GB2336847A - A method for producing polyurethane compositions which exhibit a high flexural resistance - Google Patents

Abstract

A method for producing polyurethane compositions that exhibit a high flexural resistance which comprises: (a) prereacting from 6 to 30 %wt of paraphenylene diisocyanate with from 94 to 70 %wt of a polydiene diol having up to about 2 terminal hydroxyl groups per molecule and a number average molecular weight between 500 and 20,000 at a NCO to OH molar ratio ranging from 1.5:1 to 10:1, and (b) adding to the product of (a) a sufficient amount of a compatible chain extender or mixture of chain extenders to make the overall NCO/OH or NCO/(OH+NH 2 ) ratio 0.9 to 1.1 and to achieve a hard segment content of from 10 to 45 %wt.

Description

- 1 2336847 A METHOD FOR PRODUCING POLYURETHANE COMPOSITIONS WHICH EXHIBIT

A HIGH FLEXURAL RESISTANCE

Field of the Invention

This invention relates to strong polyurethane elastomer compositions containing a polydiene diol and a chain extender which exhibit a very high flexural resistance. Background of the Invention

Polyurethanes are generally composed of an isocyanate compound, a polyol, and a chain extender. A broad spectrum of properties can be achieved by varying the type and amount of each of these components. For many applications such as elastomers, adhesives, and sealants, the diisocyanate is an aromatic compound and the chain extender is a low molecular weight diol or diisocyanate. The polyol is generally a polyether or polyester although other diols have also been used. When the object is to make elastomers, adhesives, and sealants these compounds are combined and reacted in such a way to obtain soft, flexible materials. However, the combination of properties inherent in the synthesized material depends upon the chemical identify of the components, their relative amounts, and the method by which they are combined and reacted. Further, while general guidelines are sufficient for predicting the resulting hardness and stiffness of the polymer, it is not always obvious how to engineer the properties of strength, upper service temperature, or especially the dynamic properties like resilience, damping, and flexural fatigue resistance. The present invention uses a polydiene diol as the polyol to achieve novel properties.

2 - Polyurethane compositions made with polydiene diols, diisocyanates, and certain diol chain extenders are described in WO 97/00901. The compositions described therein contained chain extenders which were low molecular weight diols. The purpose of the chain extender therein and herein is to increase the level of hard segment (the amount of isocyanate plus the amount of chain extender) in the polyurethane composition and thus to make it harder and stronger. However, the flexural resistance of these materials is not significantly different from that of TPUs utilizing conventional polyethers or polyesters.

In polyurethanes of this type, it is necessary that there be a hard segment and a soft segment. The incompatibility of these segments is needed to give the polyurethane strength. Generally, the hard segment ranges from 30 to 50 percent by weight of the composition because with the currently commercially used polyesters and polyethers, that is the range in which high strength can be obtained. If the hard content is more than 50 percent by weight, then the composition is not an elastomer. The soft segment is comprised of the polyether or polyester or, in the present case, the polydiene diol, and the hard segment is comprised of the isocyanate and the chain extender. The chain extender is added to the composition to increase its strength. Since the chain extenders are highly polar and the polydiene diols, being relatively long chain, are not very polar, they are incompatible, making the hard and soft segments incompatible and thus increasing the strength of the composition.

The present invention provides polyurethane compositions that have dramatically better flexural resistance than currently available polyurethane compositions made with polydiene diols, polyethers, or polyesters.

1 - 3 Summary of the Invention

The invention herein is a method for producing polyurethane compositions, TPU and cast, which exhibit a high flexural resistance, specifically a flexural resistance of zero cut growth after 10 million running cycles as determined according to ASTM D1052-85. The process comprises: (a) prereacting from 6 to 30 percent by weight (%wt) of paraphenylene diisocyanate with from 94 to 70 %wt of a polydiene diol having up to about 2 terminal hydroxyl groups per molecule and a number average molecular weight between 500 and 20,000 at a NCO to OH molar ratio ranging from 1.5:1 to 10:1, and (b) adding to the product of (a) a sufficient amount of a compatible chain extender or mixture of chain extenders to make the overall NCO/OH (or NCO/(OH+NH2) ratio if an amine chain extender is used) ratio 0.9 to 1.1, preferably 0.95 to 1.05 for TPUs and 0.95 to 1.10 for cast polyurethanes, and to achieve a hard segment content of from 10 to 45 %wt, preferably 15 to 30%wt.

Preferably, the polydiene diol has from 1.9 to 2 hydroxyl groups per molecule and the polydiene diol has a number average molecular weight between 1,000 and 10,000. The polydiene diol preferably is a hydrogenated polybutadiene diol but it can also be a hydrogenated polyisoprene diol. Preferably, the chain extender is a chain extending diol which is a low molecular weight material having not more than two functional groups which will react with the paraphenylene diisocyanate and has a number average molecular weight from 60 to 600 and a hydroxyl equivalent weight of from 30 to 200 grams per hydroxyl group. Most preferably, the chain extending diol is a branched aliphatic diol having 5 to 40 carbon atoms and more preferably can be selected from the group consisting of 2-ethyl1,3-hexane diol (PEP diol), 2,2,4- 4 - trimethyl-1, 3-pentane diol (TMPD diol), and 2-ethyl-2butyl-1,3-propane diol (BEPD diol). The chain extender can also be an amine. Mixtures of chain extenders containing on average two or more hydroxyl or amine groups on average can also be used. Detailed Description of the Invention

The polydiene diols used in this invention are prepared anionically such as described in United States Patents Nos. 5,376,745, 5,391,663, 5,393, 843, 5,405,911, and 5,416,168, which are incorporated by reference herein. The polydiene diols have from 1.6 to 2, more preferably from 1.8 to 2, and most preferably from 1.9 to 2 terminal hydroxyl groups per molecule, and a number average molecular weight between 500 and 20,000, more preferably between 1000 and 10,000. Hydrogenated polybutadiene diols are preferred and these preferably have 1,4-addition between 30% and 70% to minimize viscosity.

Polymerization of the polydiene diols commences with a monolithium or dilithium initiator that builds a living polymer backbone at each lithium site. The conjugated diene is typically 1,3-butadiene or isoprene. The anionic polymerization is done in solution in an organic solvent, typically a hydrocarbon like hexane, cyclohexane or benzene, although polar solvents such as tetrahydrofuran can also be used. When the conjugated diene is 1,3butadiene and when the resulting polymer will be hydrogenated, the anionic polymerization of butadiene in a hydrocarbon solvent like cyclohexane is typically controlled with structure modifiers such as diethylether or glyme (1,2-diethoxyethane) to obtain the desired amount of 1,4-addition. The optimum balance between low viscosity and high solubility in a hydrogenated polybutadiene polymer occurs in the range of 40 to 60% 1,4-butadiene content. This butadiene microstructure is achieved during polymerization at 50 'C in cyclohexane 11'1 - 5 containing about 6% by volume of diethylether or about 1000 ppm of glyme.

Anionic polymerization is terminated by addition of a functionalizing agent like those in United States Patents Nos. 5,391,637, 5,393,843, and 5,418,296, which are also incorporated by reference, but preferably ethylene oxide, prior to termination.

The preferred di-lithium initiator is formed by reaction of two moles of secbutyllithium with one mole of diisopropenylbenzene. This diinitiator is used to polymerize butadiene in a solvent composed of 90 %w cyclohexane and 10 %w diethylether. The molar ratio of diinitiator to monomer determines the molecular weight of the polymer. The living polymer is then capped with two moles of ethylene oxide and terminated with two moles of methanol to yield the desired polydiene diol.

The polydiene diol can also be made using a mono lithium initiator that contains a hydroxyl group that has been blocked as the silyl ether (as in United States Patents Nos. 5,376,745 and 5,416,168, which are also incorporated by reference). A suitable initiator is hydroxypropyllithium in which the hydroxyl group is blocked as the trimethylsilyl ether. This mono-lithium initiator can be used to polymerize butadie'ne in hydrocarbon or polar solvent. The molar ratio of initiator to monomer determines the molecular weight of the polymer. The living polymer is then capped with one mole of ethylene oxide and terminated with one mole of methanol to yield the mono-hydroxy polydiene polymer. The silyl ether is then removed by acid catalyzed cleavage in the presence of water yielding the desired dihydroxy polydiene diol.

The polybutadiene diols are hydrogenated such that at least 90%, preferably at least 95%, of the carbon to carbon double bonds in the diols are saturated.

11 - 6 Hydrogenation of these polymers and copolymers may be carried out by a variety of well established processes including hydrogenation in the presence of such catalysts as cobalt, Raney Nickel, noble metals such as platinum and palladium, soluble transition metal catalysts and titanium catalysts as in U.S. Patent No. 5,039,755 which is also incorporated by reference. A particularly preferred catalyst is a mixture of nickel 2ethylhexanoate and triethylaluminum.

The polybutadiene polymer should have no less than about 30% 1,2butadiene addition because, after hydrogenation, the polymer will be a waxy solid at room temperature if it contained less than about 30% 1, 2butadiene addition. To minimize viscosity of the diol, the 1,2-butadiene content should be between about 40 and 60%. The isoprene polymers have no less than 80% 1,4isoprene addition in order to reduce Tg and viscosity. The diene microstructures are typically determined by 13C nuclear magnetic resonance (NMR) in chloroform.

The hydroxy polydiene polymers, which are diols or possibly polyols, should typically have number average molecular weights between 500 and 20, 000, preferably between 1,000 and 10,000. The polydiene diols have hydroxyl equivalent weights between about 250 and about 10,000, preferably between 500 and 5,000 (hydroxyl equivalent weight is half the number average molecular weight because its a diol and has two hydroxyls).

The molecular weights of the polymers are conveniently measured by Gel Permeation Chromatography (GPC), where the GPC system has been appropriately calibrated. The polymers can be characterized from the data in the chromatogram by calculating the number-average molecular weight (Mn) and by calculating the weight-average molecular weight (Mw) or by measuring the "peak" molecular weight. The peak molecular weight is the 7 - molecular weight of the main specie shown on the chromatogram. For anionically polymerized linear polymers, the polymer is nearly monodisperse (Mw/Mn ratio approaches unity), and usually it is adequately descriptive to report the peak molecular weight of the narrow molecular weight distribution observed. Usually, the peak molecular weight value is between Mn and Mw. The molecular weights reported here are number average molecular weights calculated from the chromatographs.

materials used in the columns of the GPC are styrene divinylbenzene gels or silica gels. The solvent is tetrahydrofuran and the detector is a refractive index detector.

Chain extenders used herein can be chain extending diols or triols (and other polyols) or amines. The preferred, especially for TPUs, chain extending diol is a low molecular weight material having not more than two functional groups that will react with the paraphenylene diisocyanate. The number average molecular weight preferably is from 60 to 600, most preferably 60 to 120.

The hydroxyl equivalent weight of the chain extending diol will usually be between about 30 and about 200 grams per hydroxyl group, preferably between about 30 and 100 grams per hydroxyl group. If the chain extending diol can be blended or cooked into the composition it is acceptable.

Chain extending diols suitable for use in the present invention include branched aliphatic diols having 5 to carbon atoms, especially branched aliphatic diols having 5 to 30 carbon atoms such as 2-ethyl-1,3hexane diol (PEP diol), 2,2,4-trimethyl-1,3-pentane diol (TMPD diol), and 2-ethyl-2-butyl-1,3-propane diol (BEPD diol) because they are substituted, branched diols and, as such, are not as polar and therefore not as incompatible with the polydiene polymers as unsubstituted, straight chain diols. Triols such as trimethylolpropane or triethylol- 1 - 8 propane may also be used. The chain extender can be a linear diol having 2 to 12 carbon atoms and can be selected from the group 1,4-butane diol, 1,5pentane diol, 1,6-hexane diol, and the like. The chain extender may also be a low molecular weight polyol having more than two hydroxyl groups per molecule such as trimethyol propane, or a mixture of diols with polyols.

The chain extender may be an aromatic amine having 6 to 40 carbon atoms. To make cast polyurethanes, the curing may be done in the presence of an aromatic amine crosslinker with a relatively low polarity and, preferably, a solubility parameter of less than 10.5 (cal/cm3)0.5. This ensures good compatibility which, in turn produces uniform materials with good physical properties. The most commonly used curing agent for cast polyurethanes is methylene bis(2aniline) (MCBA) which has a solubility parameter of 12.66. The solubility parameter is determined by the method described by Coleman, Graf, and Painter in Specific Interactions and the Miscibility of Polymer Blends, Technomics Publishing Company, 1991. This is a group contribution method in which the contribution of each segment of the molecule, such as -CH2- or -NH2, which are based on a consistent set of molar values are combined to determine the solubility parameter of the total molecule. Hydrogen bonding interactions are not included in this calculation. Other examples of curing agents are 4,4'-methylene bis(3chloro2,6-ethylaniline) available from Air Products Corporation and diethylene toluene diamine available from Ethyl Corporation.

In order to achieve the advantages of this invention, the diisocyanate used in the polyurethane composition must be paraphenylene diisocyanate (PPDI). Other diisocyanates commonly used do not make a composition with 9 - flexural resistance close to that of PPDI polyurethane compositions.

In the process of this invention, 6 to 30 percent by weight of the PPDI is prereacted with from 94 to 70 percent by weight of the polydiene diol at a NCO to OH molar ratio ranging from 1.5:1 to 10:1. If less than 6 percent of the PPDI is used or if the NCO to OH or NCOMOH + NH2) molar ratio is less than 1.5:1, then the prepolymer will have too high a viscosity to handle by normal processing methods. If more than 30 percent is used or if the NCO to OH or NCOMOH + NH2) is more than 10:1, then the resulting high hard segment content of the polyurethane will produce a plastic rather than an elastomer.

The next step of the process is adding to the prereacted component above a sufficient amount of a compatible chain extender or mixture of chain extenders to make the overall NCO/OH or NCOhOH+NH2) ratio 0.9 to 1.1 and to achieve a hard segment content of from 10 to 45 percent by weight. If the NCO/OH or NCO/(OH+NH2) ratio i less than 0.9, then the molecular weight of the polyurethane will be too low, and if it is more than 1.1, then the polyurethane may be too highly cross-linked. The hard segment content must be at least 10 percent by weight because below 10% the strength of the polyurethane will be too low. The hard segment content should be no more than 45 percent by weight because above 45% hard segment content the polyurethane becomes a plastic and is no longer an elastomer. If it is desired to make a thermoplastic polyurethane, then it is preferred that the NCO/OH ratio range from 0.95 to 1.05. If a cast polyurethane is desired, then the NCO/OH or NCO/(OH+ NH2) ratio preferably should range from 0.95 to 1.10.

_11 - 10 A preferred way to make these polyurethanes is by the prepolymer method where the isocyanate component (PPDI) is reacted first with the polydiene diol to form an isocyanate terminated prepolymer, which can then be reacted further with the reinforcing diol of choice. polyurethane compositions can be formulated to make elastomers using a solventless prepolymer method.

In the solventless prepolymer method, the polydiene diol is heated to at least 60 'C and not more than 130 'C, and then mixed with the desired amount of PPDI for at least 30 minutes under nitrogen flow. The desired amount of reinforcing diol or other chain extender is added and thoroughly mixed. The mixture is then poured into a heated mold treated with a mold release compound. Curing in the mold for several hours at 90 to 130 OC forms the polyurethane composition.

A second preferred way to make these polyurethanes is by the one-shot method. In this method the polydiene diol and chain extenders are mixed and heated to 90 OC to 100 OC. The diisocyanate is heated separately to 70 OC to 80 C. The PPDI is introduced to the polydiene diol plus chain extenders and this multicomponent mixture is stirred vigorously for 1 minute. The reacting mixture is poured into a TEFLONcoated mold that is preheated to 120 'C and 20,000 psi pressure and held in this condition for 1 hour. The resulting polyurethane is then post-cured at ambient pressure and 120 OC for 16 hours.

The polymerization process can be conducted in the presence of catalysts. Catalysts useful in accelerating the NCO/OH reaction are tertiary amines such as tetramethyl butane diamine, and triethylamine, pyridine, 1,4diaza(2,2,2)bicyclo-octane and organometallic compounds such as tin dioctoate and dibutyl tin dilaurate. These catalysts are used at levels ranging from 0.001% by weight to 1.0% by weight.

1, A wide variety of fillers can be used in formulations with the present invention. Suitable fillers include calcium carbonate, clays, talcs, zinc oxide, titanium dioxide, silica and the like. The amount of filler usually is in the range of 0 to about 800 phr, depending on the type of filler used and on the application for which the formulation is intended. Preferred fillers are silica and titanium dioxide. The filler should be thoroughly dried in order that adsorbed moisture will not interfere with the reaction between the polyisocyanate and the saturated, polyhydroxylated polydiene polymer.

A composition of the instant invention may contain plasticizers, such as oils used in conventional rubber compounds. Such oils can be used in the present TPU's because the polydiene diol is a rubber. Rubber compounding oils are well-known in the art and include both high saturates content oils and high aromatics content oils. Preferred plasticizers are highly saturated oils (like TUFFLO 6056 and 6204 oil made by Arco) and process oils (like SHELLFLEX 371 oil made by Shell)(TUFFLO and SHELLFLEX are trade marks). The amounts of rubber compounding oil employed in the invention composition can vary from 0 to about 500 phr, preferably between about 0 to about 100 phr, and most preferably between about 0 and about 60 phr.

Stabilizers known in the art may also be incorporated into the composition. These may be for protection during the life of the product against, for example, oxygen,, ozone and ultra-violet radiation. These may also be for stabilization against thermo-oxidative degradation during elevated temperature processing. Antioxidants and UV inhibitors that interfere with the urethane curing reaction must be avoided. Preferred antioxidants are the sterically hindered phenolic compounds like butylated hydroxy toluene. Preferred UV inhibitors are UV absorbers - 12 such as benzotriazole compounds. The amount of stabilizer in the formulation will depend greatly on the intended application of the product. If processing and durability requirements are modest, the amount of stabilizer in the formulation will be less than about 1 pbw. If the polyurethane will be mixed at high temperature or if the product must survive many years in service, stabilizer concentration could be as much as about 10 pbw. EXAMPLES These experiments compare results for the polymers of the invention to results with poly(oxytetramethylene)glycol. Polyurethane elastomers were prepared by the twostep prepolymer procedure or the one-shot procedure. Table 1 lists the raw materials used in these examples. As an example of the synthetic protocol employed, the preparation of elastomers based on Polymer A, a hydrogenated polybutadiene diol having a hydroxyl equivalent weight of 1700, paraphenyldiisocyanate (PPDI), and MPD at 22% hard segment concentration and NCO/OH ratio of 1.05 is described. The two-step prepolymer procedure was used In the first step the NCO-prepolymer was prepared. The synthesis of prepolymer was carried out so as to minimize the loss of PPDI due to sublimation. 63.02 g (0.787 equivalents) of PPDI was placed in a 1 1 glass reaction kettle which was equipped with a heating mantle, stirrer, and nitrogen inlet-outlet. 351.7 g (0.207 OH equivalents) of Polymer A with antioxidant IRGANOX 565(0.8 %wt) was then added to the reactor at room temperature under a continuous flow of nitrogen and constant mixing (IRGANOX is a trademark). The mixture was then gradually heated to 70 'C and kept at 70 to 75 'C for an additional two hours. Afterwards, the nitrogen was cut off, the reactor closed, and reaction continued at 120 'C in an oven for one hour. After very fast stirring for one minute a sample for the isocyanate determination was taken. The measured value of NCO (5.62 %wt) agreed well with the expected theoretical value (5.67 %wt). The prepolymer was stored in a 200 ml glass bottle under nitrogen and kept in a refrigerator before use.

Table 1 Materials Designation Chemical Eq. Supplier Identification wt.

Polymer A Hydroxyl-terminated 1700 Shell Chemical Co.

poly(ethylene butylene) polymer PTMO 2000 Poly(oxytetramethyl- 1017 E.I. duPont de ene)glycol Nemours & Co.

1,4-BD 1,4-Butanediol 45 GAF Corporation 1,3-PDO 1,3-Propanediol 38 Shell Chemical Co.

MPD 2, 2, 4-Trimethyl-1, 3- 73 Aldrich Chemical Co.

pentanediol BEPD 2 -Butyl2 -ethyl -1, 3- 80 Aldrich Chemical Co.

propanediol 1,4-CHD 1,4-Cyclohexanediol 58 Eastman Chemicals 1,4-CHDM 1,4-Cyclohexanedi- 72 Eastman Chemicals methanol CURENE 442 4,4'-Methylene 133.5 Anderson Development (MOCA) bis(2-chloroaniline) Co.

ETHACURE 3,5-Dimethylthio- 107 Albemarle 300 2,4-toluenediamine/ Corporation 3,5-dimethylthio 2,6-toluenediamine PPDI 1,4-Phenylene 80 E.I. duPont de diisocyanate Nemours & Co.

T-12 Dibutyltin dilaurate Aldrich Chemical Co.

IRGANOX 565 Anti oxidant Ciba Geigy Co.

CURENE and ETHACURE are trademarks 1 1. 1.

1 - 14 In the second step, the prepolymer in the closed glass bottle was heated in an oven at 110 OC and 38.8 g of prepolymer was weighed into a 250 ml plastic cup. 3.61 g of TMPD chain extender containing a small amount of T-12 catalyst (0.02 %wt based on the amount of polyol) was added. The mixture was vigorously stirred for one minute, poured into a mold covered with TEFLON sheets (TEFLON is a trademark), and placed in a Carver press until gelation occurred. In this case the gel time was about 8 minutes at 125 QC. The mold was first maintained at lower pressure for 30 minutes and then compressed to 22,000 lbf and kept in the mold for one hour. The sheets were then postcured in an oven for 24 hours at 125 OC.

Physical and mechanical properties of polyurethane elastomers were determined by the following test methods:

- Shore hardness (ASTM D-2240-75) - Stressstrain properties at room temperature and OC (tensile strength at break, ultimate elongation, 100% and 300% modulus) (ASTM D-412-68) - Compression set (ASTM D-395-69, Method B) Resilience, Bashore rebound (ASTM D-430-73) - Abrasion resistance (Taber Abrader with H-22 abrasive wheel, 500 g weight, 2000 test cycles) Fatigue Cut Growth (ASTM D-1052-85 using a Ross Flexometer).

EXAMPLE 1

Five polyurethane elastomers (E1 through E5) were prepared using Polymer A, PPDI, and a chain extender. In this example BEPD, TMPD, and 1,4-BD were used as chain extenders. These polymers were prepared using the two step prepolymer process. The composition of the polymers are given in Table 2. E1 and E2 were made using BEPD as the chain extender at 22% and 28% hard segment content respectively. E3 and E4 were made using TMPD as the chain I extender at 22% and 28% hard segment content respectively. E5 was made using 1,4-butane diol as the chain extender at a hard segment content of 25%.

The resulting physical properties are listed in Table 3. The elastomers made with BEPD and MPD have tensile strengths greater than 2000 psi. The tensile strength of the elastomer made with 1,4-butane diol has a tensile strength greater than 1500 psi. All five of the elastomers have resilience values over 50%. Both the BEPD and the MPD extended elastomers have low Taber wear indices and low compression sets as demonstrated by the 22% hard segment elastomers El and E3.

The elevated temperature tensile properties of elastomers extended with BEPD and MPD were excellent as demonstrated by the retention of modulus of elastomers El and E3 at 100 OC. Table 4 shows the unexpected resistance of these elastomers to cut growth during continuous cyclic deformation. No growth of the initial cut was experienced after 10,000,000 flex cycles. The properties of high strength, low wear and outstanding fatigue resistance are achieved while maintaining the softness of the elastomers. This combination of properties is highly desired. The hardness of the elastomers of this example are equal to or less than 70 Shore A.

Table 2 Composition of Elastomers El through E5 Designation El E2 E3 E4 E5 Hard segment 22 28 22 28 25 -NCO% in prepolymer 5.41 7.50 5.50 7.57 7.57 Wt (prepolymer) (g) 100 100 100 100 100 Chain extender BEPD BEPD MPD MPD 1,4-BD Wt(extender) (g) 9.83 13.65 9.14 12.55 7.54 T-12 (%) 0.01 0.005 0.02 0.02 0.02 1 16 - Table 3 Properties of Elastomers E1 through E5 Designation E1 E2 E3 E4 E5 Hardness (Shore A) 64 70 61 65 65 Resilience 61 61 58 55 60 Ultimate tensile strength 2249 2184 2665 2853 1530 (psi) Elongation at break 899 516 1030 813 444 Modulus at 100% elongation 281 403 284 399 444 at RT (psi) Modulus at 100% elongation 84 --- 85 -- -- at 100 'C (psi) Modulus at 300% elongation 705 1182 651 952 1002 at RT (psi) Modulus at 300% elongation 128 --- 134 --- -- at 100 'C (psi) Taber wear index (mg/1000 12 --- 19 --- -- cycles) Compression set at RT (%) 4 --- 7 --- Table 4 Ross Flex Test (Cut Growth) Results of Elastomers E1 and E3 Designation El E2 Cut growth (running cycles) 0% growth >10,000,000 >10,000,000 EXAMPLE 2

Three polyurethane elastomers (E6 through E8) were prepared using Polymer A, PPDI and a chain extender. In this example the chain extenders were 1, 4-CHDM and 1,4CHD. These polymers were prepared using the prepolymer method. The compositions of the polymers are given in Table 5. E6 and E7 were made with 1,4-CHDM as the chain extender at 22% and 28% hard segment content respectively. E8 was made using 1,4-CHD as the chain extender at 28% hard segment content.

The resulting physical properties are listed in Table 6. The elastomers all have tensile strengths greater than 1500 psi and resilience values greater than 45%. These properties are achieved while maintaining hardness at values less than 70 Shore A.

Table 5 Composition of Elastomers E6 through E8 Designation E6 E7 E8 Hard segment 22 28 28 -NCO/OH equivalent 1.08 1.08 1.05 ratio -NCO% in prepolymer 5.50 7.57 7.57 Wt (prepolymer) (g) 100 100 100 Wt(new added PPDI) 0 0 2.10 (g) Chain extender 1,4-CHDM 1,4-CHDM 1,4-CHD Wt(extender) (g) 8.84 12.04 11.18 T12(%) 0.005 0.005 0.005 Table 6 Properties of Elastomers E6 through E8 Designation E6 E7 E8 Hardness (Shore A) 67 69 66 Resilience 59 57 47 Ultimate tensile strength (psi) 1824 1518 1854 Elongation at break (%) 614 607 736 Modulus at 100% elongation (psi) 353 334 401 Modulus at 300% elongation (psi) 781 719 865 18 - EXAMPLE 3

Two polyurethane elastomers (E9 and E10) were made using Polymer A, PPDIand a chain extender. In this example the chain extenders were ETHACURE 300 and MOCA. These polymers were prepared using the two-step prepolymer process. The compositions of the polymers are given in Table 7. E9 was made with a 25% hard segment content using ETHACURE 300 as the chain extender. E10 was made at 22% hard segment content using MOCA as the chain extender.

The resulting physical Table 8. Elastomer E9 has and a hardness of 64 Shore strength of 852 psi and a reduced tensile strength marginal compatibility of properties are listed in a tensile strength of 1660 psi A. Elastomer E10 has a tensile hardness of 74 Shore A. The of E10 is attributable to the MOCA in this comnosition.

Table 7 Composition of Elastomers E9 and E10 Designation E9 E10 Formulation (pbw) Hard segment (%) 25 22 -NCO/-OH equivalent ratio 1.08 1.05 -NCO% in prepolymer 5._50 4.19 Wt(prepolymer) (g) 100 100 Chain extender ETHACURE 300 MOCA Wt (extender) (g) 12.97 12.48 i 19 - Table 8 Properties of Elastomers E9 and E10 Designation E9 E10 Hardness (Shore A) 64 74 Resilience 58 59 Ultimate tensile strength (psi) 1666 852 Elongation at break (%) 441 271 Modulus at 100% elongation (psi) 437 508 Modulus at 300% elongation (psi) 1128 - COMPARATIVE EXAMPLE 1 Two comparative polyurethane elastomers (CE1 and CE2) were made using a conventional polyether polyol, PTMO, and PPDI. The chain extender was 1,4- butane diol. The comparative elastomers CE1 and CE2 have hard segment contents of 22% and 28% respectively. These comparative elastomers were made using the twostep prepolymer process. The compositions of the comparative elastomers are listed in Table 9.

The resulting physical properties are listed in Table 10. While the tensile strengths are high, the elastomers even at these low hard segment contents are hard. Their hardness is greater than 90 Shore A. Further, the flexural fatigue resistance is substantially poorer than that of the polymers of the present invention. Table 11 lists the Ross flex test results of comparative elastomer CE1. This comparative elastomer experiences 5% cut growth after only 2,000,000 flex cycles. After 10,400, 000 flex cycles this elastomer experiences 130% cut growth. This result is to be compared to those for elastomers E1 and E3 in Table 4. Even after 10,000,000 flex cycles the elastomers of the present invention experience no cut growth.

Table 9 Composition of Elastomers CE1 and CE2 Designation CE1 CE2 Hard segment (%) 22 28 Wt(prepolymer, NCO%=5.63%) (g) 100 100 Wt(new added PPDI) (g) 0 5.98 Wt(1,4BD) (g) 5.75 8.96 Table 10 Properties of Elastomers CE1 and CE1 Designation CE1 CE2 Properties Hardness (Shore A) 92 94 Resilience 58 56 Ultimate tensile strength (psi) 5255 5052 Elongation at break (%) 1156 911 Modulus at 100% elongation at RT (psi) 885 1215 Modulus at 100% elongation at 1000C (psi) 847 --- Modulus at 300% elongation (psi) at RT (psi) 1434 1929 Modulus at 300% elongation (psi) at 1OCC (psi) 1092 --- Taber wear indexa (mg/1000 cycles) 12 --- Compression set at RT (%) 7 --- 21 Table 11 Ross Flex Tests (Cut Growth) Results of CE1 Designation CE1 Cut growth (running cycles) 0% growth 1,700,000 5% growth 2,000,000 10% growth 2,500,000 25% growth 3,000,000 30% growth 3,700,000 50% growth 4,800,000 60% growth 5,300,000 90% growth 7,400,000 120% growth 9,100,000 130% growth 10,400,000 COMPARATIVE EXAMPLE 2 Two comparative polyurethane elastomers (CE3 and CE4) were made with PTMO and Polymer A. In this comparative example the diisocyanate was 4,4'-MDI. Comparative elastomer CE3 was made at 22% hard segment content using PTMO and 1,4-butane diol as the chain extender. The overall NCO/OH molar ratio was 1.02 for polymer CE3. Comparative elastomer CE4 was made at 22% hard segment content using Polymer A and BEPD as the chain extender. The overall NCO/OH molar ratio was 1.04 for polymer CE4.

The comparative elastomers were made using the oneshot process. The Polymer A and the chain extender were heated to 100 OC and then mixed using a high speed laboratory mixer for 2 minutes in a 250 ml plastic beaker under ambient atmosphere. Molten 4,41-MDI (70 to 80 OC) was added and all components were mixed for one additional minute. The reacting mixture was then poured into a TEFLON-coated mold at 105 OC and placed in a Carver press and held at 105 OC and ambient pressure. Once gelation occurred the mold was subjected to a 20,000 lb compressive force. The mold was held in this state for 1 hour. The polyurethane sheet was then removed from the press and postcured at 105 'C for 16 hours.

The resulting physical properties are listed in Table 13. The comparative polymer based on PTMO and 4,41-MDI, CE3, experiences 100% cut growth after only 45,000 flex cycles. The comparative polymer based on Polymer A and 4,4'-MM experiences some cut growth less than 100% after only 500,000 flex cycles. The properties characteristic of these comparative elastomers are significantly inferior to those of the present invention.

Table 12 Composition of CE3 and CE4 Designation CE3 CE4 Polyol PTMO 2000 Polymer A Chain extender 1,4-BD BEP diol Isocyanate 4,41-MDI 4,41-MDI Hard segment 22 22 T-12 (%) 0.005 0.005 Table 13 Ross Flex Tests (Cut Growth) Results of CE3 and CE4 Designation CE3 CE4 Cut growth (running cycles) 0% growth 500,000 100% growth 45,000 >1,060,000 300% growth 60,000 Break 83,000

Claims (16)

1. C L A I M S

   TH 1109 1. A method for producing polyurethane compositions that exhibit a high flexural resistance of zero cut growth after 10 million running cycles as determined according to ASTM D1052 85 which comprises: (a) prereacting from 6 to 30 %wt of paraphenylene diisocyanate with from 94 to 70 %wt of a polydiene diol having up to about 2 terminal hydroxyl groups per molecule and a number average molecular weight between 500 and 20,000 at a NCO to OH molar ratio ranging from 1.5:1 to 10:1, and (b) adding to the product of (a) a sufficient amount of a compatible chain extender or mixture of chain extenders to make the overall NCO/OH or NCOMOH+NH2) ratio 0.9 to 1.1 and to achieve a hard segment content of from 10 to 45 %wt.
2. 2. The method of claim 1 wherein the polydiene diol has from 1.9 to 2 hydroxyl groups per molecule.
3. 3. The method of claim 1 or 2 wherein the polydiene diol has a number average molecular weight between 1,000 and 10, 000.
4. 4. The method of any one of claims 1-3 wherein the polydiene diol is a hydrogenated polybutadiene diol, or a hydrogenated polyisoprene diol.
5. 5. The method of any one of the preceding claims wherein the chain extender is a low molecular weight material having not more than two functional groups which will react with the paraphenylene diisocyanate and has a number average molecular weight from 60 to 600.
6. 6. The method of claim 5 wherein the chain extender is a branched aliphatic diol having 5 to 40 carbon atoms.

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7. 7. The method of claim 6 wherein the chain extender is selected from the group consisting of 2-ethyl-1,3-hexane diol (PEP diol), 2,2,4-trimethyl-1, 3-pentane diol (TMPD diol), and 2-ethyl-2butyl-1,3-propane diol (BEPD diol).
8. 8. The method of claim 5 wherein the chain extender is a linear aliphatic diol having from 2 to 12 carbon atoms.
9. 9. The method of claim 8 wherein the chain extender is 1,4-butane diol.
10. 10. The method of claim 5 wherein the chain extender is an aromatic amine having 6 to 40 carbon atoms.
11. 11. The method of claim 10 wherein the chain extender is selected from the group of diethylene toluene diamine; 4,4 -methylene bis(3-chloro- 2,6-diethylaniline); 4,4 methylene bis(2,6-diethylaniline); 3,5dimethylthio-2,4toluenediamine/3,5-dimethylthio-2,6-toluenediamie; trimethylene glycol di-p-aminobenzoate; and 4,4 methylene bis (2chloroaniline).
12. 12. The method of claim 11 wherein the chain extender is selected form the group of diethylene toluene diamine; 4,4-methylene bis(3-chloro-2,6-diethylaniline); and 4,4-methylene bis(2,6diethylaniline).
13. 13. The method of any one of the preceding claims wherein a thermoplastic polyurethane is made by using an overall NCO/OH ratio of 0.95 to 1.05.
14. 14. The method of any one of claims 1-12 wherein a cast polyurethane is made by using an overall NCO/OH or NCOMOH+NH2) ratio of 0.95 to 1.10.
15. 15. The method of any one of the preceding claims wherein the hard segment content is from 15 to 30 %wt.
16. 16. The method of claim 1 wherein the chain extender contains more than two hydroxyl or amine groups on average.

    D14/TH1109FF