PHENOLIC CONNECTIONS AS WELL AS YOUR GLYCIDYLETHER
This invention relates to novel phenolic compounds, per se suitable for use as curing agents for epoxy resins, and to glycidyl ether derivatives thereof. It is known that epoxy resin compositions have wide structural-, coating- and electronic applications. For high-performance electronic applications, such as circuit boards for high-speed computers, epoxy resin compositions having increasingly low melt viscosity and low water absorbance in the cured state are required (for ease and speed of processing during the prepregging stage of electrical lamination preparation). Therefor in epoxy resin-based electrical lamination formulations, it is desirable for both the epoxy resin and the curing agent to have a low melt viscosity. Thus the problem underlying the present invention can be seen in providing novel phenolic and epoxy resin compounds having a low melt viscosity. The present invention relates to a phenolic compound of the formula I EMI1.1 in which Ar is a C6-20 aromatic group, L is a cyclohexanenorbornane linking group, L' is a divalent cycloaliphatic moiety, and each of m and n is a number of from 0 to 10. The polyphenols according to the present invention can be prepared by the addition reaction of a phenol with a cyclohexenenorbornene compound such as 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene. Suitable phenols include mono- and polynuclear phenols having at least one unsubstituted position ortho- or para-to a phenolic hydroxyl group, such as phenol, cresol, 3,4- and 3,5-dimethylphenol, resorcinol, biphenol, 1-naphthol and bisphenol A or F. Phenol is preferred. Suitable cyclohexenenorbornene compounds include EMI2.1 referred to herein as "monoadduct," "diadduct" and "triadduct," respectively, and isomers thereof. The cyclohexenenorbornene itself is an adduct of 4-vinylcyclohexene and cyclopentadiene which can be prepared by contacting 4-vinylcyclohexene and dicyclopentadiene, preferably in the presence of a polymerization inhibitor such as t-butyl catechol, at a temperature of at least 180 DEG C, preferably of from 220 to 260 DEG C, for a time of from 2 to 8 hours. Under these conditions, the dicyclopentadiene is cracked to cyclopentadiene, and the vinylcyclohexene and cyclopentadiene undergo an addition reaction to produce a mixture of mono-, di- and poly-adducts along with cyclopentadiene oligomers (e.g., trimer, tetramer, pentamer, etc.). The reaction product mixture containing predominately 5-(3-cyclohexen-1-yl)-2-norbornene (monoadduct) is allowed to cool to 50 - 70 DEG C and is stirred under reduced pressure to strip off unreacted vinylcyclohexene.The reaction product is then purified by fractional vacuum distillation to remove by-products including, optionally, di- and poly-adducts and cyclopentadiene oligomers, and the purified product is passed through an adsorbent bed for removal of t-butyl catechol. Preparation of a vinylcyclohexene/cyclopentadiene adduct is illustrated in Example 1. The polyphenols comprising the group L' are prepared by carrying out the reaction between the phenol and the cyclohexene norbornene compound in the presence of a cyclic diene such as, for example, dicyclopentadiene, cyclopentadiene, norbornadiene dimer, norbornadiene, methylcyclopentadiene dimer, limonene, 1,3- and 1,5-cyclooctadiene, alpha - and gamma -terpinene, 5-vinylnorbornene, 5-(3-propenyl)-2-norbornene, and cyclopentadiene oligomers. The preparation of such a phenolic compound is illustrated in Example 4. The reaction between the phenol and the cyclohexenenorbornene and optionally the cyclic diene is generally carried out by contacting, under addition reaction conditions, the cyclohexenenorbornene and optionally the cyclic diene, with a molar excess, preferably from 10 to 30 moles, of the selected phenol per mole of the cyclohexenenorbornene plus diene. The above reaction is most efficiently carried out in the presence of a Lewis acid addition catalyst such as BF3, coordination complexes thereof such as boron trifluoride etherate, AlCl3, FeCl3, SnCl4, ZnCl2, silica and silica-alumina complexes and at an elevated temperature of from 70 to 200 DEG C, preferably of from 100 to 180 DEG C. The reaction is continued until the desired degree of reaction has been completed, usually for a period of 30 minutes to 10 hours. Normally a period of from 1 hour to 3 hours will be sufficient. Examples 2, 4, 5 and 6 further illustrate the preparation of polyphenols. The phenolic compound can be combined with an epoxy resin by, for example, melt-blending, preferably in the presence of a curing catalyst such as an imidazole. Subsequent cure of the epoxy resin is effected by heating the epoxy/phenol mixture at a temperature higher than 150 DEG C, preferably of from 200 to 300 DEG C, for at least 0.25 hour. Cure of epoxy resins with phenols according to the present invention is illustrated in Examples 7, 8 and 9 herein. As indicated above the polyphenols of the present invention are particularly suitable as curing agents for epoxy resins. Such epoxy resin compositions are useful in moulding powder-, coating-and electrical encapsulation and laminating applications. In addition the polyphenols of the present invention may also be used as stabilizing additives for thermoplastics and as precursors for thermosettable resins. In particular they were found to be suitable as precursors for epoxy resins compounds. Accordingly the present invention relates to epoxy resin compounds of the formula II EMI4.1 wherein L, L', m and n are as defined above and Gly is a glycidyl ether group. The epoxy resin compounds according to the present invention can be prepared by reacting the precursor polyphenols of the formula I as described above with an epihalohydrin such as epichlorohydrin in the presence of a catalyst such as a quaternary ammonium salt or phosphonium halide, followed by dehydrochlorination under reduced pressure in the presence of aqueous caustic. The reaction can be carried out at a temperature within the range of about 40 to about 120 DEG C, preferably about 80 to about 110 DEG C. Glycidation of the polyphenols according to the present invention to prepare the epoxy resin compounds is described in Examples 11 and 12 herein. The epoxy resin compounds of the formula II can be combined with a curing agent at a temperature of from 150 to about 250 DEG C for a period of time which can vary widely depending on the cure schedule and thickness of the part, which is generally greater than 0.25 hour. Suitable curing agents include amines such as diamino-diphenyl sulfone and methylene dianiline, and phenols such as phenolic novolacs and the precursor phenols. Optimum properties of the cured resin can be achieved by a staged heating process employing higher temperature in each stage. The epoxy resins can be co-cured with other thermosettable resins such as for example bismaleimides and cyanate esters. Since the epoxy resin compounds of the formula II have in particular low melt viscosity and low water absorption in the cured state they are particularly suitable for use in electrical laminates, structural composites and moulding compounds. Example 1 Preparation of 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene An equimolar molar of dicyclopentadiene and 4-vinylcyclohexene in equimolar mixture were heated in an autoclave at 240 DEG C for 4-4.5 hours. The reaction product was diluted with cyclohexane and passed through a packed bed of alumina to remove the t-butylcatechol inhibitor introduced with the reactants. The resulting product mixture was distilled in a wiped film evaporator at 3 mm Hg pressure at 90 DEG C to produce a light fraction containing unreacted vinylcyclohexene and dicyclopentadiene and the mono-adducts of 4-vinylcyclohexene and cyclopentadiene. A 150g sample of this distillate was vacuum distilled using a 10-tray Oldershaw column to give four fractions.The fourth fraction, 65g, was shown by gas chromatographic analysis to consist of 0.15% dicyclo-pentadiene, 88.3% endo-5-(3-cyclohexen-1-yl)-2-norbornene, 6.1% exo-5-(3-cyclohexen-1-yl)-2-norbornene and two additional components present in the amount of 1.9% and 2.4% which are believed to be isomeric adducts of the formula EMI5.1 several additional components totalling about 0.4%, 0.4% tricyclopentadiene and about 0.4% unidentified components. Analysis of the fraction by nuclear magnetic resonance indicated about 87 mole percent of the endo adduct, about 9 mole percent of the exo adduct and about 5% of the isomeric adducts. Example 2 Preparation of Polyphenol Based on 5-(3-cyclohexen-1-yl)bicyclo [2.2.1]hept-2-ene To a reactor equipped with a stirrer, condensor and addition funnel were added 188.2g (2.0 mole) of phenol and 1.0g BF3Et2O catalyst. The reaction mixture was heated to 70 DEG C, and 17.4g (0.1 mole) of 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene was added over a 20-minute period. The temperature was raised to 150 DEG C over a 1 1/2-hour period and held for 2 1/2 hours. Unreacted phenol was distilled. The recovered product had a melting range of 70-80 DEG C, a phenolic hydroxyl content of 0.495 eq/100g and a melt viscosity of 240 mPa.s (115 DEG C). The product polyphenol can be represented structurally as EMI6.1 Example 3 Preparation of Polyphenol Based on Dicyclopentadiene (Comparison) To a reactor equipped with a stirrer, condensor and addition funnel were added 188.2g (2.0 mole) of phenol and 1.0g of BF3Et2O catalyst. The reaction mixture was heated to 70 DEG C, and 13.2g (0.1 mole) of dicyclopentadiene was added over a 20-minute period and held for 2 1/2 hours. Unreacted phenol was distilled. The recovered product had a melting range of 115-120 DEG C, a phenolic hydroxyl content of 0.62 eq/100g, and a melt viscosity of 635 mPa.s (115 DEG C). The product can be represented structurally as EMI6.2 Example 4 Preparation of Polyphenol Based on 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene/dicyclopentadiene. To a reactor equipped with a stirrer, condensor and addition funnel were added 295.7 (3.14 mole) of phenol and 2.0g of BF3Et2O catalyst. The reaction mixture was heated to 70 DEG C, and 13.7g (0.079 mole) of 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene and 10.3 (0.079 mole) of dicyclopentadiene were added over a 20-minute period. The temperature was raised to 150 DEG C over a 1 1/2-hour period and held for 2 1/2 hours. Unreacted phenol was distilled. The recovered product had a melting range of 70-78 DEG C. The product polyphenol includes repeating structural units EMI7.1 Example 5 Preparation of Polyphenol Based on Vinylcyclohexene/Cyclopentadiene Diadduct. To a reactor equipped with a stirrer, condensor and addition funnel were added 376g (4.0 mole) of phenol and 2.0g of BF3Et2O catalyst. The reaction mixture was heated to 70 DEG C, and 48g (0.2 mole) of diadduct was added over a 20-minute period. The temperature was raised to 150 DEG C over a 1 1/2-hour period and held for about 2 1/2 hours. Unreacted phenol was distilled. The recovered product had a melting range of 85-95 DEG C. The product polyphenol can be represented structurally as EMI7.2 Example 6 Preparation of Polyphenol from Mixed Dienes. To a reactor equipped with a stirrer, condensor and addition funnel were added 376g (4.0 mole) of phenol and 2.0g of BF3Et2O catalyst. The reaction mixture was heated to 70 DEG C, and 48g of a diene mixture obtained from the Diels-Alder reaction of cyclopentadiene and vinylcyclohexene were added over a 20-minute period. The temperature was raised to 150 DEG C over a 1 1/2-hour period and held for 2 1/2 hours. Unreacted phenol was distilled. The recovered product had a melting range of 87-100 DEG C. The product polyphenol includes repeating structural units EMI8.1 Example 7 Cure of Epoxy Resin. 27.5g of a 67/33 (wt) blend of the diglycidyl ether of bisphenol A and tetrabromo-BPA, 4.8g of the polyphenol prepared in Example 2 and 0.03g 2-imidazole were melt-blended at 150 DEG C. The mixture was then heated at 250 DEG C for 20 minutes. The resulting cured epoxy resin had a Tg of 91 DEG C. Example 8 Cure of Epoxy Resin. 27.5g of a 67/33 (wt) blend of the diglycidyl ether of bisphenol A and tetrabromo-BPA, 4.7g of the polyphenol prepared in Example 5 and 0.03g 2-imidazole were melt-blended at 150 DEG C. The mixture was then heated at 250 DEG C for 20 minutes. The resulting cured epoxy resin had a Tg of 91 DEG C. Example 9 Cure of Epoxy Resin. 2g of the tetraglycidyl ether of the tetraphenol of ethane, 2g of the polyphenol prepared in Example 5 and 0.03g of 2-imidazole were melt-blended at 150 DEG C. The mixture was then heated at 250 DEG C for 20 minutes. The resulting cured epoxy resin had a Tg of 185 DEG C. Example 10 Cure of Epoxy Resin (Comparison). 4.08g of a 67/33 (wt) blend of the diglycidyl ether of bisphenol A and tetrabromo-BPA, 1.61g of the polyphenol prepared in Example 3, and 0.03g of 2-imidazole were melt-blended at 150 DEG C. The mixture was then heated at 250 DEG C for 20 minutes. The resulting cured epoxy resin had a Tg of 118 DEG C. Example 11 Preparation and Curing of Epoxy Resin A. A mixture of 200g of a polyphenolic addition product of phenol and 5-(3-cyclohexen-1-yl)bicyclo-[2.2.1]hept-2-ene prepared by a process as described in Example 1, 200g of epichlorohydrin and 4.4g of ethyltriphenylphosphonium bromide was placed in a 2L round-bottomed flask equipped with a mechanical stirrer and condensor. The mixture was heated with stirring to 100 and was maintained at 100 - 110 DEG C for 4 hours. The reaction mixture was then cooled to 80 - 90 DEG C. 150 ml of toluene and 88g of 50% NaOH solution were added dropwise with distillation of H2O. The toluene and excess epichlorohydrin were removed under reduced pressure to provide 235.8g of a liquid resin (WPE 292).The product epoxy resin can be represented structurally as EMI9.1 Heating 61.86g of the product with 13.14g 4,4'-diaminodiphenyl sulfone curing agent at 180 DEG C for 2 hours, 200 DEG C for 2 hours and 220 DEG C for 2 hours gave a cured material having the physical properties shown in Table 1. Example 12 Preparation and Cure of Epoxy Resin B. The procedure described in Example 11 was repeated starting with 220g of a polyphenol prepared by a process as described in Example 5 (hydroxyl content 0.44 eq/100g), 4.4g ETPPB and 220g ECH in 150ml of toluene. 248g of epoxy resin B was isolated as a solid product having a melting point of 65 - 70 DEG C and WPE OF 342. Heating 59.26g of the product with 10.74 g of 4,4-diaminodiphenyl sulfone at 180 DEG C for 2 hours, 200 DEG C for 2 hours and 220 DEG C for 2 hours gave a cured material having the physical properties shown in Table 1. The product epoxy resin can be represented structurally as EMI10.1 Example 13 Preparation and Cure of Epoxy Resin C (Comparison). The procedure described in Example 11 was repeated starting with 25g of a polyphenol prepared by a process as described in Example 3 (0.62 eq. OH/100g), 41.3g ECH and 0.7g ETPPB. 25g of epoxy resin C (WPE 260) was isolated. Curing 9.92g of the material with 2.37g of diaminodiphenyl sulfone according to the cure schedule described in Example 11 gave a cured resin having the physical properties shown in Table 1. <tb><TABLE> Id=Table 1 Columns=5 Comparison of Physical Properties of Resins A, B and C <tb>Head Col 1 to 2: <tb>Head Col 3: A <tb>Head Col 4: B <tb>Head Col 5: C <tb>Tg, DEG C<SEP>DSC<SEP>180<SEP>198<SEP>196 <tb><SEP>DMA<SEP>190<SEP>210<SEP>210 <tb> <tb>SubHead Col 1 to 2 AL=L: Flex Properties, RT/Dry <tb><SEP>Strength 10<3>.kPa (ksi)<SEP>126 (18.3)<SEP>124 (18.0)<SEP>141 (20.5) <tb><SEP>Modulus 10<5>.kPa (ksi)<SEP>32.9 (478)<SEP>30.5 (442)<SEP>30.5 (442) <tb><SEP>Elongation, %<SEP>4.3<SEP>4.5<SEP>5.7 <tb> <tb>SubHead Col 1 to 2 AL=L:Flex Properties (Hot/Wet) <tb><SEP>Strength 10<3>.kPa (ksi)<SEP>85.4 (12.4)<SEP>88.9 (12.9)<SEP>82.7 (12.0) <tb><SEP>Modulus 10<5>.kPa (ksi)<SEP>28.1 (408)<SEP>25.6 (371)<SEP>26.3 (382) <tb><SEP>Elongation, %<SEP>3.3<SEP>3.8<SEP>3.4 <tb><SEP>Modulus Retention, %<SEP>85<SEP>84<SEP>86 <tb> <tb>SubHead Col 1 to 2 AL=L: Fracture Toughness <tb><SEP>10<6>.kPa (cm)<0.5>, (Kq)<SEP>11.7 (463)<SEP>12.3 (486)<SEP>- <tb> <tb>SubHead Col 1 to 2 AL=L: Moisture Gain, % <tb><SEP>200 h.<SEP>1.43<SEP>1.35<SEP>1.87 <tb><SEP>14 days<SEP>1.48<SEP>1.37<SEP>1.98 <tb><SEP>Dielectric Constant<SEP>3.31<SEP>3.31<SEP>- <tb><SEP>Viscosity at 100 DEG C, mPa.s<SEP>170-180<SEP>1500<SEP>170-180 <tb></TABLE> The present invention relates to a phenolic compound of formula I: <CHEM> and to an epoxy resin of the formula II: <CHEM> In the above formulae I and II Ar is an aromatic moiety, L is a divalent hexanenorbornane linking moiety, L' is a divalent cycloaliphatic moiety, Gly is a glycidyl ether group, and each of m and n is a number within the range of 0 to 10. The above phenols include the product of addition reaction of phenol with a cyclohexenenorbornene compound such as 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene and the above epoxy resins include the glycidation product thereof. Epoxy resin compositions comprising either the above phenolic compound or the above epoxy resin have in particular low melt viscosity are useful as resinous component of high-performance electrical laminating and encapsulation formulations. 1. A phenolic compound of the formula (I) EMI12.1 in which each Ar is a C6-20 aromatic moiety, L is a divalent cyclohexane-norbornane moiety, L' is a divalent cycloaliphatic moiety, and each of m and n is a number within the range of 0 to 10. 2. A phenolic compound as claimed in claim 1 in which each Ar is phenyl. 3. A phenolic compound as claimed in claim 1 or 2 in which L is selected from at least one of the groups represented by the following structural formula: EMI12.2 4. A phenolic compound as claimed in any one of the claims 1 to 3 in which L' is a group represented by the following structural formula EMI12.3 5. A phenolic compound as claimed in any one of the claims 1 to 3 in which m is 0. 6. A composition comprising an epoxy resin and a phenolic compound as claimed in any one of the claims 1 to 5. 7. A process for preparing a phenolic compound as claimed in any one of the claims 1 to 6 by contacting in a reaction mixture at least one cyclohexenenorbornene compound and optionally a cyclic diene compound with a molar excess, with respect to the cyclohexenenorbornene and the diene compound(s), of at least one phenolic compound in the presence of a Lewis acid addition catalyst at a temperature within the range of 70 to 200 DEG C. 8. A process as claimed in claim 7 wherein the reaction mixture further comprises dicyclopentadiene as the cyclic diene. 9. A process as claimed in claim 7 or 8 wherein the cyclohexenenorbornene compound used comprises 5-(3-cyclohexen-1-yl)bicyclo[2.2.1]hept-2-ene. 10. A process as claimed in any one of the claims 7 to 9 wherein the phenolic compound used is phenol. 11. An epoxy resin of the formula II EMI13.1 in which Gly is a glycidyl ether group, Ar is a C6-20 aromatic moiety, L is a divalent cyclohexanenorbornane linking moiety, L' is a divalent cyclo-aliphatic linking moiety, and each of m and n is a number within the range of 0 to 10. 12. An epoxy resin as claimed in claim 11 wherein each Ar is phenyl. 13. An epoxy resin as claimed in claim 11 or 12 wherein L is selected from at least one of the groups represented by the following structural formula EMI14.1 14. An epoxy resin as claimed in any one of the claims 11 to 13 wherein L' is a group represented by the following structural formula EMI14.2 15. An epoxy resin as claimed in claims 13 or 14 of the formula EMI14.3 16. A process for the preparation of an epoxy resin, as claimed in any one of the claims 11 to 15 by reacting a phenolic compound of the formula I EMI14.4 with an epihalohydrin in the presence of a catalyst followed by dehydrochlorination under reduced pressure in the presence of aqueous caustic. 17. An epoxy resin composition comprising an epoxy resin as claimed in any one of the claims 11 to 15 and an effective amount of a curing agent for the epoxy resin. 18. An epoxy resin composition as claimed in claim 17 wherein curing agent is diaminodiphenyl sulfone or methylenediamine. 19. A cured product obtainable by subjecting a composition as claimed in claims 6, 17 or 18 to a temperature of at least 150 DEG C for at least 0.25 hour. 20. An article comprising a cured product as claimed in claim 19.