Heat stabilizers for polyvinyl chloride (β-amino-β-arylacrylamides)
This invention relates to stabilizing vinyl chloride polymers against degradation on exposure to heat. More particularly, it relates to improving the thermal stability of vinyl chloride polymers by incorporating therein an effective amount of a certain type of β-amino-β-arylacrylamide. 
     It is well known that vinyl chloride polymers deteriorate upon exposure to elevated temperatures and that such deterioration is accompanied by progressive discoloration of the polymer, generally from clear colorless to pale yellow to yellow to yellow-orange to red-orange to red to reddish brown to brown to black. It is known to inhibit such thermal degradation by the addition of stabilizers, such as those disclosed in U.S. Pat. No. 3,518,224. Illustrative of such known stabilizers are esters of β-aminocrotonic acid with 1,4-butyleneglycol or octyl alcohol or thioether alcohols, such as thiodiethylene glycol or dithiotriethylene glycol. However, since all such stabilizers found to date suffer from one deficiency or another, the search continues to discover ever better thermal stabilizers for vinyl chloride polymers. 
     In accordance with the present invention, it has been discovered that effective thermal stabilization of vinyl chloride polymers can be achieved by incorporation therein of an effective amount of a compound of the formula: ##EQU2## wherein R 1  is aryl or lower alkyl-substituted aryl, R 2  is hydrogen or lower alkyl; n is 1 or 2; and R 3  is hydrogen or lower alkyl when n is 1 and is alkylene of 1 to 4 carbon atoms or thiodiethylene when n is 2, alone or in admixture with a divalent metal salt of a fatty acid or mixture of fatty acids of 12-20 carbon atoms in a weight ratio of 1:2 to 2:1. Preferably, said compound is one wherein R 1  is phenyl, lower aklyl-substituted phenyl, or naphthyl; R 2  is hydrogen; n is 1; and R 3  is hydrogen or lower alkyl, especially hydrogen. Preferably said salt is calcium, barium, zinc, lead, or cadmium stearate, laurate, or oleate. 
     While the compounds useful for the practice of the present invention have been represented herein by the formula ##EQU3## as noted above, it is to be understood that these compounds can also exist in the isomeric form ##EQU4## or mixtures of the two forms, and such is intended by the single formula first presented above. Illustrative of the aryl moieties of R 1  are such monovalent aromatic groups as phenyl, naphthyl, and biphenyl. Illustrative of the lower alkyl moieties of R 2  or R 3  or which may be substituted on the other carbons of the aryl moieties of R 1  are such groups as methyl, ethyl, isopropyl, n-butyl, t-butyl, and the like having up to four carbon atoms, of which one or more may be present on such aryl group. Illustrative of the alkylene of 1 to 4 carbon atoms of R 3  are such groups as methylene, ethylene, propylene, and butylene. Therefore, illustrative of the β-amino-β-arylacrylamide compounds of the above formula useful in the practice of the present invention are β-amino-β-phenylacrylamide, β-amino-β-p-tolylacrylamide, N-methyl-β-amino-β-phenylacrylamide, N,N-dimethyl-β-amino-β-phenylacrylamide, Nn-butyl-β-amino-β-(4-n-butylphenyl)acrylamide, N-i-propyl -amino-β-phenylacrylamide, N-methyl- N-ethyl-β-amino-β-phenylacrylamide, β-amino-β-(2-naphthyl)acrylamide, N-methyl-N-ethyl-β-amino- -β-o-tolylacrylamide, N,N&#39;-methylenebis(N-methyl-β-amino-β-phenylacrylamide), N,N&#39;-(1,4-butylene)bis(N-ethyl-β-amino-β-phenylacrylamide), N,N&#39;-(1,2-ethylene)bis(β-amino-β-[2-naphthyl]acrylamide), N,N&#39;-(1,2-ethylene)bis(β-amino-β-p-tolylacrylamide), N,N&#39;-(1,2-ethylene)bis(β-amino-β-[4-t-butylphenyl]acrylamide), N,N&#39;-(thiodiethylene)bis(β-amino-β-phenylacrylamide), N,N&#39;-(thiodiethylene)bis(N-methyl-β-amino-β-o-tolylacrylamide), N,N&#39;-(thiodiethylene)bis(β-amino-β-[2-naphthyl]acrylamide), N,N&#39;-(thiodiethylene)bis(N-n-butyl-β-amino-β-phenylacrylamide), N,N&#39;-(thiodiethylene)bis-(N-isopropyl-β-amino-β-[4-n-butylphenyl]acrylamide), and the like. 
     In the practice of the present invention, it is preferred that the foregoing compounds be ones wherein R 1  is phenyl, lower alkyl-substituted phenyl, or naphthyl; R 2  is hydrogen; n is 1; and R 3  is hydrogen or lower alkyl, especially hydrogen, such as β-amino-β-phenylacrylamide, β-amino-β-p-tolylacrylamide, β-amino-β-(2naphthyl)acrylamide, and the like. alai, 
     In general, these compounds, useable in the practice of the present invention, can be prepared by several well-known methods, such as by condensing the reaction product of sodium and acetonitrile with the appropriate aromatic nitrile R 1  C.tbd.N where R 1  is as defined above to form an intermediate ##EQU5## The preparations of several of these β-amino-β-arylacrylonitrile compounds are described in R. Holtzwart, J. Praktische Chemie [2] 39, 230 (1889); E. von Meyer, J. Praktische Chemie [2] 52, 81 (1895) and [2] 78, 497 (1908); Dornow et al., Chemische Berichte 82, 254 (1949); J. Kuthan et al, Collect. Czech. Chem. Commun, 32 (12) 4309-18 (1967) and Chem. Abstracts 68, 39315k (1968); and J. Kethan, Collect. Czech. Chem. Commun. 34 (10), 2942-51 (1969), which, inter alaia, discuss β-amino-β-methylacrylonitrile, β-amino-β-phenylacrylonitrile, β-amino-β-p-tolylacrylonitrile, and β-amino-β-(p-ethylphenyl)acrylonitrile. Thereafter, these intermediates can be hydrolyzed to the corresponding β-amino-β-arylacrylamides, as described in Dornow et al., supra. Also see Shaw et al., J. Chem. Soc. 1954, 665-8 for preparation of β-amino-β-phenylacrylamide. 
     To secure effective stabilization of the vinyl chloride polymer against thermal degradation, it is generally desirable to use these compounds in the polymer in approximately a concentration of 0.5% to 5.0% on weight of the polymer, although approximately 1.0% to 3.0% on weight of polymer is preferred. Other additives also may be present in the vinyl chloride polymer to modify it for its intended application, such as fillers, anti-static agents, lubricants, light stabilizers, pigments dyes, plasticizers, etc. as is conventional practice. 
     In accordance with the present invention, vinyl chloride polymers can be stabilized against thermal degradation by use of these β-amino-β-arylacrylamide compounds alone or in admixture with a divalent metal salt of a fatty acid or mixture of fatty acids of 12-20 carbon atoms in a weight ratio of 1:2 to 2:1. Illustrative of the divalent metals are calcium, barium, zinc, lead, and cadmium. Illustrative of the fatty acids are lauric, oleic, and stearic acids. Representative such salts include calcium stearate, calcium laurate, calcium oleate, barium stearate, barium laurate, zinc oleate, zinc stearate, lead stearate, cadmium stearate, and the like. 
     These stabilizers, along with other additives, if used, are readily incorporated into the vinyl chloride polymer by such conventional processes as casting, molding, extruding, milling, mixing, and the like. 
    
    
     The following examples are given to illustrate the present invention. All parts are by weight unless otherwise specified. 
     EXAMPLE 1 
     To a solution of 2.0 grams (0.087 mole) of sodium in 125 milliliters of liquid ammonia was added a solution of 3.67 grams (0.089 mole) of acetonitrile in 10 milliliters of diethyl ether over a period of about five minutes. The reaction mixture was then cooled in a dry ice-acetone bath and a solution of 10.0 grams (0.065 mole) of 2-cyanonaphthalene in a minimum of dry diethyl ether was rapidly added within about five minutes after completion of the acetonitrile addition. The reaction mixture was stirred for about one and one-half hours and the ammonia was then allowed to evaporate. Water was cautiously added to the reaction mixture under nitrogen and the resulting mixture was extracted with diethyl ether. The ether was separated and the residue recrystallized from a mixture of chloroform and hexane. There was obtained 2.8 grams (22% of theoretical) of β-amino-β-(2naphthyl)acrylonitrile, melting point 85°-90°C. By the process described in Dornow et al., Chemische Berichte 82, 254-6 (1949), the β-amino-β-(2-naphthyl)acrylonitrile was hydrolyzed to β-amino-β-(2-naphthyl)acrylamide. 
     EXAMPLE 2 
     To a 16.7% solution of Geon 10EP polyvinyl chloride in tetrahydrofuran was added an amount of stabilizer to provide 3% by weight of stabilizer on weight of polyvinyl chloride and a film was cast therefrom and dried. The film was then exposed to heat at 193.3°C. (380°F.) or 204.4°C. (400°F.) in a press under a pressure of fifteen tons for twenty minutes, after which the films were observed for discoloration. As noted above, thermal degradation of polyvinyl chloride is accompanied by progressive discoloration of the polymer from clear colorless through various stages to black. Table I shows the results of tests with β-amino-β-phenylacrylamide stabilizer and control films similarly made and tested but without stabilizer. 
     
                       Table I                                                     
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             Color of Stabilized                                          
                             Color of                                     
Temperature  Film            Control Film                                 
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193.3°C. (380°F.)                                           
             essentially colorless                                        
                             reddish brown                                
204.4°C. (400°F.)                                           
             pale yellow     red brown                                    
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     EXAMPLE 3 
     The procedure of Example 2 is employed using β-amino-β-(2-naphthyl)acrylamide as the stabilizer. Similar results are obtained. 
     EXAMPLE 4 
     The precedure of Example 2 is employed using β-amino-β-p-tolylacrylamide as the stabilizer. Similar results are obtained. 
     EXAMPLE 5 
     The procedure of Example 2 was used to test various mixtures of β-amino-β-phenylacrylamide and calcium stearate at a total concentration of 3% on weight of polyvinyl chloride. However, in this test, the heat treatment under pressure lasted for thirty minutes at 193.3°C. (380°F.) prior to observation of the films. Table II shows the results of this series of tests which show the efficacy of approximately equal weight mixtures of the two additives for thermal stabilization. 
     
                       Table II                                                    
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Mixture Proportion                                                        
(parts β-amino-β-phenyl-                                        
acrylamide to parts calcium                                               
                  Color of Fillm - 30 mins.                               
stearate)         at 380°F.                                        
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1 to 1            almost colorless                                        
control - no additives                                                    
                  red brown with black spots                              
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