Wire coated with fluorocarbon polymers cross-linked with dialyl ester of 4,4&#39;-dicarboxydiphenyl ester
This invention relates to polymeric compositions comprising fluorocarbon polymers containing an ester of diphenyl ether as a crosslinking agent and to wire coated with the crosslinked composition. 
     High temperature processing fluorocarbon polymers possess a combination of mechanical, dielectric and chemical properties which make them particularly useful as electrical insulation materials. In order to maximize utilization of these fluorocarbon polymers under high temperature or overload conditions, crosslinking of the fluorocarbon polymers is required. 
     Crosslinking of high temperature resistant fluorocarbon polymers is particularly difficult since the polymers are normally processed at temperatures which are too high for most chemical crosslinking agents. As an alternative to chemical crosslinking, irradiation crosslinking of these polymers has been tried. However, to avoid massive doses of irradiation, it is necessary to add a chemical crosslinking agent or coreactant to the fluorocarbon polymers. Among such known crosslinking coreactants are diallylic esters of phenyl indan, which are shown in U.S. Pat. No. 3,763,222 and triallyl esters of aryl polycarboxylic acids, such as those disclosed in U.S. Pat. No. 3,840,619. 
     I have now discovered that the addition of the diallyl ester of 4,4&#39;-dicarboxydiphenyl ether to fluorocarbon polymers accelerates the crosslinking of fluorocarbon polymers when they are subjected to ionizing radiation activation and improves to a remarkable extent the properties, and particularly the elevated temperature properties, of the resulting crosslinked compositions. In addition, because of the plasticizing and lubricating nature of the ester of the invention, the extrusion of the polymers may be carried out at a lower temperature profile. 
     The ester of the invention has been disclosed as a crosslinking agent for a totally different polymer system, namely unsaturated polyesters. See Chemical Abstracts, Volume 75, Abstract No. 21778Y, 1971. A method for the ester&#39;s preparation is also disclosed in the foregoing reference. Another method of preparation of the ester is by reaction of 4,4&#39;-dicarboxydiphenyl ether with thionyl chloride to produce the corresponding diacyl chloride. The diacyl chloride is then reacted with allyl alcohol to produce the ester. Alternatively, the ester can be prepared by other methods including direct esterification, catalyzed esterification or interchange esterification from saturated esters of the dicarboxydiphenyl ether. Additionally, the compounds can be produced from the diphenyl ether dinitrile or dialdehyde or like intermediates by known techniques. 
     The diallyl ester of dicarboxy diphenyl ether is particularly useful as an additive for accelerating the crosslinking of high temperature processing fluorocarbon polymers, that is polymers which are extruded, or in certain instances, molded at temperatures above 260°C. These include homopolymers and copolymers such as ethylene-tetrafluoroethylene copolymers, ethylene-chlorotrifluoroethylene copolymers, polyvinylidene fluoride homopolymers, tetrafluoroethylene-vinylidene fluoride copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers and the like. 
     The diallyl esters of the invention may be used alone, or in combination with other polyfunctional crosslinking additives. Among such additives useful in combination are the diallylic and dimethallylic esters of phenyl indan as shown in U.S. Pat. No. 3,763,222. A number of other polyfunctional crosslinking additives, useful in combination with the present esters, are disclosed in application Ser. No. 402,302 filed Oct. 1, 1973. Examples of the latter are diallyl brassylate, triallyl trimesate, triallyl trimellitate and triallyl isocyanurate. Others will occur to those skilled in the art. 
     The crosslinking compound or compounds are added in amounts sufficient to plasticize the polymer or polymer blends for processing and to impart deformation resistance upon crosslinking. This amount may range from 0.5 to 20 parts by weight per 100 parts by weight of polymer, but will normally be from 1 to 10 parts of the crosslinker per 100 parts of polymer. The polymer or polymers and crosslinking compounds are blended, processed in the melt at an elevated temperature for a period of time sufficient to melt process, but insufficient to crosslink. The formed mixture is then cooled to ambient temperature and irradiated at a dosage between, for example, about 5 and 10 megarads. 
    
    
     The following examples illustrate the practice of the present invention. All parts are by weight, unless otherwise indicated. 
     EXAMPLE 1 
     Five parts of diallyl 4,4&#39;-dicarboxydiphenyl ether were blended with 100 parts of various fluorocarbon polymers. Table I shows the decrease in torque values achieved by these blends as compared with the same polymers without additive. 
     
                       TABLE I                                                     
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                     Mixing                                               
          Additive   Chamber      Torque                                  
Polymer   (Parts)    Temp. (°C)                                    
                                  (Metergrams)                            
______________________________________                                    
E/TFE.sup.1                                                               
          None       288           850                                    
 &#34;        5          288           750                                    
E/CTFE.sup.2                                                              
          None       260          1750                                    
 &#34;5       260        1650                                                 
PVDF.sup.3                                                                
          None       288          1075                                    
 &#34;        5          288           875                                    
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 .sup.1 Ethylene-tetrafluoroethylene copolymer.                           
 .sup.2 Ethylene-chlorotrifluoroethylene copolymer.                       
 .sup.3 Polyvinylidene fluoride homopolymer.                              
 
    
     The torque data was obtained in a &#34;Brabender&#34; Sigma type mixer, using a 63 gram total charge, in each case employing the noted temperature at a shear rate of 80 r.p.m. 
     The reduction in torque values indicates that the polymeric compositions containing the diallyl ester can be processed at lower temperatures, for example, to provide continuous thin wall extrusions or at equivalent temperatures to provide thinner wall extrusions. 
     The following examples illustrate the excellent mechanical and aging properties of crosslinked polymeric compositions containing the compounds of the invention. 
     EXAMPLES 2 - 8 
     A polymeric composition was prepared by powder blending 100 grams of an ethylene-tetrafluoroethylene (E/TFE) copolymer with 5 grams of the diallyl ester of 4,4&#39;-dicarboxydiphenyl ether and 0.5 grams of magnesium oxide. The blended mixture was compression molded at 254°C and subjected to irradiation at 10 and 20 megarad doses in 1.5 mev. electron beam accelerator to produce samples of crosslinked slabs of the polymeric composition. 
     Similar samples were prepared from an ethylene-chlorotrifluoroethylene (E/CTFE) copolymer and a polyvinylidene fluoride (PVDF) homopolymer, respectively, as the polymeric component. An additional sample was prepared using a blend of crosslinking agents, namely the diallyl ester of the invention plus triallyl trimesate and a small amount of antioxidant. The room temperature (about 25°C) and elevated temperature properties of the compression molded, crosslinked samples are set forth in Table II. In each case, they are compared with samples containing no crosslinking additive. In the case of the elevated temperature properties, the tensile strength and elongation tests were at 250°C for E/TFE and E/CTFE polymers, and at 200°C for PVDF. The hot modulus tests were at 275°C for E/TFE, 250°C for E/CTFE and 200°C for PVDF. 
     
                                           TABLE II                                
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                  Radi-                                                   
                      Room Temperature                                    
                                   Elevated Temperature                   
                  ation                                                   
                      Tensile      Tensile                                
                  Dose                                                    
                      Strength                                            
                           Elongation                                     
                                   Strength                               
                                        Elongation                        
                                                Hot Modulus               
Ex.                                                                       
   Composition                                                            
             Parts                                                        
                  (MR)                                                    
                      (psi)                                               
                           (10&#34;/min.) (%)                                 
                                   (psi)                                  
                                        (10&#34;/min.) (%)                    
                                                50 psi                    
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2  E/TFE alone    10  5635 281     350  758     Would not sup-            
                  20  4241  83     295  409     port 50 psi.              
                  40  4656  38     251  186     53                        
3  E/TFE     100  10  6082 154     630  200     20                        
   Diallyl Ester                                                          
             5                                                            
   MgO       0.5  20  6028 100     705  168     17                        
4  E/CTFE alone   10  6426 263      18  680     Would not sup-            
                  20  5127 213      37  124     port 50 psi.              
5  E/CTFE    100  10  5971 146     155  127     29                        
   Diallyl Ester                                                          
             5                                                            
   MgO       1    20  5474 113      62   27     20                        
6  PVDF alone     10  3776 220      70  435     302                       
                  20  3979 117      66  104     67                        
7  PVDF      100  10  4286 167     149  151     39                        
   Diallyl Ester                                                          
             5    20  4181 104     149  198     23                        
8  E/TFEE    100  10  5662 129     565  243     39                        
   Triallyl trimesate                                                     
             2                                                            
   Diallyl Ester                                                          
             3    20  4633  83     473  135     22                        
   Irganox 1010                                                           
             0.25                                                         
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     The samples of Example 2 - 8 were aged at elevated temperatures after irradiation crosslinking and tested for tensile strength (psi) and elongation (%) after cooling to room temperature. The E/TFE copolymers were aged at 260°C, E/CTFE copolymers were aged at 225°C and the PVDF homopolymer at 200°C. The results are set forth in Table III. 
     
                                           TABLE III                               
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                 Radi-                                                    
                 ation                                                    
                     AGING PERIOD (DAYS)                                  
                 Dose                                                     
                     0      1      3      5      7      11                
Ex.                                                                       
   Composition                                                            
            Parts                                                         
                 (MR)                                                     
                     T.S.                                                 
                        Elong.                                            
                            T.S.                                          
                               Elong.                                     
                                   T.S.                                   
                                      Elong.                              
                                          T.S.                            
                                             Elong.                       
                                                 T.S.                     
                                                    Elong.                
                                                        T.S.              
                                                           Elong.         
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2  E/TFE alone   20  4241                                                 
                         83 -- --  4139                                   
                                       19 4300                            
                                             13  Too Brittle              
                                                        Too Brittle       
                                                 to test                  
                                                        to test           
                 40  4656                                                 
                         38 -- --  4238                                   
                                       25 4429                            
                                             13  4380                     
                                                    6   Too Brittle       
                                                        to test           
3  E/TFE    100  10  6082                                                 
                        154 -- --  4915                                   
                                      125 4472                            
                                             50  4013                     
                                                    38  4110              
                                                           29             
   Diallyl Ester                                                          
            5                                                             
   MgO      0.5  20  6028                                                 
                        100 -- --  4662                                   
                                       58 4352                            
                                             38  4907                     
                                                    25  4336              
                                                           21             
4  E/CTFE alone  10  6426                                                 
                        263 5972                                          
                               229 5003                                   
                                      194 4632                            
                                             171 4620                     
                                                    113 4143              
                                                           58             
                 20  5127                                                 
                        213 5382                                          
                               192 4958                                   
                                      167 4882                            
                                             121 4560                     
                                                    96  4602              
                                                           54             
5  E/CTFE   100  10  5971                                                 
                        146 5618                                          
                               142 5091                                   
                                      100 5073                            
                                             79  4682                     
                                                    71  4527              
                                                           54             
   Diallyl Ester                                                          
            5                                                             
   MgO      1    20  5474                                                 
                        113 5321                                          
                               113 4826                                   
                                       71 4848                            
                                             54  4724                     
                                                    58  4710              
                                                           50             
6  PVDF alone    10  3776                                                 
                        220 4108                                          
                               417 3782                                   
                                      267 3663                            
                                             269 3548                     
                                                    158 4024              
                                                           329            
                 20  3779                                                 
                        117 3270                                          
                               113 3466                                   
                                      118 3436                            
                                             75  4745                     
                                                    58  3528              
                                                           58             
7  PVDF     100  10  4286                                                 
                        167 4660                                          
                               313 4690                                   
                                      196 4204                            
                                             200 4248                     
                                                    263 5623              
                                                           225            
   Diallyl Ester                                                          
            5    20  4181                                                 
                        104 3944                                          
                               104 3717                                   
                                       54 4014                            
                                             63  3885                     
                                                    75  3839              
                                                           83             
8  E/TFE    100  10  5662                                                 
                        129 -- --  4304                                   
                                       83 3855                            
                                             58  3939                     
                                                    50  4194              
                                                           33             
   Triallyl                                                               
    Trimesate                                                             
            2                                                             
   Diallyl Ester                                                          
            3    20  4633                                                 
                         83 -- --  4382                                   
                                      108 4124                            
                                             63  4188                     
                                                    63  4278              
                                                           25             
   Irganox 1010                                                           
            0.25                                                          
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     EXAMPLE 9 
     A polymeric composition was prepared by powder blending 100 grams of an E/TFE copolymer with 5 grams of the diallyl ester of 4,4&#39;-dicarboxyphenyl ether, 0.5 grams of MgO and 0.25 grams of Irganox 1010. (Irganox 1010 is tetrakis (methylene 3-(3&#39;,5&#39;-di-tert-butyl-4&#39;-hydroxyphenyl) propionate) methane.) The blend in powder form was extruded through an extruder head having a head temperature of 277°C to form rods. The rods were pelletized and the pellets were extruded onto the surface of an 18 AWG bare copper wire to form a 15 mil coating. 
     For comparison a second wire coating was prepared in the same manner from an E/TFE copolymer containing no additive. The extrusion conditions for the two samples were as follows: 
     
                   Temperature (°C)                                         
Composition 1       2       3     Die   Head                              
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E/TFE copolymer                                                           
            254     271     282   329   357                               
(with additive)                                                           
E/TFE copolymer                                                           
            304     316     316   354   377                               
(no additive)                                                             
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     The insulated wires were then subjected to irradiation with high energy electrons by a 1.0 mev. resonant beam transformer. The resulting insulated wires with irradiation crosslinked coatings were then annealed and subsequently tested to determine their mechanical and electrical properties. The results are set forth in Table IV. 
     
                       TABLE IV                                                    
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             Composition of Wire Coatings                                 
             (No additive)                                                
                       (With diallyl ester)                               
Test           10MR    20MR    10MR   20MR                                
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Room Temperature                                                          
Tensile Strength (psi)                                                    
               5229    5480    4964   5253                                
Elongation (%) 133     170      83    100                                 
At 250°C                                                           
Tensile Strength (psi)                                                    
               340     290     303    340                                 
Elongation (%) 700     395     105     85                                 
Hot Modulus                                                               
(275°C/50 psi)                                                     
               Failed  280      43     40                                 
High Voltage Cut-thru                                                     
(at 225°C one lb.                                                  
               Failed  Failed  Pass   Pass                                
load on each end                                                          
and 900 V(rms)                                                            
Sequential                                                                
Heat Aging*    Failed  Failed  Pass   Pass                                
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 *Specimen should pass 10 cycles of 6 hr. each at 260°C (mandrel   
 diameter 0.75 in. and suspension weight of 2 lbs. on each side), after   
 each cycle, the specimen is immersed in 5% salt solution for 5 hrs. and  
 while immersed in salt solution should withstand the application of 3000 
 V(rms) at 60 cps frequency for 1 min. without rupture of the insulation. 
 
    
     Table IV indicates the generally improved properties obtained by inclusion of the diallyl ester. The high temperature properties -- hot modulus, high voltage cut-thru and sequential heat aging -- of the wire coating compositions of the invention are shown to be particularly outstanding.