Salicylimines as cure activators for nonhalogenated rubbers
TECHNICAL FIELD 
     This invention is concerned with the enhancement of rates of cure or vulcanization of sulfur vulcanizable elastomers without detrimentally reducing the processing safety of the elastomer. 
     BACKGROUND ART 
     The primary achievement of the instant invention resides in the discovery that certain specific salicylimines either in free form or complexed with zinc in the plus 2 valence state will dramatically increase the rate of cure of certain elastomers while simultaneously providing adequate processing safety. In the manufacture of vulcanized rubber articles, significant cost savings can be realized through a reduction of time the article is required to spend in the mold. Through enhanced rates of vulcanization, the in mold time required to meet minimum cure levels (physical properties) can be reduced; however, processing safety (or scorch) of the stock must be maintained. 
     Vulcanization, or curing, is a term applied to the process where elastomers, natural and synthetic, are treated with certain chemicals to improve their strength and durability. In general, vulcanization will effect the following changes in raw elastomers: increase tensile strength, eliminate tackiness, decrease solubility in various solvents, increase elasticity and decrease temperature sensitivity. These improved properties can be obtained by treating the raw elastomer with sulfur in the presence of other chemicals such as accelerators. It is known that the presence of accelerators in the vulcanization process is desirable since accelerators enable the vulcanization reaction to be carried out in a shorter period of time and at a lower temperature. 
     If large amounts of accelerators are used in the vulcanization process, the resulting composition contains appreciable amounts of the accelerator or decomposition products thereof. Although the presence of appreciable amounts of accelerators in the final composition is not usually detrimental, there are applications where the presence of the accelerator is undesirable, for example, accelerators such as the thiazoles, are skin irritant. Thus, consideration of the amount and type of accelerator present in the vulcanized composition is important where the vulcanized composition is to be used in the preparation of fabrics and articles which may come in contact with the skin. 
     Vulcanization accelerators presently used in the industry also present other problems. For example, dithioacid salts such as dithiocarbamates or thiurams, so called &#34;ultra accelerators&#34;, rapidly accelerate vulcanization at conventional vulcanization temperature but have the problem of prematurely vulcanizing the rubber compositions during processing steps such as mixing or molding due to the heat generated by the mixing which results in the undesired scorching of the rubber. Sulfenamides, so called &#34;delayed action accelerators&#34;, do not possess scorching problems, but they tend to retard the rate of vulcanization. 
     Accordingly, it has become important in the rubber industry to find novel accelerator systems that prevent scorching of the rubber at processing temperatures, but that allow vulcanization to take place rapidly at vulcanization temperatures and to provide final compositions which do not have accelerators bloom, or come to the surface, of the rubber article. 
     U.S. Pat. No. 2,615,860 is concerned with the protection of synthetic resin compositions from degradation caused by light, especially ultraviolet radiation. This patent discloses the use of metal chelates as stabilizers. Specifically, this patent is concerned with a solid polymer of ethylene and not more than 10% by weight of a metal chelate compound, wherein the metal chelate compound is a nickel derivative of the Schiff&#39;s base derived from ethylenediamine and salicylaldehyde. 
     Chemical Abstract 77(22):141163g discloses that several Russian investigators have determined that compounds such as N,N&#39;-disalicylideneethylenediamine chelates of certain metals are vulcanizing agents for chloro butyl rubbers. The abstract discloses that the degree of crosslinking was evaluated by swelling, and that vulcanization by the chelates without zinc oxide imparted enhanced tensile strength to the rubber. This reference does not suggest or disclose the instant invention which is concerned with the use of certain specific chelates of zinc in certain enhancers. 
     U.S. Pat. No. 4,139,523 discloses a polyphosphazene composition stabilized against thermal aging comprising (1) a polyphosphazene represented by the general formula: ##STR2## and wherein n represents an integer from 20 up to about 50,000 and X and X 1  each represent a monovalent radical selected from the group consisting of alkoxy, aryloxy and amino; and (2) a stabilizer consisting of an organic compound compatible with said polyphosphazene and present in an amount sufficient to stabilize said polyphosphazene against thermal degradation, said organic compound represented by the structure: ##STR3## wherein W is 
     
         --CRR&#39;--CRR&#39;--, 
    
     or: ##STR4## and wherein R and R&#39; are selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl or mixtures thereof, and M is zinc or magnesium. 
     DISCLOSURE OF THE INVENTION 
     There is disclosed a sulfur vulcanizable rubber composition comprising a nonhalogenated sulfur vulcanizable rubber, a vulcanizing agent, accelerator and a cure activator, wherein said cure activator has the structural formula: ##STR5## wherein X is a radical of the structural formula: 
     
         --CH.sub.2 --CH.sub.2 --NH--CH.sub.2 --CH.sub.2 --.sub.y 
    
     wherein y is 0,1,2 or 3. 
     There is also disclosed a method for enhancing the rate of sulfur vulcanization of a sulfur vulcanizable elastomer or blend of elastomers which comprises adding to said elastomer a compound or compounds of the structural formula: ##STR6## wherein X is a radical of the structural formula: 
     
         --CH.sub.2 --CH.sub.2 --NH--CH.sub.2 --CH.sub.2 --.sub.y 
    
     wherein y can equal 0, 1, 2, or 3. 
     These compounds either in free form (structural formula I) or as preformed complexes with zinc (structural formula II) offer significantly enhanced rates of cure and excellent final physical properties of the vulcanizate without a significant loss of processing safety. These compounds may be added to the sulfur vulcanizable rubbers as preformed complexes at levels that provide typical levels of zinc to the rubber compound. 
     The term &#34;rubber&#34; or &#34;elastomer&#34; as used herein embraces both natural rubber and all its various raw and reclaim forms as well as various synthetic rubbers, i.e., rubber polymers of the type which may be vulcanized with sulfur while specifically excluding the halogenated rubbers such as chloroprene or neoprene. Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, as for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated organic compounds. Among the latter are acetylenes, e.g. vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, vinylchloride, acrylic acid, acrylonitrile (which polymerizes with butadiene to form buna-N rubber), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form Buna-S rubber, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g. acrolein, methylisopropyl ketone and vinylethyl ether. Also included are the various synthetic rubbers prepared from the homopolymerization of isoprene and the copolymerization of isoprene with other diolefins and various unsaturated organic compounds. Additionally, included are the synthetic rubbers such as 1,4-cis polybutadiene and 1,4-cis polyisoprene and similar synthetic rubbers which have been developed in recent years, such as EPDM. Such recently developed rubbers include those that have polymer bound functionality such as antioxidants and antiozonants. These polymer bound materials are known in the art and can have functionalities that provide antidegradative properties, synergism, and other properties. Polymer bound functions have great value since the pendant functionality possessing the desired activity cannot be extracted (or migrate) since it is chemically attached to the backbone of the polymer. 
     The preferred rubbers used with the instant invention are styrene/butadiene copolymers, polybutadiene and polyisoprene. 
     The cure activators of this invention can be used with any conventional compounding additives such as carbon black, zinc oxide, antidegradants and stearic acid. For the purposes of this invention, &#34;sulfur vulcanizing agent&#34; means elemental sulfur or sulfur donating vulcanizing agents, for example, an amine disulfide or a polymeric polysulfide. Preferably, the activators of this invention are used with free sulfur. The invention is applicable to various classes and conventional amounts of vulcanization agents. 
     The accelerators that can be used in conjunction with the compounds of this invention are those that are known and typically used in the sulfur vulcanization of rubbers. 
     The following examples illustrate the preparation and use of various vulcanization accelerators of the present invention and are not intended to limit the scope of the present invention. All parts are by weight unless otherwise noted. 
    
    
     BEST MODE 
     EXAMPLE 1 
     Preparation of a Compound of Structural Formula I when y=0 
     In a 500 ml round bottom flask was placed 9.84 g of ethylene diamine dissolved in 100 ml of ethanol. To this solution was added 40.0 g of salicylaldehyde dissolved in 100 ml of ethanol. The mixture was stirred at reflux for 2 hours after which the reaction mixture was cooled and the yellow crystalline product was collected by filtration and washed with cold ethanol. After drying 43 g of salen was obtained. 
     To prepare compounds of structural formula I when y is 1, 2 or 3, the above procedure would be used except that the ethylene diamine would be replaced with compounds such as diethylene triamine, triethylene tetramine and tetraethylene pentamine. 
     EXAMPLE 2 
     Preparation of a Compound of Structural Formula II when y=0 
     [[α,α-(Ethylenedintrilo) di -o- cresolato](2-)]-Zinc 
     Sodium hydroxide (8 g) was dissolved in 250 ml of water and placed in a 3 neck 1 liter flask with 26.8 g of Salen (Salicyaldehyde-ethylenediamine Schiff base compound prepared in Example 1). The mixture was heated to 45° C. with stirring and then 28.7 g of ZnSO 4  dissolved in 200 ml of water was added dropwise over about 1/2 hour. After the reaction mixture had stirred overnight at room temperature, the product was collected by filtration, washed with water and dried over P 2  O 5  under vacuum. Product yield was approximately 100%. IR 1630 cm -1  (C=N); no O-H peak. 
     For compounds of structural formula II wherein y=1, 2, or 3, a compound of structural formula I is obtained as described in Example 1 when y=1, 2 or 3 and then reacted as described in this example to yield the zinc complex. 
     EXAMPLE 3 
     Compound in Natural Rubber 
     Compounds of this invention and several comparatives were milled into a productive masterbatch. The nonproductive masterbatch had the following composition: 
     
                       TABLE I                                                     
______________________________________                                    
Component       Amount (phr)                                              
______________________________________                                    
Natural rubber  100                                                       
Processing oil  3.0                                                       
Wax             1.0                                                       
Antiozonant     2.0                                                       
Antioxidant     1.0                                                       
Carbon Black    50.0                                                      
______________________________________                                    
 
    
     This nonproductive masterbatch was mixed on a Banbury for about 5 minutes and then transferred to a mill for incorporation of the productive ingredients listed in Table II. 
     
                       TABLE II                                                    
______________________________________                                    
Component         Amount (phr)                                            
______________________________________                                    
Stearic acid      1.0                                                     
Zn complex        Variable                                                
Sulfur            1.8                                                     
Primary accelerator                                                       
                  0.8                                                     
Secondary accelerator                                                     
                   0.15                                                   
______________________________________                                    
 
    
     The compounds were mill mixed for about 3 minutes and then sheeted and samples of the compound placed in a Monsanto Model MPV rheometer and a Scott Mooney Viscometer. 
     Table III sets out by structural formula the zinc complex evaluated, the amount of complex added to achieve approximate equal levels of zinc, the time to achieve 25% of the ultimate modulus observed for the compound on the rheometer - t25, the time required to achieve 90% of the ultimate modulus observed for the compound on the rheometer - t90, the total torque developed on rheometer (final torque minus initial torque) - Δtorque and the time in minutes to a five point rise in the Mooney viscosity of the compound at 120° C. as determined on the Scott Mooney Viscometer - scorch. 
     
                                           TABLE III                               
__________________________________________________________________________
Sample                                                                    
    Zn                  Amt Complex  Δ                              
No. Complex             (phr)  t25                                        
                                  t90                                     
                                     Torque                               
                                          Scorch                          
__________________________________________________________________________
1   ZnO (Control)       1.3    4.5                                        
                                  6.4                                     
                                     25.4 14.7                            
     ##STR7##           5.3    2.7                                        
                                  4.0                                     
                                     23.6 10.1                            
     ##STR8##           4.0    2.2                                        
                                  3.3                                     
                                      4.6 18.8                            
4                                                                         
     ##STR9##           4.6    1.3                                        
                                  1.9                                     
                                     20.1  3.0                            
     ##STR10##          9.2    1.2                                        
                                  2.0                                     
                                     23.8  2.2                            
     ##STR11##          7.8    1.5                                        
                                  2.5                                     
                                     14.9   3.3                           
     ##STR12##          9.2    3.5                                        
                                  10.0                                    
                                     18.8 12.0                            
8                                                                         
     ##STR13##          5.4    4.3                                        
                                  5.5                                     
                                      8.2 17.9                            
9                                                                         
     ##STR14##          6.2    4.7                                        
                                  6.3                                     
                                     17.0 17.5                            
__________________________________________________________________________
 
    
     The data contained in Table III demonstrate that only Sample 2 (compound of this invention) provided for an enhanced rate of cure, without significant decrease in scorch time and maintained the state of cure as indicated by Δ torque. 
     EXAMPLE 4 
     Compounding in an SBR/ Polybutadiene Blend 
     Compounds of this invention and comparatives were milled into a productive masterbatch. The nonproductive masterbatch had the following composition: 
     
                       TABLE IV                                                    
______________________________________                                    
Component           Amount (phr)                                          
______________________________________                                    
SBR (cold recipe-23% styrene)                                             
                    70.0                                                  
Polybutadiene       30.0                                                  
Wax                 3.0                                                   
Antiozonant         2.0                                                   
Carbon Black        65.0                                                  
Oil                 33.75                                                 
______________________________________                                    
 
    
     This nonproductive materbatch was mixed on a Banbury for about 5 minutes and then transferred to a mill for incorporation of the productive ingredients listed in Table V. 
     
                       TABLE V                                                     
______________________________________                                    
Component         Amount (phr)                                            
______________________________________                                    
Sulfur            1.6                                                     
Antioxidant       1.0                                                     
Primary accelerator                                                       
                  1.0                                                     
Secondary accelerator                                                     
                  0.2                                                     
Zinc complex      Variable                                                
______________________________________                                    
 
    
     The compounds were mill mixed for about 3 minutes and sheeted and test samples of the compound were placed in the rheometer. 
     Table VI sets out zinc complexes and the test results. 
     
                                           TABLE VI                                
__________________________________________________________________________
Sample                  Actual     Δ                                
No.                     &#34;Zn&#34; phr                                          
                             t25                                          
                                t90                                       
                                   Torque                                 
                                        Scorch                            
__________________________________________________________________________
10  Control No. 1; ZnO, 3 phr                                             
                        2.4  6.8                                          
                                13.8                                      
                                   21.2 22.4                              
11  Control No. 2; ZnO, 1 phr                                             
                        0.8  7.4                                          
                                13.4                                      
                                   20.0 23.5                              
12                                                                        
     ##STR15##          1.0  5.0                                          
                                7.2                                       
                                   20.5 18.1                              
    5.2 phr                                                               
13                                                                        
     ##STR16##          1.8  5.8                                          
                                9.6                                       
                                   24.1 12.0                              
    5.2 phr; ZnO, 1 phr                                                   
14                                                                        
     ##STR17##          1.0  4.6                                          
                                13.4                                      
                                   14.3 8.0                               
    4.0 phr                                                               
15                                                                        
     ##STR18##          1.8  4.9                                          
                                16.7                                      
                                   15.8 8.2                               
    4.0 phr; ZnO, 1 phr                                                   
16                                                                        
     ##STR19##          1.0  1.3                                          
                                2.3                                       
                                   16.6 2.4                               
    4.5 phr                                                               
17                                                                        
     ##STR20##          1.8  1.7                                          
                                3.3                                       
                                   22.1 3.0                               
    4.5 phr; ZnO, 1 phr                                                   
18                                                                        
     ##STR21##          1.8  2.3                                          
                                5.8                                       
                                   23.1 3.5                               
    6.1 phr; ZnO, 1 phr                                                   
19                                                                        
     ##STR22##          1.0  3.0                                          
                                12.1                                      
                                   19.9 5.4                               
    7.7 phr                                                               
20                                                                        
     ##STR23##          1.8  4.2                                          
                                12.9                                      
                                   25.6 6.4                               
    7.7 phr; ZnO, 1 phr                                                   
21                                                                        
     ##STR24##          1.0  4.9                                          
                                9.2                                       
                                   17.2 16.6                              
    9.2 phr                                                               
__________________________________________________________________________
 
    
     Table VI demonstrates that the compound of structural formula II enhance rates of vulcanization without significantly reducing scorch. Table VI also shows that a balance between the complexing agent and free ZnO will result in improved rates of cure without a reduction of scorch. 
     EXAMPLE 5 
     Compounding of Structural Formula I in Rubber 
     The masterbatch set out in Tables I and II was used to evaluate the uncomplexed compounds in these rubber formulations. As in Example 3 and 4, a non-productive mix was followed by the productive mix. The productive mix recipe of Tables II and V were used except that 3.0 phr of ZnO was used in the sample and the zinc complex was replaced with a variable amount of the complexing agent. 
     As in previous examples, the samples were sheeted and evaluated on a rheometer. Table VII sets out the results. Values are expressed in terms of percent reduction to t90 and percent reduction of scorch. These values were calculated based on a control which contained only 3.0 phr ZnO and 0.0 phr of a complexing agent. 
     
                       TABLE VII                                                   
______________________________________                                    
Sam-                      % t90     Scorch                                
ple              Amount   Reduction Reduction                             
No.              (phr)    SBR/BR NR   SBR/BR NR                           
______________________________________                                    
22   Salen*      .74      15.7    9.5   4.3   13.5                        
23   Saldiene**  .74      25.0   17.5  11.1   21.5                        
24   Saltrien*** .74      28.0   17.5  10.7   26.0                        
25   Saltetren+  .74      32.6    9.5  13.8   13.5                        
26   Salpenten++ .74      37.9   23.8  25.0   40.0                        
     (Comparative)                                                        
27   X = (CH.sub.2).sub.3                                                 
                 .74      13.6   14.7  11.5   4.5                         
     (Comparative)                                                        
28   X = (CH.sub.2).sub.6                                                 
                 .74      15.7   16.2   9.6   12.6                        
     (Comparative)                                                        
29   Para+++     .74      19.8   15.9  14.1   22.0                        
______________________________________                                    
     (Comparative)                                                        
 *Structural formula I when y = 0.                                        
 **Structural formula I when y = 1.                                       
 ***Structural formula I when y = 2.                                      
 +Structural formula I when y = 3.                                        
 ++Structural formula I when y = 4.                                       
 +++Compound of structural formula I where y = 0 and the --OH group is par
 to benzylidene group.                                                    
 
    
     The information contained in Table VII shows that the compounds of this invention (Sample Nos 22-26) provide enhanced rates of cure while only moderately decreasing scorch protection. In comparison, the comparative (Sample Nos 27-29) do not demonstrate the same level of beneficial properties. 
     EXAMPLE 6 
     Varying Levels in SBR/BR 
     In an effort to optimize the level of compounds of structural formula I in an SBR/polybutadiene rubber blend, the following experiment was conducted. To the masterbatch of Table IV and the productive recipe of Table V was added varying levels of Salen and 3.0 phr of ZnO. Table VIII sets out the results. 
     
                       TABLE VIII                                                  
______________________________________                                    
                                % Mooney                                  
         Amount Salen                                                     
                     % Cure Time                                          
                                Scorch Time                               
Sample No.                                                                
         (phr)       Reduction  Reduction                                 
______________________________________                                    
30       0.0         --         --                                        
31       .37          3.0        1.5                                      
32       .74         14.7        4.8                                      
33       1.50        23.5       10.6                                      
34       2.94        33.8       16.3                                      
35       5.88        42.6       22.1                                      
36       10.0        52.9       34.6                                      
37       11.8        57.4       42.3                                      
______________________________________                                    
 
    
     The data evidences that as the level of the Salen is increased the percent cure time reduction also increased. However, the percent of Mooney scorch time reduction also increases. It was noted that Δ torque decreases at very high levels of Salen. 
     EXAMPLE 7 
     Effect of Replacing ZnO with Zn Salen 
     Using the masterbatch and productive recipe of Tables IV and V, the effect of replacing ZnO with Zn Salen was investigated. Table IX sets out the results. 
     
                       TABLE IX                                                    
______________________________________                                    
       Amount                       % Mooney                              
Sample Zn Salen Amount ZnO % Cure Time                                    
                                    Scorch Time                           
No.    (phr)    (phr)      Reduction                                      
                                    Reduction                             
______________________________________                                    
38     0.0      3.0        --       --                                    
39     .46      2.89       11.7     +                                     
40     .91      2.78       14.1     +                                     
41     1.81     2.55       24.2     +                                     
42     3.64     2.11       28.1     +                                     
43     7.27     1.51       21.9     +                                     
44     12.31    0.0        34.4     +                                     
______________________________________                                    
 +Indicates that scorch time was equal to or longer than the control      
 (without Salen #38)                                                      
 
    
     Table IX demonstrates that levels of Zn Salen may be increased to result in increased percent of cure time reduction, however, scorch time was not significantly decreased. 
     In an attempt to evaluate the teachings of CA 77(22):141163 g, discussed in Background Art, the following example was conducted: 
     EXAMPLE 8 
     Use in Chlorobutyl Rubber 
     100 parts of chlorobutyl rubber, 13 parts of oil and 60 parts of carbon black were mixed in a Banbury for about 5 minutes and then various combinations of curative packages were mixed into the chlorobutyl stock on a Banbury for about 3 minutes. As previously described, the stocks were evaluated. Table X sets out the results. 
     
                                           TABLE X                                 
__________________________________________________________________________
        Sample                                                            
             Sample                                                       
                 Sample                                                   
                      Sample                                              
                          Sample                                          
                               Sample                                     
                                   Sample                                 
Component                                                                 
        No. 45                                                            
             No. 46                                                       
                 No. 47                                                   
                      No. 48                                              
                          No. 49                                          
                               No. 50                                     
                                   No. 51                                 
__________________________________________________________________________
ZnO     5.0  5.0 4.0  3.0 3.0  2.0 0                                      
Sulfur  0    0   0    0.5 0.5  0.5 0.5                                    
Accelerator                                                               
        0    0   0    1.5 1.5  1.5 1.5                                    
Salen   0    1.5 0    0   3.0  0   3.0                                    
Zn Salen                                                                  
        0    0   1.8  0   0    2.0 0                                      
Test                                                                      
t 25 min                                                                  
        12.6 12.5                                                         
                 13.0 10.2                                                
                          22.6 14.5                                       
                                   42.7                                   
t 90 min                                                                  
        56.0 124.0                                                        
                 117.0                                                    
                      30.0                                                
                          89.5 57.5                                       
                                   159.5                                  
Δtorque d N.sup.19 m                                                
        13.3 11.0                                                         
                 12.0 12.0                                                
                          11.7 13.3                                       
                                   8.8                                    
Scorch  93   120 115  24.7                                                
                          76.4 36.0                                       
                                   146.5                                  
__________________________________________________________________________
 
    
     The data discloses that the use of Salen or Zn Salen in chlorobutyl rubber provided no reduction in cure time. As cure time increased, so did scorch, thus, the use of the compounds of structural formula I and structural formula II in halogenated rubbers would not be beneficial and is outside the scope of this invention. 
     The Russian investigator made no comment on cure rate reduction, but it appears from this example that cure rate reduction is not realized when using Salen or Zn Salen in chlorobutyl rubber. Thus, the teachings of the Russian reference in combination with this example would lead one away from the instant invention. 
     EXAMPLE 9 
     Use of Salen and Zn Salen in Various Rubbers 
     The following compounding series were run with the results listed in Table XI. 
     
                                           TABLE XI                                
__________________________________________________________________________
             Sample                                                       
                 Sample                                                   
                     Sample                                               
                         Sample                                           
                             Sample                                       
                                 Sample                                   
                                     Sample                               
                                         Sample                           
                                             Sample                       
             No. 52                                                       
                 No. 53                                                   
                     No. 54                                               
                         No. 55                                           
                             No. 56                                       
                                 No. 57                                   
                                     No. 58                               
                                         No. 59                           
                                             No. 60                       
__________________________________________________________________________
NON-PRODUCTIVE                                                            
SBR-A*           100 100 100 --  --  --  --  --                           
SBR-B*       --  --  --  100 100 100 --  --  --                           
PBd*         --  --  --  100 --  --  100 100 100                          
Wax          1   1   1   1   1   1   1   1   1                            
Antiozonant  2   2   2   2   2   2   2   2   2                            
Carbon Black 45  45  45  45  45  45  45  45  45                           
PRODUCTIVE                                                                
ZnO          3   3   2   3   3   2   3   3   2                            
Stearic acid 2   2   --  2   2   --  2   2   --                           
Sulfur       1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6                          
Primary Accelerator                                                       
             1   1   1   1   1   1   1   1   1                            
2nd day ACC  0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2                          
Antiozonant  1   1   1   1   1   1   1   1   1                            
Salen        --  3   --  --  3   --  --  3   --                           
Zn Salen     --  --  3.5 --  --  3.5 --  --  3.5                          
SCORCH                                                                    
Mins         22.5                                                         
                 20.2                                                     
                     22.3                                                 
                         20.4                                             
                             18.7                                         
                                 22.5                                     
                                     19.3                                 
                                         16.8                             
                                             18.7                         
ΔTorque                                                             
             15.4                                                         
                 16.6                                                     
                     17.1                                                 
                         15.4                                             
                             16.7                                         
                                 16.4                                     
                                     21.1                                 
                                         22.8                             
                                             22.4                         
t 25, min    7.3 5.6 6.6 6.3 5.6 6.8 7.1 5.7 6.2                          
t 90, min    16.5                                                         
                 10.2                                                     
                     11.6                                                 
                         15.2                                             
                             9.8 11.7                                     
                                     10.4                                 
                                         7.8 7.8                          
CHANGE IN SCORCH                                                          
+/-%             -10.0                                                    
                     -1.0    -8.3                                         
                                 +10.3   -13.0                            
                                             -3.1                         
CHANGE IN CURE                                                            
+/-%             -38.2                                                    
                     -29.7   -35.5                                        
                                 -23.0   -25.0                            
                                             -25.0                        
__________________________________________________________________________
 *SBR-A -- 23.5% styrene SBR                                              
 *SBR-B -- 36.0% styrene SBR                                              
 *PBd -- polybutadiene                                                    
 The data demonstrate that Salen and Zn Salen work in both SBR and PBd to 
 increase the cure rate with modest (or no) decreases in scorch time.     
 Further, Zn Salen continues to perform better than its uncomplexed versio
 and there is only a minor difference in the performance with increased   
 styrene content in SBR&#39;s.                                                
 
    
     EXAMPLE 10 
     In an effort to demonstrate the effectiveness of the compounds of this invention with other accelerator systems, the following experiment was conducted. 
     The control non-productive masterbatch had the following composition: 
     
                       TABLE XII                                                   
______________________________________                                    
Component       Amount (phr)                                              
______________________________________                                    
SBR             75.0                                                      
Polyisoprene    25.0                                                      
Processing Oil  28.0                                                      
Carbon Black    60.0                                                      
Antiozonant     2.0                                                       
Antioxidant     1.0                                                       
Wax             1.0                                                       
Stearic Acid    3.0                                                       
ZnO             3.0                                                       
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     An experimental non-productive masterbatch had a similar composition, except that the level of ZnO was reduced to 2.0 phr. 
     Four different accelerators were added to a series of control non-productive batches and in like fashion the four accelerators were added to a series of experimental non-productive materbatches which also included 3.5 phr zinc salen per sample. 
     1.5 phr sulfur and 1.0 phr accelerator were in each sample. Thus, Table XIII sets out sample number, type of accelerator, Zn source, t90, and scorch for each sample. 
     
                       TABLE XIII                                                  
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                                t90   Scorch                              
Sample No.                                                                
        Accelerator                                                       
                   ZN Source    (min) (min)                               
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61      A          ZnO          27.1  24.2                                
62      A          ZnO + Zn Salen                                         
                                18.8  28.5                                
63      B          ZnO          25.7  44.5                                
64      B          ZnO + Zn Salen                                         
                                20.7  40.8                                
65      C          ZnO          37.1  53.5                                
66      C          ZnO + Zn Salen                                         
                                30.5  68.6                                
67      D          ZnO          41.7  65.5                                
68      D          ZnO + Zn Salen                                         
                                35.5  61.0                                
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     This invention confirms that the samples of this invention are useful with other accelerators and still evidence beneficial properties. 
     INDUSTRIAL APPLICABILITY 
     The instant invention provides enhanced rate of vulcanization which, in the production of tires, hoses and belts can have a positive impact on the production rates and energy expenditures. The cure activators of this invention do not adversely affect rubber/wire adhesion or final physical properties of the vulcanizate. Other benefits derived from the use of the materials of this invention will be obvious to those skilled in the art.