SOLUBLE POLYIMIDE-SILOXANE PRECURSOR, PROCESS FOR PRODUCING SAME AND CROSS-LINKED POLYIMIDE-SILOXANE

Abstract: A novel soluble polyimide-siloxane precursor having a good storage stability in solution and forming a superior coating on silicon wafer, glass, etc. under heating conditions of low temperature and short time; a process for producing the same; and a cross-linked polyimide-siloxane obtained by heating the above precursor are provided, which precursor has an imide-amic acid chain part expressed by the formula (1) bonded by a bonding structure expressed by the formula (5) -SiR⁷ 3-k Y¹ k-1 -O-SiR⁷ 3-k Y¹ k-1 - (5) wherein the respective (l)s in the number of m+n+1 represent independently either one of constituting units expressed by the following formulas (2), (3) and (4): wherein R¹ represents a tetravalent carbocyclic aromatic group; R², R⁴, R⁵, R⁶, R⁷ and Y¹ each are a specified group; ℓ is 1 to 100; m is 0 or an integer; and n is an integer, and which process comprises a first step of reacting a tetracarboxylic acid dianhydride, a diaminosiloxane, a di­ amine and an aminosilicon compound, each specified, in a solvent under specified conditions and a second step of heating the resulting reaction solution in the presence of a silylating agent under specified reaction conditions.

Description: BACKGROUND OF THE INVENTION This invention relates to a novel polyimide-siloxane precursor, a process for producing the same, and a crosslinked polyimide-siloxane. Polyimide resins have so far been widely used for protecting materials, insulating materials and adhesives in the field of electronic equipments or films, structural materials, etc., mainly in the aspect of heat resistance. The process of using the resins has relied, in most cases, on a process of applying a precursor prior to forming a cyclized polymer, as it is, onto an object, followed by baking to thereby complete imidization and also effect cross-linking, and various proposals have been made for improving the functions and effects after baking suitable to the above-mentioned various uses. Such prior art, however, cannot always be said to sufficiently satisfy current diversificated, indivisualized and sophisticated needs. For example, polyamic acids which have so far been used for a polyimide precursor for electronic materials have been applied in the form of their solution on a substrate, followed by baking to effect imidization and curing, but at the time of their use, various problems (drawbacks) have been raised such that baking requires as high a temperature as 300° ∼ 400°C which often exceeds the heat-resistant temperature of substrates; and adhesion of the coating solution onto silicon wafer and glass is insufficient. As to such adhesion among these problems,a number of copolymers of polyamic acid with silicon compounds have been proposed for improving the adhesion. For example, Japanese patent application laid-open Nos. Sho 57-143328/1982, Sho 58-7473/1983 and Sho 58-13631/1983 propose a technique that a polyimide precursor obtained by replacing a portion of a diamine component as raw material by a polysiloxane terminated with diamines at both the ends thereof is used to prepare a polyimide-siloxane copolymer. In this case, however, a problem has been raised that in place of improving the adhesion to a certain extent, the polymerization degree decreases with the increase of the siloxane content in the resulting copolymer to lower the coating-formability. Further, Japanese patent publication Nos. Sho 58-32162/1983 and Sho 58-32163/1983 disclose a process wherein a suitable carboxylic acid derivative such as tetracarboxylic acid dianhydrides is reacted with a diamine, to form a polyamidecarboxylic acid having a terminal group such as acid anhydrides, followed by reacting this polyamidecarboxylic acid with an aminosilicon compound at _20°C to +50°C, to obtain a silicon-containing polyamidecarboxylic acid prepolymer (a precursor), which is not imidized or imidized (chemically cyclized) under mild conditions (low temperature, preferably 50°C or lower, particularly _20°C to +25°C) in the presence of a dehydrating agent to form an organic silicon-modified polyimide precursor, followed by heating the former unimidized precursor or the latter polyimide precursor in the form of solution in the presence or absence of a silane diol or a siloxane diol to effect completion of imidization and also cross-linking to thereby obtain a polyimide-siloxane precursor. However, this polyimide-siloxane precursor has raised various problems that in the case where it is not cyclized, it requires baking at a high temperature of about 200°C or higher, up to 350°C for imidizing it after coating as in the case of conventional polyimide precursor composed mainly of polyamidecarboxylic acid; if the resulting cyclized substance has a high silicon content, the coating formability is inferior, while if it has a low silicon content, adhesion onto silicon wafer, glass, etc. is inferior; and in the case where a pre-cyclized (preimidized) polyimide-siloxane precursor is prepared, cyclization by low temperature treatment in the presence of a dehydrating agent is carried out, but this requires a long time and hence is not practical, while if cyclization is promoted by heating, the whole solution gels to lose fluidity. In view of the above various problems of the prior art, it has been desired to develop a precursor which is soluble in a suitable solvent; has a suitable viscosity in the form of solution to afford good operability; can be baked and cured at a relatively low temperature and for a relatively short time; has a good coating-formability; has a superior storage stability; and has superior adhesion onto silicon wafer and, glass, so that the resulting solution may be suitable to surface-protection of semiconductors or insulating film between multilayer interconnections. The object of the present invention is to provide such a soluble polyimide-siloxane precursor having overcome the above problems, a process for producing the same, and a cross-linked polyimide-siloxane. SUMMARY OF THE INVENTION The present invention resides in a soluble polyimide-siloxane precursor having an imide-amic acid chain part expressed by the formula (1): bonded by a bonding structure expressed by the formula (5) wherein each chaim part (I) is the same or different and represents one of the units expressed by the following formulae (2), (3) and (4): wherein R¹ represents independently a tetravalent carbocyclic aromatic group; each R² is the same or different and represents an alkyl group of 1 to 6 carbon atoms, a phenyl group, or an alkyl-substituted phenyl group of 7 to 12 carbon atoms; each R⁴ and each R⁶ is the same or different and represents wherein s represents an integer of 1 to 4; R⁵ represents an aliphatic group of 2 to 12 carbon atoms, an alicyclic group of 4 to 30 carbon atoms, an aromatic aliphatic group of 6 to 30 carbon atoms or a carbocyclic aromatic group of 6 to 30 carbon atoms: ℓ represents an integer of 1 to 100; m represents zero or a positive integer; n represents a positive integer; each R⁷ is the same or different and represents an alkyl group of 1 to 6 carbon atoms, a phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon atoms; each Y¹ is the same or different and represents an alkoxy group, an acetoxy group, a halogen atom, a hydroxy group, (_O) ½ or a group expressed by the formula (6): wherein R⁸, R⁹ and R¹⁰ are the same or different and each represents an alkyl group of 1 to 6 carbon atoms, a phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon atoms, and k is 1, 2 or 3; the said soluble polyimide-siloxane precursor being terminated by groups expressed by the following formula (7): wherein each Y² is the same or different and represents an alkoxy group, acetoxy group, halogen atom, hydroxy group or a group expressed by the formula (6); and R⁷ and k are as defined for the formula (5); and the inherent viscosity of the said soluble polyinide-siloxane precursor as measured in a concentration of 0.5 g/dℓ in a solvent at 30° ± 0.01°C being in the range of 0.05 to 5 dℓ/g. For preference, the soluble polyinide-siloxane precursor has a percentage imidization a of 50 to 100%, this a being defined in terms of the whole of the molecule by the following equation (8); wherein W: the total number of units expressed by the formula (2); P: the total number of units expressed by the formula (3) and Q: the total number of units expressed by the formula (4); for the whole of the molecule, and 2B₁, E₁ and D₁, which are respectively the total numbers of R⁴, R⁵ and R⁶, having a relationship expressed by the following expressions (9) and (9′): The soluble polyimide-siloxane precursors of this invention can be obtained by a process which comprises a first step of reacting a tetracarboxylic acid dianhydride expressed by the following formula (10), a diaminosiloxane expressed by the following formula (11), a diamine expressed by the following formula (12) and an aminosilicon compound expressed by the following formula (13) in the presence of a solvent at a temperature of 0°C to 60°C for a time of 0.2 to 6 hours so as to form a uniform reaction product fluid; and further a second step of heating the reaction product fluid as a temperature of 60°C to 200°C for a time of 0.5 to 30 hours, in the presence of a silylating agent expressed by the following formula (17), to effect an imidization reaction, and hydrolyzing X¹ and X² with water generated during said imidization reaction and if necessary, water from other sources, and further effecting siloxane condensation, to give a soluble polyimide-siloxane precursor with an inherent viscosity as measured in a solvent in a concentration of 0.5 g/dℓ at a temperature of 30 ± 0.01°C of 0.05 to 5 dℓ/g: wherein R¹, R², R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, ℓ and k are as defined above; X¹ is an alkoxy or acetoxy group or a halogen atom; and X² is a hydroxyl, acetoxy or alkoxy group or a halogen atom. For preference, the process comprises in the first step, reacting A mols of the tetracarboxylic acid dianhydride expressed by the formula (10), B₂ mols of the diaminosiloxane expressed by the formula (11), E₂ mols of the diamine expressed by the formula (12) and D₂ mols of the aminosilicon compound expressed by the formula (13), the values of A, B₂, E₂ and D₂ being selected so as to comply with relationships expressed by the following expressions (14) and (14′), and to approximately satisfy the equation (15); in the second step, heating the reaction, product fluid in the presence of F mols of the silylating agent expressed by the formula (17), the value of F being selected to comply with the following expression (16), and the percentage imidization a of the resulting product being 50 to 100%, as defined by the following equation (18). wherein W: the total number of units expressed by the formula (2); P: the total number of units expressed by the formula (3) and Q: the total number of units expressed by the formula (4). The present invention further resides in a cross-linked polyimide-siloxane obtained by heating the soluble polyimide-siloxane precursor according to the present invention, to the temperature of 100° to 300°C. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows an infrared absorption spectrum chart of a soluble polyimide-siloxane precursor obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The soluble polyimide-siloxane precursor of the present invention in the first aspect is an oligomer or polymer having an imide-amic acid chain part expressed by the formula (1) (hereinafter abbreviated often to imide-amic acid chain part (1); those expressed by other formulas, often similarly abbreviated), cross-linked or extended through bonding by means of a bonding structure expressed by the formula (5) to form a skeleton, and being terminated with a group expressed by the formula (7). R¹ has preferably at least one six-membered ring. R¹ is particularly a monocyclic aryl group, condensed polycyclic aryl group or polycyclic aryl group having a few condensed rings or non-condensed rings (these rings being combined with each other directly or through a cross-linking group). Examples of such cross-linking groups are _O_, _CO_, _SO₂_. Examples of R¹ are wherein R¹¹ represents _O_, _CO_ or _SO₂_, and when it has two or more aromatic rings (including condensed ring), the bonds of the respective rings are at o-position to each other. R⁵ includes not only a group consisting only of C and H, but also a hydrocarbon having a group containing a hetero atom other than Examples of such a group are Examples of R⁵ are wherein R¹² represents an alkyl group of 1 to 4 carbon atoms; wherein R¹³ represents _O_, _S_, _SO₂_, _CO_, _CH₂_ wherein p represents an integer of 2 to 12; and The precursor of the present invention has a suitable range of molecular weight defined in terms of an inherent viscosity of 0.05 to 5dℓ/g as measured under specified conditions, and is soluble in a suitable solvent. The above inherent viscosity (η inh) is expressed by the following equation: η inh = ℓn η/η₀ c wherein η is a value measured by Ubbellohde viscometer, of a solution of polymer in a concentration of 0.5 g/dℓ in a solvent at a temperature of 30 ± 0.01°C; η o is a value of the solvent measured by Ubbellohde viscometer at the same temperature; and c is a concentration of 0.5 g/dℓ. When the respective total numbers of R⁴, R⁵ and R⁶ in the molecule, of the above imide-amic acid chain part (1) are referred to as 2B¹, E¹ and D¹, the Si concentration in the polymer is expressed by these values, and the preferred range is expressed by the expression (9). If the expression (9) is not satisfied, the total number of Si is sometimes reduced and the adhesion lowers. Further, if the expression (9′) is not satisfied, the number of crosslinkable, residual group expressed by Y¹ in the formula (5) is reduced; hence when a film is prepared, the coating-formability, mechanical strengths, etc. are reduced. Further, the respective (I)s in the imide-amic acid chain part (1) independently represent either one of the constituting units (2), (3) or (4), and the percentage imidization a is within a range of 50 to 100% in terms of the whole of the molecule; hence the product has an increased percentage of imidization in spite of being only a precursor. Thus, for example, it is possible to effect completion of the imidization by heating at a relatively low temperature and in a relatively short time. The determination of the imide group required for deciding the percentage imidization a may be carried out according to known infrared absorption spectrum method. Next, the raw materials to be used in the process of the present invention will be described. R¹ in the tetracarboxylic acid dianhydride expressed by the formula (10) is defined as above. Examples of the tetracarboxylic acid dianhydride expressed by the formula (10) are as follows: pyromellitic acid dianhydride, 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride, 2,2′,3,3′-biphenyltetracarboxylic acid dianhydride, 2,3,3′,4′-biphenyltetracarboxylic acid dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride, 2,3,3′,4′-benzophenonetetracarboxylic acid dianhydride, 2,2′,3,3′-benzophenonetetracarboxylic acid dianhydride, bis (3,4-dicarboxyphenyl)-ether dianhydride, bis (3,4-dicarboxyphenyl)-sulfone dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride and 2,3,6,7-naphthalenetetracarboxylic acid dianhydride. Further, examples of the diaminosiloxane expressed by the formula (11) are as follows: In these diaminosiloxanes, ℓ is in the range of 1 to 100. If ℓ exceeds 100, the resulting silicone-polyimide precursor has a reduced solubility in solvents; hence such a precursor is not practical. Next, R⁵ in the diamine expressed by the formula (12) is defined as above. Further, examples of the diamine expressed by the formula (12) are as follows: aryl diamines such as 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfide, 4,4′-diaminodiphenyl thioether, 4,4′-di(m-aminophenoxy)diphenylsulfone, 4,4′-di(p-aminophenoxy)diphenylsulfone, o-phenylene-diamine, m-phenylenediamine, p-phenylenediamine, benzidine, 2,2′-diaminobenzophenone, 4,4′-diaminobenzophenone and 4,4′-diaminodiphenyl-2,2-propane, aliphatic diamines such as trimethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4-dimethylheptamethylenediamine, 2,11-dodecanediamine, etc., silicic diamines such as bis(p-aminophenoxy)-dimethylsilane, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 1,4-bis(3-aminopropyldimethylsilyl) benzene, etc., alicyclic diamines such as 1,4-diaminocyclohexane and aminoalkyl-substituted aryl compounds such as o-xylylenediamine and m-xylylenediamine. Next, examples of aminosilicon compounds expressed by the formula (13) are as follows: NH₂-(CH₂)₃-Si(OCH₃)₃, NH₂-(CH₂)₃-Si(OC₂H₅)₃, NH₂-(CH₂)₃-Si(CH₃)(OCH₃)₂, NH₂-(CH₂)₃-Si(CH₃)(OC₂H₅)₂, NH₂-(CH₂)₃-Si(C₂H₅)(On-C₂H₇)₂, NH₂-(CH₂)₄-Si(OCH₃)₃, NH₂-(CH₂)₄-Si(OC₂H₅)₃, NH₂-(CH₂)₄-Si(CH₃)(OC₂H₅)₂, Further, examples of the silylating agent expressed by the formula (17) are as follows: (CH₃)₃Si(OCH₃), (CH₃)₃Si(OC₂H₅), (CH₃)₃Si(O n -C₃H₇)₃, (CH₃)₂ (C₂H₅)Si(OCH₃), (CH₃)₂ (C₂H₅)Si(OC₂H₅), (CH₃)₃SiOH, Examples of preferable solvents for reacting the raw material compounds in a solvent in the process of the present invention (hereinafter referred to as reaction solvent) are as follows: N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl sulfone, hexamethylphosphoroamide, methylformamide, N-acetyl-2-pyrrolidone, toluene, xylene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, cyclopentanone and cyclohexanone. These solvents may be used alone or in admixture, and also may be used in the form of a mixed solvent thereof with other solvents containing 30% by weight or more of the above solvents. Next, the reaction process will be described. A mols of a tetracarboxylic acid dianhydride expressed by the formula (10) are reacted with B₂ mols of a diaminosiloxane expressed by the formula (11), E₂ mols fo a diamine expressed by the formula (12) and D₂ mols of an aminosilicon compound expressed by the formula (13) in a reaction solvent. A, B₂, E₂ and D₂ are determined so as to satisfy the expression (14), (14′) and also approximately satisfy the equation (15). The expression (14) defines the range where the resulting soluble polyimide-siloxane precursor, when used as a surface-protecting film for semiconductors, can maintain a superior adhesion thereof onto silicon wafer or glass. The expression (14′) defines the range where superior coating-formability and mechanical strengths are maintained. The equation (15) refers to a relationship in the case where the total amino group in the diaminosiloxane, the diamine and the aminosilicon compound is equivalently reacted with the total in the tetracarboxylic acid dianhydride, but the reaction may not always be just equivalently carried out. For example, if the practical number of mols of (A) falls within the range where the theoretical number of mols of (A) defined by the equation (15) ± 10%, it is possible to completely obtain the precursor of the present invention in the first aspect. The above terms "approximately satisfy the equation (15)" refers to such a range. In the process of the present invention, the respective raw materials are reacted in a solvent in two steps: In the first step the tetracarboxylic dianhydride is reacted with the diaminosiloxane, the diamine and the aminosilicon compound at a relatively low temperature; in the second step, after completion of the first step reaction, the resulting reaction fluid (hereinafter referred to often as fluid after completion of the first step reaction) is heated in the presence of a silylating agent at a relatively high temperature to carry out the reaction along with at least the water venerated at that time. The quantity of the reaction solvent used is preferably 60% by weight or more based on the total weight of the solvent and raw materials added thereto, since such a quantity makes the agitating operation easy, but 98% by weight or more is unnecessary. The first step reaction is carried out in the presence of the reaction solvent at a temperature of 0° to 60°C, preferably 3° to 30°C and for a time of 0.2 to 6 hours. Concretely, the tetracarboxylic acid dianhydride, the diaminosiloxane, the diamine and the aminosilicon compound may be at the same time added to the reaction solvent to react these together and thereby produce a random copolymer, but by selecting the addition order, it is possible to produce a copolymer having a block-like structure. For example, when a tetracarboxylic acid dianhydride is reacted almost equivalently with a diaminosiloxane and an aminosilicon compound, folllowed by reacting the remaining tetracarboxylic acid dianhydride and diamine almost equivalently with the remaining aminosilicon compound, then two kinds of intermediates completed at the respective steps are obtained. When these intermediates are mixed and subjected to the second step reaction, it is possible to obtain a block-like copolymer having the intermediates bonded with each other. Alternatively, when a tetracarboxylic acid dianhydride is reacted with a diaminosiloxane in a mixing ratio of the tetracarboxylic acid dianhydride in excess, to prepare an oligomer having the anhydrides at both the ends thereof, while, in another reactor, the tetracarboxylic acid dianhydride is reacted with a diamine in a mixing ratio of the diamine in excess, to prepare an oligomer having the amines at both the ends thereof, followed by mixing and reacting both the oligomers, and thereafter reacting an aminosilicon compound at both the ends thereof whereby it is possible to obtain an intermediate. Besides, by selecting the addition manner at the first step, it is possible to obtain various intermediates. In this case, there is no particular limitation to the addition order of the above four raw materials, but when the aminosilicon compound is finally added in the respective steps of the first step reaction, then a polymer having a higher molecular weight is liable to be obtained. In the first step reaction, the above four raw materials dissolve in the solvent and the reaction proceeds relatively rapidly to form a uniform and transparent reaction fluid. At that time the reaction has been almost complete, but it it preferred to further continue the reaction for a while to thereby ensure completion of the reaction. The reaction mainly comprises formation of a polyamide-carboxylic acid having the aminosilicon compounds bonded to both the ends thereof (hereinafter referred to often as intermediate G), as described later. The second step reaction is directed to a reaction wherein after completion of the first step reaction, the reaction temperature is raised in the presence of a silylating agent expressed by the formula (17) in a quantity of F mols within the range expressed by the expression (16) and the mixture is heated to a temperature of 60° to 200°C, preferably 80° to 130°C for a time of 0.5 to 30 hours to carry out imidization reaction, and further X¹ of the aminosilicon compounds at both the ends of the intermediate G and X² of the silylating compound are hydrolyzed with water generated at the imidization reaction and if necessary, water from other sources, and still further, siloxane condensation reaction is carried out. The silylating agent may be added when the second stage reaction is initiated, but alternatively it may be added together with the raw materials in advance of initiating the first step reaction and in this case, there is no substantial influence upon the first step reaction, and further this case is rather preferable since the operation of transferring the reaction from the first step to the second step is easy. The greater the proportion of the diaminosiloxane in the raw materials, or the smaller the k value in the formula (13) (for example, k = 2 or less), the slower the advance of the second step reaction. In such a case, it is also possible to carry out the second step reaction without adding any silylating agent. Further, the increase in the proportion of the diaminosiloxane affords a more highly linear polymer as compared with the case where the increase in the silicon content in the polymer as a means for enhancing the adhesion of silicon compounds is relied only on the aminosilicon compound, and also reduces the proportions of Y¹ and Y² which are reactive groups in the polymer chain and hence contributes to the stability of varnishes at the time of their storage. The second step reaction comprises mainly a reaction wherein the amide-carboxylic acid part in the intermediate G formed in the first step reaction is cyclized to imidize it, as described below, and at the same time, when X¹ in the aminosilicon compound forming the terminal of the intermediate G and X² in the free silylating agent are each a hydrolyzable group i.e. alkoxy group, acetoxy group or halogen, the half quantity or more of such a hydrolyzable group is hydrolyzed into hydroxyl group (there may often be a case where X² is initially _OH), and there occurs at least partly between the intermediate Gs themselves, between the intermediate G and the silylating agent or between the silylating agents themselves, a condensation reaction of hydroxyl groups bonded to Si between each other or a condensation reaction of hydroxyl group with hydrolyzable group, to form siloxane bonds (hereinafter referred to often as siloxane condensation reaction). As to the siloxane condensation of the silylating agent between each other, the silylating agent merely forms an inert compound which is present in dissolved state in the solvent, but other siloxane bonds constitute a reticulate structure or enhance the Si content in the high-molecular compound; hence in the resulting polyimide-siloxane precursor, siloxane bonds in a considerably large quantity are not only formed at the sites of X¹ and X², but also when the precursor is baked, the resulting siloxane bonds are preferred to be formed at the sites of all or nearly all X¹s and X²s of Si, and hence it is preferred to hydrolyse 1/2 or the whole of X¹ and X² to form _OH. Thus, the minimum quantity of water required for such a hydrolysis, that is, the minimum quantity of water required for subjecting the whole of X¹ and X² to the hydrolysis-siloxane condensation is (D₂ × k + F) = 1/2 mols (if X² is a hydroxyl group, the quantity of water is reduced as much). At least a part of the quantity of water consumed in the hydrolysis is covered with the quantity of water generated when the polyamic acid is imidized. The quantity of water generated is 2A × a × 1/100 mols wherein a represents the percentage imidization. Thus, in the second step reaction, the quantity of water to be added to the fluid after completion of the first step reaction is preferably [{D₂ × k + F) × 1/2 ∼ (D₂ × k + F)} _ 2A × a × 1/100] mols, but if the water content in the reaction solvent used is not neglegible, it is necessary to take this water content into account. As described above, the quantity of water to be added in the second stage reaction varies depending on the quantity of water generated by the imidization, the water content in the reaction solvent and further the quantity of siloxane bonds, and there may be a case where water addition is unnecessary, depending on the quantity of water generated by the imidization or the water content in the solvent. The silylating agent is used for molecular weight modification in order to avoid that the intermediate G forms siloxane bonds between each other at both the ends thereof and endlessly develops into a high molecular weight polymer. The expression (16) indicates that the quantity of the silylating agent used, i.e. F mol is l or less in terms of F/(D₂ × k), and it is not always necessary to add the silylating agent in excess of 1. If the reaction temperature at the second step is lower than 60°C, the reaction is slow and hence such a temperature is not practical. At 60°C or higher, the reaction can be carried out without any gelation, but temperatures exceeding 200°C are unnecessary. A promotor for imidization reaction such as tertiary amines may be added in carrying out the second step reaction, but this is not always necessary since, in the present invention, the water generated by imidization is immediately consumed for hydrolysis to direct the reaction toward imidization and as a result the imidization reaction proceeds rapidly. An acid catalyst for promoting the hydrolysis reaction may be added, but no addition is preferred taking into account its bad influence in the case where it remains. In the second reaction step, usually it is possible to allow the imidization reaction and the siloxane condensation reaction to proceed smoothly without gelling the reaction fluid, by reacting the silylating agent, and it is also possible to optionally control the viscosity of the reaction fluid i.e. the molecular weight of the precursor, by varying the quantity of the silylating agent used and the reaction conditions within the above ranges, respectively. Thus it is possible to obtain a soluble polyimide-siloxane precursor in the form of oligomer or polymer, having a suitable inherent viscosity of 0.05 to 5 dℓ/g, soluble in solvents and yet having a percentage imidization of 50% or more. If the inherent viscosity is less than 0.05 dℓ/g, the coating state of the coating fluid is inferior and hence the coating formation is insufficient. If it exceeds 5 dℓ/g, the polymer is difficultly soluble or insoluble and hence is difficult to apply to practical use. As described above, by carrying out the first reaction step followed by the second reaction step, it is possible to obtain a soluble polyimide-siloxane precursor having a percentage imidization of 50% or more and also an inherent viscosity of 0.05 to 5dℓ/g. According to the process of the present invention, even when a polyamide-carboxylic acid having aminosilicon compounds bonded at both the ends thereof (intermediate G) obtained from a tetracarboxylic acid dianhydride, a diaminosiloxane, a diamine and an aminosilicon compound at a low temperature in the first reaction step is heated in the presence of a silylating agent in the second reaction step to effect imidization and at the same time hydrolysis and siloxane condensation reaction, the second reaction step process smoothly without causing gelation. This is because the silylating agent participates in the reaction to effect siloxane condensation, whereby a part of the Si active sites of the intermediate G is inactivated to terminate an endless siloxane condensation of the intermediate G with itself. This fact will be described as follows, referring to reaction equations as an example: In this example, for simplicity of description, NH₂-L-NH₂ wherein L represents is used as the diaminosiloxane; NH₂-R⁶-Si(OEt)₃ wherein OEt represents ethoxy group, is used as the aminosilicon compound; the percentage imidization is made 100%; and (CH₃)₃Si(OEt) is used as the silylating agent. A tetracarboxylic acid dianhydride is reacted with the diaminosiloxane and the diamine as follows: At both the ends of the resulting product, each one mol of NH₂-R⁶-Si(OEt)₃ reacts to form an intermediate G expressed by the following formula (19): This intermediate G is imidized by heating and at the same time releases water, as shown in the following equation (20): The part enclosed by broken line in the formula (20) will hereinafter be referred to as J. Water present in the reaction fluid including water formed herein immediately reacts with the whole or a part of si(OEt)₃ at both the ends of a fresh intermediate expressed by the formula (20) to form an intermediate K expressed by the following formula (21): (OEt) 3-y (OH) y Si-R⁶-J-R⁶-Si(OH) x (OEt) 3-x wherein x and y each represents 1, 2 or 3. in an intermediate K formed herein readily causes siloxane condensation reaction with in another intermediate K, as shown in the following equations (22) and (23): Thus, the intermediate J may be regarded as a monomer having three active sites at each of both the ends thereof (six active sites in total) in this case. Accordingly, if the intermediate K is heated in the absence of the silylating agent, no reaction occurs at a part of the active sites, while siloxane condensation reaction successively occurs at other active sites as shown in the following formula to form a crosslinked structure and also make its molecular weight giant: This reaction occurs rapidly to make its control impossible; hence the reaction fluid gels at once. Whereas according to the process of the present invention, a silylating agent is present in the second reaction step, whereby a part of the active sites of Si is inactivated for example as shown in the following formula (24): As shown in the above formula, the active sites subjected to siloxane condensation reaction with the silylating agent are inactivated so that the subsequent siloxane condensation reaction is terminated. Thus, the number of crosslinks formed is restricted and also formation of giant molecular weight is prevented so that the reaction proceeds smoothly without gelling of the reaction fluid. In addition, as described above, the larger the proportion of the diaminosiloxane in the raw materials (for example, 100%), and the smaller the k value in the formula (13) (for example, 2 or less), and further, the greater the dilution of the raw materials in the reaction solvent, and still further, the relatively lower the temperature of the siloxane condensation reaction, the more smoothly the siloxane condensation reaction can be advanced without causing any gelation even when no silylating agent is added. The resulting polyimide-siloxane precursor obtained according to the above reaction under adjusted quantity of silylating agent used and reaction conditions, has a percentage imidization having already advanced to 50% or more and also a molecular weight as expressed by an inherent viscosity of 0.05 to 5 dℓ/g; it is soluble in solvents; and it has an enhanced Si content due to the simultaneous use with the diaminosiloxane. The polyimide-siloxane precursor of the invention (hereinafter abbreviated often to precursor) can be widely used as precursor for affording protecting materials, insulating materials or adhesives, in the field of electronic equipments or films and structural material. In most cases, the precursor is used in the form of a solution wherein it is dissolved in a solvent, as in the case of varnishes; hence it is used preferably in a state where the solution obtained according to the process of the present invention is concentrated of diluted with a solvent (such a solution will hereinafter be referred to often as precursor solution). As such a solvent, the same as the reaction solvent may be used. For example, when the precursor solution is used as protecting material for electronic materials, the solution may be, if necessary, freed from ionic substances e.g. by means of a solid adsorbent and further freed from minute solid impurities by means of a filter of 1 µm or less, and the resulting solution may be used as a coating fluid. The concentration of such a coating fluid is determined depending on the thickness of coating required. It is preferably 40% by weight or less, and a range of 0.3 to 25% by weight is often particularly preferable for practical use. The coating fluid is uniformly coated e.g. on silicon wafer or glass by means of a spinner in conventional manner, followed by heating. The heating conditions somewhat vary depending on the solvent used, the thickness of coating, etc., but those of a relative short time of about 0.5 to 1.5 hour and a temperature of 100° to 300°C may be sufficient. By such heating, the percentage imidization of the precursor reaches 100%; the precursor having a not yet so large molecular weight and soluble in solvents increases in the number of crosslinks through siloxane bonds to form a solvent-insoluble, endlessly reticulate structure, and the transparent, pale-yellow color of the precursor solution turns e.g. to a transparent, brown color (but pale-yellow to colorless in the case of a thin product of several µms or less, thick) to form a very hard and highly heat-resistant substance; hence the precursor can be utilized as protecting materials in the field of electronic equipment. The precursor obtained according to the process of the present invention, when used as a liquid crystal aligning agent, exhibits good results. The soluble polyimide-siloxane precursor of the present invention has a suitable inherent viscosity and hence its solution has a suitable viscosity so that it is possible to well carry out coating. Heating of the precursor is carried out for imidizing a remaining unimidized part and also for completing siloxane condensation reaction at unreacted active sites; hence a relatively low temperature and a relatively short time may be sufficient for heating. Further, the presence of a high Si content and hence a large quantity of siloxane bonds imparts to the precursor a good coating-formability on and a strong adhesion onto silicon wafer and glass, and the crosslinking to a suitable extent reinforces the siloxane bond which is liable to become soft. Production of the polyimide-siloxane having such various performances is effected by heating the intermediate G obtained at the first step, to a high temperature in the presence of water and if necessary, a silylating agent at the second step. Further, the precursor of the present invention is superior in the storage stability of its solution, due to the siloxane chain originating from the diaminosiloxane as raw material. The present invention will be described in more details by way of Examples, Comparative examples and Use tests. Example 1 A 1 ℓ flask equipped with stirrer, dropping funnel, thermometer, condenser and nitrogen gas-purging means was fixed in cold water. Into the flask purged with nitrogen gas were fed dewatered, purified cyclohexanone (500 mℓ), ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (84.79 g, 0.0833 mol) expressed by the formula (11) wherein ℓ = 11,6, 3-aminopropyltriethoxysilane (36.88 g, 0.167 mol) and trimethylethoxysilane (2.96 g, 0.0250 mol), followed by dissolving together these materials with stirring, and gradually feeding to the resulting solution, powdery pyromellitic acid dianhydride (36.33 g, 0.167 mol) through the dropping funnel over 30 minutes and continuing reaction, during which the reaction temperature was 3 to 10°C. The reaction was further continued at the temperature for 2 hours, followed by raising the temperature to effect the reaction at 25° to 30°C for 2 hours. This first step reaction formed a pale-yellow, transparent fluid having a rotational viscosity at 25°C of 26 mPa · s. This rotational viscosity referred to herein means a viscosity measured at 25°C using an E type viscometer (VISCONIC EMD, manufactured by Tokyo Keiki Company) (this definition will be applied to the following). Next the temperature of the reaction fluid was further raised and reaction was carried out at 100°C for 4 hours (the second step reaction) to obtain a pale-brown, transparent fluid, having a rotational viscosity at 25°C of 65 mPa · s, that is, a solution of a soluble polyimide-siloxane precursor. A portion of this precursor solution was taken and dried at room temperature under reduced pressure to obtain a pale-brown, solid precursor having a percentage imidization of 95% or more, as determined by its infrared absorption spectra, and the precursor had an inherent viscosity of 0.11 dℓ/g in cyclohexanone as solvent. When the precursor solution was kept at a temperature of 5 ∼ 10°C for 30 days, the resulting rotational viscosity at 25°C was 65 mPa · s, and a very good storage stability was exhibited. Fig. 1 shows the infrared absorption spectrum chart of the precursor obtained in this Example 1. It is observed from Fig. 1 that the absorption spectra of imide group (5.63 µm and 13.85 µm) are clearly present while the absorption spectrum of amidic acid (N-H band 3.08 µm) is extinct. Example 2 Using the same apparatus and process as in Example 1, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (49.82 g, 0.0810 mol) expressed by the formula (11) wherein ℓ = 5.96, 3-aminopropylmethyldiethoxysilane (10.33 g, 0.0540 mol) and trimethylethoxysilane (0.64 g, 0.00540 mol) were dissolved in cyclohexanone (500 mℓ), followed by adding to the solution, pyromellitic acid dianhydride (23.54 g, 0.108 mol) over 30 minutes while keeping the solution at 3 ∼ 10°C, and carrying out reaction at the temperature for 2 hours and further at 30 ∼ 35°C for one hour to obtain a uniform solution. After completion of the first step reaction, the temperature of the resulting fluid was raised and the second step reaction was carried out at 110°C for 12 hours. As a result, a pale brown, transparent solution of a polyimidesiloxane precursor having a rotational viscosity at 25°C of 120 mPa · s was obtained. This precursor had an inherent viscosity of 0,34 dℓ/g and the percentage imidization was 95% or more. The precursor solution exhibited a very good storage stability. Comparative example 1 Using the same apparatus and process as in Example 1, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (87.46 g, 0.142 mol) expressed by the formula (11) wherein ℓ = 5.96 was dissolved in cyclohexanone (500 mℓ), followed by adding pyromellic acid dianhydride (31.02 g, 0.142 mol) to the solution over 30 minutes while keeping the solution at 3 ∼ 10°C, carrying out reaction at the temperature for 2 hours and further at 30°C for 12 hours to obtain a pale yellow uniform solution having a rotational viscosity at 25°C of 22 mPa · s. When this solution was heated to 100°C for imidization, the viscosity lowered rapidly to give an oligomer solution having a rotational viscosity of 5 mPa · s as measured at 25°C. Example 3 Using the same apparatus and process as in Example 1, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (2.68 g, 0.00436 mol) expressed by the formula (11) wherein ℓ = 5.96, diaminodiphenyl ether (12.22 g, 0.0610 mol), 3-aminopropyltriethoxysilane (9.65 g, 0.0436 mol) and trimethylethoxysilane (1.29 g, 0.0109 mol) were dissolved in N-methyl-2-pyrrolidone (400 mℓ) and ethylene glycol monobutyl ether (100 mℓ), followed by adding pyromellitic acid dianhydride (19.01 g, 0.0872 mol) to the solution over 30 minutes while keeping the solution at 0 ∼ 5°C, carrying out reaction at the temperature for one hour and further at 20 ∼ 25°C for 3 hours to obtain a uniform solution. The temperature of the solution after the first reaction step was raised and reaction was carried out at 100°C for 11 hours to effect the second reaction step. As a result, a brown transparent solution of a polyimide-siloxane precursor having a rotational viscosity at 25°C of 216 mPa · s. This precursor had an inherent viscosity of 1.3 dℓ/g and the percentage imidization was 86%. The solution of the precursor exhibited a good storage stability. Example 4 Using the same apparatus and process as in Example 1, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (1.50 g, 0.00604 mol), diaminodiphenyl ether (9.67 g, 0.0483 mol), 3-aminopropyltrimethoxysilane (2.16 g, 0.0121 mol) and trimethylmethoxysilane (0.31 g, 0.00298 mol) were dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by adding benzophenonetetracarboxylic acid dianhydride (19.45 g, 0.0604 mol) to the solution over 30 minutes while keeping the solution at 10 ∼ 15°C, carrying out reaction at the temperature for 2 hours and further at 45 ∼ 50°C for one hour, to obtain a uniform solution. The temperature of this solution after completion of the first step reaction was further raised and reaction was carried out at 90°C for 13 hours to complete the second reaction step. As a result, a pale brown transparent solution of a polyimide-siloxane precursor having a rotational viscosity at 25°C of 970 mPa · s was obtained. This precursor has an inherent viscosity of 2.7 dℓ/g, and the percentage imidization was 65%. The solution of the precursor exhibited a good storage stability. Example 5 Using the same apparatus and process as in Example 1, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (51.98 g, 0.0845 mol) expressed by the formula (11) wherein ℓ = 5.96, 4,4′-diaminodiphenylmethane (4.19 g, 0.0211 mol) and p-aminophenyltrimethoxysilane (9.01 g, 0.0422 mol) were dissolved in a mixed solvent of N-metyl-2-pyrrolidone (250 mℓ) and ethylene glycol monobutyl ether (250 mℓ), followed by adding benzophenonetetracarboxylic acid dianhydride (40.85 g, 0.127 mol) to the solution over 30 minutes while keeping the solution at 0 ∼ 5°C, and carrying out reaction at the temperature for one hour and further at 20 ∼ 25°C for 4 hours to obtain a uniform solution. The temperature of the solution after the first reaction step was raised and reaction was carried out at 120°C for 2 hours, to obtain a brown transparent solution of a polyimide-siloxane precursor having a rotational viscosity at 25°C of 83 mPa · s. This precursor had an inherent viscosity of 0.20 dℓ/g and the percentage of imidization was 95% or more. The precursor solution exhibited a very good storage stability. Example 6 Using the same apparatus and process as in Example 1, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane (99.23 g, 0.0177 mol) expressed by the formula (11) wherein ℓ = 73.3, 3-aminopropyltriethoxysilane (7.838 g, 0.0354 mol) and trimethylsilyl acetate (1.64 g, 0.0124 mol) were dissolved in cyclohexanone (500 mℓ), followed by adding benzophenonetetracarboxylic acid dianhydride (11.42 g, 0.0354 mol) to the solution over 30 minutes while keeping the solution at 10 ∼ 15°C, and carrying out reaction at the temperature for one hour and further at 50 ∼ 55°C for 2 hours to obtain a uniform solution, adding water (0.32 g, 0.0178 mol) to the solution after the first reaction step, raising the temperature and carrying out reaction at 100°C for 5 hours to effect the second reaction step. As a result, a pale yellow solution of a polyimide-siloxane precursor having a rotational viscosity at 25°C of 360 mPa · s was obtained. This precursor had an inherent viscosity of 0.53 dℓ/g and the percentage imidization was 95% or more. The precursor solution exhibited a very good storage stability. Example 7 Using the same apparatus and process as in Example 1, 4,4′-diaminodiphenyl ether (15.42 g, 0.0770 mol) was dissolved in N,N-dimethylacetamide (500 mℓ), followed by adding benzophenonetetracarboxylic acid dianhydride (37.21 g, 0.116 mol) to the solution over 30 minutes while maintaining the solution at 15 ∼ 20°C, carrying out reaction at the temperature for one hour, thereafter adding 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (9.57 g, 0.0385 mol) to the solution, further adding, after 30 minutes, benzophenonetetracarboxylic acid dianhydride (12.42 g, 0.039 mol) over 30 minutes, carrying out reaction at the temperature for one hour, successively adding 3-aminopropyltriethoxysilane (17.05 g, 0.0770 mol) and trimethylethoxysilane (2.28 g, 0.0193 mol), carrying out reaction at 30 ∼ 35°C for one hour to obtain a uniform solution, raising the temperature of this solution after the first step reaction and carrying out reaction at 100°C for 8 hours to effect the second reaction step. As a result, a pale brown solution of a polyimidesiloxane precursor having a rotational precursor at 25°C of 330 mPa · s was obtained. This precursor had an inherent viscosity of 0.36 dℓ/g and the percentage imidization was 95% or more. This precursor solution exhibited a good storage stability. Comparative example 2 Using the same apparatus and process as in Example 1, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (5.34 g, 0.0215 mol) and 4,4'-diaminodiphenyl ether (38.70 g, 0.193 mol) were dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by adding pyromellitic acid dianhydride (46.85 g, 0.215 mol) to the solution over 30 minutes while keeping the solution at 10 ∼ 15°C, and carrying out reaction at the temperature for 2 hours and further at 45 ∼ 50°C for one hour to obtain a pale yellow uniform solution having a rotational viscosity at 25°C of 420 mPa · s. When this solution was heated to 90°C for imidization, the viscosity lowered rapidly, and after 3 hours, an oligomer solution having a rotational viscosity of 9 mPa · s as measured at 25°C was obtained. Comparative example 3 Using the same apparatus and process as in Example 1, 3-aminopropyltriethoxysilane (52.83 g, 0.239 mol), 4,4′-diaminodiphenyl ether (23.89 g, 0.119 mol) and trimethylethoxysilane (10.60 g, 0.0896 mol) were dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by adding pyromellitic acid dianhydride (52.05 g, 0.239 mol) to the solution over 30 minutes while keeping the solution at 3 ∼ 8°C, carrying out reaction at the temperature for 2 hours and further at 25 ∼ 30°C for one hour to obtain a pale yellow uniform solution having a rotational viscosity at 25°C of 23 mPa · s, thereafter further raising the temperature of this reaction solution, and carrying out reaction at 120°C for 9 hours to obtain a pale yellow transparent solution of a soluble polyimide-siloxane precursor having a rotational viscosity at 25°C of 130 mPa · s. This precursor had a percentage imidization of 95% or higher and an inherent viscosity of 0.13. The precursor solution was kept at a temperature of 5 ∼ 10°C for 30 days. The resulting rotational viscosity at 25°C increased to 240 mPa · s. Example 8 The following coating-heating test was carried out: The solutions of the polyimide-siloxane precursor obtained in Examples 1 ∼ 7 and the final reaction solutions obtained in Comparative examples 1 and 2 were used as coating solution. These solutions were filtered through a filter of 1 µm, followed by applying them onto a glass plate by means of a spinner, heating to 150°C, 200°C or 250°C for 2 hours to observe the condition of the resulting coatings. The results are shown in Table 1. Example 9 The following adhesion test was carried out: Various coating solutions shown in Table 2 were applied onto the surface of a slide glass by means of a spinner and heated to 150°C, 200°C or 250°C for 2 hours to form coatings of 1 ∼ 2 µm thick, followed by treating them for 4 hours in a constant temperature and constant humidity chamber kept at 90°C and a relative humidity of 95%, notching the resulting coatings, into small pieces of a square having sides of 2 mm, applying a cellophane tape onto the surface thereof, and just thereafter peeling off the tape. The adhesion was expressed in terms of the number of small pieces of coatings peeled off at that time together with the cellophane tape per 100 small pieces prior to peeling off. The results are shown in Table 2. * A varnish of a polyamidecarboxylic acid which is a conventional polyimide precursor prepared from pyromellitic acid dianhydride and 4,4′-diaminodiphenyl ether. Solvent: N-methyl-2-pyrrolidone. Concentration of solids: 18%. Rotational viscosity at 25°C: 1,050 mPa · s. As seen from the results of Tables 1 and 2, the precursor of the present invention forms a coating having a sufficient strength and adhesion even when the heating conditions carried out after applying its solution are a low temperature (150°C) and a short time (2 hours).

Claims: 1. A soluble polyimide-siloxane precursor having an imide-amic acid chain part expressed by the formula (1): bonded by a bonding structure expressed by the formula (5) wherein each chain part (I) is the same or different and represents one of the units expressed by the following formulae (2), (3) and (4): wherein R¹ represents independently a tetravalent carbocyclic aromatic group; each R² is the same or different and represente an alkyl group of 1 to 6 carbon atoms, a phenyl group, or an alkyl-Substituted phenyl group of 7 to 12 carbon atoms; each R⁴ and each R⁶ is the same or different and represents wherein s represents an integer of 1 to 4; R⁵ represents an aliphatic group of 2 to 12 carbon atoms, an alicyclic group of 4 to 30 carbon atoms, an aromatic aliphatic group of 6 to 30 carbon atoms or a carbocyclic aromatic group of 6 to 30 carbon atoms; ℓ represents an integer of 1 to 100; m represents zero or a positive integer; n represents a positive integer; each R⁷ is the same or different and represents an alkyl group of 1 to 6 carbon atoms, a phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon atoms; each Y¹ is the same or different and represents an alkoxy group, an acetoxy group, a halogen atom, a hydroxy group, (_O_) ½ or a group expressed by the formula (6) wherein R⁸, R⁹ and R¹⁰ are the same or different and each represents an alkyl group of 1 to 6 carbon atoms, a phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon atoms; and k is 1, 2 or 3; the said soluble polyimide-siloxane precursor being terminated by groups expressed by the following formula (7): wherein each Y² is the same or different and represents an alkoxy group, acetoxy group, halogen atom, hydroxy group or a group expressed by the formula (6); and R⁷ and k are as defined for the formula (5); and the inherent viscosity of the said soluble polyimide-siloxane precursor as measured in a concentration of 0.5 g/dℓ in a solvent at 30° ± 0.01°C is in the range of 0.05 to 5 dℓ/g. 2. A soluble polyimide-siloxane precursor according to claim 1 and having a percentage imidization a of 50 to 100%, this a being defined in terms of the whole of the molecule by the following equation (8); a = (2W + P) × 100 2W + 2P + 2Q (%) wherein W: the total number of units expressed by the formula (2); P: the total number of units expressed by the formula (3) and q: the total number of units expressed by the formula (4); for the whole of the molecule, and 2B₁, E₁ and D₁, which are respectively the total numbers of R⁴, R⁵ and R⁶, having a relationship expressed by the following expressions (9) and (9′): 3. A process for producing a soluble polyimide-siloxane precursor, which process comprises a first step of reactiig a tetracarboxylic acid dianhydride expressed by the following formula (10), a diaminosiloxane expressed by the following formula (11), a diamine expressed by the following formula (12) and an aminosilicon compound expressed by the following formula (13) in the presence of a solvent at a temperature of 0°C to 60°C for a time of 0.2 to 6 hours so as to form a uniform reaction product fluid; and further a second step of heating the reaction product fluid at a temperature of 60°C to 200°C for a time of 0.5 to 30 hours, in the presence of a silylating agent expressed by the following formula (17), to effect an imidization reaction, and hydrolyzing X¹ and X² with water generated during said imidization reaction and if necessary, water from other sources, and further effecting siloxane condensation, to give a soluble polyimide-siloxane precursor with inherent viscosity as measured in a solvent in a concentration of 0.5 g/dℓ at a temperature of 30 ± 0.01°C of 0.05 to 5 dℓ/g: wherein R¹, R², R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ R¹⁰ and l and k are as defined in claim 1; X¹ is a halogen atom or an alkoxy or acetoxy group; and X² is a halogen atom or a hydroxyl, alkoxy or acetoxy group. 4. A process according to claim 3 which comprises in the first step, reacting A mols of the tetracarboxylic acid dianhydride expressed by the formula (10), B₂ mols of the diaminosiloxane expressed by the formula (11), E₂ mols of the diamine expressed by the formula (12) and D₂ mols of the aminosilicon compound expressed by the formula (13), the values of A, B₂, E₂ and D₂ being selected so as to comply with relationship expressed by the following expressions (14) and (14′), and to approximately satisfy the equation (15); in the second step, heating the reaction product fluid in the presence of F mols of the silylating agent expressed by the formula (17), the value of F being selected to comply with the following expression (16), and the percentage imidization a of the resulting product being 50 to 100%, as defined by the following equation (18). wherein W: the total number of units expressed by the formula (2); P: the total number of units expressed by the formula (3) and Q: the total number of units expressed by the formula (4). 5. A process according to claim 3 or 4 wherein the second step is carried out by adding water to supplement water generated during the reaction. 6. A cross-linked polyimide-siloxane obtained by heating to a temperature of 100°C to 300°C a soluble polyimide-siloxane precursor according to claim 1. 7. A cross-linked polyimide-siloxane precursor according to claim 6, wherein the heating is carried out for 0.5 to 1.5 hour.

Inventors: KONOTSUNE, SHIRO, KUNIMUNE, KOUICHI, KUTSUZAWA, YOSHIYA NOJIMARYO
Applicants: CHISSO CORPORATION
Application year: 1986
Main classification: C08G77
IPC codes: H01L21, C08G73, C08G77