WO2013002974A1 - Polyurethanes made using substituted bicyclic amidine catalysts - Google Patents

Abstract

Cast polyurethane elastomers are made using certain substituted bicyclic amidine catalysts. These catalysts provide a desirably long open time followed by rapid cure rates. Elastomers made in accordance with the process have physical properties and surface appearance that are comparable to elastomers made using an organomercury catalyst. The substituted bicyclic amidine catalysts therefore are viable replacements for organomercury catalysts, and have the advantage of being more environmentally friendly.

Description

POLYURETHANES MADE USING SUBSTITUTED BICYCLIC AMIDINE

CATALYSTS

This application claims priority from United States Provisional Patent Application No. 61/501,838, filed 28 June 2011.

This invention relates to processes for making cast polyurethane elastomers.

Many solid or microcellular polyurethane elastomers are manufactured using cast elastomer methods. These elastomers are made by reacting a high equivalent weight polyol and a chain extender material with a polyisocyanate compound. Because it is usually intended to form a highly flexible, rubbery product, the amount of chain extender in the formulation is usually somewhat small. The elastomer is produced by mixing the starting materials and transferring the mixture into a mold where it is cured, usually with application of heat. Some or all of the high equivalent weight polyol may be pre-reacted with the polyisocyanate in a preliminary step to form an isocyanate- terminated prepolymer or quasi-prepolymer. Such a prepolymer is then caused to react with the chain extender and optionally a remaining portion of the high equivalent weight polyol during the molding step.

Open time is very important in cast elastomer processes. Once the starting materials are mixed, they must remain in an uncured, flowable state for several minutes to allow the mixture to be degassed (in most cases) and transferred into the mold. If the reaction proceeds too quickly, the mold may not fill completely, and/or flow lines or other defects appear in the parts, which can lead to high reject rates.

Once the mold is filled, however, a rapid cure is wanted to reduce cycle times and maximize mold usage.

Organomercury compounds are often the catalysts of choice for cast elastomer processes. Organomercury catalysts offer an important combination of attributes that have been extremely difficult to duplicate with other catalyst systems. These organomercury catalysts provide a very desirable curing profile in which a long open time is followed by a rapid cure. A second attribute of organomercury catalysts is that they produce polyurethane elastomers that have very desirable physical and mechanical properties.

A third attribute of organomercury catalysts relates to the appearance of the finished polyurethane product. Organomercury catalysts tend to produce elastomers that have a highly uniform surface appearance. When many other catalyst systems are used in place of the organomercury catalysts, the resulting elastomers exhibit a surface appearance characterized by the presence of discrete transparent regions together with discrete opaque regions. Such an appearance is often cosmetically unacceptable to the consumer, again resulting in a high reject rate.

Mercury catalysts are undesirable from an environmental and worker exposure standpoint, and in many jurisdictions these are being phased out. Therefore, a replacement catalyst system is needed. Such a replacement catalyst system ideally would provide the attributes of organomercury catalysts, including a desirable cure profile, good property development in the product, and good surface appearance.

This invention is a process for preparing a polyurethane, comprising curing at least one polyisocyanate with at least one isocyanate-reactive compound in the presence of a substituted bicyclic amidine catalyst, wherein the substituted bicyclic amidine catalyst is substituted on at least one ring carbon with a substituent that contains at least one non-protic nucleophilic group.

In certain embodiments, the invention is a process for preparing a cast polyurethane elastomer, comprising mixing a polyisocyanate with a chain extender and/or mixture of chain extender and at least one polyol having a hydroxyl equivalent weight of at least 250, and curing the mixture in the presence of a substituted bicyclic amidine catalyst in a mold, wherein the substituted bicyclic amidine catalyst is substituted on at least one ring carbon atom with a substituent that contains at least one non-protic nucleophilic group.

These substituted bicyclic amidine catalysts provide the desirable attributes of organomercury catalysts, including a long open time followed by a rapid cure, good physical properties and good surface appearance in the elastomer product.

The nucleophilic group is preferably a tertiary amine group or a tertiary phosphine group. The nucleophilic group is most preferably a tertiary amine. By "non- protic", it is meant that the nucleophilic group does not contain a hydrogen atom bonded to a heteroatom, such as amine or phosphine hydrogens. The substituent as a whole should be devoid of hydrogen atoms that are reactive towards hydroxyl groups and isocyanate groups.

The substituted bicyclic amidine catalyst can be represented by Structure I as follows:

wherein each A is a group bonded to a ring carbon atom and contains a non-protic nucleophilic group. In structure I, m and n are each independently zero or a positive integer, provided that m+n equals at least one. m+n preferably equals 1 or 2 and more preferably equals 1. m is most preferably zero and n is most preferably 1. p is zero or a positive number, preferably 1, 2 or 3 and more preferably 3. The A group as a whole should be devoid of hydrogen atoms that are reactive towards hydroxyl groups and isocyanate groups.

It is preferred that an A group is bonded to the ring carbon atom alpha to the bridge carbon atom (the bridge carbon atom is designated by "b" in structure I).

The nucleophilic group contained in the A substituent(s) may be, for example, a tertiary phosphine or tertiary amino group, with substituents containing a tertiary amino group being preferred. The nitrogen atom of an amino group or phosphorus atom of a phosphine group may be bonded directly to a carbon atom of the ring structure. Alternatively, the amine nitrogen or phosphine phosphorus atom may be indirectly bonded to a carbon atom of the ring structure through some bridging group which may be, for example, alkylene or other hydrocarbyl group. The A group may take the form -(CH2)xN(R)2 or -(CH2)_XP(R)2, wherein x is from 0 to 6, preferably 0, 1 or 2, more preferably 0, and each R is independently an alkyl group, inertly substituted alkyl group, phenyl group, or inertly substituted phenyl group. When x is 0, a tertiary amino or phosphine group is bonded directly to a ring carbon. An "inert" substituent is one that is not reactive towards hydroxyl groups or isocyanate groups. The R groups preferably each contain from 1 to 16, more preferably from 1 to 8 carbon atoms. Most preferred R groups are alkyl groups that contain from 2 to 4 carbon atoms. The two R groups may also form a ring structure that includes the nitrogen or phosphorus atom to which they are attached. Such a ring structure may include one or more heteroatoms such as ether oxygen atoms or nitrogen atoms, but as before such a ring structure should be devoid of groups that are reactive towards hydroxyl groups or isocyanate groups. In some embodiments, the substituted bicyclic amidine catalysts have the structure II, in which x, p and R are as defined before:

In structure II, the -(CH2)x-NR2 group preferably is bonded to the carbon atom alpha to the bridge carbon (the bridge carbon being indicated as "b" in structure II).

An especially preferred substituted bicyclic amidine catalyst has a structure according to Structure III:

(_ΙΠ)

in which x and R are as defined before.

A specific substituted bicyclic amidine catalyst is 6-(dibutylamino)- l,8- diazabicyclo[5.4.0]undec-7-ene, where the butyl groups may be n-butyl, sec-butyl or t- butyl groups.

The substituted bicyclic amidine catalyst may be acid-blocked by combining the catalyst with a Bronsted acid (i.e., an acid that donates a proton). Suitable Bronsted acids are carboxylic acids, sulfonic acids, phosphonic and phosphinic acids, a phenolic compound and the like. The carboxylic acid may be, for example, an aliphatic carboxylic acid having from one to 18 carbon atoms, or a substituted or unsubstituted benzoic acid. The acid may also, for example, have unsaturation within the aliphatic chain or contain pendant heteroatoms on the aliphatic chain. Formic acid, acetic acid, 2-ethyl hexanoic acid, benzoic acid, acrylic acid, ricinoleic acid and the like are suitable carboxylic acids. Phenol or substituted phenol compounds are also useful blocking agents. Blocking agents are typically used in an amount from 0.01 to 5, preferably from 0.2 to 1, mole of blocking agent per equivalent of amine nitrogens on the substituted bicyclic amidine catalyst.

The substituted bicyclic amidine catalyst is useful for making polyurethanes in a reaction of at least one polyisocyanate with at least one isocyanate-reactive compound. A polyurethane-forming process of interest is a cast elastomer process. A cast elastomer is formed by mixing a polyisocyanate, typically in the form of a prepolymer or quasi- prepolymer, with a chain extender and/or mixture of chain extender and at least one polyol having a hydroxyl equivalent weight of at least 250, preferably at least 500, and allowing the mixture to cure in the presence of the substituted bicyclic amidine catalyst in a mold. A degassing step may be interposed between the mixing and mold-filling steps if a non-cellular part is to be produced. Conversely, a frothing step may be performed on the reaction mixture to whip air or other gas into it before the mixture is transferred into the mold. Suitable frothing methods are described in U.S. Pat. Nos. 3,755,212; 3,849,156 and 3,821,130.

The molding conditions are not generally considered to be critical provided that the mixture cures adequately. The components or the mixture may be preheated before being introduced into the mold. A mixture of polyol and chain extender may be preheated, such as to a temperature of 40 to 70°C, prior to combining them with the polyisocyanate. The temperature of the reaction mixture, after the chain extender or polyol/chain extender mixture is combined with the polyisocyanate, should be at least 40 °C.

The mold may be preheated. It is usually necessary to cure the mixture at elevated temperature; for that reason the filled mold is generally heated in an oven or other suitable apparatus. Mold temperatures may be from 40 to 90°C. Curing times can range from as little as one minute to 60 minutes or more. After curing at least to the extent that the resulting elastomer can be removed from the mold without permanent damage or permanent deformation, the part can be demolded. If necessary, the part can be post-cured at an elevated temperature to complete the cure.

Cast elastomer processes often need a significant open time to allow for mold filling, after which a rapid cure is needed.

The organic polyisocyanate used to make the cast elastomer contains an average of at least 1.5 and preferably at least 2.0 isocyanate groups per molecule. It may contain as many as 8 isocyanate groups per molecule, but typically contains no more than about 4 isocyanate groups per molecule. The organic polyisocyanate may contain as little as 0.5% by weight isocyanate groups, or may contain as much as about 50% by weight isocyanate groups. The isocyanate groups may be bonded to aromatic, aliphatic or cycloaliphatic carbon atoms. Examples of polyisocyanates include m-phenylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylene-1,6- diisocyanate, tetramethylene-l,4-diisocyanate, cyclohexane-l,4-diisocyanate, hexahydrotoluene diisocyanate, naphthylene-l,5-diisocyanate, methoxyphenyl-2,4- diisocyanate, diphenylmethane-4,4'-diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'- dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-dimethyl-4-4'-biphenyl diisocyanate, 3,3'- dimethyldiphenyl methane-4,4'-diisocyanate, 4,4',4"-triphenyl methane triisocyanate, a polymethylene polyphenylisocyanate (PMDI), tolylene-2,4,6-triisocyanate and 4,4'- dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate. Preferably the polyisocyanate is diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, PMDI, tolylene- 2,4-diisocyanate, toluene-2,6-diisocyanate or mixtures thereof. Diphenylmethane-4,4'- diisocyanate, diphenylmethane-2,4'-diisocyanate and mixtures thereof are generically referred to as MDI, and all can be used. Toluene-2,4-diisocyanate, toluene-2,6- diisocyanate and mixtures thereof are generically referred to as TDI, and all can be used.

Any of the foregoing isocyanates can be modified to include urethane, urea, biuret, carbodiimide, allophonate, uretonimine, isocyanurate, amide or like linkages. Examples of modified isocyanates of these types include various urethane group and/or urea group-containing prepolymers, some of which are described in more detail below, so-called "liquid MDI" products, and the like.

It is generally preferable to use urethane-modified polyisocyanates (prepolymers) or mixtures of urethane-modified polyisocyanates with monomeric polyisocyanates (quasi-prepolymers) in the cast elastomer process. Such a prepolymer or quasi- prepolymer is prepared by reacting a polyisocyanate with at least one polyol that has a molecular weight of at least 400, preferably at least 800. The polyol(s) may have a molecular weight as high as about 12,000. A preferred molecular weight is up to 4000 and a more preferred molecular weight is up to 2000. The polyol(s) used in making the quasi-prepolymer preferably have an average of from 1.8 to 3.0, preferably from 1.8 to 2.5 and still more preferably about 1.9 to 2.2 hydroxyl groups per molecule.

A low (up to 300) molecular weight diol may be used to make the quasi- prepolymer, in addition to the foregoing ingredients. This low molecular weight diol preferably has a molecular weight of from 62 to 200. Examples of the low molecular weight diol include ethane diol, 1,2- or 1,3-propane diol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, cyclohexanedimethanol, and the like. This material is usually used in small amounts, if at all. If used in making the quasi- prepolymer, from 1 up to 25 parts by weight thereof may be used per 100 parts by weight of the poly(propylene oxide) homopolymer.

The polyisocyanate used to make the prepolymer or quasi-prepolymer preferably contains an average of from 1.8 to 3.5, more preferably from 1.8 to 2.5 isocyanate groups per molecule and has an isocyanate content of at least 25% by weight. Aliphatic polyisocyanates are preferred when light stability is needed. In other cases, TDI, MDI or an MDI derivative is often useful. MDI may be the 2,2'-, 2,4'- or 4,4'-isomer, with the 4,4'- isomer, or mixtures of the 4,4'- and 2,4'- isomer, being preferred. "Derivatives" of MDI are MDI that has been modified to include urea, biuret, carbodiimide, uretonimine or like linkages, and which has an isocyanate content of at least 25% by weight.

About two equivalents of the polyisocyanate are used per equivalent of the diol(s) to make a prepolymer. More than two equivalents of the polyisocyanate, typically at least 2.2 equivalents, are used per equivalent of the diol(s) used to make a quasi- prepolymer. The resulting product includes molecules formed by capping the diol(s) with the polyisocyanate and, in the case of a quasi-prepolymer, some quantity of unreacted starting polyisocyanate. The prepolymer or quasi-prepolymer should have an isocyanate content of at least 4%, and preferably at least 8% by weight. The isocyanate content should not exceed 20% and preferably does not exceed 18% by weight. The prepolymer or quasi-prepolymer should contain an average of from about 1.9 to about 2.5, preferably from 1.9 to 2.3 and more preferably from 2.0 to 2.2 isocyanate groups per molecule.

The prepolymer or quasi-prepolymer is cured with a chain extender and/or mixture of chain extender and at least one high equivalent weight polyol. The chain extender may in some embodiments constitute from 2 to 25%, preferably from 4 to 20%, of the combined weight of the combined weight of chain extender(s) and polyols having a hydroxyl equivalent weight of at least 250.

Chain extenders for the purposes of this invention are materials having exactly two isocyanate-reactive groups per molecule and an equivalent weight per isocyanate- reactive group of up to 249, especially 31 to 125. The isocyanate reactive groups are preferably hydroxyl, primary aliphatic or aromatic amine or secondary aliphatic or aromatic amine groups. Representative chain extenders include ethylene glycol, (Methylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4- butane diol, 1,6-hexane diol, neopentyl glycol, dipropylene glycol, tripropylene glycol, poly(propylene oxide) diols of up to 249 equivalent weight, cyclohexanedimethanol, poly(ethylene oxide) diols of up to 249 equivalent weight, aminated poly(propylene oxide) diols of up to 249 equivalent weight, ethylene diamine, phenylene diamine, diphenylmethane diamine, bis(3-chloro-4-aminophenyl)methane and 2,4-diamino-3,5- diethyl toluene. A mixture of chain extenders may be used.

The high equivalent weight polyol has a hydroxyl equivalent weight of at least 250, preferably at least 500. The equivalent weights of the high equivalent weight polyol(s) in this application may be up to 3000, preferably up to 2000. The average nominal functionality of the high equivalent weight polyol(s) is preferably from about 2 to about 3, more preferably from about 2 to about 2.3.

Various types of high equivalent weight isocyanate-reactive materials are useful, including hydroxyl-functional acrylate polymers and copolymers, hydroxyl-functional polybutadiene polymers, polyether polyols, polyester polyols, amine-terminated polyethers, and various polyols that are based on vegetable oils or animal fats.

Polyether polyols include, for example, polymers of propylene oxide, ethylene oxide, 1,2-butylene oxide, tetramethylene oxide, block and/or random copolymers thereof, and the like. Of particular interest for many high- volume applications are poly(propylene oxide) homopolymers, random copolymers of propylene oxide and ethylene oxide in which the oxyethylene content is, for example, from about 1 to about 30% by weight, ethylene oxide-capped poly(propylene oxide) polymers which contain 70 to 100% primary hydroxyl groups and ethylene oxide-capped random copolymers of propylene oxide and ethylene oxide in which the oxyethylene content is about 1 to about 30% by weight. The polyether polyols may contain low terminal unsaturation (for example, less than 0.02 meq/g or less than 0.01 meq/g), such as those made using so- called double metal cyanide (DMC) catalysts, as described for example in US Patent Nos. 3,278,457, 3,278,458, 3,278,459, 3,404,109, 3,427,256, 3,427,334, 3,427,335, 5,470,813 and 5,627,120. Polymer polyols of various sorts may be used as well. Polymer polyols include dispersions of polymer particles, such as polyurea, polyurethane-urea, polystyrene, polyacrylonitrile and polystyrene-co-acrylonitrile polymer particles, in a polyol, typically a polyether polyol. Suitable polymer polyols are described in US Patent Nos. 4,581,418 and 4,574,137. Useful high equivalent weight isocyanate-reactive polyesters include reaction products of polyols, preferably diols, with polycarboxylic acids or their anhydrides, preferably dicarboxylic acids or dicarboxylic acid anhydrides. The polycarboxylic acids or anhydrides may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may be substituted, such as with halogen atoms. The polycarboxylic acids may be unsaturated. Examples of these polycarboxylic acids include succinic acid, adipic acid, terephthalic acid, isophthalic acid, trimellitic anhydride, phthalic anhydride, maleic acid, maleic acid anhydride and fumaric acid. The polyols used in making the polyester polyols preferably have an equivalent weight of 150 or less and include ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butane diol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, cyclohexane dimethanol, 2-methyl-l,3-propane diol, glycerine, trimethylol propane, 1,2,6-hexane triol, 1,2,4-butane triol, trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, methyl glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, dibutylene glycol and the like. Polycaprolactone polyols are useful. Polymer polyols of various sorts may be used as well.

High equivalent weight isocyanate-reactive materials based on vegetable oils and/or animal fats include, for example, castor oil, hydroxymethyl group-containing polyols as described in WO 2004/096882 and WO 2004/096883, amide group-containing polyols as described in WO 2007/019063, hydroxyl ester-substituted fatty acid esters as described in WO 2007/019051, "blown" soybean oils as described in US Published Patent Applications 2002/0121328, 2002/0119321 and 2002/0090488, oligomerized vegetable oil or animal fat as described in WO 06/116456, hydroxyl-containing cellulose-lignin materials, hydroxyl-containing modified starches as well as the various types of renewable-resource polyols described in Ionescu, Chemistry and Technology of Polyols for Poly ur ethanes, Rapra Publishers 2005.

The chain extender or chain extender/high equivalent weight polyol mixture may also contain one or more crosslinkers. A crosslinker is a polyol or aminoalcohol that contains at least three isocyanate-reactive groups per molecule and has a molecular weight per isocyanate-reactive group of up to 249, preferably from about 30 to about 200. These materials may have up to 8 or more isocyanate-reactive groups per molecule. They most typically include no more than one primary or secondary amino group, and two or more primary or secondary hydroxyl groups. Examples of crosslinkers include diethanolamine, triethanolamine, di- or tri(isopropanol) amine, glycerine, trimethylol propane, pentaerythritol, various polyester polyols that have at least three hydroxyl groups per molecule and an equivalent weight of up to 249, and various polyether polyols that have at least three hydroxyl groups per molecule and an equivalent weight of up to 249. The low equivalent weight polyether polyols include, for example, ethoxylates and/or propoxylates of an aromatic diamine such as toluene diamine and phenylene diamine, an aliphatic diamine such as ethylene diamine, cyclohexanedimethanol and the like, or of a polyol having at least three hydroxyl groups, such as, for example, glycerine, sucrose, sorbitol, pentaerythritol, trimethylolpropane, trimethylolethane and the like.

To prepare the elastomer, the starting materials are generally mixed in ratios that produce an isocyanate index of at least 70 to about 130. A preferred isocyanate index is from 80 to 120, and a more preferred index is from 90 to 110.

Enough of the substituted bicyclic amidine catalyst is present to provide a commercially acceptable polymerization rate. A typical amount is from 0.001 to 5 parts per 100 parts of isocyanate-reactive materials present in the polymerization process, although amounts may vary depending on the particular polymerization process and the particular reactants that are present. A preferred amount is from 0.005 to 0.5 parts per 100 parts by weight of isocyanate-reactive materials.

The substituted bicyclic amidine catalyst may be blended into the chain extender or chain extender/high equivalent weight polyol mixture, into the polyisocyanate, or blended in as a separate stream.

A wide variety of other materials may be present in the reaction mixture. Among these materials are surfactants; blowing agents; cell openers; fillers; pigments and/or colorants; desiccants, reinforcing agents; biocides; preservatives; antioxidants; flame retardants; and the like.

One or more surfactants may be present, especially when some blowing agent is incorporated into the formulation. Examples of suitable surfactants include alkali metal and amine salts of fatty acids, such as sodium oleate, sodium stearate, diethanolamine oleate, diethanolamine stearate, diethanolamine ricinoleate, and the like; alkali metal and amine salts of sulfonic acids such as dodecylbenzenesulfonic acid and dinaphthylmethanedisulfonic acid; ricinoleic acid; siloxane-oxyalkylene polymers or copolymers and other organopolysiloxanes; oxyethylated alkylphenols (such as Tergitol NP9 and Triton X100, from The Dow Chemical Company); oxyethylated fatty alcohols such as Tergitol 15-S-9, from The Dow Chemical Company; paraffin oils; castor oil; ricinoleic acid esters; turkey red oil; peanut oil; paraffins; fatty alcohols; dimethyl polysiloxanes and oligomeric acrylates with polyoxyalkylene and fluoroalkane side groups. These surfactants are generally used in amounts of 0.01 to 1 parts by weight based on 100 parts by weight of the polyols.

A blowing agent may be present if it is desired to form a cellular or microcellular elastomer. Water, which is an isocyanate-reactive material, also functions as a blowing agent if present in sufficient quantities, because it reacts with isocyanate groups to liberate carbon dioxide, which then serves a blowing gas. However, other chemical and/or physical blowing agents can be used instead of or in addition to water. Chemical blowing agents react under the conditions of the elastomer-forming step to produce a gas, which is typically carbon dioxide or nitrogen. Physical blowing agents volatilize under the conditions of the elastomer-forming step. Suitable physical blowing agents include various low-boiling chlorofluorocarbons, fluorocarbons, hydrocarbons and the like. Fluorocarbons and hydrocarbons having low or zero global warming and ozone- depletion potentials are preferred among the physical blowing agents.

The amount of blowing agent, if any, or frothing gas, is generally selected to produce an elastomer having a density of at least 500 kg/m³.

One or more fillers may also be present. Suitable fillers include particulate inorganic and organic materials that are stable and do not melt at the temperatures encountered during the polyurethane-forming reaction. Examples of suitable fillers include kaolin, montmorillonite, calcium carbonate, wollastonite, talc, high-melting thermoplastics, glass, fly ash, carbon black, titanium dioxide, iron oxide, chromium oxide, azo/diazo dyes, phthalocyanines, dioxazines, colloidal silica and the like. The filler may impart thixotropic properties. Fumed silica is an example of such a filler. When used, fillers advantageously constitute from about 0.5 to about 30%, especially about 0.5 to about 10%, by weight of the polymer.

Some of the foregoing fillers may also impart color to the polymer. Examples of these include titanium dioxide, iron oxide, chromium oxide and carbon black. Other colorants such as azo/diazo dyes, phthalocyanines and dioxazines also can be used.

Reinforcing agents may also be present. The reinforcing agents take the form of particles and/or fibers that have an aspect ratio (ratio of longest dimension to shortest dimension) of at least 3, preferably at least 10. Examples of reinforcing agents include mica flakes, fiber glass, carbon fibers, boron or other ceramic fibers, metal fibers, flaked glass and the like. Reinforcing agents may be formed into mats or other preformed masses. It is also possible to include one or more catalysts, in addition to the substituted bicyclic amidine catalyst described before. Suitable such additional catalysts include, for example:

i) a tertiary amine compound, such as trimethylamine, triethylamine, N- methylmorpholine, N-ethylmorpholine, Ν,Ν-dimethylbenzylamine, N,N- dimethylethanolamine, Ν,Ν,Ν',Ν'-tetramethyl- 1,4-butanediamine, N,N- dimethylpiperazine, l,4-diazobicyclo-2,2,2-octane, bis(dimethylaminoethyl)ether, bis(2- dimethylaminoethyl) ether, morpholine,4,4'-(oxydi-2, 1- ethane diyl)bis, triethylenediamine, pentamethyl diethylene triamine, dimethyl cyclohexyl amine, N- cetyl Ν,Ν-dimethyl amine, N-coco-morpholine, Ν,Ν-dimethyl aminomethyl N-methyl ethanol amine, N, N, N'-trimethyl-N'-hydroxyethyl bis(aminoethyl) ether, N,N-bis(3- dimethylaminopropyl)N-isopropanolamine, (Ν,Ν-dimethyl) amino-ethoxy ethanol, N, N, N', N'-tetramethyl hexane diamine, l,8-diazabicyclo-5,4,0-undecene-7, N,N- dimorpholinodiethyl ether, N-methyl imidazole, dimethyl aminopropyl dipropanolamine, bis(dimethylaminopropyl)amino-2-propanol, tetramethylamino bis (propylamine), (dimethyl(aminoethoxyethyl))((dimethyl amine)ethyl)ether, tris(dimethylamino propyl) amine, dicyclohexyl methyl amine, bis(N,N-dimethyl-3-aminopropyl) amine, 1,2- ethylene piperidine and methyl-hydroxyethyl piperazine;

ii) a tertiary phosphine such as a trialkylphosphine or dialkylbenzylphosphine; ii) chelates of any of various metals, such as those which can be obtained from acetylacetone, benzoylacetone, trifluoroacetyl acetone, ethyl acetoacetate and the like, with metals such as Be, Mg, Zn, Cd, Pd, Ti, Zr, Al, Sn, As, Bi, Cr, Mo, Mn, Fe, Co and Ni;

iv) an acidic metal salt of a strong acid, such as ferric chloride, stannic chloride, stannous chloride, antimony trichloride, bismuth nitrate and bismuth chloride; strong bases, such as alkali and alkaline earth metal hydroxides, alkoxides and phenoxides;

(v) an alcoholate or phenolate of various metals, such as Ti(OR)4, Sn(OR)4 and Al(OR)3, wherein R is alkyl or aryl, and the reaction products of the alcoholates with carboxylic acids, beta-diketones and 2-(N,N-dialkylamino)alcohols;

(vi) an alkaline earth metal, Bi, Pb, Sn or Al carboxylate salt; and

(vii) a tetravalent tin compound, or a tri- or pentavalent bismuth, antimony or arsenic compound. In preferred aspects, the substituted bicyclic amidine catalyst is the only catalyst present in the reaction mixture. The substituted bicyclic amidine catalyst often provides a long open time followed by a rapid cure. The physical properties of the resulting elastomer are often comparable to those obtained using conventional mercury catalysts. In addition, the elastomers usually have a good surface appearance, notably little or none of the surface inhomogeneity problem described above.

The elastomer produced in accordance with the invention will of course take the shape of the internal cavity of the mold; therefore the mold is designed to produce a part having the desired external shape and dimensions. A wide range of elastomeric parts can be produced, including gaskets, bushings, wheels, belts, and the like. However, shoe soles are an application of particular interest. The shoe sole may be, for example, a midsole, an insole, and outsole, or an integrated sole that performs two or more of these functions.

The cast elastomer may be produced at a density as low as about 500 kg/m³, by frothing the reaction mixture before curing it, or by including a blowing agent in the formulation. The cast elastomer may have a density of at least 650 kg/m³ or at least 750 kg/m³.

The following examples are provided to illustrate the invention but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

Examples

Catalyst solution A is prepared by mixing 0.5 g of 6-dibutylamino-l,8- diaza[5.4.0]bicycloundec-7-ene with 4.5 grams of diethylene glycol to form a light yellow solution.

Catalyst solution B is prepared by mixing 0.5 g of 6-dibutylamino-l,8- diazabicyclo [5.4.0] undec-7-ene with 1.25 grams of diethylene glycol to form a light yellow solution. To this is added 0.257 g of 2-ethyl-hexanoic acid.

Catalyst solution C is prepared by mixing 0.5 g of 6-dibutylamino-l,8- diazabicyclo [5.4.0] undec-7-ene with 1.0 grams of diethylene glycol to form a light yellow solution. To this is added 0.514 g of 2-ethyl-hexanoic acid.

The curing profile of Catalyst solution C is evaluated as follows: A masterbatch of 7774 parts of a 6000 molecular weight, ethylene oxide-capped poly(propylene oxide) triol, 1078 parts of 1,4-butane diol and 177 parts of a molecular sieve paste is blended in a mechanical mixer. A 66.7 g sample of this masterbatch is dispensed and to this is added 0.10 g of Catalyst solution C. After mixing, 35.19 g of an MDI prepolymer having an isocyanate equivalent weight of 160 and an isocyanate functionality of 2.1 is added and mixed in by hand for 30 seconds. The temperature of the mixture at this point is about 23°C. About 95 grams of the resulting mixture is poured into a cup and its viscosity is measured using a Brookfield rheometer equipped with an RV4 spindle at a rotation speed of 20 RPM. Measurements are made every 15 seconds as the reaction mixture cures without external heating or cooling. The time interval between data points is fixed at 15 seconds. The first data point is captured 75 seconds after the addition of the isocyanate to the polyol mixture. No increase in viscosity is seen on this test until almost 350 seconds has elapsed after the isocyanate is added to the polyol mixture. After that, an increase in viscosity is observed from less than 1000 mPa ' s to over 10,000 mPa ' s in less than 25 seconds. These results are indicative of a desirable delayed curing profile.

Elastomer Examples 1-3 are prepared from Catalyst solutions A, B and C, respectively. A 66.7 part sample of the masterbatch is dispensed into a plastic cup suitable for use on a FlakTex Speedmixer. Catalyst (in an amount as shown in Table I below) is added to the masterbatch, and the mixture is mechanically mixed. Then, 34.5 parts of a modified MDI (103 index) having an isocyanate functionality of about 2.1 is mixed in mechanically. The reaction mixture is then poured into a steel plaque mold that is sprayed with an external mold release and preheated to 80 °C. Tack-free and demold times are measured, with demold time being the amount of time necessary before the part can be demolded without damage. Following demold, the parts are postcured for 1 hour at 80 °C in a forced air oven and allowed to sit overnight at room temperature.

After cooling, tensile bars are cut from the cured elastomers, and tensile properties are measured at a stretching rate of 5 inches (12.75 cm) per minute. Tensile modulus at 100% elongation tensile strength and % elongation for these samples are as described in Table 1 below. The amount of the catalyst solution used in each case is also reported in Table 1.

For comparison, another elastomer (Comparative Sample A) is prepared in the same manner using a commercially available mercury catalyst (Thorcat 535, from Polymed). The properties of that elastomer also are as reported in Table 1. Table 1

The results in Table 1 demonstrate that the substituted bicyclic amidine catalysts produce elastomers having physical properties very comparable to those produced with a conventional organomercury catalyst (Comparative Sample A). In addition, the surface quality of all of Examples 1-3 is comparable to that of Comparative Sample A, which is a distinct advantage that is not generally realized when other catalysts are substituted for organomercury catalysts. For example, substitution of a blocked unsubstituted bicyclic amidine catalyst such as DBU into this formulation produces an elastomer having similar physical properties but very poor surface appearance.

Claims

WHAT IS CLAIMED IS:

1. A process for preparing a polyurethane, comprising curing at least one polyisocyanate with at least one isocyanate-reactive compound in the presence of a substituted bicyclic amidine catalyst, wherein the substituted bicyclic amidine catalyst is substituted on at least one ring carbon with a substituent that contains at least one non-protic nucleophilic group.

2. A process for preparing a cast polyurethane elastomer, comprising mixing a polyisocyanate with a chain extender and/or mixture of chain extender and at least one polyol having a hydroxyl equivalent weight of at least 250, and curing the mixture in the presence of a substituted bicyclic amidine catalyst in a mold, wherein the substituted bicyclic amidine catalyst is substituted on at least one ring carbon atom with a substituent that contains at least one non-protic nucleophilic group.

3. The process of claim 2 wherein the nucleophilic group is a tertiary amine group or a tertiary phosphine group.

4. The process of claim 2 wherein the nucleophilic group is a tertiary amine group.

5. The process of any preceding claim wherein the bicyclic amidine is

represented by the structure

wherein each A is a group bonded to a ring carbon atom and contains a non-protic nucleophilic group, m and n are each independently zero or a positive integer, provided that m+n equals at least one, and p is zero or a positive number.

6. The process of claim 5 wherein m is zero, n is 1 and the A group is bonded to the ring carbon atom alpha to the bridge carbon atom.

7. The process of claim 5 or 6 wherein each A group has the structure - (CH2)xN(R)2 or -(CH2)xP(R)2, wherein x is from 0 to 6 and each R is independently an alkyl group, inertly substituted alkyl group, phenyl group, or inertly substituted phenyl group, or the two R groups together with the nitrogen or phosphorus atom to which they are attached form a ring structure.

8. The process of any preceding claim wherein the substituted bicyclic amidine catalyst has the struc

wherein p is zero or a positive number, x is from 0 to 6 and each R is independently an alkyl group, inertly substituted alkyl group, phenyl group, or inertly substituted phenyl group, or the two R groups together with the nitrogen or phosphorus atom to which they are attached form a ring structure.

9. The process of claim 8 wherein the substituted bicyclic amidine catalyst is 6 (dibutylamino)-l,8-diazabicyclo[5.4.0]undec-7-ene.

10. The process of any preceding claim wherein the substituted bicyclic amidine catalyst is blocked with a Bronsted acid.