Abstract:
Blends of a polyacrylate elastomer with a partially hydrogenated rubber, when peroxide-cured, provide a product which is excellent in resistance to degradation by heat or contact with oil, and which is particularly suitable for making belts, hoses, gaskets and the like for use in automobile engines.

Description:
This invention relates to peroxide-curable blends of acrylate elastomers and partially hydrogenated nitrile rubbers, and to the blends which have been peroxide-cured. The cured blends exhibit excellent resistance to the degrading effects of oil and heat and are particularly useful as belts, hoses, seals, gaskets and the like in automobile engines. 
     BACKGROUND OF THE INVENTION 
     Polyacrylates are elastomeric polymers or copolymers of acrylic acid esters having a saturated main chain with the ester groups constituting side chains on the main chain. Polyacrylates are resistant to ozone and to aging in air at moderately elevated temperatures up to about 200° C., and resist swelling, hardening, and other changes that take place when contacted with hot oils in an automobile engine. 
     Partially hydrogenated nitrile rubbers have excellent resistance to degradation when contacted by hot oils but are not as resistant to high temperatures as are polyacrylates. Unlike polyacrylates made by polymerizing mixtures of alkyl acrylate esters, partially hydrogenated nitrile rubbers contain carbon-carbon unsaturation and are readily peroxide-curable. Peroxide curing is advantageous in that a good cure is obtained with a minimum of scorch (premature crosslinking during cure), and the cured product, where the polymer chains are crosslinked by carbon-carbon linkages, is generally more stable than a product obtained by vulcanization with nitrogen- or sulfur-containing compounds. 
     It is, therefore, an object of the present invention to provide a blend of elastomers which can be peroxide-cured to yield a cured product which is resistant to deterioration caused by exposure to both heat and oil. 
     BRIEF SUMMARY OF THE INVENTION 
     It has now been discovered that the desirable properties of oil-resistance and high service temperature in a blend of elastomers can be realized in a peroxide-cured composition which comprises from 10 to 90 parts by weight of a particular polyacrylate elastomer and 90 to 10 parts by weight of a partially hydrogenated nitrile rubber. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one composition aspect, the present invention is a peroxide-cured blend comprising: 
     10 to 90 parts by weight of a polyacrylate elastomer comprising at least 10 mole % of the structural unit ##STR1## wherein R 1  is a C 4-8  alkyl group; up to 30 mole % and preferably 20 to 30 mole % of the structural unit ##STR2## wherein R 2  is an alkoxyalkyl group containing 2-12 carbon atoms; and the balance to a total of 100 mole % of the structural unit ##STR3## wherein R 3  is a C 1-3  alkyl group; and 
     90 to 10 parts by weight of a partially hydrogenated nitrile rubber having a degree of unsaturation of from 0.1 to 20%. 
     Particularly preferred are blends wherein the polyacrylate elastomer additionally contains 1 to 10% of structural units derived from acrylonitrile. Such polyacrylate elastomers comprise at least 10 mole % of the structural unit ##STR4## wherein R 1  is a C 4-8  alkyl group; up to 30 mole % and preferably 20 to 30 mole % of the structural unit ##STR5## wherein R 2  is an alkoxylakyl group containing 2-12 carbon atoms; 1 to 20 mole % of the structural unit ##STR6## and the balance to a total of 100 mole % of the structural unit ##STR7## wherein R 3  is a C 1-3  alkyl group. 
     The present invention also contemplates curable compositions comprising the above-described blends and containing a peroxide curing system, particularly a peroxide curing system comprising an organic peroxide and m-phenylenediamine bis-maleimide. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The polyacrylate elastomers utilized in practicing the method of the present invention are copolymers formed by copolymerizing a mixture containing two alkyl acrylates and containing at least 10 mole % of a C 4-8  acrylate, wherein the alkyl groups may be straight-chain or branched-chain alkyl groups such as isobutyl, n-pentyl, isoamyl, n-hexyl, 2-ethylhexyl and n-octyl, with n-butyl acrylate being preferred. The other alkyl acrylate monomer may be a C 1-3  acrylate, such as methyl, ethyl or propyl acrylate, where the alkyl groups may be straight-chain or branched-chain alkyl groups; and/or an alkoxyalkyl group containing 2-12 carbon atoms, such as methoxyethyl, methoxymethyl, ethoxyethyl, butoxyethyl and ethoxypropyl and with methoxyethyl being preferred. Preferably, the mixture may contain 1 to 20 mole %, of structural units derived from acrylonitrile. These polyacrylates do not contain reactive sites, such as chlorine or an epoxy group in their side chains, characteristic of sulfur and nitrogen-vulcanizable polyacrylates. 
     Polyacrylate elastomers or rubbers are prepared by emulsion, suspension, solution or bulk polymerization. Emulsion and suspension polymerization are more commonly employed, and polymerization is generally initiated by free-radical generating agents. Methods for making polyacrylates are well known to those skilled in the art and are not part of the present invention. 
     The nitrile rubbers blended with the polyacrylate elastomers are partially hydrogenated copolymers of 75-25 parts of 1,3-butadiene and 25-50 parts acrylonitrile having a degree of unsaturation of from 0.1 to 20%. Partially hydrogenated nitrile rubbers having a degree of unsaturation lower than 0.1% are not readily peroxide curable. And those having a degree of unsaturation above 20% are less resistant to heat aging and to attack by ozone. 
     The curable blends of the present invention are cured by heating at 140°-220° C. for up to 30 minutes, preferably 4-10 minutes, with a peroxide-curing system containing a dialkyl peroxide such as di-1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane as the peroxide curing agent and m-phenylenediamine bis-maleimide as the coagent or promoter. A polyacrylate elastomer and hydrogenated nitrile rubber masterbatch is prepared in the customary manner and admixed with the curing system using conventional equipment, such as blenders, mixers, extruders or the like. The curable or vulcanizable composition, may contain, in addition to the curing system, a conventional lubricant such as stearic acid, a carbon black filler and an antioxidant. As is well known to those skilled in the art, compression set is an art-recognized measure of the extent of curing and is determined by compressing an article between flat plates for a specified time at the test temperature, after which the compressing force is released and the article allowed to recover for a specified period of time. The amount of unrecovered height, calculated as a percentage, is compression set. 
     Articles made from acrylic elastomer and hydrogenated nitrile rubber blends are processed in the same general manner as articles made from other elastomers, and can be shaped by compression, transfer or injection molding, with the latter being preferred. Articles made from conventionally vulcanized or cured polyacrylate parts are usually post-cured after primary curing because of the stringent requirements for articles to be used in automotive applications. As shown by their compression set values, articles made from the peroxide-cured polyacrylates of the present invention do not require post-curing. 
    
    
     Our invention is further illustrated by means of the following non-limiting examples: 
     EXAMPLE 1 
     This example illustrates compositions comprising a variety of polyacrylate elastomers admixed with the same partially hydrogenated nitrile rubber. (Example 1A does not contain a polyacrylate rubber and is not a composition according to the present invention). 
     The curable compositions were prepared by mixing all components, except for the curing system, in a Banbury mixer. The curing system, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane and m-phenylenediamine bis-maleimide, and antioxidant when utilized, were added, and the compositions uniformly blended using the Banbury mixer. The components of the curable compositions, the times and temperatures of curing, processing properties during curing and the properties of the cured product, including the results of tests on aged products, are summarized below. 
     
         ______________________________________       1A   1B     1C     1D   1E   1F______________________________________Nitrile rubber         100.0  80.0   80.0 80.0 80.0 80.0Polyacylate I        20.0Polyacylate II              20.0Polyacylate III                  20.0Polyacylate IV                        20.0Polyacylate V                              20.0Carbon black  50.0   50.0   50.0 50.0 50.0 50.0Magnesium oxide         5.0    5.0    5.0  5.0  5.0  5.0Plasticizer   5.0    5.0    5.0  5.0  5.0  5.0Amine antioxidant         1.5    1.5    1.5  1.5  1.5  1.52-mercaptolimidazone         0.5    0.5    0.5  0.5  0.5  0.5Peroxide      8.0    8.0    8.0  8.0  8.0  8.0Bis-maleimide 2.0    2.0    2.0  2.0  2.0  2.0         172.0  172.0  172.0                            172.0                                 172.0                                      172.0______________________________________ 
    
     The nitrile rubber is a partially hydrogenated nitrile rubber containing about 36% of acrylonitrile having a degree of unsaturation of about 4%. Polyacrylate I contains about 55% by weight of structural units derived from ethyl acrylate and 45% by weight of structural units derived from n-butyl acrylate. Polyacrylates II-V contain about 6-23% by weight of structural units derived from ethyl acrylate, 47-62% by weight of structural units derived from butyl acrylate, about 26-30% by weight of structural units derived from methoxyethyl acrylate and 4-9% by weight of structural units derived from acrylonitrile. 
     The processess properties of the curable compositions were measured using a Mooney Viscometer, large rotor, at 125° C., and a rheometer oscillating disc using a microdie at 100 cpm, 3° arc at 190° C. 
     
         ______________________________________     1A    1B     1C      1D   1E    1F______________________________________MOONEYVISCOMETER:VISC. MINIMUM       58      45     47    47   47    45T5, minutes 12.2    10.7   9.7   9.6  9.5   8.9REHEOMETER,MICRODIEML,1bf*in   17.9    14.8   15.1  14.9 14.8  14.1ML,N*m      2.0     1.6    1.7   1.6  1.6   1.6MH,1bf*in   121.0   91.7   98.2  98.2 100.0 96.0MH,N*m      13.4    10.2   10.9  10.9 11.1  10.7Ts2, minutes       1.2     1.1    1.1   1.1  1.1   1.0T90, minutes       13.0    11.9   11.5  11.3 11.6  11.8CURE RATE   11.8    10.8   10.2  10.5 10.5  10.8______________________________________ 
    
     Properties of the cured composition, 20 minutes cure time at 170° C. with no post-cure, are as follows: 
     
         __________________________________________________________________________                1A  1B  1C  1D  1E  1F__________________________________________________________________________STRESS 100%, psi     1175                    945 1010                            1060                                1065                                    1045STRESS 100%, MPa     8.1 6.5 7.0 7.3 7.3 7.2TENSILE, psl         3990                    3150                        3240                            3435                                3490                                    3200TENSILE, MPa         27.5                    21.7                        22.4                            23.7                                24.1                                    22.1ELONGATION, %        255 240 235 250 260 230HARDNESS, A pts      75  72  73  71  70  74COMPRESSION SET,METHOD B, BUTTONS70 hrs @ 150° C.                19  23  25  24  27  23168 hrs @ 150° C.                21  30  34  34  37  34GEHMAN LOW TEMPERATURETORISON TEST, ASTM D1053ORIGINAL ANGLE TWISTT2, °C.       -20 -16 -16 -16 -15 -15T5, °C.       -30 -32 -33 -32 -32 -32LOW TEMPERATURE BRITTLENESS,ASTM D 2137Tp, °C.       -33 -27 -30 -30 -26 -36__________________________________________________________________________ 
    
     Stability of the peroxide cured acrylates to oxidation was measured using accelerated aging tests in which dumbbells cut from the material to be tested were exposed to circulating hot air in an oven. Their stability, when exposed to hot oil, a particularly important property from articles intended for automotive applications, was also measured. The results of aging the cured composition are summarized below: 
     
         __________________________________________________________________________HEATING IN AIR OVEN          1A  1B  1C  1D  1E  1F__________________________________________________________________________70 hours at 150° C.TENSILE, psi   4195              3195                  3615                      3465                          3265                              3365TENSILE, MPa   28.9              22.0                  24.9                      23.9                          22.5                              23.2TENSILE CHANGE, %          5   1   12  1   -6  5ELONGATION, %  220 215 230 220 200 205ELONG, CHANGE, %          -14 -10 -2  -12 -23 -11HARDNESS A, pt&#39;s          81  79  79  80  79  80HARD CHANGE, pt&#39;s          6   7   6   9   9   6168 hours at 150° C.TENSILE, psi   3905              2895                  3155                      3135                          3290                              2825TENSILE, MPa   26.9              20.0                  21.8                      21.6                          22.7                              19.5TENSILE CHANGE, %          -2  -8  -3  .9  -6  -12ELONGATION, %  205 195 185 200 195 165ELONG, CHANGE %          -20 -19 -21 -20 -25 -28HARDNESS A, pt&#39;s          79  77  81  82  81  80HARD CHANGE, pt&#39;s          4   5   8   11  11  6504 hours at 150° C.TENSILE, psi   3420              2705                  3005                      2980                          3080                              2875TENSILE, MPa   22.4              18.7                  20.7                      20.6                          21.3                              19.8TENSILE CHANGE, %          -19 -14 -7  -13 -12 -10ELONGATION, %  120 120 120 120 130 110ELONG, CHANGE %          -53 -50 -49 -52 -50 -52HARDNESS A, pt&#39;s          84  80  84  87  87  85HARD CHANGE, pt&#39;s          9   8   11  16  17  111008 hours at 150° C.TENSILE, psi   3420              2560                  2775                      2920                          2720                              2540TENSILE, MFs   23.6              17.7                  19.1                      20.1                          18.8                              17.5TENSILE CHANGE, %          -14 -19 -14 -15 -22 -21ELONGATION, %  75  55  55  65  60  50ELONG CHANGE, %          -71 -77 -77 -74 -77 -78HARDNESS A, pt&#39;s          91  90  87  92  92  87HARD CHANGE, pt&#39;s          16  18  14  21  22  13ASTM 903 OIL70 hours at 150° C.TENSILE, psi   3540              2750                  3130                      3095                          3415                              2875TENSILE, MPa   25.1              19.0                  21.6                      21.4                          23.6                              19.8TENSILE CHANGE, %          -9  -13 -3  -10 -2  -10ELONGATION, %  220 200 215 220 230 205ELONG, CHANGE, %          -14 -17 -9  -12 -12 -11HARDNESS A, pt&#39;s          69  64  67  67  67  64HARD CHANGE, pt&#39;s          -6  -8  -6  -4  -3  -10VOLUME CHANGE, %          14  15  14  12  12  15168 hours at 150° C.TENSILE, psi   3640              2040                  3165                      2775                          3265                              2840TENSILE, MPa   25.1              14.1                  21.8                      19.1                          22.5                              19.6TENSILE CHANGE, %          -9  -35 -2  -19 -6  -11ELONGATION, %  250 160 215 195 215 205ELONG CHANGE, %          -2  -33 -9  -22 -17 -11HARDNESS A, pt&#39;s          63  62  67  65  66  64HARD CHANGE, pt&#39;s          -12 -10 -6  -6  -4  -10VOLUME CHANGE, %__________________________________________________________________________ 
    
     EXAMPLE 2 
     This example illustrates compositions comprising a variety of partially hydrogenated nitrile rubbers admixed with the same polyacrylate elastomer. The experimental and test procedures utilized were the same as those of Example 1. The polyacrylate contains about 55% by weight of structural units derived from ethyl acrylate and about 45% by weight of structural units derived from n-butyl acrylate. The nitrile rubbers are partially hydrogenated nitrile rubbers containing from about 17 to 50% by weight of acrylonitrile and having a degree of unsaturation in the range of about 91-99%. Those partially hydrogenated rubbers containing about 17-25% of acrylonitrile also contain units derived from a third monomer, such as an alkyl ester or a dialkyl ester of an unsaturated carboxylic acid. The components of the curable compositions, the times and temperatures of curing, processing properties during curing, and the properties of the cured product, including the results of tests on aged products, are summarized below: 
     
         __________________________________________________________________________          2A  2B  2C  2D  2E  2F  2G  2H  2I  2J  2K  2L__________________________________________________________________________Polyacralyte   80.0              80.0                  80.0                      80.0                          80.0                              80.0                                  80.0                                      80.0                                          80.0                                              80.0                                                  80.0                                                      80.0Nitrile Rubber I          20.0Nitrile Rubber II  20.0Nitrile Rubber III     20.0Nitrile Rubber IV          20.0Nitrile Rubber V               20.0Nitrile Rubber VI                  20.0Nitrile Rubber VII                     20.0Nitrile Rubber VIII                        20.0Nitrile Rubber IX                              20.0Nitrile Rubber X                                   20.0Nitrile Rubber XI                                      20.0Nitrile Rubber XII                                         20.0Carbon black   60.0              60.0                  60.0                      60.0                          60.0                              60.0                                  60.0                                      60.0                                          60.0                                              60.0                                                  60.0                                                      60.0Stearic Acid   3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Amine antioxidant          2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0Peroxide       3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Bis-maleimide  2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL          170.0              170.0                  170.0                      170.0                          170.0                              170.0                                  170.0                                      170.0                                          170.0                                              170.0                                                  170.00                                                      170.0PROCESSINGPROPERTIESMOONEY VISCOMETER:Large Rotor, 125° C.VISC. MINIMUM  46  45  45  45  45  44  44  44  42  42  42  42T5, minutes    30  30  30  30  30  30  30  30  30  30  30  30RHEOMETER, MICRODIE,100 cpm, 3° ARCML,lbf*in      11.7              11.3                  11.7                      11.7                          11.3                              11.0                                  11.3                                      11.3                                          10.9                                              11.1                                                  10.9                                                      10.9ML,N*m         1.3 1.3 1.3 1.3 1.3 1.2 1.3 1.3 1.2 1.2 1.2 1.2MH,lbf*in      30.3              33.7                  31.0                      34.8                          28.6                              30.6                                  32.4                                      38.6                                          30.1                                              31.3                                                  30.5                                                      31.1MH,N*m         3.4 3.7 3.4 3.9 3.2 3.4 3.6 4.3 3.3 3.5 3.4 3.5Ts2, minutes   1.2 1.2 1.2 1.1 1.3 1.1 1.1 1.1 1.3 1.3 1.4 1.3T.sup.1 90, minutes          2.6 2.9 2.7 2.8 2.7 2.6 2.8 3.3 2.6 2.7 2.7 2.7VULCANIZEDPROPERTIES4 minutes at 190° C.STRESS 100%, psi          835 920 1045                      925 770 810 520 865 765 735 595 645STRESS 100%, MPa          5.8 6.3 7.2 6.4 5.3 5.6 3.6 6.0 5.3 5.1 4.1 4.5TENSILE, psi   1430              1250                  1375                      1355                          1440                              1360                                  1125                                      1335                                          1375                                              1285                                                  1220                                                      1235TENSILE, MPa   9.9 8.6 9.5 9.3 9.9 9.4 7.8 9.2 9.5 8.9 8.4 8.5ELONGATION, %  190 155 145 60  200 190 210 170 200 185 205 200HARDNESS, A pts          72  77  75  72  70  72  70  73  66  70  67  68COMPRESSION SET,METHOD B, BUTTONS,cure time 6 minutes at 190° C.70 h @ 150° C.          45  49  54  48  41  46  45  46  39  39  41  41168 h @ 150° C.          55  57  56  51  50  52  54  55  41  48  43  41GEHMAN LOW TEMPER-ATURE TORSION TESTT2, °C. 4   11  8   6   5   6   10  9   9   0   4   9T5, °C. -12 -3  -7  -8  -11 -9  -9  -9  -9  -16 -13 -8T10, °C.          -20 -10 -15 -15 -20 -19 -17 -18 -17 -22 -21 -18T100, °C.          -32 -29 -31 -32 -32 -31 -30 -31 -32 -35 -34 -34FREEZE PT, °C.          -30 -20 -27 -28 -34 -33 -33 -33 -34 -35 -37 -37AGING: ENVIRON-MENAIR OVEN70 hours at 150° C.Tensile, psi   1135              1410                  1415                      1300                          1480                              1320                                  1065                                      1335                                          1095                                              1110                                                  985 830Tensile, MPa   9.2 9.7 9.8 9.0 10.2                              9.1 7.3 9.2 7.6 7.7 6.8 5.7Tensile change, %          -7  13  3   -4  3   -3  -5  0   -20 -14 -19 -33Elongation, %  160 95  120 115 175 155 165 95  205 185 235 260Elong. Change, %          -16 -39 -17 -28 -13 -18 -21 -44 3   0   15  30Hardness A, pt&#39;s          81  87  84  88  80  83  83  83  78  79  75  77Hard change, pt&#39;s          9   10  9   16  10  11  13  10  12  9   8   9180° Bend          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      Pass                                          Pass                                              Pass                                                  Pass                                                      PassAGING: ENVIRON-MENAIR OVEN168 hours at 150° C.TENSILE, psi   1355              1315                  1580                      1425                          1315                              1340                                  1340                                      1495                                          1005                                              1015                                                  885 745TENSILE, MPa   9.3 9.1 10.9                      9.8 9.1 9.2 9.2 10.3                                          6.9 7.0 6.1 5.1TENSILE CHANGE, %          -5  5   15  5   -9  -1  19  12  -27 -21 -27 -40ELONGATION, %  145 76  110 80  165 115 95  60  205 170 250 255ELONG. CHANGE, %          -24 -51 -24 -50 -18 -39 -55 -65 3   -8  22  28HARDNESS A, pt&#39;s          82  90  87  91  82  86  86  90  81  83  81  80HARD CHANGE, pt&#39;s          10  13  12  19  12  14  16  17  15  13  14  12180° BEND          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      FAIL                                          Pass                                              Pass                                                  Pass                                                      PassAGING: ENVIRON-MENAIR OVEN1008 hours at 150° C.TENSILE, psi   1430              2330                  1840                      2230                          1460                              1900                                  2030                                      2485                                          1370                                              1665                                                  1195                                                      1350TENSILE, MPa   9.9 16.1                  12.7                      15.4                          10.1                              13.1                                  14.0                                      17.1                                          9.5 11.5                                                  8.2 9.3TENSILE CHANGE, %          0   86  34  65  1   40  80  86  0   30  -2  9ELONGATION, %  35  8   15  8   45  20  10  10  40  20  47  30ELONG. CHANGE  -82 -95 -90 -95 -78 -89 -95 -94 -80 -89 -77 -85HARDNESS A, pt&#39;s          95  92  88  94  93  86  96  96  93  90  93  94HARD CHANGE, pt&#39;s          20  15  13  22  23  14  26  23  27  20  26  26180° BEND          Fail              Fail                  Fail                      Fail                          Pass                              Fail                                  Fail                                      Fail                                          Fail                                              Fail                                                  Pass                                                      FailAGING: ASTM 903 OIL70 hours at 150° C.TENSILE, psi   980 945 1070                      975 1005                              910 950 1020                                          975 890 750 715TENSILE, MPa   6.8 6.5 7.4 6.7 6.9 6.3 6.6 7.0 6.7 6.1 5.2 4.9TENSILE CHANGE, %          -31 -24 -22 -28 -30 -33 -16 -24 -29 -31 -39 -42ELONGATION, %  180 120 135 125 185 165 165 125 185 155 170 165ELONG. CHANGE, %          -5  -23 -7  -22 -8  -13 -21 -26 -8  -16 -17 -18HARDNESS A, pt&#39;s          40  54  49  54  40  45  46  51  39  40  34  34HARD CHANGE, pt&#39;s          -32 -23 -26 -18 -30 -27 -24 -22 -27 -30 -33 -34VOLUME CHANGE, %          32  27  27  27  30  30  31  29  33  34  43  43180° BEND          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      Pass                                          Pass                                              Pass                                                  Pass                                                      PassAGING: ASTM 903 OIL168 hours at 150° C.TENSILE, psi   875 855 875 890 955 890 875 905 740 880 685 670TENSILE, MPa   6.0 5.9 6.0 6.1 6.6 6.1 6.0 6.2 5.1 6.1 4.7 4.6TENSILE CHANGE, %          -39 -32 -36 -34 -34 -35 -22 -32 -46 -32 -44 -46ELONGATION, %  170 115 115 125 190 150 150 115 180 165 175 165ELONG. CHANGE, %          -11 -26 -21 -22 -5  -21 -29 -32 -10 -11 -15 -18HARDNESS A, pt&#39;s          43  5   51  53  41  46  47  51  39  40  34  35HARDNESS CHANGE, pt&#39;s          -29 -22 -24 -19 -29 -26 -23 -22 -27 -30 -33 -33VOLUME CHANGE, %          32  27  27  27  30  30  31  29  33  34  43  43180° BEND          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      Pass                                          Pass                                              Pass                                                  Pass                                                      PassAGING: 10W40 OIL70 hours at 150° C.TENSILE, psi   1135              1225                  1440                      1345                          1285                              1140                                  1215                                      1005                                          1270                                              1210                                                  1145                                                      1150TENSILE, MPa   7.8 8.5 9.9 9.3 8.9 7.9 8.4 6.9 8.8 8.3 7.9 7.9TENSILE CHANGE, %          -21 -2  5   -1  -11 -16 8   -25 -8  -6  -6  -7ELONGATION, %  85  155 110 80  170 125 100 140 150 115 175 155ELONG. CHANGE, %          -55 0   -24 -50 -15 -34 -52 394 -25 -38 -15 -23HARDNESS A, pt&#39;s          69  69  74  77  65  70  71  75  65  67  61  63HARD CHANGE, pt&#39;s          -3  -8  -1  5   -5  -2  1   3   -1  -3  -6  -5VOLUME CHANGE, %          7   5   5   6   7   6   6   6   8   8   11  11180° BEND          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      Pass                                          Pass                                              Pass                                                  Pass                                                      PassAGING: 10W40 OIL168 hours at 150° C.TENSILE, psi   1230              1135                  1335                      1200                          1265                              1315                                  1325                                      1000                                          1165                                              1150                                                  1125                                                      1040TENSILE, MPa   7.8 8.5 9.9 9.3 8.9 7.9 8.4 6.9 8.8 8.3 7.9 7.9TENSILE CHANGE, %          -21 -2  5   -1  -11 -16 8   -25 -8  -6  -6  -7ELONGATION, %  150 70  90  65  155 105 95  55  130 115 165 135ELONG. CHANGE, %          -55 0   -24 -50 -15 -34 -52 394 -25 -38 -15 -23HARDNESS A, pt&#39;s          70  81  75  78  70  73  74  78  67  67  61  63HARD CHANGE, pt&#39;s          -3  -8  -1  6   -5  -2  1   2   -1  -3  -6  -5VOLUME CHANGE, %          6   5   5   6   6   6   6   6   8   7   11  10180° BEND          Pass              Pass                  Pass                      Pass                          Pass                              Pass                                  Pass                                      Pass                                          Pass                                              Pass                                                  Pass                                                      Pass__________________________________________________________________________ 
    
     EXAMPLE 3 
     This example illustrates the effect of varying the relative proportions of the polyacrylate elastomer and the partially hydrogenated nitrile rubber in the mixture being peroxide-cured. Examples 3A and 3B are for comparative purposes and do not represent compositions within the scope of the present invention. The experimental and testing procedures utilized were the same as those of Example 1. The components of the curable compositions, the times and temperatures of curing, processing properties during curing and the properties of the cured product, including the results of aging tests, are summarized below: 
     
         __________________________________________________________________________                 3A 3B  3C  3D  3E  3F  3G  3H  3I__________________________________________________________________________Polyacrylate          100.0                    95.0                        90.0                            85.0                                80.0                                    70.0                                        70.0                                            60.0                                                60.0Nitrile rubber           5.0 10.0                            15.0                                20.0                                    30.0                                        30.0                                            40.0                                                40.0Carbon                60.0                    60.0                        60.0                            60.0                                60.0                                    60.0                                        60.0                                            60.0                                                60.0Stearic Acid          3.0                    3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0Amine antioxidant     2.0                    2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0Peroxide              2.0                    2.0 2.0 2.0 2.0 2.0 3.0 2.0 3.0Bis-maleimide         2.0                    2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL                 169.0                    169.0                        169.0                            169.0                                169.0                                    169.0                                        170.0                                            169.0                                                170.0PROCESSING PROPERTIESMOONEY VISCOMETER:VISC. MINIMUM         36 42  44  45  46  49  49  51  51T5, minutes           30 30  30  30  30  30  30  30  30RHEOMETER, MICRODIE,100 cpm, 3° ARC at 190° C.ML,lbf*in             8.2                    10.7                        11.5                            11.5                                11.5                                    11.9                                        11.7                                            11.9                                                12.0ML,N + m              0.9                    1.2 1.3 1.3 1.3 1.3 1.3 1.3 1.3MH,lbf*in             20.0                    24.0                        25.0                            25.0                                25.0                                    29.0                                        29.0                                            30.0                                                31.0MH,N*m                2.2                    2.7 2.8 2.8 2.8 3.2 3.2 3.3 3.4Ts2, minutes          1.6                    1.5 1.5 1.5 1.5 1.6 1.5 1.5 1.5T.sup.1 90, minutes   5.1                    3.7 3.3 3.6 3.5 4.4 4.3 4.5 4.3VULCANIZED PROPERTIESCURE TIME 4 minutes at 190° C.STRESS 100%, psi      250                    420 545 625 610 680 675 725 675STRESS 100%, MPa      1.7                    2.9 3.8 4.3 4.2 4.7 4.7 5.0 4.7TENSILE, psi          980                    1015                        1170                            1270                                1365                                    1640                                        1660                                            1910                                                1920TENSILE, MPa          6.8                    7.0 8.1 8.8 9.4 11.3                                        11.5                                            13.2                                                13.2ELONGATION, %         325                    270 265 240 255 240 250 280 280HARDNESS, A pts       54 67  69  68  70  71  73  76  75COMPRESSION SET, METHOD B,CURE TIME 6 minutes at 190° C.BUTTONS 70 hrs @ 150° C.                 39 34  37  40  40  46  49  53  55AGING: ENVIRONMENT AIR OVEN70 hours at 175° C.TENSILE, psi          770                    835 935 1105                                1320                                    1460                                        1525                                            1810                                                1775TENSILE, MPa          6.1                    5.8 6.5 7.6 9.1 10.1                                        10.5                                            12.5                                                12.2TENSILE CHANGE, %     -21                    -18 -20 -13 -3  -11 -8  -5  -8ELONGATION, %         285                    235 175 150 140 130 140 145 135ELONG. CHANGE, %      -12                    -13 -34 -38 -45 -46 -44 -48 -52HARDNESS A, pt&#39;s      72 84  86  86  88  88  89  88  89HARD CHANGE, pt&#39;s     -81                    -17 -17 -18 -18 -17 -16 -12 -14180° BEND      Pass                    Pass                        Pass                            Pass                                Pass                                    Pass                                        Pass                                            Pass                                                PassAGING: ASTM 902 Oil70 hours at 150° C.TENSILE, psi          975                    1005                        1125                            1250                                1370                                    1635                                        1625                                            1955                                                1920TENSILE, MPa          6.7                    6.9 7.8 8.6 9.5 11.3                                        11.2                                            13.5                                                13.2TENSILE CHANGE, %     -1 -1  -4  -2  0   0   -2  2   0ELONGATION, %         355                    315 255 255 245 250 230 255 265ELONG. CHANGE, %      9  17  -4  6   -4  4   -8  -9  -5HARDNESS A, pt&#39;s      46 53  59  60  62  65  64  68  68HARD CHANGE, pt&#39;s     -8 -14 -10 -8  -8  -6  -9  -8  -7VOLUME CHANGE, %      12 10  10  10  9   10  9.5 9   9180° BEND      Pass                    Pass                        Pass                            Pass                                Pass                                    Pass                                        Pass                                            Pass                                                PassAGING: ENVIRONMENT ASTM 903 OIL70 hours at 150° C.TENSILE, psi          700                    730 820 875 100 1235                                        1225                                            1565                                                1345TENSILE, MPa          4.8                    5.0 5.7 6.0 6.9 8.5 8.5 10.8                                                9.3TENSILE CHANGE, %     -29                    -28 -30 -31 -27 -25 -26 -18 -30ELONGATION, %         265                    230 230 225 215 215 235 250 225ELONG. CHANGE, %      -18                    -15 -13 -6  -16 -10 -6  -11 -20HARDNESS A, pt&#39;s      26 33  36  38  40  44  45  49  49HARD CHANGE, pt&#39;s     -28                    -34 -33 -30 -30 -27 -28 -27 -26VOLUME CHANGE, %      43 39  38  36  34  32  32  28  29180° BEND      Pass                    Pass                        Pass                            Pass                                Pass                                    Pass                                        Pass                                            Pass                                                Pass__________________________________________________________________________ 
    
     EXAMPLE 4 
     This example, like the previous example, illustrates the effect, in a somewhat different formulation, of varying the proportions of the polyacrylate elastomer and the partially hydrogenated nitrile rubber in the mixture being peroxide-cured. Examples 4A and 4B are for comparative purposes and do not represent compositions within the scope of the present invention. The experimental and test procedures utlized were the same as those of Example 1. The components of the curable composition, the times and temperatures of curing, processing conditions during curing and the properties of the cured product, including the results of testing of the aged products, are summarized below: 
     
         __________________________________________________________________________                   4A  4B  4C  4D  4E  4F  4G__________________________________________________________________________Nitrile Rubber          100.0                       100.0                           90.0                               80.0                                   80.0                                       70.0                                           70.0Polyacylate                 5.0 10.0                               20.0                                   20.0                                       30.0                                           30.0Carbon black            50.0                       50.0                           50.0                               50.0                                   50.0                                       50.0                                           50.0Magnesium Oxide         5.0 5.0 5.0 5.0 5.0 5.0 5.0Stearic acid            0.5 0.5 0.5 0.5 0.5 0.5 0.5Plasticizer             5.0Amine antioxidant       1.5 1.5 1.5 1.5 1.5 1.5 1.5Vanox MTI               0.5 0.5 0.5 0.5 0.5 0.5 0.5Peroxide                8.0 8.0 8.0 8.0 8.0 8.0 8.0Bis-Maleimide           2.0 2.0 2.0 2.0 2.0 2.0 2.0TOTAL:                  172.5                       172.5                           167.5                               167.5                                   167.5                                       167.5                                           167.5PROCESSING PROPERTIESMOONEY VISCOMETER:Large Rotor, 125° C.VISC. MINIMUM           48  54  52  48  48  42  42T5, minutes             21  18.5                           19.8                               18.4                                   19  18.4                                           17.6RHEOMETER, MICRODIE,100 cpm, 3° ARC at 170° C.ML,lbf*IN               14.8                       17.5                           16.5                               14.4                                   15.1                                       13.4                                           14.5ML,N*m                  1.6 1.9 1.8 1.6 1.7 1.5 1.6MH,lbf*in               115.0                       118.0                           115.0                               102.0                                   102.0                                       91.0                                           87.5MH,N*m                  12.8                       13.1                           12.8                               11.3                                   11.3                                       10.1                                           9.7Ts2, minutes            1.3 1.3 1.3 1.2 1.2 1.2 1.2T.sup.1 90, minutes     12.5                       13.0                           13.1                               13.5                                   13.5                                       13.0                                           12.5VULCANIZED PROPERTIESCURE TIME 20 minutes at 170° C.STRESS 100%, psi        1060                       1075                           1235                               1175                                   1145                                       1120                                           1105STRESS 100%, MPa        7.3 7.4 8.5 8.1 7.9 7.7 7.6TENSILE, psi            3940                       3780                           3670                               3265                                   2465                                       3085                                           2870TENSILE, MPa            27.2                       26.1                           25.3                               22.5                                   17.0                                       21.3                                           19.8ELONGATION, %           265 260 235 225 170 225 220HARDNESS, A pts         73  75  77  75  75  73  73COMPRESSION SET, METHOD B,BUTTONS 70 hrs @ 150° C. %                   21  22  23  26  24  27  26GEHMAN LOW TEMPERATURE TORSIONT2, °C.          -18 -17 -17 -15 -15 -13 -18T5, °C.          -23 -22 -22 -21 -22 -22 -23T10, °C.         -26 -24 -24 -23 -24 -24 -25T100, °C.        -32 -30 -30 -30 -30 -30 -35FREEZE PT, °C.   -31 -29 -30 -27 -29 -30 -30AGING: ENVIRONMENTAIR OVEN 70 hours at 150° C.TENSILE, psi            4135                       4055                           3565                               3375                                   3280                                       2805                                           2860TENSILE, MPa            28.5                       28.0                           24.6                               23.3                                   22.6                                       19.4                                           19.7TENSILE CHANGE, %       5   7   -3  3   33  -9  0ELONGATION, %           240 230 200 205 190 175 185ELONG. CHANGE, %        -9  -12 -15 -9  12  -22 -16HARDNESS A, pt&#39;s        80  80  81  81  81  78  79HARD CHANGE, pt&#39;s       7   5   4   6   6   5   6180° BEND        Pass                       Pass                           Pass                               Pass                                   Pass                                       Pass                                           PassAGING: ENVIRONMENTASTM 903 OIL 70 hours at 150° C.TENSILE, psi            3085                       3475                           3225                               2985                                   2405                                       2345                                           2320TENSILE, MPa            21.3                       24.0                           22.3                               20.6                                   16.6                                       16.2                                           16.0TENSILE CHANGE, %       -22 -8  -12 -9  -2  -24 -19ELONGATION, %           215 235 225 215 235 185 180ELONG. CHANGE, %        -19 -10 -4  -4  38  -18 -18HARDNESS A, pt&#39;s        65  66  68  65  68  61  62HARD CHANGE, pt&#39;s       -8  -9  -9  -10 -7  -12 -11VOLUME CHANGE, %        13  17  17  19  19  20  20180° BEND        Pass                       Pass                           Pass                               Pass                                   Pass                                       Pass                                           Pass__________________________________________________________________________ 
    
     Our invention has been described in terms of specific embodiments and non-limiting examples. Various modifications in the compositions of the present invention will be apparent to those skilled in the art and are included within the scope of the invention.