Abstract:
A hydrophilic tetramethylxylylenecarbodiimide represented by the following formula (1): ##STR1## wherein n is an average polymerization degree and is an integer of 1 to 30; R 1  is a residue of an organic compound having a hydrophilic segment and at least one functional group reactive with an isocyanate group; and X is a group formed by the reaction of the functional group with the isocyanate group. The carbodiimide is free from the problems of the prior art, has good storage stability and accordingly is usable as an easy-to-handle crosslinking agent for hydrophilic resin.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a novel hydrophilic carbodiimide. More particularly, the present invention relates to a hydrophilic carbodiimide having good storage stability owing to the reduced reactivity and accordingly usable as an easy-to-handle crosslinking agent for hydrophilic resin. 
     2. Description of the Prior Art 
     Carbodiimides, particularly polycarbodiimides, are known as a thermosetting resin having high heat resistance and find applications in molded materials, etc. obtained, for example, by hot-pressing a powdery polycarbodiimide. 
     Of the polycarbodiimides, aromatic polycarbodiimides have hitherto been used mainly. Recently, however, production and application of aliphatic polycarbodiimides were reported. For example, Japanese Patent Application Kokai (Laid-Open) No. 187029/1984 and Japanese Patent Publication No. 27450/1993 disclose a polycarbodiimide derived from isophorone diisocyanate and a method for crosslinking a resin for aqueous coating with said polycarbodiimide. 
     The above crosslinking of resin for aqueous coating utilizes a reaction between the carbodiimide group of polycarbodiimide and the active hydrogen of active-hydrogen compound. The reaction includes, for example, one between carbodiimide group and a carboxylic acid residue present in hydrophilic acrylic resin. 
     Conventional aliphatic polycarbodiimides (e.g. a polycarbodiimide derived from isophorone diisocyanate), however, are highly reactive. Therefore, they give rise to a reaction even after their addition to a resin for aqueous coating, providing a coating of poor storage stability and short shelf life. 
     Further, conventional aliphatic polycarbodiimides, when added to a resin for aqueous coating, etc., must be emulsified beforehand together with a surfactant, mechanically by the use of an expensive high-shear mixer, making complicated the emulsification operation. Moreover, conventional aliphatic polycarbodiimides, when emulsified, inevitably generate urea owing to the reaction with water, making short the storage stability of the emulsion. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The present invention aims at providing a hydrophilic carbodiimide which is free from the problems of the prior art and which has good storage stability and accordingly is usable as an easy-to-handle crosslinking agent for hydrophilic resin. 
     According to the present invention there is provided a hydrophilic tetramethylxylylenecarbodiimide represented by the following general formula (1): ##STR2## (wherein n is an average polymerization degree and is an integer of 1 to 30; R 1  is a residue of an organic compound having a hydrophilic segment and at least one functional group reactive with an isocyanate group; and X is a group formed by the reaction of said functional group with said isocyanate group). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is hereinafter described in detail. 
     The hydrophilic carbodiimide of the present invention is represented by the above general formula (1) and is synthesized from (a) an isocyanate-terminated tetramethylxylylenecarbodiimide obtained from, for example, m-tetramethylxylylene diisocyanate ##STR3## or p-tetramethylxylylene diisocyanate ##STR4## and (b) an organic compound having a hydrophilic segment and at least one functional group reactive with an isocyanate group (said organic compound is hereinafter abbreviated as hydrophilic segment compound). 
     In the above general formula (1), n is an integer of 1--30 and is an average polymerization degree of the hydrophilic carbodiimide of the present invention. As easily appreciated from the formula, the present carbodiimide has stereoisomers. 
     The present hydrophilic carbodiimide can be produced specifically by subjecting tetramethylxylylene diisocyanate to a condensation reaction (carbon dioxide removal takes place in the reaction) to synthesize an isocyanate-terminated tetramethylxylylenecarbodiimide and then reacting it with a hydrophilic segment compound. 
     The above production of isocyanate-terminated tetramethylxylylenecarbodiimide can be conducted basically by conventional processes for production of polycarbodiimide  U.S. Pat. No. 2,941,956; Japanese Patent Publication No. 33279/1972; J. Org. Chem., 28, 2069-2076 (1963); Chemical Review 1981, Vol. 81, No. 4, pp. 619-621!. 
     The above condensation reaction of tetramethylxylylene diisocyanate wherein carbon dioxide removal takes place, proceeds in the presence of a carbodiimidization catalyst. The catalyst includes, for example, 1-phenyl-2-phospholene-1-oxide, 3-methyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene-1-oxide, 3-methyl-l-phenyl-2-phospholene-1-oxide and 3-phospholene isomers thereof. Of these, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferred in view of the reactivity. 
     The temperature of the above condensation reaction is preferably about 80°-180° C. When the temperature is lower than 80° C., the reaction time is very long. When the temperature is higher than 180° C., side reactions take place, making it difficult to obtain a carbodiimide of good quality. 
     The condensation degree obtained is preferably 30 or less. A condensation degree higher than 30 results in lower water dispersibility. In order to complete the condensation reaction quickly, the reaction of tetramethylxylylene diisocyanate is conducted in a stream of an inert gas such as nitrogen or the like. 
     As the hydrophilic segment compound, there can be used various compounds. They include, for example, a dialkylamino-alcohol represented by the following general formula: 
     
         (R.sub.2).sub.2 --N--R.sub.3 --OH 
    
     (wherein R 2  is a lower alkyl group of, for example, 1-4 carbon atoms; and R 3  is an alkylene or oxyalkylene of, for example, 1-10 carbon atoms). Specific examples of the dialkylamino-alcohol are 2-dimethylaminoethanol, 2-diethylaminoethanol, 3-methylamino-1-propanol, 3-diethylamino-1-propanol, 1-diethyl-amino-2-propanol, 5-diethylamino-2-propanol and 2-(di-n-butyl-amino)ethanol. 2-Dimethylaminoethanol is particularly preferred. 
     The reaction product between isocyanate-terminated tetramethylxylylenecarbodiimide and dialkylaminoalcohol is quaternized with a known quaternizing agent such as dimethyl sulfate, methyl p-toluenesulfonate or the like, whereby an intended hydrophilic tetramethylxylylenecarbodiimide can be obtained. 
     When the dialkylaminoalcohol is used as the hydrophilic segment compound, the resulting hydrophilic tetramethylxylylene-carbodiimide of the present invention has the following molecular structure and is a cationic type. In the following formula, R&#39; is a group derived from the quaternizing agent used. ##STR5## 
     The hydrophilic segment compound also includes a salt of an alkylsulfonic acid having at least one reactive hydroxyl group, said salt being represented by the following general formula: 
     
         R.sub.5 --SO.sub.3 --R.sub.4 --OH 
    
     (wherein R 4  is an alkylene of 1-10 carbon atoms; and R 5  is an alkali metal). Specific examples of the alkylsulfonic acid salt are sodium hydroxyethanesulfonate and sodium hydroxypropane-sulfonate. Sodium hydroxypropanesulfonate is preferred particularly. 
     When the salt of an alkylsulfonic acid having at least one reactive hydroxyl group is used as the hydrophilic segment compound, the resulting hydrophilic tetramethylxylylenecarbodiimide of the present invention has the following molecular structure and is an anionic type. ##STR6## 
     The hydrophilic segment compound also includes a poly(alkylene oxide) having at least one reactive hydroxyl group, blocked with an alkoxyl group at one end, said poly (alkylene oxide) being represented by the following general formula: 
     
         R.sub.6 --O--(CH.sub.2 --CHR.sub.7 --O--).sub.m H 
    
     (wherein m is an integer of 4-30; R 6  is a lower alkyl group of, for example, 1-4 carbon atoms; and R 7  is a hydrogen atom or a methyl group). Specific examples of the poly(alkylene oxide) are poly(ethylene oxide) monomethyl ether, poly(ethylene oxide) monoethyl ether, poly(ethylene oxide-propylene oxide) monomethyl ether and poly(ethylene oxide-propylene oxide) monoethyl ether. Poly(ethylene oxide) monomethyl ether is preferred particularly. 
     When the poly(alkylene oxide) having at least one reactive hydroxyl group, blocked with an alkoxyl group at one end is used as the hydrophilic segment compound, the resulting hydrophilic tetramethylxylylenecarbodiimide of the present invention has the following molecular structure and is a nonionic type. ##STR7## 
     The hydrophilic segment compound also includes a dialkylaminoalkylamine represented by the following general formula: 
     
         (R.sub.8).sub.2 --N--R.sub.9 --NH.sub.2 
    
     (wherein R 8  is a lower alkyl group of, for example, 1-4 carbon atoms; and R 9  is an alkylene or oxyalkylene of, for example, 1-10 carbon atoms). Specific examples of the dialkylaminoalkylamine are 3-dimethylamino-n-propylamine, 3-diethylamino-n-propylamine and 2-diethylamino-ethylamine. 3-Dimethylamino-n-propylamine is preferred particularly. 
     The reaction product between isocyanate-terminated tetramethylxylylenecarbodiimide and dialkylaminoalkylamine is quaternized with a known quaternizing agent such as dimethyl sulfate, methyl p-toluenesulfonate or the like, whereby an intended hydrophilic tetramethylxylylenecarbodiimide can be obtained. 
     When the dialkylaminoalkylamine is used as the hydrophilic segment compound, the resulting hydrophilic tetramethylxylylenecarbodiimide of the present invention has the following molecular structure and is a cationic type. In the following formula, R&#34; is a group derived from the quaternizing agent. ##STR8## The above addition reaction between isocyante terminated tetramethylxylylenecarbodiimide and hydrophilic segment compound may use a catalyst but proceeds easily only by heating. The reaction temperature can be about 60°-40° C., preferably about 80°-120° C. When the reaction temperature is lower than about 60° C., the reaction time is very long. When the reaction temperature is higher than about 140° C., side reactions take place, making it impossible to obtain a hydrophilic carbodiimide of good quality. 
     The quaternization reaction of the addition product between isocyanate-terminated tetramethylxylylenecarbodiimide and hydrophilic segment compound (dialkylaminoalcohol or dialkylaminoalkylamine), with the quaternizing agent can be conducted by reacting said addition product with an equivalent amount of a quaternizing agent. 
     The hydrophilic tetramethylxylylenecarbodiimide produced as above can be used in various forms. When it is added to an aqueous coating, etc., it may be added as it is, but it is preferably added in the form of an aqueous solution or dispersion in view of easier mixing. In the present invention, the term &#34;hydrophilic&#34; used for tetramethylxylylenecarbodiimide refers to that the tetramethylxylylenecarbodiimide is water-soluble or self-emulsifiable in water and is uniformly compatible with water. 
     Appropriate selection of the hydrophilic segment compound allows for production of any of three kinds (cationic type, anionic type and nonionic type) of hydrophilic tetramethylxylylenecarbodiimides. Therefore, it is possible to provide any hydrophilic carbodiimide suited for the ionicity of a hydrophilic resin to which said carbodiimide is to be added. 
     The present invention is hereinafter described in more detail with reference to Examples. 
     (Synthesis of hydrophilic tetramethylxylylenecarbodiimides) 
     EXAMPLE 1 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 18 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=4). 50.2 g of the carbodiimide was reacted with 8.9 g. of 2-dimethylaminoethanol at 80° C. for 24 hours. Thereto was added 18.6 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 77.7 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 2 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 18 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=4). 50.2 g of the carbodiimide was reacted with 10.2 g of 3-dimethylamino-n-propyl-amine at 80° C. for 1 hour. Thereto was added 18.6 g of methyl-p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 79 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 3 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 52.7 g of the carbodiimide was reacted with 5.1 g of 3-dimethylamino-n-propylamine at 80° C. for 1 hour. Thereto was added 9.3 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 67.1 g of distilled water so as to give a resin concentration of 50% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 4 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 18 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=4). 210.5 g of the carbodiimide was reacted with 40.9 g of 3-dimethylamino-n-propylamine at 80° C. for 1 hour. Thereto was added 50.5 g of dimethyl sulfate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 301.9 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 5 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 105.3 g of the carbodiimide was reacted with 10.2 g of 3-dimethylamino-n-propylamine at 80° C. for 1 hour. Thereto was added 12.6 g of dimethyl sulfate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 128.1 g of distilled water so as to give a resin concentration of 50% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 6 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 224.4 g of the carbodiimide was reacted with 41.2 g of sodium hydroxypropanesulfonate at 100° C. for 24 hours. Thereto was slowly added, at 80° C., 619.7 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 7 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 22 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=5). 124.4 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 282.0 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 8 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 22 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=5). 124.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100° C. for 48 hours. Thereto was slowly added, at 50° C. 359.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 9 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 224.4 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 432 g of distilled water so as to give a resin concentration of 40% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 10 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 224.4 g of the carbodiimide was reacted with 82.6 g of poly(oxyethylene) monomethylether having a polymerization degree (m) of about 8 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 716.3 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 11 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 32 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=10). 224.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 509.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 12 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 58 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=15). 324.4 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 659.1 g of distilled water so as to give a resin concentration of 40% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     EXAMPLE 13 
     700 g of m-tetramethylxylylene diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 58 hours to obtain an isocyanate-terminated tetramethylxylylenecarbodiimide (polymerization degree=15). 324.4 g of the carbodiimide was reacted with 160.2 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 18 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 726.9 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C. for 12 months, showed neither separation nor precipitation and was very stable. 
     Comparative Example 1 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 6 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=4). 93.4 g of the carbodiimide was reacted with 17.8 g of 2-dimethylaminoethanol at 80° C. for 24 hours. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 148.4 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., became cloudy and showed separation in 3 months. 
     Comparative Example 2 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 6 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=4). 93.4 g of the carbodiimide was reacted with 20.4 g of 3-dimethylamine-n-propylamine at 80° C. for 1 hour. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 151 g of distilled water so as to give a resin concentration of 50% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., became cloudy and showed separation in 3 months. 
     Comparative Example 3 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=10). 200.2 g of the carbodiimide was reacted with 20.4 g of 3-dimethylamine-n-propylamine at 80° C. for 1 hour. Thereto was added 37.2 g of methyl p-toluenesulfonate, followed by stirring for 1 hour to conduct quaternization. Thereto was slowly added 257.8 g of distilled water so as to give a resin concentration of 50% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., showed separation in 2 months. 
     Comparative Example 4 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=10). 200.2 g of the carbodiimide was reacted with 41.2 g of sodium hydroxypropanesulfonate at 100° C. for 24 hours. Thereto was slowly added, at 80° C., 563.3 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., showed separation in 2 months. 
     Comparative Example 5 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 8 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=5). 111.2 g of the carbodiimide was reacted with 63.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 6 at 100° C. for 24 hours. Thereto was slowly added, at 50° C., 262.2 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., became cloudy and showed separation in 4 months. 
     Comparative Example 6 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=10). 200.2 g of the carbodiimide was reacted with 82.6 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 8 at 100° C. for 48 hours. Thereto was slowly added, at 50° C., 660 g of distilled water so as to give a resin concentration of 30% by weight, to obtain an emulsion-like carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., showed separation in 2 months. 
     Comparative Example 7 
     700 g of isophorone diisocyanate was reacted with 14 g of a carbodiimidization catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) at 180° C. for 14 hours to obtain an isocyanate-terminated isophoronecarbodiimide (polymerization degree=10). 200.2 g of the carbodiimide was reacted with 115.0 g of poly(oxyethylene) monomethyl ether having a polymerization degree (m) of about 12 at 100° C. for 24 hours. Thereto was slowly added, at 50° C., 472.8 g of distilled water so as to give a resin concentration of 40% by weight, to obtain a yellow transparent carbodiimide solution. The solution, when stored in a constant-temperature chamber of 25° C., became cloudy and showed separation in 4 months. 
     The results of syntheses in Examples 1-13 and Comparative Examples 1-7 are shown in Tables 1-1 and 1-2. As is clear from Tables 1-1 and 1-2, the hydrophilic tetramethylxylylenecarbodiimides of Examples 1-13 according to the present invention are superior in storage stability to the hydrophilic isophoronecarbodiimides of Comparative Examples 1-7. 
     
                                           TABLE 1-1__________________________________________________________________________Number                            Concent-of                         Appearance of                             ration ofcarbodi- Hydrophilic segment                      aqueous solu-                             aqueousimide    compound     Ionicity                      tion   solution                                  stability__________________________________________________________________________Example 14   Quaternary salt of                 Cationic                      Transparent                             50%  No change after 12    2-dimethyl-aminoethanol       months2    4   Quaternary salt of 3-di-                 Cationic                      Transparent                             50%  Same as above    methylamino-n-propyl-amine3    10  Same as above                 Cationic                      Emulsion-like                             50%  Same as above4    4   Same as above                 Cationic                      Transparent                             50%  Same as above5    10  Same as above                 Cationic                      Emulsion-like                             50%  Same as above6    10  Sodium hydroxy-                 Anionic                      Emulsion-like                             30%  Same as above    propanesulfonate7    5   Polyoxyethylene monomethyl                 Nonionic                      Transparent                             40%  Same as above    ether (m = about 6)8    5   Polyoxyethylene monomethyl                 Nonionic                      Transparent                             40%  Same as above    ether (m = about 12)9    10  Polyoxyethylene monomethyl                 Nonionic                      Emulsion-like                             40%  Same as above    ether (m = about 6)10   10  Polyoxethylene monomethyl                 Nonionic                      Emulsion-like                             30%  Same as above    ether (m = about 8)11   10  Polyoxyethylene monomethyl                 Nonionic                      Transparent                             40%  Same as above    ether (m = about 12)12   15  Same as above                 Nonionic                      Emulsion-like                             40%  Same as above13   15  Polyoxyethylene monomethyl                 Nonionic                      Transparent                             40%  Same as above    ether (m = about 18)__________________________________________________________________________ 
    
     
                                           TABLE 1-2__________________________________________________________________________Number                             Concent-of                          Appearance of                              ration ofcarbodi-  Hydrophilic segment                       aqueous solu-                              aqueousimide     compound     Ionicity                       tion   solution                                   stability__________________________________________________________________________Comparative 4   Quaternary salt of                  Cationic                       Transparent                              50%  Became cloudy andExample 1 2-dimethyl-aminoethanol       showed separation                                   in 3 months2     4   Quaternary salt of 3-di-                  Cationic                       Transparent                              50%  Same as above     methylamino-n-propylamine3     10  Same as above                  Cationic                       Emulsion-like                              50%  Showed separation                                   in 2 months4     10  Sodium hydroxypropane-                  Anionic                       Emulsion-like                              30%  Same as above     sulfonate5     5   polyoxyethylene monomethyl                  Nonionic                       Transparent                              40%  Became cloudy and     ether (m = about 6)           showed separation                                   in 4 months6     10  polyoxyethylene monomethyl                  Nonionic                       Emulsion-like                              30%  Showed separation     ether (m = about 8)           in 2 months7     10  polyoxyethylene monomethyl                  Nonionic                       Transparent                              40%  Became cloudy and     ether (m = about 12)          showed separation                                   in 4 months__________________________________________________________________________ 
    
     Reference Example 
     (Reactions between hydrophilic tetramethylxylylenecarbodiimides and aqueous resins) 
     Each of the aqueous carbodiimide solutions obtained in Examples 7, 10, and 11 and Comparative Examples 5, 6 and 7 was added to a solution of a styrene-acrylic resin of acid value=300 (solvent in solution: water/alcohol=95/5, resin concentration in solution=30% by weight) so that the carbodiimide group and the carboxyl group became 1:1 in equivalent. Each of the resulting mixtures was measured for viscosity change at 25° C. Further, each mixture was coated on a polyethylene terephthalate film by the use of an applicator so that the resulting film had a thickness of 100 μm; the film was dried at 80° C. for 5 minutes; and the dried film was cut into a piece of 5 cm×5 cm and immersed in 300 ml of distilled water for 24 hours to observe the change of the film condition. 
     The results of the above test are shown in Table 2. 
     
                                           TABLE 2__________________________________________________________________________ Weight of      Weight of           Mixture                Mixture                     Mixture                          Appearance of                                 Appearance ofKind of carbodi-      styrene-           viscosity                viscosity                     viscosity                          film before                                 film after 24carbodiimide imide      acrylic           right af-ter                after 3                     after 1                          immersion in                                 hours immersionsolution solution      resin           mixing                days week water  in water__________________________________________________________________________Example 7 45.7 g      30 g 181 cp                215 cp                     325 cp                          Transparent                                 Transparent                                 (no Change)10    49.7 g      30 g 170 cp                228 cp                     380 cp                          Transparent                                 Transparent                                 (no Change)11    41.2 g      30 g 195 cp                235 cp                     392 cp                          Transparent                                 Transparent                                 (no Change)Comparative 42.5 g      30 g 190 cp                795 cp                     gelling                          Transparent                                 WhiteExample 5 6    45.8 g      30 g 178 cp                850 cp                     gelling                          Transparent                                 White and partial                                 peeling 7    38.3 g      30 g 206 cp                830 cp                     gelling                          Transparent                                 White__________________________________________________________________________ 
    
     As is clear from Table 2, the hydrophilic tetramethylxylylenecarbodimides of Examples 7, 10 and 11 according to the present invention are superior to the aqueous isophoronecarbodiimides of Comparative Examples 5, 6 and 7 in stability after addition to hydrophilic resin as well as in potency as crosslinking agent.