present invention need not be soluble in the solvating fluid. In other words, the product can precipitate out ofthe reaction mixture.

The product can be a simple condensation product (i.e., the combination of just two reactants), an oligomer (i.e., a lower molecular weight combination of an isocyanate and a coreactant that includes just a few reaction units), or a polymer (i.e., the higher molecular weight combination of a polyisocyanate and a compound with more than one coreactive functional group).

Once the condensation reaction is complete (or has proceeded to the desired level of completion), the (thio)urethane product can be collected by cooling and venting the reaction vessel. Where reactants also remain, the product can be isolated by standard purification techniques known in the art. Where desired, the product can be used as is or can be further reacted or processed. Urethanes and thiourethanes are useful in rubber products and plastics including flexible and rigid foam products, elastomers, coatings, and adhesives. Fluorourethanes prepared by the method ofthe invention are useful as low surface energy coatings and materials (e.g., release agents) and as protective agents against water, soil, grease, oil and/or stains for textiles such as wearing apparel, upholstery, draperies and carpeting, as well as leather goods, wool and other natural materials. They can be applied by methods known in the art, including solvent- and emulsion-based application systems.

Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

EXAMPLES

Unless indicated to the contrary, all reagents, solvents, catalysts, etc., used in the following examples are commercially available from Aldrich Chemical Co. (Milwaukee, WI). Example 1

In a 10 mL high pressure reactor cell that had been purged with nitrogen for five minutes, 1.198 g EtFOSE (prepared according to the teaching of U.S. Patent No. 3,734,962) was mixed with one drop of dibutyltin dilaurate. To this was added, via syringe through a ball valve, 0.15 mL TDI. The cell was then filled with liquid CO ₂ , heated to 72°C, and pressurized to approximately 32.3 x 10 ⁶ Pa. These conditions were maintained for 20 hours.

A yellow transparent solution was observed throughout the reaction period. On cooling and depressurizing the cell, 1.09 g of a foamed yellow solid was obtained. Proton and ¹³ C nuclear magnetic resonance spectroscopy were used to confirm the structure ofthe urethane and the absence of residual TDI. Fourier transform infrared (FT-LR) spectroscopy showed the disappearance of signals due to isocyanate and alcohol absoφtions and the formation of a urethane.

Example 2 In a 10 mL high pressure cell were added .07 g n-octyl alcohol, 0.93 g

IPDI (Hϋls America, Inc.; Piscataway, NJ), and one drop of stannous octoate (ICN Biomedicals, Inc.; Cleveland, OH). The cell was purged with nitrogen for five minutes before being filled with liquid CO ₂ , heated to 70°C, and pressurized to approximately 32.3 x 10 ⁶ Pa. These conditions were maintained for 17 hours. On cooling and venting the cell, 0.89 g of a milky white viscous liquid was recovered. This liquid became clear and colorless upon standing. FT-IR spectroscopy showed the disappearance of signals due to isocyanate and alcohol absoφtions and the formation of a urethane linkage.

Example 3 To a 10 mL high pressure reactor cell was added 2.344 g FOSEE diol (prepared according to the teaching of U.S. Patent No. 2,803,656), 0.665 g HMDI, and one drop dibutyltin dilaurate. The cell was purged with nitrogen for five minutes, then filled with liquid CO ₂ , heated to 70°C, and pressurized to approximately 33.8 x 10 ⁶ Pa. These conditions were maintained for 17 hours.

On cooling and venting the cell, 2.56 g of a white powder was recovered. FT-IR spectroscopy showed the absence of alcohol and isocyanate absoφtions and the presence of urethane linkages. Gel permeation chromatography analysis in methyl ethyl ketone (against polystyrene standards) showed a weight average molecular weight of 25,000 and a polydispersity of 1.24.

Various modifications and alterations that do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be unduly limited to the illustrative embodiments set forth herein.