Abstract:
A method for producing a urethane elastomer is disclosed. The method involves mixing benzotriazole or a tolyl triazole with an isocyanate terminated prepolymer while the prepolymer is at a temperature sufficiently high that it is a liquid. The proportion of benzotriazole or tolyl triazole used can range from 0.1 to 1.0 equivalent per equivalent of isocyanate in the prepolymer, and must be sufficient to increase the pot life of a mixture of the prepolymer with a diamine, but insufficient to cause substantial impairment of the physical properties of the cured elastomer. A substantially equivalent amount of a diamine is then mixed with the stabilized prepolymer, and the resulting composition is heated to produce the elastomer.

Description:
BACKGROUND OF THE INVENTION 
     Urethane elastomers are produced in large quantities from various isocyanate terminated prepolymers by reaction with a hindered diamine. Historically, 4,4&#39;-methylene bis (o-chloroaniline) (hereinafter &#34;MOCA&#34;) has probably been the most widely used hindered amine. However, MOCA is a carcinogen suspect agent, and, as a consequence, taking the necessary safety precautions to safeguard the health of workers substantially increases the cost involved in producing elastomers using MOCA as the hindered amine. Another hindered amine that has also seen considerable use is 4,4&#39;-methylene bis (methyl-anthranilate) (hereinafter &#34;MBMA&#34;). 
     So far as is known, unhindered diamines have not heretofore been used for reaction with an isocyanate terminated prepolymer to produce an elastomer. Pot life is short, only a few minutes, even when MOCA and MBMA are used as the diamines. In a recent experiment wherein an attempt was made to produce a urethane elastomer from an isocyanate terminated prepolymer and an unhindered diamine the pot life was estimated to be five seconds; the specific unhindered diamine used was 4,4&#39;-methylene dianiline (hereinafter &#34;MDA&#34;). 
     BRIEF DESCRIPTION OF THE INSTANT INVENTION 
     The present invention is based upon the discovery that an isocyanate terminated prepolymer can be stabilized by reaction with benzotriazole* or a tolyl triazole, and that a mixture of the stabilized prepolymer with a diamine has a longer pot life than does a mixture of the unstabilized prepolymer with that diamine. When a hindered diamine is used in producing a urethane elastomer according to the invention, e.g. MOCA or MBMA, the pot life is increased substantially so that the labor required for carrying out the mixing operation can be minimized, and the prepolymer is preferably stabilized with from 0.1 to 0.5 equivalent of the triazole per equivalent of isocyanate in the prepolymer. On the other hand, when the diamine is unhindered, urethane elastomers which, so far as is known, had not been made are the result of practicing the instant invention, and it is usually preferred that the prepolymer be stabilized with from 0.5 to 1.0 equivalent of the triazole per equivalent of isocyanate in the prepolymer. 
    
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following Examples, which are presented solely for the purpose of illustrating and disclosing the invention, set forth the best presently known mode. 
     EXAMPLE 1 
     An isocyanate-terminated prepolymer was prepared from 1 mole of a poly(oxytetramethylene)glycol having a molecular weight of 1000 and a melting temperature of 50° C. (hereinafter &#34;PTMG 1000&#34;) and 2 moles of tolylene diisocyanate (hereinafter &#34;TDL&#34;). The specific TDL used was an 80/20 blend of 2,4- and 2,6-isomers. The isocyanate (hereinafter &#34;NCO&#34;) content of the prepolymer, determined by di-n-butyl amine titration, was 6.2 percent. Benzotriazole (hereinafter &#34;BT&#34;) was then melted, vacuum degassed, and mixed with a sample of the prepolymer which had been preheated to 75° C. The BT was added in the proportion of 0.25 equivalent (mole) thereof per isocyanate equivalent of the prepolymer. The resulting mixture was stirred at 80° C. for 1 hour to insure complete reaction between the BT and the free NCO groups of the prepolymer. The stabilized prepolymer which resulted, at 80° C., was mixed with MBMA, which had been vacuum degassed at 150° C., mixing temperature 140° C., at an NCO: NH 2  ratio of substantially 1:1. The resulting composition was found to have a pot life of 20 minutes at 100° C.; it was vacuum degassed and poured into a mold preheated to 100° C. The mold, which had a central cavity 6 inches by 6 inches by 0.06 inch in depth, was then covered by a flat plate and placed in a hydraulic press where a compressive force of 10,000 pounds per square inch was applied to the mold and plate. After approximately one hour in the mold at 100° C. the partially cured elastomer was removed from the mold and transferred to an oven where it was cured for an additional 19 hours at 100° C. 
     After conditioning at room temperature and 50 percent relative humidity for one week the elastomer was found to have the following physical properties: 
     
         __________________________________________________________________________                  Test Procedure__________________________________________________________________________100% modulus, pounds per square inch,  1260300% modulus, pounds per square inch,  2500                  ASTM-D-412Tensile strength, pounds per square inch,                                  4380Elongation at break, percent           440A                                      92Shore hardness         ASTM-D-2240D                                      47Graves tear strength, pounds per inch                } ASTM-D-624      400                                  248Bashore rebound, percent                  Bashore rebound tester                                  242 percent              duPont 950 Thermogravimetric                                  250Thermal degradation, ° C.10 percent             Analyzer        305__________________________________________________________________________ 
    
     Other urethane elastomers according to the invention, and controls in which no triazole was used, have been produced by the method described above in Example 1. The starting materials used, the ratio of equivalents of triazole used to equivalents of NCO, the mixing temperatures, the curing conditions, the pot life and the physical properties of the various elastomers, determined by the tests identified above, are set forth in Table 1, below. The following abbreviations, all used in Table 1, have the indicated meanings: 
     
         ______________________________________PTMG 650:   A poly (oxytetramethylene)glycol       having a molecular weight of       650 and a melting point of 30° C.PPG 1010:   A poly(oxypropylene)glycol having       a molecular weight of 1030.H.sub.12 MDI:       4,4&#39;-dicyclohexylmethane       diisocyanatem-PDA:      m-phenylene diamine1,3-BAC:    1,3-bis(aminomethyl)cyclohexaneMXDA:       m-xylylene diamineIPDA:       isophorone diamineTT:         toyltriazole; the material used was       a blend of approximately equal parts       of 4-methylbenzotriazole and 5-       methylbenzotriazole______________________________________ 
    
     The curing was for approximately 1 hour in a mold at the temperature reported in Table 1 followed by oven curing at that temperature for the remainder of the time for each elastomer. In each case, the prepolymer was produced by reacting two moles of the indicated isocyanate with one mole of the polyol. 
     
                                           TABLE 1__________________________________________________________________________                                  Mixing Temperature, ° C.                          Triazole/NCO                                  Prepolymer                                         Diamine +Example  Polyol  Isocyanate                Triazole                     Diamine                          Equivalent                                  + Triazole                                         Prepolymer__________________________________________________________________________2      PTMG 1000          TDI   BT   MBMA 0.50    80     140Control* (1,2)  PTMG 1000          TDI   None MBMA --      --     1403      PTMG 1000          TDI   TT   MBMA 0.25    90     1404      PTMG 1000+          TDI   TT   MBMA 0.25    90     120  PTMG 650**5      PTMG 1000          TDI   TT   MOCA 0.25    80     110Control*(5)  PTMG 1000          TDI   None MOCA --      --     1106      PTMG 1000          TDI   TT   MOCA 0.25    80     1107      PTMG 1000          TDI   TT   MDA  0.5     60     90Control*(7)  PTMG 1000          TDI   None MDA  --      --     908      MTMG 1000          TDI   TT   MDA  1.0     60     909      PTMG 1000          TDI   BT   m-PDA                          0.5     40     7010     PTMG 1000          H.sub.12 MDI                BT   m-PDA                          0.27    90     8011     PPG     H.sub.12 MDI                TT   1,3 BAC                          0.5     60     2512     PPG     H.sub.12 MDI                TT   MXDA 0.5     60     2513     PPG     H.sub.12 MDI                TT   IPDA 0.5     60     2514     PPG     H.sub.12 MDI                TT   IPDA 1.0     60     25__________________________________________________________________________ *Not according to the present invention; presented for purposes of comparison with example(s) in parentheses. **Equimolecular proportions. 
    
     
                            Pot   100% 300% Tensile                                   Elongation                                          Shore  Cure Conditions              Life  Modulus,                         Modulus,                              Strength                                   at     HardnessExample  Time (hrs)        Temp (° C.)              Min/° C.                    Psi  Psi  Psi  Break, %                                          A D__________________________________________________________________________2      20    100   30/100                    1200 1900 3050 460    92                                            45Control*(1,2)  20    100    4/100                    2022      4043 231    94                                            503      20    100   22/140                    1667 2318 4263 360    92                                            464      20    110   30/120                     770 2283 4650 378    88                                            455      20    100    9/110                    1745 2740 4820 479    93                                            45Control*(5)  20    100    4/110                    1987 3465 4871 383    96                                            556       3    125   10/110                    1700 2400 4600 488    94                                            487       3    125    3/90 1126 1824 4500 520    95                                            46Control*(7)  --    --    5 sec/90**                    --   --   --   --     --                                            --8      2.5   125   15/90   650                         1000 3020 640    87                                            359      20    100    4/50  924 1389 4151 600    92                                            4310     22    110   0.5/80                     690 1380 3070 515    78                                            3611      3    100   0.5/60                     573 1650 3679 462    72                                            ND***12     18    100   0.5/60                     380 1216 3369 508    71                                            ND13     19    100   0.5/60                     636 2419 4019 390    74                                            ND14     18     90    1/60  419 1201 2957 485    74                                            ND__________________________________________________________________________ *Not according to the present invention; presented for purposes of comparison with example(s) in parentheses. **The pot life was too short for processing. ***Not determined. 
    
     
         Graves                      Rebound,   TGA, ° C.Example       Tear Strength, pi                       %          2%      10%__________________________________________________________________________2             400           29         225     296Control*(1,2) 364           ND**       250     2953             388           ND         ND      ND4             370           ND         ND      ND5             462           ND         ND      NDControl*(5)   489           ND         ND      ND6             480           ND         ND      ND7             390           ND         ND      NDControl*(7)   --            --         --      --8             410           ND         ND      ND9             392           ND         ND      ND10                          ND         ND      ND11            247           ND         240     31212            187           ND         240     32213            270           ND         235     30914            203           ND         235     305__________________________________________________________________________ *Not according to the present invention; presented for purposes of comparison with example(s) in parentheses. **Not determined. 
    
     EXAMPLES 15-17 
     Substantially the procedure described above in Example 1, except that the prepolymer:diamine blend was merely poured into a pan mold after degassing, was used to produce urethane elastomers according to the method of the invention from a prepolymer made from TDL and a polyester which was hydroxy-terminated. The specific prepolymer had an NCO content of approximately 3.5 percent by weight; it is commercially available under the trade designation &#34;Vibrathane 6025&#34;. Data concerning the elastomers are set forth in Table 11, below: 
     
                                           TABLE 11__________________________________________________________________________                      Mixing Temperature ° C.             Triazole/NCO                      Diamine +Example  Triazole        Diamine             Equivalent                      Prepolymer__________________________________________________________________________15     TT    MOCA 0.5      10016     TT    MDA  1.0      10017     TT    m-PDA             1.0      100Control*(15)  --    MOCA --       100__________________________________________________________________________ *Not according to the present invention; presented for purposes of comparison with the example in parentheses. 
    
     
                            Pot   Tensile                         Elongation                               Shore  Cure Conditions              Life  Strength                         at    HardnessExample  Time(hrs)        Temp(° C.)              Min/° C.                    Psi  Break, %                               A__________________________________________________________________________15     16    107   13    3760 550   8016     16    107   9     3210 590   7817     16    107   9     3870 600   80Control*(15)  16    100   7     3640 685   80__________________________________________________________________________ *Not according to the present invention; presented for purposes of comparison with example(s) in parentheses. 
    
     It is known e.g., in U.S. Pat. No. 3,721,645, that triazoles other than BT and TT are capable of reaction with NCO groups, and that the reaction is reversible in the sense that apparently normal cure occurs at an elevated temperature. It will be apparent that an equivalent amount of any of the other triazoles could be substituted for BT and TT in each of the foregoing Examples, and with similar results. However, BT and TT are the preferred triazoles because of availability, low volatility, anti-corrosive properties and price. 
     The curing times reported in the foregoing Examples are those which were actually used. It has been found, however, that the 18 to 20 hour curing times used in many instances are unnecessary in the sense that substantially the same physical properties result after a shorter cure. In most cases, a cure time of three to six hours has been found to be adequate. 
     Various changes and modifications can be made, as will be apparent to one skilled in the art, from the specific embodiments described above without departing from the spirit and scope of the invention as defined in the following claims: