Abstract:
The specification relates to a stabilized composition of epihalohydrin homopolymers or copolymers of epihalohydrin with an alkylene oxide and a nickel salt of a branched-chain dialkyldithiocarbamate. The specification also relates to a process for stabilizing epihalohydrin homopolymers and copolymers against adverse effects of aging by compounding the polymers with a nickel salt of a branched-chain dialkyldithiocarbamate.

Description:
BACKGROUND OF THE INVENTION 
     Epihalohydrin polymers are known to be susceptible to degradation reactions during aging and normal use of the vulcanizate. The principal degradation reaction is oxidation which may destroy the structural integrity of the polymer, as evidenced by the loss of molecular weight and the deterioration of physical properties to the point of mechanical failure. Such degradation may occur both before and after processing, for example, upon exposure to heat and light. 
     Degradation may also occur during the use of the finished article. For example, epihalohydrin polymers are employed extensively in the manufacture of hoses, gaskets, O-rings, and oil seals; all of these during use come in contact with various organic solvents, particularly, petroleum hydrocarbons. Such solvents, in combination with heat and weathering, cause articles composed of epihalohydrin polymers to deteriorate as evidenced by softening and deformation of the articles. 
     In the past, a number of various nitrogen-containing compounds have been used to slow down oxidative degradation of epihalohydrin polymers. For example, U.S. Pat. No, 3,239,486 discloses various metal salts of dialkyldithiocarbamates as antioxidants for use with epihalohydrin polymers. Metal salts of dialkyldithiocarbamates have also been used as antioxidative stabilizers in other polymeric materials, e.g., in polyethers (French Pat. No. 1,439,852), in cellular rubber (Chemical Abstracts, Vol. 28 (1951), Abstract 10646(b)) and in butadiene hydrocarbon elastomers (British Pat. No. 660,477). The nickel salt of di-n-butyldithiocarbamate has been utilized as an antioxidant for various epichlorohydrin vulcanization compositions (Encyclopedia of Polymer Science and Technology, Vol. 76, pp. 198-201; Chemical Abstracts, Vol. 76 (1972), Abstract 47154n; and Chemical Abstracts, Vol. 78, (1973), Abstract (137686h). 
     The prior art antioxidants, however, have imparted only limited overall aging resistance to epihalohydrin polymers with regard to degradation by oxygen, ozone, heat and ultraviolet light. Moreover, the prior art antioxidants often had to be supplemented with other stabilizers. 
     SUMMARY OF THE INVENTION 
     It has now been discovered that improved aging resistance can be imparted to epihalohydrin homopolymers and copolymers by compounding the polymer with at least one nickel (II) salt of a branched-chain dialkyldithiocarbamate having 3 to 5 carbon atoms. The nickel salts improve aging resistance not only when the polymer is under atmospheric conditions, but also when the polymer is in contact with organic solvents. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As defined herein, a branched-chain dialkyldithiocarbamate is one in which the alkyl groups contain 3 to 5 carbon atoms selected from isopropyl, isobutyl, secondary butyl, secondary pentyl, isopentyl, tertiary pentyl and neopentyl. The preferred compounds are nickel (II) diisobutyldithiocarbamate and nickel (II) di-sec-butyldithiocarbamate. 
     The amount of the nickel salt of the branched-chain dialkyldithiocarbamate required to impart aging resistance can vary over a wide range, i.e., about 0.2 to 5 parts per 100 parts of epihalohydrin polymer. Preferably, the range should be between about 0.5 and 2 parts per 100 parts of epihalohydrin resin. 
     The nickel salts of the branched-chain dialkyldithiocarbamates used as an antioxidant in the present invention can be prepared by any appropriate method. In one method, molar equivalents of the corresponding dialkylamine, sodium hydroxide and carbon disulfide are reacted to form a sodium dialkyldithiocarbamate. The sodium dialkyldithiocarbamate is then converted to the nickel salt by treatment with nickelous sulfate hexahydrate. 
     The epihalohydrin polymers that can be stabilized by treatment with the nickel salts of the invention are also known (U.S. Pat. No. 3,158,150 which is incorporated herein by reference). These polymers include both homopolymers and copolymers of epihalohydrins. The homopolymers consist of repeating units of the following structure: ##STR1## wherein X is a fluoro, chloro, bromo or iodo group, and n is a positive integer. 
     The nickel salts of the branched-chain dialkyldithiocarbamates may also be used with copolymers of epihalohydrin and one or more epoxides, e.g., alkylene oxides. Such copolymers are linked through the epoxide linkage although other polymerizable groups may be present. A typical epihalohydrin-alkylene oxide copolymer may be represented by the following structural formula: ##STR2## wherein X is a fluoro, chloro, bromo or iodo group, and n is a positive integer. 
     Other suitable copolymers for the present invention include, among other, epihalohydrin copolymerized with epoxide ethers, namely glycidyl ethers, trimethylene oxide (oxetane), alkyl substituted oxetane, alkoxy-substituted oxetane, and haloalkoxyalkyl-substituted oxetane. 
     The epihalohydrin polymers can be prepared by known methods, e.g., by the methods disclosed in U.S. Pat. No. 3,158,581 which is incorporated herein by reference. Typically, homopolymerization of an epihalohydrin is conducted in an inert solvent at moderate temperatures (usually below 100° C) in the presence of an organo aluminum catalyst. The catalyst may be modified by chelating agents, and other additives. By similar procedures, epihalohydrins may be copolymerized with alkylene oxides and the like. 
     Certain optional ingredients may also be included in the epihalohydrin polymers. For instance, the epihalohydrin polymers may be cross-linked with such conventional cross-linking agents as diamines, imidazolines, ureas, thioureas, and ammonium salts. Some specific cross-linking agents, among others, are 2-mercaptobenzimidazole, 2-mercaptoimidazoline, hexamethylenetetramine, triethylenetetramine, hexamethylenediamine carbamate, mercaptobenzothiazyl disulfide, trimethylthiourea, and piperazine hexahydrate. Accelerators and activators, such as dibasic lead phosphite, red lead, basic lead carbonate, diethylene glycol and triethanolamine, may be incorporated into the polymers. The epihalohydrin polymers may also contain pigments, fillers, and reinforcing agents, e.g., carbon black, alumina, hydrated silica, calcium carbonate, titanium dioxide and other suitable standard color pigments. The composition of the invention further may contain, optionally, other compounding ingredients, such as processing aids, lubricants and plasticizers. 
     The epihalohydrin polymers may be compounded with the nickel salts of the branched-chain dialkyldithiocarbamates and the optional ingredients by methods well-known in the art. For example, the epihalohydrin polymers and the nickel salts of the branched-chain dialkyldithiocarbamates may be mixed on a Banbury, and thereafter the vulcanizate may be sheeted off on a mill. 
     The conditions for curing the epihalohydrin polymers vary somewhat with the ingredients employed. Generally, however, curing is conducted at about 135° to 205° C for about 5 to 120 minutes. 
    
    
     The following example is intended to illustrate but not to limit the invention. Unless otherwise stated, all parts and percentages in the specification and claims are by weight. 
     EXAMPLE I 
     Vulcanizates A to F were prepared by compounding an epichlorohydrin polymer with certain dithiocarbamates and other compounding ingredients as indicated in Table 1 below. Vulcanizates A, B &amp; C contained a dithiocarbamate in accordance with the invention, while vulcanizates D, E and F contained other dithiocarbamates. Vulcanizate G served as a control. 
     
                       TABLE 1______________________________________ Component            Parts by Weight______________________________________Epichlorohydrin .sup.(a)                 100Zinc Stearate         1Red Lead              5Processing Lubricant .sup.(b)                 2Carbon Black .sup.(c) 50Ethylene Thiourea     1.5Dithiocarbamate       1______________________________________ .sup.(a) Herchlor C manufactured by Hercules, Inc. .sup.(b) VANFRE AP manufactured by R.T. Vanderbilt Company, Inc. .sup.(c) FEF Black (n-550) 
    
     These vulcanizates were press cured at 171° C for 20-45 minutes. The physical properties of the vulcanizates were then evaluated on the basis of stress, tensile strength, percent elongation and hardness, all of which were determined according to the ASTM D-412 Test Method. 
     The vulcanizates were aged subsequently in test tubes (Al blocks) for 4 and 7 days at 150° C and the aforementioned physical properties were reevaluated. The results are compiled in Table 2 here below. 
     
                                           TABLE 2__________________________________________________________________________          Vul-          can-          iza-              Stress at 200%                         Tensile Strength                                    ElongationVul-       Parts          tion              (psi)      (psi)      (%)        Hardnesscan-   Dithio- by  Time              Un-                 Aged                     Aged                         Un-                            Aged                                Aged                                    Un-                                       Aged                                           Aged                                               Un-                                                  Aged                                                      Agedizate   carbamate      Weight          (min)              Aged                 4days                     7days                         Aged                            4days                                7days                                    Aged                                       4days                                           7days                                               Aged                                                  4days                                                      7days__________________________________________________________________________A  Nickel (II)      1   20  1270                 1550                     1240                         1640                            1800                                1420                                    440                                       240 220 70 72  69   diiso-   butyldithio-          30  1290                 1550                     1100                         1660                            1790                                1290                                    400                                       240 220 71 72  67   carbamate   45  1410                 1570                     1000                         1730                            1820                                1220                                    350                                       230 220 72 72  66B  Nickel (II) 20  1230                 1590                     1300                         1660                            1870                                1500                                    400                                       240 230 70 72  68   di-sec-   butyldithio-      1   30  1270                 1580                     1380                         1690                            1870                                1560                                    360                                       240 230 71 72  67   carbamate   45  1290                 1620                     1320                         1730                            1860                                1470                                    360                                       240 230 72 72  66C  Nickel (II) 20  1230                 1630                     1290                         1690                            1820                                1430                                    400                                       230 220 71 73  69   diisopro-   pyldithio-      1   30  1280                 1670                     1170                         1690                            1870                                1320                                    370                                       230 220 72 73  68   carbamate   45  1400                 1670                     1080                         1760                            1870                                1280                                    350                                       230 230 73 73  67D  Nickel (II) 20  1270                 1620                      800                         1660                            1810                                 970                                    400                                       230 250 71 73  67   di-n-   butyldithio-      1   30  1350                 1670                      800                         1710                            1800                                 950                                    360                                       260 250 72 73  64   carbamate   45  1400                 1640                      730                         1770                            1810                                 880                                    340                                       220 250 73 73  63E  Nickel (II) 20  1210                 1650                      920                         1670                            1820                                1100                                    470                                       220 240 71 74  67   di-n-   propyldithio-      1   30  1310                 1630                      830                         1680                            1770                                1000                                    380                                       210 250 72 74  65   carbamate   45  1400                 1610                      760                         1680                            1720                                 920                                    330                                       210 250 73 74  64F  Zinc diiso-      1   20  1180                  810                     melted                         1510                            1080                                melted                                    360                                       290 melted                                               70 66  melted   propyl-   dithio-     30  1190                  900    1530                            1150    360                                       270     71 66   carbamate   45  1260                  900    1600                            1150    340                                       260     72 67G  None    --  20  1310                  850                      150                         1680                            1050                                 150                                    410                                       250 250 70 66  57          30  1380                  950                      200                         1720                            1120                                 200                                    400                                       250 250 71 66  57          45  1450                  975                      200                         1780                            1150                                 200                                    360                                       250 250 72 67  56__________________________________________________________________________ 
    
     The results demonstrate the superior aging qualities imparted to vulcanizates A, B and C by the antioxidants of the invention as compared with vulcanizates D, E and F. The loss in tensile strength and elongation upon aging vulcanizates A, B, and C for 7 days is relatively small. 
     Moreover, vulcanizates A, B and C were smooth and dry in appearance after aging whereas vulcanizates D, E and F were tacky. 
     It is manifest from this example that the nickel salts of branched-chain dialkyldithiocarbamates of the invention provide superior antioxidant properties in epihalohydrin polymers. 
     Having set forth the general nature and specific embodiments of the present invention, the true scope is now particularly pointed out in the appended claims.