GB2334720A

GB2334720A - Method for preparing urethane prepolymer comopsitions

Info

Publication number: GB2334720A
Application number: GB9827161A
Authority: GB
Inventors: Thirumurti Narayan; Calvin T Peeler
Original assignee: BASF Corp
Current assignee: BASF Corp
Priority date: 1998-02-26
Filing date: 1998-12-10
Publication date: 1999-09-01
Also published as: GB9827161D0; CA2262131A1

Abstract

A method for producing urethane-based prepolymers, especially for use in polyurethane elastomers, comprises the steps of: (a) providing a monomeric methylene bis(phenylisocyanate) composition having at least about 65.0 weight percent of diphenylmethane 4,4' -diisocyanate based on the total weight of all isomers; and (b) introducing a polyol composition having an average molecular weight of less than about 600 to said methylene bis(phenylisocyanate) composition with mixing; wherein the resulting prepolymer has an average NCO content of between about 20.0 percent to less than about 30.0. The prepolymers provide finished products that exhibit high clarity and high gloss when polished. An added feature of the present invention is that the prepolymers are stable liquids at room temperature.

Description

METHOD FOR PREPARING URETHANE PREPOLVMCp rMpOSITIONS The present invention relates to a method for producing prepolymer compositions and, more particularly, to methods for producing prepolymers useful for the production of polyurethane elastomers. The resulting polyurethane elastomers are characterized as having a shore D durometer hardness of at least 75, good clearness, high gloss when polished and an excellent pattern.

Prepolymers useful for the production of polyurethane elastomers have been known for many years. However, the known and currently employed prepolymers suffer from many perceived disadvantages.

For example, many of the known prepolymers, which typically have a relatively high viscosity and low NCO content, require external mold heating to generate pearlized patterns. The slow reactivity of many of the known prepolymers result in sink marks occurring around the pin and also extend the demold time to unacceptably high rates, i. e., one hour or more.

Attempts to reduce the mold times have generally involved lowering the mixed viscosity by employing plasticizers. This approach however has met with the problems such as the finished product appearing dull and having poor impact strength. Other attempts focused on employing various chain extenders. However, the resulting elastomers were not clear and colorless as desired.

Still other attempts have focused on employing various polyol compositions. It was quickly discovered, however, that polyols other than clear, colorless propylene oxide capped polyol led to phased or cloudy elastomers. Further, the propylene oxide capped polyols, while fairly clear and colorless, exhibited poor green strength.

Thus, there is a need for methods of producing prepolymers which are stable at room temperature, have good green strengths and which when mixed with an appropriate resin have an outstanding pattern and balance of properties, for various end products such as pearlizing bowling balls, for example.

According to a preferred embodiment, the present invention relates to a method for producing a prepolymer which comprises the steps of: (a) providing a monomeric diphenylmethane diisocyanate composi tion having at least about 65.0 percent of diphenylmethane 4,4 (-diisocyanate based on the total weight of all isomers; and (b) introducing a polyol composition having an average molecular weight of less than about 600, to said monomeric diphenyl methane diisocyanate composition with mixing; wherein the resulting prepolymer has an average NCO content of between about 20.0 percent to less than about 30.0 per cent.

Under an alternative preferred embodiment, the present invention relates to a prepolymer having an average NCO content of at least about 24.0 weight percent and an average viscosity of less than about 250 cps at 25 C formed by reacting a monomeric diphenylmethane diisocyanate composition having at least about 65.0 weight percent of diphenylmethane 4,4'-diisocyanate based on the total weight of all isomers with a polyol composition having a weight average molecular weight of less than about 600 while mixing the same.

The prepolymers produced as a result of the foregoing methods can be used to form elastomers which can be used in the production of various commercial products including, but not limited to, the production of bowling balls.

An unique aspect of the prepolymer compositions formed by the methods of the present invention is that they have a relatively high NCO content and low viscosity which gives rise to products that have an excellent pattern and balance of properties.

Moreover, the resulting prepolymers are stable liquids at room temperature.

The elastomers of the present invention can be demolded in as little as 20 minutes generally without requiring that the external mold be heated. Still other objects and advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description and claims.

The prepolymers formed in accordance with the methods of the present invention can be used to form elastomers which in turn are useful for the production of a number of commercial products, including but not limited to, bowling ball covers, for example.

The prepolymers of the present invention are prepared by reacting a monomeric diphenylmethane diisocyanate (otherwise referred to herein as monomeric MDI) with a relatively low molecular weight polyol as will be described in greater detail below.

Under a preferred embodiment, the prepolymer, after reaction of the monomeric MDI and low molecular weight polyol will include at least about 40.0 weight percent monomeric MDI and, more preferably, between about 50.0 to about 70.0 weight percent monomeric MDI based on the total weight of the prepolymer.

Additionally, the resulting prepolymer preferably has an average viscosity of less than about 250 cps at 25 C and, more preferably, from about 50 cps to less than about 250 cps at 25 C.

The monomeric MDI composition employed to form the prepolymer will preferably include a high concentration of diphenylmethane 4,4'-diisocyanate. By a high concentration, it is meant that the monomeric MDI composition will include at least 65.0 weight percent and up to about 98.0 weight percent diphenylmethane 4,4'-diisocyanate. In addition, the monomeric MDI composition will also preferably include a limited amount of diphenylmethane 2,4'-diphenylmethane 2,4'-diisocyanate. While it is contemplated that the monomeric MDI may include up to about 35.0 weight percent diphenylmethane 2,4Z-diisocyanate, preferably the monomeric MDI composition employed will include from about 0.05 to about 10.0 weight percent diphenylmethane 2,4'-diisocyanate and still more preferably from about 0.1 to about 3.0 weight percent.

The polyol composition used to form the prepolymer of the present invention is preferably a polyether polyol having an average molecular weight of less than about 600. The polyether polyol may be produced, for example, by the base catalyzed addition of'an alkylene oxide to an initiator molecule containing an average of two or more active hydrogens, such as polyhydrin alcohol.

Examples of alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, amylene oxide, mixtures thereof, tetrahydrofuran, alkylene oxide-tetrahydrofuran mixtures, epihalohydrins, and aralkylene oxides such as styrene oxide. Suitable initiators include both aliphatics and aromatics, such as ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, glycerol, 1,1,1-trimethylolpropane, 1,1,1-trimethylolethane, 1,2,6-hexanetriol, a-methyl glucoside pentaerythritol, and sorbitol. Also included with the term"poly- hydric alcohol"are compounds derived from phenol such as 2,2-bis (4-hydroxyphenyl) propane, commonly known as Bisphenol A.

The polyoxyalkylene polyether polyols may have either primary or secondary hydroxyl groups. Included among the most highly preferred polyether polyols are polyoxethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1, 2-oxybutylene and polyoxyethylene glycols, poly-1, 4-oxybutylene and polyoxyethylene glycols, and random copolymer glycols prepared from blends of two or more alkylene oxides or by the sequential addition of two or more alkylene oxides. The polyoxyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U. S. Patent No. 1,922,459.

Polyethers which are preferred include the alkylene oxide addition products of trimethyolpropane, glycerine, propylene glycol, dipropylene glycol, and 2,2t-(4, 4t-hydroxyphenyl) propane and mixtures of diols and triols such as propylene glycol-glycerine blends. Particularly preferred are dipropylene and tripropylene glycols.

Alkylene oxides which are preferred are ethylene oxide and propylene oxide or mixtures thereof reacting with the initiator molecule to make polyoxyalkylene polyether polyols having predominately polyoxypropylene groups with from 0 to about 30.0 percent by weight polyoxyethylene groups as an end cap, a bloc, or heteric, preferably as a cap.

As noted above, the polyether polyols of the prepolymer have a number average molecular weight of less than about 600. The preferred polyether polyols have a number average molecular weight ranging from about 76 to about 400 and average functionalities of from 2.0 to 3.4, preferably about 2.4 to 3.0.

The amount of polyether polyol reacted with the monomeric MDI is an amount effective to suitably adjust the free NCO content of the prepolymer to a desired level. Preferred amounts of polyether polyol include a positive amount up to about 20.0 weight percent, based on a total of 100 parts by weight of the prepolymer. It is to be understood, however, that the present invention is not limited to this weight percent of the polyether polyol, but includes levels where the polyether polyol is present in an amount of about 25.0 weight percent or less based on the total weight of the prepolymer.

The overall free NCO content of the prepolymer is preferably about 20.0 to about 30.0 weight percent, more preferably from about 24.0 to less than 29.0 weight percent. It is also preferred that the resulting prepolymer have an average viscosity of between about 50 cps to less than about 250 cps at 25 C.

Once the prepolymer of the present invention is obtained, polyurethane elastomers can be produced by reacting the prepolymer with a suitable isocyanate reactive component. The isocyanate reactive component preferably is a polyhydroxyl compound having a functionality of 1.7 to 8, more preferably 1.7 to 4, and an average hydroxyl number of 15 to 850, more preferably 20 to 400.

Polyols having hydroxyl numbers outside this range may be used, but it is preferred that the average hydroxyl number for the total amount of polyols used fall within the range of 20 to 50.

Examples include polythioether polyols, polyester amides and polyacetals containing hydroxyl groups, aliphatic polycarbonates containing hydroxyl groups, amine terminated polyoxyalkylene polyethers, polyester polyols, and preferably polyoxyalkylene polyether polyols, and graft dispersion polyols. In addition, mixtures of at least two of the aforesaid polyols can be used as long as the combination has an average hydroxyl number in the aforesaid range.

Polyoxyalkylene polyether polyols, can also be used as the polyhydroxyl compounds. For example, polyether polyols can be produced by anionic polymerization with alkali hydroxides such as sodium hydroxide or potassium hydroxide or alkali alcoholates, such as sodium methylate, sodium ethylate, or potassium ethylate or potassium ethylate or potassium isopropylate as catalysts and with the addition of at least one initiator molecule containing 1.7 to 8, preferably 1.7 to 4, reactive hydrogens or by cationic polymerization with Lewis acids such as antimony pentachloride, boron trifluoride etherate, etc., or bleaching earth as catalysts from one or more alkylene oxides with 2 to 4 carbons in the alkylene radical. Any suitable alkylene oxide may be used such as 1,3-propylene oxide, 1,2- and 2,3-butylene oxide, amylene oxides, styrene oxide, and preferably ethylene oxide and 1,2-propylene oxide and mixtures of these oxides. the polyalkylene polyether polyols may be prepared from other starting materials such as tetrahydrofuran and alkylene oxide-tetrahydrofuran mixtures; epihalohydrins such as epichlorohydrin; as well as aralkylene oxides such as styrene oxide. the polyalkylene polyether polyols may have either primary or secondary hydroxyl groups.

Included among the polyether polyols are polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4-tetramethylene and polyoxyethylene glycols, and copolymer glycols prepared from blends of sequential addition of two or more alkylene oxides, the polyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed in Wurtz in 1859 and Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951) or in U. S. Patent No. 1,922,459.

Polyethers which are preferred include the alkylene oxide addition products of polyhydric alcohols such as ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1, 4-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone, resorcinol, glycerol, glycerine, 1, 1,1-trimethylolpropane, 1, 1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol, a-methylglucoside, sucrose and sorbitol. Also included within the term"polyhydric alcohol"are compounds derived from phenol such as 2,2-bis (4-hydroxyphenyl)-propane, commonly known as Bisphenol A. Particularly preferred are those polyether polyols having low unsaturation and consequent higher functionality.

Suitable organic amine starting materials include aliphatic and cycloaliphatic amines and mixtures thereof, having at least one primary amino group, preferably two or more primary amino groups, and most preferable are the diamines. Specific non-limiting examples of aliphatic amines include monoamines having 1 to 12, preferably 1 to 6, carbon atoms such as methylamine, ethylamine, butylamine, hexylamine, octylamine, decylamine and dodecylamine; aliphatic diamines such as 1, 2-diaminoethane, propylene diamine, 1,4-diaminobutane, 1,6-diaminohexane, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1, 5-pentadiamine, 2,5-dimethyl, 2,5-hexanediamine, and 4-aminomethyloctane-1, 8-diamine, and amino acid-based polyamines such as lysine methyl ester, lysine aminoethyl ester and cystine dimethyl ester; cycloaliphatic monoamines of 5 to 12, preferably of 5 to 8, carbon atoms in the cycloalkyl radical, such as cyclohexylamine and cyclo-octylamine and preferably cycloaliphatic diamines of 6 to 13 carbon atoms, such as cyclohexylenediamine, 4,4Z-, 2,4'-, and 2,2t-diaminocyclohexylmethane and mixtures thereof; aromatic monoamines of 5 to 18 carbon atoms, such as aniline, benzylamine, toluidine and naphthylamine and preferably aromatic diamines of 6 to 15 carbon atoms, such as phenylenediamine, naphthylenediamine, fluorenediamine, diphenyldiamine, anthracenediamine, and preferably 2,4-and 2,6-toluenediamine and 4,4'-, 2,4'-, and 2,2'-diaminophenylmethane, and aromatic polyamines such as 2,4,6-triaminotoluene, mixtures of polyphenyl-polymethylene-polyamines, and mixtures of diaminidiphenylmethanes and polyphenyl-polymethylene polyamines. Preferred are ethylenediamine, propylenediamine, decanediamine, 4,4'-diamonphenylmethane, 4,4'-diaminocyclohexylmethane, and toluenediamine.

Suitable initiator molecules also include alkanolamines such as ethanolamine, diethanolamine, N-methyl-and N-ethylethanolamine, N-methyl-and N-ethyldiethanolamine and triethanolamine plus ammonia.

Suitable polyhydric polythioethers which may be condensed with alkylene oxides include the condensation product of thiodiglycol or the reaction product of a dicarboxylic acid.

Polyhydroxyl-containing phosphorus compounds which may be used include those compunds disclosed in U. S. Patent No. 3,639,542.

Preferred polyhydroxyl-containing phosphorus compounds are prepared from alkylene oxides and acids of phosphorus having a P205 equivalency of from about 72 percent to about 95 percent.

Suitable polyacetals which may be condensed with alkylene oxides include the reaction product of formaldehyde or other suitable aldehyde with a dihydric alcohol or an alkylene oxide such as those disclosed above.

Suitable aliphatic thiols which may be condensed with alkylene oxides include alkanethiols containing at least two-SH groups such as 1,2-ethanediol, 1,2-propanedithiol, 1,6-hexanedithiol; alkene thiols such as 2-butene-1, 4-dithiol; and alkyne thiols such as 3-hexyne-1, 6-dithiol.

Also preferred as the polyol are polymer modified polyols, in particular, the so-called graft polyols. graft polyols are well known to the art and are prepared by the in situ polymerization of one or more vinyl monomers, preferably acrylonitrile and styrene, in the presence of a polyether or polyester polyol, particularly polyols containing a minor amount of natural or induced unsaturation. Methods of preparing such graft polyols may be found in columns 1-5 and in the Examples of U. S. Patent No. 3,652,639; in columns 1-6 and in the Examples of U. S.

Patent No. 3,823,201; particularly in columns 2-8 and the Examples of U. S. Patent No. 4,690,956; and in U. S. Patent No. 4,524,157; all of which patents are herein incorporated by reference.

Non-graft polymer modified polyols are also preferred by example those prepared by the reaction of a polyisocyanate with an alkanolamine in the presence of a polyol as taught by U. S. Patent Nos. 4,293,470 ; 4,296,213; and 4,374,209 ; dispersions of polyisocyanurates containing pendant urea groups as taught by U. S.

Patent No 4,386,167; and polyisocyanurate dispersions also containing biuret linkages as taught by U. S. Patent No.

4,359,451. Other polymer modified polyols may be prepared by the in situ size reduction of polymers until the particle size is less than 20 jtim, preferably less than 10 Sm.

Illustrative polymerization initiators which may be employed are the well known free radical types of vinyl polymerization initiators such as the peroxides, persulfates, perborates, percarbonates, azo compounds, etc. These include hydrogen peroxide, dibenzoyl peroxide, acetyl peroxide, benzoyl hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, lauroyl peroxide, butyryl peroxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, diacctyl peroxide, dia-cumyl peroxide, dipropyl peroxide, diisopropyl peroxide, isopropylt-butyl peroxide, butyl-t-butyl peroxide, difuroyl peroxide, bis (triphenylmehtyl) peroxide, bis (p-methoxybenzoyl) peroxide, p-monomethoxybenzoyl peroxide, rubene peroxide, ascaridol, t-butyl peroxybenzoate, diethyl peroxyterphthalate, propyl hydroperoxide, isopropyl hydroperoxide, n-butyl hydroperoxide, t-butyl hydroperoxide, cyclohexyl hydroperoxide, trans-decalin hydroperoxide, a-methylbenzyl hydroperoxide, a-methyl-a-ethyl benzyl hydroperoxide, tetralin hydroperoxide, triphenylmethyl hydroperoxide, diphenylmethyl hydroperoxide, a, B-azobis-(2-methyl heptonitrile), 1-t-butylazo-l-cyanocyclohexane, persuccinic acid, diisopropyl peroxy dicarbonate, 2,2'-azobis (2,4-dimethylvaleronitrile), 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane, 2,2'-azobis-2-methylbutanenitrile, 2-t-butylazo-2-cyanobutane, 1-t-amyla zol-1-cyanocyclohexane, 2,2'-azobis (2,4-dimethyl-4-methoxyvalcronitrile, 2,2'-azo-bis-1-methylbutyronitirle, 2-t-butylazo-2-cyano-r-methylpentane, 2-t-butylazo-2-isobutyronitrile, to butylperoxyisopropyl carbonate and the like; a mixture of initiators may also be used. The preferred initiators are 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (isobutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2-t-buty lazo-2-cyano-4-methoxy-4-methyl pentane, 2-t-buty lazo-2-cyano-4-methylpentane, 2-t-butylazo-2-cyano-butane and lauroylperoxide. Generally, from about 0.1 percent to about 10 percent, perferably from about 1 percent to about 4 percent, by weight of initiator based on the weight of the monomer will be emplyed in the process of the invention.

Representative ethylenically unsaturated monomers which may be employed in the preparation of graft polymers used in the present invention include butadiene, isoprene, 1,4-pentadiene, 1,6-hexadiene, 1,7-octadiene, styrene, a-methylstyrene, 2-methylstyrene, 3-methylstyrene, and 4-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, and the like; substituted styrenes such as cyanostyrene, nitrostyrene, N, N-dimethylaminostyrene, acetoxystyrene, methyl 4-vinylbenzoate, phenoxystyrene, p-vinylphenyl oxide, and the like; the acrylic and substituted acrylic monomers such as acrylonitrile, acrylic acid, methacrylic acid, methyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, isopropyl methacrylate, octyl methacrylate, methacrylonitrile, ethyl a-ethoxyacrylate, methyl a-acetaminoacrylate, butyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, phenyl methacrylate, N, N-dimethylacrylamide, N, N-dibenzylacrylamide, N-butylacrylamide, methacrylyl formamide, and the like ; the vinyl esters, vinyl ethers, vinyl ketones, etc., such as vinylacetate, vinyl butyrate, isopropenyl acetate, vinyl formate, vinyl acrylate, vinyl methacrylate, vinyl methoxyacetate, vinyl benzoate, vinyltoluene, vinylnaphthalene, vinyl methyl ether, vinyl ethyl ether, vinyl propyl ethers, vinyl butyl ethers, vinyl 2-ethylhexyl ether, vinyl phenyl ether, vinyl 2-methoxyethyl ether, methoxybutadiene, vinyl 2-butoxyethyl ether, 3,4-di hydro-1, 2-pyran, 2-butoxy-2Z-vinyloxydiethyl ether, vinyl methyl ketone, vinyl ethyl ketone, vinyl phosphonates such as vinyl phenyl ketone, vinyl ethyl sulfone, N-methyl-N-vinyl acetamide, N-vinyl-pyrrole and the like; dimethyl fumarate, dimethyl maleate, maleic acid, crotonic acid, fumaric acid, itaconic acid, monomethyl itaconate, t-butylaminoethyl methacrylate, dimethylaminoehtyl methacrylate, glycidyl acrylate, allyl alcohol, glycol monoesters of itaconic acid, vinyl pyridine, and the like. Any ofthe known polymerizable monomers can be used and compounds listed above are illustrative and are not restrictive of the monomers suitable for use in this invention. Preferably, the monomer is selected from the group consisting of acrylonitrile, styrene and mixtures thereof, and most preferably comprises a mixture of styrene and acrylonitrile.

The amount of polymerized ethylenically unsaturated monomer typically present in the graft polyol, alternatively known as the level of solids, ranges from 5 weight percent to about 50 weight percent, preferably from 10 weight percent to about 40 weight percent, based on the weight of the graft polyol, and most preferably from 20 to 40.

Graft polyol will most preferably have from between 10 to 55 percent by weight polymerized monomer, and more preferably from between 15 to 35 percent. While the foregoing discussion provides representative ethylenically unsaturated monomers which may be employed in the present invention, the most preferred monomer will be selected from the group consisting of acrylonitrile, styrene, and mixtures thereof, and most preferably will comprise a mixture of acrylonitrile and styrene. Polyol (b2) will generally have an average molecular weight of from 3000 to 9000, preferably from 4000 to 7000, and most preferably from 4500 to 6500. The hydroxyl number for polyol (b2) will generally be from 10 to 40, preferably from 15 to 35, and most preferably from 20 to 30, The carrier polyol for graft polyol will generally have a hydroxyl number of from 20 to 50, preferably from 25 to 45, and most preferably from 30 to 40. The molecular weight of the carrier polyol will generally be from between 2000 to 7000, preferably from 3000 to 6000, and most preferably from 3000 to 5000. While the carrier polyol may result from the reaction of one or more alkylene oxides with the polyhydric initiator molecules described above, it has been found that a preferred carrier polyol is one having a triol initiator and most preferably a triol such as glycerine or trimethylolpropane. In addition, it has been found that a mixture of propylene oxide and ethylene oxide is particularly advantageous, especially one' wherein the resulting carrier polyol has between 65 to 95 percent of residual alkylene oxide units attributable to propylene oxide and most preferably from 75 to 85 percent with the remaining residual alkylene oxide units attributable to ethylene oxide.

In addition to the foregoing elements, the polyurethane composition of the invention may further comprise one or more optional additives selected from the group consisting of catalyst, chain extenders, oxo alcohols and mixtures thereof.

Catalyst may be employed which greatly accelerate the reaction of the compounds containing hydroxyl groups with the modified or unmodified polyisocyanates. Examples of suitable compounds are cure catalyst which also function to shorten tack time, promote green strength, and prevent foam shrinkage. suitable cure catalysts are organometallic catalysts, preferably organotin catalysts, although it is possible to employ metals such as lead, titanium, copper, mercury, cobalt, nickel, iron, vanadium, antimony and manganese. Suitable organometallic catalysts, exemplified here by tin as the metal, are represented by the formula: R, =Sn [X--Rl--Y] 2, wherein R is a C1-C2 alkyl or aryl group. R1 is a Co-Cis methylene group optionally substituted or branched with a C1-C4 alkyl group, Y is hydrogen or an hydroxyl group, preferably hydrogen, X is methylene, an--S--, an--SR2COO--,--SOOC--, an --03S--, or an--OOC--group wherein R2 is a C1-C4 alkyl, n is 0 or 2, provided that RI is a Co only when X is a methylene group.

Specific examples are tin (II) acetate, tin (II) octanoate, tin (II) ethylhexanoate and tin (II) laurate ; and dialkyl (1-8C) tin (IV) salts of organic carboxylic acids having 1-32 carbon atoms, preferably 1-20 carbon atoms, e. g., diethyltin diacetate, dibutyltin diacetate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dihexyltin diacetate, and dioctyltin diacetate.

Other suitable organotin catalysts are organotin alkoxides and mono or polyaklyl (1-8C) tin (IV) salts of inorganic compounds such as butyltin trichloride, dimethyl-and diethyl-and dibutyland dioctyl-and diphenyltin oxide, dibutyltin dichloride, and dioctyltin dioxide. Preferred, however, are tin catalysts with tin-sulfur bonds which are resistant to hydrolysis, such as dialkyl (1-20C) tin dimercaptides, including dimethyl-, dibutyl-, and dioctyl-tin dimecarptides.

Tertiary amines also promote urethane linkage formation, and include triethylamine, 3-methoxypropyldimethylamine, triethylenediamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-, and N-cyclohexylmorpholine, N, N, N', N'-tetramethylethylenediamine, N, N, N', N'-tetramethylbutanediamine or-hexanediamine, N, N, N'-tri- methyl isopropyl propylenediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis (dimethylaminopropyl) urca, dimethylpiperazine, 1-methyl-4-dimethylaminoethylpiperazine, 1,2-dimethylimidazole, 1-azabicylo [3,3,0] octane and preferably 1, 4-diazabiclo [2,2,2] octane, and alkanolamine compounds, such as triethanolamine, triisopropanolamine, N-methyl-and N-ethyldiethanolamine and dimethylethanolamine.

Particularly suitable catalysts have been found to be dibutyltin dilaurate and tertiary amines, particularly triethylenediamine.

Mixtures of such preferred catalysts are especially preferred.

Chain extending agents which may optionally be employed in the preparation of the polyurethane foams include those compounds having at least two functional groups beating active hydrogen atoms, and preferably having number average molecular weights less than 400, more preferably 6 to 300, such as water, hydraxzine, primary and secondary diamines, amino alcohols, amino acids, hydroxy acids, glycols, or mixtures thereof. A preferred group of alcohol chain extending agents includes water, ethylene glycol, 1,3-propanediol, 1,10-decanediol, o,-m-p-dihydroxycyclohexane, diethylene glycol, 1,6-hexanediol, glycerine, trimethylol propane, 1,2,4-, 1,3,5-trihydroxycyclohexane, bis (2-hydroxyethyl) hydroquinone, 1,4-butanediol.

Examples of secondary aromatic diamines are N, N'-dialkyl-substi- tuted aromatic diamines, which are unsubstituted or substituted on the aromatic radical by alkyl radicals, having 1 to 20, preferably 1 to 4, carbon atoms in the N-alkyl radical, e. g., N, N'diethyl-, N, N'-di-sec-pentyl-, N, N'-di-sec-hexyl-, N, N'-di-sec- decyl-, and N, N'-dicyclohexyl-p-and M-phenyenediamine, N, N'- dimethyl-, N, N'-diethyl-, N, N'-diisopropyl-, N, N'-di-sec-butyl- and N, N'-diclohexyl-r, 4'-diaminodiphenylmethane and N, N'-di-sec- butylbenzidine.

If aromatic diamines are used, it is best to use those which have at least one alkyl substituent in the orthoposition to the amino groups, are liquid at room temperature, and are miscible with the polyether polyols. Furthermore, alkyl-substituted meta-phenylenediamines are considered useful.

Examples of suitable alkyl-substituted M-phenylenediamines are 2,4-dimethyl-6-cyclohexyl-, 2-cyclohexyl-4,6-diethyl-, 2-cyclohexyl-2,36-isopropyl-, 2,4-dimethyl-6- (1-ethyl-n-propyl)-, 2,4-dimethyl-6- (1, 1-dimethyl-1,3-phenylenediamine. Preference is given to 1-methyl-3, 5-diethyl-2,4- and-2,6-phenylenediamines, 2,4-dimethyl-6-tert-butyl-, 2,4-dimethyl-6-isooctyl- and 2,4-dimethyl-6-cyclohexyl-1,3-phenylenediamine.

Examples of suitable 3,3'-di- and 3,3', 5,5'-tetra-n-alkyl-substituted 4,4'-diaminodiphenylmethanes are 3,3'-di-, 3,3', 5,5'-tetraethyl-, 3,3'-di-and 3,3', 5,5'-tetra-n-propyl-4,4'-diaminodiphenylmethane.

Of the foregoing, short chain diols are particularly preferred chain extending agents, especially those having from 1 to 4 carbon atoms. Particularly desirable chain extenders are 1,4-butanediol, ethylene glycol, diethylene glycol, tripropylene glycol, tripropylene glycol, dipropylene glycol, and propylene glycol. 1,4-butanediol is especially preferred for use in shoe sole applications.

Additives (e) may include other alcohols typically described as oxoalcohols. Such alcohols are generally primary alcohols produced from monoolefins having from about 2 to about 20 carbons.

With the exception of 2-ethylhexanol, oxoalcohols contain one more carbon than the starting olefin. They are generally supplied as a mixture of homologs and contain some branching. Examples of some commercially available products include LIAL 125 from Chemica Augusta Spa or NEODOL 25 produced by Shell. Especially preferred is LIAL 125.

The additives (c) may further comprise other additives such as surfactants, fillers, W stabilizers, pigments and mixtures thereof.

Polyurethane elastomers having a shore D durometer hardness of at least 75, good cleanness, high gloss when polished and an excellent pattern can thus be obtained.

The following examples illustrate the nature of the invention with regard to the formation of both prepolymers and the resulting polymethane elastomers prepared therefrom. The examples presented herein are intended to demonstrate the objects of the invention but should not be considered as limitations thereto.

Unless otherwise indicated, all parts are expressed in parts by weight.

Isocyanate X polymethylene polyphenyl isocyanate having a free NCO content of 31.5% by weight, a viscosity of 200 and a nominal functionality of 2.7.

Isocyanate Y a prepolymer prepared by mixing in a reaction ves sel, 1075.1 parts (89.59 weight %) of methylene bis (phenylisocyanate) comprising of 98.0% 4,4'-, and 2.0% 2,4'- isomers in a reaction vessel and heating the same to 105 C, thereafter adding in a dropwise fashion at a constant rate 78.0 (6.51 weight %) parts of dipropylene glycol and 46.9 parts (3.90 weight %) of 400 molecular weight polypropylene glycol over a period of 30 minutes.

The temperature was then raised to 105 C and the contents were reacted for one hour. Thereafter the contents were cooled and the product was charac terized as being a free NCO content of 25.2% by weight and the viscosity was 182 cps at 25 C.

Isocyanate Z a prepolymer prepared by mixing 87.2 weight % of methylene bis (phenylisocyanate), 8.0 weight % dipropylene glycol and 4.8 weight % of 400 molecu lar weight polypropylene glycol at 50 C to give a product characterized as having a free NCO content of 22.9% by weight and a viscosity was 700 cps at 25 C.

Resin A: (Equivalent weight, 204.8) Prepared by mixing 14.36 weight % of 400 molecular weight polyoxypropylated trimethylol propane, 28.25 weight % of 292 molecular weight oxypropy lated ethylene diamine and 57.39 weight % of a plasticizer known as KODAFLEX TXIB which is avail able from EASTMAN Chemical.

Resin B: (Equivalent weight, 171.8) Prepared by mixing 74.244 weight % of 400 molecu lar weight polyoxypropylated trimethylol propane, 24.748 weight % of 1250 molecular weight polyoxethylated polyoxypropylated propylene glycol, 1.00 weight % of a tertiary amine catalyst known commercially as DABCO XFE 1028, which is available from Air Products Company and 0.008 weight % of a tin catalyst known commercially as FOMREZ UL-1 which is available from WITCO Corpora tion.

Resin C: (Equivalent weight, 183.3) Prepared by mixing 24.873 weight % of 4500 molecu lar weight polyoxyethylated polyoxypropylated tri methylol propane, 74.619 weight % of 400 molecular weight polypropylated trimethyol propane, a ter tiary amine catalyst known commercially as DABCO XFE 1028 which is available from Air Products Company and 0.008 weight % of a tin catalyst known commercially as FOMREZ UL-1 which is available from WITCO Corporation.

Resin D (Equivalent weight: 180.2) Prepared by mixing 50.544 weight % of 4500 molecu lar weight polyoxyethylated polyoxypropylated tri methylol propane, 34.578 weight % of 3000 molecu lar weight polyoxypropylated glycerine, 14.863 weight % of diethylene glycol and 0.015 weight % of a tin catalyst known commercially as FOMREZ UL-1 which is available from WITCO Corporation Table 1

Isocyanate Functionality of iso-Viscosity of isocyana-Resin Component Isocyanate Index Mixed viscosity at Remarks cyanate telprepolymer at (viscosity, cps at 25 C 25 C, cps 25 C) 2. 7 200 A (47) 95 to 105 104 Very good pattern, poor impact strength and the color of the iso limits the color selection 2. 0 180 B 8471) 9S to 105 346 Good pattern, excellent impact strength, high gloss and no splits even when using foam cores.

2. 0 700 C (775) 95 to 105 345 Acceptable pattern, but high number of splits especially when usig foam cores.

Good impact strength.

2. 0 180 D (1120) 95 to 105 517 Poor. Unacceptable pattern.

2. 0 700 E 9S to 105 914 Blank. No pattern.

Claims

1. A method for producing a prepolymer composition comprising the steps of: (a) providing a monomeric methylene bis (phenylisocyanate) composition having at least about 65.0 weight percent of diphenylmethane 4,4'-diisocyanate based on the total weight of all isomers; and (b) introducing a polyol composition having an average mole cular weight of less than about 600, to said methylene bis (phenylisocyanate) composition with mixing; wherein the resulting prepolymer has an average NCO con tent of between about 20.0 percent to less than about

30.0.

2. The method of Claim 1 wherein said prepolymer has an average viscosity of less than about 250 cps at 25 C.

3. The method of Claim 2 wherein said prepolymer has an average viscosity of between about 50 to 250 centipoise at 25 C.

4. The method of Claim 1 wherein said 4,4'-diisocyanate is present prior to reaction with said polyol in an amount of at least about 65.0 weight percent up to about 98.0 weight percent based on the total weight of monomeric isocyanate prior to reactiion with said polyol composition.

5. The method of Claim 1 wherein said monomeric isocyanate is present in an amount of at least 40.0 weight percent based on the total weight of the prepolymer after reaction with said polyol composition.

6. The method of Claim 4 wherein said monomeric isocyanate is present in an amount of between about 50.0 to about 70.0 weight percent based on the total weight of the prepolymer after reaction with said polyol composition.

7. The method of Claim 1 wherein said polyol is a polyether polyol.

8. The method of Claim 7 wherein said polyether polyol is selected from the group consisting of dipropylene glycol, tripropylene glycols and mixtures thereof.

9. The method of Claim 1 wherein said monomeric isocyanate composition includes 2,4'-diisocyanate.

10. The method of Claim 9 wherein said 2,4'-diisocyanate is present in an amount of between about 0.1 to about 2.8 weight percent based on the total weight of the monomeric isocyanate composition.

11. The method of Claim 1 further comprising a positive amount of -stabilizer up to about 0.005 weight percent based on the total weight of the prepolymer.

12. The method of Claim 11 wherein said stabilizer is benzoyl chloride.

13. The prepolymer produced by the method of Claim 1.

14. A method for producing a prepolymer useful in preparing poly urethane elastomers, comprising the steps of : (a) providing a monomeric methylene bisphenyl isocyanate composition, having at least about 65.0 weight percent 4,4'-diphenylmethane diisocyanate; and (b) introducing a positive amount up to about 20.0 weight percent based on the total weight of the prepolymer of a diol selected from the group consisting of dipropylene glycols, tripropylene glycols and mixtures thereof; wherein the resulting prepolymer has an average NCO content of at least about 24 percent and has an average viscosity of less than about 250 cps at 25 C.

15. The method of Claim 14 wherein said prepolymer has an average viscosity of between about 50 to less than about 250 cps at 25 C.

16. The method of Claim 14 wherein said 4,4'-diisocyanate is present prior to reaction with said polyol in an amount of at least about 65.0 weight percent up to about 98.0 weight percent based on the total weight of monomeric isocyanate prior to reactiion with said polyol composition. The method of Claim 1 wherein said monomeric isocyanate is present in an amount of at least 40.0 weight percent based on the total weight of the prepolymer after reaction with said polyol composition.

17. The method of Claim 14 wherein said monomeric isocyanate is present in an amount of at least 40.0 weight percent based on the total weight of the prepolymer after reaction with said polyol composition.

18. The method of Claim 14 wherein said monomeric isocyanate is present in an amount of between about 50.0 to about 70.0 weight percent based on the total weight of the prepolymer after reaction with said polyol composition.

19. The method of Claim 14 wherein said polyol is a polyether polyol.

20. The method of Claim 19 wherein said polyether polyol is selected from the group consisting of dipropylene glycol, tripropylene glycols and mixtures thereof.

21. The method of Claim 14 wherein said monomeric isocyanate composition includes a certain amount of 2,4'-diisocyanate.

22. The method of Claim 14 wherein said 2,4'-diisocyanate is present in an amount of between about 0.1 to about 2.8 weight percent based on the total weight of the monomeric isocyanate composition.

23. The method of Claim 14 further comprising a positive amount of stabilizer up to about 0.005 weight percent based on the total weight of the prepolymer.

24. The method of Claim 23 wherein said stabilizer is benzoyl chloride.

25. A prepolymer having an average NCO content of at least about 24 percent and an average viscosity of below about 250 centi poise at 25 C formed by reacting a methylene bis (phenyliso- cyanate) composition having at least about 65.0 weight percent of diphenylmethane 4,4'-diisocyanate based on the total weight of all isomers with a polyol composition having an average molecular weight of less than about 600 while mixing the same.

26. A method of producing a prepolymer as claimed in claim 1 or claim 14, carried out substantially as hereinbefore described or illustrated in any of the foregoing Examples.