TECHNICAL FIELD The present invention relates to a novel tetracarboxylic acid dialkyl ester, a bis(chlorocarbonyl) compound obtained by chlorinating it, processes for their production, and a liquid crystal aligning agent comprising a polyamic acid/or a polyimide prepared by using such a compound as a starting material. BACKGROUND ART Tetracarboxylic acid derivatives such as a tetracarboxylic acid dialkyi ester and a bis(chlorocarbonyl) compound obtained by chlorinating it, are important substances which will be starting materials for polyamides, polyesters or polyimides. For example, as a preparation example for a polyimide having a cyclobutane structure in its main chain, a case has been reported wherein a bis(chlorocarbonyl)cyclobutanedicarboxylic acid dimethyl ester is reacted with a diamine to obtain a polyamic acid methyl ester, which is then heated to obtain a polyimide (Non-Patent Document 1). However, with respect to cyclobutanetetracarboxylic acids having substituents on a cyclobutane ring, no case has been reported wherein a tetracarboxylic acid dialkyi ester or a bis(chlorocarbonyl) compound prepared by chlorinating it has been synthesized. On the other hand, a resin such as a polyimide is widely used as a protective material in liquid crystal display elements or semiconductors, as an insulating material or as an electronic material for e.g. color filters, due to its characteristics such as high mechanical strength, heat resistance, insulating properties or solvent resistance. Further, recently, it is expected to be used as a material for optical communication such as a material for optical waveguide. And, in recent years, the resin to be used in such a field has been required to have high properties and quality, and the structure, quality. etc. of a monomer to be used as a starting material for such a resin, have become more important than ever. On the other hand, in a liquid crystal display element to be used for e.g. a liquid crystal TV or a liquid crystal display, a liquid crystal alignment film is usually provided in the element to control the alignment state of liquid crystal. At present, according to the industrially most prevailing method, such a liquid crystal alignment film is prepared by carrying out so-called rubbing treatment wherein the surface of a polyimide film formed on an electrode substrate is rubbed in one direction with a cloth of e.g. cotton, nylon or polyester. A method of subjecting a polyimide film to rubbing treatment is an industrially useful method which is simple and excellent in the productivity. However, due to increasing demands for high perfonnance, high refinement and larger sizes of liquid crystal display elements, various problems have been pointed out such as scars on the alignment film surface formed by the rubbing treatment, dusting, influences by mechanical forces or static electricity, in-plane uniformity in alignment treatment, etc. As an altemative means to such rubbing treatment, a photo-alignment method has been known wherein polarized radiation is applied to impart a liquid crystal alignment function. With respect to the mechanism for liquid crystal alignment by the photo-alignment method, one utilizing a photo isomerization reaction, one utilizing a photo crosslinking reaction or one utilizing a photolytic reaction has, for example, been proposed (Non-Patent Document 2). Patent Document 1 proposes to use a polyimide having an alicyclic structure such as a cyclobutane ring in its main chain, in the photo-alignment method. When such a polyimide is used for an alignment film for photo-alignment, it has a high heat resistance as compared with other materials, and its usefulness is expected. Such a photo-alignment method is advantageous in that as a rubbing-less alignment method, an alignment film can be produced by an industrially simple production process, and it has attracted attention as a new liquid crystal alignment method. However, in order to use it for a liquid crystal TV, a liquid crystal display, etc., it still has problems with respect to alignment control power of liquid crystals, electrical properties as a liquid crystal display element, the stability of such properties, etc., and it has not been commonly used. That is, in a liquid crystal alignment film having alignment treatment carried out by a rubbing method, the polymer chains are stretched by a physical force, and it thus has a high anisotropy against the rubbing direction. As such an anisotropy is higher, a higher controlling power for liquid crystal alignment will be obtained. Whereas, a liquid crystal alignment film obtainable by the photo-alignment method has had a problem that as compared with one obtained by rubbing, the anisotropy against the alignment treatment direction of a polymer film is small. PRIOR ART DOCUMENTS PATENT DOCUMENT Patent Document 1: JP-A-9-297313 NON-PATENT DOCUMENTS Non-Patent Document 1: High Perfomnance Polymers, (1998), 10(1), p.11-21 Non-Patent Document 2: Masatoshi Kidowaki, Kunihiro Ichimura, Liquid Crystal Photo-Alignment Film, Monthly Functional Materials 1997 November issue, published by Kabushiki Kaisha CMC, vol. 17, No. 11, p.-13-22 DISCLOSURE OF INVENTION TECHNICAL PROBLEM It is an object of the present invention to provide a novel tetracarboxylic acid dialkyl ester having alkyl groups on a cyclobutane ring and a novel bis(chlorocarbonyl) compound obtained by chlorinating it, as well as processes for their production, and processes for producing specific isomers of such compounds. Further, it is another object of the present invention to provide a liquid crystal aligning agent comprising a polyamic acid and/or a polyimide prepared from the above bis(chlorocarbonyl) compound as the starting material. SOLUTION TO PROBLEM The present invention is one to solve the above problem and provides the following. 1. A tetracarboxylic acid dialkyi ester represented by the following formula [1] or [2]: wherein R1 is a C1-5 alky! group, R2 is a C1-5 alkyl group, and n is from 1 to 4. 2. Tine tetracarboxylic acid dialkyi ester according to the above 1, which is represented by the following formula [1-a], [2-a] or [2-b]: 1 wherein R1 is a C1-5 alkyl group, and R2 is a C1-5 alkyl group. 3. A bis(chlorocarbonyl) compound represented by the following formula [3] or [4]: wherein R1 is a C1-5 alkyl group, R2 is a C1-5 alkyl group, and n is from 1 to 4. 4. The bis(chlorocarbonyl) compound according to the above 3, which is represented by the following formula [3-a], [4-a] or [4-b]: wherein R1 is a C1-5 alkyl group, and R2 is a C1-5 alkyl group. 5. A process for producing a tetracarboxylic acid dialkyi ester represented by the formula [1] or [2] as defined in the above 1, which comprises reacting a tetracarboxylic acid dianhydride represented by the following formula [5] with a C1-5 alcohol: wherein R2 is a C1-5 alkyl group, and n is from 1 to 4. 6. A process for producing a tetracarboxylic acid dialkyi ester represented by the formula [1-a] or [2-a] as defined in the above 2, which comprises reacting a tetracarboxylic acid dianhydride represented by the following formula [5-a] with a C1-5 alcohol: wherein R2 is a C1-5 alkyl group. 7. A process for producing a tetracarboxylic acid dialkyl ester represented by the formula [2-b] as defined in the above 2, which comprises reacting a tetracarboxylic acid dianhydride represented by the following formula [5-b] with a C1.5 alcohol: wherein R2 is a C1-5 alkyl group. 8. The process according to any one of the above 5 to 7, wherein the tetracarboxylic acid dianhydride is reacted with the C1-5 alcohol in the presence of an acidic compound or a basic compound. 9. The process according to any one of the above 5 to 7, wherein the tetracarboxylic acid dianhydride is reacted with the C1-5 alcohol in the presence of a basic compound. 10. A process for producing a bis(chlorocarbonyl) compound represented by the formula [3] or [4] as defined in the above 3, which comprises reacting a tetracarboxylic acid dialkyi ester represented by the fonnula [1] or [2] as defined in the above 1, with a chlorinating agent. 11. A process for producing a bis(chlorocarbonyl) compound represented by the formula [3-a] as defined in the above 4, which comprises reacting a tetracarboxylic acid dialkyi ester represented by the fonnula [1-a] as defined in the above 2, with a chlorinating agent. 12. A process for producing a bis(chlorocarbonyl) compound represented by the formula [4-a] as defined in the above 4, which comprises reacting a tetracarboxylic acid dialkyl ester represented by the formula [2-a] as defined in the above 2, with a chlorinating agent. 13. A process for producing a bis(chlorocarbonyl) compound represented by the formula [4-b] as defined in the above 4, which comprises reacting a tetracarboxylic acid dialkyi ester represented by the formula [2-b] as defined in the above 2, with a chlorinating agent. 14. The process according to any one of the above 10 to 13, wherein the tetracarboxylic acid dialkyi ester is reacted with the chlorinating agent in the presence of a basic compound. 15. The process according to any one of the above 10 to 13, wherein the tetracarboxylic acid dialkyi ester is reacted with the chlorinating agent in the presence of pyridine. 16. A liquid crystal aligning agent comprising a polyamic acid ester which is obtained by reacting a diamine and a bis(chlorocarbonyl) compound containing at least 60 mol% of an acid chloride represented by the following fomnula (101) having chlorocarbonyl groups bonded at 1- and 3-positions of the cyclobutane ring and alkyl ester groups bonded at 2- and 4-positions thereof: wherein R1 is a C1-5 alkyl group, and each of R2, R3, R4 and R5 which may be the same or different, is a hydrogen atom or a C1-30 monovalent hydrocarbon group. 17. The liquid crystal aligning agent according to the above 16, wherein the acid chloride has a structure represented by the following formula (102): wherein R1 is a C1-5 alkyl group, and R6 is a C1-30 monovalent hydrocarbon group. 18. The liquid crystal aligning agent according to the above 16, wherein the acid chloride has a structure represented by the following formula (103): wherein R1 is a C1-5 alkyl group. 19. A liquid crystal alignment film obtained by applying polarized radiation to a coating film formed by applying and firing the liquid crystal aligning agent as defined in any one of the above 16 to 18. 20. A process for producing a liquid crystal alignment film, which comprises applying polarized radiation to a coating film fomned by applying and firing the liquid crystal aligning agent as defined in any one of the above 16 to 18. ADVANTAGEOUS EFFECTS OF INVENTION According to the present invention, it is possible to obtain a novel tetracarboxylic acid dialkyl ester having alkyl groups on a cyclobutane ring, and a novel bis(chlorocarbonyl) compound having alkyl groups on a cyclobutane ring. Further, it is possible to efficiently produce their specific isomers. The liquid crystal aligning agent according to the present invention is free from a decomposition reaction of polymer chains at the time of heating for imidation, and it is thereby possible to obtain a polymer film having a high regularity, and thus, it is possible to obtain a liquid crystal alignment film having a high anisotropy against the alignment treatment direction also in the photo-alignment method. Further, the liquid crystal alignment film according to the present invention is stable against an extemal environment such as a temperature or humidity, and when made into a liquid crystal display element, it has a high voltage retention at a high temperature and a low ion density, whereby it is possible to obtain a liquid crystal display element having stable and good display characteristics. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is an ORTEP model representing the results of single crystal X-ray analysis of compound (1-1). Fig. 2 is an ORTEP model representing the results of single crystal X-ray analysis of compound (2-1). DESCRIPTION OF EMBODIMENTS [Tetracarboxylic acid dialkyl ester] The tetracarboxylic acid dialkyi ester of the present invention is a compound represented by the following formula [1] or [2]: wherein R1 is a C1-5 alkyl group, R2 is a C1-5 alkyl group, and n is from 1 to 4. R1 is a C1-5 alkyl group, and specific examples of the alkyl group include, for example, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group and a normal pentyl group. In a case where from the tetracarboxylic acid dialkyi ester of the present invention, a polyamic acid ester is prepared and then imidated to use it as a polyimide, R1 is preferably one having a small number of carbon atoms and being readily detached, more preferably a methyl group. R2 is a C1-5 alkyl group, and specific examples of the alkyl group include, for example, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group and a normal pentyl group. n is from 1 to 4, preferably 2. Now, specific examples of the tetracarboxylic acid dialkyi ester of the present invention wherein R2 is a methyl group and n is 2 will be mentioned, but it should be understood that the tetracarboxylic acid dialkyi ester of the present invention is by no means limited thereto. In the following Tables, a1 to a4 and b1 to b4 represent the respective positions shown in the following formula [6], and symbols in the Table have the following meanings, respectively. Me: methyl group, Et: ethyl group, Pr-n: normal propyl group, Pr-iso: isopropyl group, Bu-n: normal butyl group, Bu-sec: secondary butyl group, Bu-iso: isobutyl group, Bu-t: tertiary butyl group, Pen-n: nomnal pentyl group, OMe: methoxy group, OEt: ethoxy group, OPr-n: normal propyl ether group, OPr-iso: isopropyl ether group, OBun: normal butoxy group, OBu-sec: secondary butoxy group, OBu-iso: isobutoxy group, OBu-t: tertiary butoxy group, OPen-n: normal pentyl ether group TABLE 1 TABLE 2 Further, as the compound wherein n is 2, and R2 is an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group or a normal pentyl group, compounds may be exemplified wherein in the above Tables, each Me for b1 to b4 is replaced by Et, Pr-n, Pr-iso, Bu-n, Bu-sec, Bu-iso, Bu-t or Pen-n. Among tetracarboxylic acid dialkyl esters of the present invention, a particularly preferred compound is a compound represented by the following formula [1-a], [2-a] or [2-b] from the viewpoint of the preparation efficiency and yield of the compound. Further, in a case where a high purity product of [1-a] is used, it is possible to obtain a polymer having a higher molecular weight and lower dispersion than a polymer obtained by using a high purity product of [2-a] or a mixture of [1-a] and [2-a]. Therefore, with a view to obtaining a high molecular weight and low dispersion polymer, a tetracarboxylic acid dialkyl ester represented by the formula [1-a] is preferred. As shown by the following reaction formula, the tetracarboxylic acid dialkyi ester of the present invention can be produced by reacting a tetracarboxylic acid dianhydride [5] with a C1-5 alcohol represented by R1OH. wherein R1 is a C1-5 alkyl group, R2 is a C1-5 alkyl group, and n is from 1 to 4. The above reaction can be carried out in the corresponding alcohol (R1OH), and a solvent may be used as the case requires. The solvent is not particularly limited so long as it is inert to the reaction, and it may, for example, be a hydrocarbon such as hexane, heptane or toluene, a halogenated hydrocarbon such as chlorofomn, 1,2- dichloroethane or chlorobenzene, a ether such as diethyl ether or 1,4-dioxane, an ester such as ethyl acetate, a ketone such as acetone or methyl ethyl ketone, a nitrile such as acetonitrile or propionitrile, or a mixture thereof. It is preferably ethyl acetate or acetonitrile, more preferably acetonitrile. The alcohol (R1OH) is used usually in an amount of from 2 to 100 times by mole, preferably from 2 to 40 times by mole, more preferably from 2 to 20 times by mole, to the tetracarboxylic acid dianhydride [5]. The above reaction proceeds under a neutral condition, but a base or an acid may be added. Such a base or an acid is not particularly limited. The base may, for example, be an inorganic base such as sodium hydroxide, potassium hydroxide, potassium carbonate or sodium hydrogencarbonate, an organic base such as diethylamine, pyridine, quinoline, 8-quinolinol, 1,10-phenanthroline, bathophenanthroline, bathocuproin, 2,2'-bipyridyl, 2-phenylpyridine, 2,6- diphenylaminopyridine, 2-dimethylaminopyridine, 4-dimethylaminopyridine, 2-(2- hydroxyethyl)pyridine, N,N-dimethylaniline or 1,8-azadiazabicyclo[5,4,0]-7-undene (DBU), or a metal alkoxide such as sodium methoxide, potassium methoxide or potassium t-butoxide. It is preferably sodium methoxide, potassium methoxide or pyridine, more preferably pyridine. The acid may, for example, be a heteropolyacid such as phosphomolybdic acid or phosphotungstic acid, an organic acid such as trimethylborate or triphenylphosphine, an inorganic acid such as hydrochloric acid, sulfuric acid or phosphoric acid, a hydrocarbon acid such as formic acid, acetic acid or p-toluenesulfonic acid, or a halogenated hydrocarbon acid such as trifluoroacetic acid. It is preferably ptoluenesulfonic acid, phosphoric acid or acetic acid, more preferably p-toluenesulfonic acid. The base or the acid is used usually in an amount of from 0 to 100 times by mole, preferably from 0.01 to 10 times by mole, to the tetracarboxylic acid dianhydride [5]. The reaction temperature is not particulariy limited, and it may, for example, be from -90 to 200°C, preferably from -30 to 100°C. The reaction time is usually from 0.05 to 200 hours, preferably from 0.5 to 100 hours. A process for efficiently producing a compound represented by the above formula [1-a], [2-a] or [2-b] being a specific position isomer among tetracarboxylic acid dialkyi esters of the present invention of the fonnula [1] or [2] wherein n is 2, will be described below. A compound represented by the fomnula [1-a] or [2-a] can be produced by using a tetracarboxylic dianhydride represented by the following formula [5-a] as the tetracarboxylic acid dianhydride [5] in the above reaction formula. wherein R2 is a C1-5 alkyl group. At that time, the selectivity for the formula [1-a] will be improved as the reaction temperature is low. Therefore, when it is desired to improve the reaction yield of the formula [1-a], a more preferred reaction temperature is from 10 to 30°C. On the other hand, in a case where it is desired to improve the reaction yield of the formula [2-a], a more preferred reaction temperature is from 50 to 100°C. Further, it is possible to improve the reaction rate and the selectivity for the formula [1-a] also when the reaction is carried out by adding a base or an acid, and it is more preferred to add a basic compound. As the base or the acid to be used here, the above exemplified one may be mentioned, and the preferred base or acid and the preferred amount are also as mentioned above. A compound represented by the formula [2-b] can be produced by reacting a tetracarboxylic acid dianhydride represented by the following formula [5-b] with a C1-5 alcohol (the above mentioned R1OH). wherein R2 is a C1-5 alkyl group. At that time, it is possible to improve the reaction rate and the selectivity for the formula [2-b] by adding a base or an acid for the reaction, it is more preferred to add a basic compound. As the base or acid to be used here, the above exemplified one may be mentioned, and the preferred base or acid and the preferred amount are also as mentioned above. wherein R1 is a C1-5 alkyl group, and R2 is a C1-5 alkyl group. Further, the present invention is characterized in that separation of the desired product formed by the reaction is easy. For example, when the formula [5-a] is a starting material, after completion of the reaction, the alcohol used is distilled off, and precipitated crystals are heated and refluxed in an organic solvent, followed by cooling, whereupon precipitated crystals are collected by filtration, followed by washing and drying, whereby primary crystals of a high purity product of the formula [1-a] can be obtained. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/n-heptane mixed liquid, an ethyl acetate/various alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Such various alcohols may be methanol, ethanol, propanol, butanol, isopropanol, etc. The primary crystals may have the purity further improved by washing or recrystallization. A recrystallization method may be a method wherein an organic solvent is added to the primary crystals, followed by heating and then by cooling with ice, filtration and drying. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/n-heptane mixed liquid, an ethyl acetate/various alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Such various alcohols may be methanol, ethanol, propanol, butanol, isopropanol, etc. The amount of the organic solvent to be used to obtain such primary crystals, is usually from 2 to 20 times based on the weight of the desired product on the assumption that the desired product is obtained from the starting material in a yield of 100%. Here, when it is desired to improve the yield, it is prefen'ed to reduce the amount of the organic solvent to be used, and when it is desired to obtain a high purity product, it is preferred to increase the amount of the organic solvent to be used. In consideration of such yield and purity, the amount is more preferably from 2.5 to 5 times. On the other hand, by washing and recrystallizing the filtrate at the time of obtaining the primary crystals, it is possible to obtain a high purity product of the formula [2-a]. That is, the obtained filtrate is subjected to distillation to remove the solvent, and precipitated crystals are heated and refluxed in an organic solvent, followed by cooling, whereupon precipitated crystals are collected by filtration, followed by washing and drying, whereby the desired secondary crystals of a high purity product of the formula [2-a] are obtainable. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/n-heptane mixed liquid, an ethyl acetate/various alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Such various alcohols may be methanol, ethanol, propanol, butanol, isopropanol, etc. The secondary crystals may have the purity further improved by washing or recrystallization. A recrystallization method may be a method wherein an organic solvent is added to the secondary crystals, followed by heating and then by cooling with ice, filtration and drying. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/n-heptane mixed liquid, an ethyl acetate/various alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Such various alcohols may be methanol, ethanol, propanol, butanol, isopropanol, etc. The amount of the organic solvent to be used to obtain such secondary crystals, is usually from 2 to 20 times based on the weight obtained by subtracting the weight of primary crystals taken out, from the weight of the desired product on the assumption that the desired product is obtained from the starting material in a yield of 100%. Here, when it is desired to improve the yield, it is preferred to reduce the amount of the organic solvent to be used, and when it is desired to obtain a high purity product, it is preferred to increase the amount of the organic solvent to be used. In consideration of such yield and purity, the amount is more preferably from 2.5 to 5 times. In a case where the formula [5-b] is the starting material, after completion of the reaction, the alcohol used is distilled off, and precipitated crystals are heated and refluxed in an organic solvent, followed by cooling, whereupon precipitated crystals are collected by filtration, followed by washing and drying, whereby primary crystals of a high purity product of the formula [2-b] can be obtained. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/nheptane mixed liquid, an ethyl acetate/vaiious alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Further, as a purification method of primary crystals, it is possible to further increase the purity by a washing method or a recrystallization method. The washing method may be a method wherein an organic solvent is added to the primary crystals, followed by heating and then by cooling with ice, filtration and drying. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, an ethyl acetate/nheptane mixed liquid, an ethyl acetate/various alcohol mixed liquid, or an acetonitrile/various alcohol mixed liquid. Preferred is acetonitrile, ethyl acetate, an ethyl acetate/various alcohol mixed liquid or an acetonitrile/various alcohol mixed liquid. Such various alcohols may be methanol, ethanol, propanol, butanol, isopropanol, etc. The amount of the organic solvent to be used to obtain such primary crystals, is usually from 2 to 20 times based on the weight of the desired product on the assumption that the desired product is obtained from the starting material in a yield of 100%. Here, when it is desired to improve the yield, it is preferred to reduce the amount of the organic solvent to be used, and when it is desired to obtain a high purity product, it is preferred to increase the amount of the organic solvent to be used. In consideration of such yield and purity, the amount is more preferably from 2.5 to 5 times. [Bis(chlorocarbonyl) compound] The bis(chlorocarbonyl) compound of the present invention is a compound represented by the following formula [3] or [4]: wherein R1 is a C1-5 alkyl group, R2 is a C1-5 alkyl group, and n is from 1 to 4. R1 is a C1-5 alkyl group, and specific examples of the alkyl group include, for example, a methyl group, an ethyl group, a nomrial propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group and a normal pentyl group. Here, in a case where from the bis(chlorocarbonyl) compound of the present invention, a poiyamic ester is prepared and then imidated to use it as a polyimide, R2 is preferably one having a small number of carbon atoms and Being easily detached, more preferably a methyl group. R2 is a C1-5 alky! group, and specific examples of the alkyl group include, for example, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group and a normal pentyl group. n is from 1 to 4, preferably 2. Now, specific examples of the bis(chlorocarbonyl) compound of the present invention wherein R2 is a methyl group and n is 2 will be given, but it should be understood that the bis(chlorocarbonyl) compound of the present invention is by no means limited thereto. In the following Tables, a1 to a4 and b1 to b4 represent the respective positions shown in the following formula [6], and symbols in the Tables have the following meanings, respectively. Me: methyl group, Et: ethyl group, Pr-n: normal propyl group, Pr-iso: isopropyl group, Bu-n: normal butyl group, Bu-sec: secondary butyl group, Bu-iso: isobutyl group, Bu-t: tertiary butyl group, Pen-n: normal pentyl group, OMe: methoxy group, OEt: ethoxy group, OPr-n: normal propyl ether group, OPr-iso: isopropyl ether group, OBun: normal butoxy group, OBu-sec: secondary butoxy group, OBu-iso: isobutoxy group, OBu-t: tertiary butoxy group, OPen-n: normal pentyl ether group TABLE 3 TABLE 4 Further, as the compound wherein n is 2, and R2 is an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group or a nomnal pentyl group, compounds may be exemplified wherein in the above Tables, each Me for b1 to b4 is replaced by Et, Pr-n, Pr-iso, Bu-n, Bu-sec, Bu-iso, Bu-t or Pen-n. Among bis(chlorocarbonyl) compounds of the present invention, a compound represented by the following fomnula [3-a], [4-a] or [4-b] is particularly preferred, since the tetracarboxylic acid dialkyl ester as the starting material is readily available, and it is obtainable in high yield. wherein R1 is a C1-5 alkyl group, and R2 is a C1-5 alkyl group. Further, with respect to a polymer obtained by using a high purity product of the fornnula [3-a], it is possible to obtain a polymer having a higher molecular weight and lower dispersion than a polymer obtained by using a high purity product of the formula [4-a] or a mixture of the formula [3-a] and the formula [4-a]. Accordingly, a compound represented by the fomnula [3-a] is preferred with a view to obtaining a polymer having a high molecular weight and low dispersion. The bis(chlorocarbonyl) compound [3] or [4] of the present invention can be produced by chlorinating a tetracarboxylic acid dialkyl ester represented by the formula [1] or [2] as shown by the following reaction formulae. X Chlorinating || (R2)n|| OR^ agent CI-«^_p^OR^ OH R^O-TT-''^"^pCI 0 0 0 0 II] [31 II (R2)n|| Chlorinating 11 ( R 2 ) .1 HO-U^|_p^OH agent Cl-"0!J^CI R^O-rr-"^^^OR^ R^O-ir-'^^^OR^ 0 0 0 0 [2] 14] wherein R1 is a C1-5 alkyl group, R2 is a C1-5 alkyl group, and n is from 1 to 4. In the above reaction formulae, the substitution positions of R2 in the fomnulae [3] and [4] are the same substitution positions as in the corresponding formulae [1] and [2]. That is, the bis(chlorocarbonyl) compound [3-a] can be produced by chlorinating the above tetracarboxylic acid dialkyi ester [1-a]. Likewise, the compound [4-a] can be produced by chlorinating the compound [2-a], and the compound [4-b] can be produced by chlorinating the compound [2-b]. The chlorinating agent to be used for the above reactions may, for example, be thionyl chloride, oxalyl chloride, phosgene, chlorine, phosphorus oxychloride, phosphorus pentachloride or N-chlorosuccinic acid imide. Preferred is thionyl chloride, oxalyl chloride, phosgene, chlorine, phosphorus oxychloride or phosphorus pentachloride. More preferred is thionyl chloride, oxalyl chloride or phosgene. The chlorinating agent is used in an amount of usually from 2 to 100 times by mole, preferably from 2 to 30 times by mole, more preferably from 2 to 3 times by mole, to the tetracarboxylic acid dialkyi ester. The above reactions may be carried out in a chlorinating agent such as thionyl chloride, but it is possible to use a solvent, as the case requires. The solvent is not particularly limited so long as it is inert to the reaction, and it may, for example, be a hydrocarbon such as hexane, heptane or toluene, a halogenated hydrocarbon such as chloroform, 1,2-dichloroethane or chlorobenzene, an ether such as diethyl ether or 1,4- dioxane, an ester such as ethyl acetate, a ketone such as acetone or methyl ethyl ketone, a nitrile such as acetonitrile or propionitrile, or a mixture thereof. It is preferably hexane, heptane or toluene, more preferably hexane or heptane. Further, the above reactions may proceed without a catalyst, but by adding a catalyst, it is possible to reduce the amount of the chlorinating agent to be used, and further, it is possible to promote the progress of the reactions. A specific example of the catalyst may, for example, be an organic base such as triethylamine, pyridine, quinoline, N,N-dlmethylaniline or N,N-dimethylformamide, or a metal alkoxide such as sodium methoxide, potassium methoxide or potassium t-butoxide. However, the catalyst is not limited thereto. It is preferably triethylamine, pyridine or N,Ndimethylformamide, more preferably pyridine. Such a catalyst is used in an amount of usually from 0 to 100 times by mole, preferably from 0.01 to 10 times by mole, to the tetracarboxylic acid dialkyi ester. The reaction temperature is not particulariy limited, but it is usually from -90 to 200°C, preferably from -30 to 100°C, more preferably from 50 to 80°C. The reaction time is usually from 0.05 to 200 hours, preferably from 0.5 to 100 hours, more preferably from 0.5 to 5 hours. Further, the bis(chlorocarbonyl) compound obtained as described above can be isolated and purified, for example, as follows. After completion of the reaction, the chlorinating agent is distilled off, and then, a certain amount of a solvent is added, followed by heating and stining. Then, cooling is carried out, and precipitated crystals are collected by filtration, followed by washing and drying to obtain primary crystals of the desired product. Further, at the time of the above heating and stirring, after dissolving the crystals, insolubles may further be removed by filtration while being hot, as the case requires, followed by the same operation to obtain the desired product in higher purity. Further, in a case where the chlorinating agent is more readily removable by distillation than the solvent used, after distilling off a certain amount of the chlorinating agent and solvent remaining after completion of the reaction, the residual liquid is heated to dissolve the crystals or to heat and stir them, followed by cooling, whereupon precipitated crystals are collected by filtration, followed by washing and drying to obtain primary crystals of the desired product. The temperature for the above solvent distillation, and the heating and dissolving or the heating and stirring may, for example, be from 30 to 100°C, preferably from 30 to 50°C. As the organic solvent, it is possible to use, for example, toluene, acetonitrile, ethyl acetate, n-hexane, n-heptane, an ethyl acetate/n-heptane mixed liquid, or an ethyl acetate/n-hexane mixed liquid. Preferred is n-hexane, n-heptane, an ethyl acetate/n-hexane mixed liquid or an ethyl acetate/n-heptane mixed liquid. Further, by a purification method of single crystals, such as a washing method or a recrystallization method, it is possible to further increase the purity. As a recrystallization method, toluene, acetonitrile, ethyl acetate, n-hexane, n-heptane, an ethyl acetate/n-heptane mixed liquid or an ethyl acetate/n-hexane mixed liquid may, for example, be added to the primary crystals, followed by heating to dissolve the crystals and then by cooling with ice, filtration and drying to obtain a high purity product. As another treating method, after completion of the reaction, the remaining chlorinating agent may be distilled off, and the residual liquid may be distilled to obtain the desired product. On the other hand, by carrying out a chlorination reaction by using a single stereoisomer [1] of high purity obtained by purifying the tetracarboxylic acid dialkyi ester as the starting material and after completion of the reaction, by carrying out the same operation as described above, it is possible to obtain the compound [3] of a higher purity in high yield. Likewise, by using a single stereoisomer [2] of high purity, it is possible to obtain the compound [4] of high purity in high yield. The tetracarboxylic acid dialkyi ester or the bis(chiorocarbonyl) compound of the present invention obtained as described above can be used as a monomer starting material for a polyamide, a polyimide, a polyester, etc. For example, a polyamide can be prepared by subjecting the tetracarboxylic acid dialkyl ester of the present invention and various diamine compound to polycondensation in the presence of a condensing agent, or by reacting the bis(chlorocarbonyl) compound and various diamine compound. Further, it is possible to prepare a polyimide by adding a catalyst to such a polyamide, as the case requires, followed by heating. On the other hand, it is possible to prepare a polyester by using a various dialcohol compound instead of the above diamine compound. As described above, these compounds of the present invention are capable of providing polyimides, polyamides or polyesters having alkyl groups on a cyclobutane ring, which are useful in the field of materials, etc. [Liquid crystal aligning agent] A liquid crystal alignment film obtained by a photo-alignment method utilizing an anisotropic photolytic reaction of a polyimide by polarized radiation usually has a smaller anisotropy against the alignment direction of polymer chains as compared with one obtained by rubbing. This is considered to be attributable to a decrease in the molecular weight of the polyimide by the photolytic reaction and to the substantial presence of low molecular weight components in other than the alignment direction. In a case where a polyamic acid is used as a polyimide precursor, at the time of the firing, at the same time as the imidation, a reverse reaction to a diamine and an acid dianhydride tends to proceed, and consequently, the molecular weight of the polyimide thereby obtainable tends to be lower than the initial polyamic acid. Accordingly, the decrease in the molecular weight due to the firing will also be a factor to lower the anisotropy. Further, in the polyamic acid obtainable from the acid dianhydride and the diamine, four types of structures different in the bonding positions of amide bonds are present as shown by the following formulae (A), (B), (C) and (D), and in the molecular chain, these structures are randomly present. The coating film of a polyamic acid undergoes dehydration ring closure by the firing to form a polyimide. However, in a case where the imidation does not proceed completely, a polyamic acid wherein the above four types of structures are randomly present, will remain, whereby the regularity of the polymer chains tends to deteriorate. If the regularity of polymer chains deteriorates, the interaction among polymer molecules tends to deteriorate by steric repulsion, and it will be difficult to obtain a polyimide film having a high regularity. Therefore, it is considered that if the bonding positions of amide groups are random as in a polyamic acid, the anisotropy against the alignment direction of the obtainable polyimide film tends to be small. As a result of an expensive research, the present inventors have found that by using a polyimide precursor having a high regularity of polymer chains and being free from lowering of the molecular weight during the firing, it is possible to obtain a polyimide film having a high anisotropy against the alignment direction even by the above-mentioned photo-alignment method. Specifically, it has been found that by using, as a liquid crystal aligning agent, a polyamic acid ester having a high regularity which is obtained from a diamine and a highly symmetric acid chloride having the substitution positions of chlorocarbonyl groups and ester groups on a cyclobutane ring controlled, it is possible to obtain a polyimide film having a high anisotropy against the alignment treatment direction, even by the above-mentioned photo-alignment method, and based on such a discovery, the present invention has been accomplished. [Acid chloride] The acid chloride to be used in the present invention wherein chlorocarbonyl groups are bonded at 1- and 3-positions of a cyclobutane ring and ester groups are bonded at 2- and 4-positions of the cyclobutane ring, is represented by the following formula (101): 25 wherein R1 is a C1-5 alkyl group, and each of R2, R3, R4 and R5 which may be the same or different, is a hydrogen atom or a C1-30 monovalent hydrocarbon group. In the acid chloride represented by the formula (101), Ri is a C1-5 alkyl group. Here, specific examples of the alkyl group include, for example, a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a nonnal butyl group, a secondary butyl group, an isobutyl group, a tertiary butyl group and a normal pentyl group. Usually, with a polyamic acid ester, the temperature for imidation tends to be high as the number of carbon atoms increases in the order of a methyl group, an ethyl group and a propyl group. Accordingly, from the viewpoint of efficiency for imidation by heat, a methyl group or an ethyl group is preferred, and a methyl group is particularly preferred. In the acid chloride represented by the formula (101), each of R2, R3, R4 and R5 which may be the same or different, is a hydrogen atom or a C1-30 monovalent hydrocarbon group. The monovalent hydrocarbon group may, for example, be an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group, a hexyl group, an octyl group or a decyl group; a cycloalkyi group such as a cyclopentyl group or a cyclohexyl group; a bicycloalkyl group such as a bicyclohexyl group; an alkenyl group such as a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, a 1-methyl-2-propenyl group, a 1-, 2- or 3-butenyl group or a hexenyl group; an aryl group such as a phenyl group, a xylyl group, a tolyl group, a biphenyl group or a naphthyl group; or an aralkyi group such as a benzyl group, a phenylethyl group or a phenylcyclohexyl group. Further, some or all of hydrogen atoms in such a monovalent hydrocarbon group may be substituted by e.g. a halogen atom, a phosphoric acid ester group, an ester group, a thioester group, an amide group, a nitro group, an organooxy group, an organosilyl group, an organothio group, an acyl group, an alkyl group, a cycloalkyl group, a bicycloalkyi group, an alkenyl group, an aryl group or an aralkyl group. From the viewpoint of tine liquid crystal alignment properties, for each of R2, R3, R4 and R5, a substituent having a small steric hindrance is preferred, and a hydrogen atom or a methyl group is particularly preferred. Further, to obtain a liquid crystal alignment film having a high anisotropy against the alignment direction, it is preferred that all of R2, R3, R4 and R5 are the same substituents, or R2 and R4, or R3 and R5 are the same substituents. The following formulae (106) to (121) may be mentioned as specific examples of the steric configuration of R2, R3, R4, R5, chlorocarbonyl groups and ester groups. Among the above, formulae (106), (107), (108) and (109) are particularly preferred, since it is thereby possible to obtain a polyamic acid ester having a high regularity as the symmetry of the acid chloride is high and to obtain a polymer film having a high regularity even if the imidation rate is low, as the linearity of polymer chains is high thereby to obtain a liquid crystal alignment film having a high anisotropy against the alignment direction. The following formulae (122) to (129) may be mentioned as specific structures of the acid chloride of the formula (101) wherein at least one of R2, R3, R4 and R5 is a hydrogen atom. Among the above, the formula (126) or (127) is preferred, since it is thereby possible to obtain a polyamic acid ester having a high regularity as the symmetry of the acid chloride is high, and to obtain a polymer film having a high regularity even if the imidation ratio is low, as the linearity of the polymer chains is high, thereby to obtain a liquid crystal alignment film having a high anisotropy. Further, the formula (126) is particularly preferred, since isomerization by heat is suppressed as a chlorocarbonyl group and R2 or R4 are substituted on the same carbon in the cyclobutane ring, and the symmetry of the monomer or polymer is stable even at a high temperature. In addition, the following fonnula (102) is preferred, since in a case where R2, R3, R4 and R5 are the same substituents, the symmetry of the acid chloride is improved, and it is possible to obtain a polyamic acid ester having a high regularity. In the formula (102), R1 is a C1-4 alkyl group, and R6 is a C1.30 monovalent hydrocarbon group. The monovalent hydrocarbon group may be the same structure as exemplified as the structure of R2, R3, R4 and R5. From the foregoing, the formula (103) or (104) is particularly preferred as a specific example of the acid chloride represented by the formula (101). The acid chloride of the formula (101) can be prepared by two step reactions i.e. esterification of a tetracarboxylic acid dianhydride and chlorination of a carboxylic acid, as shown below. The esterification reaction in the first step can be carried out by reacting the tetracarboxylic acid dianhydride with an alcohol represented by the R1OH. The reaction temperature may, for example, be from -90 to 200°C, preferably from -30 to 100°C. The reaction time may, for example, be from 0.5 to 200 hours, preferably from 0.5 to 100 hours. The alcohol to be used for this reaction is in an amount of, for example, from 2 to 100 times by mole, preferably from 2 to 40 times by mole, more preferably from 2 to 20 times by mole, to the tetracarboxylic acid dianhydride. After the above esterification reaction, isomers having ester groups at positions other than 2- and 4-positions may be substantially contained in many cases, and in order to obtain an acid chloride to be used for the present invention, it is advisable to purify the diester product having ester groups at 2- and 4-positions. As the purification method, various purification methods such as recrystallization and column chromatography may be mentioned, and from the simplicity of the operation, purification by recrystallization is preferred. As the solvent for recrystallization, various organic solvents may be used in combination. The chlorination reaction in the second step can be carried out by reacting the ester product obtained as described above with a chlorinating agent in the presence of an organic solvent. The reaction temperature may, for example, be from -90 to 200°C, preferably from -30 to 100°C, more preferably from 50 to 80°C. The reaction time may, for example, be from 0.5 to 200 hours, preferably from 0.5 to 100 hours, more preferably from 0.5 to 5 hours. The chlorinating agent to be used for this reaction is in an amount of, for example, from 2 to 100 times by mole, preferably from 2 to 30 times by mole, more preferably from 2 to 3 times by mole, to the ester product. The chlorinating agent may, for example, be thionyl chloride, oxalyl chloride, phosgene, chlorine, phosphorus oxychloride, phosphorus pentachloride or Nchlorosuccinic acid imide. The solvent for the reaction is not particularly limited so long as it is inert to the reaction, and for example, it may be a hydrocarbon such as hexane, heptane or toluene, a halogenated hydrocarbon such as chlorofomri, 1,2-dichloroethane or chlorobenzene, an ether such as diethyl ether or 1,4-dioxane, an ester such as ethyl acetate, a ketone such as acetone or methyl ethyl ketone, a nitriie such as acetonitrile or propionitrile, or a mixture thereof. The above chlorination reaction may proceed even without a catalyst, but by adding a catalyst, it is possible to reduce the amount of the chlorinating agent to be used, and it is possible to promote the progress of the reaction. The catalyst may, for example, be an organic base such as triethylamine, pyridine, quinoline, N,Ndimethylaniline or N.N-dimethylformamide, or a metal alkoxide such as sodium methoxide, potassium methoxide or potassium t-butoxide. Such a catalyst is used in an amount of, for example, from 0 to 100 times by mole, preferably from 0.01 to 10 times by mole, to the ester product. As the purity of the acid chloride is high, the molecular weight of the obtainable polyamic acid ester will be improved, and therefore, after the chlorination reaction, the reaction product is preferably purified. As a purification method, recrystallization may be mentioned, and the solvent for the recrystallization is not particularly limited so long as it is an organic solvent not reactive with the acid chloride. [Polyamic acid ester] The polyamic acid ester to be used for the liquid crystal aligning agent of the present invention is one obtained by a reaction of a diamine and a bis(chlorocarbonyl) compound containing, as an essential component, an acid chloride represented by the above formula (101). The bis(chlorocarbonyl) compound to be used for this reaction may include an acid chloride other than the one represented by the formula (101), e.g. an acid chloride wherein chlorocarbonyl groups are bonded at 1- and 4-positions of the cyclobutane ring and alkyl esters bonded to 2- and 3-positions thereof. However, in such a case, it is preferred that the acid chloride represented by the formula (101) is at least 60 moi%. With a view to making the obtainable polyamic acid ester to have higher regularity and to further increase the anisotropy against the alignment treatment direction, the acid chloride represented by the formula (101) is preferably at least 80 mol%, more preferably from 95 to 100 mol%. The diamine to be reacted with the bis(chlorocarbonyl) compound may be a diamine represented by the following formula (130). wherein X is a bivalent organic group. Specific examples of the structure of X in the formula (130) are shown below, but the present invention is by no means limited thereto. In the process for producing a liquid crystal alignment film of the present invention, in a case where an aromatic ring is present in the diamine compound, the aromatic ring will serve as a light absorption site, whereby the cleavage reaction of the cyclobutane ring will be accelerated. Accordingly, from the viewpoint of the photoreaction efficiency, an aromatic diamine is preferred as the diamine compound. Further, as the linearity of the polyimide molecular chain formed by imidation is high, the liquid crystal alignment will be improved, and accordingly, A-7, A-11, A-12, A-13, A- 14, A-20, A-22, A-23, A-24, A-26, A-27, A-28, A-30, A-42. A-43, A-44, A-45, A-46, A-48, A-63, A-69, A-71, A-72, A-73, A-74 or A-75 is particularly preferred. [Preparation of polyamic acid ester] The polyamic acid ester can be prepared by reacting the diamine and the bis(chlorocarbonyl) compound in the presence of a base and an organic solvent at from -20°C to 150°C, preferably from 0°C to 50°C, for from 30 minutes to 24 hours, preferably from 1 to 4 hours. As the base, it is possible to use, for example, pyridine, triethylamine or 4- dimethylaminopyridine, but pyridine is preferred, since the reaction thereby proceeds mildly. The amount of the base to be added is preferably from 2 to 4 times by mole to the bis(chlorocarbonyl) compound, since if it is too much, the removal tends to be difficult, and if it is too small, the molecular weight tends to be small. The solvent to be used for the preparation of the polyamic acid ester is preferably N-methyl-2-pyrrolidone or ?-butyrolactone from the solubility of the monomer and polymer, and such solvents may be used alone or in combination of two or more of them. If the concentration during the preparation is too high, precipitation of the polymer is likely to take place, and if it is too low, the molecular weight will not sufficiently increase, and the concentration is preferably from 1 to 30 wt%, more preferably from 5 to 20 wt%. Further, in order to prevent hydrolysis of the bis(chlorocarbonyl) compound, the solvent to be used for the preparation of a polyamic acid ester is preferably dehydrated as much as possible, and it is preferred to cany out the reaction in a nitrogen atmosphere to prevent inclusion of the external air. While being thoroughly stirred, the polyamic acid ester solution thus obtained is poured into a poor solvent, whereby the polymer may be precipitated. Such precipitation is carried out a few times, followed by washing with the poor solvent and by drying at room temperature or under heating to obtain a purified powder of the polyamic acid ester. The above poor solvent is not particularly limited, and it may, for example, be water, methanol, ethanol, hexane, butylcellosolve, acetone or toluene. [Molecular weight of polyamic acid ester] The ratio of the diamine component to the bis(chlorocarbonyl) compound to be used for the polymerization reaction is preferably from 1.0/0.5 to 1.0/1.0 by molar ratio from the viewpoint of the molecular weight control. As the molar ratio is close to 1:1, the molecular weight of the obtainable polymer tends to be large. The molecular weight of the polymer is influential over the physical strength of the liquid crystal alignment film. If the molecular weight of the polymer is too large, the operation efficiency in application of the liquid crystal aligning agent or the uniformity of the applied film is likely to be poor, and if the molecular weight is too small, the strength of the coating film obtainable from the liquid crystal aligning agent is likely to be inadequate. Accordingly, the molecular weight of the polymer to be used for the liquid crystal aligning agent of the present invention is preferably from 2,000 to 500,000, more preferably from 5,000 to 300,000, further preferably from 10,000 to 100,000, by weight average molecular weight. [Liquid crystal aligning agent] The liquid crystal aligning agent of the present invention is an application liquid for forming a liquid crystal alignment film, wherein the polymer obtained as described above is uniformly dissolved in an organic solvent. The solvent to be used for the liquid crystal aligning agent of the present invention is not particularly limited so long as it is capable of dissolving the polymer contained in the liquid crystal aligning agent. Specific examples of the solvent include ,N-dimethylformamide, N,N-diethylfomnamide, N,N-dimethylacetamide, N-methyl-2- pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethylpyrrolidone, Nvinylpyrrolidone, dimethylsulfoxide, dimethylsulfone, hexamethylsulfoxide, ?- butyrolactone, 1,3-dimethyl-imidazolidinone, 3-methoxy-N,N-dimethylpropanamide, etc. They may be used alone, or two or more of them may be used as mixed. Further, even a solvent which is not capable of dissolving the polymer alone may be mixed within a range where the polymer will not be precipitated. Further, a solvent to improve the uniformity of an applied film at the time of applying the liquid crystal aligning agent to a substrate, may be added. Such a solvent may, for example, be ethylcellosolve, butylcellosolve, hexylcellosolve, ethylcellosolve acetate, butylcellosolve acetate, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, butyl carbitol acetate, ethylene glycol, diethylene glycol diethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, 1-phenoxy-2- propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol- 1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, dipropylene glycol, dipropylene glycol monomethyl ether, 2-(2-ethoxypropoxy)propanol, lactic acid methyl ester, lactic acid ethyl ester, lactic acid n-propyl ester, lactic acid nbutyl ester, or lactic acid isoamyl ester. Two or more of such solvents may be used in combination. The concentration of the polymer in the liquid crystal aligning agent of the present invention may suitably be changed depending upon the thickness set for the liquid crystal alignment film to be formed, but it is preferably from 1 to 10 wt%. If it is less than 1 wt%, it tends to be difficult to form a unifomi coating film free from defects, and if it is more than 10 wt%, the storage stability of the solution is likely to be poor. In order to improve the adhesion of the coating film to the substrate, an additive such as a silane coupling agent may be added to the liquid crystal aligning agent of the present invention. Such a silane coupling agent may be of any type so long as it is a conventional one. When the coupling agent is incorporated, after its addition, heating is carried out to let it react with the polymer, whereby the adhesion will be improved, and it is possible to suppress the influence over the properties of the liquid crystal aligning agent. After the addition, the reaction may be carried out preferably from 20 to 80°C, more preferably from 40 to 60°C for from 1 to 24 hours. The amount of the silane coupling agent to be added is preferably from 0.01 to 5.0 wt%, more preferably from 0.1 to 1.0 wt%, to the polymer powder, since if it is too much, non-reacted one may adversely affect the liquid crystal alignment, and if it is too small, no adequate effect to the adhesion may be obtained. Needless to say, various additives such as a crosslinking agent, an imidation promoter, etc. may further be incorporated to the liquid crystal aligning agent of the present invention. Further, two or more types of polymers may be contained in the liquid crystal aligning agent of the present invention, and so long as at least one type is the polyamic acid ester of the present invention, the types of other polymers are not particularly limited. [Process for producing liquid crystal aligning agent] The liquid crystal aligning agent of the present invention can be produced by the following process. A powder of a polyamic acid ester is dissolved in the above-mentioned solvent to obtain a polyamic acid ester solution. At that time, the polymer concentration is preferably from 10 to 30%, particularly preferably from 10 to 15%. Further, at the time of dissolving the powder of a polyamic acid ester, heating may be carried out. The heating temperature is preferably from 20 to 150°C, particularly preferably from 20 to 80°C. The obtained polyamic acid ester solution is diluted by the above-mentioned solvent to a predetermined polymer concentration, to obtain the liquid crystal aligning agent of the present invention. In a case where a silane coupling agent or a crosslinking agent is to be added, in order to prevent precipitation of the polymer, it is preferred to add it before adding a solvent having a low solubility of the polymer. In a case where an imidation accelerator is to be added, it is preferred to add it after the dilution step, since imidation may proceed under heating. [Process for producing liquid crystal alignment film] The liquid crystal aligning agent of the present invention is filtered and then applied to a substrate, followed by drying and firing to form a coating film, which will be used as a liquid crystal alignment film by subjecting the coating film surface to aligning treatment. The method for application of the liquid crystal aligning agent may, for example, be a spin coating method, a printing method or an ink jetting method. In the drying and firing steps after applying the liquid crystal aligning agent, optional temperatures and times may be selected for use. For example, in order to sufficiently remove the organic solvent contained in the liquid crystal aligning agent, the drying is carried out at a temperature of from 50 to 120°C for 1 to 10 minutes, followed by firing at a temperature of from 150 to 300°C for from 5 to 120 minutes. The thickness of the coating film after the firing is from 5 to 300 nm, preferably from 10 to 200 nm. If it is too thick, such is disadvantageous from the viewpoint of the power consumption by the liquid crystal display element, and if it is too thin, the reliability of the liquid crystal display element is likely to be low. The method for alignment treatment of such a coating film may, for example, be a rubbing method or a photo-alignment treatment method, but the liquid crystal aligning agent of the present invention is particulariy useful when a photo-alignment treatment method is employed. As a specific example of the photo-alignment treatment method, a method may be mentioned wherein radiation polarized in a constant direction is applied to the above coating film surface, and, as the case requires, heat treatment at a temperature of from 150 to 250°C is further carried out, to impart the liquid crystal alignment function. As the radiation, it is possible to employ ultraviolet rays having a wavelength of from 100 nm to 800 nm and visible light. Among them, ultraviolet rays having a wavelength of from 100 nm to 400 nm are preferred, and ones having a wavelength of from 200 nm to 400 nm are particulariy preferred. Further, in order to improve the liquid crystal alignment properties, the radiation may be applied while heating the coating film substrate at a temperature of from 50 to 250°C. The amount of the radiation to be applied is preferably within a range of from 1 to 10,000 mJ/cm2, particulariy preferably within a range of from 100 to 5,000 mJ/cm2. The liquid crystal alignment film prepared as described above is capable of aligning liquid crystal molecules stably in a constant direction. EXAMPLES Now, the present invention will be described in further detail with reference to Examples, but it should be understood that the present invention is by no means thereby restricted, EXAMPLE 1: Preparation of tetracarboxylic acid dialkyi ester under neutral condition at 65°C In a nitrogen stream, into a 3 L four necked flask, 220 g (0.981 mol) of 1,3- dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (compound of the formula (5-1), hereinafter referred simply as 1,3-DM-CBDA) and 2,200 g (6.87 mol, 10 times by weight to 1,3-DM-CBDA) of methanol were charged and subjected to heating and refluxing at 65°C, whereby the solution became unifomri in 30 minutes. The reaction solution was stirred as it was for 4 hours and 30 minutes under heating and refluxing. This reaction solution was measured by a high performance liquid chromatography (hereinafter referred to simply as HPLC). The analysis of the results of this measurement will be given hereinafter. By an evaporator, the solvent was distilled off from this reaction solution, and then, 1,301 g of ethyl acetate was added, followed by heating to 80°C, and the mixture was refluxed for 30 minutes Thereafter, it was cooled at a rate of from 2 to 3°C per 10 minutes until the intemal temperature became 25°C, and it was stirred at 25°C for 30 minutes. Precipitated white crystals were collected by filtration, and the crystals were washed twice with 141 g of ethyl acetate and then dried under reduced pressure to obtain 103.97 g of white crystals. From the results of the 1H NMR analysis and X-ray crystal structure analysis, the crystals were confimried to be compound (1-1) (HPLC relative area: 97.5%) (yield: 36.8%). 1H NMR (DMS0-d6, dppm);12.82 (s, 2H), 3.60 (s, 6H), 3.39 (s, 2H), 1.40 (s, 6H). Compound (1-1) being 2,4-bis(methoxycarbonyl)-1,3-dimethylcyclobutane-1,3- dicarboxylic acid may hereinafter be referred to simply as 1,3-DM-CBDE. On the other hand, the filtrate after taking out the above white crystals, was distilled by an evaporator to remove the solvent thereby to obtain 172.24 g of white crystals. To 156.01 g of the white crystals, 385.09 g of acetonitrile was added, followed by heating to 65°C, whereby crystals were completely dissolved. Thereafter, the solution was cooled to 30°C over a period of 1 hour and then cooled over 2 hours until the internal temperature became 25°C. It was stirred at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration, and the crystals were washed with 30.7 g of acetonitrile, followed by drying under reduced pressure to obtain 52.74 g of white crystals. From the results of the H NMR analysis and X-ray crystal structure analysis, the crystals were confirmed to be compound (2-1) (HPLC relative area: 99.2%) (yield: 20.6%). 1H NMR (DMS0-d6, dppm);12.82 (s, 2H), 3.60 (s, 6H), 3.48 (s, 1H), 3.30(s, 1H), 1.45 (s, 3H), 1.38(s, 3H) Further, using compound (1-1), compound (2-1), etc. obtained as described above, as samples, data of HPLC measurement at the time of completion of the reaction were analyzed, whereby the proportion of compound (1-1) based on the entire reaction products was 50% by the HPLC relative area, and the proportion of compound (2-1) was 47%. Further, with the filtrate after taking out crystals of compound (1 -1) from the reaction liquid, the proportion of compound (1-1) was 21% by the HPLC relative area, and the proportion of compound (2-1) was 74%. [X-ray crystal structure analysis] Apparatus: DIP2030 (manufactured by MacScience) X-ray: Moka (40 kV, 200 mA) Measurement temperature: 298.0 K As a sample for measurement, the obtained compound was dissolved in acetonitrile and slowly concentrated at room temperature to prepare single crystals. ORTEP model illustrating the analytical results of single crystal X-ray measurement of compound (1-1) is shown in Fig. 1. Crystal data Molecular formula: C12H16O8 Molecular weight: 288.252 Color, shape: colorless, block Crystal system: Monocllnic Space group: P21/c Lattice constants: a=8.3460(10)A, b=8.256(2)A. c=10.630(2)A a=90.00°, ß=109.738(10)°, ?=90.00° V=689.4(3)A3 Z value=2 R(gt)=0.111 wR(gt)=0.548 ORTEP model illustrating the analytical results of single crystal X-ray measurement of compound (2-1) is shown in Fig. 2. Crystal data Molecular formula: C12H16O8 Molecular weight: 288.252 Color, shape: colorless, cube Crystal system: triclinic Space group: P-1 Lattice constants: a=7.422(2) A, b=8.0390(10)A, c=12.232(2)A a=106.055(10)°, ß=99.018(10)°, 7=103.537(10)° V=662.4(2)A3 Z value=2 R(gt)=0.06 wR(gt)=0.07 EXAMPLE 2: Preparation of tetracarboxylic acid dialkyl ester under neutral condition at 20°C In a nitrogen stream, into a 200 mL four necked flask, 10 g (0.45 mol) of 1,3-DMCBDA and 50 g (1.56 mol, 5 times by weight to 1,3-DM-CBDA) were charged and stirred for 69 hours from 14 to 20°C, whereby a uniform reaction solution was obtained. This reaction solution was analyzed by HPLC, whereby the HPLC relative area of compound (1-1) was 56%, and the HPLC relative area of compound (2-1) was 44%. By an evaporator, the solvent was distilled off from this reaction solution, and then, 60 g of ethyl acetate was added, and the mixture was heated to 80°C and refluxed for 30 minutes Thereafter, it was cooled at a rate of from 2 to 3°C per 10 minutes until the internal temperature became 25°C, and stirred as it was at 25°C for minutes. Precipitated white crystals were collected by filtration and washed twice with 6.43 g of ethyl acetate, followed by drying under reduced pressure to obtain 5.50 g of white crystals. From the results of the 1H NMR analysis and X-ray crystal structure analysis, the crystals were confirmed to be compound (1-1) (HPLC relative area: 99.0%) (yield: 45.7%). EXAMPLE 3: Preparation of tetracarboxylic acid dialkyl ester under neutral condition at 40°C In a nitrogen stream, into a 200 mL four necked flask, 10 g (0.045 mol) of 1,3- DM-CBDA and 50 g (1.56 mol, 5 times by weight to 1,3-DM-CBDA) of methanol were charged and stirred at 40°C for 7 hours and 30 minutes to obtain a unifonn reaction solution. This reaction solution was analyzed by HPLC, whereby the HPLC relative area of compound (1-1) was 48%, and the HPLC relative area of compound (2-1) was 45%. EXAMPLE 4: Preparation of tetracarboxylic acid dialkyi ester in the presence of pyridine at 25°C. In a nitrogen stream, into a 3 L four necked flask, 240 g (1.07 mol) of 1,3-DMCBDA and 720 g of ethyl acetate were charged, and 8.47 g (0.107 mol) of pyridine was added, whereupon the mixture was suspended at 25°C with stirring by a magnetic stirrer. To this suspension, 600 g (18.73 mol, 2.5 times by weight to 1,3-DM-CBDA) of methanol was dropwise added over a period of 1 hour so that the intemal temperature became at most 25°C. Stining was continued for 20 minutes even after completion of the dropwise addition, whereby a uniform reaction solution was obtained. This reaction solution was analyzed by HPLC, whereby the HPLC relative area of compound (1-1) was 77%, and the HPLC relative area of compound (2-1) was 22%. By an evaporator, this reaction solution was distilled to remove the solvent in a water bath of 40°C under from 170 to 140 Torr until the internal amount became 561.65 g. Then, 1,450 g of ethyl acetate was added, and the mixture was stirred and then distilled to remove the solvent by an evaporator in a water bath of 40°C under from 170 to 140 Torr until the intemal amount became 597.51 g. Thereafter, 1,450 g of ethyl acetate was again added, and the mixture was stirred and then distilled to remove the solvent by an evaporator in a water bath of 40°C under from 170 to 140 Torr until the internal amount became 1,852 g. Further, the solvent distilled at that time was analyzed by gas chromatography, whereby the area% of methanol was 0.3%. Then, the remained slurry solution was heated to 80°C and refluxed for 30 minutes, and then cooled at a rate of from 2 to 3°C per 10 minutes until the inner temperature became 25°C. Stirring was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration, and the crystals were washed twice with 192.88 g of ethyl acetate. The washed product was dried under reduced pressure to obtain 223.77 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (1-1) (HPLC relative area: 99.0%) (yield: 72.5%). EXAMPLE 5: Preparation of tetracarboxylic acid dialkyl ester in the presence of pyridine at 0°C In a nitrogen stream, into a 100 mL four necked flask, 5 g (0.022 mol) of 1,3-DMCBDA, 25 g (0.78 mol, 5 times by weight to 1,3-DM-CBDA) of methanol and 0.176 g (0.0022 mol) of pyridine were charged and stirred at 0°C for 8 hours by a magnetic stirrer, whereby a uniform reaction solution was obtained. This reaction solution was analyzed by HPLC, whereby the HPLC relative area of compound (1-1) was 79%, and the HPLC relative area of compound (2-1) was 20%. EXAMPLE 6: Preparation of tetracarboxylic acid dialkyi ester in the presence of pyridine at 40°C In a nitrogen stream, into a 100 mL four necked flask, 5 g (0.022 mol) of 1,3-DMCBDA, 25 g (0.78 mol, 5 times by weight to 1,3-DM-CBDA) of methanol and 0.176 g (0.0022 mol) of pyridine were charged and stirred at 40°C for 20 minutes by a magnetic stirrer, whereby a uniform reaction solution was obtained. This reaction solution was analyzed by HPLC, whereby the HPLC relative area of compound (1-1) was 74%, and the HPLC relative area of compound (2-1) was 25%. EXAMPLES 7 to 14 A series of operations were camed out in the same manner as in Example 4, provided that the equivalent amount of pyridine added and the temperature were as shown in the following Table. The analytical results by HPLC of the reaction solutions thereby obtained are shown in the Table together with the results of the reaction solutions obtained in Examples 1 to 6. Conditions for HPLC analysis Column: Atlantis cd18 (Waters), 5 um, 4.6x250 mm Oven: 40°C Eluent: AGetonitrile/0.5% phosphoric acid aqueous solution=22/78, detection wavelength: 209 nm Flow rate: 1.0 mL/min, amount of sample injected: 10 μL TABLE 5 EXAMPLES 15 to 43 A series of operations were carried out in the same manner as in Example 4, and the reactions were carried out by adding various additives instead of pyridine. The types of additives, the equivalent amounts of additives, the temperature, the reaction time, the analytical results of the reaction solutions by HPLC are shown in the following Table. The additives disclosed in the Table are as shown below. Add-1: Potassium methoxide Add-2: Potassium carbonate Add-3: Triethylamine Add-4: Potassium t-butoxide Add-5: Quinoline Add-6: 8-Quinolinol Add-7: 1,10-Phenanthroline Add-8: Bathophenanthroline Adcl-9: Bathocuproin Add-10: 2,2'-Bipyridyl Add-11: 2-Phenylpyridine Add-12: 2,6-Diphenylaminopyridine Add-13: 2-Dimethylaminopyridine Add-14: 4-Dimethylaminopyridine Add-15: 2-(2-Hydroxyethyl)pyridine Add-16: 5-Bromo-2-chloropyridine Add-17: 1,8-Diazabicyclo[5,4,0]-7-undene Add-18: p-Toluenesulfonic acid Add-19: Phosphoric acid Add-20: Formic acid Add-21: Triphenylphosphine Add-22: Trimethyl borate Add-23: Phosphotungstic acid (H3[PW12O40]-30H2O) Add-24: Phosphomolybdic acid (H3[PMo12O40]-30H2O) Add-25: Water TABLE 6 EXAMPLE 44: Preparation of compounds (1-4) and (2-4) In a nitrogen stream, into a 200 mL four necked flask, 10 g (0.045 mol) of 1,3- DM-CBDA and 50 g of tetrahydrofuran were charged, and 10.59 g (0.004 mol) of pyridine was added. The mixture was suspended at 25°C with stirring by a magnetic stirrer, and then 50 g (1.561 mol, 5 times by weight to 1,3-DM-CBDA) of ethanol was dropwise added over a period of 1 hour. After completion of the dropwise addition, stirring was continued for 5 days, whereby a uniform reaction solution was obtained. This reaction solution was distilled to remove the solvent by an evaporator, and then, 70.55 g of ethyl acetate was added. The mixture was heated to 80°C with stimng and refluxed for 30 minutes, and then cooled at a rate of from 2 to 3°C per 10 minutes until the inner temperature became 25°C. Stirring was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration, and the crystals were washed twice with 7.05 g of ethyl acetate, followed by drying under reduced pressure to obtain 9.15 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (1-4) (HPLC relative area: 99.6%) (yield: 64.8%) 1H NMR (DMS0-d6, dppm): 12.82 (s, 2H), 4.09-4.04 (q, 4H), 3.36 (s, 2H), 1.41 (s, 6H), 1.16-1.41 (t, 6H). Further, the data of HPLC measurement of the reaction solution were analyzed by using samples, whereby the HPLC relative areas of compounds (1-4) and (2-4) were 83% and 17%, respectively. EXAMPLE 45: Preparation of compounds (1-10) and (2-10) In a nitrogen stream, into a 200 mL four necked flask, 10 g (0.045 mol) of 1,3- DM-CBDA and 50 g of acetonitrile were charged, and 0.353 g (0.0045 mol) of pyridine was added. The mixture was suspended at 25°C with stirring by a magnetic stirrer, and then 50 g (0.416 mol, 2.5 times by weight to 1,3-DM-CBDA) of 2-propanol was dropwise added over a period of 1 hour. After completion of the dropwise addition, stimng was carried out for 12 days. This reaction solution was distilled to remove the solvent by an evaporator (13.05 g), and then 52.20 g of acetonitrile and 6.53 g of 2-propanol were added. The mixture was heated to 71°C for dissolution and then left to cool for 1 hour so that the inner temperature became 27°C. The mixture was stirred for 1 hour under cooling with ice, whereupon precipitated white crystals were collected by filtration. The crystals were washed twice with 13.05 g of acetonitrile, followed by drying under reduced pressure to obtain 6.08 g of white crystals. From the 1H NMR analytical results, the crystals were confimied to be compound (1-10) (HPLC relative area: 88.8%) (yield: 46.6%) 1H NMR (DMS0-d6, dppm): 12.76 (s, 2H), 4.92-4.85 (m, 2H), 3.31 (s, 2H), 1.41 (s, 6H), 1.19-1.17 (q,6H). Further, the data of HPLC measurement of the reaction solution were analyzed by using samples, whereby the HPLC relative areas of compounds (1-10) and (2-10) were 88% and 12%, respectively. EXAMPLE 46 Preparation of compounds (1-10) and (2-10) In a nitrogen stream, into a 200 mL four necked flask, 10 g (0.045 mol) of 1,3- DM-CBDA and 50 g (1.22 mol, 5 times by weight to 1,3-DM-CBDA) of acetonitrile were charged, and 0.353 g (0.0045 mol) of pyridine was added. The mixture was heated to 50°C with stirring by a magnetic stirrer, and 50 g (0.416 mol, 2.5 times by weight to 1,3-DM-CBDA) of 2-propanol was dropwise added over a period of 1 hour. After completion of the dropwise addition, stirring was continued for 7 days. This reaction solution was analyzed by HPLC, whereby the HPLC relative area% of compound (1-10) and (2-10) were 83% and 17%, respectively. EXAMPLE 47: Preparation of bis(chlorocarbonyl) compound (3-1) In a nitrogen stream, into a 3 L four necked flask, 234.15 g (0.81 mol) of compound (1-1) and 1,170.77 g (11.68 mol, 5 times by weight) of n-heptane were charged, and then 0.64 g (0.01 mol) of pyridine was added. The mixture was heated to 75°C with stirring by a magnetic stirrer. Then, 289.93 g (11.68 mol) of thionyl chloride was dropwise added over a period of 1 hour. Immediately after the dropwise addition, foaming started, and upon expiration of 30 minutes from the completion of the dropwise addition, the reaction solution became uniform, and foaming terminated. Stirring was continued at 75°C for 1 hour and 30 minutes, and then the solvent was distilled off by an evaporator in a water bath of 40°C until the internal amount became 924.42 g. The obtained concentrate was heated at 60°C to dissolve crystals precipitated during the solvent distillation and subjected to filtration while being hot at 60°C to filter off insolubles. Then, the filtrate was cooled to 25°C at a rate of 1 °C per 10 minutes. Stirring was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration. The crystals were washed with 264.21 g of n-heptane, followed by drying under reduced pressure to obtain 226.09 g of white crystals. Then, in a nitrogen stream, into a 3 L four necked flask, 226.09 g of the white crystals obtained as described above and 452.18 g of n-heptane were charged, followed by heating and stining at 60°C to dissolve the crystals. Thereafter, the solution was cooled with stirring to 25°C at a rate of 1°C per 10 minutes to precipitate crystals. Stirring was continued at 25°C for 1 hour, whereupon precipitated white crystals were collected by filtration. The crystals were washed with 113.04 g of nhexane, followed by drying under reduced pressure to obtain 203.91 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (3-1) i.e. dimethyl-1,3-bis(chlorocarbonyl)-1,3-dimethylcyclobutane-2,4- dicarboxylate (hereinafter referred to as 1,3-DM-CBDE-C1) (HPLC relative area: 99.5%) (yield: 77.2%). 1H NMR (CDCI3, dppm): 3.78 (s, 6H), 3.72 (s, 2H), 1.69 (s, 6H). EXAMPLES 48 to 53 A series of operations were carried out in the same manner as in Example 47, provided that the type of the catalyst, the equivalent amount of the catalyst and the temperature were as shown in the following Table. Further, the timing for completion of the reaction was taken as the time when the reaction solution was a uniform solution and generation of the gas completely terminated. TABLE 7 EXAMPLE 54: Preparation of bis(chlorocarbonyl) compound (4-1) In a nitrogen stream, into a 200 mL four necked flask, 20.01 g (69.38 mmol) of compound (2-1) and 100 g of n-heptane were charged, and then, 0.055 g (0.69 mmol) of pyridine was added. The mixture was heated to 70°C with stirring by a magnetic stirrer. Then, 24.75 g (208.15 mmol) of thionyl chloride was dropwise added at 72°C over a period of 1 hour. Immediately after the dropwise addition, foaming started, and upon expiration of 1 hour after completion of the dropwise addition, foaming terminated. Stirring was continued at 73°C for 1 hour and 30 minutes, and then the solvent was distilled off by an evaporator in a water bath of 40°C until the internal amount became 53.9 g. Then, the residual liquid was heated to 60°C and stirred for 30 minutes and then cooled to 28°C over a period of 30 minutes. Stirring was continued at 20°C for 30 minutes, whereupon precipitated white crystals were collected by filtration. The crystals were washed with 22.57 g of n-heptane, followed by drying under reduced pressure to obtain 21.93 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (4-1) (HPLC relative area: 98.5%) (yield: 97.2%). 1H NMR (CDCI3, dppm): 4.15 (s, 1H), 3.84(s, 3H), 3.80 (s, 3H), 3.44 (s, 1H), 1.74 (s. 3H), 1.59(s, 3H). EXAMPLE 55: Preparation of compound (2-2) In a nitrogen stream, into a 3 L four necked flask, 19.9 g (0.089 mol) of 1,2- dimethylcyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (compound of the fomiula (5-2), hereinafter referred to simply as 1,2-DM-CBDA) and 49.7 g of ethyl acetate were charged, and 0.70 g (0.009 mol) of pyridine was added. The mixture was suspended at 25°C with stirring by a magnetic stirrer, and then 49.75 g (1.55 mol, 2.5 times by weight to 1,2-DM-CBDA) of methanol was dropwise added over a period of 1 hour so that the inner temperature became at most 30°C. Upon expiration of 20 minutes from the completion of the dropwise addition, the reaction solution was completely dissolved, and stirring was continued at from 20 to 30°C for 40 minutes. This reaction solution was distilled to remove the solvent in a water bath of 40°C under from 170 to 140 Torr until the internal amount became 51.18 g. Then, 127.94 g of ethyl acetate was added and stirred, and then the solvent was distilled off by an evaporator in a water bath of 40°C under from 170 to 140 Torr until the internal amount became 51.18 g . Thereafter, 127.94 g of ethyl acetate was added again and stirred, and then the solvent was distilled off by an evaporator in a water bath of 40°C under from 170 to 140 Torr until the intemal amount became 117.71 g. Further, the solvent distilled off at that time was measured by gas chromatography, whereby the area of methanol was 0.3%. Then, the remained slurry solution was heated to 80°C and refluxed for 30 minutes and then cooled at a rate of from 2 to 3°C per 10 minutes until the intemal temperature became 25°C. Stirring was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration. The crystals were washed twice with 12.8 g of ethyl acetate, followed by drying under reduced pressure to obtain 16.96 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (2-2) (HPLC relative area: 95.5%) (yield: 66.7%). 1H NMR (DMS0-d6, dppm): 13.16 (s, 2H), 3.56 (s, 6H), 3.21 (s, 2H), 1.30 (s, 6H). Further, the data of HPLC measurement of the reaction solution were analyzed by using samples, whereby the HPLC relative area of compound (2-2) was 96%. EXAMPLE 56: Preparation of bis(chlorocarbonyl) compound (4-2) In a nitrogen stream, into a 3 L four necked flask, 16.46 g (0.06 mol) of compound (2-2) and 82.3 g of n-heptane were charged, and then, 0.045 g (0.6 mmol) of pyridine was added. The mixture was heated to 75°C with stirring by a magnetic stirrer. Then, 20.38 g (0.17 mol) of thionyl chloride was dropwise added over a period of 1 hour. Immediately after the dropwise addition, foaming started, and upon expiration of 30 minutes from the termination of the dropwise addition, the reaction solution became unifomn, and foaming terminated. Then, stirring was continued at 75°C for 1 hour and 30 minutes, and then, the solvent was distilled off by an evaporator in a water bath of 40°C until the internal amount became 64.98 g. The residual liquid was heated to 60°C to dissolve the crystals precipitated during the solvent distillation, and filtration was carried out while being hot at 60°C to filter off insolubles. Then, the filtrate was cooled to 25°C at a rate of 1 °C per 10 minutes. Stining was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration. The crystals were washed with 18.57 g of n-heptane, followed by drying under reduced pressure to obtain 16.42 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be compound (4-2) (HPLC relative area: 95.5%) (yield: 88.5%). 1H NMR (CDCI3, dppm): 3.72 (s, 6H), 3.42 (s, 2H), 1.82 (s, 6H). REFERENCE EXAMPLE 1 In a nitrogen stream, into a 3 L four necked flask, 300 g (1.53 mol) of cyclobutane-1,2,3,4-tetracarboxyliG acid-1:2,3:4-dianhydride (hereinafter referred to simply as CBDA) and 900 g of acetonitrile were charged, and 12.1 g (0.153 mol) of pyridine was added. The mixture was suspended at 25°C with stirring by a magnetic stirrer, and then 750 g (23.4 mol, 2.5 times by weight to CBDA) of methanol was dropwise added over a period of 1 hour so that the internal temperature became at most 30°C. Upon expiration of 20 minutes after completion of the dropwise addition, the reaction solution was completely dissolved, and stirrging was continued at from 20 to 30°C for 1 hour. This reaction solution was analyzed by HPLC, whereby the relative areas of CB-2,4-DME and CB-2,3-DME were 49.2% and 49.8%, respectively, and thus, even when the reaction was carried out in the presence of pyridine, no selectivity for positional isomers was obtained. This reaction solution was distilled to remove the solvent by an evaporator in a water bath of 40°C until the internal amount became 796.08 g. Then, 995.10 g of acetonitrile was added and stirred, and then the solvent was distilled off by an evaporator in a water bath of 40°C until the internal amount became 796.08 g. Further, 995.10 g of acetonitrile was added again and stirred, and then the solvent was distilled off by an evaporator in a water bath of 40°C until the internal amount became 796.08 g. Further, the solvent distilled off at that time was measured by gas chromatography, whereby the area of methanol was 0.3%. Then, 398.04 g of acetonitrile was added, and the mixture was heated to 80°C and refluxed for 30 minutes and then cooled at a rate of from 2 to 3°C per 10 minutes until the intemal temperature became 25°C. Stirring was continued at 25°C for 30 minutes, whereupon precipitated white crystals were collected by filtration. The crystals were washed twice with 199.02 g of acetonitrile, followed by drying under reduced pressure to obtain 157.54 g of white crystals. From the 1H NMR analytical results, the crystals were confirmed to be CB-2,4-DME (HPLC relative area: 96.4%) (yield: 39.6%). 1H NMR (DMS0-d6, dppm): 12.81 (s, 2H), 3.61 (s, 6H), 3.59-3.54 (m, 2H). APPLICATION EXAMPLE 1: Polymerization of compound (3-1) and paraphenylenediamine In a nitrogen stream, into a 50 mL two necked flask, 0.6005 g (5.5527 mmol) of paraphenylenediamine, 10 mL of N-methylpyrrolidone, 10 mL of ?-butyrolactone and 1.06 mL of pyridine were charged and stirred by a magnetic stirrer at 25°C to completely dissolve paraphenylenediamine. Thereafter, the reaction solution was cooled with ice, and while stimng by a magnetic stirrer, compound (3-1) was added over a period of 30 seconds by using a dropping funnel. Thereafter, the dropping funnel used for the addition was washed with 3 mL of N-methylpyrrolidone, and nitrogen substitution was carried out, followed by stirring at 0°C for 20 minutes. After the 20 minutes, the temperature was raised to 20°C, and then stirring was carried out at 20°C for 3 hours. This polymerization solution was sampled after 1 hour and after 2 hours, and the viscosity was measured and found to be 1,300 mPas after 1 hour and 1,500 mPa-s after 2 hours. APPLICATION EXAMPLE 2: Polymerization of compound (4-1) and paraphenylenediamine In a nitrogen stream, into a 50 mL two necked flask, 0.6005 g (5.5527 mmol) of paraphenylenediamine, 10 mL of N-methylpyrrolidone, 10 mL of ?-butyrolactone and 1.06 mL of pyridine were charged and stirred by a magnetic stirrer at 25°C to completely dissolve paraphenylenediamine. Thereafter, the reaction solution was cooled with ice, and while stimng by a magnetic stirrer, compound (4-1) was added over a period of 30 seconds by using a dropping funnel. Thereafter, the dropping funnel used for the addition was washed with 3 mL of N-methylpyrrolidone, and nitrogen substitution was carried out, followed by stimng at 0°C for 20 minutes. After the 20 minutes, the temperature was raised to 20°C, and then stirring was carried out at 20°C for 3 hours. This polymerization solution was sampled after 1 hour and after 2 hours, and the viscosity was measured and found to be 28 mPas after 1 hour and 28 mPa.s after 2 hours. PREPARATION EXAMPLES 101 to 104, COMPARATIVE PREPARATION EXAMPLES 101 to 103, EXAMPLES 101 to 111 and COMPARATIVE EXAMPLES 101 to 107 Now, abbreviations and structures of compounds used in the following Preparation Examples, Comparative Preparation Examples, Examples and Comparative Examples will be shown. 1,3-DM-CBDA: 1,3-Dimethyl-1,2,3,4-cyclobutane tetracarboxylic acid dianhydride 1,3-DM-CBDE: 2,4-Bis(methoxycarbonyl)-1,3-dimethylcyclobutane-1,3- dicarboxylic acid p-PDA: p-Phenylenediamine (Organic solvents) NMP: N-methyl-2-pyrrolidone ?-BL: ?-Butyrolactone BCS: Butylcellosolve DMF: N,N-Dimethylformamide DEF: N.N-Diethylformamide Now, with respect to 1HNMR, FT-IR, X-ray crystal structure analysis, viscosity, molecular weight, anisotropy of an alignment film, voltage retention and ion density, the respective measuring methods will be shown. [1HNMR] Apparatus: Fourier transfonn superconducting nuclear magnetic resonance apparatus (FT-NMR) INOVA-400 (manufactured by Varian): 400 MHz Standard reference material: Tetramethylsilane (TMS) [FT-IR] Apparatus: NICOLET5700 (manufactured by Thermo ELECTRON) Smart Orbit accessory Measuring method: ATR method [X-ray crystal structure analysis] Apparatus: DIP2030 (manufactured by MacScience) X-ray: Moka (40 Kv, 200 mA) Measurement temperature: 298.0 K [Viscosity] In the Preparation Examples, the viscosities of polyamic acid ester and polyamic acid solutions were measured by means of an E-model viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) at 25°C by using a sample in an amount of 1.1 mL and a cone rotor TE-1 (1°34', R24). [Molecular weight] Further, the molecular weights of a polyamic ester acid and a polyamic acid were measured by means of a GPC (normal temperature gel permeation chromatography) apparatus, and a number average molecular weight (Mn) and weight average molecular weight (Mw) were calculated as values calculated as polyethylene glycol and polyethylene oxide. GPC apparatus: Manufactured by Shodex (GPC-101) Column: Manufactured by Shodex (KD803 and KD805 in series) Temperature of column: 50°C Eluent: N,N-dimethylformamide (as additives, 30 mmol/L of lithium bromide monohydrate (LiBrH2O), 30 mmol/L of phosphoric anhydride crystals (o-phosphoric acid), and 10 ml/L of tetrahydrofuran (THF)) Flow rate: 1.0 ml/min Standard sample for preparation of a calibration curve: Manufactured by TOSOH CORPORATION, TSK standard polyethylene oxide (weight average molecular weight (Mw): about 900,000,150,000,100,000 and 30,000), and manufactured by Polymer Laboratory, polyethylene glycol (peak top molecular weight (Mp): about 12,000, 4,000 and 1,000). For the measurement, in order to avoid overlapping of peaks, two samples i.e. a sample having four types of 900,000,100,000,12,000 and 1,000 mixed and a sample having three types of 150,000, 30,000 and 4,000 mixed, were separately measured. [Anisotropy of alignment film] The measurement of anisotropy of an alignment film was carried out as follows. The measurement was carried out by using a liquid crystal alignment film evaluation system "LayScan-LaboH" (LYS-LH30S-1A) manufactured by Moritex Corporation. A polyimide film having a thickness of 100 nm was irradiated with ultraviolet rays via a polarizer, and the degree of anisotropy against the alignment direction of the obtained alignnnent film was measured. [Voltage retention] The measurement of the voltage retention of a liquid crystal cell was carried out as follows. A voltage of 4 V was applied for 60 μs, and the voltage after 16.67 ms was measured, whereby a variation from the initial value was calculated as a voltage retention. At the time of the measurement, the temperature of the liquid crystal cell was adjusted to be 23°C or 60°C, and the measurement was carried out at each temperature. [Ion density] The measurement of the ion density of a liquid crystal cell was carried out as follows. The measurement was carried out by using 6254 model liquid crystal physical property evaluation apparatus manufactured by TOYO Corporation. Triangle waves of 0.01 Hz at 10 V were applied, and an area corresponding to an ion density of the obtained wave-form was calculated by a triangle approximation method and taken as the ion density. At the time of the measurement, the temperature of the liquid crystal cell was adjusted to be 23°C or 60°C, and the measurement was canned out at each temperature. PREPARATION EXAMPLE 101