Polyisocyanate compounds, process for producing the same and optical materials using the same

Abstract: Provided are a novel polyisocyanate compound which is useful as a starting material of an optical material having a high refractive index, a low dispersion and excellent optical characteristics, a process for producing this compound at good efficiency, and an optical material prepared from the polyisocyanate compound.

Description: The present invention relates to a polyisocyanate compound and a process for producing the same. More specifically, the present invention relates to a novel polyisocyanate compound useful as a starting material of an optical material which has a high refractive index and a low dispersion and which is excellent in optical properties, and a process for producing the same at good efficiency. Moreover, the present invention relates to an optical material and an optical product using the same. More specifically, it relates to an optical material which has excellent optical characteristics such as a high refractive index, a low dispersion, an excellent transparency, lack of optical distortion and the like, and which is also good in heat resistance, and to an optical product formed of this optical material, such as a lens, a prism, optical fibers, a substrate for a recording medium, a filter, a glass, a vase and the like. In comparison with a glass, plastics are lightweight, hard to break, and easy to dye. Therefore, plastics have been applied, in recent years, to optical use in various lenses and the like. As optical plastic materials, polyethylene glycol bisallyl carbonate (CR-39) and polymethyl methacrylate (PMMA) have been generally used. These plastic materials have, however, a refractive index of 1.5 or less. Therefore, when they are used as lens materials, for example, the thickness of the lenses has to be increased with the increasing power. Consequently, not only has the superiority of plastics which are lightweight been impaired, but also they have been undesirous in view of the aesthetic property. Further, the concave lens in particular has been problematic in that the thickness (edge thickness) of the surrounding portion of the lens is increased and a birefringence or a chromatic aberration is liable to occur. For this reason, in order to be able to decrease the thickness of the lens upon making the most of the characteristics of plastics having a low specific gravity, a plastic material having a high refractive index has been in demand. As a material having such a performance, for example, (1) a polymer comprising a xylylene diisocyanate compound and a polythiol compound (official gazette of JP-A-63-46213), (2) a resin comprising an aliphatic linear sulfur-containing diisocyanate and a polythiol compound (official gazette of JP-A-2-153302) and (3) a polymer comprising a dithian derivative substituted with two isocyanatoalkyl groups and a polythiol (official gazette of JP-A-4-159275) are disclosed. Although the resin in the above-mentioned document (1) and the resin in the above-mentioned document (2) have an increased refractive index by limiting a combination with a polythiol compound to be polymerized, the resin of (1) gives rise to problems that an Abbe number is decreased and a chromatic aberration is increased, and the resin of (2) gives rise to a problem that a heat resistance is worsened. The polymer in document (3) has a high refractive index and a low dispersion (high Abbe number) and is excellent in heat resistance. However, in recent years, the development of a material having a higher refractive index and a lower dispersion has been in demand. EP-A-0 713 105 relates to a composition for optical materials which may comprise a dithianetetrayl derivative being substituted by four S-B-NCO moieties wherein B is a methylene chain represented by -(CH 2 ) m -(m = 1 to 4) which may contain a sulfur atom. It is an object of the present invention to provide, under these circumstances, a novel polyisocyanate compound which can give an optical material having a high refractive index, a low dispersion and an excellent heat resistance, and a process for producing this compound at good efficiency. It is a further object of the present invention to provide an optical material which has excellent optical characteristics such as a high refractive index, a low dispersion, an excellent transparency, lack of optical distortion and the like, and which is also good in heat resistance, and an optical product formed of this optical material. The present inventors have assiduously conducted investigations to achieve the above-mentioned objects, and have consequently found that a polyisocyanate compound of a specific structure having a 1,4-dithian ring contributing to a high refractive index, a low dispersion and a high heat resistance in a main skeleton and an isocyanate group in a side chain through a sulfur atom is a novel compound undescribed in the literature and is adapted to the object, and that this compound can be obtained at good efficiency by a specific process. Moreover, they have found that an optical material formed of a poly(thio)urethane obtained by subjecting a component containing the specific polyisocyanate compound and a component containing a compound having two or more of hydroxyl groups or mercapto groups or both groups to a polyaddition reaction can be adapted to the object. These findings have led to the completion of the present invention. That is, the present invention is to provide a polyisocyanate compound represented by general formula (I) wherein X and Y, independently from each other, represent an alkylene group having from 1 to 5 carbon atoms or an alkylene group having from 1 to 5 carbon atoms to which group an isocyanato-(C 1-3 )-alkyl group is bound, these alkylene groups may contain one or more sulfur atom(s), and m and n, independently from each other, represent an integer of from 1 to 3. Further, this polyisocyanate compound can be produced by the following processes (production process 1 and production process 2) of the present invention. First, the production process 1 of the present invention is a process for producing a polyisocyanate compound represented by general formula (I-a) wherein m and n, independently from each other, represent an integer of from 1 to 3, X 1 and Y 1 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, and this alkylene group may contain one or more sulfur atom(s), which comprises obtaining a dicarboxylic acid ester represented by general formula (III) wherein R 1 and R 2 , independently from each other, represent a lower alkyl group, X 1 , Y 1 , and m and n are as defined above, from a 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) wherein m and n are as defined above, then converting the same to a dicarbonyl hydrazide represented by general formula (IV) wherein m, n, X 1 and Y 1 are as defined above, and thereafter converting the carbonyl hydrazide group into an isocyanate group. Next, the production process 2 of the present invention is a process for producing a polyisocyanate compound represented by general formula (I-b) wherein A 1 and A 2 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, this alkylene group may contain one or more sulfur atom(s) and the isocyanatoalkyl substituent may bind at any position of the alkylene group, B 1 and B 2 , independently from each other, represent an alkylene group having from 1 to 3 carbon atoms, m and n, independently from each other, represent an integer of from 1 to 3, and k represents 0 or 1, which comprises obtaining a tricarboxylic acid ester or a tetracarboxylic acid ester represented by general formula (V) wherein A 1 , A 2 , B 1 , B 2 , k, m and n are as defined above, and R 3 and R 4 , independently from each other, represent a lower alkyl group, from the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by the above-mentioned general formula (II), then converting the same to a tricarbonyl hydrazide or a tetracarbonyl hydrazide represented by general formula (VI) wherein A 1 , A 2 , B 1 , B 2 , m, n and k are as defined above, and subsequently converting the carbonyl hydrazide group into an isocyanate group. The present invention also provides an optical material formed of a poly(thio)urethane which is obtained by subjecting a monomer mixture containing (A) a component containing at least a polyisocyanate compound represented by general formula (I) as defined above and (B) a component containing at least one compound selected from (i) a compound having two or more mercapto groups in a molecule, (ii) a compound having two or more hydroxyl groups in a molecule and (iii) a compound having one or more hydroxyl groups and one or more mercapto groups in a molecule to a polyaddition reaction. Further, the present invention is to provide an optical product formed of the above-mentioned optical material. The polyisocyanate compound of the present invention is a novel compound represented by general formula (I) As is clear from general formula (I), this novel compound has a structure that isocyanatoalkyl groups having at least one sulfur atom are bound to the 2- and 5-positions of the 1,4-dithian ring which is an alicyclic sulfide. In the above-mentioned general formula (I), X and Y, independently from each other, represent an alkylene group having from 1 to 5 carbon atoms or an alkylene group having from 1 to 5 carbon atoms to which group an isocyanato-(C 1-3 )-alkyl group is bound, and these alkylene groups may contain one or more sulfur atom(s), preferably one or two sulfur atoms. It is preferable that the sulfur atoms are bound to two carbon atoms in the alkylene groups. As the X and Y, a methylene group or an ethylene group, or a group represented by the formula namely, (a) a methylene group to which an isocyanatomethyl group is bound, (b) an ethylene group in which an isocyanatomethyl group is bound to a carbon atom bound to a sulfur atom or (c) an ethylene group in which an isocyanatomethyl group is bound to a carbon atom bound to an isocyanate group, is preferable. Further, m and n, independently from each other, represent an integer of from 1 to 3, and 1 is especially preferable. Thus, the polyisocyanate compound represented by general formula (I) contains not only the 1,4-dithian ring but also the sulfur atoms other than the 1,4-dithian ring, whereby the refractive index and the Abbe number of the polyisocyanate compound itself are increased. Accordingly, when an optical material is produced using this polyisocyanate compound, the refractive index and the Abbe number of the optical material are also increased. Further, the 1,4-dithian ring in this polyisocyanate compound is rigid. Therefore, when an optical material is produced using this, excellent mechanical characteristics can be given to the optical material. Further, in this polyisocyanate compound, when the isocyanatoalkyl groups (provided the carbon number of the alkyl group is between 1 and 3) are bound to the alkylene groups having from 1 to 5 carbon atoms which groups may contain sulfur atom(s) as indicated at X and Y in general formula (I), this compound itself becomes a crosslinking agent. Accordingly, when the optical material is produced using this, a high heat resistance and a high solvent resistance can be imparted to the optical material without adding other crosslinking agent as a secondary component. A process for producing this polyisocyanate compound represented by general formula (I) may be a process by which a polyisocyanate compound having a desired structure is available, and it is not particularly limited. However, it can be produced at quite good efficiency according to the processes 1 and 2 of the present invention as mentioned below. For the purpose of this application a lower alkyl group is preferably a (C 1-6 )-alkyl group and more preferably a (C 1-4 )-alkyl group. Production process 1: In this production process 1, first, a 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) wherein m and n, independently from each other, represent an integer of from 1 to 3, is used as a starting material. From this, a dicarboxylic acid ester represented by general formula (III) wherein R 1 and R 2 , independently from each other, represent a lower alkyl group, X 1 and Y 1 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, and this alkylene group may contain one or more sulfur atom(s), and m and n are as defined above, is obtained. To obtain this dicarboxylic acid ester represented by general formula (III), for example, it is advisable to use a method in which the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by the above-mentioned general formula (II) is reacted with an aliphatic carboxylic acid lower alkyl ester having a halogen group such as a chlorine atom, a bromine atom or the like at the end in the presence of a hydrogen halide trapping agent, or a method in which it is reacted with an aliphatic carboxylic acid lower alkyl ester having a vinyl group at the end in the presence of a radical or anionic catalyst. For example, when X 1 and Y 1 are each a methylene group in general formula (III), it is advisable to react the same with a homohalogenoacetic acid lower alkyl ester. When X 1 and Y 1 are each an ethylene group, it is advisable to react the same with an acrylic acid lower alkyl ester. And, when X 1 and Y 1 are the same, it is advisable to react 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) with substantially 2 mols of an aliphatic carboxylic acid lower alkyl ester having a halogen group or a vinyl group in the end. On the contrary, when X 1 and Y 1 are different, it is advisable to use a two-step method in which 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) is first reacted with substantially 1 mol of an aliphatic carboxylic acid lower alkyl ester having a halogen group or a vinyl group in the end and then with substantially 1 mol of another aliphatic carboxylic acid lower alkyl ester having a halogen group or a vinyl group in the end. In the above-mentioned reaction, an appropriate solvent can be used as required. Next, the thus-obtained dicarboxylic acid ester represented by general formula (III) is reacted with hydrazine hydride or the like to convert the same to a dicarbonyl hydrazide represented by general formula (IV) wherein m, n, X 1 and Y 1 are as defined above. At this time, a solvent such as a lower alcohol or the like can be used as required. Finally, the thus-obtained dicarbonyl hydrazide represented by general formula (IV) is reacted with nitrous acid in, for example, a hydrochloric acid aqueous solution, and the heat transfer is conducted to convert a carbonyl hydrazide group into an isocyanate group, whereby a desired polyisocyanate compound represented by general formula (I-a) wherein m, n, X 1 and Y 1 are as defined above, is obtained. Production process 2: In this production process 2, first, the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by the above-mentioned general formula (II) is used as a starting material. From this, a tricarboxylic acid ester or a tetracarboxylic acid ester represented by general formula (V) wherein A 1 and A 2 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, this alkylene group may contain one or more sulfur atom(s) and the isocyanatoalkyl substituent may bind at any position of the alkylene group, R 3 and R 4 , independently from each other, represent a lower alkyl group, B 1 and B 2 , independently from each other, represent an alkylene group having from 1 to 3 carbon atoms, k represents 0 or 1, and m and n are as defined above, is obtained. To obtain the tetracarboxylic acid ester of the compounds represented by general formula (V), it is advisable to use a method in which the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by the above-mentioned general formula (II) is reacted with an aliphatic dicarboxylic acid lower alkyl ester having a halogen group such as a chlorine atom, a bromine atom or the like in the molecule in the presence of a hydrogen halide trapping agent, a method in which it is reacted with an aliphatic carboxylic acid lower alkyl ester having a vinyl group in the molecule in the presence of a radical or anionic catalyst, or the like. For example, when A 1 and A 2 are each a substituted ethylene group in which B 1 or B 2 is bound to a carbon atom bound to a sulfur atom and B 1 and B 2 are each a methylene group, it is advisable to react the same with a glutaconic acid di-lower alkyl ester (ROOC-CH 2 CH=CH-COOR, R is a lower alkyl group). When A 1 and A 2 and B 1 and B 2 are the same respectively, it is advisable to react 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) with substantially 2 mols of an aliphatic dicarboxylic acid lower alkyl ester having a halogen group or a vinyl group in the molecule. Further, when A 1 and A 2 or B 1 and B 2 are each different, it is advisable to use a two-step method in which 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) is first reacted with substantially 1 mol of an aliphatic dicarboxylic acid lower alkyl ester having a halogen group or a vinyl group in the molecule and then with substantially 1 mol of another aliphatic dicarboxylic acid lower alkyl ester having a halogen group or a vinyl group in the molecule. On the contrary, to obtain the tricarboxylic acid ester (k=0) of the compounds represented by general formula (V), it is advisable to use a method in which 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by the above-mentioned general formula (II) is first reacted with, as in the production method 1, substantially 1 mol of an aliphatic carboxylic acid lower alkyl ester having a halogen group or a vinyl group in the end and then with substantially 1 mol of an aliphatic dicarboxylic acid lower alkyl ester having a halogen group or a vinyl group in the molecule. Of course, it is also possible to conduct the reverse reaction. In the above-mentioned reaction, an appropriate solvent can be used as required. Next, the thus-obtained tricarboxylic acid ester or tetracarboxylic acid ester represented by general formula (V) is reacted with hydrazine hydride or the like to convert the same to a tricarbonyl hydrazide or a tetracarbonyl hydrazide represented by general formula (VI) wherein A 1 , A 2 , B 1 , B 2 , m, n and k are as defined above. At this time, a solvent such as a lower alcohol or the like can be used as required. Finally, the thus-obtained tricarbonyl hydrazide or tetracarbonyl hydrazide represented by general formula (VI) is reacted with nitrous acid in, for example, a hydrochloric acid aqueous solution, and the heat transfer is conducted to convert a carbonyl hydrazide group into an isocyanate group, whereby a desired polyisocyanate compound represented by general formula (I-b) wherein A 1 , A 2 , B 1 , B 2 , m, n and k are as defined above is obtained. Further, the polyisocyanate compound represented by general formula (I) can be produced by a phosgene method other than the above-mentioned methods of the present invention. Next, the phosgene method is described by taking an example. First, 1 mol of the 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) is reacted with substantially 2 mols of chloroacetonitrile in the presence of a hydrogen chloride trapping agent to obtain a dinitrile represented by general formula (VII) wherein m and n are as defined above. Then, this is subjected to hydrogenation to convert it to a diamine represented by general formula (VIII) wherein m and n are as defined above. The compound is then reacted with phosgene to obtain a desired polyisocyanate compound represented by general formula (I-c) wherein m and n are as defined above. As examples of the polyisocyanate compound represented by general formula (I) in the present invention, compounds having the following structures can be mentioned. The optical material of the present invention is formed of a poly(thio)urethane. As the component (A), one of the starting materials of the poly(thio)urethane, a component containing a polyisocyanate compound represented by general formula (I) as defined above is used. The component (A) may contain, to appropriately improve properties and the like of the optical material, one or two or more types of a compound having two or more isocyanate groups in a molecule other than the polyisocyanate compound represented by the above-mentioned general formula (I). Specific examples of these compounds include o-xylylene diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, α,α,α',α'-tetramethyl -p -xylylene diisocyanate, α,α,α',α'-tetramethyl-m-xylylene diisocyanate, 1,3,5-tris(isocyanatomethyl)benzene, hexamethylene diisocyanate, 1,4-diisocyanatobutane, isophorone diisocyanate, norbornene diisocyanate, bis(4,4'-isocyanatocyclohexyl)methane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(isocyanatomethyl)cyclohexane, 1,4-diisocyanatocyclohexane, 1,3,5-triisocyanatocyclohexane, lysine triisocyanate, 2,5-bis(isocyanatomethyl)-1,4-dithian, 1,3-dithiolan-4,5-diisocyanate, 4,5-bis (isocyanatomethyl) -1,3-dithiolan, isocyanatomethyl sulfide, 2-isocyanatoethyl sulfide, bis(isocyanatomethylthio)methane, 1,2-bis(isocyanatomethylthio)ethane, bis(2-isocyanatoethylthio)methane, 1,2-bis(2-isocyanatoethylthio)ethane, 1,7-diisocyanato-2,4,6-trithiaheptane, 1,5-diisocyanato-2-isocyanatomethyl-3-thiapentane, 1,4-diisocyanato-2-isocyanatomethyl-3-thiabutane and the like. The content of the polyisocyanate compound represented by general formula (I) in the component (A) is preferably 0.1 mol% or more, especially preferably 5 mol% or more. As the component (B), another starting material of the poly(thio)urethane, a component containing at least one compound selected from (i) a compound having two or more mercapto groups in a molecule, (ii) a compound having two or more hydroxyl groups in a molecule and (iii) a compound having one or more hydroxyl groups and one or more mercapto groups in a molecule is used. Examples of the compound having two or more mercapto groups in a molecule as the component (i) include 2,5-bis(mercaptomethyl)-1,4-dithian and its oligomer, 1,2,3-trimercaptopropane, tetrakis(7-mercapto-2,5-dithiaheptyl)methane, 1,2-ethanedithiol, 1,3-propanedithiol, tetrakismercaptomethylmethane, 2-mercaptoethyl sulfide, pentaerythritol tetrakismercaptopropionate, pentaerythritol tetrakismercaptoacetate, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 1,3,5-benzenetrithiol, 1,2-dimercaptomethylbenzene, 1,3-dimercaptomethylbenzene, 1,4-dimercaptomethylbenzene, 1,3,5-trimercaptomethylbenzene, toluene-3,4-dithiol, tris(3-mercaptopropyl) isocyanurate, 1,3-bis(mercaptomethyl)cyclohexane, 1,4-bis(mercaptomethyl)cyclohexane, 2,2-bis(mercaptomethyl)-1,3-propanediol, 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane, 4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol and the like. Further, examples of the compound having two or more hydroxyl groups in a molecule as the component (ii) include ethylene glycol, trimethylolpropane, glycerin, dihydroxybenzene, catechol, 4,4'-dihydroxyphenyl sulfide, 2-hydroxyethyl sulfide, bisphenol A·propylene oxide 5-mol adduct, glycerin.propylene oxide 3-mol adduct and the like. Examples of the compound having one or more hydroxyl groups and one or more mercapto groups in a molecule as the component (iii) include 2-mercaptoethanol, 2,3-dimercaptopropanol, 1,2-dihydroxy-3-mercaptopropane, 4-mercaptophenol and the like. As the component (B), the mercapto group-containing compound as the component (i) is preferable. Especially, 2,5-bis(mercaptomethyl)-1,4-dithian represented by general formula (IX) wherein a is an integer of from 1 to 20, is preferable. With respect to the ratio of the component (A) and the component (B) in the present invention, it is preferable that the molar ratio of the isocyanate group in the component (A) to the total amount of the mercapto group and the hydroxyl group in the component (B), NCO group/(SH group + OH group), is in the range of from 0.95 to 1.05. The monomer mixture containing the component (A) and the component (B) may contain one or two or more types of the compound having two or more vinyl groups in the molecule to appropriately improve the properties and the like of the optical material in addition to the components (A) and (B). With respect to the ratio of these compounds used at this time, it is preferable that the (isocyanate group + vinyl group)/(mercapto group + hydroxyl group) molar ratio is in the range of from 0.95 to 1.5 and the (vinyl group)/(isocyanate group) molar ratio is 0.7 or less, and that polymerizable functional groups contained in the component (B) are all mercapto groups. Specific examples of these compounds include 2,5-bis(2-thia-3-butenyl)-1,4-dithian, divinylbenzene, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, a urethane-modified (meth)acrylate containing two or more (meth)acryloxy groups in a molecule and the like. By the way, the above-mentioned (meth)acrylate means both of an acrylate and a methacrylate, and the (meth)acryloxy group means both of an acryloxy group and a methacryloxy group. To the optical material of the present invention can be added an ultraviolet absorber, a coloring matter, a pigment and the like for improving light absorption characteristics, an antioxidant, a coloration inhibitor and the like for improving a weatherability, and a release agent and the like for improving a moldability, as required. Here, examples of the ultraviolet absorber include a benzotriazole type, a benzophenone type, a salicylic acid type and the like. Examples of the coloring matter and the pigment include an anthraquinone type, an azo type and the like. Examples of the antioxidant and the coloration inhibitor include a monophenol type, a bisphenol type, a high-molecular phenol type, a sulfur type, a phosphorus type and the like. Examples of the release agent include a fluorine-type surfactant, a silicone-type surfactant, an acidic phosphate, a higher fatty acid and the like. Further, a catalyst may be used, as required, to improve an polymerization reactivity, and an amine compound, an organic metal compound and the like are effective. Specific examples thereof include triethylenediamine, hexamethylenetetramine, N,N-dimethyloctylamine, N,N,N',N'-tetramethyl-1,6-diaminohexane, 4,4'-trimethylenebis(1-methylpiperidine), 1,8-diazabicyclo-(5,4,0)-7-undecene, dimethyltin dichloride, dimethyltin bis(isooctylthioglycolate), dibutyltin dichloride, dibutyltin dilaurate, dibutyltin maleate, dibutyltin maleate polymer, dibutyltin diricinoleate, dibutyltin bis(dodecylmercaptide), dibutyltin bis(isooctylthioglycolate), dioctyltin dichloride, dioctyltin maleate, dioctyltin maleate polymer, dioctyltin bis(butylmaleate), dioctyltin dilaurate, dioctyltin diricinoleate, dioctyltin dioleate, dioctyltin di(6-hydroxy)caproate, dioctyltin bis(isooctylthioglycolate), didodecyltin diricinoleate, copper oleate, copper aceylacetonate, iron aceylacetonate, iron naphthenate, iron lactate, iron citrate, iron gluconate, potassium octanate, 2-ethylhexyl titanate and the like. The above-mentioned catalysts are effectively used either singly or in combination of two or more types. In addition, when the vinyl compound is contained in the monomer mixture, the use of an organic peroxide, an azo compound or the like other than the catalyst is effective. For example, the production of the optical material of the present invention using the polyisocyanate compound of the present invention is mentioned as follows. The uniform mixture of the component (A), the component (B), the additives and the catalyst is subjected to a known cast polymerization method, that is, it is cast into a die which is a combination of a glass or metal mold and a gasket made of a resin, and cured by heating. At this time, in order to expedite withdrawal of the resin after molding, the mold may previously be subjected to release treatment, or a release agent may be added to the mixture of the component (A), the component (B) and the like. The polymerization temperature varies depending on the compound used. It is usually between -20 and +150°C. The polymerization time is between 0.5 and 72 hours. The optical material of the present invention can easily be dyed in water or an organic solvent using an ordinary disperse dye. At this time, for further expediting the dyeing, a carrier may be added or heating may be conducted. The thus-obtained optical material is used as a plastic lens especially preferably, but is not limited thereto. Brief Description of the Drawings: Fig. 1 shows an 1 H-NMR spectrum of 2,5-bis(4-isocyanato-2-thiabutyl)-1,4-dithian obtained in Example 1. Fig. 2 shows an IR spectrum of 2,5-bis(4-isocyanato-2-thiabutyl)-1,4-dithian obtained in Example 1. Fig. 3 shows an 1 H-NMR spectrum of 2,5-bis(4-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian obtained in Example 2. Fig. 4 shows an IR spectrum of 2,5-bis(3-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian obtained in Example 2. Next, the present invention is illustrated more specifically by referring to Examples. However, the present invention is not limited at all to these Examples. The properties of the resulting polyisocyanate compounds and optical materials (polymers) were evaluated according to the following methods. (1) 1 H-NMR spectrum (proton nuclear magnetic resonance spectrum) Measured using an FT-NMR Device EX 270 Model supplied by JEOL. (2) IR spectrum (infrared absorption spectrum) Measured using a MAGNA-IR Spectrometer 560 Model supplied by Nicoley. (3) Refractive index (nD) and Abbe number (νD) Measured at 20°C using an Abbe refractometer 3T supplied by Atago. (4) Appearance Visually observed. (5) Heat resistance A dynamic viscoelasticity was measured with a static tension of 100 g and a frequency of 10 kHz by means of a dynamic viscoelasticity-measuring device supplied by Toyo Seiki Seisakusho. A heat resistance was evaluated in terms of a temperature of a decreasing point in a chart of a modulus of elasticity obtained at a rate of temperature rise of 2°C/min. (6) Weatherability A lens (optical product using an optical material) was mounted on a weather meter fitted with a sunshine carbon arc lamp. When 200 hours passed, the lens was taken out, and the color thereof was compared with that of the lens before the test.The weatherability was evaluated according to the following standard as given in Table 1: O: unchanged, Δ: slightly yellowed, ×: yellowed (7) Optical distortion Visually observed by the Schlieren method. The optical distortion was evaluated according to the following standard as given in Table 1: O: No distortion is observed, ×: Distortion is observed. Example 1 Production of 2,5-bis(4-isocyanato-2-thiabutyl) -1,4-dithian 2,5-Bis(mercaptomethyl)-1,4-dithian (31.8 g, 0.15 mols) and 25.8 g (0.3 mols) of methyl acrylate were dissolved in 150 ml of chloroform. Triton B (40% by weight methanol solution, 0.8 g) was added as a catalyst in an ice bath, and the solution was stirred under reflux for 3 hours. The reaction solution was allowed to cool, then washed with a dilute sodium hydroxide aqueous solution and with water in this order, and dried over magnesium sulfate. Thereafter, chloroform was fully removed to obtain 46.8 g (0.12 mols) of a colorless transparent ester compound. This ester compound was dissolved in 100 ml of methanol, and added dropwise to a mixed solution of 36.0 g (0.72 mols) of hydrazine hydrate and 36 ml of methanol at room temperature. After the completion of the dropwise addition, the mixture was stirred at 70°C for 4 hours. Since white crystals were precipitated while the mixture was allowed to cool, these were collected through filtration, and recrystallized from methanol-water to obtain 39.3 g (0.11 mols) of a hydrazide compound. This hydrazide compound was dissolved in 160 g of a 7.2% by weight hydrochloric acid aqueous solution, and 16.7 g (0.24 mols) of sodium nitrite were added to a suspension with 100 ml of chloroform. After the completion of the addition, the stirring was continued for 1 hour. The organic phase was withdrawn from the suspension, washed with water, dried (magnesium sulfate), and then heated to complete the transition reaction. Chloroform was fully removed from the reaction solution to obtain 22.1 g (0.063 mols) of a colorless transparent reaction product. This reaction product was identified to be desired 2,5-bis(4-isocyanato-2-thiabutyl) -1,4-dithian from the 1 H-NMR spectrum and the IR spectrum. The 1 H-NMR spectrum of this polyisocyanate compound is shown in Fig. 1, and the IR spectrum thereof in Fig. 2. Example 2 Production of 2,5-bis(3-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian 2,5-Bis(mercaptomethyl)-1,4-dithian (26.5 g, 0.125 mols) and 46.6 g (0.25 mols) of diethyl glutaconate were dissolved in 100 ml of tetrahydrofuran. Tetrabutylammonium fluoride (0.65 g, 0.0025 mols) was added as a catalyst in an ice bath, and the solution was stirred under reflux for 2 hours. The reaction solution was allowed to cool, and tetrahydrofuran was then removed. Benzene (150 ml) was added to the residue. The mixture was washed with a dilute sodium hydroxide aqueous solution and with water in this order, and dried over magnesium sulfate. Thereafter, benzene was fully removed to obtain 61.4 g (0.105 mols) of a pale yellow transparent ester compound. This ester compound was dissolved in 26 ml of methanol, and added dropwise to a mixed solution of 104.2 g (2.08 mols) of hydrazine hydrate and 26 ml of methanol at room temperature. After the completion of the dropwise addition, the mixture was stirred at 80°C for 4 hours. The reaction solution was allowed to cool, and then added to 300 ml of methanol. A yellow solid precipitated was collected through filtration, and heat-washed with ethanol-water to obtain 21.9 g (0.042 mols) of a hydrazide compound. This hydrazide compound was dissolved in 600 g of a 15% by weight hydrochloric acid aqueous solution, and 12.6 g (0.18 mols) of sodium nitrite were added to a suspension with 300 ml of toluene. After the completion of the addition, the stirring was continued for 1 hour. The organic phase was withdrawn from the suspension, washed with water, dried (magnesium sulfate), and then heated to complete the transition reaction. Toluene as a solvent was fully removed from the reaction solution to obtain 6.6 g (0.014 mols) of a colorless transparent reaction product. This reaction product was identified to be desired 2,5-bis (3-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian from the 1 H-NMR spectrum and the IR spectrum. The 1 H-NMR spectrum of this polyisocyanate compound is shown in Fig. 3, and the IR spectrum thereof in Fig. 4. Application Example 1 A mixture of 0.10 mols of 2,5-bis(4-isocyanato-2-thiabutyl)-1,4-dithian (designated DT-1 in Table 1) obtained in Example 1, 0.10 mols of 2,5-bis(mercaptomethyl)-1,4-dithian (designated DMMD in Table 1) and 1.0 x 10 -4 mols of dibutyltin dilaurate (designated DBTDL in Table 1) was uniformly stirred, and cast into two glass molds for forming a lens. The mixture was heat-polymerized at 50°C for 10 hours, then at 60°C for 5 hours and further at 120°C for 3 hours to obtain a plastic lens. The properties of the resulting plastic lens are shown in Table 1. From Table 1, it was found that the polymer obtained by using the polyisocyanate compound of Example 1 was colorless and transparent, the refractive index (n D ) was as high as 1.67, the Abbe number (ν D ) was also as high as 36 (low dispersion), the weatherability and the heat resistance (114°C) were excellent, and no optical distortion was observed. Application Example 2 A mixture of 0.06 mols of 2,5-bis(3-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian (designated DT-2 in Table 1) obtained in Example 2, 0.12 mols of DMMD and 1.2 x 10 -4 mols of dibutyltin dilaurate (designated DBTDL in Table 1) was uniformly stirred, and cast into two glass molds for forming a lens. The mixture was heat-polymerized at 50°C for 10 hours, then at 60°C for 5 hours and further at 120°C for 3 hours to obtain a plastic lens. The properties of the resulting plastic lens are shown in Table 1. From Table 1, it was found that the polymer obtained by using the polyisocyanate compound of Example 2 was colorless and transparent, the refractive index (n D ) was as high as 1.67, the Abbe number (ν D ) was also as high as 37 (low dispersion), the weatherability and the heat resistance (127°C) were excellent, and no optical distortion was observed. Application Examples 3 to 11 The same procedure as in Application Example 1 was conducted except using a monomer composition containing each of the polyisocyanate compounds DT-1 and DT-2 [indicating 2,5-bis(4-isocyanato-2-thiabutyl)-1,4-dithian and 2,5-bis(3-isocyanatomethyl-4-isocyanato-2-thiabutyl)-1,4-dithian respectivelyJ obtained in Examples 1 and 2 and 2 ,5-bis (3-isocyanato-2-thiapropyl) -1,4-dithian (designated DT-3 in Table 1) as shown in Table 1 to obtain a plastic lens. The properties of these plastic lenses were shown in Table 1. From Table 1, it was found that the resulting plastic lenses were colorless and transparent, the refractive index (n D ) was as high as between 1.65 and 1.69, the Abbe number (ν D ) was also as high as between 35 and 38 (low dispersion), the heat resistance (96 to 127°C) and the weatherability were excellent, and no optical distortion was observed. Application Comparative Example 1 A mixture of 0.06 mols of pentaerythritol tetrakismercaptopropionate (designated PETMP in Table 1), 0.12 mols of m-xylylene diisocyanate (designated XDI in Table 1) and 1.2 x 10 -4 mols of dibutyltin dilaurate (designated DBTDL in Table 1) was uniformly stirred, and cast into two glass molds for forming a lens. The mixture was heat-polymerized at 50°C for 10 hours, then at 60°C for 5 hours and further at 120°C for 3 hours to obtain a plastic lens. The properties of the resulting plastic lens are shown in Table 1. From Table 1, it was found that the plastic lens in this Application Comparative Example 1 was colorless and transparent, and no optical distortion was observed, but the refractive index was as poor as 1.59. Application Comparative Examples 2 and 3 The same procedure as in Application Comparative Example 1 was conducted except using monomer compositions shown in Table 1 to obtain plastic lenses. The properties of these plastic lenses are shown in Table 1. From Table 1, it was found that the plastic lens in this Application Comparative Example 2 had a high refractive index of 1.68 and was excellent in the heat resistance (128°C). However, it was colored yellow, the Abbe number was low (25), the weatherability was poor, and the optical distortion was observed. Further, the plastic lens in this Application Comparative Example 3 was colorless and transparent, and had a high refractive index of 1.66. However, the optical distortion was observed, and the heat resistance (71°) was also poor. Since the novel polyisocyanate compound of the present invention has the 1,4-dithian ring in the main skeleton and the sulfur atom in the side chain, the refractive index and the Abbe number are high. Since it has from 2 to 4 isocyanate groups, it is easily polymerized with at least one type of a compound having two or more hydroxyl groups in a molecule, a compound having two or more mercapto groups in a molecule and a compound having one or more hydroxyl groups and one or more mercapto groups in a molecule to provide an optical material. Further, since the optical material obtained by using this polyisocyanate compound has the 1,4-dithian ring contributing to the heat resistance and further the sulfur atom in the basic skeleton, the refractive index and the Abbe number are high, the heat resistance, the weatherability and the transparency are excellent, and no optical distortion is observed. Accordingly, it is preferably used in lenses such as a spectacle lens, a camera lens and the like, a prism, optical fibers, substrates for recording medium used in an optical disk, a magnetic disk and the like, and optical products such as a filter and the like. Further, it is used in ornamental products such as glasses, vases and the like which are obtained by making the most of the property of the high refractive index.

Claims: A polyisocyanate compound represented by general formula (I) wherein X and Y, independently from each other, represent an alkylene group having from 1 to 5 carbon atoms or an alkylene group having from 1 to 5 carbon atoms to which group an isocyanato-(C 1-3 )-alkyl group is bound, these alkylene groups may contain one or more sulfur atom(s), and m and n, independently from each other, represent an integer of from 1 to 3. The polyisocyanate compound recited in claim 1, wherein in general formula (I), X and Y are each a methylene group or an ethylene group. The polyisocyanate compound recited in claim 1, wherein in general formula (I), X and Y are each a methylene group to which an isocyanatomethyl group is bound, an ethylene group in which an isocyanatomethyl group is bound to a carbon atom bound to a sulfur atom or an ethylene group in which an isocyanatomethyl group is bound to a carbon atom bound to an isocyanate group. The polyisocyanate compound recited in claim 1, 2 or 3, wherein in general formula (I), m and n are each 1. A process for producing a polyisocyanate compound represented by general formula (I-a) wherein m and n, independently from each other, represent an integer of from 1 to 3, X 1 and Y 1 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, and this alkylene group may contain one or more sulfur atom(s), which comprises obtaining a dicarboxylic acid ester represented by general formula (III) wherein R 1 and R 2 , independently from each other, represent a lower alkyl group, and X 1 , Y 1 , m and n are as defined above, from a 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) wherein m and n are as defined above, then converting the same to a dicarbonyl hydrazide represented by general formula (IV) wherein m, n, X 1 and Y 1 are as defined above, and thereafter converting the carbonyl hydrazide group into an isocyanate group. A process for producing a polyisocyanate compound represented by general formula (I-b) wherein A 1 and A 2 , independently from each other, represent an alkylene group having from 1 to 5 carbon atoms, this alkylene group may contain one or more sulfur atom(s) and the isocyanatoalkyl substituent may bind at any position of the alkylene group, B 1 and B 2 , independently from each other, represent an alkylene group having from 1 to 3 carbon atoms, m and n, independently from each other, represent an integer of from 1 to 3, and k represents 0 or 1, which comprises obtaining a tricarboxylic acid ester or a tetracarboxylic acid ester represented by general formula (V) wherein A 1 , A 2 , B 1 , B 2 , k, m and n are as defined above, and R 3 and R 4 , independently from each other, represent a lower alkyl group, from a 2,5-bis(mercaptoalkyl)-1,4-dithian represented by general formula (II) wherein m and n are as defined above, then converting the same to a tricarbonyl hydrazide or a tetracarbonyl hydrazide represented by general formula (VI) wherein A 1 , A 2 , B 1 , B 2 , m, n and k are as defined above, and subsequently converting the carbonyl hydrazide group into an isocyanate group. The process for producing the polyisocyanate compound as recited in claim 5, wherein X 1 and Y 1 are each a methylene group or an ethylene group. The process for producing the polyisocyanate compound as recited in claim 6, wherein A 1 and A 2 are each a methylene group, an ethylene group in which B 1 or B 2 is bound to a carbon atom bound to a sulfur atom or an ethylene group in which B 1 or B 2 is bound to a carbon atom except a carbon atom bound to a sulfur atom, and B 1 and B 2 are each a methylene group. The process for producing the polyisocyanate compound as recited in any one of claims 5 to 8, wherein m and n are each 1. An optical material formed of a poly(thio)urethane which is obtainable by subjecting a monomer mixture containing (A) a component containing at least a polyisocyanate compound represented by general formula (I) as claimed in any of claims 1-4 and (B) a component containing at least one compound selected from (i) a compound having two or more mercapto groups in a molecule, (ii) a compound having two or more hydroxyl groups in a molecule and (iii) a compound having one or more hydroxyl groups and one or more mercapto groups in a molecule to a polyaddition reaction. The optical material recited in claim 10, wherein the component (i) of the component (B) is a compound represented by general formula (IX) wherein a represents an integer of from 1 to 20. The optical material recited in one of claims 10 or 11, which is optically transparent. An optical product formed of the optical material recited in any one of claims 10 to 12. The optical product recited in claim 13, which is a spectacle lens. Use of a polyisocyanate compound represented by general formula (I) as claimed in any of claims 1-4 in the preparation of optical materials.

Inventors: JIANG JIAN, KITAHARA YOSHITAKA, JIANG, JIAN, KITAHARA, YOSHITAKA
Applicants: HOYA CORP, HOYA CORPORATION
Application year: 1999
Main classification: C07D339
IPC codes: C08G18, C07D339, G02B1