Abstract:
The invention relates to a Bismaleimide-Triazine resin (BT resin ) and production method thereof and in particular, a series of novel BT resin prepared by reacting a novel bismaleimide with various aromatic cyanate esters. By combining said novel bismaleimide monomer with various proportions of cyanate esters having different structures, BT resins having various processing temperature conditions can be formulated, which, after polymerizing and crosslinking, can provide materials with various thermal stability, dielectric constants, and mechanical properties for various applications.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a bismaleimide-triazine resin and a production method thereof and in particular, to a series of novel BT resins prepared by reacting a novel bismaleimide monomer with various aromatic cyanate esters. 
     2. Description of the prior art 
     There are not so many types of BT resins known in the art and those are made predominantly by combining diphenylmethane bismaleimide with bisphenol A cyanate resin in various mole ratios. The present invention consists of preparing a series of novel BT resins by using novel bismaleimides with various aromatic cyanate esters. 
     U.S. Pat. No. 4,110,364 (Mitsubishi, Japan, 1978 ), disclosed a BT resin synthesized from bismaleimide and cyanate ester. As shown in FIG. 1, cyanate ester itself can be cyclotrimerized in to a triazine structure (10), or it can be copolymerized with a maleimide to form a pyrimidine structure(11), where R1 in FIG. 1 is as shown in FIG. 2, R2 is as shown in FIG. 3, and where R in FIG. 2 and 3 may be H, lower alkyl group (C1-C7 ), cycloalkyl(C4-C7 ), phenyl and the like, and m=0-4. 
     BT resin has excellent elevated temperature characteristics, solvent resistance, low water absorption, and low dielectric constant. Such resin compositions can be blended with other thermosetting resins and other reactive diluents such as o-diallyl phthalate, triallyl cyanurate or triallyl isocyanurate, to modify such BT resin. 
     Many BT resins known in the art are made predominantly from diphenylmethane bismaleimide and bisphenol A cyanate resin in various proportions. BT resins comprise solid, liquid and solution types, are applicable in a variety of processing uses such as laminating, preformed insulating sheet structural materials, coating, filling and the like, and can be used in multi-layer printed circuit boards and as encapsulants. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a novel BT resin having enhanced thermal stability, excellent chemical resistance, and lower moisture absorption than conventional BT resins as well as good processability and solubility without loss of thermal stability. 
     Another object of the invention is to provide a method for preparing said novel BT resin of the invention, comprising reacting a novel bismaleimide with aromatic cyanate esters. 
     Still another object of the invention is to provide a novel bismaleimide monomer useful for preparing the novel BT resin of the invention, which is 2,7-bis(4-maleimidophenoxy)-naphthalene. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages and features of the invention will be apparent form the following description in conjunction with accompanying drawings, in which: 
     FIG. 1 shows the chemical formulae of conventional triazines and pyrimidines; 
     FIG. 2 shows chemical formulae of R1 in each Figure; 
     FIG. 3 shows chemical formulae of R2 in each Figure; 
     FIG. 4 shows a flow sheet for synthesis of the bismaleimide monomer incorporated in the BT resin and its preparation method thereof according to the invention; and 
     FIG. 5 shows a flow sheet for synthesis of the cyanate ester monomers incorporated in the BT resins and their preparation method thereof according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The novel bismaleimide as one of the raw materials useful for preparing the BT resin of the invention can be synthesized, as shown in FIG. 4, by reacting dihydroxy-naphthalene or -benzene with chloronitrobenzene(30) into a dinitrocompound(31) which is reduced by hydrogenation into a diaminocompound(32), and reacting said diaminocompound with maleic anhydride into a bismaleimide which can be dehydrated and cyclized to form the desired novel bismaleimide(34). 
     Synthesis of the cyanate ester monomer as the other raw material can be accomplished, as shown in FIG. 5, by reacting a bisphenol with cyanogen bromide(40) to form an aromatic bisphenol dicyanate(41). Suitable aromatic bisphenols are hydroquinone, 4,4-biphenol,.bis(4-hydroxyphenyl)methane, 4,4&#39;-dihydroxydiphenyl ether, 2,2-bis(4-hydroxyphenyl)propane, 4,4&#39;-methylenebis(2,6-dimethylphenol), and the like. Structural formula of R1 and R2 in FIG. 2 and 3 are shown in FIG. 2 and 3, R in FIG. 2 and 3 may be H, lower alkyl (C1-C7 ), cycloalkyl(C4-C7), phenyl and the like, and m=0-4. 
     The bismaleimide is mixed thoroughly with various aromatic bisphenol cyanate in mole ratios of 4/1, 2/1, 1/1, 1/2 or 1/4 and 500 ppm of Cu(acetylacetonate) as catalyst is added, and subsequently, cured at 180° C. for 2 hours, followed by at 250° C. for 4 hours, and thereby, yield a series of novel BT resins. 
     The present invention will be better understood from the description of the following illustrative but non-limiting Examples. 
     EXAMPLE 1 
     Synthesis of 2,7-bis(4-maleimidophenoxy)naphthalene monomer, cf flow sheet in FIG. 4. 
     (a) Synthesis of 2,7-Bis(4-nitrophenoxy)naphthalene(31) 
     In a reactor provided with a stirrer, a reflux condenser, a temperature controlling apparatus and a nitrogen inlet, charged with 250 ml of dimethylformamide (DMF) solvent, 80.05 g(0.5 mole )of 2,7-dihydroxynaphthalene, 173.35 g(1.1 mole) of p-chloronitrobenzene and 82.2 g (0.6 mole) of potassium carbonate. The reaction mixture was heated to reflux (140°-145° C.) under nitrogen atmosphere for 8 hours. At the end of reaction, the reaction mixture was hot filtered to remove inorganic salts and washed the inorganic salts with 90 ml of DMF. The filtrate and washes were combined and heated to 100°-110° C., and, then, 60 ml of water was added while hot, cooled slowly down to room temperature, where the product was gradually precipitated. The product was filtered, stirred with 500 ml of methanol, filtered again, and dried in vacuo to obtain the dinitro monomer(31) in a yield of 92%, mp 167°-168° C. Analysis for C22H14N2O6, calcd: C, 65.67%;H, 3.48%;N, 6.97%; Found: C, 65.66;H, 3.47%;N, 6.92%. 
     (b) Synthesis of 2,7-Bis(4-aminophenoxy)naphthalene (32) 
     A mixture of the dinitromonomer (0.1 mole) obtained above, active carbon (2 g) and ferric chloride (FeCl3.6H2O) in ethanol (200 g) was preheated to 85° C., added dropwise 50 ml of hydrazine monohydrate (85%) into the reactor and maintained at that temperature for 4 hours. The desired diamino product was then obtained (ca. 95% in yield). The resulting diamino monomer can be recrystalized in 2-methoxyethanol or DMF . mp 166°-167° C. Analysis for C22H18N2O6, calcd: C, 77.19%; H, 5.26%; N, 8.19%; Found: C, 76.97%; H, 5,26%; N, 8.18%. 
     (c) Synthesis of 2,7-Bis(4-maleamidophenoxy)naphthalene(33) 
     In a three-necked round bottom flask provided with a droping funnel, a stirrer and a nitrogen inlet, charged with maleic anhydride (0.22 mole )and tetrahydrofuran (100 ml) and, further, under a nitrogen atmosphere, the diamino monomer obtained in (b) was dissolved in 50 ml THF and then, added dropwise into the maleic anhydride solution at room temperature, precipitation of the product and a exothermic reaction was observed immediately. The reaction mixture was reacted at room temperature for 4 hours and heated to 60° C. for one hour. Thereafter, the product was filtered and washed with THF to remove residual maleic anhydride and then dried in vacuo (ca. 99% in yield ). mp 240°-241° C. Analysis for C30H22N2O8, Calcd: C, 66.91%; H, 4.09%; N, 5.20%. Found: C, 66.88%; H, 4.13%; N, 5.21%. 
     (d) Synthesis of 2,7-Bis(4-maleimidophenoxy)naphthalene (BMPN, 34) 
     In a 250 ml round bottom flask, charged with bismaleamic acid (0.05 mole),acetone (100 ml) and triethylamine (0.03 mole, TEA), and the mixture was stirred at room temperature for 30 minutes. Magnesium chloride (0.1 g) and cobalt acetate (0.01 g )were added, and then, acetic anhydride (0.11 mole) was added dropwise at room temperature over 30 minutes. The reaction mixture was further stirred at room temperature till the product was precipitated in a period of time of about 8-10 hours. The product was filtered and washed with aqueous sodium carbonate till no more odor of acetic acid was detected, followed by washing with deionized water, and dried to obtained an yellow product (ca. 85% in yield). Mp 162°-164° C. Analysis for C30H18N2O6, Calcd: C, 71.71%; H, 3.59%; N, 5.58%. Found: C, 71.67; H, 3.75%; N, 5.42%. Results of its characterization were set forth in Table 1. 
     EXAMPLE 2 
     The bismaleimide monomer of 2,7-bis(2-hydroxyethoxy)naphthalene was synthesized according to the process outlined in the flow sheet shown in FIG. 4. By using 2,7-bis(2-hydroxyethoxy)naphthalene in stead of 2,7-dihydroxynaphthalene, reaction conditions as in Example 1 were employed and steps (a), (b), (c), and (d) were conducted to obtain 2,7-bis (4-maleimidophenoxyethoxy)naphthalene(BMPEN). Results of its characterization were set forth in Table 1. 
     EXAMPLE 3 
     The bismaleimide monomer of 1,4-dihydroxybenzene was synthesized according to the process outlined in the flow sheet shown in FIG. 4. 
     By using 1,4-dihydroxybenzene in stead of 2,7-dihydroxynaphthalene, reaction conditions as in Example 1 were employed and steps (a), (b), (c), and (d) were conducted to obtain 1,4-bis(4-maleimidophenoxy)benzene (BMPB). Results of its characterization were set forth in Table 1. 
     EXAMPLE 4 
     The bismaleimide monomer of 1,4-bis(2-hydroxyethoxy)benzene was synthesized according to the process outlined in the flow sheet shown in FIG. 4. 
     By using 1,4-bis(2-hydroxyethoxy)benzene in stead of 2,7-dihydroxynaphthalene, reaction conditions as in Example 1 were employed and steps (a),(b), (c) and (d) were conducted to obtain 1,4-bid(4-maleimidophenoxyethoxy)benzene (BMPB). Results of its characterization were set forth in Table 1. 
     EXAMPLE 5 
     Cyanate ester of 1,4-dihydroxybenzene (PB) was prepared according to the process outlined in the flow sheet shown in FIG. 5. 
     In a reactor provided with a charging fiunel, a stirrer, and a temperature controlling apparatus, charged with 1,4-dihydroxybenzene (0.05mole), cyanogen bromide (0.12 mole) and acetone (30 mole), and placed the reactor in a ice bath to maintain at -3° to 0° C. Triethylamine (0.11 mole ) was dissolved in 20 ml acetone and the resulting solution was added dropwise into the reactor. An exothermic reaction has resulted while maintained in the ice bath to keep the temperature not higher than 10° C. When the addition of triethylamine was complete, the reaction was continued for one hour. At the end of the reaction, the reaction mixture was poured slowly into a large amount of ice-water, filtered, and the solid thus obtained was washed and dried in vacuo to obtain a product PB (ca. 90% in yield). Characterization results of the product were set forth in Table 2. 
     EXAMPLE 6 
     Cyanate ester of biphenol (BB) was prepared according to a process outlined in the flow sheet shown in FIG. 5. 
     By using biphenol instead of 1,4-dihydroxybenzene, reaction conditions as in Example 5 were employed to obtain its cyanate ester. Characterization results of the product were set forth in Table 2. 
     EXAMPLE 7 
     Cyanate ester of 4,4&#39;-dihydroxydiphenylmethane (CH2) was prepared according to a process outlined in the flow sheet shown in FIG. 5. 
     By using 4,4&#39;-dihydroxydiphenylmethane instead of 1,4-dihydroxybenzene, reaction conditions as in Example 5 were employed to obtain its cyanate ester. Characterization results of the product were set forth in Table 2. 
     EXAMPLE 8 
     Cyanate ester of 4,4&#39;-dihydroxyphenylether (E) was prepared according to a process outlined in the flow sheet shown in FIG. 5. 
     By using 4,4&#39;-dihydroxyphenylether in stead of 1,4-dihydroxybenzene, reaction conditions as in Example 5 were employed to obtain its cyanate ester (E). Characterization results of the product were set forth in Table 2. 
     EXAMPLE 9 
     Cyanate ester of bisphenol A (BPA) was prepared according to a process outlined in the flow sheet shown in FIG. 5. 
     By using bisphenol A instead of 1,4-dihydroxybenzene, reaction conditions as in Example 5 were employed to obtain its cyanate ester (BPA). Characterization results of the product were set forth in Table 2. 
     EXAMPLE 10 
     Cyanate ester of 3,3&#39;5,5&#39;-tetramethyldiphenolmethane (4M) was prepared according to a process outlined in the flow sheet shown in FIG. 5. 
     By using 3,3&#39;5,5&#39;-tetramethyldiphenolmethane instead of 1,4-dihydroxybenzene, reaction conditions as in Example 5 were employed to obtain its cyanate ester (4M). Characterization results of the product were set forth in Table 2. 
     EXAMPLE 11 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester (PB) 
     Bismaleimide (BMPN) and cyanate ester (PB) in a proportion of BMI/CE=1/2 were mixed thorougbly and 500 ppm of Cu(acetylacetonate) as catalyst was added in the mixture. After being cured at 180° C. for 2 hours and then at 250° C. for 4 hours, a BT resin designated as BTPB was obtained. The analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 12 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester(BB) 
     By using cyanate ester(BB) in stead of cyanate ester(PB) as used in Example 11 and employing curing conditions as in Example 11, a BT resin designated as BTBB was obtained. Analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 13 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester (CH2) 
     By using cyanate ester (CH2) instead of cyanate ester (PB) as used in Example 11 and employing curing conditions as in Example 11, a BT resin designated as BTPB was obtained. Analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 14 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester (E) 
     By using cyanate ester (E) instead of cyanate ester (PB) as used in Example 11 and employing curing conditions as in Example 11, a BT resin designated as BTE was obtained. Analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 15 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester(BPA) 
     By using cyanate ester (BPA) instead of cyanate ester (PB) as used in Example 11 and employing curing conditions as in Example 11, a BT resin designated as BTBPA was obtained. Analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 16 
     Preparation of BT resin from bismaleimide (BMPN) and cyanate ester (4M) 
     By using cyanate ester (4M) instead of cyanate ester (PB) as used in Example 11 and employing curing conditions as in Example 11, a BT resin designated as BT4M was obtained. Analytical results of its thermal properties were set forth in Table 3, whereas its moisture absorption and dielectric constant were set forth in Table 4. 
     EXAMPLE 17 
     Bismaleimide (BMPBN) and cyanate ester (BPA) in various mole ratios of BMPN/BPA =1/0, 4/1, 2/1, 1/1, 1/2, 1/4, and 0/1 were mixed thoroughly, respectively. After adding separately 500 ppm of Cu(acetylacetonate) as catalyst, they were cured at 180 C. for 2 hours, and followed by at 250 C. for 4 hours. BT resins designated as BT1/0, BT4/1, BT2/1, BT1/1, BT1/2, BT1/4, and BT/01 were obtained. Thermal analytical results of these resins were set forth in Table 5. 
     While objects, feature and effects of the present invention has been described with reference to preferred embodiments thereof, many variations and modifications thereof without departing from the spirit and scope of the invention can be made by those skilled in the art based on the above description. Therefore, the scope of the invention is described only by the appended claim. 
     
                                           TABLE 1__________________________________________________________________________Characterization of bismaleimides       Analysis       Found        Characteristic absorption in IR spectra                    (cm.sup.-1)              NMR Chemical       (Calcd)(%)   imide ring       maleimide ring                                             shift.sup.abismaleimide formula       C   H   N    C═O                          C--N--C                                C--O--C                                     C═C (ppm)__________________________________________________________________________BMPN  C.sub.30 H.sub.18 N.sub.2 O.sub.6       70.94           3.88               5.51 1780, 1720                          1390  1250 690     7.15(s, 4H, Olefinic);       (71.71)           (3.59)               (5.58)                        7.18-8.00(m, 14H, ar)BMPEN C.sub.34 H.sub.26 N.sub.2 O.sub.8       68.80           4.75               4.96 1775, 1710                          1395  1240 680     44(s.sup.b, 8H,                                             CH.sub.2); 7.0-7.8       (69.15)           (4.41)               (4.75)                        (m.sup.c, 18H,                                             CH═CH, and                                             ar.sup.d)BMPB  C.sub.26 H.sub.16 N.sub.2 O.sub.6       68.87           3.62               6.22 1775, 1720                          1400  1245 690       (69.03)           (3.54)               (6.19)BMPEB C.sub.30 H.sub.24 N.sub.2 O.sub.8       66.59           4.54               5.26 1785, 1710                          1395  1250 680     4.2-4.3(s, 8H,                                             CH.sub.2);       (66.67)           (4.44)               (5.19)                        6.9(s, 4H, olefinic);                                             7.0-7.3(m, 12H,__________________________________________________________________________                                             ar) .sup.a Solvent DMSOd6 .sup.b Singlet .sup.c Multiplet .sup.d aromatic ring H 
    
     
                                           TABLE 2__________________________________________________________________________Characterization of cyanate ester monomers.   Analysis   Found   (Calcd)(%)               Mass spectrometrycyanate monomer   C   H   N   NMR Chemical shift                            (m/e)__________________________________________________________________________PB      60.21       2.42           15.57               764(s.sup.b, 4H, ar.sup.d)                            160(M.sup.+, 100)   (60.00)       (2.50)           (17.50)BB      71.34       3.48           11.71               7.52-7.39(m.sup.c, 8H, ar)                            236(M.sup.+, 100)   (71.19)       (3.39)           (11.86)CH2     72.15       4.06           11.14               4.02(s, 2H, CH.sub.2)                            250(M.sup.+, 98);   (72.00)       (4.00)           (11.20)               7.38(s, 8H, ar)                            208(M.sup.+ --OCN, 100)E       66.59       3.12           11.02               7.14-7.51(m, 8Har)                            252(M.sup.+, 100)   (66.67)       (3.17)           (11.11)BPA     73.31       5.09           10.15               1.63(s, 6H, CH.sub.3)                            278(M.sup.+, 22);   (73.38)       (5.04)           (10.07)               7.35(S, 8H, ar)                            263(M.sup.+ --CH.sub.3, 100)4M      71.77       4.21           11.04               2.30(s, 12H, CH.sub.2); 3.81                            306(M.sup.+, 100); 291(M.sup.+ --CH.sub.3                            , 56)   (72.00)       (4.20)           (11.20)               (s, 2H, CH.sub.2); 7.10(S, 4H, ar)                            264(M.sup.+ --OCN, 84)__________________________________________________________________________ .sup.a solvent DMSOd6 .sup.b Singlet .sup.c Multiplet .sup.d aromatic ring H 
    
     
                       TABLE 3______________________________________Results of thermal and thermogravimetric analysis of various cyanateester and bismaleimide mixture at 2/1 molar ratio.sup.c            Tg     T.sub.5% .sup.a                        T.sub.10% .sup.a                              T.sub.max .sup.b                                    Char yield atExample resin    (°C.)                   (°C.)                        (°C.)                              (°C.)                                    600° C.(%)______________________________________1       BT.sub.PB            322    439  461   464   702       BT.sub.BB            305    433  441   458   683       BT.sub.CH2            266    431  441   445   644       BT.sub.E 255    418  429   432   605       BT.sub.BPA            269    425  433   434   626       BT.sub.4M            250    403  423   435   53comparative   DGEDN.sup.d            176    350  371   403   48example______________________________________ .sup.a the temperature at which 5% or 10% of thermogravimetric loss occur in a nitrogen system at a heating rate of 20° C. per minute. .sup.b the temperature at which the maximum thermal decomposition rate occurs. .sup.c cured at 180° C. for 2 hours and then at 250° C. for 4 hours. .sup.d an dihydroxynaphthalenebased epoxy resin cured with diaminodiphenolmethane (DDM), used as a comparative example. 
    
     
                       TABLE 4______________________________________Moisture absorption and dielectric constant of BT resins             moisture             absorption(a)Examples   BT resins (wt %)       dielectric constant(b)______________________________________1       BT.sub.PB 1.7          3.202       BT.sub.BB 1.4          3.283       BT.sub.CH2             1.2          3.074       BT.sub.E  1.3          3.135       BT.sub.BPA             1.1          3.046       BT.sub.4M 0.8          2.93comparative   DGEDN.sup.(C)             3.3          3.92example______________________________________ 
    
     (a) Moisture absorption test 
     Place a cured resin test disc, 1 mm(T)×50 mm(D), in a vacuum oven (110° C., 1 hour) to remove its moisture. Then, cooled in a desiccator and measured their weight (Wo), respetively. After immersing again in 100° C. water for 72 hours, their weights were measured (W), respectively, and moisture absorption rates were calculated based on the following formula: ##EQU1## (b) Measurement of dielectric constant 
     Test samples were placed in a vacuum oven maintained at 100° C. and dried under reduced pressure for 8 hours. The dielectric analyzer was warmed up previously for 30 minutes, purged with nitrogen at a flow rate of 500 ml/min., set under two parallel plate mode, and measured test samples by using two parallel gold-plated plate sensor at a constant temperature of 30° C., a pressure between two parallel plates of 300N, and a scanning frequency of 1 MHz. 
     (c) a dihydroxynaphthalene-based epoxy resin cured with diaminodiphenylmethane (DDM), used as a comparative example. 
     
                       TABLE 5______________________________________Results of thermogravimetric analysis of cured cyanate ester BPA withbismaleimide mixture at various molar ratio.sup.cT.sub.5% .sup.a      T.sub.10% .sup.a                  T.sub.max .sup.b                          Char yield(°C.)      (°C.)                  (°C.)                          at 600° C.(%)______________________________________BT.sub.1/0   475    487         491   67BT.sub.4/1   431    449         434   71BT.sub.2/1   434    443         434   64BT.sub.1/1   429    435         440   47BT.sub.1/2   425    433         434   62BT.sub.1/4   413    429         437   62BT.sub.0/1   401    423         428   42______________________________________ .sup.a the temperature at which 5% or 10% of thermogravimetric loss occur in a nitrogen system at a heating rate of 20° C. per minute. .sup.b the temperature at which the maximum thermal decomposition rate occurs. .sup.c cured at 180° C. for 2 hours and then at 250° C. for 4 hours.