A two-step process for preparing polyurethane elastomers using mixtures of chain extenders

Abstract: This invention relates to a process for preparing poly­ urethane and/or polyurea elastomer comprising reacting a liquid preformed isocyanate-terminated prepolymer with a chain exten­ der mixture, which chain extender mixture comprises (a) a mixture comprising a hydroxyl-terminated chain exten­ der and an aromatic amine-terminated chain extender, and/or aliphatic amine-terminated compound, or (b) a mixture comprising an aromatic amine-terminated chain extender and an aliphatic amine-terminated compound, wherein the isocyanate index is from 70 to 200. The prepolymer is the reaction product of a stoichiometric excess of a polyisocyanate and a relatively high equivalent weight isocyanate-reactive compound. In this process, it is possible to prepare elastomers having excellent properties, particularly excellent flexural and thermal properties, which properties are difficult to obtain in a one-step process. The reactivity of the chain extender mixture with the prepolymer is such that this process is easily carried out, making it possible to mix the reactants and fill the mold before gelling occurs, yet providing an elastomer which has good green strength at demold.

Description: This invention relates to the production of polyurethane and/or polyurea elastomers, more particularly to the production of such elastomers in a reaction injection molding process. Polyurethane elastomers are generally prepared by reacting a polyisocyanate with a relatively high equivalent weight material having active hydrogen atoms, or mixture of such materials having active hydrogen atoms and a relatively low equivalent weight compound or mixture thereof which also contains a plurality of active hydrogens (chain extender). In the commercial production of many such elastomers, the foregoing components are mixed and reacted in a reaction injection molding (RIM) process. In the RIM process, a stream containing the active hydrogen-containing materials and a second stream containing the polyisocyanate are injected under high pressure through a mixing zone and into a mold where curing takes place. Typically, the complete mixing and filling operation takes place in 0.5 to 10 seconds, depending on the particular materials used and the size and configuration of the mold. The reactivity of the materials used must therefore be such that the mold can be filled before the reactants gel. In addition, it is desirable to demold the elastomer as rapidly as possible in order to produce the maximum number of molded parts per mold per period of time. Thus, it is desired that the materials used cure rapidly so that the elastomer can be removed from the mold in a short period of time. In order to remove the elastomer from the mold, it must have enough physical integrity to withstand the stresses encountered during the actual removal process. For example, in demolding an elastomer, it is often necessary to pull, bend, twist or otherwise distort it in order to effect release from the mold. In many cases, the complex geometry of the mold requires that the elastomer be stretched in the demolding process. Accordingly, the elastomer must be able to withstand these actions without tearing. This ability is usually referred to in the art as the "green strength" (or hot tear strength) of the elastomer. For the foregoing reasons, the materials used in preparing RIM elastomers and the method of preparing the elastomer, must be chosen for their processing characteristics as well as for the properties they impart to the product elastomer. In preparing elastomers via a RIM process, it is now standard practice to use a "one-shot" (one-step) process. In the one-step process, the polyisocyanate is reacted simultaneously with the high equivalent weight active hydrogen-containing material and the chain extender. The polyisocyanate is either not prereacted with any of the active hydrogen-containing materials, or is reacted with only a minor portion thereof to form a so-called "quasi-prepolymer". This process is used because it enables the practitioner to balance the weights of the streams which are injected into the mixing head. Because of mechanical limitations in some RIM equipment, it has not been possible to mix streams of significantly different weights. The one-step process also has the advantage of requiring one less process step, since the prepolymer need not be formed. The major drawback of the one-step process is that it is difficult to prepare high modulus elastomers in this manner. For example, to prepare high modulus polymers for applications such as automobile body panels, it has been found necessary to employ a filler such as milled or flaked glass. As a result, the impact strength and elongation of the elastomer suffer greatly. In the two-step process, the polyisocyanate is reacted in a first step with all or a major portion of the high equivalent active hydrogen-containing material to form a prepolymer. This prepolymer is then reacted in RIM equipment with the chain extender and any remaining high equivalent weight material to form the elastomer. Unfortunately, it has heretofore been difficult to process these two-step systems. Due to the fast reactivity of the chain extenders, particularly amine-terminated chain extenders such as diethyltoluenediamine (DETDA) it has been particularly difficult to completely mix the components and fill the mold before gelling occurs. In addition, elastomers prepared according to a two-step process have often been extremely brittle at demold. One-step ("one-shot") processes are for example disclosed in US-A-4442235, EP-A-93336 and EP-A-33498. US-A-4530941 concerns isocyanate-reactive compositions mostly containing at least one high equivalent weight component; in this reference, which refers also to a one-step process, it is indicated that also prepolymers and quasi-prepolymers prepared from polyisocyanates and compounds having two or more active hydrogen atoms are suitable for reacting with the chain extender. US-A-4374210 discloses polyurea-polyurethans from a mixture of a polyol, an aromatic diamine, and an isocyanate-terminated prepolymer; the prepolymer is reacted with a polyol having a minimum equivalent weight of 450. Due to the disadvantages encountered with the one-step process and the previously known two-step processes, it would be desirable to provide a process for preparing a polyurethane and/or polyurea polymer in which an elastomer having excellent physical properties can be obtained, and in which the difficulties of two-step processes are minimized or overcome. Subject matter of the present invention is a two-step process for preparing a polyurethane and/or polyurea elastomer according to claim 1. Preferred embodiments of this process are subject matter of claims 2 to 9. This process is a prepolymer process for preparing polyurethane and/or polyurea elastomers. In this process, it is possible to prepare elastomers having excellent properties, particularly flexural and thermal properties, which properties are difficult to obtain in a one-step process. Surprisingly, the reactivity of the chain extender mixture with the prepolymer is such that this process is easily carried out, making it possible to mix the reactants and fill the mold before gelling occurs, yet providing an elastomer which has good green strength at demold. With this process, it is possible to prepare very high flexural modulus polymers without using fillers, and to further increase the flexural modulus of filled elastomers. In this invention, a polyurethane and/or polyurea elastomer is prepared by reacting a liquid isocyanate-terminated prepolymer as described herein with a certain chain extender mixture. The prepolymer employed herein is an isocyanate-terminated reaction product of a reaction mixture comprising a relatively high equivalent weight material having an equivalent weight of 700 to 2500 and containing at least two groups containing active hydrogen atoms (hereinafter "isocyanate reactive material") and at least one polyisocyanate. The prepolymer is a liquid, i.e., has a melting point such that it is a liquid at the temperature at which it is processed to form an elastomer and preferably is a liquid at ambient temperatures (5-30°C). This prepolymer advantageously has an equivalent weight of 168 to 2100, preferably 200 to 840, more preferably 200 to 525. It will be recognized by the practitioner that the equivalent weight of the prepolymer is a means by which the flexural modulus of the elastomer can be controlled. A lower equivalent weight in the prepolymer requires a greater amount of chain extender per unit weight. Greater amounts of chain extender generally produce a higher flexural modulus elastomer. Thus, it is contemplated to employ a lower equivalent weight prepolymer when preparing a higher modulus elastomer, and a higher equivalent weight prepolymer when preparing a lower modulus elastomer. The isocyanate-reactive material used to prepare the prepolymer is a compound or mixture of compounds having at least two moieties containing hydrogen atoms which are reactive with an isocyanate group, and which has an equivalent weight (based on the number of such moieties) of at least 700. Suitable such compounds are described, for example, in U.S. Patent No. 4,394,391. Preferred compounds are hydroxyl and/or amine-terminated polyethers and polyesters having an average functionality of from 1.8 to 4, preferably 1.8 to 3.0, wherein functionality refers to the number of moieties containing at least one active hydrogen atom. Most preferred are polyether diols and triols of 700 to 2500 equivalent weight, and the corresponding amine-terminated polyethers. The most preferred polyethers can be prepared by polymerizing tetrahydrofuran and alkylene oxide, or epihalohydrin in the presence of a polyhydric initiator and an alkaline catalyst, as is described, for example, in U.S. Patent No. 2,902,478, 3,040,076, 3,317,508, 3,341,599 and 3,445,525. These polyethers can be reacted with ammonia or a primary amine and hydrogen to form amine-terminated polyethers as described, for example, in U.S. Patent No. 3,654,376. The isocyanate-reactive material is reacted with a stoichiometric excess of a polyisocyanate to form the liquid isocyanate-terminated prepolymer. Suitable polyisocyanates include aliphatic polyisocyanates as well as aromatic polyisocyanates. Such polyisocyanates are described, for example, in U.S. Patent Nos. 4,065,410, 3,401,180, 3,454,606, 3,152,162, 3,492,330, 3,001,973, 3,594,164 and 3,164,605. Aromatic polyisocyanates particularly useful herein include 2,4- and/or 2,6-toluene diisocyanate, diphenylmethanediisocyanate, p-phenylene diisocyanate, polymethylenepolyphenylpolyisocyanates, and mixtures thereof. Also useful are polymeric derivatives of diphenylmethanediisocyanate, the so-called "liquid MDI" materials. Particularly useful aliphatic polyisocyanates include, for example, the hydrogenated derivatives of the foregoing aromatic polyisocyanates, as well as hexamethylene diisocyanate, isophoronediisocyanate and 1,4-cyclohexane diisocyanate. The prepolymer is prepared in any convenient manner by reacting a stoichiometric excess of the polyisocyanate with the isocyanate-reactive material under conditions that an isocyanate-terminated prepolymer is obtained. When more reactive polyisocyanates or isocyanate reactive materials are used, it is possible to simply mix the components at ambient or a slightly elevated temperature to form the prepolymer. when less reactive materials are used, it may be desirable to employ higher temperatures and/or a urethane catalyst as described hereinafter to form the prepolymer. It is also within the scope of this invention to employ a low equivalent weight active hydrogen-containing compound in the preparation of the prepolymer. Such low equivalent weight compound is used in addition to the relatively high equivalent weight isocyanate reactive material described hereinbefore. The prepolymer thus formed can be reacted immediately with the chain extender mixture as described herein, or can be recovered and stored for later use. In normal commercial practice, it is contemplated that the prepolymer will be recovered and packaged for later use. In making an elastomer in accordance with this invention, the prepolymer is reacted with a mixture or chain extenders. This mixture of chain extenders comprises (a) a mixture comprising a hydroxyl-terminated chain extender having an equivalent weight of 31 to 300 and an aromatic amine terminated chain extender and/or an aliphatic amine-terminated chain extender, wherein said aliphatic amine-terminated chain extenders have 2-4 aliphatic amine groups which contain an active hydrogen per molecule and the equivalent weight of said aliphatic amine-terminated chain extender is from 32 to 300 or (b) a mixture comprising an aromatic amine-terminated chain extender and an aliphatic amine-terminated compound, wherein the molecular weight of the aliphatic amine-terminated chain extender is lower than 1000. The amounts of prepolymer and chain extender mixture are chosen to provide an isocyanate index (100 times the ratio of isocyanate groups to isocyanate-reactive groups) of 70-200, preferably 95-125, more preferably 100-115. Hydroxyl-terminated chain extenders useful herein include those compounds having 2-4, preferably 2 hydroxyl groups per molecule and an equivalent weight of 31 to 300, preferably 31 to 150. Exemplary such compounds are ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,4-butanediol, various bisphenols, trimethylolpropane, hydroquinone, catechol, resorcinol, tetraethylene glycol, glycerine, low molecular weight ethylene and/or propylene oxide derivatives of dihydric initiators and mixtures thereof. Suitable aromatic amine-terminated chain extenders include those compounds which have 2-4, preferably 2 amine groups containing an active hydrogen per molecule. They also advantageously have an equivalent weight (based on the number of such amine groups) of 54 to 300, preferably 54 to 250, and are preferably soluble or miscible in the other components of the chain extender mixture in the relative amounts present therein. Exemplary of such chain extenders are phenylene diamine, 2,4-bis(p-aminobenzyl)aniline, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4'-diphenylmethanediamine, 2,6'-diphenylmethanediamine, naphthalene-1,5-diamine, triphenylmethane-4,4',4''triamine, 4,4'-di-(methylamine)--diphenylmethane, 1-methyl-2-methylamine-4-aminobenzene, polyphenylpolymethylene polyamines, 1,3-diethyl-2,4--diaminobenzene, 1-methyl-3,5-diethyl-2,4-diaminobenzene, 1-methyl-3,5-diethyl-2,6-diaminobenzene, 1,3,5-triethyl-2,6-diaminobenzene and mixtures thereof. The isomers of methyldiethyldiaminobenzene are referred to in the art as DETDA. In general, sterically hindered aromatic diamines such as are described in U.S. Patent No. 4,218,543 to Weber are useful. Chemically blocked aromatic amines such as the sodium chloride complex of diphenylmethanediamine are also useful. Suitable aliphatic amine chain extenders have 2-4, preferably 2 aliphatic amine groups which contain an active hydrogen per molecule. Such compounds also have an equivalent weight (based on number of such amine groups) of 32 to 300, preferably 32-250. Exemplary of such chain extender compounds are ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, diethylenetriamine, aminoethylethanolamine, diaminocyclohexane, hexamethylenediamine, methyliminobispropylamine, iminobispropylamine, bis(aminopropyl)piperazine, aminoethylpiperazine, 1,2-diaminocyclohexane, bis-(p-aminocyclohexyl)methane, triethylenetetraamine, and amine-terminated polyethers having 2-3 terminal amine groups and an equivalent weight of 100 to 300, more preferably 150-300. The preferred aliphatic amine chain extenders are the amine-terminated polyethers. The preferred aromatic amine chain extenders are the sterically and/or chemically hindered aromatic diamines. When mixture of a hydroxyl-terminated chain extender and an aromatic amine-terminated chain extender is used, the hydroxyl-terminated chain tender advantageously comprises 15-85, preferably 20-80, more preferably 25-75 percent of the combined weight of the hydroxyl- and aromatic amine-terminated chain extenders. When an aliphatic amine-terminated chain extender is employed in an admixture with either a hydroxyl-terminated chain extender or an aromatic amine-terminated compound, it is advantageous to use 0.01 to 0.5, preferably 0.01 to 0.25, more preferably 0.02 to 0.1 equivalent of the aliphatic amine-terminated chain extender per equivalent of the aromatic amine-terminated chain extender or hydroxyl-terminated chain extender. In a most preferred embodiment, the aliphatic amine-terminated chain extender also comprises 15-80 percent of the weight of the chain extender mixture. Preferred chain extender mixtures include mixtures of ethylene glycol and an isomeric mixture of DETDA, diethylene glycol and DETDA, triethyleneglycol and DETDA, propylene glycol and DETDA, 1,4-butanediol and DETDA, a 100- 300 equivalent weight di- or trifunctional amine-terminated polyether and DETDA, mixtures of ethylene glycol, DETDA and a 100- 300 equivalent weight di- or trifunctional amine-terminated polyether and the corresponding mixtures in which DETDA is replaced with another aromatic diamine which is stearically or chemically hindered to reduce the reactivity of the amine groups relative to the amine groups in phenylene diamine. In addition to the critical components described before, the chain extender mixture may also contain minor amounts of a relatively high equivalent weight active hydrogen-containing compound. In certain embodiments of the invention an amine-terminated polyether is used as a relatively high equivalent weight material. In such cases, the number of equivalents of the high equivalent weight compound(s) used in the chain extender mixture does not exceed 50 percent, preferably 36 percent, more preferably 20 percent, and most preferably 10 percent of the number of equivalents of relatively high equivalent weight active hydrogen containing compound used in preparing the prepolymer. In addition to the prepolymer and chain extender mixture, other optional components may be employed in preparing the elastomer. These materials are conventionally combined with the chain extender mixture before molding the elastomer, but may be added to the mold in separate streams or be mixed with the prepolymer. A catalyst for the reaction of the chain extender mixture and the prepolymer is advantageously employed. Catalysts for such reactions are well-known and described, for example, in U.S. Patent No 4, 495, 081. Preferred catalysts include tertiary amine compounds and organometallic compounds. Generally, from 0.01 to 1 part of catalyst is used per 100 parts of isocyanate-reactive materials in the reaction mixture, although the precise amount used is a matter of choice to the skilled artisan. Preferred tertiary amine catalysts include, for example, triethylenediamine, triethylamine, tetramethylbutanediamine, N,N-dimethylethanolamine, N-ethylmorpholine and N-methylmorpholine. Preferred organometallic catalysts include organometallic compounds of tin, zinc, lead, mercury, cadmium, bismuth, antimony, iron, manganese, cobalt, copper, vanadium and organotin compounds such as dimethyltindilaurate and dibutyltindilaurate. In addition, materials, such as, for example, pigments, coloring agents, mold release agents, fire retardant agents, fillers, reaction modifiers, antioxidants, and preservatives may be employed in the preparation of the elastomer. Although it is possible to employ a filler material in order to increase the flexural modulus of the elastomer, an advantage of this invention is that it permits the preparation of very high flexural modulus elastomers without the use of such fillers. Thus, it may be found that the use of such fillers is not required, or that lesser amounts thereof are needed, in order to obtain a desired modulus. It is generally preferred to employ an internal mold release agent in order to facilitate the removal of the elastomer from the mold. Suitable mold release agents are described, for example, in U.S. Patent Nos. 3,726,952 and 4,111,861. The preferred mold release agent comprises a mixture of an amine-containing material and a metallic salt of a carboxylic acid, as described in copending application serial no. 570,141, filed January 12, 1984. It is generally preferred to prepare a non-cellular or microcellular elastomer. Accordingly, the use of blowing agents is generally not preferred when the use thereof is in an amount sufficient to produce an elastomer with a density of less than 0.85 g/cm 3 (850 kg/m 3 ). However, it is within the scope of this invention to employ a blowing agent, particularly in small amounts so as to produce an elastomer having a density of 0.85, (850) preferably 0.95 (950), more preferably 1.0 g/cm 3 (1000 kg/m 3 ) or more. Suitable blowing agents include water, low boiling organic compounds, and compounds which decompose or react to release a gas during the molding process. It is also possible to slightly reduce the density of the elastomer by whipping or bubbling air or another inert gas through the prepolymer and/or chain extender mixture prior to their reaction. This process is commonly referred to as "nucleation" and is commonly used to prepare microcellular elastomers having a density of from 0.85-1.1 g/cm 3 (850-1100 kg/m 3 ) In preparing an elastomer, the prepolymer is reacted with the chain extender mixture. An isocyanate index of 90-120 is preferred. In conducting this reaction, the prepolymer and chain extender advantageously are thoroughly mixed and placed into a mold before the mixture gels. Since this reaction takes place rapidly, it is preferred to use high pressure mixing and mold-filling equipment. The high pressure impingement mixing equipment conventionally used in reaction injection molding (RIM) is suitable. However, any apparatus which provides the required rapid mixing and mold filling can be used. In molding the elastomer, it is common to preheat the prepolymer and the chain extender mixture to a slightly elevated temperature, i.e. 60-150° F (15-66° C), preferably 60-110° F (15.45 °C), prior to mixing. An elevated mold temperature, i.e. about 100-350° F (38-177° C), preferably 150-250° F (65-122° C), is also desirable. The residence time in the mold is selected such that at demold, the elastomer has sufficient mechanical strength to withstand the demolding operation. Preferred residence times in the mold, in order to obtain the greatest economic advantage, are from 10 to 300, more preferably 10 to 120, most preferably 15-45 seconds. Following demolding of the elastomer, it may be desirable to postcure the part in order to further improve its properties. Typical postcuring conditions include a temperature of 100-400 °F (38-205° C) for 5 minutes to 2 hours. The elastomer of this invention is useful, for example, in preparing automobile fascia, body panels and beer keg skirts. Preferred elastomers prepared according to this invention exhibit an unfilled flexural modulus (at a density of 1.15 g/cm 3 ) of at least 25,000 psi (0.17 GPa), preferably at least 75,000 psi (0.51 GPa), more preferably at least 150,000 psi (1.02 GPa), and most preferably 180,000 psi (1.24 GPa). 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. The properties of the elastomer were determined in accordance with the following test procedures: Properties Test Proceudres Flexural Modulus ASTM D-790 Tensile Strength ASTM D-412 Tear Strength ASTM D-470C Tear Resistance ASTM D-624 Shore D Hardness ASTM D-2240 Notched Izod ASTM D-256 Gardner Impact ASTM D-3029 CLTE (Coefficient of Linear Thermal Expansion ASTM D-696 Heat Sag Determined at 163 °C for 30 minutes with a 6" (152.4 mm) overhang In the tables, "A/B ratio" is the weight ratio of prepolymer (A-side) to chain extender (B-side); "RT" is room temperature. Example I Elastomer Sample Nos. 1-2 were prepared from the following formulation: 1,4-butanediol 60 parts by weight 400-MW amine-terminated polyether 7 parts by weight tin catalyst 0.12% by weight of chain extenders Prepolymer A to provide index indicated below Prepolymer A was prepared by reacting diphenylmethanediisocyanate (MDI) with a 6000 molecular weight poly(propylene oxide) triol to form a prepolymer containing 12 percent by weight -NCO groups, and then diluting this prepolymer with additional MDI to obtain a prepolymer solution containing 20.5 percent -NCO groups (205 equivalent weight). The butanediol, amine-terminated polyether and catalyst were thoroughly blended. This mixture was then heated to 100° F (38° C). Prepolymer A was separately heated to 143° F (62° C). Using a Krauss-Maffei PU-80 RIM machine, the chain extender mixture and prepolymer were reacted at a 100 index to form a 1/8" (3.175 mm) thick plaque. The mold was preheated to 160° F (72° C) prior to injecting the reactants. The residence time in the mold was five minutes. After demolding the part, it was post cured at 325° F (163 °C) for 30 minutes. This elastomer is designated as Sample No. 1. Elastomer Sample No. 2 was prepared in like manner, except the isocyanate index was 105. Comparative Sample Nos. A and B were prepared in similar manner as Sample Nos. 1 and 2, respectively, except none of the amine terminated polyether was used. The resulting Samples and Comparative Samples were tested for tensile strength, flexural modulus, tear strength, hardness and heat sag, with results as reported in Table I following. As can be seen from the data in Table I, a significant increase in flexural modulus was obtained with the practice of this invention. In addition, the Comparative Samples showed gel lines, indicating that the system processed poorly. Example II Elastomer Sample Nos. 3-6 were prepared from the following formulation: ethylene glycol 44 parts by weight 400-MW amine-terminated polyether 7 parts by weight tin catalyst 0.05% by weight of chain extenders Prepolymer A to provide index indicated below The chain extenders and catalyst were blended as described in Example 1, and heated to 100° F (38° C). Prepolymer A was separately heated to 160° F (72° C). The components were processed on a Krauss-Maffei PU-80 RIM machine at a 100 index, using a 1/8" (3.175 mm) flat plaque tool which was preheated to 165° F (74° C). The part was demolded after 2 minutes in the mold, and tested as described in Example 1. This elastomer was designated Sample No. 3. Sample Nos. 4, 5 and 6 were prepared and tested in like manner, at a 105, 110, and 115 index, respectively. Comparative Sample Nos. C-F were prepared and tested as described with respect to Sample Nos. 3-6, respectively, except none of the amine-terminated polyether was used. The results obtained by testing Sample Nos. 3-6 and Comparative Sample Nos. C-F are as reported in Table II. As can be seen from this data, the samples prepared in accordance with this invention all exhibited increases in flexural modulus compared with the Comparative Samples. These increases were substantial in three of four cases, despite the fact that the density of each Sample was lower than the corresponding Comparative Sample. Other properties were roughly comparable, except that a substantial increase in elongation was seen when comparing Sample 3 with Comparative Sample C, and Sample Nos. 5 and 6 had much better heat sag values than their respective Comparative Samples. Example III Elastomer Sample Nos. 7-11 were prepared according to the general process described in Example 1, using a Cincinnati-Millicron HT RIM machine and a formulation as indicated in Table III following. In each instance, the chain extender mixture was preheated to 80° F (27° C) and the prepolymer to 100° F (38° C). The mold temperature was 165° F (74° C). Demold time was 45 seconds. The part was postcured for 15 minutes at 300° F (149° C) before physical properties are measured. Component Sample No. 7 8 9 10 11 A-side Prepolymer B (index) 105 Prepolymer C (index) 103 103 110 Prepolymer D (index) 95 B-side Parts by weight Chain extender A 85 85 75 50 50 Chain extender B - - 25 50 50 Chain extender C 15 15 - - - Tin Catalyst 0.1 0.1 0.1 0.1 0.1 A/B ratio 3.83 4.52 4.31 3.95 3.58 Prepolymer B was prepared by reacting equal quantities of a 143 equivalent weight "liquid MDI" and a 5000 molecular weight poly(propylene oxide) triol, and diluting to 198 equivalent weight with additional liquid MDI. Prepolymer C was prepared by reacting 47.9 parts MDI, 11.4 parts liquid MDI, 27.4 parts of a 1600 equivalent weight ethylene oxide-capped poly(propylene oxide) triol and 5.3 parts triethylene glycol, and diluting to 215 equivalent weight with MDI. Prepolymer D was prepared by reacting MDI with a 4000 molecular weight amine-terminated poly(propylene oxide) diol to obtain a 226 equivalent weight prepolymer. Chain extender A was 1,4-butanediol. Chain extender B was diethyltoluenediamine, mixture of 2,4 and 2,6 isomers. Chain extender C was 400 molecular weight difunctional amine-terminated poly(propylene oxide). The ratio of the weight of the A-side to that of the B-side is indicated in the above table as "A/B ratio." The properties of the samples are as reported in Table IV following. As can be seen from this data, very high modulus polymers can be prepared according to this invention. In addition, these elastomers have surprisingly high tensile strengths and excellent elongation for such stiff polymers. Example IV (Comparative) An isocyanate-terminated prepolymer was prepared by reacting approximately equal weights of a 2000 molecular weight pcly(propylene oxide) diol with hexamethylenediisocyanate at 50°C. The resulting prepolymer was a liquid containing 22.5 percent free isocyanate groups and had an equivalent weight of 184.2. An active hydrogen-containing composition (B-side) was prepared by thoroughly mixing 100 parts of DETDA, 30 parts of a 5000 molecular weight, trifunctional, amine-terminated poly(propylene oxide) (T-5000, available from Texaco Chemical Company), and 20 parts of a 2000 molecular weight, difunctional, amine-terminated poly(propylene oxide) (D-2000, available from Texaco Chemical Company). The prepolymer was reacted with the active hydrogen-containing composition at a 100 index using a Krauss-Maffei PU 80 RIM machine. The weight ratio of prepolymer to B-side was 1.427. Before molding, the prepolymer was heated to 110°F (44°C) and the B-side was heated to 100°F (38°C). The mold, a flat 1/8" (3.175 mm) plaque mold, was preheated to 275-295°F (135-146°C). After 5 minutes in the mold, the part was removed and tested, with results as indicated in Table V following (Sample No. 12). Sample No. 13 was similarily made, except it was post cured as indicated in Table V. The experiment was again repeated, (Sample No. 14) this time using a weight ratio of 1.5 to provide an isocyanate index of 105. A fourth experiment was run (Sample No. 15) which was identical to Sample No. 14 except it was postcured as indicated in Table V. The experiment was again repeated, this time adding 75 parts milled glass and 1.5 percent, based on isocyanate-reactive components, of a silicone surfactant to the formulation used to prepare Sample No. 12. The weight ratio of prepolymer to B-side was adjusted to 1.02 to provide a 105 index, and the mold temperature was increased to 305-315° F (151-158° C). This sample was designated Sample No. 16. Each of the moldings was tested for physical properties, with the results as indicated in Table V following. These elastomers have excellent properties, based on their hardness and densities. Particularly good low temperature impact values are seen, even when no postcuring is done.

Claims: A two-step process for preparing a polyurethane and/or polyurea elastomer comprising (1) reacting a stoichiometric excess of a polyisocyanate and an isocyanate-reactive compound having an equivalent weight of 700 to 2500, and reacting this preformed, liquid, isocyanate-terminated prepolymer with (2) a chain extender mixture, which chain extender mixture comprises (a) a mixture comprising a hydroxyl-terminated chain extender having an equivalent weight of 31 to 300 and an aromatic amine-terminated chain extender and/or an aliphatic amine-terminated chain extender, or (b) a mixture comprising an aromatic amine-terminated chain extender and an aliphatic amine-terminated chain extender, wherein the isocyanate index is from 70 to 200, and wherein said chain extender mixture contains fewer than 0.5 equivalents of an isocyanate-reactive material having an equivalent weight of 700 to 2500 per equivalent of the isocyanate-reactive compound used in step (1), wherein in the chain extender mixture of (2) (a) said aliphatic amine-terminated chain extenders have 2-4 aliphatic amine groups which contain an active hydrogen per molecule and the equivalent weight of said aliphatic amine-terminated chain extender is from 32 to 300 and wherein in the chain extender mixture of (2) (b) the molecular weight of the aliphatic amine-terminated chain extender is lower than 1000. The process of claim 1 wherein said prepolymer has an equivalent weight of from 200 to 525. The process of Claim 2, wherein said prepolymer is prepared from an aliphatic diisocyanate. The process of Claim 2, wherein the isocyanate index is from 100 to 115. The process of Claim 2, wherein said elastomer has an unfilled flexural modulus of at least 150,000 psi (1.03 GPa) at a density of 1.15 g/cm 3 (1150 kg/m 3 ). The process of claim 2, wherein said chain extender mixture comprises (A) a mixture of a hydroxyl-terminated chain extender and a sterically hindered aromatic diamine, or (B) a mixture of an amine-terminated polyether having 2-3 amine groups per molecule and an equivalent weight of at least 100 and a sterically hindered aromatic diamine, or (C) a mixture of an amine-terminated polyether having 2-3 amine groups per molecule and an equivalent weight of at least 100, and a hydroxyl-terminated chain extender. The process of claim 6, wherein said hydroxyl-terminated chain extender comprises 25-75 percent of the combined weight of the hydroxyl-terminated chain extender and the amine-terminated chain extender; said chain extender mixture (B) contains 0.01 to 0.5 equivalent of the amine-terminated poylether per equivalent of aromatic diamine; and said chain extender mixture (C) contains 0.01 to 0.5 equivalent of the amine-terminated polyether per equivalent of the hydroxyl-terminated chain extender. The process of claim 6 or 7, wherein said chain extender mixture (A) comprises a mixture of ethylene glycol, propylene glycol or 1,4-butanediol, and diethyltoluenediamine; said sterically hindered aromatic diamine is diethyltoluenediamine; and said amine-terminated poylether has an equivalent weight of at least 150. The process of Claim 7, wherein said prepolymer is (A) the reaction product of a reaction mixture comprising an aromatic diisocyanate and a polyether polyol having an equivalent weight of from 700 to 2500, or (B) the reaction product of a reaction mixture comprising an aromatic diisocyanate and an amine-terminated polyether having an equivalent weight of from 700 to 2500.

Inventors: PEFFLEY RICHARD D, SPELLS JOHN HENRY, VANDERHIDER JAMES A, PEFFLEY, RICHARD D., SPELLS, JOHN HENRY, VANDERHIDER, JAMES A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08G18
IPC codes: C08G18