Diamino compounds, polyamic acids, polyimides, liquid crystal aligning films using said polyimide films and liquid crystal display devices using said aligning films

This invention relates to a diamino compound represented by the formula [1]: ##STR1## in which G.sub.1 is a trivalent organic group of 2-20 carbon atoms, G.sub.2 is independently a single bond, --COO--, --OCO--, --NHCO--, --CONH--, --O--, --O--, or --CO--, G.sub.3 is a single bond or an alkylene group of 1-20 carbon atoms, X and Y are each independently a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, or an alkyl group, a haloalkyl group, an alkoxy group or a haloalkoxy group, each alkyl or alkoxy group having 1-12 carbon atoms, or a cycloalkyl group of 3-8 carbon atoms or a trans-4-alkylcyclohexyl group of 9-14 carbon atoms, and m is an integer of 0-3; a polyamic acid and polyimide using the said diamino compound, an aligning film using the said polyimide and a liquid crystal display device using the said aligning film. The aligning film is prepared by irradiation of a polarized ultraviolet light to the polyimide film.

TECHNICAL FIELD
 This invention relates to a diamino compound having a photosensitive group
 in the side chain thereof, a polyamic acid and a photo crosslinking
 polyimide, a liquid crystal aligning film using said polyimide, and a
 liquid crystal display device using said aligning film.
 BACKGROUND ART
 Recently, there have been demands for the display of word processors,
 notebook computers, etc. to have a lighter weight and a thinner thickness
 and to consume less electric power, and a superior liquid crystal display
 device is expected to be developed for a flat display satisfying these
 requirements. A liquid crystal display device is provided with a liquid
 crystal aligning film having a predetermined pretilt angle so as to align
 liquid crystal molecules to a given direction. As a method for preparing
 such aligning films, a rubbing process wherein a thin film of a polymeric
 compound such as a polyimide formed on a substrate is rubbed toward a
 certain direction with a cloth such as rayon, a process wherein silicon
 dioxide is subjected to oblique evaporation, etc. are known.
 However, although the rubbing process has been widely applied in the
 industrial field as a convenient and inexpensive process, it has the
 problems of the formation of dusts, the generation of static electricity
 and the like.
 The oblique evaporation process costs too much to be scaled up.
 Under these circumstances, a photo-orientation process has recently
 attracted attention of the industry. In such a process for the preparation
 of an aligning film according to this photo-orientation method, a thin
 film of a photosensitive polymeric compound is formed on a substrate and a
 polarized ultraviolet light or a laser light is irradiated thereto,
 whereby only the photosensitive groups in line with the irradiated
 polarized light may photochemically react to develop anisotropy on the
 aligning film and align liquid crystal molecules. This process can provide
 the advantages of no generation of static electricity or no contamination
 of impurities because the other members are not in contact with the thin
 film coated over the substrate.
 Several photo-aligning films utilizing photodimerization of a polarized
 light irradiated to polyvinyl cinnamate and derivatives thereof are
 disclosed, for example, in M. Schadt et al., Jpn. J. Appl. Phys., 31, 2155
 (1992) or Japanese Patent No. 2608661. However, these aligning films have
 the drawbacks of a low heat stability, an inferior retention of shape and
 an easily turbulent alignment of liquid crystal.
 Vinyl polymers having arylmaleimide residues in the side chain thereof are
 disclosed as a photosensitive group having a higher sensitivity in
 Japanese Patent Publication No. 13198/1976 and so on, but no examples of
 utilizing them as an aligning film for liquid crystal display device is
 disclosed therein.
 The present inventors have made earnest studies, and as a result, have
 found out that a polyimide having an .beta.,.beta.-substituted maleimide
 group in the side chain thereof may be rapidly dimerized in the side chain
 thereof at a high sensitivity, and that the crosslinked film is excellent
 in a heat stability and a retention of shape and also shows a favorable
 alignment of liquid crystal, upon which this invention has been completed.
 DISCLOSURE OF INVENTION
 More specifically, the constitution of this invention is as described
 below.
 (1) A diamino compound represented by the formula [1]:
 ##STR2##
 in which G.sub.1 is a trivalent organic group of 2-20 carbon atoms, G.sub.2
 is independently a single bond, --COO--, --OCO--, --NHO--, --CONH--,
 --O--, --S--, or --CO--, G.sub.3 is a single bond or an alkylene group of
 1-20 carbon atoms, X and Y are each independently a hydrogen atom, a
 fluorine atom, a chlorine atom, a cyano group, a nitro group, or an alkyl
 group, a haloalkyl group, an alkoxy group or a haloalkoxy group, each
 alkyl or alkoxy group having 1-12 carbon atoms, or a cycloalkyl group of
 3-8 carbon atoms or a trans-4-alkylcyclohexyl group of 9-14 carbon atoms,
 and m is an integer of 0-3.
 (2) A polyamic acid which comprises a structural unit represented by the
 formula [2]:
 ##STR3##
 in which G.sub.1, G.sub.2, G.sub.3, X and Y are as defined above, G.sub.5
 is independently a single bond, or a bond of --CH.sub.2 --, --O--, --CO--,
 --SO.sub.2 --, --C(CH.sub.3).sub.2 -- or --C(CF.sub.3).sub.2 --, and rings
 A and B are each independently a benzene ring or a cyclohexane ring; and
 has a logarithmic viscosity number of 0.1-5.0 dl/g as measured in
 N-methyl-2-pyrrolidone at the concentration of 0.5 g/dl at the temperature
 of 30.+-.0.01.degree. C.
 (3) A polyamic acid which comprises a structural unit represented by the
 above formula [2] and a structural unit represented by the formula [3]:
 ##STR4##
 in which G.sub.6 is independently a single bond, or a bond of --CH.sub.2
 --, --O--, --CO--, --SO.sub.2 --, --C(CH.sub.3).sub.2 -- or
 --C(CF.sub.3).sub.2 --, rings A and B are each independently a benzene
 ring or a cyclohexane ring, and G.sub.4 is a divalent organic group of
 2-36 carbon atoms or a polysiloxane group of the formula [4]:
 ##STR5##
 in which R.sub.99 is an alkylene group of 1-6 carbon atoms or a phenylene
 group, R.sub.100 independently may be the same or different and is an
 alkyl group of 1-3 carbon atoms or a phenyl group, and a, b, and c are 0
 or a positive number with a relation of 1.ltoreq.a+b+c .ltoreq.100; and
 has a logarithmic viscosity number of 0.1-5.0 dl/g as measured in
 N-methyl-2-pyrrolidone at the concentration of 0.5 g/dl at the temperature
 of 30.+-.0.01.degree. C.
 (4) A polyimide obtained by imidation of the polyamic acid as disclosed in
 the above (2) or (3) and subsequent irradiation of a polarized ultraviolet
 light.
 (5) An aligning film for a liquid crystal display device using a thin film
 comprising the polyimide as disclosed in the above (4).
 (6) An aligning film for a liquid crystal display device which is obtained
 by imidation of the polyamic acid as disclosed in the above (2) or (3),
 subsequent irradiation of a polarized ultraviolet light and the resulting
 photoreaction of a portion of the polyimide side chains.
 (7) A liquid crystal display device which comprises an aligning film for a
 liquid crystal display device as disclosed in the above (4)-(6).
 (8) A liquid crystal display device as disclosed in the above (7) wherein a
 liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the formulae [5], [6] and [7]:
 ##STR6##
 in which R.sub.1 is an alkyl group of 1-10 carbon atoms wherein any
 non-adjacent methylene groups may be substituted with --O-- or
 --CH.dbd.CH-- and any hydrogen atoms may be substituted with fluorine
 atoms; R.sub.2 is a fluorine atom, a chlorine atom, --OCF.sub.3,
 --OCF.sub.2 H, --CF.sub.3, --CF.sub.2 H, --CFH.sub.2, --OCF.sub.2 CF.sub.2
 H or --OCF.sub.2 CFHCF.sub.3 ; L.sub.1 and L.sub.2 are each independently
 a hydrogen atom or a fluorine atom; Z.sub.1 and Z.sub.2 are each
 independently 1,2-ethylene, 1,4-butylene, --COO--, --CF.sub.2 O--,
 --OCF.sub.2 --, --CH=CH-- or a single bond; ring C is
 trans-1,4-cyclohexylene, 1,3-dioxane-2,5-diyl or 1,4-phenylene wherein a
 hydrogen atom may be substituted with a fluorine atom; and ring D is
 trans-1,4-cyclohexylene or 1,4-phenylene wherein a hydrogen atom may be
 substituted with a fluorine atom.
 (9) A liquid crystal display device as disclosed in the above (7) wherein a
 liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the formulae [8] and [9]:
 ##STR7##
 in which R.sub.3 and R.sub.5 are each independently an alkyl group of 1-10
 carbon atoms wherein any non-adjacent methylene groups may be substituted
 with --O-- or --CH.dbd.CH-- and any hydrogen atoms may be substituted with
 fluorine atoms; R.sub.4 is a group of --CN or --C.tbd.C--CN; ring E is
 trans-1,4-cyclohexylene, 1,4-phenylene, 1,3-dioxane-2,5-diyl or
 pyrimidine-2,5-diyl; ring F is trans-1,4-cyclohexylene, 1,4-phenylene
 wherein a hydrogen atom may be substituted with a fluorine atom, or
 pyrimidine-2,5-diyl; ring G is trans-1,4-cyclohexylene or 1,4-phenylene;
 Z.sub.3 is 1,2-ethylene, --COO--, or a single bond; L.sub.3, L.sub.4 and
 L.sub.5 are each independently a hydrogen atom or a fluorine atom; and e,
 f and g are each independently 0 or 1.
 (10) A liquid crystal display device as disclosed in the above (7) wherein
 a liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the formulae [10], [11] and [12]:
 ##STR8##
 in which R.sub.6 and R.sub.7 are each independently an alkyl group of 1-10
 carbon atoms wherein any non-adjacent methylene groups may be substituted
 with --O-- or --CH.dbd.CH-- and any hydrogen atoms may be substituted with
 fluorine atoms; rings I and J are each independently
 trans-1,4-cyclohexylene or 1,4-phenylene; L.sub.6 and L.sub.7 are each
 independently a hydrogen atom or a fluorine atom, provided that they do
 not simultaneously represent hydrogen atoms; and Z.sub.4 and Z.sub.5 are
 each independently 1,2-ethylene, --COO--, or a single bond.
 (11) A liquid crystal display device as disclosed in the above (7) wherein
 a liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the said formulae [5], [6] and
 [7], and as a second component at least one compound selected from the
 group consisting of the compounds of the formulae [13], [14] and [15]:
 ##STR9##
 in which R.sub.8 and R.sub.9 are each independently an alkyl group of 1-10
 carbon atoms wherein any non-adjacent methylene groups may be substituted
 with --O-- or --CH.dbd.CH-- and any hydrogen atoms may be substituted with
 fluorine atoms; rings K, L and M are each independently
 trans-1,4-cyclohexylene, pyrimidine-2,5-diyl or 1,4-phenylene wherein a
 hydrogen atom may be substituted with a fluorine atom; and Z.sub.6 and
 Z.sub.7 are each independently 1,2-ethylene, --C.tbd.C--, --COO--,
 --CH.dbd.CH-- or a single bond.
 (12) A liquid crystal display device as disclosed in the above (7) wherein
 a liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the said formulae [8] and [9],
 and as a second component at least one compound selected from the group
 consisting of the compounds of the said formulae [13], [14] and [15].
 (13) A liquid crystal display device as disclosed in the above (7) wherein
 a liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the said formulae [10], [11] and
 [12], and as a second component at least one compound selected from the
 group consisting of the compounds of the said formulae [13], [14] and
 [15].
 (14) A liquid crystal display device as disclosed in the above (7) wherein
 a liquid crystal composition comprises at least one compound selected from
 the group consisting of the compounds of the said formulae [5], [6] and
 [7], as a second component at least one compound selected from the group
 consisting of the compounds of the said formulae [8] and [9] and as a
 third component at least one compound selected from the group consisting
 of the compounds of the said formulae [13], [14] and [15].
 (15) A liquid crystal display device as disclosed in the above (8)-(14)
 wherein a liquid crystal composition further comprises one or more of
 optically active compounds.
 The diamine of this invention may be represented by the above formula [1].
 The structure of the moiety G.sub.1 in the formula [1] is not particularly
 restricted as far as it is a trivalent organic group of 2-20 carbon atoms.
 Specific examples thereof are the following groups:
 ##STR10##
 in which p is an integer of 0-10 and q is an integer of 1-10. Of these
 groups,
 ##STR11##
 are preferable and most preferable is
 ##STR12##
 In the diamino compound of this invention represented by the formula [1],
 the group G.sub.1 in the diamine moiety is bound to the photosensitive
 moiety via the linking group G.sub.2. Accordingly, in the preparation of
 the compound, if both the diamine moiety and the photosensitive base
 moiety have functional groups capable of reacting each other, the reaction
 may be performed by utilizing said functional groups for linking both
 moieties. Unless either moiety has such groups, necessary functional
 groups may be first introduced into the moieties, which are allowed to
 react and link together. These linking reactions will be briefly
 illustrated below in line with the sort of G.sub.2. The synthesis may be
 performed according to any well-known methods, such as a dehydration
 reaction of a carboxyl group and a hydroxyl group for an ester bond, a
 dehydration reaction of an amino group and a carboxyl group for an amide
 bond, a removal of a sodium salt with a sodium alcoholate and a halide for
 an ether bond, a conversion of both groups to an alkyl halide and
 subsequent dehalogenation with potassium sulfide for a sulfide bond, a
 reaction of a cyano group with Grignard reagent and subsequent hydrolysis
 for a carbonyl bond, and a dehydration reaction between an alcohol with an
 .alpha.-arylmaleimide for a single bond.
 A specific example of a process for the preparation of a diamino compound
 is the process in the case where G.sub.2 is a single bond, wherein a
 dinitroalcohol and an arymaleimide are subjected to a dehydration reaction
 such as Mitsunobu reaction to form a dinitroalkylene-.alpha.-arylmaleimide
 and the nitro group thereof is reduced with a metal such as tin or iron
 and conc. hydrochloric acid to produce a diamino compound. This may be
 illustrated by the following reaction scheme.
 ##STR13##
 In the case where G.sub.2 is an ester bond, an acid chloride is synthesized
 from a dinitrocarboxylic acid with thionyl chloride or phosphorus
 pentachloride, while a hydroxyalkyl-.alpha.-arylmaleimide is synthesized
 by the reaction of an arylmaleic anhydride with an amino alcohol. Both
 products are condensed in the presence of a base such as triethylamine or
 pyridine to form a dinitroester, and then the nitro group thereof may be
 similarly reduced as described above. The reaction scheme will be shown
 below.
 ##STR14##
 In the case where G.sub.3 is an ether bond, a
 hydroxyalkyl-.alpha.-arylmaleimide is synthesized by the reaction of an
 arylmaleic anhydride with an amino alcohol. The hydroxyl group of this
 compound is halogenated by thionyl chloride, phosphorus trichloride, etc.
 to form a haloalkyl-.alpha.-arylmaleimide. This product is reacted with a
 dinitroalcohol or phenol in the presence of a base such as potassium
 carbonate and sodium hydride to form a dinitroether, which is then reduced
 to form the final compound. This is shown by the following reaction
 scheme.
 ##STR15##
 Of the above linking groups G.sub.2, a single bond, an ester bond and an
 ether bond are more preferable and a single bond is particularly
 preferred.
 The diamino compound synthesized as described above which has an
 .alpha.,.beta.-substituted maleimide residue in the side chain thereof may
 be subjected to the polymerization reaction with a tetracarboxylic
 dianhydride represented by the formula [16]:
 ##STR16##
 wherein G.sub.5, ring A and ring B are as defined above; while retaining
 said maleimide group, to afford a solution of a polyamic acid having an
 .alpha.,.beta.-substituted maleimide residue in the side chain thereof.
 This polyamic acid is subjected to imidation by any publicly known method
 such as heating or chemical dehydration and then irradiated with a
 polarized ultraviolet light to afford the polyimide of this invention. The
 maleimide residues may be polymerized by irradiation of said polarized
 ultraviolet light and the polymeric product may be used as an aligning
 film without any rubbing treatment. The aligning film for liquid crystal
 display device according to this invention is prepared by coating a
 solution of the present polyamic acid having an .alpha.,.beta.-substituted
 maleimide residue in the side chain thereof over a substrate, imidating by
 heating or the like, and then irradiating a polarized ultraviolet light to
 provide the film surface with anisotropy.
 As alternative embodiment of this invention, a polyamic acid comprising the
 structural units of [2] and [3] may be mentioned. Another diamine as
 illustrated hereafter is added to a diamino compound represented by the
 formula [1] to form diamine components, which may be reacted as described
 above with a tetracarboxylic dianhydride represented by the formula [17]:
 ##STR17##
 wherein G.sub.6, ring A and ring B are as defined above; to obtain the
 polyamic acid, and further, the polyimide.
 The diamines which may provide a divalent organic group of 2-36 carbon
 atoms as G.sub.4 may include the following compounds, but are not
 particularly limited thereto.
 More specifically, they may include aliphatic diamines such as
 trimethylenediamine, tetramethylenediamine, hexamethylenediamine,
 4,4-dimethylheptamethylenediamine and 2,11-dodecanediamine; aromatic
 diamines such as bis(4-aminophenyl) ether, bis (4-aminophenyl)methane, bis
 (4-amino-3-methylphenyl)methane, bis(4-amino-3,5-dimethylphenyl)methane,
 bis(4-aminophenyl)sulfone, bis(4-aminophenyl)sulfide,
 bis(4-(3-aminophenoxy)phenyl)sulfone,
 2,2-bis(4-(4-aminophenoxy)phenyl)propane,
 bis(4-(4-aminophenoxy)phenyl)sulfone, 1,2-diaminobenzene,
 1,3-diaminobenzene, 1,4-diaminobenzene, 1,4-diamino-2-butylbenzene,
 1,4-diamino-2-dodecyloxybenzene, benzidine, 2,2-diaminobenzophenone,
 4,4-diaminobenzophenone, 2,2-bis(4-aminophenyl)propane,
 1,5-diaminonaphthalene, 4,4-diamino-3-octyldiphenylmethane,
 2,2-bis(4-(4-aminophenoxy)phenyl)-1,1,1,3,3,3-hexafluoropropane,
 4,4-bis(4-aminophenoxy)biphenyl, 1,2-bis(4-aminophenyl)ethane,
 1,2-bis(4-amino-2-methylphenyl)ethane,
 1,1-bis(4-(4-aminophenoxy)phenyl)cyclohexane,
 1,1-bis(4-(4-aminophenoxy)phenyl)-4-propylcyclohexane,
 1,1-bis(4-(4-aminobenzyl)phenyl)cyclohexane,
 1,3-bis(4-(4-aminobenzyl)phenyl)propane and
 1,4-bis(4-aminophenoxy)benzene, bis-p-aminophenylaniline; alicyclic
 diamines such as 1,4-diaminocyclohexane, 4,4-diaminodicyclohexylmethane,
 4,4-diamino-3,3-dimethyldicyclohexylmethane and
 4,4-diamino-3,3-dimethyldicyclohexyl, etc. These compounds may include
 isomers thereof and a mixture of these isomers may be similarly used. A
 combination of two or more of these compounds may also be used.
 As specific examples of diamines which have a polysiloxane as the skelton
 thereof, the following compounds may be illustrated:
 ##STR18##
 wherein a, b and c are an integer of 1 or more.
 The tetracarboxylic dianhydride which may be used in this invention is
 represented by the formula [16] or [17].
 These compounds may be specifically illustrated as follows:
 3,3',4,4'-biphenyltetracarboxylic dianhydride,
 2,2',3,3'-biphenyltetracarboxylic dianhydride,
 2,3,3',4'-biphenyltetracarboxylic dianhydride,
 3,3',4,4'-benzophenonetetracarboxylic dianhydride,
 2,3,3',4'-benzophenonetetracarboxylic dianhydride,
 2,2'3,3'-benzophenonetetracarboxylic dianhydride,
 bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone
 dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride,
 3,3',4,4'-hexafluoroisopropylidenediphthalic dianhydride,
 3,3',4,4'-bicyclohexanetetracarboxylic dianhydride,
 bis(3,4-dicarboxycyclohexyl)ether dianhydride,
 bis(3,4-dicarboxycyclohexyl)sulfone dianhydride,
 bis(3,3-dicarboyycyclohexyl)methane dianhydride, and the like. These
 compounds may include isomers thereof and a mixture of these isomers may
 be similarly used. A combination of two or more of these compounds may
 also be used. The tetracarboxylic dianhydride which may be used in this
 invention are not particularly limited to the above-mentioned compounds.
 An aminosilicone compound represented by the formula [18] may be used, if
 necessary, in the polyimide, the liquid crystal aligning film and the
 liquid crystal display device of this invention.
 ##STR19##
 In the formula [18], G.sub.7 is an alkylene group of 2-10 carbon atoms or a
 phenylene group, R.sub.45 is an alkyl group of 1-10 carbon atoms, an
 alkenyl group of 2-10 carbon atoms or a phenyl group, R.sub.46 is an alkyl
 group of 1-10 carbon atoms, an alkenyl group of 2-12 carbon atoms, a
 phenyl group or an alkoxyalkyl group of 2-10 carbon atoms, and n is an
 integer of 1-3.
 Specific chemical names thereof may be mentioned below:
 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,
 3-aminopropylmethydimethoxysilane, 3-aminopropylmethydiethoxysilane,
 3-aminopropyltris(2-methoxyethoxy)silane, 2-aminoethyltrimethoxysilane,
 2-aminoethyltriethoxysilane, 2-aminoethylmethyldimethoxy-silane,
 2-aminoethylmethyldiethoxysilane, 4-aminobutyltrimethoxysilane,
 4-aminophenyltrimethoxysilane, 4-aminophenyltriethoxysilane,
 4-aminophenylmethyldimethoxysilane, 4-aminophenylmethyldiethoxysilane,
 4-aminophenyltris(2-methoxyethoxy)silane,
 3-(4-aminophenyl)propyltrimethoxysilane,
 3-(4-aminophenyl)propyltriethoxysilane, 3-aminophenyltrimethoxysilane,
 3-aminophenyltriethoxysilane,
 3-(4-aminophenyl)propylmethyldimethoxysilane,
 3-(4-aminophenyl)propylmethyldiethoxysilane,
 3-aminophenylmethyldimethoxysilane, 3-aminophenylmethyldiethoxysilane,
 etc.
 The said amino compound, diamine, tetracarboxylic dianhydride and
 diaminosilicone compound may be reacted with the acid anhydride group and
 the amino group in the presence of a publicly known solvent such as
 N-methyl-2-pyrrolidone (NMP) according to a publicly known method to
 afford the polyamic acid or the polyimide precursor of this invention.
 In this reaction, the diamino compound represented by the formula [1] may
 preferably comprise 10 molar percent or more, and more preferably 50% or
 more, of the total amine. If the amount is reduced, the photosensitivity
 is lowered, whereby anisotropy by a polarized light would hardly develop.
 The aminosilicone compound may comprise preferably 30 molar percent or
 less, and more preferably 10% or less, of the total starting materials.
 These starting materials may be random-polymerized, block-polymerized or
 admixed with polymers (co)polymerized at a different composition. In the
 case where a tetracarboxylic dianhydride having an asymmetric
 configuration, the linked form of the said acid to the diamine is not
 necessarily in a given direction and the head-to-tail structure and the
 head-to-head structure may be intermingled. A polyimide composed of a
 plurality of tetracarboxylic dianhydrides or a plurality of the diamines
 may also be used.
 In the compound represented by the said formula [1] and the structural unit
 represented by the formula [2], a length of the spacer G.sub.3 may be
 preferably that of 0-12 carbon atoms, and more preferably that of 0-6. If
 the number of carbon atoms is more than 12, the structure has such an
 inferior heat resistance that the heat stability of the photocrosslinked
 film would be adversely affected.
 In the formulae [1] and [2], the number m of the benzene rings to be
 substituted at the .alpha.-position of the side chain imido ring is
 preferably 1-2. If the ring number is more than the said range, the
 substituent will be so rigid that the solubility or coating property of
 the resulting polyamic acid may extremely decrease or there may be a risk
 of inhibiting the photoreaction because of steric hindrance.
 The substituents X and Y in the formulae [1] and [2] may include the
 following atoms or functional groups, but they are not necessarily
 intended to be limited thereto. More specifically, they may include the
 atoms or cyclic substituents such as a hydrogen atom, a fluorine atom, a
 chlorine atom, a cyano group, a nitro group, a cyclopropyl group, a
 cyclobutyl group, a cyclopentyl group, a methylcyclopropyl group, an
 ethylcyclopropyl group, a propylcyclopropyl group, a n-butylcyclopropyl
 group, a methylcyclobutyl group, an ethylcyclobutyl group, a
 propylcyclobutyl group, a n-butylcyclobutyl group, a methylcyclopentyl
 group, an ethylcyclopentyl group, a propylcyclopentyl group, and a
 n-butylcyclopentyl group.
 The alkyl group may include a methyl group, an ethyl group, a n-propyl
 group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl
 group, a t-butyl group, a n-pentyl group, an isopentyl group, a neo-pentyl
 group, a t-pentyl group, a n-hexyl group, an isohexyl group, a heptyl
 group, an octyl group, a nonyl group, a decyl group, an undecyl group, a
 dodecyl group, etc.
 The haloalkyl group may include a trifluoromethyl group, a trichloromethyl
 group, a tribromomethyl group, a triiodomethyl group, a pentafluoroethyl
 group, a pentachloroethyl group, a pentabromoethyl group, a pentaiodoethyl
 group, a 1,1,1-trichloroethyl group, a 1,1,1-trifluoroethyl group, a
 1,1,1-tribromoethyl group, a 1,1,1-triiodoethyl group, a heptafluoropropyl
 group, a heptachloropropyl group, a heptabromopropyl group, a
 heptaiodopropyl group, a 1,1,1-trifluoropropyl group, a
 1,1,1-trichloropropyl group, a 1,1,1-tribromopropyl group, a
 1,1,1-triiodopropyl group, a nonafluorobutyl group, a nonachlorobutyl
 group, a nonabromobutyl group, a nonaiodobutyl group, a perfluoropentyl
 group, a perchloropentyl group, a perbromopentyl group, a perfluorohexyl
 group, a perchlorohexyl group, a perbromohexyl group, a periodohexyl
 group, a perfluoroheptyl group, a perchloroheptyl group, a perbromoheptyl
 group, a perfluorooctyl group, a perchlorooctyl group, a perbromooctyl
 group, a perfluorononyl group, a perchlorononyl group, a perbromononyl
 group, a perfluorodecyl group, a perchlorodecyl group, a perbromodecyl
 group, etc.
 The alkoxy group or the haloalkoxy group may include a methoxy group, an
 ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, an
 isobutoxy group, a sec-butoxy group, a t-butoxy group, a n-pentyloxy
 group, an isopentyloxy group, a neo-pentyloxy group, a t-pentyloxy group,
 a n-hexyloxy group, an isohexyloxy group, a heptyloxy group, an octyloxy
 group, a nonyloxy group, a decyloxy group, an undecyloxy group, a
 dodecyloxy group, a trifluoromethoxy group, a trichloromethoxy group, a
 tribromomethoxy group, a triiodomethoxy group, a pentafluoroethoxy group,
 a pentachloroethoxy group, a pentabromoethoxy group, a pentaiodoethoxy
 group, a 1,1,1-trichloroethoxy group, a 1,1,1-trifluoroethoxy group, a
 1,1,1-tribromoethoxy group, a 1,1,1-triiodoethoxy group, a
 heptafluoropropoxy group, a heptachloropropoxy group, a heptabromopropoxy
 group, a heptaiodopropoxy group, a 1,1,1-trifluoropropoxy group, a
 1,1,1-trichloropropoxy group, a 1,1,1-tribromopropoxy group, a
 1,1,1-triiodopropoxy group, a nonafluorobutoxy group, a nonachlorobutoxy
 group, a nonabromobutoxy group, a nonaiodobutoxy group, a
 perfluoropentyloxy group, a perchloropentyloxy group, a perbromopentyloxy
 group, a perfluorohexyloxy group, a perchlorohexyloxy group, a
 perbromohexyloxy group, a periodohexyloxy group, a perfluoroheptyloxy
 group, a perchloroheptyloxy group, a perbromoheptyloxy group, a
 perfluorooctyloxy group, a perchlorooctyloxy group, a perbromooctyloxy
 group, a perfluorononyloxy group, a perchlorononyloxy group, a
 perbromononyloxy group, a perfluorodecyloxy group, a perchlorodecyloxy
 group, a perbromodecyloxy group, etc.
 Of the said substituents, preferable are a hydrogen atom, a fluorine atom,
 a cyano group, a methyl group, an ethyl group, a n-propyl group, a n-butyl
 group, a n-pentyl group, a n-hexyl group, a heptyl group, an octyl group,
 a nonyl group, a decyl group, an undecyl group, a dodecyl group, a
 heptafluoropropyl group, a nonafluorobutyl group, a perfluoropentyl group,
 a perfluorohexyl group, a perfluoroheptyl group, a perfluorooctyl group, a
 perfluorononyl group, a perfluorodecyl group, a methoxy group, an ethoxy
 group, a n-propoxy group, a n-butoxy group, a n-pentyloxy group, a
 n-hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group,
 a decyloxy group, an undecyloxy group, a dodecyloxy group, a
 heptafluoropropoxy group, a nonafluorobutoxy group, a perfluoropentyloxy
 group, a perfluorohexyloxy group, a perfluoroheptyloxy group, a
 perfluorooctyloxy group, a perfluorononyloxy group, a perfluorodecyloxy
 group, etc. More preferable are a hydrogen atom, a fluorine atom, a cyano
 group, a n-propyl group, a n-butyl group, a n-pentyl group, a n-hexyl
 group, a heptyl group, an octyl group, a nonyl group, a decyl group, an
 undecyl group, a dodecyl group, a perfluorohexyl group, a perfluoroheptyl
 group, a perfluorooctyl group, a perfluorononyl group, a perfluorodecyl
 group, a n-hexyloxy group, a heptyloxy group, an octyloxy group, a
 nonyloxy group, a decyloxy group, an undecyloxy group, a dodecyloxy group,
 a perfluorohexyloxy group, a perfluoroheptyloxy group, a perfluorooctyloxy
 group, a perfluorononyloxy group and a perfluorodecyloxy group.
 For the preparation of the polyimide used for the aligning film for liquid
 crystal display device according to this invention, preferable is a method
 wherein a solution of the polyamic acid having the structural units
 represented by the formulae [2] and [3] is coated over a substrate and
 dehydration reaction is effected by heat treatment at 150-300.degree. C.
 to form a polyimide thin film over the substrate, or a method wherein the
 polyamic acid is chemically dehydrated using acetic anhydride and the like
 to obtain the polyimide and then a solution of the polyimide is coated
 over a substrate and dried to form a thin film.
 The solvent used for the polyamic acid represented by the formulae [2] and
 [3], which is applied for the aligning film for liquid crystal display
 device according to this invention, may include any solvent which is
 conventionally used for an aligning film for liquid crystal display
 device. More specifically, it may include aprotic polar organic solvents
 which are good solvents for these polymeric compounds, such as
 N-methyl-2-pyrrolidone, dimethyl-imidozolidinone, N-methyl-caprolactam,
 N-methylpropionamide, N,N-dimethyl-acetamide, dimethyl sulfoxide,
 N,N-dimethylformamide, N,N-diethyl-formamide, diethylacetamide and
 y-butyllactone.
 If necessary, other solvent systems having a lowered surface tension may be
 used for the purpose of improving coating property. Examples thereof are
 an alkyl lactate, 3-methyl or 3-methoxy-butanol, tetralin, isophorone, an
 ethylene glycol monoalkyl ether such as ethylene glycol monobutyl ether, a
 diethylene glycol monoalkyl ether such as diethylene glycol monoethyl
 ether, an ethylene glycol monoalkyl or phenylacetate, a triethylene glycol
 monoalkyl ether, a propylene glycol monoalkyl ether such as propylene
 glycol monobutyl ether, a dialkyl malonate such as diethyl malonate, and
 the like. Many of these are rather poor solvents as compared with the good
 solvents as mentioned hereinbefore.
 As a method for coating a solution dissolved in the said solvent onto a
 substrate to form liquid crystal display device, any conventional methods
 can be employed. Coating may be performed, for example, by a spinner
 method, a printing method, a dipping method, a dropping method and the
 like.
 The heat treatment required for drying of the solvent after coating with
 the said solution may be carried out by any similar method to the
 procedures conventionally employed for aligning films of liquid crystal
 display device. For example, the heat treatment in an oven, a hot plate,
 an infrared furnace and the like is feasible. After coating with the
 solution, it is preferable that the solvent is evaporated at a relatively
 lower temperature and that the heat treatment is then performed at a
 temperature of around 150-300.degree. C., preferably 180-250.degree. C. It
 is also possible to add a surfactant used for improving coating property
 or an antistatic agent used for preventing static electricity and the
 like. It is further possible to mix a silane coupling agent or a titanium
 coupling agent for improving adhesion to the substrate.
 Subsequently, the polyimide thin film is provided with anisotropy over the
 film surface by the irradiation of a polarized ultraviolet light thereto.
 A wavelength of the light irradiated to an .alpha.,.beta.-substituted
 maleimide group, which is the photosensitive group used for the present
 aligning film for liquid crystal display device, is preferably 200-410 nm,
 more preferably 310-380 nm. An exposure of the polarized ultraviolet
 lights is at 0.05-15.0 J/cm.sup.2, preferably 0.1-10.0 J/cm.sup.2, and
 more preferably 0.1-5.0 J/cm.sup.2.
 The substrate for a liquid crystal display device may be conventionally a
 substrate on which an electrode, or specifically, a transparent electrode
 such as ITO (indium oxide--tin oxide) or tin oxide is formed. An
 insulating film for preventing alkali elution of the substrate, or a
 protective film such as a color filter and a color filter overcoat may be
 further provided between the electrode and the substrate, and an
 insulating film or an overcoat film such as a color filter film may be
 further provided on the electrode. An active element such as a TFT
 (Thin-Film-Transistor) element and a MIM (Metal-Insulation-Metal) element
 may also be formed on the electrode. As these electrodes, undercoats and
 other constitutions within a liquid crystal cell, any conventional
 constitutions of a liquid crystal display device may be applied.
 A liquid crystal device may be prepared by forming a cell using the
 substrate thus formed, injecting a liquid crystal and sealing an injection
 inlet. As the liquid crystal to be enclosed, a wide variety of liquid
 crystals may be used, such as conventional nematic liquid crystals, and
 liquid crystals with a dichroic dye incorporated.
 Specific examples of the liquid crystal composition which may be preferably
 used in combination with the present aligning film in this invention are
 the compositions which contain at least one compound selected from the
 group consisting of the compounds of the formulae [5], [6] and [7].
 Examples thereof are also the liquid crystal compositions which contain at
 least one compound selected from the group consisting of the compounds of
 the formulae [8] and [9].
 Examples thereof are also the liquid crystal compositions which contain at
 least one compound selected from the group consisting of the compounds of
 the formulae [10], [11] and [12].
 Examples thereof are also the liquid crystal compositions which contain at
 least one compound selected from the group consisting of the compounds of
 the formulae [5], [6] and [7] and as a second component at least one
 compound selected from the group consisting of the compounds of the
 formulae [13], [14] and [15].
 Examples thereof are also the liquid crystal compositions which contain at
 least one compound selected from the group consisting of the compounds of
 the formulae [8] and [9] and as a second component at least one compound
 selected from the group consisting of the compounds of the formulae [13],
 [14] and [15].
 Examples thereof are also the liquid crystal compositions which contain at
 least one compound selected from the group consisting of the compounds
 ofrthe formulae [10], [11] and [12] and as a second component at least one
 compound selected from the group consisting of the compounds of the
 formulae [13], [14] and [15].
 Moreover, examples thereof are the liquid crystal compositions which
 contain at least one compound selected from the group consisting of the
 compounds of the formulae [5], [6] and [7], as a second component at least
 one compound selected from the group consisting of the compounds of the
 formulae [8] and [9] and as a third component at least one compound
 selected from the group consisting of the compounds of the formulae [13],
 [14] and [15].
 The said liquid crystal compositions can further include one or more of
 optically active compounds.
 As the compounds of the formulae [5]-[7], the following compounds of the
 formulae (5-1) to (7-53) may be preferably mentioned.
 ##STR20##
 ##STR21##
 ##STR22##
 ##STR23##
 ##STR24##
 ##STR25##
 ##STR26##
 ##STR27##
 ##STR28##
 ##STR29##
 ##STR30##
 The compounds of the formulae [5]-[7] have a positive dielectric anisotropy
 and superior thermal and chemical stabilities, so that they are especially
 essential for the preparation of a liquid crystal composition for TFT
 which requires a high reliability such as a high voltage holding ratio and
 a large specific resistance.
 As the compounds of the formulae [8] and [9], the following compounds of
 the formulae (8-1) to (9-3) may be preferably mentioned.
 ##STR31##
 ##STR32##
 ##STR33##
 The compounds of the formulae [8] and [9] have a largely positive
 dielectric anisotropy, so that they are used especially for reducing a
 threshold voltage. They are also used for controlling a viscosity,
 controlling a refractive index anisotropy or broadening a nematic range
 such as raising a clear point. They are futher used for improving the
 steepness of a threshold voltage.
 As the compounds of the formulae [10]-[12], the following compounds of the
 formulae (10-1) to (12-3) may be preferably mentioned.
 ##STR34##
 The compounds of the formulae [10]-[12] have a negative dielectric
 anisotropy. Since the compounds of the formula [10] are bicyclic
 compounds, they are used mainly for controlling a threshold voltage,
 controlling a viscosity or controlling a refractive index anisotropy. The
 compounds of the formula [11] are used for broadening a nematic range such
 as raising a clear point and also for controlling a refractive index
 anisotropy. The compounds of the formula [12] are used for controlling a
 refractive index anisotropy.
 The compounds of the formulae [10]-[12] are used mainly for a liquid
 crystal composition having a negative dielectric anisotropy. If an amount
 of the compound of the formulae [10]-[12] is increased in a liquid crystal
 composition, a threshold voltage of the liquid crystal composition will be
 lower and a viscosity thereof will be higher. Accordingly, the compound
 may be preferably used in a less amount as far as the threshold voltage is
 within the required value. However, since an absolute value of dielectric
 anisotropy of the compounds of the formulae [10]-[12] is 5 or less,
 driving at a low voltage may not be performed in some cases if these
 compounds comprise less than 40% by weight.
 In case of preparing a composition for TFT having a negative dielectric
 anisotropy, it is desirable that the compounds of the formulae [10]-[12]
 are used in the range of 40% by weight or more, and more preferably 50-95%
 by weight, based on the total weight of the liquid crystal composition.
 For the purpose of improving the steepness of a voltage-transmittance
 curve by controlling an elastic constant, the compounds of the formulae
 [10]-[12] may be blended with a composition having a positive dielectric
 anisotropy. In this case, it is preferred that the compound of the
 formulae [10]-[12] comprises 30% by weight or less of the liquid crystal
 composition.
 As the compounds of the formulae [13]-[15], the compounds of the formulae
 (13-1) to (15-13) may be preferably mentioned.
 ##STR35##
 ##STR36##
 ##STR37##
 The compounds of the formulae [13]-[15] have a negative or weakly positive
 dielectric anisotropy. The compounds of the formula [13] are used mainly
 for reducing a viscosity or controlling a dielectric anisotropy. The
 compounds of the formula [15] are used for broadening a nematic range such
 as raising a clear point or for controlling a refractive index anisotropy.
 Specific examples of the optically active compounds which may be used in
 this invention will be illustrated below.
 Examples of the optically active compounds
 ##STR38##
 The liquid crystal display device of this invention is usually composed of
 a substrate, a voltage application means, a liquid crystal aligning film,
 a liquid crystal layer and so on. It is characterized by that it comprises
 an aligning film which can be rapidly photodimerized at a high sensitivity
 and is excellent in its thermal stability and shape retaining ability
 after crosslinked and has a good liquid crystal alignment, i.e., that it
 comprises the aligning film for liquid crystal display device of this
 invention.

BEST MODE FOR CARRYING OUT THE INVENTION
 This invention will be explained in detail by way of the following
 examples, but this invention is in no way to be limited by these examples.
 Physical properties of the compounds obtained by these examples were
 determined according to the following methods.
 Melting point: measured at an elevated temperature by 5.degree. C. per
 minute by means of a polarization microscope equipped with a hot stage
 (FP-82 manufactured by Metler Co., Inc.)
 Nuclear Magnetic Resonance spectrum (NMR): EX-90A manufactured by JEOL
 LTD., using tetramethylsilane as an internal standard substance.
 Rotation viscosity: measured by E-type viscometer at 25.degree. C.
 Logarithmic viscosity number: measured by Ubbelhode's viscometer in
 N-methyl-2-pyrrolidone at the polymer concentration of 0.5 g/dl at the
 temperature of 30.+-.0.01.degree. C.
 EXAMPLE 1
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR39##
 In a 11 three-necked flask equipped with a dropping funnel and a stirring
 means were placed 11.0 g of N-(2-hydroxyethyl)-a-phenylmaleimide and 500
 ml of dioxane, and 7.70 ml of triethylamine was added at 0.degree. C.
 under stirring. A dioxane solution of 11.5 g of 3,5-dinitrobenzoyl
 chloride was added dropwise thereto at 0.degree. C. and stirring was
 continued at room temperature overnight. After completion of the reaction,
 11 of water was added to the reaction solution and the resulting
 crystalline substance was collected by filtration. It was recrystallized
 twice from ethyl acetate to afford 6.10 g of
 N-(2-(3,5-dinitrobenzoyl)oxyethyl)-.alpha.-phenylmaleimide. This compound
 was subjected to reduction of a nitro group without any further
 purification. This compound had a melting point of 179.1-180.7.degree. C.
 In a 300 ml three-necked flask equipped with a dropping funnel and a
 stirring means were placed 8.22 g of
 N-(2-(3,5-dinitrobenzoyl)oxyethyl)-.alpha.-phenylmaleimide and 150 ml of
 dioxane, and 30.2 g of stannous chloride (dihydrate) was added at room
 temperature under stirring. Then, 30.2 g of conc. hydrochloric acid was
 added dropwise thereto, and thereafter, stirring was continued at room
 temperature for 3 hours. After completion of the reaction, a 2N aqueous
 solution of sodium hydroxide was added dropwise thereto until it was
 neutral, and the reaction solution was filtered with Celite. The filtrate
 was extracted twice with ethyl acetate, and the organic phase was washed
 three times with water and dried over anhydrous magnesium sulfate. After
 the drying agent was filtered off, the filtrate was concentrated under
 reduced pressure to afford a yellow solid. This solid was recrystallized
 twice from ethyl acetate to afford 6.42 g of
 N-(2-(3,5-diaminobenzoyl)oxyethyl)-.alpha.-phenylmaleimide.
 This compound had the following melting point and NMR:
 Melting point: 182-184.degree. C.; .sup.1 H-NMR (90 MHz, DMSO-d.sub.6 :
 .delta. 3.82 (t, 2H), 4.39 (t, 2H), 4.90 (bs, 4H), 6.04 (t, 1H), 6.40 (d,
 2H), 7.27 (s, 1H), 7.50-8.09 (m, 5H).
 2) Polymerization Reaction
 In a 100 ml three-necked flask were placed 3.514 g 25 of
 N-(2-(3,5-diaminobenzoyl)oxyethyl)-.alpha.-phenylmaleimide and 19.1 g of
 NMP and they were dissolved by stirring under a nitrogen stream at room
 temperature. Thereafter, the reaction solution was maintained at
 10.degree. C. and 1.611 g of 3,3',4,4'-benzophenonetetracarboxylic
 dianhydride was added thereto. The reaction was carried out at room
 temperature for 6 hours to afford a 15.0% by weight polymer solution. This
 polymer had a logarithmic viscosity number of 0.85 dl/g.
 3) Formation of an Aligning Film of a Liquid Crystal Display Device by a
 Polarized Light Irradiation
 The polyamic acid solution as obtained in the above 2) was diluted to 5.0%
 by weight with a solvent of NMP/Butyl Cellosolve=1/1 and filtered through
 a filter of 0.1 .mu.m to form a solution of a liquid crystal aligning
 agent. It was coated over an ITO glass substrate according to a rotational
 coating (a spinner method). After coating, heating at 230.degree. C. for
 60 minutes provided a thin film about 740 .ANG. thick. The surface of the
 thin film was exposed to a linear polarized ultraviolet light with a
 wavelength of around 365 nm from an ultra-high pressure mercury lamp at
 2.0 J/cm.sup.2.
 4) Preparation of a Liquid Crystal Cell and Assessment of Alignment
 The substrates as obtained in the above 3) were laminated so as to produce
 a paralleled polarization direction of an ultraviolet light, which
 provided a liquid crystal cell having a liquid crystal layer 20 .mu.m
 thick. Into the cell was injected the liquid crystal JC-5006 manufactured
 by Chisso Corporation and heat treatment was performed at 110.degree. C.
 for 30 minutes. After the heat treatment, it was allowed to cool and the
 alignment of the liquid crystal was proved to be satisfactory.
 EXAMPLE 2
 Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR40##
 Synthesis of a polyamic acid was carried out in the entirely same manner as
 in Example 1 except that 3,3',4,4'-biphenyltetracarboxylic dianhydride was
 used as the tetracarboxylic dianhydride while a molar ratio of the
 tetracarboxylic dianhydride to the diamine was maintained at 1. The
 resulting polymer had a logarithmic viscosity number of 0.82 dl/g. The
 polymer was treated in the same manner as in Example 1, and an aligning
 film was prepared. The alignment of the liquid crystal was investigated
 and proved to be satisfactory.
 EXAMPLE 3
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR41##
 Synthesis was carried out in the same manner as in Example 1 except that
 N-(6-hydroxyhexyl)-.alpha.-phenylmaleimide was used instead of the
 N-(2-hydroxyethyl)-.alpha.-phenylmaleimide as used in 1) of Example 1, to
 afford N-(6-(3,5-diaminobenzoyl)oxyhexyl)-a-phenylmaleimide. This compound
 had the following melting point and NMR:
 Melting point: 106.8-108.9.degree. C.; .sup.1 H-NMR (90 MHz, CDCl.sub.3):
 .delta.1.26-1.84 (m, 8H), 3.51-3.76 (m, 6H), 4.24 (t, 2H), 6.16 (t, 1H),
 6.71 (s, 1H), 6.78 (d, 2H), 7.41-7.97 (m, 5H).
 2) Polymerization Reaction
 A solution of a polyamic acid having a logarithmic viscosity number of 0.68
 dl/g was obtained in the same manner as in Example 2 except that 4.076 g
 of N-(6-(3,5-diaminobenzoyl)oxyhexyl)-.alpha.-phenylmaleimide was used as
 the diamine component while a molar ratio of the tetracarboxylic
 dianhydride to the diamine was maintained at 1.
 3) Polarized Light Irradiation, Formation of Cell and Assessment of
 Alignment
 In the same manner as in Example 1, the alignment of the liquid crystal was
 proved to be satisfactory.
 EXAMPLE 4
 Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR42##
 A polyamic acid was synthesized in the same manner as in Example 1 except
 that the molar ratio 3,3',4,4'-biphenyltetracarboxylic
 dianhydride/N-(2-(3,5-diaminobenzoyl)oxyethyl)-.alpha.-phenylmaleimide/
 metaphenylenediamine=1/0.6/0.4 was used as the ratio of the
 tetracarboxylic dianhydride to the diamine, to obtain a polymer solution
 having a logarithmic viscosity number of 1.3 dl/g. An aligning film was
 similarly prepared using this polymer and the alignment of the liquid
 crystal was investigated and proved to be satisfactory.
 EXAMPLE 5
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR43##
 Synthesis was carried out in the same manner as in Example 1 except that
 N-(2-hydroxyethyl)-.alpha.-(4-hexyloxy)phenylmaleimide was used instead of
 the N-(2-hydroxyethyl)-.alpha.-phenylmaleimide as used in 1) of Example 1,
 to afford
 N-(2-(3,5-diaminobenzoyl)oxyethyl)-.alpha.-(4-hexyloxy)phenylmaleimide.
 This compound had the following melting point and NMR:
 Melting point: 134.4-135.9.degree. C.; .sup.1 H-NMP (90 MHz, CDCl.sub.3) :
 .delta.0.906 (t, 3H), 1.23-1.87 (m, 8H), 3.62 (bs, 4H), 3.93-4.08 (m, 4H),
 4.38 (t, 2H), 6.17 (t, 1H), 6.62 (d, 2H), 6.69 (s, 1H), 7.43 (ABq, 4H).
 2) Polymerization Reaction
 A solution of a polyamic acid having a logarithmic viscosity number of 0.59
 dl/g was obtained in the same manner as in Example 2 except that 4.515 g
 of N-(6-(3,5-diaminobenzoyl)oxyhexyl)-.alpha.-(4-hexyloxy)phenylmaleimide
 was used as the diamine component while a molar ratio of the
 tetracarboxylic dianhydride to the diamine was maintained at 1.
 3) Polarized Light Irradiation, Formation of Cell and Assessment of
 Alignment
 In the same manner as in Example 1, the alignment of the liquid crystal was
 proved to be satisfactory.
 EXAMPLE 6
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR44##
 Synthesis was carried out in the same manner as in Example 1 except that
 N-(2-hydroxyethyl)-.alpha.-(4-fluorophenyl)maleimide was used instead of
 the N-(2-hydroxyethyl)-.alpha.-phenylmaleimide as used in 1) of Example 1,
 to afford
 N-(2-(3,5-diaminobenzoyl)oxyethyl)-.alpha.-(4-fluorophenyl)maleimide. This
 compound had the following melting point and NMR:
 Melting point: 154.4-156.1.degree. C.; .sup.1 H-NMR (90 MHz, DMSO-d.sub.6):
 .delta.3.99 (t, 2H), 4.37 (t, 2H), 4.91 (bs, 4H), 6.07 (t, 1H), 6.40 (d,
 2H), 7.24 (s, 1H), 7.32-8.25 (m, 4H).
 2) Polymerization Reaction
 A solution of a polyamic acid having a logarithmic viscosity number of 0.85
 dl/g was obtained in the same manner as in Example 2 except that 3.694 g
 of N-(6-(3,5-diaminobenzoyl)oxyhexyl)-.alpha.-(4-fluorophenyl)maleimide
 was used as to the diamine component while a molar ratio of the
 tetracarboxylic dianhydride to the diamine was maintained at 1.
 3) Polarized Light Irradiation, Formation of Cell and Assessment of
 Alignment
 In the same manner as in Example 1, the alignment of the liquid crystal was
 proved to be satisfactory.
 EXAMPLE 7
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR45##
 In 200 ml of acetone was suspended 20.3 g of
 N-hydroxymethyl-.alpha.-phenylmaleimide and then 4.6 ml of phosphorus
 trichloride was added in one portion at room temperature. After the
 mixture was stirred for 30 minutes, 5.0 ml of phosphorus trichloride was
 further added. After stirring for another one hour, the reaction solution
 was poured into ice-water and the crystals thus separated were collected
 by filtration. The crude crystal was dried under reduced pressure and then
 recrystallized from n-theptane/ethyl acetate to afford 12.1 g of
 N-chloromethyl-.alpha.-phenylmaleimide.
 In a 500 ml three-necked flask equipped with a stirring means and a
 condenser were placed 10.0 g of N-5 chloromethyl-.alpha.-phenylmaleimide
 and 200 ml of DMF, and dissolved at room temperature with stirring.
 Further, 10.3 g of 2,4-dinitrophenol sodium salt was added and the
 reaction was carried out at 80.degree. C. for 12 hours. After completion
 of the reaction, the reaction solution was poured into a large volume of
 water and extracted three times with ethyl acetate. The organic layer was
 washed three times with water and dried over anhydrous magnesium sulfate.
 The drying agent was separated by filtration and the organic layer was
 concentrated under reduced pressure. The resulting yellow crystal was
 collected by filtration with n-heptane to afford
 N-(2,4-dinitrophenyl)oxymethyl-.alpha.-phenylmaleimide. This compound was
 used as such for the subsequent reaction.
 Reduction reaction was carried out in the same manner as in Example 1
 except that N-(2,4-dinitrophenyl)oxymethyl-.alpha.-phenylmaleimide was
 used instead of the
 N-(2-(3,5-dinitrobenzoyl)oxyethyl)-.alpha.-phenylmaleimide as used in 1)
 of Example 1, to afford 6.40 g of
 N-(2,4-diaminophenyl)oxymethyl-.alpha.-phenylmaleimide. This compound had
 the 25 following melting point and NMR:
 Melting point: 183.7-185.6.degree. C. .sup.1 H-NMR (90 MHz, DMSO-d.sub.6):
 .delta.3.37 (bs, 4H), 5.19 (s, 2H), 7.14 (s, 1H), 7.25-8.00 (m, 8H). ps 2)
 Polymerization Reaction
 A solution of a polyamic acid having a logarithmic viscosity number of 0.44
 dl/g was obtained in the same manner as in Example 2 except that 3.093 g
 of N-(2,4-diaminophenyl)oxymethyl-.alpha.-phenylmaleimide was used as the
 diamine component while a molar ratio of the tetracarboxylic dianhydride
 to the diamine was maintained at 1.
 3) Polarized Light Irradiation, Formation of Cell and Assessment of
 Alignment
 In the same manner as in Example 1, the alignment of the liquid crystal was
 proved to be satisfactory.
 EXAMPLE 8
 1) Synthesis of a Polyimide Represented by the Following Structural Units:
 ##STR46##
 In a 500 ml three-necked flask equipped with a stirring means and a
 dropping funnel were placed 7.92 g of 3,5-dinitrobenzyl alcohol, 6.90 g of
 .alpha.-phenylmaleimide and 11.5 g of triphenylphosphine, and the mixture
 was dissolved in 200 ml of THF with stirring. To the solution was added
 dropwise 20.9 g of diethyl azodicarboxylate (as a 40% toluene solution) at
 0.degree. C. or lower. After the dropwise addition, the temperature was
 allowed to rise to room temperature and stirring was continued for 24
 hours. The reaction solution was poured into water and extracted three
 times with ethyl acetate. The organic layer was washed three times with
 water and dried over anhydrous magnesium sulfate. The drying agent was
 separated by filtration and the organic layer was concentrated under
 reduced pressure. The resulting pale yellow crystal was collected by
 filtration with n-heptane and recrystallized twice from ethyl acetate to
 afford 10.41 g of N-(3,5-dinitrophenyl)methyl-.alpha.-phenylmaleimide.
 Reduction of the nitro group was carried out in the same manner as in
 Example 1 except that N-(3,5-dinitrophenyl)methyl-.alpha.-phenylmaleimide
 was used instead of the
 N-(2-(3,5-dinitrobenzoyl)oxyethyl)-.alpha.-phenylmaleimide as used in 1)
 of Example 1. The subsequent purification by a silica gel column
 (n-heptane/ethyl acetate=1/1) gave 3.14 g of
 N-(2,4-diaminophenyl)-methyl-.alpha.-phenylmaleimide as a yellow oily
 substance. This compound had the following NMR:
 .sup.1 H-NMR (90 MHz, CDCl.sub.3): .delta.3.56 (bs, 4H), 5.01 (s, 2H), 5.96
 (d, 1H), 6.09 (d, 2H), 6.35 (s, 1H), 7.42 (s, 5H).
 2) Polymerization Reaction
 A solution of a polyamic acid having a logarithmic viscosity number of 0.68
 dl/g was afforded in the same manner as in Example 2 except that 2.93 g of
 N-(3,5-diaminophenyl)methyl-.alpha.-phenylmaleimide was used as the
 diamine component while a molar ratio of the tetracarboxylic dianhydride
 to the diamine was maintained at 1.
 3) Polarized Light Irradiation, Formation of Cell and Assessment of
 Alignment
 In the same manner as in Example 1 except that an irradiation intensity of
 ultraviolet light was changed to 0.1 J/cm.sup.2, the alignment of the
 liquid crystal was proved to be satisfactory.
 EXAMPLE 9
 Using the same polyamic acid as in Example 2, liquid crystal cells were
 prepared in the same manner as in Example 2 except that the liquid crystal
 compositions (LA)-(LE) were used as those for TFT, and the alignment
 thereof was proved to be satisfactory. Formulations of the liquid crystal
 compositions (LA)-(LE) as used herein will be shown below.
 Liquid Crystal Composition (LA)

##STR107## 12%
 ##STR108## 7%
 ##STR109## 20%
 ##STR110## 8%
 ##STR111## 8%
 ##STR112## 6%
 ##STR113## 5%
 ##STR114## 5%
 ##STR115## 5%
 ##STR116## 2%
 ##STR117## 1%
 ##STR118## 2%
 ##STR119## 4%
 ##STR120## 4%
 ##STR121## 4%
 ##STR122## 3%
 ##STR123## 4%
 EXAMPLE 10
 Using the same polyamic acid as in Example 2, liquid crystal cells were
 prepared in the same manner as in Example 2 except that the liquid crystal
 compositions (LF)-(LK) were used as those for STN, the alignment thereof
 was proved to be satisfactory. Formulations of the liquid crystal
 compositions (LF)-(LK) as used herein will be shown below.
 Liquid Crystal Composition (LF)

##STR190## 18%
 ##STR191## 3%
 ##STR192## 10%
 ##STR193## 10%
 ##STR194## 2%
 ##STR195## 2%
 ##STR196## 2%
 ##STR197## 7%
 ##STR198## 7%
 ##STR199## 7%
 ##STR200## 4%
 ##STR201## 4%
 ##STR202## 8%
 ##STR203## 3%
 ##STR204## 3%
 ##STR205## 4%
 ##STR206## 3%
 ##STR207## 3%
 COMATIVE EXAMPLE 1
 The same procedures as in Example 2 were followed except that the polyimide
 having the following structural unit was used, and any alignment of the
 liquid crystal was not observed.
 ##STR208##
 INDUSTRIAL APPLICABILITY
 The polyimide derived from the polyamic acid according to this invention
 which has an .alpha.,.beta.-substituted maleimide residue in the side
 chain thereof has a high sensitivity to polarized ultraviolet light and
 may rapidly photoreact when said ultraviolet light is irradiated. The film
 after the photoreaction is excellent in heat stability and shape retaining
 ability and it is especially useful as an aligning film having a good
 alignment of liquid crystal.