BIS-DICYANDIAMIDES AS CURING AGENTS FOR EXPOXY RESINS

Abstract: A curing agent for epoxy resins having improved solubility characteristics has formula (I). Such bis-dicyandiamides are soluble in various solvents and do not require the use of undesirable solvents necessary with dicyandiamide.

Description: BIS-DICYANDIAMIDES AS CURING AGENTS FOR EPOXY RESINS BACKGROUND OF THE INVENTION The invention relates generally to the curing of epoxy resins and, more particularly, to improvement of the curing agents used with epoxy resins. Dicyandiamide (also called cyanoguanidine) is well- known as a curing agent for epoxy resins, but it is also known to have a serious deficiency. It is only soluble in solvents which are undesirable, either because they are not usable in most applications, such as water, or because the solvents are relatively expensive and environmentally undesirable, such as dimethylformamide and the like. In U.S. Pat. No. 3,553,166 a curing agent is disclosed which combines a metal salt of an imidazole and another compound, which may be dicyandiamide. These curing agents are used in a one-part epoxy composition which is curable at elevated temperatures, but which can be stored at ambient temperature for long periods. Another combination of dicyandiamide with a second compound is found in U.S. Pat. No. 4,311,753 where dicyandiamide is combined with tetraalkyl guanidine to provide a curing agent for mixtures of di- and tetra- functional epoxides. The reaction product of dicyandiamide with formaldehyde and an amine terminated polyether may be used to cure epoxy resins, as is shown in U.S. Pat. No. 4,581,422. A somewhat similar composition is disclosed in Japanese published patent application 61-207425 which employs an epoxy hardener combining cyanoguanidine compounds, polyethera ines, and guanide compounds. Two recent published European patent applications cover certain substituted cyanoguanidines said to be useful as curing agents for epoxy resins. In EP 306,451 oligomers of substituted 3-cyanoguanidines are discussed. Such compounds are produced by the reaction of a monoisocyanate with a diisocyanate to form the oligomer, followed by reaction with cyanamide to form compounds having the formula: N-CN N-CN 1 1 II 2 R -[-NH-C-NH-R-]-NH -C-NH-R n These compounds differ from those of the present inventors in that they are oligomers and both the terminal amino groups are substituted, thus reducing the functionality of these compounds. The applicants recognized the problem discussed above which is inherent with the use of dicyandiamide, namely, the need to use objectionable solvents. The new oligomeric cyanoguanidines are said to dissolve well in suitable solvents and to produce epoxy resins having a high glass transition temperature. Another published application is EP 310,545 (U.S. Pat. No. 4,859,761) in which di-substituted cyanoguanidines having the formula: N-CN 1 II R -NH-C-NH-R are said to be useful as curing agents for epoxy resins. These substituted cyanoguanidines are prepared by reacting a di- substituted carbodiimide (R 1 -N=C=N-R 2 ) with cyanamide (NH 2 C-≡N) . As with the compounds of EP 306,451, these di-substituted cyanoguanidines are substituted at both the terminal amine groups. Substituted cyanoguanidines have also been suggeste as being useful in the preparation of polyurethanes as shown in U.S. Pat. No. 3,734,868. Related materials have also been used as precursors to various pharmaceuticals, an example of which is U.S. Pat. No. 4,560,690. U.S. Pat. No. 2,455,807 is relevant to the preferred method of preparing the bis-dicyandiamide compounds of the present invention. The reaction of dicyanamide with the desired amine is shown to produce the bis-dicyandiamide. In co-pending application USSN 07/557,445 we disclosed the use of mono-substituted cyanoguanidines of the following formula as curing agents for epoxy resins. NCN I RNH-C-NH 2 We now have found another family of curing agents for epoxy resins which are disclosed in detail below. SUMMARY OF THE INVENTION A curing agent for epoxy resins having improved solubility characteristics is found in bis- dicyandiamides having the formula: NCN NCN o ft NH -C-N-R-N-C-NH 2 I I : R»" R'" where R is CH, -O --CH 2 - 7 TT - CH 2 -;--C ) c ( •CHJ R' is sigma bond, 0, S, R" R' and R" are independently selected from -H, -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , -CH 2 CH(CH 3 ) 2 n is an integer from 2 to 12 a is 0 or an integer from 1 to 5 b is 0 or an integer from 1 to 5 c is 0 or an integer from 1 to 5 d is an integer from 1 to 4 R ,H is -H, -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , - Such bis-dicyandia ides are soluble in various solvents, preferably acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, isopropanol, acetone/methanol , acetone/ethanol, acetone/isopropanol, methyl ethyl ketone/methanol, methyl ethyl ketone/ethano1, and methyl ethyl ketone/isopropanol. In service as curing agents the substituted bis-dicyandiamides will be employed in amounts up to about 24 wt.% of the epoxy resin precursors, preferably 2 to 16 wt.%. In another aspect, the invention is a method for curing epoxy resins and the product of that method in which a reactive amount of a bis-dicyandiamides as defined above is added to an epoxy resin precursor in amounts up to about 24 wt.%, preferably 2 to 16 wt.%, and the curing carried out under curing conditions. DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been recognized that dicyandiamide (i.e. cyanoguanidine), although widely used, is an undesirable curing agent for epoxy resins, since it requires the use of objectionable solvents such as dimethylformamide and the like. If more soluble compounds could be found which provide equivalent or improved curing properties, then cyanoguanidine could be replaced and the undesirable solvents avoided. Reduced production costs from the use of less expensive solvents also could be the result of such a change in curing agents. The present inventors have found a group of bis-dicyandiamides which have significant advantages over the presently used compound. Composition of Bis-Dicyandiamides The inventors have found that bis- dicyandiamides having the formula NCN NCN 0 I NH -C-N-R-N-C-NH 2 I I 2 R'" R'" where R is R CH, I CH 3 X is sigma bond, 0, S, R* and R" are independently selected from -H, -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , -CH 2 CH(CH 3 ) 2 n is an integer from 2 to 12 a is 0 or an integer from 1 to 5 b is 0 or an integer from 1 to 5 c is 0 or an integer from 1 to 5 d is an integer from 1 to 4 R' » is -H, -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , -Q) have improved solubility over the parent compound and still retain a high curing ability so that they are effective in amounts of up to about 24 wt. percent, preferably 2 to 16 wt. percent, of the epoxy resin precursors. The bis-dicyandiamides of this invention and the di-substituted cyanoguanidines of EP 310,545 differ in the degree of reactive functionality. In order for the curing agent to react and generate a cross-linked epoxy based polymer network, the amine radicals react with the epoxide radicals. The degree of reactive functionality of the cyanoguanidine will depend on the degree of functionalization for the cyanoguanidine, which is related to the number of exchangeable nitrogen hydrogens of the cyanoguanidine. For example, dicyandiamide (cyanoguanidine) has a defined degree of functionality of four, that is, it is capable of addition to four epoxide radicals. In the case of a mono-substituted cyanoguanidine the degree of functionality is three and it is capable of reacting with three epoxide radicals. For a di-substituted cyanoguanidine as in EP 310,545 (U.S. Pat. No. 4,859,761) the degree of functionality is two, and it is capable of reacting with two epoxide radicals. The bis-dicyandiamides of the present invention have a degree of functionality of four to six. The degree of reactive functionality for the curing agent will affect the type of polymer network formed in the cured polymer system and consequently will affect the performance properties in B-Stage or a prepreg, such as the viscosity as a function of cure, the solvent resistance for the polymer, the glass transition temperature (Tg) for the polymer, and the coefficient of thermal expansion (α g ) . For example, when a curing agent with a degree of reactive functionality of two (EP 310,545/U.S. Pat. No. 4,859,761) is employed, the network will have a high degree of linear structures with only a minor degree of branching. When a curing agent with a degree of reactive functionality of three or more is employed as in the present invention, the polymer network will have a high degree of branched or star-like structures and a minimum of linear type structures. The branched or star-like structures will affect the resin flow properties (resin flow viscosity) for the B- Staged resin during lamination. If the resin flow viscosity is low then the laminates or composites formed will experience a high degree of resin flow, generating laminates or composites with voids or resin-poor products. Linear structures in the cured polymer will yield poor solvent resistance due to the solvation of the polymer fragments or swelling of the polymer. Branched or star-like structures provide improved solvent resistance due to the formation of a more highly cross-linked network. Linear structures will yield a polymer of lower Tg and may yield higher coefficient of thermal expansion than a polymer with branched structures. Solvents The parent compound, dicyandiamide, is soluble only in a small group of generally available solvents, including dimethylformamide , di ethylsulfoxide, dimethylacetamide, N-methyl-2- pyrrolidinone and methanol. The bis-dicyandiamides of the invention are soluble in a number of more desirable solvents, including acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, and isopropanol or mixed solvents such as acetone/methanol, acetone/ethanol, acetone/isopropanol, methyl ethyl ketone/methanol, methyl ethyl ketone/ethanol, methyl ethyl ketone/isopopanol, methyl isobutyl ketone/methanol, methyl isobutyl ketone/ethanol, and methyl isobutyl ketone/isopropanol, or neat epoxy resins. In particular, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetone/methanol, acetone/ethanol, acetone/isopropanol, methyl ethyl ketone/methanol, methyl ethyl ketone/ethanol, and methyl ethyl ketone/isopropanol are preferred solvents. The compounds of the invention are generally soluble in amounts up to about 20 wt.% in such solvents. In many cases the desired amount of the substituted cyanoguanidine is dissolved in enough solvent to make a solution containing about 8 to 20 wt.% of the compound and thereafter the solution is mixed with the epoxy precursors and cured under curing conditions. EPOXV Resins The bis-dicyandiamides of the invention may be used with various epoxy resin precursors known in the art. In general, these will include diglycidyl bisphenol-A (DGEBA) , diglycidyl tetrabromobis-phenol-A, triglycidyl triphenol methane, triglycidyl triphenol ethane, tetraglycidyl tetraphenolethane, tetraglycidyl methylene dianiline and oligomers and mixtures thereof. More particularly, diglycidyl bisphenol-A (DGEBA) types have been found to provide suitable results with the curing agents of the invention. Catalyst for Epoxy Resins In order to facilitate the reaction of the bis-dicyandiamides with the epoxy resin it may prove useful to employ a catalyst. There are various catalysts known in the art which can be employed. The catalysts which we believe offer distinct advantages over others will be free of transition metals. In general, the catalyst will include imidazole, 2- methylimidazole, 2-phenylimidazole, l-cyanoethyl-2- phenyli idazole, 1-(2-cyanoethyl)-2-ethyl-4- methylimidazole, 4-phenylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, benzyldimethyla ine, 4-(dimethylamino) -N r N-dimethylbenzylamine, 4- m e t h o x y - N , N - d i m e t h y l b e n z y l a m i n e , 4-methyl-N, N-dimethylbenzylamine , and the like. Preparation of Laminates An advantage of the bis-dicyandiamides of the invention is their ability to replace the dicyandiamide commonly used to cross-link epoxy resins in the preparation of reinforced laminates for the electronics industry and without requiring the use of undesirable solvents. The methods used to prepare such laminates are well known to those skilled in the art and need not be discussed in detail here in connection with the present invention since the procedures are not revised significantly to accommodate the bis-dicyandiamides of the invention. In general, it may be stated that the fabric which is to be used to reinforce the laminate, typically made of glass fibers, is coated with epoxy resins combined with the crosslinking agents and a catalyst as desired. The coated fabric is then heated in order to drive off solvents and to cure (polymerize and crosslink) the epoxy resins and the crosslinking agents. Multiple layers of coated fabric are commonly combined to provide the laminates needed for electronic circuit boards. When only a partial cure is carried out, the resulting product is often referred to as a "prepreg" or "B-stage" material. Further curing is later carried out to complete the laminate. These processes are carried out in batch or continuous processes familiar to those skilled in the art. Preparation of the Bis-dicyandiamides The curing agents of the invention may be prepared by various methods known to those skilled in the art. For example, the method of May (J. Org. Chem. , 12, 437-442, 442-445 (1947)) and Curd (J. Chem. Soc, 1630-1636 (1948)) reaction of an aryl isothiocyanate with sodium cyanamide, followed by reaction with methyl iodide to generate a N-cyano-S-methyl-N'-arylisothioureawhichupon reaction with ammonia yields a cyanoguanidine. The method of Curd (J. Chem. Soc, 729-737 (1946))) and Rose (Brit. Patent 577,843) employs the reaction of an aryl diazonium salt with dicyandiamide to yield a substituted aryl-azo-dicyandiamide or triazene which thermally decomposes to yield nitrogen and the corresponding substituted cyanoguanidine. The inventors consider the method disclosed by Redmon et al. in U.S. Pat. No. 2,455,807 to be of particular value in preparing their bis-dicyandiamides. This method may be described generically by the following reaction according to Redmon et al. R H R NH 1 1 2 \ I ■ \ I N-H + CN-N -CN —► N-C=NCN / / R R 2 2 In practice, a metal salt of dicyana ide (CN-NH-CN) preferably is used, such as sodium dicyanamide. In the present invention, a bis-dicyandiamide is made by dissolving a diamine in a suitable solvent, such as butanol, ethanol, propanol and water, or mixed with hydrochloric acid to form a slurry. Sodium dicyanamide is added in an approximately stoichiometric quantity. The reaction is carried out at temperatures between about 75* and 110'C and at pressures of atmospheric to 2068 kPa for a period of time necessary to complete the reaction. Preferably, a temperature of about 100* to 110*C will be used with the reaction time being about 2 to 24 hours. Thereafter, if used, the solvent is distilled off and the bis-dicyandiamine is recovered by crystallization and washing. If hydrochloric acid is used, the solids are filtered, washed, and then redissolved and crystallized from solution. Example 1: Synthesis of 1.3-bis (cyanoσuanidino. -2.2- dimethylpropane (DMPDICY) : 50.0 g (0.286 mol) of 2,2- dimethyl-l,3-propanediamine hydrochloride, 55.27 g (0.56 mol) of sodium dicyanamide and 30 mL of water were charged into a 500 mL three neck round bottom flask equipped with a mechanical stirrer and heating mantle. The temperature was raised to 100"C under flowing air to help remove water. After removing the water, 80 mL of butanol was added to the flask and the mixture was heated at 105*C for 17 hours. 300 L of water was added and the butanol removed via an 4 azeotropic distillation. On cooling, a tan gum precipitated. The water was decanted and the product was dissolved in methanol. This solution was rotary evaporated leaving 55.3 g (81.8%) of a pale yellow, amorphous powder. Example 2: Synthesis of 4.4 '-methylene-bisfcvanoαuanidino cvclohexane. fMCDICY. : 51.0 g (0.242 mol) of 4,4'- methylene-bis(cyclohexylamine) and 250 mL of isopropanol were charged to a 500 mL three necked flask fitted with an addition funnel, condenser, mechanical stirrer and heating mantle. The mixture was stirred until dissolution then 40.0 mL (0.484 mol) of concentrated HCl diluted with 50 L of isopropanol was added dropwise forming a white precipitate. 47.4 g (6.532 mol) of sodium dicyanamide was added and the mixture was brought to reflux. The mixture was refluxed for 4 hours and then the water was distilled azeotropically. The mixture was allowed to cool and a white precipitate formed. The solvent was removed on a rotary evaporator and water was added to leach the salt from the product. A second liquid phase that was more dense than water formed and was separated and stripped on a rotary evaporator leaving 11 g (13% yield) of a white amorphous resin. Example 3: Synthesis of 1.5-bisfcyano uanidino. -2-methylpentane fDYDICY. : 430.0 g (3.70 mol) of l,5-diamino-2- methylpentane was charged to a 2 L three neck round bottom flask fitted with a mechanical stirrer and an addition funnel. The flask was placed in an ice bath and 615 mL (7.40 mol) of concentrated HCl was added dropwise and a clear yellow solution was obtained. 658.8 g (7.40 mol) of sodium dicyanamide was added to the 30"C solution and the temperature was raised to 100*C. The mixture was placed under flowing nitrogen to help remove water and the mixture became very viscous. After five hours of heating, three liters of water and 1.5 liters of 1-pentanol were added to the flask and the mixture was allowed to cool. The aqueous phase was separated and the organic phase was washed with 2 L of 5% NaOH (aqueous) and 2 L of 5% acetic acid (aqueous) . The organic phase was dried over sodium sul ate and rotary evaporated leaving a yellow, glass¬ like resin. The yield was 662 g (71.4%). Elemental analysis. Found C 48.48%, H 7.78%, N 39.80%, Calculated C 47.97%, H 7.26%, N 44.77%. Example 4: Synthesis of α.c-'-bis.cyanoquanidino. -1.3-xylylene fXYDICYϊ : 103.2 g (0.758 mol) of 1,3-xylylene diamine and 800 mL of butanol were charged into a 2000 mL three neck round bottom flask equipped with a condenser, addition funnel, mechanical stirrer and heating mantle. 47.3 mL (0.849 mol) of concentrated sulfuric acid diluted with 200 L of butanol was added to the flask dropwise. 158.7 g (1.78 mol) of sodium dicyanamide and 35 mL of water were then added and the mixture heated to 100*C. A flow of nitrogen was begun to aid in the removal of water. After two hours the temperature was raised to 110*C and 35 additional mL of water was added. This temperature was maintained for six hours. 1.5 L of water was added and the butanol was removed via an azeotropic distillation. On cooling, a white solid precipitated and was collected on a Buchner funnel. The solid was washed with 400 mL of 5% NaOH (aqueous), 400 mL of 5% acetic acid and 1.5 L of hot ethanol. 49 g (24% yield) of a fine white powder was collected m.p. 204-207 C. Elemental analysis. Found C 53.88%, H 5.72%, N 40.19%, Calculated C 53.31%, H 5.23%, N 41.46%. Example 5: Synthesis of 1.6-bis(cyanoquanidino. hexane .DAHDICY. : 50.0 g (0.264 mol) of 1,6-hexanediamine hydrochloride, 51.7 g (0.581 mol) of sodium dicyanamide and 30 L of water were charged to a 250 L three neck round bottom flask equipped with a nitrogen inlet, mechanical stirrer and heating mantle. The temperature was gradually raised to 100"C under flowing nitrogen and the water was removed. 75 mL of butanol was then added and the temperature maintained at 100*C for six hours. The mixture was cooled and the white solid collected and recrystallized from aqueous ethanol. 38 g (57% yield) of product with a melting range of 177-190*C was collected. Elemental analysis, Found C 47.98%, H 7.75%, N 41.88%, Calculated C 47.97%, H 7.26%, N 44.77%. Example 6: Synthesis of 1.2 bisfl-phenyl-3-cyanoσuanidino. ethane .DIANEDICY. : 23.58 g (0.238 mol) of sodium dicyanamide in 35 mL of water was charged to a 250 L three neck round bottom flask equipped with a mechanical stirrer, condenser, addition funnel, thermometer, and nitrogen purge. To this reaction was added 25.3 g (0.119 mol) of 1,2-dianilino ethane and the mixture heated to 80* C with mixing. 19.6 mL of concentrated hydrochloric acid was diluted with 20 mL of water and added to the heated mixture over 30 minutes. The mixture was heated an additional hour and a precipitate began to form. The mixture was allowed to cool, the water was decanted and the resinous precipitate taken up in acetone. The solution was filtered to remove insoluble materials, and then dried and the acetone removed by rotary evaporation leaving 25 g (60.6% of theoretical) of a brown solid. Elemental analysis, Found C 66.88%, H 6.82%, N 24.24%, Calculated C 62.4%, H 5.2%, N 32.4%. Example 7: Synthesis of 1.4 bis,l-phenyl-3-cvanocruanidino) benzene .DIPPDICY) : 19.83 g (0.200 mol) of sodium dicyanamide dissolved in 35 mL of water was charged to a 250 mL round bottom three neck flask equipped with a mechanical stirrer, condenser, addition funnel, thermometer, and nitrogen purge. To this reaction mixture was added 26.1 g (0.100 mol) of N,N'-diphenyl- 1,4-phenylene dia ine and the mixture heated to 80° C with stirring. 16.5 mL of concentrated hydrochloric acid was diluted with 20 L of water and added to the heated mixture over 30 minutes. The mixture was stirred at temperature for an additional hour and a grey solid began to precipitate. The mixture was cooled and filtered and the solid was mixed with acetone and filtered. The acetone solution was dried and stripped on a rotary evaporator leaving 24 g (60.8% of theoretical) of a grey powder. Elemental analysis, Found C 80.95%, H 6.38%, N 11.53%. Calculated C 67.0%, H 4.6%, N 28.4%. Example 8: Solubility testing for all bis-dicyandiamide derivatives and the unsubstituted parent compound (DICY) were conducted by using a weight ratio of dicyandiamide to solvent of 1:10. For example, to 0.1 grams of the substituted dicyandiamide was added 1.0 gram of solvent. The sample was agitated slightly and dissolution recorded at 25"C; complete dissolution receives a rating of +, partial dissolution is +5, and no dissolution is rated as -. The sample was then heated to 50°C for 30 minutes and the solubility recorded using the same rating system. TABLE 1 Experimental Solubility for Substituted Bis-Dicyandi amides Solvent Substituted Bis-Dic andi amide 10 0 15 20 25 NT = not tested TABLE 2 Experimental Solubility for Substituted Bis-Dicyandi amides Solvent Substituted Bis-Dic andi amide 10 15 20 25 Example 9: Part A: 2.22 g of DYDICY was dissolved in 5.60 g of 1- methoxy-2-propanol and heated to 50*C for 30 minutes with stirring. 0.044 g of 2-Methyl-imidazole (2MI) and 6.92 g of methyl ethyl ketone (MEK) was added to the above solution with stirring. Part B: 50.0 g of Dow epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours. The resin varnish was then B-Staged on a hot plate in thin casting pan. The B-Staged resin was ground into fine powder and then cured at 170'C in hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. The final polymer properties after 360 minutes of cure at 170-C: Tg (DSC) = 136'C, Tg (TMA) = 120±7 * C, α g = 50±12 ppm/*C, α 180 = 103±3 ppm/ β C. Example 10: Part A: 1.24 g of DYDICY was dissolved in 9.06 g of 1- methoxy-2-propanol and heated to 50*C for 30 minutes with stirring. 0.11 g of 2-Methyl-imidazole (2MI) and 11.15 g of methyl ethyl ketone (MEK) was added to the above solution with stirring. Part B: 50.0 g of Dow epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours. The resin varnish was then B-Staged on a hot plate in thin casting pan. The B-Staged resin was ground into fine powder and then cured at 170 * C in hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. The final polymer properties after 360 minutes of cure aatt 117700''CC:: TTgg ((DDSSCC)) == 112277°°CC,, TTg (TMA) = 113±3'C, __ g 44±2 ppm/°C, α 180 = 96±2 ppm/ * C. Example 11: Part A: 2.30 g of DIANEDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170°C in a hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. The final polymer properties after 180 minutes of cure at 170'C: Tg (DSC) = 106*C, Tg (TMA) = 101 ± 2*C, α - 40 ± 2 ppm/*C, α 180 = 129 ± 5 ppm/*C. The dielectric properties at 1 MHz, 25 'C, and 0% relative humidity are ε r = 3.46 and tan δ = 0.006, and at 50% relative humidity are ε 1 = 3.54 and tan δ = 0.002. Example 12: Part A: 1.28 g of DIANEDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170 β C in a hydraulic press at 200 psi. The final polymer properties after 180 minutes of cure at 170'C: Tg (DSC) = 116"C, Tg (TMA) = 109±2*C, α g = 31±2 ppm/'C, α 180 = 107±5 ppm/°C. The dielectric properties at 1 MHz, 25 * C, and 0% relative humidity are ε' = 3.51 and tan δ = 0.010, and at 50% relative humidity are ε' = 3.61 and tan «S = 0.010. Example 13: Part A: 1.46 g of DIPPDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170°C in a hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. The final polymer properties after 180 minutes of cure at 170*C: Tg (DSC) = 117 * C, Tg (TMA) = 79 ± 3'C. The dielectric properties at 1 MHz, 25*C, and 0% relative humidity are ε' = 3.60 and tan δ = 0.006, and at 50% relative humidity are ε' = 3.71 and tan δ = 0.005. Example 14: Part A: 2.62 g of DIPPDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170'C in a hydraulic press at 200 psi. 120 77 150 80 180 86 360 96 The final polymer properties after 180 minutes of cure at 170°C: Tg (DSC) = 86'C, Tg (TMA) - 69 ± 4 β C, α g - 50 ± 4 ppm/'C, α 180 = 194 ± 8 ppm/'C. The dielectric properties at 1 MHz, 25'C, and 0% relative humidity are ε' = 3.80 and tan δ = 0.011, and at 50% relative humidity are ε' = 3.85 and tan δ = 0.005. Example 15: Part A: 2.30 g of DIANEDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170°C in a hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. Time (min.. Tσ C O 0 38 30 92 60 91 90 101 120 108 150 105 180 112 360 112 The final polymer properties after 360 minutes of cure at 170'C: Tg (DSC) = 112 'C. Example 16: Part A: 1.46 g of DIPPDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol, 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170 * C in a hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. Time (min.) Tσ CO 0 32 30 47 60 51 90 73 120 84 150 86 180 90 360 104 The final polymer properties after 360 minutes of cure at 170°C: Tg (DSC) = 10 "C. Example 17: Part A: 2.62 g of DIPPDICY was dissolved in a mixture of 7.50 g of l-methoxy-2-propanol , 7.50 g of methyl ethyl ketone and 0.054 g of 2-MI with stirring. Part B: 25.0 g of Dow Epoxy 71881 resin (diglycidyl- Bisphenol-A (DGEBA) and brominated DGEBA) . Part A and Part B were mixed together and allowed to age for 24 hours at room temperature. The resin varnish was then B-Staged on a hot plate in a thin casting pan. The B-Staged resin was ground into a fine powder and then cured at 170°C in a hydraulic press at 200 psi. The polymer yields the following properties as a function of cure. Time .min.. Tg ('C. 0 29 30 49 60 51 90 71 120 84 150 85 180 90 360 101 The final polymer properties after 360 minutes of cure at 170'C: Tg (DSC) = lOl'C.

Claims: 28 CLAIMS 1. A curing agent for epoxy resins having the formula where R is * * - Λ-, -f-CH 2 7 - C-7 - CH2 7 τ- . CH 3 I I CH 3 X is sigma bond, O, S, R' and R* are independently selected from -H, -CH 3 , —CH 2 CH 3 , —CHCHCH , —CH 2 CH(CH) 2 n is an integer from 2 to 12 a is 0 or an integer from 1 to 5 b is 0 or an integer from 1 to 5 c is 0 or an integer from 1 to 5 d is an integer from 1 to 4 R is —H, —CH , —CH 2 CH 3 , —CH 2 CH 2 CH , 2. A method for curing epoxy resins comprising combining a precursor of said epoxy resin with an effective amount of a bis-dicyandiamide having the formula CH, , - -CHzT-a-f-C ) c ( CH 27T - , CH 3 I I CH 3 R' and R* are independently selected from -H, -CH 3 , —CH 2 CH 3 , —CH 2 CH 2 CH , —CH 2 CH(CH 3 ) - n is an integer from 2 to 12 a is 0 or an integer from 1 to 5 b is 0 or an integer from 1 to 5 c is 0 or an integer from 1 to 5 d is an integer from 1 to 4 R* is -H, -CH 3 , -CH 2 CH 3 , -CH 2 CH 2 CH 3 , 3. The method of Claim 2 wherein said bis- dicyandiamide is present in amounts up to about 24 weight percent. 4. The method of Claim 2 wherein R is -CH 2 - C(CH 3 ) 2 -CH 2 -, and R" is H. _5. The method of Claim 2 wherein R is CH(CH 3 )CH 2 CH 2 and R" is H. 7. The method of Claim 2 wherein R is 8. The method of Claim 2 wherein R is 9. wherein R is -CH 2 CH 2 - and R" is ^λ 10. The method of Claim 2 wherein R is -(CH 2 )g- and R" is H.

Inventors: CONRAD JEFFREY PAUL, ZUPANCIC JOSEPH JAMES, CONRAD, JEFFREY, PAUL, ZUPANCIC, JOSEPH, JAMES
Applicants: ALLIED SIGNAL INC, ALLIED-SIGNAL INC.
Application year: 1992
Main classification: C07C279
IPC codes: C07C279, C08G59