Epoxy resin composition containing a curing agent which is a reaction product of hydantoins, formaldehyde and an amine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to curable epoxy resins, and more particularly to epoxy resins cured with a reaction product of hydantoins, amine and formaldehyde. 
     2. Related Publications 
     A series of epoxy resins based on hydantoins were developed. These products have better mechanical and thermal properties than resins based on Bisphenol A. These are discussed, for example, in Epoxy Resin Technology, Developments Since 1979, Noyes Data Corporation (1982), pgs 81-83. 
     Polyoxyalkylene amines have been disclosed in many patents and publications as curing agents for epoxy resins. For example, U.S. Pat. Nos. 4,115,360; 4,141,885; 4,115,361; 4,146,700 and 4,169,177. 
     In the present invention it has been discovered that a reaction product of hydantoins, formaldehyde and an amine, especially a polyoxyalkylene amine, provide, in most cases, a fluid, viscous liquid which is easily dispersed uniformly into epoxy resins thereby providing a new and useful epoxy resin curing agent. 
     SUMMARY OF THE INVENTION 
     The invention is an epoxy resin composition comprising a vicinal polyepoxide having an epoxide equivalency of greater than about 1.8 and a curing amount of the reaction product of hydantoins, formaldehyde and a primary or secondary amine, especially a polyoxyalkylene amine. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the instant inventive concept, a new epoxy resin curing composition is provided which is the reaction product of hydantoins, formaldehyde and a primary or secondary amine. This reaction product is mixed in a curing amount with a vicinal polyepoxide having an epoxide equivalency of greater than about 1.8 to provide a cured epoxy material. 
     The epoxy resin curing agent is prepared from a reaction product of hydantoins, formaldehyde and amines of the following description. 
     Hydantoin or its alkyl derivatives are useful in this invention. Useful hydantoin derivatives include 5,5-dimethyl hydantoin, 5-methyl-5-ethyl, 5-methyl-5-propyl, etc. 
     The amine terminated polyethers (polyoxyalkylene amines) useful in this invention are polyethers of about 200 molecular weight or more made from an appropriate initiator to which lower alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide or mixtures thereof are added with the resulting hydroxyl terminated polyol then being aminated. When two or more oxides are used, they may be present as random mixtures or as blocks of one or the other polyether. 
     In the amination step it is highly desirable that the terminal hydroxyl groups in the polyol be essentially all secondary hydroxyl groups for ease of amination. Normally, the amination step does not completely replace all of the hydroxyl groups. However, the majority of hydroxyl groups are replaced by amine groups. Therefore, the amine terminated polyether resins useful in this invention have greater than 50% of their active hydrogens in the form of amine hydrogens. If ethylene oxide is used it is desirable to cap the hydroxyl terminated polyol with a small amount of higher alkylene oxide to ensure that the terminal hydroxyl groups are essentially all secondary hydroxyl groups. The polyols so prepared are then reductively aminated as outlined, for example, in U.S. Pat. No. 3,654,370 and other prior art techniques. 
     Polyoxyalkylene polyamines having the structure ##STR1## wherein Y is hydrogen, a methyl radical or an ethyl radical, Z is a hydrocarbon radical of 2-5 carbon atoms, n is a number sufficient to impart a molecular weight of about 200-2000 to the molecule and r is a number 2 or greater are useful. 
     Other useful amines include the JEFFAMINE® M-series which are mono functional amines represented by the general structure ##STR2## where R and R&#39; are alkyl groups and n is a number of 1 or more. Examples of useful amines of this type are as follows: 
     JEFFAMINE M-1000: 
     CH 3  O(C 2  H 4  O) 18 .6 [CH 2  CH(CH 3 )O] 1 .6 CH 2  CH(CH 3 )NH 2   
     JEFFAMINE-600: 
     CH 3  OC 2  H 4  [CH 2  CH(CH 3 )O] 8  CH 2  CH(CH 3 )NH 2   
     JEFFAMINE M-360: 
     CH 3  OC 4  H 9  (OCH 2  CH 2 ) 4  OCH 2  CH(CH 3 )OCH 2  CH(CH 3 )NH 2   
     Another example of a suitable amine to be used in accordance with the present invention is a polyoxyethylenediamine such as one having the formula ##STR3## 
     Examples of suitable polyoxyethylenediamines having this formula are as follows: 
     
         ______________________________________                                    
                 Approximate Value                                        
                 b      a + c                                             
______________________________________                                    
JEFFAMINE ED-600   13.5     3.5                                           
JEFFAMINE ED-900   20.5     3.5                                           
JEFFAMINE ED-2001  45.5     3.5                                           
______________________________________                                    
 
    
     Condensation of these polyoxyalkylene damines with formaldehyde and hydantoins produces materials that can be used to cure epoxy resins. Use of such materials as curatives results in cured epoxy products with unique properties. Condensation reactions are simple and straightforward and proceed, it is believed, as follows: ##STR4## 
     Products also useful as epoxy curatives may be prepared by reacting one mole (or less) hydantoin with one mole of amine and one mole of formaldehyde. ##STR5## The reaction is preferably carried out at about 90° C. for about four hours. Thereafter the water of condensation and the water in any reactants is removed at about 90°-120° C. and pressures of about 10-50 mm. The preferred ratios are 1:1:1 for the reactants; however, an excess of the amine or hydantoin may generally be used. With selected amines less than one mole may also be useful as the following examples will show. 
     The exact useful ratios for particular reactants are easily determined by one skilled in the art using the teachings herein. A satisfactory ratio should provide a product viscosity suitable for various applications such as molding, casting, encapsulating or spraying or brushing to form a coating. 
     Generally, the amine cured vicinal polyepoxide containing compositions are organic materials having an average of at least 1.8 reactive 1,2-epoxy groups per molecule. These polyepoxide materials can be monomeric or polymeric, saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, and may be substituted if desired with other substituents besides the epoxy groups; e.g., hydroxyl groups, ether radicals, aromatic halogen atoms and the like. 
     Preferred polyepoxides are those of glycidyl ethers prepared by epoxidizing the corresponding allyl ethers or reacting, by known procedures, a molar excess of epichlorohydrin and an aromatic polyhydroxy compound; i.e., isopropylidene bisphenol, novolak, resorcinol, etc. The epoxy derivatives of methylene or isopropylidene bisphenols are especially preferred. 
     A widely used class of polyepoxides which are useful according to the instant invention includes the resinous epoxy polyethers obtained by reacting an epihalohydrin, such as epichlorohydrin, and the like, with either a polyhydric phenol or a polyhydric alcohol. An illustration, but by no means exhaustive, listing of suitable dihydric phenols includes 4,4&#39;-isopropylidene bisphenol, 2,4&#39;-dihydroxydiphenylethylmethane, 3,3&#39;-dihydroxydiphenyldiethylmethane, 3,4&#39;dihydroxydiphenylmethylpropylmethane, 2,3&#39;-dihydroxydiphenylethylphenylmethane, 4,4&#39;-dihydroxydiphenylpropylphenylmethane, 4,4&#39;-dihydroxydiphenylbutylphenylmethane, 2,2&#39;-dihydroxydiphenylditolylmethane, 4,4&#39;-dihydroxydiphenyltolylmethylmethane and the like. Other polyhydric phenols which may also be co-reacted with an epihalohydrin to provide these epoxy polyethers are such compounds as resorcinol, hydroquinone, substituted hydroquinones; e.g., methylhydroquinone, and the like. 
     Among the polyhydric alcohols which can be co-reacted with an epihalohydrin to provide these resinous epoxy polyethers are such compounds as ethylene glycol, propylene glycols, butylene glycols, pentane diols, bis(4-hydroxycyclohexyl)dimethylmethane, 1,4-dimethylolbenzene, glycerol, 1,2,6-hexanetriol, trimethylolpropane, manniatol, sorbitol, erythritol, pentaerythritol, their dimers, trimers and higher polymers; e.g., polyethylene glycols, polypropylene glycols, triglycerol, dipentaerythritol and the like, polyallyl alcohol, polyhydric thioethers, such as 2,2&#39;-, 3,3&#39;-tetrahydroxydipropylsulfide and the like, mercapto alcohols such as monothioglycerol, dithioglycerol, and the like, polyhydric alcohol partial esters, such as monostearin, pentaerythritol monoacetate, and the like, and halogenated polyhydric alcohols such as the monochlorohydrins of glycerol, sorbitol, pentaerythritol and the like. 
     Another class of polymeric polyepoxides which can be amine cured and are in accordance with the instant invention includes the epoxy novolak resins obtained by reacting, preferably in the presence of a basic catalyst; e.g., sodium or potassium hydroxide, an epihalohydrin, such as epichlorohydrin, with the resinous condensate of an aldehyde; e.g., formaldehyde, and either a monohydric phenol; e.g., phenol itself, or a polyhydric phenol. Further details concerning the nature and preparation of these epoxy novolak resins can be obtained in Lee, H. and Neville, K., Handbook of Epoxy Resins, McGraw-Hill Book Co., New York, 1967. 
     Other polyepoxides known to those skilled in the art may be useful in this invention. 
     Optionally, the epoxy resin formulations of the instant invention can include an &#34;accelerator&#34; to speed the amine cure of the epoxy resin, especially at ambient temperatures. In several applications, such acceleration is beneficial, especially when an epoxy resin is used as an adhesive in flammable environment, thus making elevated temperature cure inconvenient or even hazardous. Lee, H. and Neville, K., Handbook of Epoxy Resins, pp. 7-14 describes  the use of certain amine-containing compounds as epoxy curing agent-accelerators. 
     Many accelerators are known in the art which can be utilized in accordance with the instant invention. Examples include salts of phenols, salicyclic acids, amine salts of fatty acids, such as those disclosed in U.S. Pat. No. 2,681,901, and tertiary amines such as those disclosed in U.S. Pat. No. 2,839,480. Preferred accelerators in accordance with the instant invention are disclosed in U.S. Pat. Nos. 3,875,072 and 4,195,153. 
     It will further be realized that various conveniently employed additives can be admixed with the polyepoxide containing composition of the instant invention prior to final cure. For example, in certain instances it may be desired to add minor amounts of other polyalkyleneamine co-catalysts as herein described, or hardeners along with various other accelerators and curing agent systems well known in the art. 
     Additionally, conventional pigments, dyes, fillers, flame retarding agents and the like which are compatible; natural or synthetic resins can be added. Furthermore, although not preferred, known solvents for polyepoxide materials such as toluene, benzene, xylene, dioxane, ethylene glycol monomethyl ether and the like can be used. The compositions of the instant invention can be used as impregnants, surface coatings, encapsulating compositions, laminants and, particularly and most importantly, as adhesives for bonding metallic elements or structures permanently together. 
    
    
     The following examples illustrate the nature of the instant invention but are not intended to be limitative thereof. 
     EXAMPLE 1 
     The quantities used in preparing the samples of this invention are described in Tables I and II. The procedure used for condensing hydantoin with formaldehyde and JEFFAMINE® D-400 amine is described below. This procedure is typical of that used to make the other Mannich condensates. 
     To a 250 ml, three-necked flask equipped with a stirrer, thermometer and dropping funnel were added 20 g of hydantoin (0.2 moles) and 80 g of JEFFAMINE D-400 amine (0.2 moles). Then 16.2 g of 37% formalin was added, keeping the temperature at 26° to 30° C. The contents were heated to 90° C. and stirred for about 2.5 hours at 90° C. The mixture was then heated to 110°-114° C. to remove most of the water. The last traces of water were removed at 5 mm pressure and 90° C. to give 101.7 g of yellow liquid. 
     
                                           TABLE I                                 
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Effect of Molar Ratios on the                                             
Reaction of Hydantoin, Formalin and Amines                                
Hydantoin  Formalin                                                       
                   JEFFAMINE ® Product                                
No.                                                                       
   Grams                                                                  
       Moles                                                              
           Grams                                                          
               Moles                                                      
                   or Amine Grams/Moles                                   
                                   Wt, g                                  
__________________________________________________________________________
1  20  0.2 32.4                                                           
               0.4 D-400    160                                           
                               0.4 183.8                                  
2  20  0.2 16.2                                                           
               0.2 D-400     80                                           
                               0.2 101.7                                  
3  20  0.2 16.2                                                           
               0.2 DPTA     26.2                                          
                               0.2  44.5                                  
4  20  0.2 16.2                                                           
               0.2 2,4-diamino                                            
                            23.2                                          
                               0.2  42.5                                  
                   2-Methyl-                                              
                   pentane                                                
5  40  0.4 32.4                                                           
               0.2 ED-600   240                                           
                               0.4 284.5                                  
6  50  0.5 40.5                                                           
               0.5 DETA     46.5                                          
                               0.5 102.6                                  
7  50  0.5 41.0                                                           
               0.5 D-2000   500                                           
                                0.25                                      
                                   551.1                                  
8  20  0.2 32.4                                                           
               0.4 D-400    160                                           
                               0.4 183.8                                  
9  20  0.2 16.2                                                           
               0.2 D-400     80                                           
                               0.2 101.7                                  
10 40  0.4 32.4                                                           
               0.4 ED-600   240                                           
                               0.4 184.5                                  
11 50  0.5 40.5                                                           
               0.5 DETA     46.5                                          
                               0.5 102.6                                  
12 50  0.5 41.0                                                           
               0.5 D-2000   500                                           
                                0.25                                      
                                   551.1                                  
13 100 1.0 91.0                                                           
               1.0 D-400    200                                           
                               0.5 309.9                                  
14 30  0.3 24.3                                                           
               0.3 T-403    40.3                                          
                               0.1  70.9                                  
15 20  0.2 16.2                                                           
               0.2 M-360     72                                           
                               0.2  93.9                                  
16 60  0.6 49.0                                                           
               0.6 D-230     70                                           
                               0.3 134.5                                  
17 60  0.6 49  0.6 Isophorone                                             
                            221                                           
                               1.2 288.5                                  
                   diamine                                                
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Product Appearance                                                        
1 Fluid, clear gold color.                                                
2 Yellow turbid liquid.                                                   
3 Brittle red-orange solid at room temp. Very difficult to get out of     
  flask.                                                                  
4 Burnt orange - turbid brittle solids at room temp.                      
5 Clear, gold colored liquid, warm.                                       
6 Dark cherry-red solid at room temp. Very viscous even at 90° C.  
7 Gold turbid viscous liquid at room temp. Still has small suspended      
  solids.                                                                 
8 Fluid clear gold color.                                                 
9 Yellow turbid liquid.                                                   
10                                                                        
  Clear, gold colored liquid.                                             
11                                                                        
  Dark cherry-red soid at room temp. Very viscous even at 90° C.   
12                                                                        
  Gold, turbid viscous at room temp. with small suspended solids.         
13                                                                        
  Solid - burnt orange turbid color.                                      
14                                                                        
  Brown solid.                                                            
15                                                                        
  Yellow liquid with some turbidity.                                      
16                                                                        
  Dark, crystalline solid.                                                
17                                                                        
  Clear, orange solid                                                     
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 NOTE: Products 3, 4, 6, 11 and 17 are shown for comparative purposes only
 
    
     
                                           TABLE II                                
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Effect of Molar Ratios on the                                             
Reaction of 5,5-Dimethylhydantoin, Formalin and Amines                    
Dimethyl-                                                                 
hydantoin  Formalin                                                       
                   JEFFAMINE ® Product                                
No.                                                                       
   Grams                                                                  
       Moles                                                              
           Grams                                                          
               Moles                                                      
                   or Amine Grams/Moles                                   
                                   Wt, g                                  
__________________________________________________________________________
1  64.0                                                                   
       0.5 41.0                                                           
               0.5 D-400    200                                           
                               0.5 269.4                                  
2  25.7                                                                   
       0.2 32.4                                                           
               0.9 Isophorone                                             
                            73.6                                          
                               0.4 101.5                                  
                   diamine                                                
3  32.0                                                                   
        0.25                                                              
           21.0                                                           
                0.25                                                      
                   D-2000   500                                           
                                0.25                                      
                                   534.0                                  
4  64.0                                                                   
       0.5 41.0                                                           
               0.5 T-403    200                                           
                               0.5 269.0                                  
5  128 1.0 162 2.0 D-400    200                                           
                               0.5 276.4                                  
6  64.0                                                                   
       0.5 41.0                                                           
               0.5 M-360    180                                           
                               0.5 249.1                                  
7  64.0                                                                   
       0.5 41.0                                                           
               0.5 D-2000   500                                           
                                0.25                                      
                                   568.8                                  
8  64.0                                                                   
       0.5 41.0                                                           
               0.5 ED-600   150                                           
                                0.25                                      
                                   219.9                                  
9  64.0                                                                   
       0.5 41.0                                                           
               0.5 T-403     67    130.9                                  
10 64.0                                                                   
       0.5 4.10                                                           
               0.5 N--butylamine                                          
                             37                                           
                               0.5                                        
11 38.4                                                                   
       0.3 24.3                                                           
               0.3 T-5000   500                                           
                               0.1 541.4                                  
12 51.0                                                                   
       0.4 32.4                                                           
               0.4 Isophorone                                             
                            36.8                                          
                               0.2  90.7                                  
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Product Appearance                                                        
1 Nice light yellow color.                                                
2 Clear, pale yellow - solid at room temp. Not real soluble in water,     
  acetone -                                                               
  also tacky or sticky.                                                   
3 Clear, gold color. fluid when warm.                                     
4 Clear, yellow green liquid.                                             
5 Clear, amber liquid.                                                    
6 Clear, light yellow fluid at room temp.                                 
7 Clear, amber, slightly viscous product.                                 
8 Clear, amber, viscous liquid.                                           
9 Clear, amber brittle solid at room temp.                                
10                                                                        
  Nonpourable solid at room temp.                                         
11                                                                        
  Clear, light yellow, viscous but pourable.                              
12                                                                        
  Amber, brittle solid.                                                   
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 NOTE: Products 2, 10 and 12 are given for comparative purposes.          
 
    
     
         ______________________________________                                    
Properties of an Epoxy Resin System Cured With                            
Amine.Hydantoin.Formaldehyde Condensates                                  
Formulation            A        B                                         
______________________________________                                    
Liquid epoxy resin.sup.1                                                  
                       100      100                                       
JEFFAMINE ® D-400.Hydantoin.CH.sub.2 O                                
                        54       --                                       
Cond..sup.2                                                               
JEFFAMINE ® D-400.Hydantoin.CH.sub.2 O                                
                        --       52                                       
Cond..sup.3                                                               
Properties of Cured 1/8 in Castings.sup.4                                 
Izod impact strength, ft-lbs/in                                           
                       0.16     0.15                                      
Tensile strength, psi  9050      --                                       
Tensile modulus, psi   437000    --                                       
Elongation at break, % 9.0      1.5                                       
Flexural strength, psi 13600    15500                                     
Flexural modulus, psi  477000   495000                                    
HDT, °C., 264 psi/66 psi                                           
                       54/56    57/60                                     
Shore D hardness, 0-10 sec                                                
                       76-73    77-75                                     
% weight gain, 24 hour water boil                                         
                       5.4      6.6                                       
% weight gain, 3 hour acetone boil                                        
                       23.5     18.1                                      
Compression yield strength, psi                                           
                       10950     --                                       
Compression strength at failure, psi                                      
                       35400    11700                                     
Adhesive Properties                                                       
Tensile shear strength, psi                                               
                        --      3650                                      
T-peel strength, pli    --      4.9                                       
______________________________________                                    
 .sup.1 Epoxy equivalent weight ˜185.                               
 .sup.2 See Table I, No. 2.                                               
 .sup.3 See Table I, No. 13.                                              
 .sup.4 Cured 2 hours at 100° C., 3 hours at 150° C.        
 
    
     
         __________________________________________________________________________
Amine.Hydantoin.Formaldehyde Condensate                                   
Formulations With Epoxy Resin                                             
                        Formulation                                       
Component, pbw          A  B  C  D  E                                     
__________________________________________________________________________
Liquid epoxy resin      100                                               
                           100                                            
                              100                                         
                                 100                                      
                                    100                                   
JEFFAMINE ® D-400.Hydantoin.CH.sub.2 O Cond.                          
mole ratio = 1.0· 1.0· 1.0, #2, Table                   
                         54                                               
                           -- -- -- --                                    
mole ratio = 1.0· 2.0· 2.0, #13, Table                  
                        --  52                                            
                              -- -- --                                    
2,4-Diamino-2-Me--pentane.Hydantoin.                                      
                        -- --  .sup. 46.sup.1                             
                                 -- --                                    
CH.sub.2 O Condensate                                                     
Diethylenetriamine.Hydantoin.CH.sub.2 O Cond.                             
                        -- -- --  .sup. 46.sup.1                          
                                    --                                    
JEFFAMINE ® T-403.Hydantoin.CH.sub. 2 O Cond.                         
                        -- -- -- --  .sup. 44.sup.1                       
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 .sup.1 50% solution in isopropanol.                                      
 
    
     
         ______________________________________                                    
Curing Characteristics of Amine.Hydantoin.Formaldehyde                    
Condensates                                                               
           Onset Temp., Peak Temp.,                                       
                                   Tg.,                                   
Formulation No..sup.1                                                     
           °C.   °C. °C.                             
______________________________________                                    
A           94.0        145.1      69.4                                   
B          126.3        146.5      83.8                                   
C          131.6        163.4      112.5                                  
D          174.5        206.2      112.6                                  
E          161.7        205.1      59.2                                   
______________________________________                                    
 .sup.1 From Example 3.                                                   
 
    
     GLOSSARY 
     JEFFAMINE® D-400 
     a polyoxyalkylene diamine of about 400 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE T-403 
     a polyoxyalkylene triamine of about 400 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE D-230 
     a polyoxyalkylene diamine of about 230 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE M-360 
     a polyoxyalkylene monoamine of about 360 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE ED-600 
     a water soluble polyoxyalkylene diamine of about 600 molecular weight. A product of Texaco Chemical Co. 
     EPON® 828 
     liquid epoxy resin--a diglycidyl ether of Bisphenol A of EEW˜185. EEW is epoxy equivalent weight. 
     JEFFAMINE T-5000 
     a polyoxyalkylene triamine of about 5000 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE ED-900 
     a water soluble polyoxyalkylene diamine of about 900 molecular weight. A product of Texaco Chemical Co. 
     JEFFAMINE D-2000 
     a polyoxyalkylene diamine of about 2000 molecular weight. A product of Texaco Chemical Co. 
     DPTA 
     Dipropylenetriamine: ##STR6## DETA Diethylenetriamine: 
     NH 2  CH 2  CH 2  NH--CH 2  CH 2  NH 2