Polyurethanes useful as engineering plastics

Abstract: Polyurethane resins are described having high impact strength and other structural strength properties, and si­ gnificantly improved resistance to deformation by heat. The properties of these materials are such as to make them comparable to engineering thermoplastics such as nylon and like materials commonly used to fabricate structural components such as automotive parts, equipment housing, sporting goods, furniture, toys, household and like con­ sumer goods. The resins are prepared from organic polyisocyanates, an isocyanate-reactive material (polyol, polyamine, etc.) having an average functionality of at least 1.9, a Tg less than 20°C and molecular weight of 500-20 000, and one or more low molecular weight extenders the major distinguishing feature being the markedly lower proportion by weight (2 to 25 percent) in which the isocyanate-reactive material is employed as compared with polyurethane resins conven­ tionally prepared in the art. Depending upon the particular combination of reactants employed the polyurethanes of the invention can be thermoplastic or thermoset and can be prepared in both cellular and non-cellular form.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to thermoplastic polyurethane resins and is more particularly concerned with polyurethane resins both cellular and non-cellular having improved structural strength properties and with methods for their preparation. 2. Description of the Prior Art The preparation of pclyurethanes, both cellular and non-cellular, by the reaction of organic polyisocyanates, polymeric polyols, and low molecular weight extenders such as glycols, alkanolamines and diamines, is so well-known in the art as not to require detailed description herein. E.g. in FR-A-2 238 726 there is disclosed a process for the preparation of polyurethanes resistant to electric current from specific non-aromatic base isocyanate compounds, isocyanate-reactive materials and extenders. US-A-4 174 436 describes polyurethanes suitable for food casings, especially sausage casings, wherein the polyol and disocyanate base units consist to a substantial extent of linear aliphatic C 6 - units. FR-A-1 350 904 discloses the preparation of thermoplastic polyurethanes which are crosslinked to a certair amount. Therefore in their preparation there has to be used in the reactant mixture a sufficient amount of components having a functionality of greater than 2. Polyurethanes hitherto available have been used extensively in the fabrication of a wide variety of components, particularly the thermoplastic polyurethane elastomers which can be fabricated by injection molding or by reaction injection molding (RIM) techniques. However, the use of these materials to prepare components having structural strength properties which match those derived from engineering thermoplastics such as nylon has been limited by the need to provide extensive reinforcement using materials such as fiberglass in order to achieve desirable levels of stiffness, impact resistance and related properties. We have now found that thermoplastic polyurethanes with markedly improved structural strength properties can be prepared by departing significantly from the previous teachings of the art as to the relative proportions of reactants to be employed. Thus, we have found that very substantial reduction in the amount by weight of the polymeric active-hydrogen containing material (e.g. polyol) employed in the preparation of the polyurethanes is a major factor in producing a highly surprising and dramatic change in the properties of the resulting polyurethanes. The change in properties is enhanced by selection of particular combinations of reactants as will be discussed in detail below. These changes enable us to produce resins which can be employed, without the necessity to incorporate reinforcing fillers and the like, to produce structural components which possess all the desirable impact resistance, stiffness, and other structural strength properties which have been achievable heretofore by the use of other polymers such as nylon and other engineering thermoplastics but not by polyurethanes alone. To the best of our belief it has not been recognized that such a result as that described herein could be achieved. Thus it has been well-known since the inception of the polyurethane art that linear polyurethanes could be obtained by reaction of organic diisocyanates with one or more low molecular weight diols and or diamines; see, for example Otto Bayer, Angewandte Chemie, A59, No. 9, at pp. 255-288, September 1947; see also U.S. Patent 2,284,637, 2,284,896, 2,511,544 and 2,873,266. Such products have found utility chiefly in the fiber field. It was also recognized early in the history of polyurethane chemistry (see Otto Bayer, supra) that a wide variety of useful products both cellular and non-cellular, could be obtained by reaction of organic polyisocyanates, polymeric polyols and low molecular, di- or polyfunctional active-hydrogen containing compounds such as glycols (usually termed extenders). These products are obtained by the one-shot procedure by reacting all the components together simultaneously or by the prepolymer method which involves prereacting the organic polyisocyanate with a portion or all of the polymeric polyol and then reacting the resulting isocyanate-terminated prepolymer with the low molecular weight extender and any polymeric polyol which was not used In preparing the prepolymer. In general, the above types of product are prepared using a combination of polymeric polyol and low molecular weight extender in which there is at least one equivalent, and more usually several equivalents, of the low molecular weight extender for each equivalent of polymeric polyol. However, since the molecular weight of the polymeric polyol is substantially higher than that of the extender, the proportion by weight of the polymeric polyol used in preparing the polyurethane is substantially in excess of the proportion by weight of the low molecular weight extender. The relative proportions of the polymeric polyol to the low molecular weight extender used in preparing such polyurethanes greatly influences the properties of the polyurethane which is obtained. Thus the polymer chain units derived from the low molecular weight extender are referred to as "hard segments" since they are relatively rigid, i.e. they exhibit high moduli of elasticity. The polymer chain units derived from the polymeric polyols are referred to as "soft segments" since, because of the presence of the relatively large polyol residues, particularly where the polyol is a linear polymeric diol, they exhibit low moduli of elasticity. In the case, for example, of a relatively linear polyurethane, prepared from a diisocyanate, a polymeric glycol and difunctional extender, increasing the proportion of extender to polymeric polyol gives progressively more rigid polyurethanes and, beyond a certain point, the polymer becomes relatively brittle and shows very low impact resistance when fabricated in the form of structural components. In further illustration of this point it has generally been conventional, in order to prepare thermoplastic polyurethanes with reasonable levels of impact resistance, to avoid the formation of brittle polymers by maintaining sufficiently high proportions of soft segments (i.e. by using a substantial proportion by weight of polymeric polyol) and to generate a desirable level of stiffness by incorporating reinforcing fillers such as glass fibers into the polymer. However, this leads to additional problems caused by the difficulties of handling such mixtures particularly when the molding operation is being carried out as part of a RIM process. Accordingly, we believe that it is all the more surprising to find that it is possible to choose certain combinations of organic polyisocyanate, polymeric polyol (or like active-hydrogen containing material) and low molecular extender in which the level of the polymeric polyol (i.e. the level of soft segments in the resulting polyurethane) is reduced to a very low order of magnitude and the level of the extender (i.e. the level of hard segments in the resulting polyurethane) is increased beyond a point at which it would have been expected that the resulting polymer would be too brittle, and to obtain products which are suitable for the fabrication of component parts having satisfactory structural strength including impact resistance. While the substantially reduced level of polymeric polyol or like active-hydrogen contcining material employed in preparing the compositions of the invention is one of the major characteristics of the latter which distinguish them from products hitherto known in the art, it is to be understood that there are additional considerations, to be discussed in detail below, which serve to differentiate these compositions very clearly from the compositions hitherto described in the art which is known to us. Specification for the following Contracting States: BE, CH, DE, FR, GB, IT, LI, NL, SE This invention encompasses a polyurethane characterized by high at ambient conditions impact resistance, high flexural modulus, and a heat deflection temperature of at least 50°C at 1820 kPa which comprises the product of a one-shot reaction of (a) an orpanic polyisocyanate comprising a diisocyanate selected from 4,4'-methylenebis(phenyl isocyanate) and mixtures of 4,4'-methylenebis(phenyl isocyanate) with the corresponding 2,4'-isomer in an amount up to about 70 percent by weight based on the total diisocyanate mixture, or an organic polyisocyanate corresponding to said diisocyanate wherein said 4,4'-methylenebis(pheny isocyanate) or the mixture thereof with the 2,4'-isomer is in the form of a liquid at ambient temperature and which has been obtained by (al converting a minor proportion thereof to the corresponding carbodiimide or (b) reacting the 4,4'-methylenebis(phenyl isocyanate) or its admixture with the 2,4'-isomer with a minor amount of at least one aliphatic diol. (b) an isocyanate-reactive material having an average functionality of at least 1.9 and not exceeding 4 a glass transition temperature (Tg) of less than 20°C, and a molecular weight in the range of 500 to 20,000; and (c) at least one aliphatic diol chain extender having a molecular weight from 50 to 400; said polyurethane being further characterized in that the proportion by weight of said isocyanate-reactive material (b) in said polyurethane is from about 4 to about 15 percent and the overall ratio of isocyanate groups to active hydrogen groups in said reactants employed to prepare said polyurethane is in the range of 0.95:1 to about 1.05:1. Specification for the following Contracting State : AT This invention encompasses a process for the preparation of a polyurethane characterized by high impact resistance at ambient conditions, high flexural modulus, and a heat deflection temperature of at least 50°C at 1820 kPa which process comprises reacting in a one-shot reaction (a) an organic polyisocyanate comprising a diisocyanate selected from 4,4'-methylenebis(phenyl isocyanate) and mixtures of 4,4'-methytenebis(phenyl isocyanate) with the corresponding 2,4'-isomer in an amount up to about 70 percent by weight based on the total diisocyanate mixture, or an organic polyisocyanate corresponding to said diisocyanate wherein said 4,4'-methylenebis(phenyl isocyanate) or the mixture thereof with the 2,4'-isomer is in the form of a liquid at ambient temperature and which has been obtained by (a) converting a minor proportion thereof to the corresponding carbodiimide or (b) reacting the 4,4'-methylenebis(phenyl isocyanate) or its admixture with the 2,4'-isomer with a minor amount of at least one aliphatic diol. (b) an isocyanate-reactive material having an average functionality of at least 1.9 and not exceeding 4 a glass transition temperature (Tg) of less than 20°C, and a molecular weight in the range of about 500 to about 20,000; and (c) at least one aliphatic diol chain extendar having a molecular weight from 50 to 400; said process being further characterized in that said isocyanate-reactive material (b) is employed in a proportion by weight of from about 4 to about 15 percent of the polyurethane weight and the overall ratio of isocyanate groups in which said reactants are employed is in the range of 0.95:1 to about 1.05:1. Specification for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, NL, SE The thermoplastic polyurethanes of the invention can be obtained in both cellular and non-cellular form. By the term "high impact resistance" at ambient conditions is meant an impact strength at ambient conditions (circa 20°C) of at least 5.44 mkg/m and preferably at least 16.3 mkg/m of notch as measured by the notched Izod test (ASTM D 256-56). The "heat deflection temperature" is a measure of the resistance of the polymer to deformation by heat and is the temperature (in °C) at which deformation of a specimen of the polyurothane of predetermined size and shape occurs when subjected to a flexural load of a stated amount (e.g. 1820 kPa). All such temperatures recorded herein were obtained using the procedure of ASTM D 648-56. The term "high flexural modulus" means a flexural modulus under ambient conditions (see above) of at least about 1034.5 MPa as measured by ASTM-D790. The term "isocyanate-reactive material" means a compound (as hereinafter described and exemplified in detail) which contains groups such as hydroxy, mercapto, and amino which contain active hydrogen atoms and which therefore will enter into reaction with isocyanate groups. The term "average functionality of at least 1.9 und not exceeding 4" means that said material contains an average of at least 1.9 und not exceeding 4 such active hydrogen-containing groups per molecule. DETAILED DESCRIPTION OF THE INVENTION The polyurethanes of the invention are prepared by the one-shot procedure. In the case of the one-shot procedure, the non-cellular polyurethanes of the invention are made advantageously by preblending the isocyanate-active material (b) [hereinafter referred to as "component (b)" for the sake of convenience] and the extender (c) and feeding these to the reaction mixture as a single component, the other major component being the polyisocyanate. The mixing of the reactants can be accomplished by any of the procedures and apparatus conventional in the art. Preferably, the individual components are rendered substantially free from the presence of extraneous moisture using conventional procedures, for example by heating under reduced pressure at a temperature above the boiling point of water at the pressure employed. The mixing of the reactants can be carried out at ambient temperature (i.e. of the order of 20 to 25°C) and the resulting mixture is then generally heated to a temperature of the order of about 40°C to about 130°C preferably to a temperature of about 50°C to about 100°C. Advantageously and preferably, one or more of the reactants is preheated to a temperature within the above ranges before the admixing is carried out. Advantageously, in a batch procedure, the heated reaction components, prior to admixture, are subjected to degassing in order to remove entrained bubbles of air or other gases before the reaction takes place. This is accomplished conveniently by reducing the pressure under which the components are maintained until no further evolution of bubbles occurs. The degassed reaction components are then admixed and transferred to suitable molds, extruders and flexible belts and allowed to cure at temperatures of the order of ambient temperature to about 250°C. Pressure may also be applied during the curing reaction. The time required for curing will vary according to the temperature of curing and also with the nature of the particular composition. The time required in any given case can be determined by a process of trial and error. It is frequently desirable, but not essential, to include a catalyst in the reaction mixture employed to prepare the compositions of the invention. Any of the catalysts conventionally employed in the art to catalyze the reaction of an isocyanate with a reactive hydrogen containing compound can be employed for this purpose. A detailed listing of such catalysts is to be found, for example, in U.S. Patent 4,202,957 at Column 5, lines 45 to 67. The amount of catalyst employed is generally within the range of 0.02 to 2.0 percent by weight based on the total weighf of the reactants. In a particular embodiment of the one-shot procedure the reaction is carried out on a continuous basis using apparatus and procedures such as that which is disclosed in U.S. Patent 3,642,964. The organic polyisocyanate employed in the invention is methylenebis(phenyl isocyanate), in the form of the 4,4'-isomer as well as mixtures of the 4,4'-isomer with amounts (up to about 70 percent by weight) of the 2,4'-isomer, and modified forms of this diisocyanate. By the latter are meant those forms of methylenebis(phenyl isocyanate) which have been treated to render them stable liquids at ambient temperature (circa 20°C). Such products include those which have been reacted with a minor amount (up to about 0.2 equivalents per equivalent of polyisocyanate) of an aliphatic glycol or a mixture of aliphatic glycols such as the modified methylenebis(phenyl isocyanates) described in U.S. Patents 3,394,164; 3,644,457; 3,883,571; 4,031,026; 4,115,429; 4,118,411; and 4,299,347. The modified methylenebis(phenyl isocyanates) also include those which have been treated so as to convert a minor proportion of the diisocyanate to the corresponding carbodiimide which then interacts with further diisocyanate to form uretone-imine groups, the resulting product being a stable liquid at ambient temperatures as described, for example, in U.S. Patent 3,384,653. Mixtures of any of the above-named polyisocyanates can be employed if desired. The isocyanate-reactive materials ["component (b)"] employed in the preparation of the polyurethanes of the invention can be any of those previously known in the art and employed In the preparation of polyurethanes which materials contain active hydrogen groups and which also meet the criteria set forth above, namely, have a functionality of at least 1.9, and not exceeding 4, a glass transition temperature (Tg) of less than 20°C, and a molecular weight in the range of about 500 to about 20,000. The glass transition tenperature is a well-recognized property; see, for example, Encyclopedia of Polymer Science and Technology, Vol. 3, p. 620, Interscience Publishers, New York, 1965. The method employed to determine the Tg of any material can take a number of forms; the particular method employed to determine Tg for starting materials and polymers produced in accordance with the present invention is that described in Example 2 hereafter. As set forth above the proportion of isocyanate-reactive material employed in the compositions of the invention is in the range of 4 to 15 percent by weight and preferably is in the range of 4 to 10 percent by weight based on the weight of polyurethane. Exemplary of isocyanate-reactive materials which can be employed in the preparation of the polymers of the invention are: polyether polyols, polyester polyols, amine-terminated polyethers, hydroxy-terminated polycarbonates, hydroxy-terminated polybutadienes, hydroxy-terminated polybutadiene-acrylonitrile copolymers, amino-terminated polybutadiene-acrylonitrile copolymers, hydroxy-terminated copolymers of dialkyl siloxane and alkylene oxides such as ethylene oxide, propylene oxide and provided that all of said compounds also meet the criteria of Tg, molecular weight and functionality listed above. Preferably the molecular weights of the materials are within the range of 1250 to 10,000 and, most preferably, in the range of 2000 to 8000. The functionality of these materials is in the range of about 1,9 to 4. Illustrative of polyether polyols are polyoxyethylene glycols, polyoxypropylene glycols which, optionally, have been capped with ethylene oxide residues, random and block copolymers of ethylene oxide and propylene oxide, propoxylated tri- and tetrahydric alcohols such as glycerine, trimethylolpropane and pentaerythritol, which propoxylated compounds have been capped with ethylene oxide; polytetramethylene glycol, random and block copolymers of tetrahydrofuran and ethylene oxide and or propylene oxide, and products derived from any of the above by reaction with di- or higher functional carboxylic acids or esters derived from said acids in which latter case ester interchange occurs and the esterifying radicals are replaced by polyether polyol radicals. Advantageously, the polyether polyols employed as component (b) in the polyurethanes of the invention have a primary hydroxyl group content of at least 80 percent. The preferred polyether polyols are random and block copolymers of ethylene and propylene oxide of functionality approximately 3.0 and polytetramethylene glycol polymers of functionality greater than or equal to 2.0. In a particular embodiment of the invention the component (b) which is employed can be a polyol obtained by reacting any of the above polyether polyols with a di- or trifunctional aliphatic or aromatic carboxylic acid to form the corresponding polyether-esters. Examples of acids which can be used are adipic, azelaic, glutaric, isophthalic, terephthalic and trimellitic. The polyether polyols which can be employed as component (b) also Include the vinyl reinforced polyether polyols, e.g. those obtained by the polymerization of styrene and or acrylonitrile In the presence of the polyether. Illustrative of polyester polyols are those prepared by polymerizing ε-caprolactone using an initiator such as ethylene glycol and ethanolamine, and those prepared by esterification of polycarboxylic acids such as phthalic, terephthalic, succinic, glutaric, adipic, azelaic and the like acids with polyhydric alcohols such as ethylene glycol, butanediol, glycerol, trimethylolpropane, 1,2,6-hexanetriol, cyclohexanedimethanol. A preferred group of polyesters are those obtained by esterifying a dimeric or trimeric fatty acid, optionally mixed with a relatively long chain aliphatic diol such as hexane-1,6-diol. Illustrative of the amine-terminated polyethers are the aliphatic primary di- and tri-amines structurally derived from polyoxypropylene glycols and triols and having structures represented by and Polyether diamines of this type are available from Jefferson Chemical Company under the trademark JEFFAMINE®. Illustrative of polycarbonates containing hydroxyl groups are those prepared by reaction of diols such as propane-1,3-diol, butane-1,4-diol, hexan-1,6-diol, diethylene glycol, triethylene glycol, dipropylene glycol and the like with diarylcarbonates such as diphenylcarbonate or with phosgene. Illustrative of the silicon-containing polyethers are the copolymers of alkylene oxides with dialkylsiloxanes such as dimethylsiloxane see, for example, U.S. 4,057,595. Illustrative of the hydroxy-terminated poly-butadiene copolymers are the compounds available under the trade name Poly BD Liquid Resins®" from Arco Chemical Company. Illustrative of the hydroxy- and amine-terminated butadiene/acrylonitrile copolymers are the materials available under the trade name HYCAR® hydroxyl-terminated (HT) Uquld Polymers and amine-terminated (AT) Uquid Polymers, respectively. The extenders which are used in preparing the compositions of the invention are aliphatic straight and branched chain diols. Including cycle aliphatic diols, preferably having from about 2 to 8 carbon atoms, inclusive, in the chain. Illustrative of such diols are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 1,3-pentanediol, 1,2-hexanediol, 3-methylpentane-1,5-diol and 1,4-cyclohexanedimethanol, including mixtures of two or more such diols. The extenders, which can be used alone or in admixture with each other or any of the above diols, also include diethylene glycol, dipropylene glycol, tripropylene glycol, N-methyl-diethanol-amine snd N-ethyl-diethanolamine, as well as ester diols obtained by esterifying adipic, azelaic, glutaric and like aliphatic dicarboxylic acids with aliphatic diols such as those exemplified above utilizing from about 0.01 to about 0.8 mole of acid per mole of diol. The compositions of the invention include thermoplastic resins obtained by employing substantially difunctional polyisocyanates and difunctional extenders and a component (b) having a functionality not exceeding 4. Since the amount by weight of the component (b) employed in the compositions of the invention is relatively small, it is possible to employ such components having functionalities from 1,9 up to 4 without detracting from the thermoplasticity of the resulting product. Further, although in general it is desirable to employ a substantially pure diisocyanate, i.e. polyisocyanate free from isocyanates of functionality greater than 2.0, in order to prepare the thermoplastic compositions of the invention, it is found that certain modified methylenebis(phenyl isocyanates) can be employed without detracting from the desired properties. In particular, it is found that a methylenebis(phenyl isocyanate) which has been converted to a stable liquid as described above by reaction with a minor amount of one or more glycols of low molecular weight can give the desired thermoplastic properties in combination with the difunctional extender as described above. In addition, methylenebis(phenyl isocyanate) can be used in admixture with minor proportions, up to about 25 percent by weight, of other modified liquid methylenebis(phenyl isocyanates) such as those described above in which a portion of the diisocyanate has been converted to carbodiimide. However, in general it is not possible to utilize the latter type of isocyanate itself without the admixture with major proportions of methylenebis(phenyl isocyanate) and still obtain thermoplastic polyurethanes. While any of the diol extenders described and exemplified above can be employed in preparing the thermoplastic compositions of the invention, alone, or in admixture, it is preferred to use 1,4-cyclohexanedimethanol, ethylene glycol, and diethylene glycol either alone or in admixture with each other or with one or more aliphatic diols previously named. A particularly preferred diol for the preparation of thermoplastic products is 1,6-hexanediol either as the sole extender or in combination with one or more of the above-named group. In addition to being characterized by the substantially reduced amount of component (b) which is employed In accordance with the invention, the polyurethanes of the invention are characterized by very specific properties which are believed to be evidence of the existence of a two-phase morphology in the compositions. In particular, it is believed that the soft segment of the polymer, which is the minor segment by weight, exists in a separate phase which forms the other phase of the polymer. Some evidence of this is apparent from visual inspection since polymers which are prepared in accordance with the invention, and which are characterized by the higher impact resistance, high flexural modulus and the minimum heat deflection temperature set forth above, are opaque in appearance presumably due to differing refractive indices of the two phases. This is in direct contrast to polyurethanes prepared substantially in accordance with the invention, but replacing the component (b) by a different material not within the above definition and or by using a combination of extenders or isocyanates which is outside the limits discussed above. In such cases the resulting polymer Is found to be clear in appearance, i.e. transparent, and Is devoid of the high impact resistance and other properties discussed above. More quantitative evidence of the existence of the two-phase structure discussed above is found from studies of the dynamic mechanical spectroscopy of the polymers of the invention. Such studies are well-known In the art (see, for example, I. M. Ward, Mechanical Properties of Solid Polymers, Wiley-Interscience, New York, 1971 at p. 138 et seq.). Generally they involve measurement of the change of stiffness and loss factor ("tan δ") in tension, shear, or flexure as a function of temperature or frequency. A homopolymer generally exhibits a single primary damping peak in a plot of tan δ versus temperature or frequency, which peak is associated with its glass transition whereas a two phase system shows two such damping peaks. It is found that, using this method of determination, the plots of tan δ versus temperature obtained in the case of the compositions of this invention show two well-defined and well separated primary damping peaks which correspond to the glass transition temperatures of the component (b) on the one hand and the hard segment on the other. This clearly suggests that the compositions of the invention do exhibit the above-described two-phase morphology consisting of a dispersion of a component (b) rich phase in a hard urethane matrix. The glass transition temperature of the component (b) rich phase usually occurs below room temperature, while that of the urethane glass phase occurs at approximately 100°C. It is to be understood that the above discussion of the morphology of the polyurethanes of the invention is offered by way of explanation and is not intended to be in any way limiting as to the scope of the present invention. In some of the compositions prepared in accordance with the invention using polyols as the component (b) It is found that, unless careful control is exercised in maintaining molding temperatures of the polymer within certain ranges which will be discussed further below, there is a tendency for parts molded from some of the compositions to delaminate. Some compositions may outgas during molding unless careful control of processing temperatures is maintained. It is found, in a particular embodiment of the invention, that these tendencies can be greatly reduced by introducing Into the components used to prepare the compositions a minor amount of a polyester polyol. The latter, which can be any of those described and exemplified above as useful in its own right as component (b), is believed to render the two phases more compatible, one with the other and to minimize outgassing by lowering processing temperatures. When a polyester is employed in the above manner, the combined amount of polyether and polyester polyol used still falls in the range of 2 to 25% w/w based on total polymer set forth above for the polyether polyol alone. The preferred and most preferred amounts given earlier for the polyether polyol alone also apply to the total polyol when polyester polyol is present. The compositions of the invention can also incorporate various additives such as fillers, antioxidants, pigments, fire retardants, plasticizers, reinforcing agents and the like commonly employed in the art in such compositions. The compositions of the invention can be obtained in both cellular and non-cellular form. The cellular compositions of the invention can be prepared by methods well recognized in the art. For example, a blowing agent can be incorporated in the reaction mixture employed in the preparation of the compounds described above. Preferably, the blowing agent is a volatile organic liquid which is vaporized during the exothermic reaction which takes place in forming the compositions of the invention but, in the case of those compositions which are thermoset, it is also possible to use water as the blowing agent. The reaction of the water with polyisocyanate utilized in the reaction mixture generates carbon dioxide which acts as the blowing agent. Examples of organic liquids which can be used as blowing agents are inert liquids, i.e. liquids which do not react chemically with any of the components of the reaction mixture and which do not interfere in any way with the desired course of the reaction, having boiling points in the range of about -20°C to about 110°C. Illustrative of such liquids are butane, hexane, heptane, methylene chloride, chloroform, monofluorotrichloromethane, chlorodifluoromethane and dichlorodifluoromethane. In the case of the thermoplastic compositions of the invention which may be prepared and isolated in flake, pellet or like form and then be subsequently molded by injection molding and like techniques, it is also possible to prepare cellular compositions therefrom by blowing with Inert gases such as nitrogen, air or carbon dioxide during the final molding process using techniques well-known in the art for thermoplastic materials such as nylon, polycarbonate, polystyrene and polyethylene. The compositions of the invention can be fabricated in any desired configuration for use as automobile body parts, equipment housings, mechanical goods, gears, gaskets and a wide variety of other such articles which require the high impact resistance and other properties possessed by the polyurethanes of the invention. The methods of fabrication can be any of those known in the art of molding thermoplastic or thermoset polyurethanes. Such methods include reaction injection molding, cast molding in the case of thermosets and injection molding, extrusion, blow molding, calendering and thermoforming in the case of thermoplastics The marked resistance of the polyurethanes of the invention to deformation or decomposition upon exposure to temperatures involved in melt processing greatly facilitates the fabrication of articles from the thermoplastic compositions of the invention. It has also been found that, in the case of many compositions of the invention, exposure of the compositions to moisture at elevated temperatures of the order of 37.78°C (100°F) or higher for limited periods of time can result in significant increase in impact resistance over and above the high value of impact resistance possessed by the material before exposure to moisture and heat. Accordingly, subjecting the fabricated compositions of the invention to curing by exposure to moist air at ambient temperature or elevated temperatures is a valuable final step in the manufacture of articles in which high impact strength is particularly desirable. The following examples describe the manner and process of making and using the invention and set forth the best mode contemplated by the inventors of carrying out the invention. Example 1 A series of thermoplastic polyurethanes was prepared from 4,4'-methylenebis(phenyl isocyanate) and different combinations of glycol extenders and polyether polyols (details of which are given below) using the following general procedure. The glycol extender(s) and polyether polyol were blended and dried and degassed by heating under vacuum (266-3990 Pa) for about 2 hours at 80-100°C. The resulting mixture, without cooling, was admixed quickly with the molten diisocyanate, 1 drop (0.05 g.) of stannous octoate (50% solution in dioctyl phthalate) was added and the mixture was vigorously stirred by mechanical stirrer or hy hand for 5-30 seconds before being poured into a Teflon-linked open tray at room temperature. The mixture solidified and was then chopped mechanically into small pieces and dried in a dehumidifying drier. Polyurethane sheets were then molded by injection molding using barrel temperatures of 210-243.3°C, mold temperatures of 26.7-65.6°C; total cycle times ranged from 30-60 seconds. The test samples used for the tensile and flexure tests were prepared using an Arburg press 221E/150 and the sheets used for the remainder of the tests were prepared on a Modern Plastics Machinery SKM75® press. The operating conditions for both apparatus were within the limits given above. The various polyurethanes so obtained were opaque in appearance after molding. The physical properties of the samples are recorded in the following Table I together with the identity of extenders and polyols used in each case, the proportions, in equivalents per equivalents of diisocyanate in which the extenders were used and the proportion, in terms of weight percent based on finished polyurethane, in which the polyol was employed. It will be seen that all the samples showed excellent impact resistance as measured by the Notched Izod test, and that the tensile and flexural strength properties were also eminently satisfactory for materials to be employed as engineering plastics. The following abbreviations are used in TABLE I. BD = 1,4-butanediol DPG = dipropylene glycol NPG = neopentyl glycol PEHQ = p,p'-di(2-hydroxyethyl)hydroquinone CHDM = 1,4-cyclohexanedimethanol HD = 1,6-hexanediol TPG = tripropylene glycol TEG = triethylene glycol N.T. = not tested HDT = Heat deflection temperature Tg = Glass transition temperature Identity of polyols in TABLE I:- T-2000 = polytetramethylene glycol: mol. wt=2000: DuPont. SF-6503 = see Example 1. T-1340 = polytetramethylene glycol: mol. wt.=1340: DuPont. T-1500 = polytetramethylene glycol: mol. wt.=1500: DuPont. 55-37 = polyoxyethylene polyoxypropylene glycol: mol. wt. = 4000: Olin. Identity of extenders in Runs 6-16, 6-17 end 6-18:- Diol A: Ester diol eq. wt. = 123.5 obtained by esterifying adipic acid with CHDM. Diol B: Ester diol eq. wt. = 119.5 obtained by ester interchange between CHDM and dimethyl azelate. Diol C: Ester diol eq. wt. = 146 obtained by ester interchange between CHDM and dimethyl azelate. Example 2 Using the procedure described in Example 1 there was prepared a series of thermoplastic polyurethanes, samples of each of which were injection molded as described in Example 1 to give sheets for physical testing. The various polyurethanes so obtained were opaque in appearance and retained their opaqueness throughout the molding process. The following TABLE II gives details of the extenders and polyols used [the diisocyanate was 4,4'-methylenebis(phenyl isocyanate) in all cases] together with the proportions, in equivalents per equivalent of diisocyanate, in which the extenders were used and the proportion, in terms of weight percent based on finished polyurethane, in which the polyol was employed. It will be seen that all the samples showed excellent impact resistance as measured by the Notched Izod test, and that the tensile and flexural strength properties were also eminently satisfactory for materials to be employed as engineering plastics. The abbreviations used in TABLE II are the same as those used in TABLE I. The identity of the polyols, other than those previously described, used in TABLE II is as follows: NIAX 11-27®: polyoxyethylene-polyoxypropylene glycol: Mol. wt. = 6000: Union Carbide MDS 0509®: polyoxyethylene polyoxypropylene glycol: Mol. wt. = 4200: Texaco Chemical 4480-22®: polyoxyethylene polyoxypropylene glycol: Mol. wt. = 3700: Witco Chemical Company LHT 28®: polyoxypropylene triol: Mol. wt. = 6000: Union Carbide T-1000 "triol"®: Ether ester triol eq. wt. = 1010 obtained by esterification of trimellitic anhydride with T-1000 in xylene solution followed by removal of xylene. Example 3 Using the procedure described in Example 1 there was prepared a series of thermoplastic urethanes using mixtures of two different polymeric polyols and only a single extender. Samples of each of the polyurethanes were injection molded and cured as described in Example 1 to give sheets for physical testing. The various polyurethanes so obtained were opaque In appearance and retained their opaqueness throughout the molding process. The following TABLE III gives details of the extenders and polyols used [the diisocyanate was 4,4'-methylenebis(phenyl isocyanate) in all cases] together with the proportions, in equivalents per equivalent of diisocyanate, in which the extenders were used and the proportion, in terms of weight percent based on finished polyurethane, In which the polyols were used. It will be seen that all the samples showed good Impact resistance as measured by the Notched Izod test, and that the tensile and flexural strength properties were also eminently satisfactory for materials to be employed as engineering plastics. The abbreviations used in TABLE III are the seme as those used in TABLE I. The identity of the polyols, other than those described previously, used in TABLE III is as follows: E 2105®: polyoxyethylene polyoxypropylene glycol: Mol. wt. = 2000: Texaco Chemical PCP 2000®: polycaprolactonediol: Mol. wt. = 2000: Union Carbide S102-55®: poly(butylene adipate): Mol. wt. = 2000: Ruco S102-135®: poly(butylene adipate): Mol. wt. = 830: Ruco Example 4 This Example illustrates the behaviour upon exposure to moisture and to dry heat of a thermoplastic polyurethane prepared in accordance with the invention. The polyurethane employed in the experiments was obtained using essentially the procedure described in Example 1 but carrying cut the reaction on a continuous basis utilizing a Werner-Pfleiderer extruder-mixer, extruding the finished polymer in the form of strands and chopping the latter into pellets. Aliquots of the pellets were then molded under pressure at ca. 218.3°C (barrel temperature) using a mold of dimensions 15.24 × 7.62 × 0.32 cm and employing a Modern Plastics Machinery SKM 75® press. The various specimens so obtained were subjected to various conditions of moisture and heat and the Notched Izod Impact value determined after each exposure was compared with the value determined on the sample immediately prior to the test. The various reactants employed in preparing the samples and the proportions, by equivalents, are given below. 4,4'-methylenebis(phenyl isocyanate: 1.02 equivs. 1,4-butanediol: 0.74 equivs. neopentyl glycol: 0.25 equivs. T-2000®: 7.5% by weight based on total reactants. The results of the various tests are summarized below. Notched Izod Impact (0.32 cm: mkg/m) Treatment Wt. change % Before drying After drying As molded - 12.8 - Boiling water: 24 hr. +2.26 106.1 89.3 Humid age at 75.6°C: 8 days +2.1 130.6 76.2 115°C Dry air: 16 hr. -0.1 50.6 - Example 5 Using exactly the procedure described in Example 1 a thermoplastic polyurethane was prepared from an aromatic diisocyanate which comprised a blend of equal parts by weight of 4,4'-methylenebis(phenyl isocyonate) and a methylenebis(phenyl isocyanate) containing 80 percent by weight of 4,4'-isomer and 20 percent by weight of 2,4'-isomer. The proportions in equivalents and identity of this and the other reactants were as follows. Aromatic diisocyanate: 1.02 equivalents 1,4-butanediol: 0.9 equivalents Neopentyl glycol: 0.1 equivalents Polyol T-2000: 8.5 percent by weight (based on final product) The resulting polyurethane was opaque. Samples were molded as described in Example 1 (the molded Samples were also opaque) and found to have the following physical properties. Notched Izod Impact ft.lbs/in.: 0.32 cm: 62.6 Flexural strength: MPa: 101.4 Flexural modulus: MPa: 2524 Heat deflection temperature at 1820 kPa: 90°C Tg: 96°C Example 6 Using the procedure described in Example 1 there was prepared a thermoplastic polyurethane using 4,4'-methylenebis(phenyl isocyanate), SF-6503 and an extender diol which had been prepared in the following manner. A mixture of 432.63 g (3 moles) of 1,4-cyclohexanedimethanol, 114.14 g. (1 mole) of ε-caprolactone and 15 ml. of toluene were charged to a reaction vessel and heated to 160°C, with stirring under an atmosphere of argon, and held at that temperature for 45 minutes to remove water by azeotrope using a Dean Stark apparatus. To the resulting mixture was added 0.08 g. (3 drops) of stannous octoate and the temperature was then raised to 190° to 195°C and held thereat, with stirring, for approximately 6 hours. Examination of aliquots by infrared spectra at intervals during the reaction showed that no ε-caprolactone was still present in the reaction after 2 hours. The resulting mixture was heated at 100°C under vacuum for 2.5 hours to remove toluene and was then allowed to cool to room temperature. There was thus obtained an adduct having an equivalent weight of 91.1. The polyurethane was prepared using the following proportions of reactants: 0.975 equivalents of the above adduct, 1 equivalent of the diisocyanate and 6 percent by weight (based on total reactants) of the polyol SF-6503 using exactly the reaction procedure and molding procedure set forth in Example 1. The molded sheet of polyurethane so obtained was opaque in appearance and was found to have a Notched Izod Impact of 104.5 mkg/m (0.32 cm). Example 7 Using exactly the procedure and reactant proportions described in Example 1, Run 6-14, but replacing the SF-6503® polyol there used by a number of different polyols there was prepared a series of thermoplastic polyurethanes in accordance with the invention. The various elastomers so obtained were molded into sheets for testing purposes using the molding procedure described in Example 1. The following TABLE IV shows the polyol used, the amount of polyol used, and the Notched Izod Impact value of the product. The extender was hexane-1,6-diol in all cases and the diisocyanate was 4,4'-methylenebis(phenyl isocyanate) in the proportions shown in Run 6-14. All the products so obtained were opaque in appearance. Run Polyol Wt.% Notched Izod Impact (0.32 cm: mkg/m) 12-1 Arco R45HT® 9.12 14.7 12-2 DCQ4-3667® 10 43.5 12-3 Hycar 1300X16® 6 6.5 12-4 Hycar 1300X17® 6 12.0 12-5 Jeffamine D2000® 6 23.4 12-6 Niax 34-28® 6 35.4

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, NL, SE A thermoplastic polyurethane characterized by high impact resistance at ambient conditions of at least 5.44 mKg/m (ASTM D 256-56) of notch as measured by the notched Izod test, high flexural modulus of at least 1 034.5 MPa (ASTM-D 790) and a heat deflection temperature of at least 50°C at 1820 kPa (ASTM D 648-56) which comprises the product of a one-shot reaction of (a) an organic polyisocyanate comprising a diisocyanate selected from 4,4'-methylenebis(phenyl isocyanate) and mixtures of 4,4'-methylenebis(phenyl isocyanate) with the corresponding 2,4'-isomer in an amount up to 70 percent by weight based on the total diisocyanate mixture, or an organic polyisocyanate corresponding to said diisocyanate wherein said 4,4'-methylenebis(phenyl isocyanate) or the mixture thereof with the 2,4'-isomer is in the form of a liquid at ambient temperature and which has been obtained by (a) converting a minor proportion thereof to the corresponding carbodiimide or (b) reacting the 4,4'-methylenebis(phenyl isocyanate) or its admixture with the 2,4'-isomer with a minor amount of at least one aliphatic diol, (b) an isocyanate-reactive material having an average functionality of at least 1.9 and not exceeding 4, a glass transition temperature (Tg) of less than 20°C, and a molecular weight in the range of 500 to 20,000 and (c) at least one aliphatic diol chain extender having a molecular weight from 50 to 400; said polyurethane being further characterized in that the proportion by weight of said isocyanate-reactive material (b) in said polyurethane is from 4 to 15 percent and the overall ratio of isocyanate groups to active hydrogen groups in said reactants employed to prepare said polyurethane is in the range of 0.95:1 to 1.05:1. A polyurethane according to Claim 1 wherein the component (b) comprises a polyether polyol. A polyurethane according to Claim 2 wherein the polyether polyol is selected from (a) random and block copolymers of ethylene and propylene oxide having a primary hydroxyl content of at least 80 percent and a functionality of approximately 3.0 and (b) a polytetramethylene glycol of a functionality greater than or equal to 2.0. A polyurethane according to Claim 1 wherein the component (b) comprises a polyester polyol. A polyurethane according to Claim 1, wherein said aliphatic diol is selected from 1,6-hexanediol, 1,4-butanediol, a mixture of 1,4-butanediol and neopentyl glycol, 1,4-cyclohexanedimethanol, a mixture of 1,4-cyclohexanedimethanol and 1,6-hexanediol, and the product obtained by reacting an aliphatic diol with a member selected from (a) caprolactone in the mole ratio of from 0.01 to 2 moles of caprolactone per mole of aliphatic diol and (b) adipic acid in the mole ratio of from 0.01 to 0.8 mole of acid per mole of aliphatic diol. Claims for the following Contracting State : AT A process for the preparation of a thermoplastic polyurethane characterized by high impact resistance at ambient conditions of at least 5.44 mKg/m (ASTM-D 256-56) of notch as measured by the notched Izod test, high flexural modulus of at least 1 034.5 MPa (ASTM-D 790) and a heat deflection temperature of at least 50°C at 1820 kPa (ASTM-D 648-56) which process comprises reacting in a one-shot reaction (a) an organic polyisocyanate comprising a diisocyanate selected from 4,4'-methylenebis(phenyl isocyanate) and mixtures of 4,4'-methylenebis (phenyl isocyanate) with the corresponding 2,4'-isomer in an amount up to 70 percent by weight based on the total diisocyanate mixture, or an organic polyisocyanate corresponding to said diisocyanate wherein said 4,4'-methylenebis(phenyl isocyanate) or the mixture thereof with the 2,4'-isomer is in the form of a liquid at ambient temperature and which has been obtained by (a) converting a minor proportion thereof to the corresponding carbodiimide or (b) reacting the 4,4'-methylenebis(phenyl isocyanate) or its admixture with the 2,4'-isomer with a minor amount of at least one aliphatic diol, (b) an isocyanate-reactive material having an average functionality of at least 1.9 and not exceeding 4, a glass transition temperature (Tg) of less than 20°C, and a molecular weight in the range of 500 to 20,000 and (c) at least one aliphatic diol chain extender having a molecular weight from 50 to 400; said process being further characterized in that the said isocyanate-reactive material (b) is employed in a proportion by weight of from 4 to 15 percent of the polyurethane weight and the overall ratio of isocyanate groups to active hydrogen groups in which said reactants are employed is in the range of 0.95:1 to 1.05:1. A process according to Claim 1 wherein the component (b) comprises a polyether polyol. A process according to Claim 2 wherein the polyether polyol is selected from (a) random and block copolymers of ethylene and propylene oxide having a primary hydroxyl content of at least 80 percent and a functionality of approximately 3.0 and (b) a polytetramethylene glycol of a functionality greater than or equal to 2.0. A process according to Claim 1 wherein the component (b) comprises a polyester polyol. A process according to Claim 1 wherein said aliphatic diol is selected from 1,6-hexanediol, 1,4-butanediol, a mixture of 1,4-butanediol and neopentyl glycol, 1,4-cyclohexanedimethanol, a mixture of 1,4-cyclohexanedimethanol and 1,6-hexanediol, and the product obtained by reacting an aliphatic diol with a member selected from (a) caprolactone in the mole ratio of from 0.01 to 2 moles of caprolactone per mole of aliphatic diol and (b) adipic acid in the mole ratio of from 0.01 to 0.8 mole of acid per mole of aliphatic diol.

Inventors: GOLDWASSER DAVID JAY, ONDER KEMAL, GOLDWASSER, DAVID JAY, ONDER, KEMAL
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1982
Main classification: C08G18
IPC codes: C08G18