Patent Publication Number: US-5292857-A

Title: Preparation of nylon 66 polymers from 1,8-diazacyclotetradecane-2,7-dione

Description:
FIELD OF THE INVENTION 
     This invention relates to the preparation of nylon 66 homo and copolymers using 1,8-diazacyclotetradecane-2,7-dione as an ingredient in the starting reaction mixture. 
     BACKGROUND OF THE INVENTION 
     In the conventional commercial processes for the preparation of nylon 66 polymer, adipic acid and hexamethylene diamine are reacted. High molecular weight polymer is produced, but a by-product of this reaction is the formation of cyclic nylon 66 monomer, i.e. 1,8-diazacyclotetradecane-2,7-dione. 1,8-diazacyclotetradecane-2,7-dione has in the past been usually considered a waste product. It tends to be washed out of nylon fibers when the fibers are dyed. 
     1,8-diazacyclotetradecane-2,7-dione is disclosed in U.S. Pat. No. 2,241,323 to Greenewalt as a material suitable for use in the preparation of nylon polymers. In this patent the monomer is referred to as cyclic monomeric hexamethylene adipamide (14 annular atoms; M.P. 248 degrees C.) 
     SUMMARY OF THE INVENTION 
     The present invention is a process for the production of nylon 66 polymer (or copolymer when epsilon-caprolactam is included in the reaction mix) from 1,8-diazacyclotetradecane-2,7-dione which comprises (a) forming a reaction mixture containing 10 to 90 parts by weight 1,8-diazacyclotetradecane-2,7-dione and a complementary amount of the salt of adipic acid and hexamethylenediamine, and/or epsilon-caprolactam, (b) heating said mixture under a pressure greater than atmospheric pressure, (c) slowly lowering the pressure to atmospheric pressure while increasing the temperature to about 275 degrees C, (d) maintaining the temperature at about 275 degrees C and at a pressure no more than atmospheric pressure until polymer having a relative viscosity of at least about 25 is obtained. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1,8-diazacyclotetradecane-2,7-dione can be recovered from nylon 66 polymer production processes involving condensation of adipic acid and hexamethylenediamine; however if this material, 1,8-diazacyclotetradecane-2,7-dione, is used as the sole starting monomer for production of 66 nylon using standard polymerization conditions, about 25 percent of the monomer will not react, and the product will not be useful as a polymer. A process has now been developed to produce satisfactory product from 1,8-diazacyclotetradecane-2,7-dione. 
     In order to produce satisfactory polymer from 1,8-diazacyclotetradecane-2,7-dione it is necessary for the reaction mixture to contain at least 10 percent by weight of the salt of adipic acid and hexamethylenediamine and/or epsilon-caprolactam. The reaction mixture is then processed in accordance with the steps outlined above. The recovered nylon 66 polymer (or copolymer) will be of high molecular weight; with a relative viscosity of at least about 25, where relative viscosity is measured at 25 degrees C. in a solution of 8.4% by weight polymer in formic acid containing 10% by weight water. 
     The conventional nylon additives: catalysts, pigments, anti-foam agents, antioxidants, and the like can be used in the process of the invention, or added to the nylon produced by the process of this invention. 
     EXAMPLES 
     1. A 300 cc stainless steel autoclave was charged with 26.7 grams of 1,8-diazacyclotetradecane-2,7-dione and 60.0 grams of a 51% aqueous nylon 66 salt solution. 
     2. A regulator controlling the pressure of the system was set for 250 psig. 
     3. The autoclave was closed and purged with nitrogen. 
     4. The contents of the autoclave were agitated and heated in 60 minutes to 250 degrees C. 
     5. After reaching 250 degrees C., the pressure was gradually reduced from 250 psig to atmospheric pressure over a one hour period by adjusting the pressure regulator. During the one hour the temperature was increased slowly to 275 degrees C. 
     6. The temperature of the autoclave was maintained at 275 degrees C. for 45 minutes. 
     8. The agitation was turned off and the autoclave was then allowed to cool. 
     8. After cooling the polymer was removed from the autoclave and the polymer dried at 90 degrees C. The relative viscosity was measured and found to be 49. This examples is contained in the table below as Item 5. 
     The table below summarizes the results obtained when the process was repeated using varying conditions. Items 1,2, and 8 are not examples of the invention, but instead controls. In items 6, 7 and 8, 0.2 grams of anhydrous was also charged to the autoclave with the other ingredients. Hexamethylenediamine 
     
                       TABLE                                                       
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                 wt %    wt %         % Methanol                          
Item Additive    CM*     additive                                         
                                 RV   extractables                        
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1    none        100      0      15   --                                  
2    none        100      0      15   25                                  
3    66 salt     89      11      33   7.5                                 
4    66 salt     75      25      44   6.8                                 
5    66 salt     50      50      49   3.7                                 
6    66 salt     25      75      51   1.8                                 
7    66 salt     10      90      57   1.2                                 
8    66 salt      0      100     57   1.2                                 
9    caprolactam 50      50      36   --                                  
10   caprolactam 10      90      41   --                                  
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 CM* is cyclic monomer: 1,8diazacyclotetradecane-2,7-dione.