Process for grafting maleic anhydride onto unsaturated polyolefinic elastomers by mass reaction
DESCRIPTION OF THE INVENTION 
     The present invention relates to the preparation of functionalized olefinic elastomeric terpolymers by the grafting of maleic anhydride, which preparation is carried out by mass reaction. 
     The grafting of maleic anhydride onto olefinic polymers by mass reaction is known in the prior art. 
     According to U.S. Pat. No. 3,236,917, maleic anhydride is grafted onto ethylene/propylene copolymers by heating a mixture of the two components in the presence of an organic peroxide. This process presents the drawback of causing besides the graft of maleic anhydride, a partial cross-linking between the chains of the copolymer as well. 
     According to U.S. Pat. No. 3,884,882, one obtains adducts of maleic anhydride and terpolymers consisting of ethylene, an alpha olefin, and a non-conjugated dienic compound, by heating mixtures of terpolymer with the anhydride at temperatures ranging from 225° to 350° C. This process, while allowing one to obtain products having a low gel content, presents the drawback of requiring in the reaction a considerable excess of maleic anhydride to achieve the desired graft levels. 
     In accordance with the present invention it has now been discovered that, surprisingly, the grafting of maleic anhydride onto unsaturated olefinic polymers may be carried out by mass reaction, without incurring the above-mentioned drawbacks, by carrying out the reaction in the presence of a catalyst consisting of a compound of a metal of group VIII of the periodic system, having the formula 
     
         M.sub.n X.sub.z 
    
     wherein: 
     M=a metal of group VIII of the periodic system; 
     X=a counterion; 
     n=valence of the counterion; and 
     z=valence of the metal. 
     The olefinic polymers which react in such a way with maleic anhydride are represented by unsaturated terpolymers consisting of monomeric units coming from at least two different monomers having the formula 
     
         R--CH═CH.sub.2 
    
     wherein R=hydrogen or an alkyl group containing from 1 to 6 carbon atoms, and of lower amounts of monomeric units coming from a conjugated or non-conjugated diene. 
     Therefore the main object of the present invention consists in a process for carrying out the grafting of maleic anhydride onto olefinic polymers consisting or consisting essentially of arranging for the maleic anhydride to mass react with an unsaturated olefinic terpolymer consisting of monomeric units coming from at least two different monomers having the formula 
     
         R--CH═CH.sub.2                                         (I) 
    
     wherein R=hydrogen or an alkyl group having from 1 to 6 carbon atoms and of lower amounts of a conjugated or nonconjugated dienic monomer, in the presence of a compound having the formula: 
     
         M.sub.n X.sub.z                                            (II) 
    
     wherein: 
     M=a metal of group VIII of the periodic system; 
     X=a counterion; 
     n=valence of the counterion; and 
     z=valence of the metal. 
     The metal in the compounds having the formula (II) is preferably Rh or Ru, while the counterion consists of a halogen or of an NO 3  group. 
     Examples of utilizable compounds are RhCl 3 , RhBr 3 , RuCl 3 , Rh(NO 3 ) 3 . Among these compounds RhCl 3  is preferred. 
     Among the preferred olefinic polymers which may be used for the purpose of the present invention, may be cited ethylene-propylene conjugated or non-conjugated diene terpolymers, wherein the diene may be, for instance, 5-ethylidene, 2-norbornene; 1,4-hexadiene; dicyclopentadiene; 5-methylene, 2-norbornene; 1,3-butadiene. 
     The corresponding amounts of monomers in such copolymers are not critical; they may range over very wide limits, without impairing their usefulness in the process of this invention. 
     Preferred terpolymers are those consisting of ehtylene with at least an alpha-olefin comprised in formula (I), preferably propylene, and with at least one of the above-mentioned dienic monomers and comprising preferably, by weight, from 30 to 80% of ethylene and from 0.5 to 15% of dienic termonomer. 
     Terpolymers of ethylene with an alpha-olefin containing from 3 to 8 carbon atoms and at least one dienic monomer are well known in the prior art. Methods for their preparation are described for instance in U.S. Pat. Nos. 2,933,480; 2,962,451; 3,000,866; 3,093,620; 3,093,621; 3,063,973; 3,147,230; 3,154,528; 3,260,708. 
     The reaction between the above-described unsaturated olefinic polymer and maleic anhydride, in the presence of the compound having the formula (II) (catalyst) according to the invention may be carried out by any mass process in which one achieves a good mixing of the polymer with the other components, without any substantial formation of free radicals. 
     The mixing may be carried out for instance in a plastograph of the Brabender type or in an extruder, by feeding maleic anhydride in the molten state or in the form of a powder. The catalyst may be introduced in the form of a powder or in a masterbatch based on the reaction polymer or incorporated in the molten maleic anhydride. The amount of catalyst to be used may range from 0.001 to 0.1 g per 100 g of elastomeric polymer. 
     The reaction temperature may range from 120° to 350° C., but is preferably from 220° to 280° C. 
     The residence times of the reagents in the mixing phase at such temperatures generally, but not necessarily, range from 0.5 to 5 minutes, and thereby a polymer is obtained containing from 0.5 to 2.5% by weight of grafted maleic anhydride. 
     The grafted polymer obtained by the process according to this invention requires no substantial purification, as free maleic anhydride is present in said polymer in very low amount. 
     Upon extraction in xylene at 23° C., after having kept the reaction mixture at reflux temperature for 1 hour, an insoluble fraction comes out consisting of an irreversibly grafted polymer, which is always below 2% by weight based on the reaction raw product. 
     The following examples will be given to illustrate the present invention without limiting, however, the same. 
     According to such examples the following polymers are used: 
     elastomer (A), consisting of an ethylene-propylene-ethylidene norbornene (ENB) terpolymer, containing, by weight, 40% of propylene and 3.5% of ENB, having a Mooney ML(1+4) viscosity at 100° C.=42; and 
     elastomer (B), consisting of an ethylene-propylene-butadiene terpolymer, containing, by weight, 28% of propylene, and 1.2% of butadiene, having a Mooney ML (1+4) viscosity at 100° C.=32. 
     The amount of grafted maleic anhydride present in the washed polymer was calculated on the reaction products by acidimetry or IR spectroscopy. The washing of the raw reaction product was carried out by dissolving the polymer in xylene, by precipitating it again with acetone, then by filtering, and by washing the precipitate with acetone several times. 
    
    
     In all the examples the concentrations of the fed catalyst and maleic anhydride are referred to 100 parts by weight of elastomeric polymer. 
     EXAMPLES 1-2 
     Comparison Examples 
     Copolymer A was fed into a Brabender PLE 651 plastograph, heated to the temperature of 270° C., keeping the round number of the rotors equal to 20 rpm. When the mass reached the required temperature and the recorded stress was constant, the round number was increased to 60 rpm and powdered maleic anhydride (M.A.) was added. The mixture was then allowed to react for 5 minutes, after which it was discharged. 
     The content in anhydride was determined both on the raw mixture and on the washed polymer. The part insoluble in xylene at 23° C. was determined. 
     The conversion was calculated on the basis of the ratio between maleic anhydride in the washed product and fed maleic anhydride. 
     The amounts of the reagents and the results are reported in Table I. 
     EXAMPLES 3-6 
     Operation here was as in the preceding Examples (1-2), inserting however, at the time of addition of the monomer (maleic anhydride), the catalyst RhCl 3  in powder form. 
     The amounts of the reagents and the results are reported in Table I. 
     EXAMPLES 7-8 
     Comparison Examples 
     Copolymer B was loaded into a Brabender PLE 651 plastograph, heated to the temperature of 270° C., keeping the round number of the rotors at 20 rpm. After setting of the temperature and stress, the speed was increased to 60 rpm and powdered maleic anhydride was added. 
     The mixture was allowed to react for 5 minutes, after which it was discharged. 
     The amounts of the reagents and the results are reported in Table II. 
     EXAMPLES 9-12 
     Here operation was as in Examples 7-8, inserting however, at the time of addition of the monomer, the catalyst RhCl 3  in powder form. 
     The amounts of the reagents and the results are reported in Table II. 
     EXAMPLES 13-16 
     Operation here was as in Example 11, discharging however the mixture after different reaction times. 
     The amounts of the reagents and the results are reported in Table III. 
     EXAMPLES 17-19 
     Operating as in Example 12 using as catalyst RhBr 3 , Rh(NO 3 ) 3  and RuCl 3  instead of RhCl 3 , the amounts of the reagents and the results are as reported in Table IV. 
     
                       TABLE I                                                     
______________________________________                                    
            1    2      3      4    5    6                                
______________________________________                                    
Catalyst      --     --     0.1  0.1  0.05 0.001                          
(% by weight)                                                             
Fed maleic    1      2      1    2    1    1                              
anhydride (%)                                                             
Maleic anhydride                                                          
              0.62   0.81   0.99 1.54 1.10 0.86                           
in the raw product (%)                                                    
Maleic anhydride in the                                                   
              0.31   0.44   0.99 0.92 0.99 0.80                           
product after                                                             
washing (%)                                                               
Conversion (%)                                                            
              31     22     99   46   99   80                             
Part insoluble in                                                         
              2      2      2    2    2    2                              
xylene at 23° C. (%)                                               
______________________________________                                    
 
    
     
                       TABLE II                                                    
______________________________________                                    
          7    8      9       10   11    12                               
______________________________________                                    
Catalyst    --     --     0.1   0.1  0.05  0.001                          
(% by weight)                                                             
Fed maleic  1      2      1     2    1     1                              
anhydride (%)                                                             
Maleic anhydride                                                          
            0.62   0.56   1.11  1.85 1.17  1.11                           
in the raw                                                                
product (%)                                                               
Maleic anhydride                                                          
            0.37   0.37   1.11  1.54 1.10  1.11                           
in the product                                                            
after washing (%)                                                         
Conversion (%)                                                            
            37     28     100   77   100   100                            
Part insoluble in                                                         
            2      2      2     2    2     2                              
xylene at 23° C. (%)                                               
______________________________________                                    
 
    
     
                       TABLE III                                                   
______________________________________                                    
Influence of the reaction time                                            
                13    14      15     16                                   
______________________________________                                    
Time (min)        1       2       3    4                                  
Fed maleic anhydride (%)                                                  
                  1       1       1    1                                  
Maleic anhydride in the raw                                               
                  1.05    --      --   1.11                               
product (%)                                                               
Maleic anhydride in the product                                           
                  1.05    0.99    0.99 1.05                               
after washing (%)                                                         
Conversion (%)    100     99      99   100                                
______________________________________                                    
 
    
     
                       TABLE IV                                                    
______________________________________                                    
             17      18        19                                         
______________________________________                                    
Catalyst       RhBr.sub.3                                                 
                         Rh(NO.sub.3).sub.3                               
                                   RuCl.sub.3                             
Concentration of the                                                      
               0.0017    0.0013    0.0010                                 
catalyst (%)                                                              
Fed maleic anhydride (%)                                                  
               1         1         1                                      
Maleic anhydride in the                                                   
               0.98      0.80      0.75                                   
raw product (%)                                                           
Maleic anhydride in the                                                   
               0.98      0.67      0.69                                   
washed product (%)                                                        
Conversion (%) 98        67        69                                     
______________________________________                                    
 
    
     EXAMPLES 20 AND 21 
     Comparative Examples 
     In these two examples the reaction is carried out between maleic anhydride and elastomer using benzoyl peroxide as radicalic initiator. 
     The elastomeric copolymer was fed into a plastograph type Brabender PLE 651, heated to 120° C. and working at 20 r/m. When the mass reached the required temperature and the recorded stress was constant, the round number was increased to 60 r/m, and maleic anhydride and peroxide were added. The mixture was allowed to react for 8 hours, after which it was discharged. 
     The amounts of reagents and the results obtained are reported in Table V. All the indicated amounts are expressed by weight. 
     
                       TABLE V                                                     
______________________________________                                    
                  20    21                                                
______________________________________                                    
Types of elastomer  A       B                                             
Peroxide concentration (%)                                                
                    0.4     0.4                                           
Fed maleic anhydride (%)                                                  
                    1       1                                             
Maleic anhydride in the                                                   
                    1.11    0.11                                          
raw reaction product (%)                                                  
Maleic anhydride in the                                                   
                    1.05    1.05                                          
washed product (%)                                                        
Conversion (%)      100     100                                           
Part insoluble in xylene                                                  
                    37      45                                            
at 23° C. (%)                                                      
______________________________________