Soluble polyimide-siloxane precursor, process for producing same and cross-linked polyimide-siloxane

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 polyimidesiloxane obtained by heating the above precursor are provided, which precursor has PA1 an imide-amic acid chain part expressed by the formula (1) ##STR1## bonded by a bonding structure expressed by the formula (5) EQU --SiR.sup.7.sub.3-k Y.sup.1.sub.k-1 --O--SiR.sup.7.sub.3-k Y.sup.1.sub.k-1 -- (5) PA1 wherein each I, in a total number of m+n+1, represents independently any one of constituting units expressed by the following formulas (2), (3) and (4): ##STR2## wherein R.sup.1 represents a tetravalent carbocyclic aromatic group; R.sup.2, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and Y.sup.1 each are a specified group; l is 1 to 100; m is 0 or an integer; n is an integer; and 1.ltoreq.k.ltoreq.3, and PA1 which process comprises a first step of reacting a tetracarboxylic acid dianhydride, a diaminosiloxane, a diamine 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.

BACKGROUND OF THE INVENTION 
This invention relates to a novel polyimide-siloxane precursor, a process 
for producing the same, and a cross-linked polyimide-siloxane. 
Polyimide resins have so far been widely used for protecting materials, 
insulating materials and adhesives in the field of electronic equipment 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 diversified, 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 have been raised 
such that baking requires as high a temperature as 300.degree.-400.degree. 
C. which often exceeds the heat-resistant temperature of the substrates; 
and adhesion of the coating solution onto silicon wafer, glass, etc. is 
insufficient; etc. 
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 a tetracarboxylic acid dianhydride is reacted with a 
diamine, to form a polyamidecarboxylic acid having a terminal group such 
as acid anhydride. This polyamidecarboxylic acid is reacted with an 
aminosilicon compound at -20.degree. C. to +50.degree. 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.degree. C. or lower, 
particularly -20.degree. C. to +25.degree. C.) in the presence of a 
dehydrating agent to form an organic silicon-modified polyimide precursor. 
The former unimidized precursor or the latter polyimide precursor is 
heated in the form of a 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.degree. C. or higher, up to 350.degree. 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. 
Further, the present inventors have previously proposed a soluble 
polyimide-siloxane precursor using a tetracarboxylic acid dianhydride, a 
diamine, an amino-silicon compound and a silylating agent as raw materials 
which are in part the same as those used in the present invention 
(Japanese patent application No. Sho 59-230428/1984). This precursor has 
superior, practical characteristics, but on the other hand, it has a 
drawback of being somewhat inferior in storage stability. 
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 a 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, glass, 
etc., so that the resulting solution may be suitable for 
surface-protection of semiconductors, insulating film between multilayer 
interconnections, etc. 
The object of the present invention is to provide such a soluble 
polyimide-siloxane precursor which overcomes the above problems (in a 
first aspect), a process for producing the same (in a second aspect), and 
a cross-linked polyimide-siloxane (in a third aspect). 
SUMMARY OF THE INVENTION 
The present invention in a first aspect resides in: 
a soluble polyimide-siloxane precursor having an imide-amic acid chain part 
expressed by the formula (1) 
##STR3## 
bonded by a bonding structure expressed by the formula (5) 
EQU --SiR.sup.7.sub.3-k Y.sup.1.sub.k-1 --O--SiR.sup.7.sub.3-k Y.sup.1.sub.k-1 
-- (5) 
wherein each I, in a total number of m+n+l, represents independently any 
one of constituting units expressed by the following formulas (2), (3) and 
(4): 
##STR4## 
wherein PR.sup.1 represents independently a tetravalent carbocyclic 
aromatic group; 
each R.sup.2 represents independently an alkyl group of 1 to 6 carbon 
atoms, phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon 
atoms; 
each R.sup.4 and each R.sup.6 represents independently --CH.sub.2).sub.5, 
##STR5## 
wherein s represents an integer of 1 to 4; 
R.sup.5 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 R.sup.7 represents independently an alkyl group of 1 to 6 carbon 
atoms, phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon 
atoms; 
each Y.sup.1 represents independently an alkoxy group, acetoxy group, a 
halogen atom, hydroxyl group, (--O--).sub.1/2 or a group expressed by the 
formula (6) 
EQU R.sup.8 R.sup.9 R.sup.10 Si--O-- (6) 
wherein R.sup.8, R.sup.9 and R.sup.10 represent independently an alkyl 
group of 1 to 6 carbon atoms, phenyl group or an alkyl-substituted phenyl 
group of 7 to 12 carbon atoms; and 
k represents a value of 1.ltoreq.k.ltoreq.3, 
said soluble polyimide-siloxane precursor further being terminated by 
groups expressed by the following formula (7): 
EQU Y.sup.2.sub.k R.sup.7.sub.3-k Si-- (7) 
wherein Y.sup.2 independently represents an alkoxy group, acetoxy group, a 
halogen atom, hydroxyl group or a group expressed by said formula (6); 
R.sup.7 and k are as defined in said formula (5); 
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): 
##EQU1## 
wherein W: the total number of constituting units expressed by said 
formula (2); 
P: the total number of constituting units expressed by said formula (3) and 
Q: the total number of constituting units expressed by said formula (4); 
as the whole of the molecule, 2B.sup.1, E.sup.1 and D.sup.1 which are 
respectively the total numbers of R.sup.4, R.sup.5 and R.sup.6 having a 
relationship expressed by the following expressions (9) and (9'): 
##EQU2## 
and 
the inherent viscosity of the precursor as measured in a concentration of 
0.5 g/dl in a solvent at 30.degree..+-.0.01.degree. C. being in the range 
of 0.05 to 5 dl/g. 
The present invention in a second aspect resides in: 
a process for producing a soluble polyimide-siloxane precursor which 
comprises 
a first step reaction of reacting A mols of a tetracarboxylic acid 
dianhydride expressed by the following formula (10), B.sup.2 mols of a 
diaminosiloxane expressed by the following formula (11), E.sup.2 mols of a 
diamine expressed by the following formula (12) and D.sup.2 mols of an 
amino-silicon compound expressed by the following formula (13) in the 
presence of a solvent at a temperature of 0.degree. C. or higher and lower 
than 60.degree. C. for a time of 0.2 to 6 hours so as to give a 
relationship among A, B.sup.2, E.sup.2 and D.sup.2, expressed by the 
following expressions (14) and (14'), and to approximately satisfy the 
equation (15), to thereby form a uniform reaction product fluid; and 
further 
a second step reaction of heating said reaction product fluid at a 
temperature of 60.degree. C. or higher and lower than 200.degree. C. for a 
time of 0.5 to 30 hours, in the presence of F mols of a silylating agent 
expressed by the following formula (17), which F falls within a range 
expressed by the following expression (16), to effect an imidization 
reaction, and hydrolyzing X.sup.1 in said aminosilicon compound expressed 
by the formula (13) and X.sup.2 in said silylating agent expressed by the 
formula (17), with water generated during said imidization reaction and if 
necessary, water from other sources, and further effecting siloxane 
condensation, 
to make the percentage imidization a of the resulting product defined by 
the following equation (18), 50 to 100%, and also make the inherent 
viscosity thereof as measured in a solvent in a concentration of 0.5 g/dl 
at a temperature of 30.+-.0.01.degree. C., 0.05 to 5 dl/g: 
##STR6## 
EQU NH.sub.2 --R.sup.5 --NH.sub.2 ( 12) 
EQU NH.sub.2 --R.sup.6 --SiR.sup.7.sub.3-k X.sup.1.sub.k ( 13) 
##EQU3## 
EQU 2A=2B.sup.2 +2E.sup.2 +D.sup.2 ( 15) 
EQU O.ltoreq.F/(D.sup.2 .times.k).ltoreq.1 (16) 
EQU R.sup.8 R.sup.9 R.sup.10 SiX.sup.2 ( 17) 
wherein R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8, 
R.sup.9, R.sup.10, l and k are as defined above; X.sup.1 represents an 
alkoxy group, acetoxy group or a halogen atom; and X.sup.2 represents an 
alkoxy group acetoxy group, a halogen atom or hydroxyl group, 
##EQU4## 
wherein W, P and Q are as defined above. 
The present invention in a third aspect resides in a cross-linked 
polyimide-siloxane obtained by heating the above-described soluble 
polyimide-siloxane precursor to a temperature of 100.degree. to 
300.degree. C.

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 
imideamic 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). 
R.sup.1 has preferably at least one six-membered ring. R.sup.1 is 
particularly, 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 group is --O--, 
--CO--, --SO.sub.2 --. 
Examples of R.sup.1 are 
##STR7## 
wherein R.sup.11 represents --O--, --CO-- or --SO.sub.2 --, 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. 
R.sup.5 includes not only an atomic group consisting only of C and H, but a 
hydrocarbon having a cross-linking group containing a different atom other 
than 
##STR8## 
Examples of such a cross-linking group are --O--, --S--, --SO.sub.2 --, 
--CO--, 
##STR9## 
etc. 
Examples of R.sup.5 are 
##STR10## 
wherein R.sup.12 represents an alkyl group of 1 to 4 carbon atoms; 
##STR11## 
wherein R.sup.13 represents --O--, --S--, --SO.sub.2 --, --CO--, 
--CH.sub.2 -- or 
##STR12## 
EQU --(CH.sub.2).sub.p -- 
wherein p represents an integer of 2 to 12; and 
##STR13## 
The precursor of the present invention has a suitable range of molecular 
weight defined in terms of an inherent viscosity of 0.05 to 5 dl/g as 
measured under specified conditions, and is soluble in a suitable solvent. 
The above inherent viscosity (.eta. inh) is expressed by the following 
equation: 
##EQU5## 
wherein .eta. 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.degree. C.; .eta..sub.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 R.sup.4, R.sup.5 and R.sup.6 in the 
molecule, of the above imide-amic acid chain part (1) are referred to as 
2B.sup.1, E.sup.1 and D.sup.1, 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 Y.sup.1 in the formula (5) is reduced; hence when a 
film is prepared, the coating-formability, mechanical strengths, etc. are 
reduced. 
Further, each I in the imide-amic acid chain part (1) independently 
represents any 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 percentage imidization of the product can 
be increased in spite of its being a precursor. Thus, for example, it is 
possible to effect completion of the imidization by heating the precursor 
at a relatively low temperature and in a relatively short time. The 
determination of the number of imide groups required for calculating the 
percentage imidization a may be carried out according to a known infrared 
absorption spectrum method. 
The soluble polyimide-siloxane precursor of the present invention in the 
first aspect is constituted as described above. 
Next, the raw materials of the present invention in the second aspect will 
be described. 
R.sup.1 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, 
2,3,6,7-naphthalenetetracarboxylic acid dianhydride, etc. 
Further, examples of the diaminosiloxane expressed by the formula (11) are 
as follows: 
##STR14## 
Among these diaminosiloxanes, those wherein l is in the range of 1 to 100 
are preferred. If l exceeds 100, the resulting silicone-polyimide 
precursor has a reduced solubility in solvents; hence such a precursor is 
not practical. 
Next, R.sup.5 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-phenylenediamine, 
m-phenylenediamine, p-phenylenediamine, benzidine, 
2,2'-diaminobenzophenone, 4,4'-diaminobenzophenone, 
4,4'-diaminodiphenyl-2,2'-propane, etc., 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, m-xylylenediamine, etc. 
Next, examples of aminosilicon compounds expressed by the formula (13) are 
as follows: 
NH.sub.2 --(CH.sub.2).sub.3 --Si(OCH.sub.3).sub.3, NH.sub.2 
--(CH.sub.2).sub.3 --Si(OC.sub.2 H.sub.5).sub.3, NH.sub.2 
--(CH.sub.2).sub.3 --Si(CH.sub.3)(OCH.sub.3).sub.2, NH.sub.2 
--(CH.sub.2).sub.3 --Si(CH.sub.3)(OC.sub.2 H.sub.5).sub.2, NH.sub.2 
--(CH.sub.2).sub.3 --Si(C.sub.2 H.sub.5)(On--C.sub.3 H.sub.7).sub.2, 
NH.sub.2 --(CH.sub.2).sub.4 --Si(OCH.sub.3).sub.3, NH.sub.2 
--(CH.sub.2).sub.4 --Si(OC.sub.2 H.sub.5).sub.3, NH.sub.2 
--(CH.sub.2).sub.4 --Si(CH.sub.3)(OC.sub.2 H.sub.5).sub.3, 
##STR15## 
Further, examples of the silylating agent expressed by the formula (17) are 
as follows: 
(CH.sub.3).sub.3 Si(OCH.sub.3), (CH.sub.3).sub.3 Si(OC.sub.2 H.sub.5), 
(CH.sub.3).sub.3 Si(O.sup.n --C.sub.3 H.sub.7).sub.3, (CH.sub.3).sub.2 
(C.sub.2 H.sub.5)Si(OCH.sub.3), (CH.sub.3).sub.2 (C.sub.2 
H.sub.5)Si(OC.sub.2 H.sub.5), (CH.sub.3).sub.3 SiOH, (CH.sub.3).sub.3 
Si(OCOCH.sub.3), 
##STR16## 
etc. 
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, 
cyclohexanone, etc. 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 B.sup.2 mols of a diamino-siloxane expressed by the 
formula (11), E.sup.2 mols of a diamine expressed by the formula (12) and 
D.sup.2 mols of an aminosilicon compound expressed by the formula (13) in 
a reaction solvent. A, B.sup.2, E.sup.2 and D.sup.2 are determined so as 
to satisfy the expressions (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, glass, etc. 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 
number of amino groups in the diaminosiloxane, the diamine and the 
aminosilicon compound are equivalently reacted with the total number of 
##STR17## 
groups 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 of 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 reaction of the respective raw 
materials in a solvent is carried out through a first step reaction 
wherein the tetracarboxylic dianhydride is reacted with the 
diaminosiloxane, the diamine and the aminosilicon compound at a relatively 
low temperature, and through a second step reaction wherein 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 
generated 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.degree. to 60.degree. C., preferably 
3.degree. to 30.degree. 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, followed 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, 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 is 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.degree. to 200.degree. C., 
preferably 80.degree. to 130.degree. C. for a time of 0.5 to 30 hours to 
carry out imidization reaction. Further, X.sup.1 of the aminoslicon 
compounds at both the ends of the intermediate G and X.sup.2 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 diamino-siloxane 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 Y.sup.1 and Y.sup.2 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 X.sup.1 in the aminosilicon compound forming the terminal of 
the intermediate G and X.sup.2 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 X.sup.2 is initially --OH). There 
also 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 
X.sup.1 and X.sup.2, but also when the precursor is baked, the resulting 
siloxane bonds are preferred to be formed at the sites of all or nearly 
all X.sup.1 and X.sup.2 of Si, and hence it is preferred to hydrolyze 1/2 
or the whole of X.sup.1 and X.sup.2 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 X.sup.1 and X.sup.2 
to the hydrolysis-siloxane condensation is (D.sup.2 .times.k +F) 
.times.1/2 mols (if X.sup.2 is hydroxyl group, the quantity of water is 
reduced as much). 
At least a part of the quantity of water consumed in the hydrolysis is 
derived from the quantity of water generated when the polyamic acid is 
imidized. The quantity of water generated is 2A.times.a.times.(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 [{(D.sup.2 
.times.k+F).times.1/2.about.(D.sup.2 .times.k+F)}-2A.times.a.times.(1/100] 
mols, but if the water content in the reaction solvent used is not 
negligible, 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 prevent that the 
intermediate G from forming siloxane bonds between each other at both the 
ends thereof and endlessly developing into a high molecular weight 
polymer. The expression (16) indicates that the quantity of the silylating 
agent used, i.e. F mol is 1 or less in terms of F/(D.sup.2 .times.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.degree. C., 
the reaction is slow and hence such a temperature is not practical. At 
60.degree. C. or higher, the reaction can be carried out without any 
abnormal reaction, but temperatures exceeding 200.degree. 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 or the like 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 step reaction, 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 difficulty soluble or insoluble and hence is difficult to apply 
to practical use. 
As described above, by carrying out the first step reaction followed by the 
second step reaction, 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 5 dl/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 step reaction is heated in the presence of 
a silylating agent in the second step reaction to effect imidization and 
at the same time hydrolysis and siloxane condensation reaction, the second 
step reaction proceeds 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 between each other. This fact will be described as follows, 
referring to reaction equations as an example. In this example, for 
simplicity of description, NH.sub.2 --L--NH.sub.2 wherein L represents 
##STR18## 
is used as the diaminosiloxane; NH.sub.2 --R.sup.6 ---Si(OEt).sub.3 
wherein OEt represents ethoxy group, is used as the aminosilicon compound; 
the percentage imidization is made 100%; and (CH.sub.3).sub.3 Si(OEt) is 
used as the silylating agent. 
A tetracarboxylic acid dianhydride is reacted with the diaminosiloxane and 
the diamine as follows: 
##STR19## 
At both the ends of the resulting product, each mol of NH.sub.2 --R.sup.6 
--Si(OEt).sub.3 reacts to form an intermediate G expressed by the 
following formula (19): 
##STR20## 
This intermediate G is imidized by heating and at the same time releases 
water, as shown in the following equation (20): 
##STR21## 
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).sub.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): 
EQU (OEt).sub.3-y (OH).sub.y Si--R.sup.6 --J--R.sup.6 --Si(OH).sub.x 
(OEt).sub.3-x (21) 
wherein x and y each represents 1, 2 or 3. 
##STR22## 
in an intermediate K formed herein readily causes siloxane condensation 
reaction with 
##STR23## 
in another intermediate K, as shown in the following equations (22) and 
(23): 
##STR24## 
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 very high: 
##STR25## 
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 made present in the second step reaction, whereby a part of the 
active sites of Si is inactivated for example as shown in the following 
formula (24): 
##STR26## 
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 a product 
with too high a 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 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, adhesives, etc. in the field 
of electronic equipment or films, structural materials, etc. 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 or 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 
by means of solid adsorbent or the like and further freed from minute 
solid impurities by means of a filter of 1 .mu.m 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 on silicon wafer, glass, etc. by means 
of spinner or the like in a 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 hours and a temperature of 100.degree. to 300.degree. C. may be 
sufficient. By such heating, the percentage imidization of the precursor 
which is less than 100% reaches 100%; the precursor having a not yet so 
large molecular weight and being 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 .mu.ms 
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 carry out coating well. 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 to silicon wafer, glass, etc. 
having Si or Si compound, 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 suprior 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 detail 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), .omega.,.omega.'-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.degree. to 10.degree. C. The 
reaction was further continued at the temperature for 2 hours, followed by 
raising the temperature to effect the 25.degree. to 30.degree. C. for 2. 
hours. This first step reaction formed a pale-yellow, transparent fluid 
having a rotational viscosity at 25.degree. C. of 26 cp. This rotational 
viscosity referred to herein means a viscosity measured at 25.degree. 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.degree. C. for 4 hours (the second step reaction) to 
obtain a pale-brown, transparent fluid having a rotational viscosity at 
25.degree. C. of 65 cp, 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.about.10.degree. 
C. for 30 days, the resulting rotational viscosity at 25.degree. C. was 67 
cp, 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 .mu.m and 13.85 .mu.m) are clearly present while the 
absorption spectrum of amidic acid (N-H band 3.08 .mu.m) is extinct. 
EXAMPLE 2 
Using the same apparatus and process as in Example 1, 
.omega.,.omega.'-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.about.10.degree. C., and carrying out reaction at the 
temperature for 2 hours and further at 30.about.35.degree. 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.degree. C. for 12 hours. As a result, a 
pale brown, transparent solution of a polyimidesiloxane precursor having a 
rotational viscosity at 25.degree. C. of 120 cp 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. 
COMATIVE EXAMPLE 1 
Using the same apparatus and process as in Example 1, 
.omega.,.omega.'-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.about.10.degree. C., carrying out reaction at the 
temperature for 2 hours and further at 30.degree. C. for 12 hours to 
obtain a pale yellow uniform solution having a rotational viscosity at 
25.degree. C. of 22 cp. When this solution was heated to 100.degree. C. 
for imidization, the viscosity lowered rapidly to give an oligomer 
solution having a rotational viscosity of 5 cp as measured at 25.degree. 
C. 
EXAMPLE 3 
Using the same apparatus and process as in Example 1, 
.omega.,.omega.'-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 mcnobutyl 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.about.5.degree. C., carrying out reaction at the temperature for one 
hour and further at 20.about.25.degree. C. for 3 hours to obtain a uniform 
solution. The temperature of the solution after the first step reaction 
was raised and reaction was carried 
out at 100.degree. C. for 11 hours to effect the second step reaction. As a 
result, a brown transparent solution of a polyimide-siloxane precursor 
having a rotational viscosity at 25.degree. C. of 216 cp. 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.about.15.degree. 
C., carrying out reaction at the temperature for 2 hours and further at 
45.about.50.degree. 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.degree. C. for 13 
hours to complete the second step reaction. As a result, a pale brown 
transparent solution of a polyimide-siloxane precursor having a rotational 
viscosity at 25.degree. C. of 970 cp was obtained. This precursor had 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, .omega.,.omega.'-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-methyl-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.about.5.degree. C., and carrying out 
reaction at the temperature for one hour and further at 
20.about.25.degree. C. for 4 hours to obtain a uniform solution. 
The temperature of the solution after the first step reaction was raised 
and reaction was carried out at 120.degree. C. for 2 hours, to obtain a 
brown transparent solution of a polyimide-siloxane precursor having a 
rotational viscosity at 25.degree. C. of 83 cp. 
This precursor had an inherent viscosity of 0.20 dl/g and the percentage 
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, 
.omega.,.omega.'-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.about.15.degree. C., and carrying out reaction at the temperature for 
one hour and further at 50.about.55.degree. C. for 2 hours to obtain a 
uniform solution, adding water (0.32 g, 0.0178 mol) to the solution after 
the first step reaction, raising the temperature and carrying out reaction 
at 100.degree. C. for 5 hours to effect the second step reaction. As a 
result, a pale yellow solution of a polyimide-siloxane precursor having a 
rotational viscosity at 25.degree. C. of 360 cp 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.about.20.degree. 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.about.35.degree. 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.degree. C. for 8 hours to effect the second 
step reaction. 
As a result, a pale brown solution of a polyimide-siloxane precursor having 
a rotational precursor at 25.degree. C. of 330 cp 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. 
COMATIVE 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.about.15.degree. C., and carrying out reaction 
at the temperature for 2 hours and further at 45.about.50.degree. C. for 
one hour to obtain a pale yellow uniform solution having a rotational 
viscosity at 25.degree. C. of 420 cp. When this solution was heated to 
90.degree. C. for imidization, the viscosity lowered rapidly, and after 3 
hours, an oligomer solution having a rotational viscosity of 9 cp as 
measured at 25.degree. C. was obtained. 
COMATIVE 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.about.8.degree. C., carrying out 
reaction at the temperature for 2 hours and further at 25.about.30.degree. 
C. for one hour to obtain a pale yellow uniform solution having a 
rotational viscosity at 25.degree. C. of 23 cp, thereafter further raising 
the temperature of this reaction solution, and carrying out reaction at 
120.degree. C. for 9 hours to obtain a pale yellow transparent solution of 
a soluble polyimide-siloxane precursor having a rotational viscosity at 
25.degree. C. of 130 cp. 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.about.10.degree. C. for 30 days. The 
resulting rotational viscosity at 25.degree. C. increased to 240 cp. 
EXAMPLE 8 
The following coating-heating test was carried out: The solutions of the 
polyimide-siloxane precursor obtained in Examples 1.about.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 
.mu.m, followed by applying them onto a glass plate by means of a spinner, 
heating to 150.degree. C., 200.degree. C. or 250.degree. C. for 2 hours to 
observe the condition of the resulting coatings. The results are shown in 
Table 1. 
TABLE 1 
______________________________________ 
Coating 
Heating temperature 
Test No. solution 150.degree. C. 
200.degree. C. 
250.degree. C. 
______________________________________ 
Example 
1 1 o o o 
2 2 o o o 
3 3 o o o 
4 4 o o o 
5 5 o o o 
6 6 o o o 
7 7 o o o 
Comp. 
ex. 
8 1 x x x 
9 2 x x x 
______________________________________ 
(Note) 
o: Coating was uniformly formed and had a practically sufficient hardness 
x: Coating was not uniformly formed. 
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.degree. C., 
200.degree. C. or 250.degree. C. for 2 hours to form coatings of 1.about.2 
.mu.m thick, followed by treating them for 4 hours in a constant 
temperature and constant humidity chamber kept at 90.degree. 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. 
TABLE 2 
______________________________________ 
Coating Heating temperature 
Test No. solution 150.degree. C. 
200.degree. C. 
250.degree. C. 
______________________________________ 
Example 
1 1 0 0 0 
2 2 0 0 0 
3 3 0 0 0 
4 4 0 0 0 
5 5 0 0 0 
6 6 0 0 0 
7 7 0 0 0 
8 Reference 100 100 100 
ex.* 
______________________________________ 
*A varnish of a polyamidecarboxylic acid which is a conventional 
polyimide precursor prepared from pyromellitic acid dianhydride and 4,4' 
diamino-diphenyl ether. 
Solvent: N--methyl2-pyrrolidone. 
Concentration of solids: 18%. 
Rotational viscosity at 25.degree. C.: 1,050 cp. 
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.degree. C.) and a short time (2 hours).