Title of Invention	A POLYIMIDE AND A PROCESS FOR THE PREPARATION OF THE SAME
Abstract	A polyimide and a process for the preparation of the same. More particularly the invention relates to a process for the preparation of a polyimide using a renewable resource, Cashew Nut Shell Liquid (CNSL). The polyimides provided by the present invention are useful particularly as alignment films for liquid crystal display devices.

Full Text

This invention relates to a polyimide and a process for the preparation of the same. More particularly the invention relates to a process for the preparation of a polymide having formula (1) (Formula Removed) using a renewable resource, Cashew Nut Shell Liquid (CNSL). The polyimides provided by the present invention are useful particularly as alignment films for liquid crystal display devices. The polyimide of formula (1) may be a homo or copolyimide comprising an aromatic diamine having at least one pentadecyl phenoxy group per benzene ring as shown in formula (2) (Formula Removed) as the essential diamine component and a tetracarboxylic acid or its derivative and optionally other common diamines having formula (2) in the case of homopolyimides Polyimides are widely used as protective materials or insulating materials in electric and electronic fields due to their high mechanical strength, heat resistance and solvent resistance. However, developments in electric and electronic fields have been remarkable in recent years, and increasingly high levels of properties have been required for the materials to be used in such fields. Especially for alignment films for liquid crystal display devices, polyimides have heretofore been employed in most cases by virtue of the uniform quality and durability of the coated film surface. However along with the trend for high densification and high performance of display devices, the surface properties of the polyimide coating films have become particularly important, and it has been necessary to impart new properties which conventional polyimides do not have. Liquid crystal display devices are display devices, which utilize electrooptical changes of liquid crystals, and they are small in size and light in weight and have a feature that their power consumption is small. Accordingly they have found remarkable developments in recent years as display devices for various displays. In certain liquid crystals cells, particularly in those with nematic and cholestric liquid crystals, the cell wall which are in contact with the liquid crystal material must be provided with alignment layers to achieve the desired molecular orientation of the liquid crystals. As a rule, the alignment layers are deposited so that molecules at opposite cell walls lie mutually at 90°C. The alignment layer consists either of inorganic substances deposited by oblique evaporation in a vacuum or of organic substances applied by dipping, brushing, or spraying. Alignment layers of inorganic materials, such as calcium fluoride or silicon monoxide, are formed by evaporating the substances in a high vacuum at a very small angle to the substrate. Such layers are not suitable for mass production because they require a large amount of work and apparatus. Alignment layers of organic materials are relatively easy to produce because the organic material, dissolved in a solvent can be applied by dipping, spraying, or brushing. In such layers, the desired molecular orientation is achieved by subjecting the applied material to directional mechanical action, particularly by rubbing the surface in a predetermined direction with a cloth of e.g. nylon, rayon, or polyester. The liquid crystal molecules then align themselves on such a layer by adhering at one end to the organic material. The organic film used may be polyvinyl alcohol, polyoxyethylene, polyamide, or polyimide. However polyimide is commonly used in view of the chemical stability, thermal stability, etc. however, the tilt angle obtainable by rubbing the polyimide is usually at a level from 1° to 3° and it has been difficult to attain a large tilt angle. In the field of liquid crystal alignment films, it has been difficult to obtain a large tilt angle constantly by rubbing an organic film of polyimide or the like. As a means to solve this problem, Japanese Unexamined Patent Publication No. 297819/1987 discloses a treating agent for liquid crystal alignment comprising of a reaction product of a long chain alkylamine with a polyimide precursor. Further, Japanese Unexamined Patent Publication No. 262527/1989 and No. 262528/1989 disclose an agent for liquid crystal alignment which comprises of a mixture comprising a long chain alkyl compound and a polyimide precursor. Japanese Unexamined Patent Publication No. 25126/1989 discloses a treating agent for liquid crystal alignment which comprises of a polyimide prepared from a diamine having an alkyl group. Thus many attempts have been made to increase the pretilt angle of the liquid crystal by introducing an alkyl group into a polyimide, and it has been possible to increase the tilt angle to some extent. On the other hand, such attempts have resulted in a new problem -when an alkyl group is introduced into a polyimide to increase the tilt angle, the wettability of liquid crystal tends to be low, and in an extreme case, the failure in liquid crystal alignment is likely to result. Consequently, the display performance of the liquid crystal display device tends to be poor. It is therefore necessary to develop a polyimide alignment film, which gives good tilt angle as well as adequate wettability. US Patent No. 5861534/1999 discloses a polyimide alignment layer prepared from different diamines with long alkyl group and a readily polarizable chemical bond group, which gives good alignment properties. The main object of the present invention is to provide a process for the preparation of the polyimides, which can be used to synthesize a polyimide liquid crystal alignment layer from a renewable and economically viable resource, cashew nut shell liquid. It is observed that reacting a diamine containing at least one mole% of the diaminobenzene derivative of formula (2), which contains a pentadecyl phenoxy group, introduced to the diamine structure from a naturally occurring renewable resource, cashew nut shell liquid and a tetracarboxylic acid or its derivatives (compound 3, Ri), optionally with other common diamines (compound 4) provides a homo or copolyimide having formula (1). The use of such a diamine, which was synthesized from a naturally occurring renewable and economically viable resource, the cashew nut shell liquid, opens a new route for the production of polyimide having on its side chain, a substituent similar to a liquid srystal molecule and with excellent aligning properties and high solubility in common organic solvents. Accordingly, the present invention provides a polyimide of formula 1 (Formula Removed) wherein R1 is tetracarboxylic acid residue or a derivative thereof and R2 is selected from the residue of a compound of formula 2 and a process for the preparation of the same the said process comprising reacting a diamine selected from aromatic diamine having at least one pentadecyl phenoxy group per benzene ring of formula (2) (Formula Removed) with tetracarboxylic acid or its derivative, optionally in presence of another diamine in a dipolar aprotic amide or sulphoxide solvent at a temperature ranging between 0°C to 15°C under a stream of inert gas for a period ranging between 5 to 24 hrs. to obtain a polyimide precursor, imidizing the said polyimide precursor thermally in the form of a film by coating on a glass substrate and subsequently heating from 100°C to 400°C or chemically by adding dehydrating agent selected from acid anhydrides in the presence of tertiary amine and heating at a temperature between 30°C to 120°C for 2 to 24 hrs, precipitating the resulting polymer in methanol, filtering and drying to obtain the said polyimide of formula 1. In an embodiment of the present invention the dipolar aprotic solvent used is selected from the group consisting of amide solvents such as N-methylpyrrolidinone, N,N-dimethylacetamide, N,N-dimethyl formamide and tetramethylurea and sulphoxides such as dimethylsulphoxide. In an another embodiment the dehydrating agent used for chemical imidization is selected from the group consisting of acetic anhydride, propionic anhydride, n-butyric anhydride and benzoic anhydride. In yet another embodiment the tertiary amine used for chemical imidization is selected from the group consisting of pyridine, methylpyridines, lutidine, N-methylmorpholine and trialkylamines. In yet another embodiment the tetracarboxylic acid or its derivative used is selected from the group consisting of pyromellitic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,4,5,8-naphthalene tetracarboxylic acid, 1,2,5,6-naphthalene tetracarboxylic acid, 2,3,6,7-anthracene tetracarboxylic acid, 1,2,5,6-anthracene tetacarboxylic acid, 3,3',4,4'-biphenyl tetracarboxylic acid, 2,3,,3',4'-biphenyl tetracarboxylic acid, bis(3,4-dicarboxyphenyl)ether, 3,3',4,4'-benzophenone tetracarboxylic acid, bis(3,4-dicarboxyphenyl) sulphone, bis(3,4-dicarboxyphenyl)methane, 2,2-bis (3,4-dicarboxyphenyl)propane, bis (3,4-dicarboxyphenyl) dimethyl silane, 1,1,1,3,3,3,-hexafluor-2,2- bis (3,4-dicarboxyphenyl) propane, bis *(3,4-dicarboxyphenyl) pyridine, and their dianhydrides, alicyclic tetracarboxylic acids such as 1,2,3,4-cyclobutane tetracarboxylic acid, 1,2,3,4-cyclopentane tetracarboxylic acid, 1,2,4,5-cyciohexane tetracarboxylic acid, 2,3,5-tricarboxycyclopentylacetic acid and 3,4-dicarboxy-1,2,3,4-tetrahydro-1 -naphthalenesuccinic acid, and their dianhydrides. In yet another embodiment the other diamine used is selected from the group consisting of p-phenylenediamine, m-phenylenediamine, 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'- diaminobiphenyl, 3,3 '-dimethyl-4,4'-diaminobiphenyl, 3,3 '-dimethoxy-4,4'- diaminobiphenyl, diaminodiphenyl methane, diaminodiphenyl ether, 2,2'-diaminodiphenyl propane, bis(3,5-diethyl-4-aminophenyl) methane, diaminodiphenyl sulphone, diaminobenzophenone, diaminonaphthalene, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenyl)benzene, 9,10-bis(4-aminophenyl) anthrazene, 1,3-bis(4-aminiophenoxy) benzene, 4,4'-bis(4-aminiophenoxy)diphenyl sulphone, 2,2'-bis[4-(4-aminiophenoxy) phenyljpropane, 2,2'bis(4-aminiophenyl) hexafluropropane and 2,2-bis[4-(4-aminiophenoxy) phenyljhexafluro propane. In yet another embodiment the diamine of formula 2 is used singly or two or more in combination. In yet another embodiment the tetracarboxylic acids are used singly or two or more in combination. In yet another embodiment the the ratio of the molar amount of the said tetracarboxylic dianhydride or combination of tetracarboxylic dianhydrides to the molar amount of the said diamine or combination of diamines is between 0.8 to 1.2. In yet another embodiment the molar amount of tetracarboxylic dianhydride or total molar amount of two or more tetracarboxylic dianhydrides is equal or almost equal to the molar amount of single diamine or total amount of two or more diamines. In yet another embodiment the concentration of the polymer solution is 5 to 40% by weight. In yet another embodiment the concentration of the polymer solution is preferably 10 to 25% by weight. In yet another embodiment the polyimide is a homo or a copolyimide. The synthesis of novel polyimides and their application as liquid crystal alignment layers are described herein below with reference to examples, which are illustrative and should not be construed as limiting the scope of the present invention in any manner. EXAMPLE-1 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethylacetamide (10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried. EXAMPLE - 2 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethylacetamide (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried EXAMPLE -3 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethylformamide (10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried. EXAMPLE -4 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethylformamide (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam'of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried. EXAMPLE-5 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N-methylpyrrolidinone (10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried. EXAMPLE -6 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N-methylpyrrolidinone (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 5 hrs and to this was added acetic anhydride (0.27 g) and pyridine (0.13 g). Then the reaction mixture was stirred at room temperature for one hour and then at 40°C for 3 hrs. The obtained solution was then put into methanol and the precipitated polymer was filtered and dried. EXAMPLE -7 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethyl acetamide (10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven in a stream of nitrogen to obtain completely imidized polyimide film. EXAMPLE -8 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethyl formamide(10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven in a stream of nitrogen to obtain completely imidized polyimide film. EXAMPLE-9 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N-methylpyrrolidinone(10.2 ml) and 0.531 g (0.0024 mol) of pyromellitic dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven in a stream of nitrogen to obtain completely imidized polyimide film. EXAMPLE -10 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethyl acetamide (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven in a stream of nitrogen to obtain completely imidized polyimide film. EXAMPLE-11 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N, N-dimethyl formamide (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven in a stream of nitrogen to obtain completely imidized polyimide film. EXAMPLE -12 1 g (0.0024 mol) of the compound having formula (2) was dissolved in N-methylpyrrolidinone (10.2 ml) and 0.785 g (0.0024 mol) of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added to this solution with stirring in a steam of nitrogen, at room temperature. The reaction mixture was then stirred under nitrogen atmosphere for 24hrs and the polyimide precursor solution obtained was poured on a glass plate and subsequently heated from 100°C to 300°C in an oven ia a stream of nitrogen to obtain completely imidized polyimide film. Advantages of present invention 1. Employment of a novel diamine synthesized from a naturally occurring renewable and economically viable resource, the cashew nut shell liquid. 2. The first novel polyimide liquid crystal alignment agent having high pretilt angle and high solubility in common organic solvents obtained from the cashew nut shell liquid. 3. A novel polyimide having on its side chain, a substituent similar to a liquid crystal molecule introduced from cashew nut shell liquid. We claim : 1. A polyimide of formula 1 (Formula Removed) wherein R1 is tetracarboxylic acid residue or a derivative thereof and R2 is selected from the residue of a compound of formula 2 as prepared by the process, the said process comprising reacting a diamine selected from aromatic diamine having at least one pentadecyl phenoxy group per benzene ring of formula (2) (Formula Removed) with tetracarboxylic acid or its derivative, optionally in presence of another diamine in a dipolar aprotic amide or sulphoxide solvent at a temperature ranging between 0°C to 15°C under a stream of inert gas for a period ranging between 5 to 24 hrs. to obtain a polyimide precursor, imidizing the said polyimide precursor thermally in the form of a film by coating on a glass substrate and subsequently heating from 100°C to 400°C or chemically by adding dehydrating agent selected from acid anhydrides in the presence of tertiarly amine and heating at a temperature between 30°C to 120°C for 2 to 24 hrs, precipitating the resulting polymer in methanol, filtering and drying to obtain the said polyimide of formula 1. 2. A pro£ss as claimed in claim 1, wherein the dipolar aprotic solvent used is selected from the group consisting of amide solvents such as N- methylpyrrolidinone, N,N-dimethylacetamide, N,N-dimethyl formamide and tetramethylurea and sulphoxides such as dimethylsulphoxide. 3. A process as claimed in claim 1 wherein the dehydrating agent used for chemical imidization is selected from the group consisting of acetic anhydride, proionic anhydride, n-butyric anhydride and benzoic anhydride. 4. A process as claimed in claim 1 wherein the tertiary amine used for chemical imidization is selected from the group consisting of pyridine, methylpyridines, lutidine, N-methylmorpholine and trialkylamines. 5. A process as claimed in claim 1 wherein the tetracarboxylic acid or its derivative used is selected from the group consisting of pyromellitic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,4,5,8-naphthalene tetracarboxylic acid, 1,2,5,6-anthracene tetracarboxylic acid, 3,3',4,4'-biphenyl tetracarboxylic acid, 2,3,3',4'-biphenyl tetracarboxylic acid, bis(3,4-dicarboxyphenyl) ether, 3,3',4,4'-benzophenone tetracarboxylic acid, bis(3,4-dicarboxyphenyl) sulphone, bis (3,4-dicarboxyphenyl) methane, 2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) dimethyl silane, 1,1,1,3,3,3-hexafluro-2,2- bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) diphenyl silane, 2,3,4,5-pyridine tetracarboxylic acid and 2,6-bis (3,4-dicarboxyphenyl) pyridine, and their dianhydrides, alicyclic tetracarboxylic acids such as 1,2,3,4-cyclobutane tetracarboxylic acid, 1,2,3,4-cyclopentane tetracarboxylic acid, 1,2,4,5-cyclohexane tetracarboxylic acid, 2,3,5-tricarboxycyclopentylacetic acid and 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, and their dianhydrides. 6. A process as claimed in claim 1 wherein the other diamine used is selected from the group consisting of p-phenylenediamine, m-phenylenediamine, 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, diaminodiphenyl methane, diaminodiphenyl ether, 2,2'-diaminodiphenyl propane, bis(3,5-diethyl-4-aminophenyl) methane, diaminodiphenyl sulphone, diaminobenzophenone, diaminonaphthalene, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenyl)benzene, 9,10-bis(4-aminophenyl) anthrazene, 1,3-bis(4-aminiophenoxy) benzene, 4,4'-bis(4-aminiophenoxy) diphenyl sulphone, 2,2'-bis[4-(4-aminiophenoxy) phenyl]propane, 2,2'bis(4-aminiophenyl) hexafluropropane and 2,2-bis[4-(4-aminiophenoxy) phenyl]hexafluro propane. 7. A process as claimed in claim 1 wherein the diamine of formula 2 is used singly or two or more in combination. 8. A process as claimed in claim 1 wherein the tetracarboxylic acids are used singly or two or more in combination. 9. A process as claimed in claim 1 wherein the ratio of the molar amount of the said tetracarboxylic diaanhydride or combination of tetracarboxylic dianhydrides to the molar amount of the said diamine or combination of diamines is between 0.8 to 1.2. 10. A process as claimed in claim 1 wherein the molar amount of tetracarboxylic dianhydride or total molar amount of two or more tetracarboxylic dianhydrides is equal or almost equal to the molar amount of single diamine or total amount of two or more diamines. 11. A process as claimed in claim 1 wherein the concentration of the polymer solution is 5 to 40% by weight. 12. A process as claimed in claim 1 wherein the concentration of the polymer solution is preferably 10 to 25% by weight. 13. A process as claimed in claim 1 wherein the polyimide is a homo or a copolyimide. 14. A process for the preparation of a polyimide of formula (1) substantially as herein described with reference to the examples.

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338-del-2001-abstract.pdf

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338-del-2001-correspondence-others.pdf

338-del-2001-correspondence-po.pdf

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338-del-2001-petition-138.pdf