HK1034269A - Polyurethane and polyurethane/urea heat-cured and moisture-cured elastomers with improved physical properties - Google Patents

Description

Polyurethane and polyurethane/urea heat-cured and moisture-cured elastomers having improved physical properties

Technical Field

The present invention relates to polyurethane and polyurethane/urea heat-cured elastomers prepared by chain extension or moisture curing of isocyanate-terminated prepolymers. More particularly, the present invention relates to prepolymers prepared by reacting a stoichiometric excess of di-or polyisocyanates (other than toluene diisocyanate) with a polyol component comprising a high molecular weight, low unsaturation polyoxypropylene polyol and a very low molecular weight polyol. The elastomers have improved hardness, resilience, tear strength and compression set compared to other similar elastomers having the same hard segment content. Films prepared from the composition have superior tensile and tear strength.

Background

In general, polyurethane thermoset elastomers can be divided into two broad categories, differing in the type of monomeric isocyanate used to prepare the elastomer precursor prepolymer. When methylene diphenylene diisocyanate (MDI) or MDI variants are used to form the prepolymer, the isocyanate group to polyol hydroxyl equivalent ratio can be very high. The possible range of isocyanate group content provides flexibility in formulation. However, the high reactivity of the isocyanate groups of MDI generally requires the use of diol chain extenders in cast elastomeric systems, since amines with suitable reactivity are not commercially available. To maintain the desired balance of properties, the elastomers prepared from MDI are therefore polyurethane elastomers, rather than the polyurethane/urea elastomers that are prominent in the art.

Thermally cured polyurethane/urea elastomers should not be confused with reaction injection molded polyurethane/urea (RIM) systems. In the latter, MDI and modified MDI are typically used with reactive diamines such as diethyltoluenediamine and injected into highly rigid molds at high pressures. Prepolymers are generally not used in such systems except in small amounts because the fast reacting mixture must traverse the entire, often relatively complex mold in a short period of time prior to gelation. Therefore, low viscosity systems are desirable in conjunction with very high pressure, short duration injection molding. The RIM method has acquired a separate place in the art. RIM systems are not thermally cured, but rather rapidly cured without the application of heat.

Toluene Diisocyanate (TDI) type elastomers are the second largest class of heat-cured elastomers, but the largest class with respect to the elastomers produced. Approximately 65% of the heat-cured polyurethane elastomers are TDI-based systems. In practice, TDI-based prepolymers with high isocyanate group content are rarely used, and amine-based rather than diol-based chain extenders are used to obtain hard segments with urea linkages. The resulting elastomer is thus a polyurethane/urea elastomer. TDI-based prepolymers typically avoid high isocyanate group content due to the volatility of TDI.

The percent NCO content of isocyanate-terminated prepolymers derived from TDI is limited to up to about 10 weight percent due to the limited NCO/OH ratio. At such limited isocyanate content, the flexibility of the formulation is reduced. Furthermore, because the urea hard segment content is related to the isocyanate group content in the amine cured system, it is more difficult to prepare elastomers having high tensile strength and other desirable physical properties.

Many attempts have been made to increase the physical properties of polyurethane elastomers, many of which have been successful in improving certain physical properties, often at the expense of other properties. For example, in U.S. patent No.4, 934, 425, the preparation of polyurethane/urea elastomers with improved dynamic properties is illustrated. The elastomers are prepared from TDI-based prepolymers containing a high molecular weight polytetramethylene ether glycol (PTMEG) having a molecular weight of 2000Da (daltons) and a medium molecular weight PTMEG having a molecular weight of 1000 Da. Elastomers prepared from the blended prepolymers show a considerable improvement in resistance to heat build-up in rubber tire applications, exhibiting lower hysteresis loss. However, when the dynamic properties are improved, no improvement is indicated with respect to tensile strength, elongation or hardness.

In U.S. patent No.3, 963, 681, the preparation of polyurethane/urea elastomers having improved cut growth and flex crack resistance for tire applications is disclosed. TDI-based prepolymers are prepared from blends of very high molecular weight PTMEG (molecular weight above 4500 Da) and medium molecular weight PTMEG, the average molecular weight of the blends being between 1000Da and 4500 Da. The molecular weight of the higher molecular weight PTMEG is required to be above the "critical molecular weight" of the PTMEG polymer, while the molecular weight of the lower molecular weight component must be below this value. Tensile strength and notch growth are improved. However, not all polyether polyols are known to have a "critical molecular weight". Moreover, the molecular weight is very important; for example, a blend of 800Da PTMEG and 3800Da PTMEG is disclosed as an unsuitable example.

U.S. patent No.5, 077, 371 illustrates hardness growth in polyurethane/urea cast elastomers. The rate of hardness increase is important because cast elastomer parts cannot be demolded before possessing sufficient green strength in order not to risk damage to the part. The rapid increase in hardness makes demolding faster. Curing can be done in an oven outside the mold and the production speed is increased accordingly. The addition of toluene diisocyanate dimer (TDI dimer) in an amount of 0.3 to 6 weight percent of the total isocyanate to the isocyanate component used to prepare the bimodal distribution PTMEG prepolymer was found to increase the rate of hardness build. Unfortunately, of the remaining physical properties, the hardness, elongation and rebound remained essentially unchanged, the tensile strength and especially elongation actually decreased, and only the tear strength showed a significant improvement. Additional time and expense is added to the elastomer formulation to make the TDI dimer.

PTMEG has been traditionally used to prepare high performance polyurethane/urea elastomers as illustrated in three of the aforementioned U.S. patents 4, 934, 425, 3, 963, 681 and 5, 077, 371. Although PTMEG requires higher cost than polyoxyalkylene polyols such as polyoxyethylene glycol and polyoxypropylene glycol, PTMEG is still in use today due to the desirable physical properties obtained by its use of polyurethanes.

Moisture-cured polyurethane elastomers are commonly used as caulks and sealants. Rather than introducing a diamine to react with isocyanate to form the linking urea hard segment, moisture-cured elastomers rely on the reaction of free isocyanate groups with moisture to form urea linkages. Many moisture-cured films and sealants exhibit relatively low physical properties, particularly tensile strength and/or tear strength, so improvements in these and other properties are desirable.

Most polyoxyalkylene polyether polyols are polymerized by base catalysis. For example, polyoxypropylene diols are prepared by base-catalyzed oxypropylation of difunctional initiators such as propylene glycol. In the base-catalyzed propoxylation, the competing rearrangement of propylene oxide to allyl alcohol continually introduces unsaturated, monofunctional, oxyalkylatable species into the reactor. Alkoxylation of the monofunctional material produces an allyl-terminated polyoxypropylene monol. Rearrangement is discussed in BLOCK AND GRAFT POLYMERIZATION, Vol.2, Ceresa, Ed _ John Willy & Sons, pp.17-21. Unsaturation is measured according to ASTM D-2849-69, "Testing Urethane Foam Polyol Raw materials," expressed as milliequivalents of unsaturation per gram of Polyol (meq/g).

Due to the continuous production of allyl alcohol and its subsequent propoxylation, the average functionality of the polyol mixture is reduced and the molecular weight distribution broadened. The base-catalyzed polyoxyalkylene polyol contains a substantial amount of low molecular weight, monofunctional material. The content of monofunctional species in the 4000Da molecular weight polyoxypropylene diol may be between 30 and 40mo 1%. In these cases, the average functionality is reduced from a nominal or theoretical functionality of 2.0 to about 1.6 to 1.7. In addition, the polyols have a high polydispersity, Mw/Mn, due to the presence of many low molecular weight fractions. Unless otherwise specified, molecular weight and equivalent weight, expressed herein in Da (daltons), are number average molecular weight and number average equivalent weight, respectively.

In the past, some researchers have suggested the use of low unsaturation, high functionality polyols to improve the physical properties of elastomers. See, for example, U.S. patent nos.4, 239, 879 and 5, 100, 997. For example, A.T. Chen et al, "comparison of dynamic properties of polyurethane elastomers based on low unsaturation polyoxypropylene glycols and poly (oxytetramethylene) glycols" POLYURETHANES WORLD CONGRESS 1993, 10.10-13.1993, page 388-399 compares the properties of elastomers derived from PTMEG with those derived from conventional polyoxypropylene glycols and low unsaturation polyoxypropylene glycols. In the Shore A90 cast elastomers, the modulus and elongation of PTMEG-MDI prepolymer derived, butanediol extended polyurethane elastomers were slightly lower than those of low unsaturation polyoxypropylene diol derived elastomers, however, the tensile strength of PTMEG elastomers was much higher. For polyurethane/urea cast elastomers, a direct comparison is not possible because the only PTMEG example uses 1000Da PTMEG, while the two low unsaturation polyoxypropylene diol examples use about 2000Da molecular weight diols. In addition to elongation, the PTMEG examples had higher physical properties, which is expected. In particular, conventional base-catalyzed polyoxypropylene diols produce polyurethane/urea cast elastomers whose physical properties are substantially indistinguishable from those prepared from low unsaturation diols.

Reducing the unsaturation of polyoxyalkylene polyols by reducing the catalyst concentration and reducing the reaction temperature is not feasible because the reaction rate is so slow that oxypropylation takes days or even weeks, although low unsaturation polyols can be prepared in this manner. Accordingly, efforts have been made to find catalysts which produce polyoxypropylated products in a reasonable time with little introduction of monofunctional groups due to allylic species. For example, in the early 60 s of the 20 th century, U.S. patent nos.3, 427, 256; 3,427, 334; 3,427, 335; 3,829, 505; and 3, 941, 849, double metal cyanide catalysts such as zinc hexacyanocobaltate complexes were developed. Although the unsaturation can be reduced to the range of about 0.018meq/g, the cost of these catalysts hinders commercialization due to the need for time and money consuming catalyst removal steps.

Alternative base catalysts such as cesium hydroxide and rubidium hydroxide as disclosed in U.S. patent nos.3, 393, 243, and oxidation and the use of barium and strontium hydroxides as disclosed in U.S. patent nos.5, 010, 187 and 5, 114, 619 have provided suitable improvements in unsaturation, however, catalyst cost and in some cases toxicity can offset these modest improvements provided, impeding its commercialization. Catalysts such as calcium naphthenate and combinations of calcium naphthenate with tertiary amines have proven successful in preparing polyols having unsaturation as low as 0.016meq/g, and more commonly in the range of 0.02-0.04meq/g, as disclosed in U.S. patent nos.4, 282, 387, 4, 687, 851 and 5, 010, 117.

Double metal cyanide complex (DMC) catalysts were once again favored in the 80's of the 20 th century, and improvements in catalytic activity and catalyst removal processes prompted manufacturers to rapidly supply DMC-catalyzed polyols in the range of 0.015-0.018meq/g of unsaturation on the market. However, base catalysis continues to be the predominant method for preparing polyoxypropylene polyols and is still dominant today.

However, a recent further development from the ARCO Chemical Co. on DMC catalysts and polyoxyalkylation processes has enabled the practical preparation of ultra-low unsaturation polyoxypropylene polyols. High molecular weight polyols, such as those in the 4000Da to 8000Da molecular weight range, typically exhibit unsaturation in the range of 0.004 to 0.007meq/g when catalyzed by the novel DMC catalysts. At these levels of unsaturation, the amount of monofunctional species is only 2 mol% or less than 2 mol%. Furthermore, GPC analysis indicates that the polyol is virtually monodisperse, often exhibiting a polydispersity of less than 1.10. Several of these polyols have recently been used as ACCLAIM^TMPolyols are produced industrially.

However, the presence of low unsaturation, high functionality polyols has not proven to be a panacea as expected by those skilled in the art. In many systems, replacing the conventional polyol with a polyol having very low unsaturation causes the system to fail, necessitating considerable effort in reformulation. In other cases, the low unsaturation polyols are easily substituted and the expected improvement is not realized. The reasons for the unexpected difficulties associated with the use of low unsaturation polyols are certainly unknown.

However, the formulation of conventional polyurethane systems uses polyether polyols, the actual and theoretical functionalities of which are often significantly different. For example, a conventional base-catalyzed 6000Da triol has only about 2.4 practical functionality due to the presence of 30-40 mol% monol. The polyol blend of low unsaturation, high functionality diol and low unsaturation, high functionality triol was replaced to simulate a functionality of 2.4 but not to get the same functionality distribution as the normal polyol. The triol portion of the conventional catalyzed triol creates three-way branched "crosslinking" sites, while the monofunctional portion serves as a chain terminator. In diol/triol blends of the same functionality, the number of three-way branching sites is less, but there is no monofunctional chain terminator.

The use of polyols having a low content of monofunctional species has been proposed as a means of increasing the molecular weight of polymers; increasing the polymer molecular weight, in turn, tends to prove desirable in producing high performance polymers. However, high molecular weight is not necessarily a desirable feature in many polymer systems. For example, as indicated by G.Odian, PRINCPLE OF POLYMERIZATION, John Wiley & Sons, 1981, pp.20-21, it is often desirable that the molecular weight be moderate rather than high. For example, in engineering thermoplastics, higher molecular weights generally increase tensile strength, melting point, modulus and the like, but if the molecular weight is too high, the polymer viscosity becomes too high to be processed. For polyurethanes, which have a molecular weight much lower than engineering thermoplastics, polymer morphology and physical properties are affected by many factors including, for example, the amount and nature of the hard segment, the stereochemistry of the isocyanate used, and the like. Often a formulation must be selected to balance conflicting properties. For example, an increase in tensile strength is often accompanied by a decrease in elongation.

Mascioli, in "POLYURETHANE applications for novel high molecular weight polyols", 32ND ANNUAL POLYURETHANE TECHNICAL/MARKETING CONFERERENCE, 10.1-4.10.1989, page 139-142, discloses that low unsaturation, 10-11,000 Da triols replace the common 6000Da triols in POLYURETHANE foam formulations to give rigid foams. Softer foams are desirable because the polyoxypropylene branches of the triols are longer in length and therefore more flexible; and lower crosslink density. The substitution of high molecular weight, low unsaturation polyols for the conventionally catalyzed polyols of limited molecular weight in polyurethane production has also been recommended as a means of using less of the more expensive isocyanates. However, suitable formulations must be developed.

In the field of high resilience polyurethane flexible foams, as disclosed in Copending U.S. application serial No.08/565, 516, it has been found that DMC-catalyzed, low unsaturation polyols replacing common base-catalyzed polyols of similar molecular weight and composition can cause foam collapse in high resilience polyurethane foam systems. Some now believe that this anomalous behavior may be attributed to very small amounts of very high molecular weight components having molecular weights within 100,000 or in the range above 100,000. This particularly high molecular weight component, even in very small amounts, can act as a surfactant and tends to destabilize the polyurethane foam or to increase viscosity, thereby interfering with normal curing mechanisms such as hard segment termination.

Thus, it is claimed that the formulation of polyurethane systems requires an unobtrusive and informal reformulation, taking advantage of the high molecular weight, high functionality, low polydispersity, and low unsaturation exhibited by low unsaturation polyols such as those prepared by DMC catalysis and the attendant lack of monofunctional species.

Summary of the invention

The present invention relates to polyurethane and polyurethane/urea elastomers prepared by chain extension or moisture cure of isocyanate-terminated prepolymers or quasi-prepolymers prepared by reacting di-or polyisocyanates other than toluene diisocyanate with a mixture containing high molecular weight, very low unsaturation polyoxypropylene diols and low molecular weight diols having a hydroxyl number between 50 and 200. The chain-extended, cured elastomers surprisingly have improved hardness, resilience, tear strength, and compression set compared to elastomers having similar hard segment contents prepared from prepolymers using the same hydroxyl number of a single polyol. Moisture-cured elastomers exhibit exceptional tensile and tear strength.

Description of the preferred embodiments

The chain-extended elastomers of the present invention are prepared by reacting an isocyanate-terminated prepolymer or quasi-prepolymer, described below, with a chain extender at an isocyanate index of from about 90 to about 120, preferably from 95 to 110, and most preferably 100-105. As is well known, the isocyanate index is the ratio of equivalents of isocyanate to equivalents of isocyanate-reactive material multiplied by 100. In determining the equivalents of isocyanate-reactive materials, 1 mole of hydroxyl or amino groups makes up 1 equivalent. The moisture-curable elastomers are cured in the presence of atmospheric moisture or in a heated chamber.

The chain-extended cast elastomers are processed by intensively mixing the prepolymer-containing A-side and the diol-or diamine-containing B-side, degassing under vacuum if necessary, and introducing the mixture into an open or closed mold. After sufficient green strength has been developed to enable demolding and post-processing, the elastomer is removed from the mold and then post-cured, typically at a slightly elevated temperature. Alternatively, the elastomer may be subjected to curing in the mold itself. The process for preparing the elastomers themselves is common and can be referred to as POLYURETHATHANE: chemerity ANDTECHNOLOGY, j.h.saunders and k.c.frieh, interscience publishers, New York, an appropriate section in 1963; and the handbook of polyurethanes, GunterOertel, Ed., Hanser Publishers, Munich, 1985, both of which are incorporated herein by reference. The moisture-cured elastomer may be formulated with conventional fillers, rheology control agents, thixotropic agents, and the like, or may be extruded or cast as neat films or processed from solution.

The isocyanate-terminated prepolymer is prepared by reacting a di-or polyisocyanate other than toluene diisocyanate with a polyol component as described below. The prepolymer preferably has an NCO group content of about 2 to about 12 weight percent.

Suitable di-or polyisocyanates for use in the present invention are aromatic, aliphatic, and cycloaliphatic species other than toluene diisocyanate generally known to those skilled in the art. Examples include 2, 2 ' -, 2, 4 ' -, or 4, 4 ' -Methylenediphenylene Diisocyanate (MDI), polymeric MDI, MDI variants, carbodiimide-modified MDI, modified di-and polyisocyanates (urea-, biuret-, urethane-, isocyanurate-, allophanate-, carbodiimide-, or uretdione-modified, etc.), hydrogenated MDI, p-phenylene diisocyanate, TMXDI, isophorone diisocyanate, 1, 4-diisocyanatobutane, 1, 4-cyclohexane diisocyanate, hexamethylene diisocyanate, and the like and mixtures thereof. For economic reasons, it is also preferred to use the commercially available isomers or mixtures thereof.

In addition to the prepolymer process, a quasi-prepolymer process can be used to prepare the elastomers of the present invention. Quasi-prepolymers are prepared from an excess of di-or polyisocyanate and a reduced proportion of polyol component in the same manner as described herein for the prepolymer. However, the% NCO content of the quasi-prepolymer is higher than the% NCO of the prepolymer due to the smaller amount of polyol component relative to the isocyanate. For example, an isocyanate group content of 12 wt% NCO to 30 wt% NCO is suitable. Any necessary remaining polyol component may be introduced together with the chain extender as a blend or in a separate stream.

The polyol component which is reacted with the di-or polyisocyanate to form the prepolymer or quasi-prepolymer is a mixture of at least two hydroxyl functional components, the first being a low molecular weight diol having a molecular weight of less than about 400Da and the second being a low unsaturation polyoxypropylene diol having a molecular weight of about 2000Da or above 2000Da, such that the hydroxyl number of the mixture of the at least two components is in the range of about 50 to about 200.

The low molecular weight diol may be any dihydroxy functional compound having a molecular weight of less than about 400 Da. Illustrative, but non-limiting examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1, 3-propanediol, 2-methyl-1, 3-propanediol, neopentyl glycol, 1, 3-and 2, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 8-octanediol, 1, 4-cyclohexanediol, 1, 4-cyclohexanedimethanol, hydroquinone bis [ 2-hydroxyethyl ether ], and various bisphenols and their bis [ hydroxyalkyl ether ] derivatives. The above alkoxylation products are also useful. Preferably, the low molecular weight diol has a molecular weight of less than about 200 Da. Mixtures of one or more such low molecular weight diols are also useful. Small amounts of low molecular weight triols, tetrols or the like, such as glycerol, trimethylolpropane, pentaerythritol, or the like, can be added to the low molecular weight diol mixture, provided that the amount of triol, tetrol or higher functionality material is about 10 mole% or less than 10 mole%. Unless otherwise indicated, "low molecular weight diols" allow for these amounts of higher functionality species.

The low unsaturation polyoxypropylene diol has a molecular weight of about 2000Da or above 2000Da, preferably 2000Da to 12,000 Da, more preferably 3000Da to 10,000 Da, and most preferably 4000Da to 8000 Da. The unsaturation must be below 0.020meq/g, preferably below 0.015meq/g, and most preferably below 0.010 meq/g. Unsaturation of between about 0.002meq/g and about 0.007meq/g is preferred. To achieve the requisite low unsaturation, any catalytic method for achieving the desired molecular weight and unsaturation may be used. However, it is desirable to use double metal cyanide complex catalysts as alkoxylation catalysts. For example, such catalysts are disclosed in U.S. patent nos.5, 470, 813 and 5, 482, 908, which are capable of producing polyols having molecular weights in the range of 2000Da to 12,000 Da and degrees of unsaturation generally in the range of about 0.004 to 0.007 meq/g. Mixtures of more than one low unsaturation polyoxypropylene diol with a low molecular weight diol component may be used.

The blend of low molecular weight diol and low unsaturation polyoxypropylene diol must have a hydroxyl number of between 50 and 200, preferably between 75 and 150, and most preferably in the range of 90-120. The hydroxyl number is calculated by adding the weight fractional hydroxyl numbers of the components of the mixture, the weight fractional hydroxyl number being the weight fraction of the component multiplied by the hydroxyl number of the component. It must be emphasized that blends of high molecular weight substances and low molecular weight substances are used to prepare the prepolymer, giving the cast elastomers of the invention a particular quality. These properties can neither be reproduced with a single component nor with bimodal blends that do not contain species having a molecular weight below about 400 Da.

The prepolymer is prepared by standard techniques. For example, the polyol component and the isocyanate component may be thoroughly mixed, typically under a nitrogen atmosphere, and stirred until the isocyanate group content drops to a constant value, indicating that the reaction is complete. It is advantageous to gently heat the mixture to a temperature in the range of, for example, 50 ℃ to 70 ℃. Urethane reaction promoting catalysts such as various well-known tin catalysts, amine catalysts or other catalysts that promote the reaction between isocyanate and hydroxyl groups may be used if desired. The reaction may be batch, semi-batch or continuous. Examples of prepolymer preparation may be found in POLYURETHANE (POLYURETHANE): chemistry and technology (CHEMISTRY ANDTECHNOLOGY), POLYURETHANE HANDBOOK (POLYURETHANE HANDBOOK), U.S. Pat. No.5, 278, 274 and Canadian published application 2, 088, 521, herein incorporated by reference.

Chain extenders useful in the present invention are the conventional diol and diamine chain extenders known to those skilled in the art. Suitable glycol chain extenders include, for example, ethylene glycol, 1, 4-butanediol, 1, 3-propanediol, 1, 5-pentanediol, neopentyl glycol, 2-methyl-1, 3-propanediol, diethylene glycol, tripropylene glycol, and the like, and mixtures thereof. Suitable diamine chain extenders include aliphatic and aromatic diamines. Preferred diamines are sterically hindered or electrically deactivated aromatic diamines. Examples of these are various cyclic alkylated toluenediamines, methylenedianilines such as 3, 5-Diethyltoluenediamine (DETA), and similar compounds such as those disclosed in U.S. patent 4,218,543. Examples of the aromatic diamine that becomes low in activity by the electrical effect of the cyclic substituent include 4, 4 '-methylene-bis (2-chloroaniline) (MOCA or MbOCA) and 4, 4' -methylene-bis (3-chloro-2, 6-diethylaniline) (MCDEA). Diamines without steric hindrance or cyclic deactivating groups react too quickly and result in insufficient pot life to fill the mold, especially when complex molds are used. The chain extender component may include a small amount of a crosslinking agent such as diethanolamine, triethanolamine and the like.

Catalysts may be used in certain systems. Catalysts have been described above with respect to prepolymer formation, and suitable catalysts are well known to those skilled in the art. Examples of suitable catalysts can be found in the handbook of polyurethanes, pages 90-95, and polyurethanes: chemistry and Process, pages 129-217, both of which are incorporated herein by reference.

Conventional additives and auxiliaries may also be added, including but not limited to fillers, plasticizers, dyes, pigments, UV stabilizers, heat stabilizers, antioxidants, flame retardants, conductive agents, internal mold release agents, foaming agents, and the like. When a blowing agent is included, the product is a microcellular elastomer. Suitable blowing agents include reactive species, such as water, and physical species, such as volatile hydrocarbons, CFCs, and the like. Mixtures of reactive and physical blowing agents may be used. Polymeric solids, such as vinyl polymer solids found in polymer polyols and isocyanate-derived solids such as those found in PIPA and PHD polyols, may also be included, for example by using a suitable polymer polyol dispersion having as its "base" or "carrier" polyol a low unsaturation polyoxypropylene diol. If the amount of polymer solids desired is low, small amounts of high solids polymer polyol dispersions prepared from conventionally catalyzed polyols can be used.

The polyoxypropylene diol may contain oxyethylene moieties, for example introduced during the preparation of the polyol by random copolymerization of ethylene oxide together with propylene oxide or by capping with ethylene oxide. The amount of ethylene oxide is generally 40 wt% or less, preferably less than 20 wt%, and more preferably from about 5 to about 15 wt%. If the polyoxypropylene diol containing oxyethylene moieties is prepared using a double metal cyanide complex catalyst, it is preferred that the oxyethylene moieties are present during most of the oxypropylation period.

The polyoxypropylene diol may also contain small amounts of higher alkylene oxides, especially oxetane, 2, 3-epoxybutane, l, 2-epoxybutane and the like. The amount of higher alkylene oxide should generally be limited to less than about 10 wt%. More preferably, the polyoxypropylene diol is essentially all of the oxypropylene moieties, or oxypropylene moieties with no more than about 10 weight percent of random oxyethylene moieties. The low unsaturation polyoxypropylene diol may also contain minor amounts of conventional, base-catalyzed polyoxypropylene diols, provided that the amount of such conventional diols does not exceed 20 mole percent of the total high molecular weight diols, and that the unsaturation of the high molecular weight portion of the diol mixture is less than 0.020meq/g, preferably less than 0.015 meq/g.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples. These examples are provided herein for illustrative purposes only and are not intended to be limiting unless otherwise specified.

Example 1 and comparative example C1

Moisture-cured films were prepared by casting a neat isocyanate-terminated prepolymer onto a glass plate at a thickness of 30 mils and curing at atmospheric humidity for 24 hours. Prior to testing, the films were cured and conditioned at 73 ° F (23 ℃) and 50% relative humidity for at least 4 weeks.

In example 1, ACCLAIM 3201 polyether diol, a low unsaturation polyoxypropylene diol having a molecular weight of about 3200Da and commercially available from ARCO Chemicals, Inc., was blended with diethylene glycol (DEG) (molecular weight about 116Da) to produce a blend having an average molecular weight of about 1000 Da. The polyol/diol mixture is then combined with Trimethylolpropane (TMP) (5: 1 equivalent ratio of polyol to TMP) and reacted with isophorone diisocyanate at a 2: 1 NCO/OH molar ratio to give an isocyanate-terminated prepolymer having a free NCO content of about 6 weight percent. The prepolymer is moisture cured as described above.

In comparative example C1, ARCOL PPG-1025, a common 1000mol.wt. polyoxypropylene diol, was used in place of the ACCLAIM 3201 diol/DEG blend. The polyol is combined with TMP (5: 1 equivalent ratio of polyol to TMP) and reacted with isophorone diisocyanate at a 2: 1 NCO/OH molar ratio to give an isocyanate-terminated prepolymer having a free NCO content of about 6 weight percent. The prepolymer is moisture cured as described above.

As shown in table 1, moisture-cured polyurethanes based on blends of ACCLAIM 3201 diol and DEG had better overall physical properties, including high tensile strength, modulus, elongation, and tear strength.

TABLE 1

Examples	1	C1
Prepolymer polyols	ACCLAIMTM3201 diol/diethylene glycol	ARCOL PPG-1025
Physical Properties
100% modulus (psi)	920	355
300% modulus (psi)	1920	1000
Tensile Strength (psi)	5600	3700
Elongation percentage(％)	520	500
Tear Strength (psi)	420	220

Examples 2 to 3 and comparative examples 2 to 3

The following quasi-prepolymer technique was used to prepare elastomers based on a mixture of 4, 4' -MDI and Carbodiimide (CD) modified MDI.

The isocyanate mixture and polyol were combined at an NCO/OH equivalent ratio of 5.67 to give a prepolymer having a free NCO content of 16% by weight. In examples 2 and 3, the polyol is a mixture of ACCLAIM4200 polyether polyol (a low unsaturation polyoxypropylene diol having a molecular weight of about 4000Da and commercially available from ARCO chemical company) and tripropylene glycol (TPG). In comparative examples 2 and 3, the polyol was PPG 1025 diol (common 1000mol.wt. polyoxypropylene diol).

The quasi-prepolymer prepared above was used to prepare elastomers having a hard segment content of 35% (example 2 and comparative example 2) or 25% (example 3 and comparative example 3). Each quasi-prepolymer was chain extended with a mixture of 1, 4-butanediol and ACCLAIM 4420 diol (about 4000mol.wt. of a low unsaturation, EO-capped polyoxypropylene diol) in the presence of dibutyltin dilaurate catalyst. The ratio of 1, 4-butanediol and ACCLAIM 4420 diol was adjusted as shown in Table 2 to vary the hard segment content of the elastomer. The amount of tin catalyst used was adjusted to give a pot life of about 90 seconds and a demold time of about 22 minutes.

TABLE 2

Table 2 summarizes the formulations of the elastomers and the results of the physical property tests. As shown in the table, the elastomers obtained from quasi-prepolymers based on a mixture of high molecular weight, low unsaturation polyether diols and diol chain extenders have superior hardness, resilience, tear strength, and compression set compared to similar elastomers wherein the quasi-prepolymers are prepared from a single common 1000mol.

Having now fully described this invention, it will be apparent to those skilled in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.

Claims (15)

1. An isocyanate-terminated prepolymer or quasi-prepolymer comprising the reaction product of a stoichiometric excess of a di-or polyisocyanate other than toluene diisocyanate and a polyol component comprising:

ai) one or more high molecular weight polyoxypropylene diols having an unsaturation of less than 0.02meq/g and a molecular weight of greater than 2000 Da; and

aii) one or more low molecular weight diols having a molecular weight of less than 400Da such that the hydroxyl number of the above polyol component is from 50 to 200.

2. A prepolymer or quasi-prepolymer according to claim 1 wherein said prepolymer has an NCO group content of 2% to 12% by weight.

3. A prepolymer or quasi-prepolymer according to claim 1 or 2 wherein said polyoxypropylene diol has an unsaturation of less than 0.015 meq/g.

4. A prepolymer or quasi-prepolymer according to any preceding claim wherein said polyoxypropylene diol has a molecular weight of 3000Da to 8000 Da.

5. A prepolymer or quasi-prepolymer according to any preceding claim wherein at least one of said low molecular weight diols has a molecular weight not higher than 200 Da.

6. A prepolymer or quasi-prepolymer according to any preceding claim wherein said low molecular weight diol is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methyl-1, 3-propanediol, and mixtures thereof.

7. A prepolymer or quasi-prepolymer according to any preceding claim wherein the hydroxyl number of the polyol component is in the range 75 to 150.

8. A polyurethane or polyurethane/urea elastomer comprising the reaction product of a) a prepolymer according to any preceding claim and b) a chain extender at an isocyanate index of 85 to 115.

9. A moisture-curable polyurethane or polyurethane/urea elastomer comprising the reaction product of a prepolymer according to any one of the preceding claims 1 to 7 and water.

10. An elastomer according to claim 8 wherein said chain extender comprises a diol or diamine.

11. An elastomer according to claim 8 or 10 wherein said chain extender is selected from the group consisting of 1, 4-butanediol, ethylene glycol, neopentyl glycol, 2-methyl-1, 3-propanediol, 4, 4' -methylenebis (3-chloro-2, 6-diethylaniline).

12. Microcellular elastomers according to any one of claims 8 to 11.

13. A process for preparing a polyurethane or polyurethane/urea elastomer, the process comprising reacting at an isocyanate index of from 85 to 115:

a) an isocyanate-terminated prepolymer or quasi-prepolymer prepared by reacting a stoichiometric excess of a di-or polyisocyanate other than toluene diisocyanate with a polyol component comprising:

a) i) one or more high molecular weight polyoxypropylene diols having an unsaturation of less than 0.02meq/g and a molecular weight of greater than 2000 Da; and

a) ii) one or more low molecular weight diols having a molecular weight below 400Da,

so that the hydroxyl number of the polyol component is 50 to 200; and

b) a chain extender.

14. A process according to claim 13, wherein the prepolymer or component ai), aii) or b) is as defined in any one of claims 2 to 7, 10 or 11.

15. The process according to claim 13 or 14, wherein the reaction is carried out in the presence of water, a physical blowing agent, or a mixture thereof to produce a microcellular elastomer.