POLYURETHANES OF IMPROVED CHARACTERISTICS

Abstract: A urea-modified polyurethane having excellent characteristics is prepared by the reaction between a polyisocyanate and a polyol in the presence of a diamine having formula (I), in which R<1> and R<2> are independently straight-chain C2-C6 alkyl, and m and n are independently either 1 or 2. The preferred polyol is castor oil, and in preferred methods the reaction is carried out by first forming a prepolymer of the polyisocyanate with the polyol, and then curing this with a solution of the diamine in a further amount of the polyol.

Description: POLYURETHANES OF IMPROVED CHARACTERISTICS 5 BACKGROUND OF THE INVENTION The present invention is related to polyure- thanes, and particularly to urea-modified polyure¬ thanes. he chemistry of urethane polymers extends 10 over a very broad scope of chemical structures, produc¬ ing products varying widely in properties and uses. A common variation from the basic urethane backbone structure (i.e., the carbamate linkage) is the incor¬ poration of urea linkages, which is generally accom- 15 pushed by the use of diamines as chain extenders. Among the many uses of polyurethanes are those involving medical devices, where polyurethanes are used as structural materials for separatory devices and prosthetic devices, and also as adhesives in such 20 devices. The polyurethanes assume a variety of forms, in these materials, including sheets, tubing, structural components, and two-component adhesive composition. In many cases, the polymer is in intimate contact with internal human tissue. In such applications, compati- 25 bility with the tissue is essential, and certain types of polyurethanes, notably those in which the polyol component is castor oil or various polyols similar in structure and properties, have been found to provide biocompatible products. 30 The various polyurethanes and their compo¬ nents have certain disadvantages which affect their utility, particularly in medical use. Biocompatibil- ity, as mentioned above, is a problem in many cases. In addition, the product color is important, particu- ~ ~ larly when the product must be observed during use. This may occur for example when one is monitoring a clinical treatment process or a patient's progress, SUBSTITUTESHEET where a high degree of clarity and transparency is desired. In two-component polyurethane systems, the stability of each of the components and possible dangers to those handling them (such as toxicity considerations, particularly carcogenicity) are a concern. Still further, certain combinations of diamines and polyols have a strong tendency to react with each other, thereby interfering with the formation of the carbamate groups in the basic polyurethane curing reaction, which not only interferes with the polyurethane formation but results in a loss of the chain-extending function of the diamine. SUMMARY OF THE INVENTION It has now been discovered that a narrowly defined class of diamines has unique qualities when used as chain extenders or modifiers in the formation of urea-modified polyurethanes. These diamines are nontoxic, highly stable, and avoid interfering re- actions with polyols, particularly those such as castor oil and its analogs, which have been found to be particularly biocompatible. These diamines thus produce an exceptional polyurethane product. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The critical diamines in accordance with the present invention are those having the formula SUBSTITUTE SHEET In this formula, R1 and R2 are either the same or different, and each is a straight-chain alkyl group of two to six carbon atoms. In preferred embodi- ments, R 1 and R2 each contain two to four carbon atoms, with ethyl and n-propyl particularly preferred. The symbols m and n are either the same or different and denote integers which may be either 1 or 2. In pre¬ ferred embodiments, m and n are both 1. In further preferred embodiments, the diamine is symmetrical, the amino groups are located at the 4-positions on the phenyl rings, and the alkyl substituents are located at the 3-positions, or the 3- and 5-positions (in the case of either or both of m and n being 2). Examples of diamines within the scope of the invention are: Di(2-ethyl-4-aminophenyl)methane Di(2-n-propyl-4-aminophenyl)methane Di(3-ethyl-4-aminophenyl)methane Di(3-n-propyl-4-aminophenyl)methane Di(3-n-butyl-4-aminophenyl)methane Di(3-n-hexyl-4-aminophenyl)methane Di(3-amino-4-ethylpheny1)methane Di(3-amino-4-n-propylphenyl)methane Di(3,5-diethyl-4-aminophenyl)methane Di(3,5-di-n-propyl-4-aminophenyl)methane Di(2,6-diethyl-4-aminophenyl)methane Further examples are asymmetrical analogs of the above, involving various combinations of the substituted-phen- yi groups. Using these diamines, polyurethanes may be prepared in accordance with the present invention by any conventional technique, including both one-shot and two-shot methods. One-shot methods may be performed using polyurethane catalysts known to those skilled in the art. Examples include triethylene diamine and various organotin compounds such as di-n-butyl tin SUBS ITUTE v= τ diacetate. Two-shot methods are likewise performed using conventional techniques. In general, the two-shot or two-package polyurethanes are prepared by first reacting a portion of the polyol with an excess of the polyisocyanate to form an isocyanate-terminated prepoly¬ mer (component A of the system). The prepolymer is then reacted with the remainder of the polyol, which is in the form of a solution containing a diamine within the scope of the .above formula (component B) . The parameters of a two-package system may vary widely in value. In most cases, however, prepoly- mers with an isocyanate content of about 5 to about 30%, preferably about 10% to about 20%, will provide the best results. Likewise, a diamine content of component B ranging from about 0.5% to about 20%, preferably about 1% to about 10% (by weight) will provide the best results. Relative amounts of components A and B used in forming the finished product may also vary. Pre- ferred proportions will generally fall within the range of about 40% to about 60% by weight for each component. Particularly preferred proportions will be about 40% to about 50% by weight of component A, with the remainder being component B. The optimum levels and proportions in each case will vary with the desired properties and intended use of the finished product. The reaction to form the polyurethane product may be conducted under conventional operating con¬ ditions. In the two-shot method, the components may be mixed at room temperature in the preselected proportions, particularly when the desired product is an adhesive. The product is then permitted to stand at room tempera¬ ture, and will generally cure within about 5-10 hours. The two components may be prepared in advance, and sold, shipped and stored as such, leaving the final polyurethane reaction to the user. ■ϋBβrmrT**** Polyisocyanates useful in the present in¬ vention are preferably diisocyanates. A wide range of diisocyanates may be used, including aromatic diisocyan¬ ates, aliphatic diisocyanates, cycloaliphatic diisocyanates, and blends of aromatic and aliphatic diisocyanates. Aromatic diisocyanates are preferred. Examples of diisocyanates are as follows: ethylene diisocyanate propylene diisocyanate trimethylene diisocyanate hexamethylene diisocyanate cyclopentylene-1,3-diisocyanate eyelohexylene-1,3-diisocyanate eyelohexylene-1,4-diisocyanate 1, -di(isocyanatomethyl)cyclohexane 1,3-di(isocyanatomethyl)cyclohexane m-phenylene diisocyanate p-phenylene diisocyanate 2,4-toluene diisocyanate 2,6-toluene diisocyanate 4,4'-methylenebis-(phenyl isocyanate) 3,3'-methylenebis-(phenyl isocyanate) dibenzyl-4,4'-diisocyanate 1,4-naphthalene diisocyanate 1,5-naphthalene diisocyanate polymeric methylenebis(phenyl isocyanates), st.ch as those obtained by the phosgenation of aniline-formaldehyde-derived polyamines 3,3'-bitolylene 6,6'-diisocyanate isophorone diisocyanate 4,4'-methylenebis(cyclohexy1 diisocyanate) 1,6-diisocyanato-2,2,4,4-tetramethylhexane 1,6-diisocyanato-2,2,4-trimethylhexane Preferred polyols for use in the present invention are mono-, di- and triglycerides of aliphatic SUBSTITUTESHEET carboxylic acids of 10 carbon atoms or more, particularly triglycerides of hydroxy-substituted aliphatic carboxylic acids. Notable examples are natural oils, particularly castor oil. A typical composition of castor oil is a combination of tri¬ glycerides of the following fatty acids: ricinoleic (cis-12-hydroxyoctadec-9-enoic) acid, 87% oleic (cis-9-octadecenoic)acid 7% linoleic ((Z,Z)-9,12-octadecadienoic) acid, 3% palmitic (n-hexadecanoic) acid 2% stearic (n-octadecanoic) acid 1% dihydroxystearic acids trace amounts The following example is offered for purposes of illustration, and is intended neither to limit nor define the invention in any manner. EXAMPLE This example compares various diamines within the scope of the present invention to those outside the scope of the present invention, in terms of stability, toxicity, and reactivity in forming the polyurethane. Those within the scope of the invention are the first two entries, MBOEA and MDPA. As the data in the table demonstrates, these two species are superior in overall properties to all others tested. SU BS TITUTESHEET TEST RESULTS ON TWO-PART URETHANES Part A (Polyisocyanate Prepolymer; all parts by weight) MDI, 54.4 parts Castor oil, 30.6 parts Isonate 143-L, 15.0 parts Part B (Polyol Component) : various diamines in castor oil, as listed below Proportion: 47 parts of Part A to 53 parts of Part B Pol ol Com onent Product *MPDA discolors tissue. SUBSTITUTE SHEET Key: 1-Year Stability: Sample is stored for 6 weeks at 140°F (equivalent to 1 year at room temperature) , then mixed with polyisocyanate component; "stable": mixture thickens, indicating occurrence of curing; "unstable": mixture does not thicken, indicating that a reaction between the diamine and the castor oil has occurred during storage. hixotropic Index: Ratio of Brookfield viscosities (measured at 25°F) at low shear (3 rpm) to high shear (30 rpm), taken immediately after polyol and polyisocyanate components are combined. Color Index (determined by visual observation after complete cure) : 3: straw-colored (i.e., excellent) 2: medium brown (i.e., good) 1: dark brown/black (i.e., poor) Abbreviations and Trade Names: MDI: 4,4'-methylenebis(phenyl isocyanate) Isonate 143-L: a carbodiimide-modified MDI product, obtained from Upjohn Polymer Chemicals, LaPorte, Texas, and also available from Dow Chemical Co., Midland, Michigan MBOEA: Di(3-ethyl-4-aminophenyl)methane t"methylenebis(o-ethylaniline)"] MDPA: Di(3,5-di-n-propyl-4-aminophenyl)methane t"methylenebis(di-n-propylaniline)"] MDIPA: Di(3,5-diisopropyl-4-aminophenyl)methane ["methylenebis(diisopropylaniline)"1 MBPMA: Di(3-propyl-5-methyl-4-aminophenylJmethane ["methylenebis(propylmethylaniline)"] MOCA: Di(3-chloro-4-aminophenyl)methane ["methylenebis(o-chloroaniline)"] MBMA: Di(3-carbomethoxy-4-aminophenyl)methane ["methylenebis(methyl anthrani1ate)"I MDA: Di(4-aminophenyl)methane ["methylene dianiline"] MPDA: m-Phenylene Diamine DETDA: 3,5-Diethyl-2,4-diaminotoluene ["diethyltoluene diamine"] SUBST I TUTESHEET ETHACURE 300: 3,5-Dimethylthio-2,6-diaminotoluene, Ethyl Corporation, Baton Rouge, Louisiana JEFFAMINE D-230 and D-2000: polyoxypropylene diamines, molecular weights approximate- ly 230 and 2000, respectively, Texaco Chemical Co., White Plains, New York. The foregoing is offered primarily for purposes of illustration. It will be readily apparent to those skilled in the art that variations, modifica¬ tions and further substitutions of the elements and features of molecular structure, system parameters and operating conditions described above may be made without departing from the spirit and scope of the invention. SUBSTITUTE SHEET

Claims: AMENDED CLAIMS [received by the International Bureau on 19 June 1989 (19.06.89) original claims 1 , 2, 7, 8 , 20, 21, 23 , 24, 27-29 , 37 and 38 amended; other claims unch.anged ( 6 pages ) ] 1. A method for the preparation of a non-foamed bioco patible urea-modified polyurethane, said method comprising reacting a polyisocyanate with a polyol in the presence of a diamine having the formula in which R 1 and R 2 are independently straight-chain C-C 6 alkyl, said diamine being the sole diamine present. 2. A method for the preparation of a non-foamed biocompatible urea-modified polyurethane, said method comprising reacting (a) a prepolymer prepared by a reaction between a polyisocyanate and a polyol, with (b) a polyol mixture comprising a diamine dissolved in said polyol, said diamine having the formula in.which R 1 and R 2 are independently straight-chain C z -C 6 alkyl, said diamine being the sole diamine present. 3. A method in accordance with claim 2 in which said prepolymer has an isocyanate content of about 5% to about 30%. 4. A method in accordance with claim 2 in which said prepolymer has an isocyanate content of about 10% to about 20%. 5. A method in accordance with claim 2 in which said diamine comprises about 0.5% to about 20% of said polyol mixture. 6. A method in accordance with claim 2 in which said diamine comprises about 1% to about 10% of said polyol mixture. 7. A method in accordance with claims 1 or 2 in which said polyol is a member selected from the group consisting of mono-, di- and triglycerides of aliphatic carboxylic acids of at least 10 carbon atoms. 8. A method in accordance with claims 1 or 2 in which said polyol is a triglyceride of a hydroxy-substituted aliphatic carboxylic acid of at least 10 carbon atoms. 9. A method in accordance with claims 1 or 2 in which said polyol is castor oil. 10. A method in accordance with claims 1 or 2 in which said polyisocyanate is a diisocyanate. 11. A method in accordance with claims 1 or 2 in which said polyisocyanate is a member selected from the group consisting of aromatic diisocyanates, aliphatic diisocyanates, cycloaliphatic diisocyanates, and blends of aromatic and aliphatic diisocyanates. 12. A method in accordance with claims 1 or 2 in which said polyisocyanate is an aromatic diisocyanate. 13. A method in accordance with claims 1 or 2 in which said polyisocyanate is a member selected from the group consisting of methylenebis-(phenyl isocyanates), poly[methylenebis-(phenyl isocyanates)], toluene diisocyanates, and naphthalene diisocyanates. 14. A method in accordance with claims 1 or 2 in which said polyisocyanate is a methylenebis-(phenyl isocyanate) . 15. A method in accordance with claims 1 or 2 in which said diisocyanate is 4,4'-methylenebis-(phenyl isocyanate) . 16. A method in accordance with claims 1 or 2 in which R 1 and R 2 are independently selected from the group consisting of ethyl and propyl; and m and n are each 1. 17. A method in accordance with claims 1 or 2 in which R 1 and R 2 are independently selected from the group consisting of ethyl and propyl; m and n are each 1; and said diamine is symmetrical. 18. A method in accordance with claims 1 or 2 in which R 1 and R 2 are each ethyl, m and n are each 1; and said diamine is symmetrical. 19. A method in accordance with claims 1 or 2 in which said diamine is di(3-ethyl-4-aminophenyl)methane. 20. A method in accordance with claims 1 or 2 in which said polyisocyanate is an aromatic diisocyanate; said polyol is a member selected from the group consisting of mono-, di- and triglycerides of aliphatic carboxylic acids of at least 10 carbon atoms; and R 1 and R 2 are independently selected from the group consisting of ethyl and n-propyl; and said diamine is symmetrical. 21. A method in accordance with claims 1 or 2 in which said polyisocyanate is a methylenebis-(phenyl isocyanate) ; said polyol is a triglyceride of a hydroxy- substituted aliphatic carboxylic acid of at least 10 carbon atoms; R 1 and R 2 are independently selected from the group consisting of ethyl and n-propyl; and said diamine is symmetrical. 22. A method in accordance with claims 1 or 2 in which said polyisocyanate is 4,4 '-methylenebis-(phenyl isocyanate) ; said polyol is castor oil; and said diamine is di(3,3 '-ethyl-4, *-aminophenyl)methane. 23. A non-foamed biocompatible urea-modified polyurethane comprising the reaction product of a polyisocyanate, a polyol, and a diamine having the formula in which R 1 and R 2 are independently straight-chain C 2 -C 6 alkyl, said diamine being the sole diamine present. 24. A non-foamed biocompatible urea-modified polyurethane comprising the reaction product of (a) a prepolymer prepared by a reaction between a polyisocyanate and a polyol, and (b) a polyol mixture comprising a diamine dissolved in said polyol, said diamine having the formula in which R 1 and R 2 are independently straight chain C 2 -C 6 alkyl, said diamine being the sole diamine present. 25. A urea-modified polyurethane in accordance with claim 24 in which said prepolymer has an isocyanate content of about 5% to about 30%. 26. A urea-modified polyurethane in accordance with claim 24 in which said prepolymer has an isocyanate content of about 10% to about 20%. 27. A urea-modified polyurethane in accordance with claim 24 in which said diamine comprises about 0.5% to about 20% of said polyol mixture. 28. A urea-modified polyurethane in accordance with claim 24 in which said diamine comprises about 1% to about 10% of said polyol mixture. 29. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyol is a member selected from the group consisting of mono-, di- and triglycerides of aliphatic carboxylic acids of at least 10 carbon atoms. 30. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyol is castor oil. 31. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is a diisocyanate. 32. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is an aromatic diisocyanate. 33. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is a methylenebis- (phenyl isocyanate) . 34. A urea-modified polyurethane in accordance with claims 23 or 24 in which R 1 and R 2 are independently selected from the group consisting of ethyl and propyl; and m and n are each 1. 35. A urea-modified polyurethane in accordance with claims 23 or 24 in which R 1 and R 2 are each ethyl, m and n are each 1; and said diamine is symmetrical. 36. A urea-modified polyurethane in accordance with claims 23 or 24 in which said diamine is di(3-ethyl-4- a inophenyl)methane. 37. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is an aromatic diisocyanate; said polyol is comprised of a member selected from the group consisting of mono-, di- and triglycerides of aliphatic carboxylic acids of at least 10 carbon atoms; R 1 and R 2 are independently selected ' from the group consisting of ethyl and n-propyl; and said diamine is symmetrical. 38. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is a methylenebis-(phenyl isocyanate) ; said polyol is a triglyceride of a hydroxy-substituted aliphatic carboxylic acid of at least 10 carbon atoms; R 1 and R 2 are independently selected from the group consisting of ethyl and n-propyl; and said diamine is symmetrical. 39. A urea-modified polyurethane in accordance with claims 23 or 24 in which said polyisocyanate is 4,4'- ethylenebis-(phenyl isocyanate) ; said polyol is castor oil; and said diamine is di(3,3'-ethyl-4,4'-aminophenyl)methane. STATEMENTUNDERARTICLE 19 This amendment reduces the scope of the claims, by restricting the R and R 2 groups to only one of each per molecule, and by stating that the formula shown is the only diamine present in the reaction mixture. The amendment also adds the words "non-foamed biocompatible" to further characterize the urea-modified polyurethane. All such changes find support in the application as filed. The two references considered the most relevant in the priority application are Schmidt, et al., US, A, 4,636,531; and Richert, et al., UK, A, 1,412,818. Schmidt, et al., disclose only the use of a combination of two classes of diamines, one including sterically hindered diamines and the other non-sterically hindered. By contrast, Applicant's claims are amended to specifically recite a single class of sterically hindered diamines. There is no disclosure in Schmidt, et al., that a single type used alone has utility in the reaction. In addition, none of the compounds disclosed in Schmidt, et al., have a single straight-chain alkyl substitution for each phenyl group. The stated purpose of the Schmidt, et al., invention is "to prepare elastic polyurethane polyurea molded parts using injection molding techniques by a process that eliminates the use of external release agents." By contrast, the purpose in Applicant's invention is to achieve a degree of intermediate tackiness (or thixotropic effect) in the potting compound. There is no suggestion in Schmidt that this effect can be achieved, much less by making the modifications necessary to place the compounds within the scope of Applicant's claims. Richert, et al., address the preparation of polyurethane foams, which are distinct from the non-foam products to which Applicant's invention is directed. Note the description on page 1 of Applicant's specification at lines 20-24 — polyurethane sheets, tubing, structural components and adhesive compositions used for medical devices are not foamed materials. The amendment submitted herewith emphasizes this distinction. Furthermore, the diamines disclosed in Richert are all asymmetrical. Many of Applicant's narrower claims, notably claims 17, 18, 20, 35 and 37, are restricted to symmetrical diamines. Finally, a significant part of Applicant's invention is the discovery that the product, is non-toxic in character, which makes it particularly useful as a biocompatible material. There is nothing in either of these two references to suggest that a totally stable and biocompatible polyurethane can be made by this method.

Inventors: CASE BARTON CARR, CASE, BARTON, CARR
Applicants: HEXCEL CORP, HEXCEL CORPORATION
Application year: 1989
Main classification: C08G18
IPC codes: C08G18