METHOD OF PREPARING PARTICULATE CROSSLINKED POLYMER

Abstract: Described is a method of preparing particulate crosslinked polymer, which comprises: (a) preparing a polymerizable organic phase; (b) forming a suspension of droplets of the organic phase in a liquid suspension medium, the organic phase being substantially insoluble in the liquid suspension medium; and (c) polymerizing the suspension of droplets of the organic phase in the liquid suspension medium, thereby forming particulate crosslinked polymer. The organic phase comprises: (1) a first component comprising, (i) at least one of a polyisocyanate having at least two isocyanate groups and a polyepoxide having at least two epoxide groups, and (ii) optionally a capped polyisocyanate having at least two capped isocyanate groups; and (2) a second component comprising an active hydrogen functional reactant having at least two active hydrogen groups that are reactive with the isocyanate groups and epoxide groups of the first component, the active hydrogen functional reactant comprises a polyamine having at least two functional groups selected from primary amine, secondary amine and combinations thereof.

Description: METHOD OF PREPARING PARTICULATE CROSSLINKED POLYMER DESCRIPTION OF THE INVENTION The present invention relates to a method of preparing particulate crosslinked polymer. In particular, the present invention relates to a method of preparing particulate polymer in which an organic phase is suspended as droplets in a liquid suspension medium, followed by polymerizing the suspension of droplets to form the particulate crosslinked polymer. More particularly, the organic phase is composed of: (i) a first component comprising, a polyisocyanate and/or a polyepoxide, and optionally a capped polyisocyanate; and (ii) a second component comprising a polyamine. Particulate crosslinked polymers are useful in a number of applications, such as additives for paints, adhesives and cosmetic products, as carriers for drugs and agricultural chemicals, and as spacers for stacked assemblies, e.g., liquid crystal displays. Particulate crosslinked polymers, such as particulate crosslinked polyepoxides and polyurethane-ureas, are also. useful in polishing pads, which are used to polish and/or planarize various substrates. Polishing pads may be prepared from a mixture of particulate crosslinked polymer and a crosslinkable organic binder, which is typically cured under pressure in a mold. During the manufacture of computer chips, for example, various substrates, such as silicon wafers, are polished and/or planarized to narrow engineering tolerances with polishing pads. The polishing pads used to polish computer chip substrates, and in particular the materials from which the pads are prepared, such as particulate crosslinked polymers, must also typically conform to a set of narrowly controlled physical properties, e.g., particle size, particle -size distribution, particle shape and crosslink density. It is known that polyurethane-urea particles can be prepared by what is commonly referred to as an interfacial polymerization method. In the interfacial polymerization method an isocyanate functional material is dispersed in water, followed by the addition of a polyamine to the dispersion, which results in the formation of polyurethane- urea particles . If the polyurethane-urea particles are isolated after completion of the interfacial polymerization, e.g., by filtration, the aqueous phase typically contains polyamine, which requires additional treatment steps prior to disposal . It is desirable to develop methods of preparing particulate crosslinked polymers, such as particulate crosslinked polyurethane-ureas and polyepoxides. It is also desirable to develop methods of preparing particulate crosslinked polymers that minimize the formation of waste streams, such as aqueous streams containing polyamines . United States Patent No. 5,041,467 describes a method of producing particulate polymers, in which a mixture of an isocyanate compound containing two or more isocyanate groups per molecule and a surfactant containing two or more hydroxyl groups per molecule is emulsified and allowed to cure in a dispersing medium, which does not dissolve the isocyanate compound. The method of the '467 patent is described as being performed in the absence of a protective colloid. United States Patent No. 5,292,829 describes a method of preparing crosslinked polyurethane polyurea spherically particulate polymer, which involves reacting an isocyanurate ring-containing polyisocyanate compound with a polyhydroxy compound to form an organic phase, dispersing the organic phase into water, and adding a polyamine to the dispersion. The v 829 patent describes the occurrence of an interfacial polymerization between the dispersed organic phase and the polyamine, and a polyurethane-forming reaction within the particles. In accordance with the present invention, there is provided a method of preparing particulate crosslinked polymer comprising: (a) preparing an organic phase comprising, (i) a first component comprising, at least one of a polyisocyanate having at least two isocyanate groups and a polyepoxide having at least two epoxide groups, and optionally a capped polyisocyanate having at least two capped isocyanate groups; and (ii) a second component comprising an active hydrogen functional reactant having at least two active hydrogen groups that are reactive with the isocyanate groups and epoxide groups of said first component, said active hydrogen functional reactant comprising a polyamine having at least two functional groups selected from primary amine, secondary amine and combinations thereof; (b) forming a suspension of droplets of said organic phase in a liquid suspension medium, said organic phase being substantially insoluble in said liquid suspension medium; and (c) polymerizing said suspension of droplets of said organic phase in said liquid suspension medium, thereby forming particulate crosslinked polymer. Other than in the operating examples, or where otherwise indicated, all numbers or expressions, such as those expressing weights, molar equivalents, weight ratios, molar equivalent ratios, etc, used in the specification and claims are to be understood as modified in all instances by the term "about . " DETAILED DESCRIPTION OF THE INVENTION As used herein and in the claims, the term "particulate crosslinked polymer" refers to particulate polymers that have a three-dimensional crosslink network and that do not have a melting or sintering point. Accordingly, the particulate crosslinked polymers of the present invention do not become sintered together upon heating. The shape of the particulate crosslinked polymer prepared according to the method of the present invention may be regular and/or irregular, and may be selected from shapes including, for example, spherical, disk, flake and combinations and/or mixtures thereof. Typically, the particulate crosslinked polymer is substantially spherical in shape. The particulate crosslinked polymer of the present invention may have a wide range of particle sizes, e.g., from colloidal to bead size. Typically, the particle size of the particulate crosslinked polymer is at least 20 microns, preferably at least 50 microns, and more preferably at least 100 microns. The particulate crosslinked polymer typically has an average particle size of less than 2 millimeters (mm) , more typically less than 500 microns, preferably less than 400 microns, and more preferably less than 300 microns. The average particle size of the particulate crosslinked polymer may range between any combination of these upper and lower values, inclusive of the recited values. The average particle size of the particulate crosslinked polymer may be determined by methods that are well known to the skilled artisan, e.g., using analytical instrumentation, such as a Coulter LS particle size analyzer. The particulate crosslinked polymer may be porous or substantially solid. By "substantially solid" is meant that the particulate polymer is not hollow, e.g., it is not in the form hollow microcapsules. Particulate crosslinked polymers that may be prepared according to the method of the present invention are, particulate crosslinked polyurethane-urea polymers, particulate crosslinked polyepoxides, and particulate crosslinked polyurethane-urea-epoxide polymers. Particulate crosslinked polyurethane-urea polymers prepared in the method of the present invention, have backbone linkages selected from urethane linkages (-NH-C (O) -0-) , urea linkages (-NH-C(O) -NH- and/or -NH-C (O) -N(R) - wherein R is hydrogen, an aliphatic, cycloaliphatic or aromatic group), and combinations thereof. Particulate crosslinked polyepoxides, prepared in accordance with the method of the present invention, have backbone linkages selected from ether linkages, amino linkages and combinations thereof. In an embodiment of the present invention, the first component of the organic phase comprises a mixture of polyisocyanate and polyepoxide, and the resulting particulate crosslinked polymer is a particulate crosslinked polyurethane-urea-epoxide polymer. As used herein, "particulate crosslinked polyurethane-urea-epoxide polymers" have backbone linkages selected from combinations of urethane linkages, urea linkages, ether linkages and amino linkages. In the method of the present invention, an organic phase comprising first and second components is initially prepared. As the first and second components typically begin to react, i.e., form covalent bonds, with each other upon their combination, the organic phase typically has a limited pot-life and will gel if allowed to stand too long prior to formation of the suspension in step (b) . While gel formation can be delayed by cooling the organic phase, e.g., to a temperature below 25°C, the organic phase is typically prepared at least at ambient room temperature, e.g., 25°C, and soon or immediately thereafter the suspension formation step (b) is performed. The organic phase may be prepared by means of batch methods, for example, by mixing the first and second components together with an impeller. Alternatively, the organic phase may be prepared continuously, for example, by combining continuously separate feed streams of the first and second components in a mixing head and expelling continuously the organic phase from the mixing head. The polyisocyanate of the first reactant of the organic phase has at least two isocyanate (-NCO) groups, e.g., from 2 to 10 isocyanate groups. Typically the polyisocyanate has from 2 to 4 isocyanate groups . The polyisocyanate may be selected from aliphatic polyisocyanate monomers, aromatic polyisocyanate monomers, polyurethane prepolymers having at least two isocyanate groups and mixtures thereof. As used herein and in the claims, the term "aliphatic polyisocyanate monomers" refers to saturated polyisocyanate monomers, ethylenically unsaturated polyisocyanate monomers, alicyclic polyisocyanate monomers and mixtures of two or more classes thereof. Aliphatic polyisocyanate monomers that are useful in the method of the present invention, typically contain at least 4 carbon atoms, e.g., from 4 to 20 carbon atoms. As used herein and in the claims, the term "aromatic polyisocyanate monomers" refers to aromatic polyisocyanate monomers wherein the isocyanate groups are not bonded directly to the aromatic ring, e.g., α,α'-xylene diisocyanate; aromatic polyisocyanate monomers wherein the isocyanate groups are bonded directly to the aromatic ring, e.g., benzene diisocyanate; and mixtures thereof. Aromatic polyisocyanate monomers that are useful in the method of the present invention, typically contain at least 8 carbon atoms, e.g., from 8 to 20 carbon atoms. Examples of aliphatic saturated polyisocyanate monomers that are useful in the method of the present invention include, but are not limited to, ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, nonamethylene diisocyanate, 2,2' -dimethylpentane diisocyanate, 2, 2, 4-trimethylhexane diisocyanate, decamethylene diisocyanate, 2, 4, 4, -trimethylhexamethylene diisocyanate, 1, 6, 11-undecanetriisocyanate, 1,3,6- hexamethylene triisocyanate, 1, 8-diisocyanato-4- (isocyanatomethyl) octane, 2,5, 7-trimethyl-l, 8-diisocyanato-5- (isocyanatomethyl) octane, bis (isocyanatoethyl) -carbonate, bis (isocyanatoethyl) ether, 2-isocyanatopropyl-2, 6- diisocyanatohexanoate, lysinediisocyanate methyl ester and lysinetriisocyanate methyl ester. Examples of ethylenically unsaturated polyisocyanate monomers from which the polyisocyanate of the first component may be selected include, but are not limited to, butene diisocyanate and 1, 3-butadiene-1, 4-diisocyanate. Alicyclic polyisocyanate monomers from which the polyisocyanate may be selected include, but are not limited to, isophorone diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, bis (isocyanatomethyl) cyclohexane, bis (isocyanatocyclohexyl)methane, bis (isocyanatocyclohexyl) - 2,2-propane, bis (isocyanatocyclohexyl) -1, 2-ethane, 2- isocyanatomethyl-3- (3-isocyanatopropyl) -5-isocyanatomethyl- bicyclo [2.2.1] -heptane, 2-isocyanatomethyl-3- (3- isocyanatopropyl) -6-isocyanatomethyl-bicyclo [2.2.1] -heptane, 2-isocyanatomethyl-2- (3-isocyanatopropyl) -5-isocyanatomethyl- bicyclo[2.2.1] -heptane, 2-isocyanatomethyl-2- (3- isocyanatopropyl) -6-isocyanatomethyl-bicyclo [2.2.1] -heptane, 2-isocyanatomethyl-3- (3-isocyanatopropyl) -6- (2- isocyanatoethyl) -bicyclo [2.2.1] -heptane, 2-isocyanatomethyl-2- (3-isocyanatopropyl) -5- (2-isocyanatoethyl) -bicyclo [2.2.1] - heptane and 2-isocyanatomethyl-2- (3-isocyanatopropyl) -6- (2- isocyanatoethyl) -bicyclo [2.2.1] -heptane . Examples of aromatic polyisocyanate monomers , wherein the isocyanate groups are not bonded directly to the aromatic ring, from which the polyisocyanate of the first component may be selected include, but are not limited to, bis (isocyanatoethyl) benzene, α,α,α' ,α' -tetramethylxylene diisocyanate, 1, 3-bis (l-isocyanato-l-methylethyl)benzene, bis (isocyanatobutyl) benzene, bis (isocyanatomethyl) naphthalene, bis (isocyanatomethyl) diphenyl ether, bis (isocyanatoethyl) phthalate, mesitylene triisocyanate and 2, 5-di (isocyanatomethyl) furan. Aromatic polyisocyanate monomers, having isocyanate groups bonded directly to the aromatic ring, from which the polyisocyanate of the first component may be selected include, but are not limited to, phenylene diisocyanate, ethylphenylene diisocyanate, isopropylphenylene diisocyanate, dimethylphenylene diisocyanate, diethylphenylene diisocyanate, diisopropylphenylene diisocyanate, trimethylbenzene triisocyanate, benzene triisocyanate, naphthalene diisocyanate, methylnaphthalene diisocyanate, biphenyl diisocyanate, ortho-tolidine diisocyanate, 4,4'- diphenylmethane diisocyanate, bis (3-methyl-4- isocyanatophenyl)methane, bis (isocyanatophenyl) ethylene , 3,3'- dimethoxy-biphenyl-4, 4' -diisocyanate, triphenylmethane triisocyanate, polymeric 4,4' -diphenylmethane diisocyanate, naphthalene triisocyanate, diphenylmethane-2,4, ' - triisocyanate, 4-methyldiphenylmethane-3, 5, 2' ,4' ,6' - pentaisocyanate, diphenylether diisocyanate, bis (isocyanatophenylether) ethyleneglycol , bis (isocyanatophenylether) -1,3-propyleneglycol, benzophenone diisocyanate, carbazole diisocyanate, ethylcarbazole diisocyanate and dichlorocarbazole diisocyanate. In an embodiment of the present invention, the polyisocyanate of the first component of the organic phase is a polyisocyanate monomer having two isocyanate groups. Examples of preferred polyisocyanate monomers having two isocyanate groups include, α,α'-xylene diisocyanate, α,cc,α' ,α' -tetramethylxylene diisocyanate, isophorone diisocyanate, bis (isocyanatocyclohexyl) ethane, toluene diisocyanate, 4, ' -diphenylme hane diisocyanate and mixtures thereof . The polyisocyanate of the first component of the organic phase may also be selected from a polyurethane prepolymer having at least two isocyanate groups. Isocyanate functional polyurethane prepolymers may be prepared according to methods that are well known to the skilled artisan. Typically, at least one polyol, e.g., a diol and/or triol, and at least one isocyanate functional monomer, e.g., a diisocyanate monomer, are reacted together to form a prepolymer having at least two isocyanate groups . Examples of isocyanate functional monomers that may be used to prepare the isocyanate functional polurethane prepolymer, include those classes and examples of polyisocyanates as recited previously herein. The molecular weight of the isocyanate functional polyurethane prepolymer can vary widely, for example, having a number average molecular weight (Mn) of from 500 to 15,000, or from 500 to 5000, as determined by gel permeation chromatography (GPC) using polystyrene standards . Classes of polyols that may be used to prepare the isocyanate functional polyurethane prepolymer of the first component of the organic phase include, but are not limited to: straight or branched chain alkane polyols, e.g., 1,2- ethanediol, 1, 3-propanediol, 1, 2-propanediol, 1, 4-butanediol, 1,3-butanediol, glycerol, neopentyl glycol, trimethylolethane, trimethylolpropane, di-trimethylolpropane, erythritol, pentaerythritol and di-pentaerythritol; polyalkylene glycols, e.g., di-, tri- and tetraethylene glycol, and di-, tri- and tetrapropylene glycol; cyclic alkane polyols, e.g., cyclopentanediol , cyclohexanediol , cyclohexanetriol , cyclohexanedimethanol , hydroxypropylcyclohexanol and cyclohexanediethanol; aromatic polyols, e.g., dihydroxybenzene, benzenetriol, hydroxybenzyl alcohol and dihydroxytoluene; bisphenols, e.g., 4,4'- isopropylidenediphenol; 4,4' -oxybisphenol, 4,4'- dihydroxybenzophenone, 4, 4' -thiobisphenol, phenolphthlalein, bis ( -hydroxyphenyl) methane, 4, 4' - (1, 2-ethenediyl)bisphenol and 4 , 4' -sulfonylbisphenol; halogenated bisphenols, e.g., 4,4' -isopropylidenebis (2, 6-dibromophenol) , 4,4'- isopropylidenebis (2 , 6-dichlorophenol) and 4,4'- isopropylidenebis (2,3, 5, 6-tetrachlorophenol) ; alkoxylated bisphenols, e.g., alkoxylated 4, 4' -isopropylidenediphenol having from 1 to 70 alkoxy groups, for example, ethoxy, propoxy, α-butoxy and β-butoxy groups; and biscyclohexanols, which can be prepared by hydrogenating the corresponding bisphenols, e.g., 4, ' -isopropylidenebiseyelohexanol, 4,4' -oxybiseyelohexanol , 4,4'- thiobiscyclohexanol and bis (4-hydroxyeyelohexanol)methane. Additional classes of polyols that by be used to prepare isocyanate functional polyurethane prepolymers, include for example, higher polyalkylene glycols, such as polyethylene glycols having number average molecular weights (Mn) of, for example, from 200 to 2000; and hydroxy functional polyesters, such as those formed from the reaction of diols, such as butane diol, and diacids or diesters, e.g., adipic acid or diethyl adipate, and having an Mn of, for example, from 200 to 2000. In an embodiment of the present invention, the isocyanate functional polyurethane prepolymer is prepared from a diisocyanate, e.g., toluene diisocyanate, and a polyalkylene glycol, e.g., poly (tetrahydrofuran) . The isocyanate functional polyurethane prepolymer may optionally be prepared in the presence of a catalyst . Classes of suitable catalysts include, but are not limited to, tertiary amines, such as triethylamine, and organometallic compounds, such as dibutyltin dilaurate. Additional examples of catalysts that may be used in the preparation of the isocyanate functional polyurethane prepolymer are recited further herein. If a catalyst is used in the preparation of the isocyanate functional polyurethane prepolymer, it is typically present in an amount of less than 5 percent by weight, preferably less than 3 percent by weight, and more preferably less than 1 percent by weight, based on the total weight of polyol and isocyanate functional monomer. The polyepoxide of the first component of the organic phase has at least two epoxide groups, e.g., from 2 to 10 epoxide groups. Typically the polyepoxide has from 2 to 4 epoxide groups . The polyepoxide of the first component may be selected from aliphatic polyepoxide monomers, aromatic polyepoxide monomers, polyepoxide prepolymers having at least two epoxide groups, and mixtures thereof. As used herein and in the claims, the term "aliphatic polyepoxide monomers" refers also to cycloaliphatic polyepoxide monomers . Aliphatic polyepoxides useful in the present invention typically have at least 4 carbon atoms, e.g., from 4 to 20 carbon atoms. Aromatic polyepoxide monomers useful in the present invention typically have at least 10 carbon atoms, e.g., from 10 t 20 carbon atoms . Epoxide functional monomers that may be used in the present invention can be prepared from the reaction of a polyol and an epihalohydrin, e.g., epichlorohydrin. Polyols that may be used to prepare epoxide functional monomers include those recited previously herein with regard to the preparation of the isocyanate functional polyurethane prepolymer. Examples of aliphatic polyepoxide monomers include, 1, 2, 3 , 4-diepoxybutane and 1, 2, 7, 8-diepoxyoctane. Examples of cycloaliphatic polyepoxide monomers include, 1, 2,4, 5-diepoxycyclohane, 1, 2, 5, 6-diepoxycyclooctane, 7-oxa- bicyclo [4.1.0] heptane-3-carboxylic acid 7-oxa- bicyclo [4.1.0] hept-3-ylmethyl ester, 1, 2-epoxy-4-oxiranyl- cyclohexane and 2, 3- (epoxypropyl) cyclohexane. Examples of aromatic polyepoxide monomers include those based on the reaction of an aromatic diol (e.g., catechol, resorcinol and bisphenols) with epichlorohydrin, e.g., 4,4'- isopropylidenediphenol diglycidyl ether. Commercially available polyepoxide monomers that may be used in the present invention include the EPON epoxy resins, e.g., EPON 828 epoxy resin and EPON 880 epoxy resin, available from Shell Chemicals . Polyepoxide prepolymers that may comprise the first component of the organic phase can be prepared from the reaction of a polymeric polyol and epichlorohydrin. Classes of polymeric polyols that may be used to prepare the epoxide functional prepolymer include, but are not limited to: polyalkylene glycols, e.g. , polyethylene glycol and polytetrahydrofuran; polyester polyols; polyurethane polyols; poly ( (meth) acrylate) polyols; and mixtures thereof. The recited classes of polymeric polyols may be prepared according to methods that are well known to the skilled artisan. In an embodiment of the present invention, the epoxide functional prepolymer is an epoxy functional poly ( (meth) acrylate) polymer prepared from (meth) acrylate monomers and epoxide functional radically polymerizable monomers, e.g., glycidyl (meth) acrylate . As used herein, the term " (meth) acrylate" refers to acrylate monomers, methacrylate monomers and mixtures of acrylate and methacrylate monomers . Polyepoxide prepolymers that may be used in the present invention may have a wide range of molecular weights, e.g., number average molecular weights of from 500 to 15,000, or from 500 to 5000, as determined by gel permeation chromatography (GPC) using polystyrene standards . The first component of the organic phase used in the preparation of the particulate crosslinked polymer may optionally further comprise a capped polyisocyanate having at least two capped isocyanate groups. As used herein and in the claims, by "capped polyisocyanate" is meant a monomer or prepolymer having terminal and/or pendent capped isocyanate groups which can be converted, under controlled conditions, to decapped, i.e., free, isocyanate groups and separate or free capping groups. The capping groups of the capped polyisocyanate may be fugitive or nonfugitive. By "nonfugitive capping groups" is meant a capping group, which upon de-capping or de-blocking from the isocyanate group, remains substantially within the three dimensional crosslink network or matrix of the particulate polymer. By "fugitive capping group" is meant a capping group, which upon de-capping or de-blocking from the isocyanate group, migrates substantially out of the three dimensional crosslink network or matrix of the particulate polymer. Capped polyisocyanates are typically characterized as having a de-capping temperature. As used herein and in the claims, the term "de-capping temperature" refers to the minimum temperature at which the capped isocyanate groups of the capped polyisocyanate are converted to decapped, i.e., free, isocyanate groups and separate or free capping groups. The de-capping temperature of many capped polyisocyanates is typically between 121°C (250°F) and 191°C (375°F) . The polyfunctional isocyanate of the capped polyisocyanate may be selected from those classes and examples of polyisocyanates as recited previously herein. Examples of nonfugitive capping groups of the capped polyisocyanate include, but are not limited to: lH-azoles, e.g., 1H- imidazole, lH-pyrazole, 3, 5-dimethyl-IH-pyrazole, 1H-1,2,3- triazole, 1H-1, 2, 3-benzotriazole, 1H-1, 2 , 4-triazole, 1H-5- methyl-1, 2, 4-triazole and lH-3-amino-l, 2, 4-triazole; lactams, e.g., e-caprolactam and 2-pyrolidinone; and others including, orpholine, 3- minopropyl morpholine and N-hydroxy phthalimide. Examples of fugitive capping groups of the capped polyisocyanate include, but are not limited to: alcohols, e.g., propanol, isopropanol, butanol, isobutanol, tert-butanol and hexanol; alkylene glycol monoalkyl ethers, such as ethylene glycol monoalkyl ethers, e.g., ethylene glycol monobutyl ether and ethylene glycol monohexyl ether, and propylene glycol monoalkyl ethers, e.g., propylene glycol monomethyl ether; and ketoximes, e.g., methyl ethyl ketoxime . Shaped articles, such as polishing pads, can be prepared by mixing the particulate crosslinked polymer of the present invention with a curable organic polymer binder, e.g. a two component polyurethane binder, and curing the mixture, typically in a mold at elevated temperature and optionally under elevated pressure. Capped polyisocyanates may be included in the first component of the organic phase to improve the dimensional stability of shaped articles, e.g., polishing pads, prepared from a mixture of the particulate crosslinked polymer of the present invention with a curable organic polymer binder. While not intending to be bound by any theory, it is believed that during formation of the shaped article, the inclusion of capped polyisocyanate in the first component of the organic phase from which the particulate crosslinked polymer is prepared, allows for the later formation of covalent bonds: (a) between at least some of the particulate crosslinked polymer particles,- and/or (b) between the particulate crosslinked polymer and the crosslinked organic polymer binder. If used, the capped polyisocyanate is typically present in an amount such that the first component of the organic phase contains capped isocyanate groups in an amount of less than 50 mole percent, based on the total molar equivalents of isocyanate groups of said polyisocyanate, epoxide groups of said polyepoxide and capped isocyanate groups of said capped polyisocyanate, e.g., from 5 mole percent to 40 mole percent, based on the total molar equivalents of isocyanate groups of said polyisocyanate, epoxide groups of said polyepoxide and capped isocyanate groups of said capped polyisocyanate. In an embodiment of the present invention, the polyisocyanate, polyepoxide and capped polyisocyanate of the first reactant are each preferably substantially free of ionic groups, e.g., cationic groups and anionic groups. As used herein and in the claims, the "ionic groups" of which each of the polyisocyanate, polyepoxide and capped polyisocyanate are preferably free, refers also to precursors of ionic groups that may be converted to ionic groups in an aqueous suspension medium, e.g., by means of adjusting the pH of the aqueous suspension medium. As used herein and in the claims, the term "substantially free of ionic groups" means that the polyisocyanate, polyepoxide and capped polyisocyanate do not contain ionic groups in an amount sufficient to result in the formation of a stable dispersion thereof. Preferably, the polyisocyanate, polyepoxide and capped polyisocyanate of the first component each contain no ionic groups. Cationic groups of which the polyisocyanate, polyepoxide and capped polyisocyanate are each preferably substantially free of include, but are not limited to: cationic amine groups, e.g., formed from the reaction of a primary or secondary amine group with a mineral or organic acid; and onium groups, e.g., sulphoniu , phosphonium and quaternary ammonium groups. Anionic groups of which the polyisocyanate, polyepoxide and capped polyisocyanate are each preferably substantially free of include, for example, carboxylic acid salts, such as those formed from the reaction of a carboxylic acid group with an amine or alkali metal hydroxide . The active hydrogen functional reactant of the second component of the organic phase has at least two active hydrogen groups, the active hydrogen groups being selected from at least primary amine and secondary amine, and optionally hydroxyl, and combinations thereof. The active hydrogen functional reactant of the second reactant comprises a polyamine having at least two functional groups selected from primary amine, secondary amine and combinations thereof. The polyamine may be selected from aliphatic polyamine monomers (including cycloaliphatic polyamines) , aromatic polyamine monomers, polyamine prepolymers and mixtures thereof . Aliphatic polyamine monomers from which the polyamine of the second component may be selected include any of the family of ethyleneamines , e.g. , ethylenediamine (EDA) , diethylenetriamine (DETA) , triethylenetetramine (TETA) , tetraethylenepentamine (TEPA) , pentaethylenehexamine (PEHA) , piperazine, i.e., diethylenediamine (DEDA) , and 2-amino-1- ethylpiperazine. Examples of aromatic polyamine monomers include, but are not limited to, one or more isomers of dialkyl toluenediamine, such as, 3, 5-dimethyl-2, 4- toluenediamine, 3 , 5-dimethyl-2, 6-toluenediamine, 3,5-diethyl- 2, 4-toluenediamine, 3, 5-diethyl-2, 6-toluenediamine, 3,5- diisopropyl-2, 4-toluenediamine, 3, 5-diisopropyl-2, 6- toluenediamine and mixtures thereof . Additional examples of aromatic polyamine monomers include, but are not limited to methylene dianiline and trimethyleneglycol di (para- aminobenzoate) . A further class of aromatic polyamine monomers that may be used in the method of the present invention include those based on 4, 4' -methylene-bis (dialkylaniline) , which may be represented by the following general formula I, I wherein R 3 and R 4 are each independently ^^ alkyl, and R 5 is selected from hydrogen and halogen, e.g., chlorine and bromine. Examples of aromatic polyamine monomers based on 4,4' -methylene-bis (dialkylaniline) include, but are not limited to, 4 , ' -methylene-bis (2 , 6-dimethylaniline) , 4,4'- methylene-bis (2, 6-diethylaniline) , 4,4' -methylene-bis (2-ethyl- 6-methylaniline) , 4, ' -methylene-bis (2, 6-diisopropylaniline) , 4,4' -methylene-bis (2-isopropyl-6-methylaniline) and 4,4'- methylene-bis (2, 6-diethyl-3-chloroaniline) . In an embodiment of the present invention, the first component comprises a polyisocyanate and optionally a capped polyisocyanate, and the polyamine of the second component is preferably selected from aromatic polyamine monomers, and more preferably from aromatic polyamine monomers based on 4,4' -methylene- bis (dialkylaniline) . Polyamine prepolymers that may be used in the present invention include polyamide prepolymers having at least two amine groups selected from primary amines, secondary amines and combinations thereof. Polyamide prepolymers having at least two amine groups are typically prepared from the reaction of a polyamine, e.g., a diamine such as dietheylenetriamine, and a pol carboxylic acid, e.g., a difunctional carboxylic acid, as is known to the skilled artisan. Commercially available polyamide prepolymers from which the polyamine of the second reactant may be selected include VERSAMID polyamide resins, available from Cognis Corporation, Coating & Inks Division. In an embodiment of the present invention, the first component comprises a polyepoxide, and the polyamine of the second component is preferably selected from polyamine prepolymers , and more preferably from polyamide prepolymers having at least two amine groups . In an embodiment of the present invention, the second component of the organic phase further comprises at least one of a polyol having at least two hydroxyl groups, and a hydroxyl-amine reactant having at least one hydroxyl group and at least one amine group selected from primary amine, secondary amine and combinations thereof. Polyols that may optionally further comprise the second reactant include aliphatic polyols, aromatic polyols, polyol prepolymers and mixtures thereof . Classes and examples of polyols that may be used include those as recited previously herein. Examples of hydroxyl-amine reactants include, but are not limited to, ethanolamine, diethanolamine, 2- (diisopropylamino) ethanol, 2- amino-1-hexanol, 6-amino-l-hexanol and 2-(tert- butylamino) ethanol . The first and second components are typically present in the organic phase in amounts relative to each other such that a particulate crosslinked polymer is obtained in the method of the present invention. The molar equivalents ratio of the sum of the molar equivalents of isocyanate, epoxide and capped isocyanate groups of the first component (a) (i) to the sum of the molar equivalents of active hydrogen groups of the second component (a) (ii) , e.g., primary amine groups, is typically from 0.5 : 1.0 to 1.5 : 1.0, e.g., from 0.7 : 1.0 to 1.3 : 1.0 or from 0.8 : 1.0 to 1.2 : 1.0. When the first component contains a polyisocyanate and/or capped polyisocyanate, the organic phase may optionally further comprise a urethane/urea formation catalyst . Examples of urethane/urea formation catalysts include, but are not limited to, tertiary amines, e.g., triethylamine, triisopropylamine and N,N-dimethylbenzylamine, and organometallic compounds, e.g., dibutyltin dilaurate, dibutyltin diacetate and stannous octoate. Additional examples of tertiary amines are listed in United States Patent No. 5,693,738 at column 10 lines 6 through 38, the disclosure of which is incorporated herein by reference. Additional examples of organometallic compounds useful as catalysts are listed in United States Patent No. 5,631,339 at column 4, lines 26 through 46, the disclosure of which is incorporated herein by reference. If used, such catalysts are typically incorporated into the second component of the organic phase prior to combining the first and second components of the organic phase. Urethane/urea formation catalyst levels are typically less than 5 percent by weight, preferably less than 3 percent by weight and more preferably less than 1 percent by weight, based on the total weight of the combined first and second components . When the first component contains a polyepoxide, the organic phase may optionally further comprise an epoxide ring opening catalyst. Epoxide ring opening catalysts that may be used include those that are known to the skilled artisan, e.g., tertiary amines, such as tri-tertiarybutyl amine, and tetrafluoroboric acid. If used, the epoxide ring opening catalyst is typically added to the second component prior to mixing the first and second components together. The epoxide ring opening catalyst, if used, is typically present in the organic phase in an amount of less than 5 percent by weight, e.g., less the 3 percent or 1 percent by weight, based on the total weight of the first and second reactants. In an embodiment of the present invention, at least one of the organic phase and the liquid suspension medium comprises an organic surfactant selected from anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and mixtures thereof. The use of an organic surfactant is desirable in that it is believed to stabilize the suspension of the organic phase in the liquid suspension medium, and to correspondingly improve control of the particle size of the resulting particulate crosslinked polymer. If used, the organic surfactant is typically present in an amount at least 0.01 percent by weight, preferably at least 0.02 percent by weight, and more preferably at least 0.05 percent by weight, based on either the total weight of the organic phase, the total weight of the liquid suspension medium, or the total weight of the organic phase and the liquid suspension medium. The organic surfactant, if used, is also typically present in an amount of less than 3 percent by weight, preferably less than 2 percent by weight, and more preferably less than 1.5 percent by weight, based on either the total weight of the organic phase, the total weight of the liquid suspension medium, or the total weight of the organic phase and the liquid suspension medium. The amount of organic surfactant used in the method of the present invention, may range between any combination of these upper and lower values, inclusive of the recited values. Anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants that may be used in the method of the present invention include those that are known to the skilled artisan. Anionic surfactants include block copolymers of alkylene oxides (e.g., block copolymers of any two of ethylene oxide, propylene oxide and butylene oxide) having terminal groups selected from carboxylic acid groups, sulfate groups, sulfonate groups, phosphate groups and combinations thereof. The terminal carboxylic acid, sulfate, sulfonate and phosphate groups may be converted into anionic groups in the presence of a base, including for example, alkali metal hydroxide, e.g., sodium hydroxide, organic amine, e.g., triethylamine, and alkanolamine, e.g., mono-, di-, or triethanolamine . Anionic surfactants that may be used in the method of the present invention are described in further detail in United States Patent No. 6,059,944 at column 6, line 57 through column 7, line 27, which disclosure is incorporated herein by reference. Cationic surfactants that may be used in the method of the present invention include those that are known to the skilled artisan, and typically contain salts of primary and/or secondary amine groups, or onium groups, e.g., ammonium, sulphonium or phosphonium groups. Examples of cationic surfactants that may be used in the present invention, include, but are not limited to, dialkanolamine salts, trialkanolamine salts, polyoxyalkylene alkylamine ether salts, trialkanolamine fatty acid ester salts, polyoxyalkylene dialkanolamine ether salts, polyoxyalkylene trialkanolamine ether salts, di (polyoxyalkylene) alkylbenzylalkylammonium salts, alkylcarbamoylmethyldi (polyoxyalkylene) ammonium salts, polyoxyalkylenealkylammonium salts, and polyoxyalkylenedialkylammonium salts . Amphoteric surfactants that may be used in the method of the present invention contain both acidic and basic hydrophilic moieties in their structure. A commercially prominent class of amphoteric surfactants are derivatives of imidazoline. Examples of amphoteric surfactants include cσcoamphopropionate, cocoamphocarboxy-propionate, cocoamphoglycinate, cocoamphocarboxyglycinate, cocoampho- propylsulfonate, and cocoamphocarboxy-propionic acid. A further class of amphoteric surfactants include the betaines and derivatives thereof, such as the sulfobetaines . Amphoteric betaine surfactants are described in further detail in United States Patent No. 6,059,944 at column 8, lines 17- 39, the disclosure of which is incorporated herein by reference . Nonionic surfactants that may be used in the method of the present invention include block copolymers of alkylene oxides having terminal groups selected from hydroxyls, alkyl groups (e.g., C^C^ alkyl groups), aromatic groups (e.g., phenyl and benzyl groups), halides (e.g., chloride and bromide), and combinations thereof. A preferred class of nonionic surfactants are block copolymers of alkylene oxides (e.g., di- and tri-block copolymers of ethylene oxide and propylene oxide) having terminal hydroxyl groups. Commercially available nonionic surfactants the may be used in the present invention include, for example, PLURONIC surfactants available from BASF Corporation. Nonionic surfactants that may be used in the method of the present invention are described in greater detail in United States Patent No. 6,059,944 at column 6 line 57 through column 8, line 5, which disclosure is incorporated herein by reference. In an embodiment of the present invention, the organic surfactant is a nonionic surfactant (e.g., a tri-block copolymer of ethylene oxide and propylene oxide having terminal hydroxyl groups) , and is only added to the organic phase. Further examples of anionic, cationic, amphoteric and nonionic surfactants that may be used in the method of the present invention (and their commercial sources) are described and listed in the publication, McCutcheon's Emulsifiers and Detergents . Volume 1, the Manufacturing Confectioner Publishing Co., McCutcheon's Division, Glen Rock, New Jersey, ISBN 944254-63-2. In an embodiment of the present invention, the organic phase further comprises an abrasive particulate material. The abrasive particulate material may be distributed uniformly or non-uniformly throughout the particulate crosslinked polymer. Typically, the abrasive particulate material is distributed substantially uniformly throughout the particulate crosslinked polymer. While the abrasive particulate materials may be combined with either the first or second components, they are typically mixed with the second component prior to preparing the organic phase (to minimize the potential for adverse reactions with the isocyanate and/or epoxide groups of the first reactant) . If used, the abrasive particulate material is typically present in the organic phase in amounts of less than 70 percent by weight, based on the total weight of the organic phase, e.g. in amounts of from 5 percent by weight to 65 percent by weight, based on the total weight of the organic phase. The abrasive particulate material may be in the form of individual particles, aggregates of individual particles, or a combination of individual particles and aggregates. The shape of the abrasive particulate material may be selected from, for example, spheres, rods, triangles, pyramids, cones, regular cubes, irregular cubes, and mixtures and/or combinations thereof. The average particle size of the abrasive particulate material is generally at least 0.001 microns, typically at least 0.01 microns, and more typically at least 0.1 microns . The average particle size of the abrasive 5 particulate material is generally less than 50 microns, typically less than 10 microns, and more typically less than 1 micron. The average particle size of the abrasive particulate material may range between any combination of these upper and lower values, inclusive of the recited values. The average 10 particle size of the abrasive particulate material is typically measured along the longest dimension of the particle. Examples of abrasive particulate materials that may be used in the present invention include, but are not limited '15 to: aluminum oxide, e.g., gamma alumina, fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, and sol gel derived alumina; silicon carbide, e.g., green silicon carbide and black silicon carbide; titanium diboride; boron carbide; silicon nitride; tungsten carbide; titanium carbide; 20 diamond; boron nitride, e.g., cubic boron nitride and hexagonal boron nitride; garnet; fused alumina zirconia; silica, e.g., fumed silica; iron oxide; cromia; ceria; zirconia; titania; tin oxide; manganese oxide; and mixtures thereof. Preferred abrasive particulate materials include, 25 for example, aluminum oxide, silica, silicon carbide, zirconia and mixtures thereof . Abrasive particulate materials used in the present invention may optionally have a surface modifier thereon. Generally, the surface modifier is selected from surfactants, 30 coupling agents and mixtures thereof. Surfactants may be used to improve the dispersibility of the abrasive particles in the organic phase from which the particulate crosslinked polymer is prepared. Coupling agents may be used to better bind the abrasive particles to the matrix of the particulate crosslinked polymer. The surface modifier, if used, is typically present in an amount of less than 25 percent by weight, based on the total weight of the abrasive particulate material and surface modifier. More typically, the surface modifier is present in an amount of from 0.5 to 10 percent by weight, based on the total weight of the abrasive particulate material and surface modifier. Classes of surfactants that may be used as surface modifiers for the abrasive particulate material include those known to the skilled artisan and as recited previously herein, e.g., anionic, cationic, amphoteric and nonionic surfactants. More specific examples of surfactants that may be used include, but are not limited to, metal alkoxides, polalkylene oxides, salts of long chain fatty carboxylic acids. Art- recognized classes of coupling agents that may be optionally used to modify the surface of the abrasive particulate material include, for example, silanes, such as organosilanes, titanates and zircoaluminates . Examples of coupling agents that may be used include, for example, SILQUEST silanes A-174 and A-1230, which are commercially available from Witco Corporation. The organic phase may optionally further comprise conventional additives. Such conventional additives may include heat stabilizers, antioxidants, static dyes, pigments, and flexibilizing additives, e.g., alkoxylated phenol benzoates and poly(alkylene glycol) dibenzoates. If used, such additives are typically present in the organic phase in amounts totaling less than 10 percent by weight, preferably less than 5 percent by weight, and more preferably less than 3 percent by weight, based on the total weight of the organic phase. While such conventional additives may be added to either of the first or second components of the organic phase, they are typically incorporated into the second component, to minimize the potential of adverse interactions with the isocyanate groups or epoxide groups of the respective first component . In a further embodiment of the present invention, the organic phase may optionally further comprise an organic solvent . The organic solvent is typically used to reduce the viscosity of the organic phase, so that it may be more controllably introduced into the liquid suspension medium in the suspension formation step of the present invention. The solvent is preferably inert, i.e., being nonreactive with isocyanate groups, epoxide groups, capped isocyanate groups and active hydrogen groups. Alternatively, the solvent may contain one or more active hydrogen groups, e.g., hydroxyl groups, and be reactive with the polyisocyanate or polyepoxide, in which case the solvent is a reactive diluent. Classes of organic solvents that may be added to the organic phase include, but are not limited to: esters, e.g., ethyl acetate; ethers, e.g., methylethyl ether; ketones, e.g., methyl isobutyl ketone; alkanes, e.g., hexane and heptane; and monoalkyl ethers of alkylene glycols, e.g., propylene glycol monomethyl ether. If used, the organic solvent is typically present in the organic phase in a minor amount, and more typically in an amount of less than 30 percent by weight, based on the total weight of the organic phase, e.g., from 5 to 25 percent by weight, based on the total weight of the organic phase. In the method of the present invention, the organic phase is suspended as droplets in a liquid suspension medium. The organic phase is substantially insoluble in the liquid suspension medium, which is selected from organic suspension mediums, e.g., an organic solvent, and aqueous suspension mediums, e.g., deionized water. Organic solvents that may be used as an organic suspension medium include those that are inert to isocyanate and epoxide groups, for example, paraffin, esters, ketones, aromatic hydrocarbons, halogen compounds, ethers and mixtures thereof . Preferably, the liquid suspension medium is an aqueous suspension medium. While the aqueous suspension medium may contain organic materials, e.g., alcohols, ethers and organic surfactants, it typically contains a major amount of water. The aqueous suspension medium typically contains water in an amount of at least 51 percent by weight, based on the total weight of the aqueous suspension medium, e.g. , from 51 percent to 99 percent by weight, based on the total weight of the aqueous suspension medium. In an embodiment of the present invention, the liquid suspension medium is substantially free of polyamines, e.g., containing less than 0.1 percent by weight of polyamine, based on the total weight of the liquid suspension medium. Ensuring that the liquid suspension medium is substantially free of polyamines, can be achieved by: (a) selecting a liquid suspension medium in which the organic phase (including the polyamine of the second component) is substantially insoluble; and (b) not adding any polyamines to the liquid suspension medium. The organic phase may be suspended as droplets in the liquid suspension medium by means that are well known to those of ordinary skill in the art. Typically, the organic phase is poured slowly into the liquid suspension medium, while the liquid suspension medium is agitated, e.g., by means of a high speed impeller. After completion of the addition of the organic phase to the liquid suspension medium, the suspension is typically stirred under high agitation for a period of time sufficient to result in a desired particle size (as is typically determined by trial and error) , followed by less agitated stirring to keep the suspension of organic droplets from settling out of the liquid suspension medium. Polymerizing the suspension of droplets of organic phase in the liquid suspension medium is typically achieved by heating the suspension to a temperature that is above room temperature but less than the boiling point of the liquid suspension medium, e.g., 100°C in the case of water under atmospheric pressure. While the suspension may be heated at pressures above or below atmospheric pressure, it is typically heated under conditions of atmospheric pressure (e.g., 760 Torr) . Generally, the suspension is heated under atmospheric pressure with continuous agitation to a temperature from 30°C to 95°C or from 50°C to 85°C. The suspension is typically stirred continuously at elevated temperature for a time sufficient to result in complete polymerization of the suspended organic droplets, e.g., from 10 minutes to 8 hours, and formation of particulate crosslinked polymer. In an embodiment of the present invention, the first component of the organic phase contains a capped polyisocyanate, and the polymerization of the suspension of droplets of the organic phase in the liquid suspension medium in step (c) is performed at a temperature that is less than the de-capping temperature of the capped polyisocyanate. For example, if the de-capping temperature of the capped polyisocyanate is 121°C (250°F) , the polymerization step is preferably performed at a temperature of less than 121°C, e.g., from 30°C to 95°C. Polymerizing the suspension of droplets at a temperature that is less than the de-capping temperature of the capped polyisocyanate allows for the formation of particulate crosslinked polymer that contains capped isocyanate groups. The capped isocyanate groups within the particulate crosslinked polymer can be later decapped and reacted by heating the particulate polymer above the de- capping temperature, as described previously herein. Upon completion of the polymerization step, the suspension of particulate crosslinked polymer is typically cooled to room temperature, e.g., 25°C, and may be stored in a suitable container for later use. While the particulate crosslinked polymer may be stored in the liquid suspension medium, it is typically isolated from the liquid suspension medium. Isolation of the particulate crosslinked polymer may be achieved by methods that are well known in the art. For example, the particulate crosslinked polymer may be allowed to settle out of the liquid suspension medium, followed by pouring the liquid suspension medium off of the settled particulate crosslinked polymer. More typically, the particulate crosslinked polymer is isolated by means of filtration, which is further typically followed by drying of the isolated particulate polymer. The present invention is more particularly described in the following examples, which are intended to be illustrative only, since numerous modifications and variations therein will be apparent to those skilled in the art. Unless otherwise specified, all parts and all percentages are by weight . Examples A and B Preparation of Particulate Crosslinked Polymers Example A Particulate crosslinked polyurethane was prepared according to the method of the present invention from the ingredients listed in Table A. Table A Ingredients Weight (grams) Charge 1 diamine curative (a) 22.5 diamine curative (b) 8.8 surfactant (c) 0.1 Charge 2 isocyanate functional prepolymer (d) 68.5 (a) LONZACURE MCDEA diamine curative obtained from Air 10 Products and Chemicals, Inc, which describes it as methylene bis (chlorodiethylanaline) . (b) VERSALINK P-650 poly(tetramethylene glycol) diamine curative obtained from Air Products and Chemicals, Inc. ±5 (c) PLURONIC F108 surfactant, obtained from BASF Corporation. (d) ARITHANE PHP-75D prepolymer, obtained from Air Products and Chemicals, Inc, which describes it as the isocyanate 20 functional reaction product of toluene diisocyanate and poly(tetrahydrofuran) . Charge 1 was added to an open container and placed on a hot plate set at a temperature of 90°C until the contents 25 of the container became molten. Charge 2 was then added to the container while still on the hot plate, and the contents were thoroughly mixed with a motor driven impeller until uniform. The contents of the container were then poured slowly into 400 grams of 80°C deionized water, with 30 concurrently vigorous stirring of the deionized water. Upon completion of the addition of the contents of the container, vigorous mixing of the deionized water was continued for an additional 10 minutes, followed by isolation of the formed particulate crosslinked polyurethane by means of filtration. The isolated particulate crosslinked polyurethane was dried in a 130°C oven for 2 hours. The dried particulate material was classified using a stack of sieves having mesh sizes from the top to the bottom of the stack of: 40 mesh (420 micron sieve openings), 50 mesh (297 micron sieve openings) , 70 mesh (210 micron sieve openings) , 140 mesh (105 micron sieve openings) and 325 mesh (44 micron sieve openings) . Particulate material was collected separately from each of the sieve screens and weighed. The weights of the particulate material collected from each of the sieve screens was used to calculate the particle size distribution of the particulate crosslinked polyurethane, which is summarized in Table 1. Particulate material collected from, for example, the 70 mesh screen was determined to have a particle size range of from about 210 to 297 microns, based on the sieve opening sizes of the 50 and 70 mesh sieves. The dried particulate crosslinked polyurethane was free flowing, and the individual particles were observed visually to be substantially spherical . Example B Particulate crosslinked polyepoxide was prepared according to the method of the present invention from the ingredients listed in Table B. Table B Ingredients Weight (grams) Charge 1 polyamine curative (e) 40.9 surfactant (c) 1.0 isopropanol solvent 15.8 solvent (f) 11.9 Charge 2 epoxy resin (g) 58.1 (e) VERSAMID 253 polyamine-polyamide curative, obtained from Cognis Corp. (f) DOWANOL PM propylene glycol monomethyl ether, obtained from Dow Chemical. (g) EPON 880 epoxy resin, obtained from Shell Chemical. Charge 1 was added to an open container and stirred with a motor driven impeller at ambient room temperature (about 25°C) until all of the components were visually observed to have dissolved and a uniform mixture was formed. Charge 2 was then added to the container, and the contents were further mixed until uniform. The contents of the container were then poured slowly into 300 grams of 80°C deionized water, with concurrently vigorous stirring of the deionized water. Upon completion of the addition of the contents of the container, vigorous mixing of the deionized water was continued for an additional 2 hours, followed by isolation of the formed particulate crosslinked polyepoxide by means of filtration. The isolated particulate crosslinked polyepoxide was dried overnight in a 100°C oven. The dried particulate crosslinked polyepoxide was classified using a stack of sieves as described in Example A. Particulate crosslinked polyepoxide was collected separately from each of the sieve screens . The weights of the particulate material collected from each of the sieve screens was used to calculate the particle size distribution of the particulate crosslinked polyepoxide, which is summarized in Table 1. The dried particulate crosslinked polyepoxide was free flowing, and the individual particles were observed visually to be substantially spherical. Table 1 Particulate Crosslinked Polymer Particle Size Distribution Data (h) Mesh Estimated Example A Example B Designation of Particle Size Percent weight Percent weight Sieve Screen Range (j ) From Each Sieve From Each Sieve (i) Screen (k) Screen (k) 40 greater than 3.1 1.5 420 microns 50 297-420 microns 3.9 5.2 70 210-297 microns 10.5 31.9 140 105-210 microns 36.6 57.8 325 44-105 microns 45.9 3.6 Pan (1) less than 44 0 0 microns (h) The crosslinked particulate polymers of each of Examples A and B were classified using a stack of sieves as described in Example A. Particulate crosslinked polymer was collected from each of the sieve screens and weighed. (i) The designation of the mesh screen, as provided by the manufacturer. As described previously herein, for example, a 40 mesh screen has sieve openings of 420 microns. (j) The estimated particle size range of the particulate crosslinked polymer removed from a mesh screen, based on the sieve openings of the screen from which the material was collected and the sieve screen directly above. For example, particulate crosslinked polymer collected from a 40 mesh screen was estimated to have a particle size of greater than 420 microns; and particulate crosslinked polymer collected from the 50 mesh screen was estimated to have a particle size rage of from 297 to 420 microns, more specifically from greater than 297 microns to 420 microns. (k) The weight of particulate crosslinked polymer collected from each sieve screen and the total weight of particulate crosslinked polymer collected from all the sieve screens was used to calculate the percent weight of particulate crosslinked polymer collected from each sieve screen. (1) The designation "Pan" refers to the pan beneath the 325 mesh screen, upon which particulate crosslinked polymer was not observed to accumulate during the classification of the particulate crosslinked polymers of Examples A and B. The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention except insofar as and to the extent that they are included in the accompanying claims .

Claims: We claim: 1. A method of preparing particulate crosslinked polymer comprising: (a) preparing an organic phase comprising, 5 (i) a first component comprising, at least one of a polyisocyanate having at least two isocyanate groups and a polyepoxide having at least two epoxide groups, and optionally a capped polyisocyanate having 10 at least two capped isocyanate groups; and (ii) a second component comprising an active hydrogen functional reactant having at least two active hydrogen groups that are reactive with the isocyanate groups and epoxide groups of said first component, said active '15 hydrogen functional reactant comprising a polyamine having at least two functional groups selected from primary amine, secondary amine and combinations thereof; (b) forming a suspension of droplets of said organic phase in a liquid suspension medium, said organic 20 phase being substantially insoluble in said liquid suspension medium; and (c) polymerizing said suspension of droplets of said organic phase in said liquid suspension medium, thereby forming particulate crosslinked polymer. 25 2. The method of claim 1 wherein said liquid suspension medium is an aqueous suspension medium. 3. The method of claim 2 wherein said aqueous 30 suspension medium is substantially free of polyamines. 4. The method of claim 1 wherein said polyisocyanate of said first component is selected from aliphatic polyisocyanate monomers, aromatic polyisocyanate monomers, polyurethane prepolymers having at least two isocyanate groups and mixtures thereof; said polyepoxide of said first reactant is selected from aliphatic polyepoxide 5 monomers, aromatic polyepoxide monomers, polyepoxide prepolymers having at least two epoxide groups, and mixtures thereof; and said optional capped polyisocyanate is selected from capped aliphatic polyisocyanate monomers, capped aromatic polyisocyanate monomers, capped polyurethane prepolymers 10 having at least two capped isocyanate groups and mixtures thereof . 5. The method of claim 4 wherein said polyisocyanate is selected from polyurethane prepolymers '15 having at least two isocyanate groups; said polyepoxide is selected from aromatic polyepoxide monomers; and said optional capped polyisocyanate is selected from capped aliphatic polyisocyanate monomers, capped aromatic polyisocyanate monomers and mixtures thereof . 20 6. The method of claim 1 wherein said polyisocyanate, said polyepoxide and said optional capped polyisocyanate of said first component are each substantially free of ionic groups. 25 7. The method of claim 1 wherein said first component (a) (i) contains capped isocyanate groups in an amount of less than 50 mole percent, based on the total molar equivalents of isocyanate groups of said polyisocyanate, 30 epoxide groups of said polyepoxide and capped isocyanate groups of said capped polyisocyanate. 8. The method of claim 7 wherein said capped polyisocyanate is present in said first component (a) (i) , and the polymerization of the suspension of droplets of said organic phase in said liquid suspension medium in step (c) is performed at a temperature that is less than the de-capping temperature of said capped polyisocyanate. 9. The method of claim 1 wherein said polyamine is selected from aliphatic polyamine monomers, aromatic polyamine monomers, polyamine prepolymers and mixtures thereof. 10. The method of claim 1 wherein said active hydrogen functional reactant of said second component (a) (ii) further comprises at least one of a polyol having at least two hydroxyl groups, and a hydroxyl-amine reactant having at least one hydroxyl group and at least one amine group selected from primary amine, secondary amine and combinations thereof. 11. The method of claim 1 wherein at least one of said organic phase and said liquid suspension medium comprises an organic surfactant selected from anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and mixtures thereof . 12. The method of claim 11 wherein said organic phase comprises a nonionic surfactant. 13. The method of claim 1 wherein said particulate crosslinked polymer has a particle size of from 20 microns to 2 millimeters. 14. The method of claim 1 wherein said organic phase further comprises an abrasive particulate material selected from aluminum oxide, silicon carbide, titanium diboride, boron carbide, silicon nitride, tungsten carbide, titanium carbide, diamond, boron nitride, garnet, fused alumina zirconia, silica, iron oxide, cromia, ceria, zirconia, titania, tin oxide, manganese oxide and mixtures thereof. 15. The method of claim 1 wherein the molar equivalents ratio of the sum of the molar equivalents of isocyanate, epoxide and capped isocyanate groups of said first component (a) (i) to the sum of the molar equivalents of active hydrogen groups of said second component (a) (ii) is from 0.5 : 1.0 to 1.5 : 1.0. 16. The method of claim 1 wherein said method further comprises isolating the particulate crosslinked polymer from said liquid suspension medium. 17. A method of preparing particulate crosslinked polymer comprising: (a) preparing an organic phase comprising, (i) a first component comprising, at least one of a polyisocyanate having at least two isocyanate groups and a polyepoxide having at least two epoxide groups, and optionally a capped polyisocyanate having at least two capped isocyanate groups; and (ii) a second component comprising an active hydrogen functional reactant having at least two active hydrogen groups that are reactive with the isocyanate groups and epoxide groups of said first component, said active hydrogen functional reactant comprising a polyamine having at least two functional groups selected from primary amine, secondary amine and combinations thereof; (b) forming a suspension of droplets of said organic phase in an aqueous suspension medium; said organic phase being substantially insoluble in said aqueous suspension medium; and 5 (c) polymerizing said suspension of droplets of said organic phase in said aqueous suspension medium, thereby forming particulate crosslinked polymer; wherein at least one of said organic phase and said aqueous suspension medium comprises an organic surfactant selected 10 from anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and mixtures thereof. 18. The method of claim 17 wherein said aqueous suspension medium is substantially free of polyamines; said '15 organic phase comprises a nonionic surfactant; and said polyisocyanate, said polyepoxide and said optional capped polyisocyanate of said first component (a) (i) are each substantially free of ionic groups . 20 19. The method of claim 18 wherein said polyisocyanate is selected from polyurethane prepolymers having at least two isocyanate groups and mixtures thereof; said polyepoxide is selected from aromatic polyepoxide monomers; and said optional capped polyisocyanate is selected 25 from capped aliphatic polyisocyanate monomers, capped aromatic polyisocyanate monomers and mixtures thereof. 20. The method of claim 19 wherein said polyamine is selected from aliphatic polyamine monomers, aromatic 30 polyamine monomers, polyamine prepolymers and mixtures thereof . 21. The method of claim 18 wherein said first component comprises polyurethane prepolymers having at least two isocyanate groups, and said polyamine is selected from polyamines represented by the following general formula, wherein R 3 and R 4 are each independently C 1 -C 3 alkyl, and R 5 is selected from hydrogen and halogen. 22. The method of claim 18 wherein said first component comprises aromatic polyepoxide monomers, and said polyamine is selected from polyamides having at least two amine groups. 23. The method of claim 18 wherein said active hydrogen functional reactant of said second component (a) (ii) further comprises at least one of a polyol having at least two hydroxyl groups, and a hydroxy1-amine reactant having at least one hydroxyl group and at least one amine group selected from primary amine, secondary amine and combinations thereof. 24. The method of claim 18 wherein said particulate crosslinked polymer has a particle size of from 20 microns to 2 millimeters. 25. The method of claim 18 wherein said method further comprises isolating the particulate crosslinked polymer from said aqueous suspension medium.

Inventors: SWISHER ROBERT G, WANG ALAN E, SWISHER, ROBERT, G., WANG, ALAN, E.
Applicants: PPG IND OHIO INC, PPG INDUSTRIES OHIO, INC.
Application year: 2001
Main classification: C08G18
IPC codes: C08G18, C08G59