Abstract:
A solvent-free, catalyst-free and contamination-free method of synthesis of polyimides is disclosed. The method includes polymerizing a diamine with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) at a pressure of 0.1-760 mm Hg, preferably a reduced pressure at about 36 mm Hg, and a temperature of 90-400° C., preferably 10-240° C.

Description:
FIELD OF THE INVENTION 
     The present invention is related to a method of synthesizing polyimides, and in particular to a solvent-free, catalyst-free and contamination-free method of synthesizing polyimides. 
     BACKGROUND OF THE INVENTION 
     Polyimides are a very versatile resin and useful in wide applications, which are heat resistant and low dielectric materials. Typical applications include an insulation layer in a semiconductor device and a protection film of a solar cell. One method for synthesizing polyimides is polymerizing a diamine compound and a dianhydride compound as shown in the following:                           
     wherein R and R 1  are the main structures of the diamine compound and dianhydride compound, respectively. 
     U.S. Pat. No. 4,244,857 (1981) discloses polyimides having the following structure:                           
     which is useful as a curing agent for polyepoxides. 
     Ger Offen 2223819 (1972) (equivalent to GB patent No. 1396331), Ger Offen 2223807 (1972) (equivalent to GB patent No. 1396332), and U.S. Pat. No. 3,959,350 (1976) disclose polyimides having the following structure:                           
     U.S. Pat. No. 3,356,648 (1967) discloses polyimides having the following structure, which can be used to form a film and fibers:                           
     In the synthesis of polyimides a special organic solvent is required, for examples N-methyl-2-pyrrolidone (NMP), m-cresol, and pyridine (Py), because the diamine compound and/or the dianhydride compound are not soluble to most of the organic solvents. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a more environmentally friendly method of synthesizing polyimides, wherein no solvent, and no Lewis acid catalyst are needed. In the method of the present application the reactants, a diamine compound and a dianhydride compound, are heated under a reduced pressure to carry out a ring-opening polyaddition reaction and a cyclodehydration reaction to form a polyimide product. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses a method of synthesizing a polyimide comprising heating a diamine compound and a dianhydride compound in the absence of an organic solvent and under a reduced pressure, so that a ring-opening polyaddition reaction and a cyclodehydration reaction are carried out to form a polyimide product, wherein said dianhydride compound is 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (hereinafter abbreviated as 6FDA). 
     Preferbly, said diamine compound is 4,4′-methylenedianiline [bis(4-aminophenyl) methane], 4-(4-aminophenoxy)aniline, 2,2-bis(4-aminophenyl)hexafluoropropane, 4-(2-trifluoromethyl-4-aminophenyl)-3-trifluoromethyl aniline or a mixture thereof in any ratio. 
     Preferably, said reduced pressure is lower than 100 mmHg, and more preferably is about 36 mmHg. Said heating causes said ring-opening polyaddition reaction and said cyclodehydration reaction being carried out at a temperature ranging from 90 to 400° C., and more preferably from 100 to 240° C. 
     Preferably, said diamine compound and said dianhydride compound are in a molar ratio of about 1:1. 
    
    
     The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. 
     Example 1 
     Synthesis of                           
     396 g (2 mmol) of 4,4′-methylenedianiline and 888 g (2 mmol) of 6FDA were added to a 50 ml round-bottom beaker, mixed, and then heated at 100° C. under 36 mmHg for one hour, and heated at 200° C. for another four hours. A polyimide product was obtained with the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 17371 
                 74312 
                 25625 
                 4.28 
               
               
                   
                   
               
               
                   
                 *Mn: number averaged molecular weight; Mw: weight averaged molecular weight; Mp: molecular weight peak value  
               
               
                   
                 Glass transition temperature (Tg): 269° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 545° C.  
               
             
          
         
       
     
     Control Example 1 
     Synthesis of                           
     396 g (2 mmol) of 4,4′-methylenedianiline, 888 g (2 mmol) of 6FDA and 10 g of N-methyl-2-pyrrolidone (NMP) were added to a 50 ml round-bottom beaker, and the mixture was stirred in N 2  atmosphere at room temperature for 48 hours. The reaction mixture was then poured into 500 ml water to form a precipitate. The precipitate was filtered out and heated at 200° C. under 36 mmHg for four hours to obtain a polyimide product. The polyimide product has the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 12045 
                 71825 
                 26398 
                 5.96 
               
               
                   
                   
               
               
                   
                 *The definitions are same as in Example 1  
               
               
                   
                 Glass transition temperature (Tg): 283° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 520° C.  
               
             
          
         
       
     
     Example 2 
     Synthesis of                           
     400 g (2 mmol) of 4-(4-aminophenoxy)aniline and 888 g (2 mmol) of 6FDA were added to a 50 ml round-bottom beaker, mixed, and then heated at 190° C. under 36 mmHg for one hour, and heated at 240° C. for another one hour. A polyimide product was obtained with the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 19139 
                 113674 
                 40807 
                 5.94 
               
               
                   
                   
               
               
                   
                 *The definitions are same as in Example 1  
               
               
                   
                 Glass transition temperature (Tg): 283° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 530° C.  
               
             
          
         
       
     
     Example 3 
     Synthesis of                           
     200 g (1 mmol) of 4-(4-aminophenoxy)aniline, 234 g (1 mmol) of 2,2-bis(4-aminophenyl)hexafluoropropane and 888 g (2 mmol) of 6FDA were added to a 50 ml round-bottom beaker, mixed, and then heated at 190° C. under 36 mmHg for one hour, and heated at 240° C. for another one hour. A polyimide product was obtained with the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 11742 
                 26112 
                 19531 
                 2.22 
               
               
                   
                   
               
               
                   
                 *The definitions are same as in Example 1  
               
               
                   
                 Glass transition temperature (Tg): 229° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 569° C.  
               
             
          
         
       
     
     Example 4 
     Synthesis of                           
     198 g (1 mmol) of 4,4′-methylenedianiline, 234 g (1 mmol) of 2,2-bis(4-aminophenyl)hexafluoropropane and 888 g (2 mmol) of 6FDA were added to a 50 ml round-bottom beaker, mixed, and then heated at 100° C. under 36 mmHg for one hour, and heated at 240° C. for another one hour. A polyimide product was obtained with the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 12331 
                 66582 
                 35938 
                 5.4 
               
               
                   
                   
               
               
                   
                 *The definitions are same as in Example 1  
               
               
                   
                 Glass transition temperature (Tg): 264° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 552° C.  
               
             
          
         
       
     
     Example 5 
     Synthesis of                           
     640 g (2 mmol) of 4-(2-trifluoromethyl-4-aminophenyl)-3-trifluoromethyl aniline and 888 g (2 mmol) of 6FDA were added to a 50 ml round-bottom beaker, mixed, and then heated at 180° C. under 36 mmHg for one hour, and heated at 240° C. for another one hour. A polyimide product was obtained with the following properties: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Mw/Mn 
               
               
                   
                 Mn* 
                 Mw* 
                 Mp* 
                 (polydispersity) 
               
               
                   
                   
               
             
             
               
                   
                 24737 
                 158133 
                 74580 
                 6.39 
               
               
                   
                   
               
               
                   
                 *The definitions are same as in Example 1  
               
               
                   
                 Glass transition temperature (Tg): 300° C.  
               
               
                   
                 10% weight loss temperature in N 2 : 559° C.  
               
             
          
         
       
     
     Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims. Many modifications and variations are possible in light of the above disclosure.