CA1310651C - Aminodicarboxylic acid intermediates for preparing polyimides - Google Patents

Abstract

ABSTRACT

An aminocarboxylic acid of the formula in which R1 and R2 are halogen, nitro, aryl, aryloxy, alkyl or alkoxy, m is 0 or a number from 1 to 4, n is 0 or a number from 1 to 3 and p is 0, 1 or 2, the free carboxyl groups are bonded in the ortho-position relative to one another and R
is a divalent aromatic radical which is substituted by at least one alkyl or aralkyl group, esters, amides, halides and anhydrides thereof are useful as intermediates in the production of polyimides useful for preparing protective films or photo-graphic relief images.

Description

1310~51 1 21~89-6831D
Aminodicarboxvlic acid intermediates for ~repari_a Polvlmides This is a divisional application of Serial No. 495,286 filed on November 14, 1985.
Application No. 495,286 relates to homopolyimides and copolyimides of substituted aromatic aminodicarboxylic acids, aromatic tetracarboxylic acids and diamines and~or unsubstituted aromatic aminodicarboxylic acids, a process for their preparation and their use for the preparation of protective fllms or photographic relief images.
The invention of this divisional application relates to an aminodicarboxylic acid of the formula IVa 2N\ ~ /R
5/X.,.X\ 7 \ X\ tlVa), in which R4, R5, R6 and R7 are C1-C4-alkyl, or the polyimide forming derivatives thereof selected from the group consisting of the esters, amides, halides and anhydrides.
Polyimides are plastics with useful thermomechanical propertles. Because of their hlgh meltlng ranges, however, they cannot be processed by the usual shap~ng methods for thermoplastlcs. Soluble polylmldes whlch can be used as varnishes for formlng coatlng layers wlth a high stability towards heat have therefore been developed, c.f. German Auslegeschrift 1,962,588 and U.S. Patent Specification 3,787,367. With the development of electronics and semiconductor technology, hlgh requlrement~ are belng lmposed on the heat stabllity of polylmldes, for example as A

~ 3 ~
la 21489-6~31D
insulating and protective films, which the known polyimides are not always capable of meeting.
It has now been found that soluble autophotocross-linkable polyimides of high heat stability are obtained if they contain structural elements of an aromatic aminoketodicarboxylic acid substituted by alkyl or aralkyl.
Application No. 495,286 relates to homopolyimides and copolyimides which contain structural elements of aromatic aminodicarboxylic acids and have an intrinsic viscosity of at least 0.1 dl/g, measured at 25C in a solution of 0.5 per cent by weight of polyimide in N-methylpyrrolidone, which contain recurring structural elements of the formula I

A

~3~5~

~-R-C

n 1l in which R1 and R2 are halogen, nitro, aryl, aryloxy, alkyl or alkoxy, m is O or a number from 1 to 4, n is O or a number from 1 to 3 and p is 0, 1 or 2, the free carbonyl groups are bonded in the ortho-position relative to one another and R
is a divalent aromatic radical ~hich is substituted by at least one alkyl group or aralkyl group.
The intrinsic viscosity is preferably at least 0.2 dl/g, in particular 0.2 to 2.0 dl/g. In formula I, m, n and p are preferably 0.
R1 and R2 as halogen are preferably F or Cl, as aryl are phenyl, as aryloxy are phenoxy and as alkyl and alkoxy preferably contain 1 to 12, in particular 1 to 4, C
atoms. Examples are methyl, ethyl, n-propyl, i-propyl, butyl, methoxy and ethoxy. The carbonyl groups are prefer-ably bonded in the 2-, 3- and 6-position.
The aromatic radical R is preferably substituted by alkyl or aralkyl in at least one, in particular in both, ortho-posit;ons relative to the N atom. The substituent as aralkyl is, in particular~ benzyl. As alkyl, the substituent preferably contains 1 to 12, in particular 1 to 4, C atoms.
The alkyl can be linear or branched. Ethyl, methyl, and isopropyl are particularly preferred. Other examples are n-propyl, n-butyl, isobutyl, pentyl, hexyl, octyl, decyl and dodecyl.
The aromatic radical R is preferably a phenylene radical or bisphenylene radical substituted by alkyl. In part;cular, the radical R has the formula II

R R ~ R R
~.~R3~ ( I I ) R R; ~ R/~

in which q is 0 or 1, R3 is a direct bond or a bridge group, R4 is alkyl with 1 to 4 C atoms and R5 to R11 are hydrogen atoms or alkyl with 1 to 4 C atoms, and the free bonds are in the meta- or para-position relative to the R3 group.
In one embodiment, R4 and R5, and R10 and R11 are bonded in the ortho-position relative to the free bond and are C1-C4-alkyl. In a particularly preferred embodiment, q in formula II is O and R4 to R7 are C1-C4-alkyl, in particular methyl or ethyl.
The bridge group R3 can have the same meaning as R13. R3 is preferably a direct bond, -S-, -0-, -S0-, -S02-, -C0-, -CH2- or C2-C6-alkylidene, for example ethylidene, 1,1- or 2,2-propylidene, butylidene, cyclopen-tylidene or cyclohexylidene.
In a particular embodiment, the polyimides according to Application No. 495,286 contain structural elements of the formula \ / 3 ll C--.~ \ / \
~.. ~ ! '! ~-CH3 CH3 ~ / \C/

In another embodiment, the polyimides contain a) 0.1-100 mol % of structural elements of the formula I and b) 99.9-0 mol % of structural elements of the formula III
and/or IIIa ~310~a~

O O O
ll 11 11 Il 11 11 O O O
in which Z is the tetravalent radical of an aromatic tetra-carboxylic ac;d onto which in each case two carbonyl groups are bonded ;n the ortho- or peri-position, Z~ is the tri-valent radical of an aromatic aminocarboxylic acid onto which two carbonyl groups are bonded in the ortho- or peri-position and X ;s the diva~ent radical of an organic diamine.
The structural elements of the formula I are prefer-ably present in an amount of 5-100 mol X, preferably 20-100 mol %, in particular 50-100 mol % and especially 80-100 mol %, and the structural elements of the formulae III or IIIa are preferably present in an amount of 95-0 mol X, preferably 80 to 0 mol %, in particular 50 to ~ mol X and especially 20 to 0 mol ~.
X in formula lII can be a divalent unsubstituted or subst;tuted aliphatic radical, which can be interrupted by heteroatoms or aromatic, heterocyclic or cycloaliphatic groups, an unsubst;tuted or substituted heterocyclic, cyclo-aliphatic or araliphatic radical, an aromatic radical in ~hich t~o aryl nuclei are linked via an aliphatic group, or an aromatic radical ~hich is substituted by at least one alkyl group, cycloalkyl group, alkoxyalkyl group, alkoxy group, alkylthio group, alkylthioalkyl groupr hydroxyalkyl group, hydroxyalko~y group, hydroxyalkylthio group or aralkyl-thio group or, on t~o adjacent C atoms of the aromatic radi-cal, by an alkylene group.
X is preferably alkylene, cycloalkylene, aralkylene or arylene, and especially substituted arylene.
X in formula III as a divalent aliphatic radical preferably contains 2 to 30, in particular 6 to 30 and especially 6 to 20, C atoms. In a preferred sub-group, X is ~ 319~

linear or branched alkylene, which can be interrupted by oxygen atoms, S, S0, S02, NH, NRa, ~ NR2a G~, cyclo-hexylene, naphthylene, phenylene or hydantoin radicals. Ra can be, for example, alkyl with 1 to 12 C atoms or cycloalky~
with 5 or 6 ring C atoms, phenyl or benzyl. ~ is an anion of a proton acid, for example halide, sulfate or phosphate.
In a preferred embodiment, R and R' are linear or branched alkylene with 6 to 3û C atoms, -(CH2)m--R14-(CH2)n--, in which R14 is phenylene, naphthylene, cyclopentylene or cyclohexylene and m' and n' independently of one another are the number 1, 2 or 3, -R15-(oR16)p-o-R15-~ in which R15 is ethylene, 1,2-propylene, 1,3-propylene or 2-methyl-1,3-propylene and R16 is ethylene, 1,2-propylene, 1,2-butylene, 1,3-propylene or 1,4-butylene and p is a number from 1 to 10û, or -(CH2)3-C\ ~ C ~ ~CH-(CH2)3-Examples of aliphatic radicals are: methylene, ethylene, 1,2- or 1,3-propylene, 2,2-dimethyl-1,3-propylene, 1,2-, 1,3- or 1,4-buty~ene, 1,3- or 1,5-penty~ene, hexylenes, heptylenes, octylenes, decylenes, dodecylenes, tetradecylenes, hexadecylenes, octadecylenes, eicosylenes, 2j4,4-trimethyl-hexylene, 1,1û-dialkyldecylene, in which the alkyl preferably contains 1 to 6 C atoms, substituted 1,11-undecylenes, such as are described, for example, in B-0,011,559, jeffamines, for example -(CH2)3tOCHCH2 ~ 0-~CH2 ~ where p' = 1 to 100, or -(CH2 ~ 2 4 ~ 2 ~ where p' = 1-100, dimethyl-enecyclohexane, xylylene and diethylbenzene. X is particu-Larly preferably longer-chain, branched alkylene with, for example, 8 to 30 C at~ms~
X in formula III asan aliphatic radical can also be a ~ 3 ~

polysiloxane radical of the formula ~ R18 R18 9 ~sio~si~ 9_ ~ l17 J l17 ;n which R18 and R17 are C1-C6-alkyl, in particular methyl~ or phenyl, R19 ;s cycloalkylene, for example cyclo-hexylene, and in particular C1-C12-, especially C1-C6-alkylene, for example 1,3-propylene or 1,4-butylene, and x is a rational number of at least 1, for example 1 to 100, preferably 1 to 10~ Such diamines containing this radical are described in U.S. Patent Specification 3,435,002 and U.S.
Patent Specification 4,0~0,948.
The aliphatic radicals interrupted by heterocyclic radicals can be, for example, those which are derived from N,N'-aminoalkylated hydantoins or benzimidazoles. Examples are N,N'-(r-aminopropyl)-5,5-dimethyl-hydantoin or -benz-;midazolone and those of the formula ~ CH
(~2N-(CH2)3 - ~\ ~ Rb \ ~2 in ~hich Rb is alkylene ~ith 1 to 12, preferably 1 to 4, C
atoms~ or -tCH2cHo)aCHzCH2-~ in which Rc is a hydrogen ~c atom or methyl and a is an integer from 1 to 20.
Fxamples of suitable substituents for the aliphatic radicals are hydroxyl, halide, such as F or Cl, and alkoxy ~ith 1 to 6 C atoms.
Heterocyclic diamine radicals are preferably derived from N-heterocyclic diamines, for example from pyrrolidine, indole, piperidine, pyridine and pyrrole, the N atom of ~hich can be alkylated, for example methylated. An example is N-methyl-4-amino-5-aminomethylpiperidine.
X in formula I as a divalent cycloaliphatic radical preferably contains 5 to 8 ring C atoms and is, in particu-lar, mononuclear or dinuclear cycloalkylene which has 5 to 7 ring C atoms and is unsubstituted or substituted by alkyl, ~hich preferably contains 1 to 4 C atoms. In a preferred embodiment, X as a cycloaliphatic radical is a radical of the formula ~20 i ~ 20 20 20 t ~ (CH2)q, or ~ + ~--X'-.\ + /.

in ~hich q' is O or 1, the radicals R20 independently of one another are hydrogen or alkyl with 1 to 6 C atoms and X' is a direct bond, O, S, S02, alkylene with 1 to 3 C atoms or alkylidene with 2 to 6 C atoms. R20 is preferably ethyl or methyl, X' is preferably methylene and the alkylidene preferably contains 2 or 3 C atoms, such as ethylidene and 1,1- or 2,2-propylidene.
Examples of X as cycloalkylene are: 1,2- or 1,3-cyclopentylene, 1~2-, 1,3- or 1,4-cyclohexylene, cycloheptyl-ene, cyclooctylene, methylcyclopentylene, methyl- or dimethyl-cyclohexylene, 3- or 4-methylcyclohex-1-yl, 5-methyl-3-methyl-enecyclohex-1-yl, 3,3'- or 4,4'-bis-cyclohexylene, 3,3'-dimethyl-4,4'-biscyclohexyLene, 4,4'-biscyclohexylene ether or sulfone or -methane or -2,2-propane and the radicals of bis-aminomethyl-tricyclodecane, bis-aminomethylnorbornane and menthanediamine.
X as a cycloaliphatic radical is particularly prefer-abLy 1,4- or 1,3-cyclohexylene, 2,2,6-trimethyl-6-methylene-cyclohex-4-yl, methylenebis(cyclohex-4-yl) or methylenebis-(3-methylcyclohex-4-yl).
X as an araliphatic radical preferably contains 7 to 30 C atoms. If the aromatic group of the araliphatic radical is bonded to the N atoms in the radical of the formula III, 1310~

which is preferred, these aromatic groups are preferably sub-stituted in the same way as X as an aromatic radical, includ-ing the preferred substitution~ The aral;phatic radical preferably contains 7 to 30, in particular 8 to Z2, C atoms.
The aromatic radical in the araliphatic radical is preferably a phenyl radical. X as an araliphatic radical is, in parti-cular, aralkylene which is unsubstituted or substituted on the aryl by alkyl, the alkylene radical being linear or branched. In a preferred embodiment, the araliphatic radical has the formula ~20 in which the radicals R20 independently of one another are hydrogen atoms or, in particular, alkyl with 1-6 C atoms and the symbols r are integers from 1 to 20.
The free bond can be in the o-position, m-position and, in particular, in the p-positior, relative to the CrH2r group, and one or both radicals R20 are preferably bonded in the o-position re~ative to the free bond.
Examples of X as an araliphatic radical are: m- or p-benzylene, 3-methyl-p-benzylene, 3-ethyl-p-benzylene, 3,5-dimethyl-p-benzylene, 3,5-diethyl-p-benzylene, 3-methyl-5-ethyl-p-benzylene, p-phenylenepropylene~ 3-methyl-p-phenylene-propylene, p-phenylenebutylene, 3-ethyl-p-phenylenepentylene and, ;n particular, longer-chain phenylenealkylene radicals, ~hich are described, for example, in A-0,069,062: 6-(p-phenylene)-6-methylhept-2-yl, 6-(3'-methyl-p-phenylene)~6-methylhept-2-yl, 6-t3l-ethyl-p-phenylene)-6-methylhept-2-yl, 6-(3',5'-dimethyl-p-phenylene~-6-methylhept-2-yl~ 11-(p-phenylene)-2,11-dimethyl-dodec-1-yl and 13-(p-phenylene~-?,12-dimethyltetradec-3-yL.
X can also be an aromatic radical in which t~o aryl nuclei, in particular phenyl, are linked via an aliphatic ~ 3 ~

group. This radical preferably has the formula ~)<.=./ \.=,/

in which the free bonds are in the p-, m- and, in particular, o-position relative to the Q' group and Q' is C1-C12-, in particular c1-c6-alkYlene~ which can be interrupted by 0 or S. ~xamples of Q' are ethylene, 1,2- or 1,3-propylene, butylene, -CH2-0-CH2, -CH2-S-CH2- and -CH2CHz-0-CH2CH2.
Particularly preferred copolyimides are those with structural elements of the formula III in which X is substi-tuted aromatic radicals. The substituent on the aromatic radical preferably contains 1 to 20, in particular 1-12 and especially 1-6 C atoms. The substituent is, in particular, C5- or C6-cycloalkyl, l;near or branched alkyl, alkoxy, alkoxyalkyl, alkylthio, alkylthioalkyl, hydroxyalkyl, hydroxyalkoxy or hydroxyalkylthio with 1 to 6 C atoms, benzyl, trimethylene or tetramethylene. The preferred alkoxyalkyl is alkoxymethyl and the preferred alkoxy is methoxy.
Examples of the substituents are: methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, octyl, dodecyl, tetradecyl, eicosyl, methoxy, ethoxy, propoxy, butoxy, pent-oxy, hexoxy, methoxymethyl, methoxyethyl, ethoxymethyl, propoxymethyl, butoxymethyl, benzyl, methylbenzyl, phenyl-ethyl, methylthio, ethylthio, hydroxyethyl, methylthioethyl and hydroxyethylthio. Preferred radicals are methoxymethyl, ethoxymethyl, methyl, ethyl, n-propyl, i-propyl, trimethylene and tetramethylene, cyclopentyl and cyclohexyl. Methyl, ethyl and i-propyl are particularly preferred. The substi-tuted aromatic radical can be a mononuclear or polynuclear, in particular dinuclear, radical. Mononuclear radicals can contain 1 to 4, preferably 1 or 2, substituents and dinuclear radicals can contain up to 4, preferably 1 or 2, substituents in each nucleus. It has been found that copolyimides have a high photosensitivity if one or two substituents are bonded in the ortho-position relative to the N atom. Substitution 1310~

in the ortho-position is therefore preferred. The aromatic radical is preferably bonded in the meta- or para-position relative to the N atom.
X as a substituted aromatic radical can contain 7 to 30, in particular 7 to 20, C atoms. The aromatic radical is preferably a hydrocarbon radical, for example phenylene, naphthylene or bisphenylenes, or a pyridine radical, these being substituted as defined above.
A preferred sub-group are those aromatic radicals of the formulae ~20~.i / ~ /' .~ ;

20 . . . 20 20- ~ 20 20 ~ 20 R -1~ U ~ RR ~R ~ R ~ . R

R ~ R21 +
il 1 \ X
./ \-/ ~20 or +R20 +

R R20 R20 ,~o in ~hich R20, in the case of monosubstitution, is alkyl ~ith 1 to 6 C atoms and the other radicals R20 are hydrogen, and 1 3 ~

in the case of di-, tri- or tetra-substitution, two radicals R20 are alkyl with 1 to 6 C atoms and the other radicals R20 are hydrogen atoms or a~kyl with 1 to 6 C atoms, or in the case of di-, tri- or tetra-substitution, two vicinal radicals R20 in the phenyl ring are trimethylene or tetra-methylene and the other radicals R20 are hydrogen atoms or alkyl with 1 to 6 C atoms, Y" is 0, S, NH, CO or CH2, R21 is a hydrogen atom or alkyl with 1 to 5 C atoms and R22 is alkyl with 1 to 5 C atoms, and Z" is a direct bond, O, S, SO, S02, O O
CO, CO, CNR23, NR23, CONH, NH, R23SjR24, R230sjoR24 ~ I ~
--si -Sit R24 ~ ~4/i alkylene with 1 to 6 C atoms, which can be interrupted by -O-or -S-, alkenylene or alkylidene with 2 to 6 C atoms, phenyl-ene or phenyldioxyl, in which R23 and R24 independentlY f one another are alkyl with 1 to 6 C atoms or phenyl and j is 1-10, in particular 1-3~ Z" can furthermore have the formula f ~)g ~ 117 ~ S - (CH2) -(G)f-;n which G is S or, in particular, O, f is O or, in particu-lar, 1, 9 is 1-6 and h is 1 to 50, in particular 1 to 10, and R18 and R17 are as defined above, or can be a radical of the formula O O R25 o o R250 in which K is -C - C-, -CR25-C- or -C-N -C-,where R25 is H, C1-C6-alkyl or phenyl. R21 and R22 are preferably methyl, 13106~

Y" is preferably -CH2- or -O- and Z" is preferably a direct bond, -O-, -CH2- or alkylidene with 2 to 4 C atoms. R23 and R24 are, in particular, methyl, ethyl and phenyl. The alkylene preferably contains 2 to 4 C atoms and ;s, in par-ticular, ethylene, Alkenylene is, in particular, ethenylene A preferred sub-group are toluylene radicals and radicals of o,o'-substituted diaminodiphenylenes, diaminodi-phenylmethanes and diaminodiphenyl ethers.
A particularly preferred group are those aromatic radicals of the formulae 3 \.~ \ / / ~ /
/ ~ XCH H3C~ ~i 3 o H C ~ ! CH CH3 ! CH
'! ~ !'! ~ ! '! ~ i "
H3C ~~ CH3 c~

Z"'~ -C H or _.~ ?~
R2~ R CH/3- =-in ~hich Z"' ;s a direct bond, O or, in particular, CH2 and R26 is a hydrogen atom, methyl, ethyl or isopropyl.
Examples of substituted aromatic radicals X are: 4-methyl-1,3-phenylene, 4-ethyl-1,3-phenylene, 2-methyl-1,3-phenylene, 4-benzyl-1,3-phenylene, 4-methoxymethyl-1,3-phenylene, tetrahydro-1,3- or -1,4-naphthylene, 3-propyl-1,3-or -1,4-phenylene, 3-isopropyl-1,4-pheny~ene, 3,5-dimethyl-1,4-phenylene, 2,4-dimethyl-1,3-phenylene, 2,3-dimethyl-1,4-phenylene, 5-methyl-1,3-phenylene, Z,3,5,6-tetramethyl-1,4-or -1,3-phenylene, 3-methyl-2,6-pyridylene, 3,5-dimethyl-2,6-131~

pyridylene, 3-ethyl-2,6-pyr;dylene, 1-methyl-2,7-naphthyLene, 1,6-dimethyl-2,7-naphthylene, H3C o CH3 , .i \. 2 \ . _ . \ . _ . /

o_~ ~ CH2 ~
.=. .=. .=.~ .--.
\.
_ \ / \ /

._Q. . . ~ 3 \. ./ ~/' \ /

\._. ._ / 3 . ~ CH2-.~ ~ -S-.

\ _ _ \ / \ /
( ~3 ~C17 ( 3 ~C~3 C1~7 ( ii3 CH~

- C~'3 CH3 CH3 2 CH3 CH3 and A\ /C \ ~ C\
--\ /--- E ~ - , A-~ E ~ -D
B/ b 1 ~ 5 1 E ~ D , ~ -E--~ ~--C and B A

A--~ ~--E-~ -C

in which A, B, C, D and E are as defined in the follswing table. The free positions in the phenyl nuclei here can be occupied by one or two other substituents G or H in each nucleus, and G or H can have the meaning of A to D given in the following table:

11 310~1 - 15 ~

_ I A - a ~ = ~ .

CH2 !Icth) l !Icthyl H H
C112 ;Ictllyl Ethyl H H
CH2 Ethyl . Ethyl H H
C112 Isopropyl Isopropyl H H
C112 letllo:c~ methyl H H
CH2 Benzyl Bcnzyl H H
.CH2 ~Icthyl ~lethyl~lethyl H
CH2 Ethyl EthylEthyl H
CH2 Iso?ropyl Isopropyl :lethyl ~:ethyl 2 ~le tho~:~ methyl ~lethyl H
CH2 `Icthyl ¦ Ethyl ~lethyl H
CH2 ~le tho~:yme thy 1 ~le tho~ ?. ~ thy 1 CH2 ;le thyl ile thyl ~Ictllyl le thyl . C~2 Ethyl EthylEthy~ Ethyl Cll2 ~lethyl ilethyl Ethyl Ethyl CH2 Ethyl EthylIsopro?ylIsopropyl CH2 Isopropyl Isopropyl Isopropyl Isopropyl CH2 Isopropyl Isopropyl `lethyl H
Cll2 l~letho.:y ~letho:iy ~ ethyl ethyl O ~lethyl ~lethyl H H
O Ethyl Ethyl H H
O ~le thy 1 ~lethy I ~le thyl H
O ~lethyl l~lethyl ~lethyl l~lethyl O l~lethyl ~lethyl Ethyl Ethyl . S !~le thv I I ~le thyl H H

1310~51 E E~hy Ethyl Il S Methyl Methyl H H
S Mcthyl Methyl ~5ethyl Mcthyl S Ethyl Ethyl Ethyl Ethyl S ~ethyl Methyl Ethyl Ethyl CO ~5ethyl ~lethyl ~ethyl H
CO Methyl ~5ethyl H H
CO Methyl Methyl Methyl Methyl S2 Mctllyl Methyl Et hy l H
S2 Methyl Methyl H H
S02 ~Sethyl Methyl Methyl Methyl S2 Ethyl Ethyl Methyl ~le;hyl SO Methyl Methyl Methyl ~lethyl SO I~lethyl Methyl H H
COO Methyl Methyl H H
COO Methyl Mcthyl Methyl ~5ethyl CO~CH3 Methyl Methyl H H
~CH3 Methyl ;~5ethyl Ethyl Ethyl XCH3 Methyl Methyl Methyl ~5ethyl CO~H `lethyl Methyl _ ~H Ethyl ~lethyl Ethyl ~5cthyl ~H Methyl M2thyl ~lethyl Methyl - 17 - 1310~51 E ~ ~ =
Si(;lethyl)2 ~lethyl "Icthyl H H
Si(Phcnyl)2 Methyl llcthyl Mcthyl ~Icthyl Si(O!iethyl)2 Ethyl Ethyl H H
si(OPhenyl)2 'lethyl Methyl Methyl ~lethyl -OSi(~lethyl)20- Mcthyl l~lethyl ~lethyl llethyl Ethylene ~le~hyl ~Scthyl H H
Ethylene ~lethyl Methyl `letl1yl ~lethyl Ethylene Ethyl Ethyl H H
Ethylene llcthyl ~Icthyl Ethyl Ethyl Phcnylcne ~lethyl ~lethyl Methyl ~lethyl Phcnylcne Ethyl Ethyl H H
3 2 < .~Sethyl Ethyl Methyl Ethyl (CH3)2C< ~ethyl ~lethyl ~lethyl ~Ic.hyl (CF3)2C\ ~lethyl ~lethyl Methyl Methyl Direct bond ~!ethyl ?~lethyl H H
Direct bond ~lethyl Ethyl ~lethyl Ethyl D;`rect bond ?~lethyl Ethy~ ~lethyl H
Direct bond Ethyl Ethyl Ethyl EthylDirect bond Methoxy ~ethoxy ~lethoxy ~Sethoxy Direct bond Isopropyl Isopropyl H H
D;rect bond ~lethox~ethyl ~Icthox~methyl ~lethoxy~ethyl Hethoxy~ethyl X ;n formula III can also be an arylene radical which ;s unsubst;tuted or substituted by F or Cl. It can have the formula ~ 27 ./ ~

in uhich R27 is a direct bond, -0-, -S-, -S0-, -S02- or -C0- and the free bonds are ;n the ortho- or para-position, and q is 0 or 1. Examples are m- or p-phenylene, 3,3'- or 4,4'-bisphenylene, 3,3'- or 4,4'-bisphenylene ether or thio-ether or -benzophenone and 3,3'-dichlorobenzidine.
It is known that some aliphatic and aromatic di-am;nes, for example phenylenediamine or di(aminophenyl)-methane, may promote the insolubility of polyimides. Such diamines are therefore preferably employed in smaller amounts.
In particular, in this case, the structural elements of the formula I are present in amounts of at least 50 mol %, in particular 80 mol % and especially 9û mol X.
Z as a tetravalent aromatic radical preferably con-tains 6 to 30, in particular 6 to 20, C atoms. In a pre-ferred sub-group, Z has the formula ~ ,!, ~' ~ , ! '! l! 'i ~ C~3 .=./
,-=., '.=., ,i!, ~!, ,! ~.-.~
~ 'CÇ;\C~3 13106~1 ,.-..~
R28 ./ X' ~ l or ll in which R28 is a direct bond or a bridge group of the formula --O-- --5-- --SO-- --C~; , --C--o--, --~;--, --Si--, R30 R30 R30 o --o--si--o--, --~--,--o--~--o--, .~=!;, ~;=.~--, --C-- , R31 o o O

o ~ R29 ~29 C-.~~, -CH2-' -CH CH -, -C~-, -C-or -0~ 0- \f /-~\ X~
\. ./ --O

in which R29, R30 and R31 are alkyl ~ith 1 to 6 C atoms, phenyl or benzyl and R3û and R31 are alkoxy with 1 to 6 C
atoms, phenyloxy or benzyloxy.
In the above formulae, in each case two of the free bonds are always in the peri- andlor ortho-position.
A preferred sub-group of Z are radicals of the formulae \ ~ \ / or --~ ~--R28~
/ ~./ \ X,=./ \ =./--" ~310~51 in which R28 is a direct bond, -0-, -S02-, -CH2- or, in particular, -C0-.
Especially preferred radicals are those of the formulae \,/ ~ / .=, ._.
~ \ and ~._.~ \.=,/

or mixtures thereof. The free bonds in the benzophenone radical are in the ortho-posi~ion.
Examples of tetracarboxylic acid anhydrides uith a radical Z are: Z,3,9,10-perylenetetracarboxylic acid di-anhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhyd-ride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4~5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene~1,4,5,8-tetracarboxylic acid dianhydride, phenanthrene-1,8,9,1~-tetracarboxylic acid dianhydride, pyromellitic acid dianhyd-ride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride~
2,2',3,3'-biphenyltetracarboxylic acid dianhydride, 4,4'-isopropylidenediphthalic acid anhydride, 3,3~-isopropylidene-diphthalic acid anhydride, 4,4'-oxydiphthalic acid anhydride, 4,4'-suLfonyldiphthalic acid anhydride, 3,3'-oxydiphthalic acid anhydride, 4,4'-methylenediphthalic acid anhydride, 4,4'-thiodiphthalic acid anhydride, 4,4'-ethylidenediphthalic acid anhydride, 2,3,6,7-naphthalenetetracarboxylic acid di-anhydride, 1,~,4,5-naphthalenetetracarboxylic acid dianhyd-ride, 1,2,5, 6-naphthalenetetracarboxylic acid dianhydride, ben~ene-1,2,3,4-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid d;anhydride, 1-(3',4' dicarboxy-phenyl~-1,3,3-trimethylindane-5,6-dicarboxylic acid dianhyd-ride, 1-(3',4'-dicarboxyphenyl)-1,3,3-trimethylindane-6,7-dicarboxylic acid dianhydride, 1-(3',4'-dicarboxyphenyl)-3-methylindane-5,6-dicarboxylic acid dianhydride, 1-(3',4'-dicarboxyphenyl)-3-methylindane-6,7-dicarboxylic acid di-anhydride, 3,3',4,4'-benzophenonetetracarboxylic acid anhyd-ride and 4,5,3',4'-benzophenonetetracarboxylic acid anhydride.

-```` 131~

It has furthermore been found that a higher photo-sensitivity is achieved ;n copolyimides if Z is the tetra-valent radical of an aromatic ketotetracarboxylic acid, and especially also if X is a substituted aromatic radical as defined above. Such copolyimides are a preferred sub-group.
Radicals of such ketocarboxylic acids are present, in parti-cular, if smaller amounts of structural elements of the formula I are present. A particularly preferred radical is o ~-\ /c\ /-~! i! i! !

in ~hich the free bonds are in the ortho-position relative to one another~ `
Other preferred radicals of ketocarboxylic acids have the formulae VIII to XI
o ~I ~ O

I 11 1 (VIII), ~ C~ (IX) _ . . . ~, O O
~ (X) and \ / \ / (XI), in ~hich T is a direct bond, -S-, -O-, -CH2-, -CO-, -NH-, NR -, -SO-, -So2-, -CHR32- or -CR32R33_ and R32 and R33 are C1_c6_alkyl~ phenyl or benzyl, and the free bonds are in the ortho-position relative to one another~
Z' in formula IIIa is preferably a radical of the formula ~ 31~$~l ~ t . or ~ R12 .~

in which R1Z is a bridge group or a direct bond and t~o free bonds are in the ortho-position relative to one another.
R1~ as a bridge group is preferably -O-, -S-, -C3- or -CH2-, or alky~idene with Z to 6 C atoms, cyclopentylidene or cyclohexyLidene.
Application No 495,286 also relates to a process for the preparation of polyimides containing structural elements of the formula I according to claim 1, which comprises sub-jecting at least one aminodicarboxylic acid of the formula IV
o- O COOH
Il f ~-~ "\ .~
H2~-R-C- ~./ ----~ COOH (IV) ~R )m ~ R2 by itself or together ~ith at least one amincdicarboxylic acid of the formula V

H N-Z'/ (V) COOH

and/or at least one tetracarboxylic acid of the formula VI
HOOC COOH
\z/ (VI ) HOOC COOH

or polyimide-forming derivatives thereof, and at least one diamine of the formula VII

HZN-X-NH2 (VII) in which R, R1, R2~ Z, Z', X, m, n and p are as defined 1310~1 above, to polycondensation and cyclisation in a manner which is knoun per se.
Instead of the tetracarboxylic acids and aminodi-carboxylic ac;ds, it is also possible to use their poLyimide-forming derivatives, for example their esters, amides, halides, ;n particular the chlorides, and anhydrides.
The amino~icarboxylic acids of the formula IV are novel and are an object of the present invention. They can be obtained, for example, in the following manner:
Mellitic acid n-butylimide is converted with 502Cl2 into O .
ClOC~ C~
i! ! ,N -n-BU ty 1 \-~ \C/
o and this is reacted in the presence of AlCl3 uith .~(R )m to give o O
./c\
~ ~n-Butyl This compound is nitrated ~ith HN03 and the nitro compound formed is hydrogenated catalytically to the desired amino compound -" 131~51 H2N~ ~ n-Butyl (R ) 11 o The imide can be converted ;nto ;ts acid derivat;ves in a known manner.
4,4'-Ketobis-(naphthalene-1,2-dicarboxylic acid) can be obtained by reacting 2 moles of 1,2-dimethylnaphthalene w;th COClz in the presence of AlCl3 and subsequent~y oxidising the 4,4'-ketob;s(1,2-d;methylnaphthalene) formed ~ith HN03 to give the tetracarboxylic acid This tetra-carboxylic acid can be partially hydrogenated to 4,4'-keto-(tetrahydronaphthalene-1,2-dicarboxylic acid). The hydro-genation can a~so be carried out before the oxidation with 4,4'-ketobis(1,2-d;methylnaphtha~ene).
Tetracarboxylic ac;ds with structural elements of the formula IV are known in some cases.
Anthraqu;nonetetracarboxylic acids are described, for example, in U.S. Patent 3,702,318 and CA 100,1006119a (1984).
Hydrogenation of the keto groups in anthraquinone-tetracarboxylic acids w;th, for example, Na~H4 gives the correspond;ng dihydroxy compound, which can be converted into anthronetetracarboxylic acid by treatment with hydrochloric acid under reflux. The CH2 group of anthronetetracarboxylic acid can be alkylated in a known manner and thus converted nto the CHR3Z or CR32R33 group.
To prepare fluorenonetetracarboxylic acid, for example, 3,4-dimethyl-magnesium bromide can be dimerised in the oresence of CuCl2 and the 3,3',4,4'-tetramethylbiphenyl formed can be reacted with COClz in the presence of AlCl3 to g;ve tetramethylfluorenone, which can be oxidised to the tetracarboxylic acid in a known manner with, for example, Xanthonetetracarboxyl;c acid is obtained by first ~310~1 converting 3,3',4,4-tetramethylphenyl ether into 2,3,6,7-tetramethylxanthone with CCl4 in the presence of AlCl3 and subsequent hydroLysis uith dilute HCl, and oxidising the pro-duct to the tetracarboxylic acid in the customary manner, for example with H~03.
Tetracarboxylic acids with structural elements of the formula YIII in which T is S, SO, S02 or NR32 can be obtained by the following route: 1-bromo-3,4-dimethylbenzene is reacted with CCl4 in the presence of AlCl3 to give bis-(2-bromo-3,4-dimethylphenyl)dichLoromethane.
Oxidation with 20% HN03 gives HOOC~ ~ BrBr\ ~ COOH
'! ! ! '!
HOOC ~ \ C/ ~- COOH
O
Reaction with Na2S gives thioxanthonetetracarboxy-lic acid, which can be oxidised to the sulfoxide or sulfone in a known manner. Reaction with NaNH2 or R32NH2 gives the acridonetetracarboxylic acids.
Aminadicarboxylic acids of the formula V and diamines of the formula VlI, and tetracarboxylic acids of the formula VI are known, are commercially available or can be prepared by known processes. Si-containing diamines are described in U.S. Patent Specification 3,435,002 and A-0,054,426.

Diamines with the -N/ \N- group can be prepared o from the diisocyanates described in A-2,318,170 Dia-mines substituted by alkyl or cyclo alkyl, in parti-cular ethyl or propyl, are accessible by alkylation of unsubstituted or partly substituted aromatic diamines with alkenes or cycloalkenes (c.f. U.S. Patent Specifi-cation 3,275,69û)o Polynuclear, especially dinuclear, aromatic diamines can be obtained via condensation ~310~

of corresponding monoamines with aldehydes or keto~es.
The polyimides according to Application No. 495,286 have average molecular weights (weight-average Mw) of at least 2,000, preferably at least 5,000. The upper limit depends largely on the properties which determine the processability, for examp~e their solubility. It can be up to 500,000, preferably up to 10û,000 and in particular up to 60,000. The polyimides can furthermore be random polyimides or block polyimides. They are prepared by customary processes in devices envisaged for this purpose. The reaction is advan-tageously carried out in solution; suitable inert solvents are listed below. The reaction temperatures can be -2a to 300C.
Specifically, a procedure is advantageously followed in which the aminodicarboxYlic acid anhydrides, tetracarboxy-lic acid dianhydride and diamine are first reacted to form a polyamide acid intermediate and this polyamide acid is then cyclised, water being detached. Cyclisation can be by means of heat. The cyclisation is advantageously carried out under the influence of dehydrating agents, for example carboxylic acid anhydrides, such as acetic anhydride. The polyimides can then be ;solated by customary processes, for example by removal of the solvent or by precipitation by adding a non-solvent.
Another preparation method comprises reacting the tetracarboxylic acid dianhydride with a diisocyanate in one stage to give the polyimide.
The polyimides according to Application No. 495~286 are soluble in various solvents, if necessary with warming, and they have high glass transition points. They are outstandingly suit-able for the production of films and protective coatings, and coating agents can be used from a solution of the polyimide in a solvent. The App~icat;orl No. 495 286 also relates to the use of the polyimides according to the said invention for the produc-tion of protective coatings and films.
To produce the coated material, the polymer or mix-tures thereof is advantageously dissolved in a suitable 131~g~.

organic solvent, if necessary with warming. Examples of suitable solvents are polar, aprotic solvents, which can be used by themselves or as mixtures of at least two solvents.
Examples are: ethers, such as dibutyl ether, tetrahydro-furan, dioxane, methylene glycol, dimethylethylene glycol, dimethyldiethylene glycol, diethyldiethylene glycol and di-methyltriethylene gLycol, halogenated hydrocarbons, such as methylene chloride, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane and 1,1,2,2-tetrachloroethane, carboxylic ac;d esters and lactones, such as ethyl acetate, methyl propionate, ethyl benzoate, 2-methoxyethyl acetate, ~-butyro-lactone, o-valerolactene and pivalolactone, carboxylic acid amides and lactams, such as formamide, acetamide, N-methyl-formamide, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, ~-butyrolactam, -caprolactam, N-methylpyrrolidone, N-acetylpyrrolidone, N-methylcaprolactam, tetramethylurea and hexamethylphosphoric acid amide, sulfoxides, such as dimethyl sulfoxide, sulfones, such as dimethyl sulfone, diethyl sulfone, trimethylene sulfone and tetramethylene sulfone, trimethylamine, triethyl-amine, N-methylpyrrolidine, N-methylpiperidine, N-methylmor-pholine and substituted benzenes, such as chlorobenzene, nitrobenzene, phenols or cresols.
Undissolved constituents can be removed by filtra-tion, preferably pressure filtration. The concentration of polymer in the coating agent thus obtained is preferably not more than 50X by weight, in particular not more than 30X by weight and especially not more than 20X by weight, based on the solution.
Other customary additives which do not adversely influence the photosensitivity can be incorporated during preparation of the solutions. Examples of these are matting agents, flow control agents, fine-particled fillers, flame-proofing agents, fluorescent brighteners, antioxidants, light stabilisers, stabilisers, dyes, pigments, adhesion promoters and antihalo-dyes, such as are described, for example, in U.S. Patent Specification 4,349r619.

- ~31~

The coating agent can be applied to suitable sub-strates or carrier materials by customary methods, such as dipping, brushing and spray;ng processes or by whirler, cas-cade and curtain coating. Examples of suitable substrates are plast;cs, metals and metal alloys, semimetals, semicon-ductors, glass, ceramics and other inorganic materials, for example SiO2 and Si3N4. The solvent is then removed, if neressary by uarming and if necessary in vacuo. Tack-free, dry, un;form f;lms are obtained. The films applied can have coating thicknesses of up to about S00 ~m or more, preferably from 0.5 to 500 ~m and especially from 1 to 50 ~m, depending on the applicat;on.
Protective films of such polyimides can be further modified by the action of radiation, increased heat stabili-ties, for example, thereby being possible. There is also the possibility of using such polyimides as photographic record-;ng material for relief ;mages. Additives such as sensi-tisers can be avoided by direct crossl;nk;ng under the in-fluence of radiation, and the protective coatings and images have excellent electrical properties. The protective coatings and images are furthermore distinguished by their high heat stability and by only little shrinkage, if at all, uhen exposed to heat, which is of considerable advantage during use because virtually no distortion of the structures re-produced is observed.
Application No. 495~286 also relates to a carrier material coated ~ith such polyimides and the use of this material for the production of protective coatings and photographic relief images. The coating thickness for this application is pre-ferably O.S to 100lum, in particular 1 to 50 ~m and especi-ally 1-10~um.
Photostructuring or pho~ocrosslinking can be caused by high-energy rad;at;on, for example by light, especially in the UV range, or by X-rays, laser light, electron beams and the like. The material according to Application No. 495,286 is outstandingly suitable for the production of protective films and passivating lacquers and as photographic recording 1310~51 .

material for heat-stable relief images.
Examples of fields of use are protective, insulating and passivating varn;shes in electrical engineering and electronics, photo-masks for electronics, textile printing and the graphics industry, etch resists for the production of printed circuits and printed circuit boards and integrated switch;ng circuits, relays for the product;on of X-ray masks, solder-stopping varnishes, dielectrics for multilayer cir-cuits and structural elements for liquid crystal displays.
Protective films are produced by direct exposure, the exposure times largely depending on the coating thicknesses and the photosensitivity.
Photographic production of the relief structure is effected by image-wise exposure through a photo-mask and subsequent development, removing the non-exposed portions with a solvent or a solvent mixture, after which, if approp-riate, the image produced can be stabilised by after-treat-ment with heat.
Application No: 495,286 also re~ates to such a process for the application of relief structures. The abovementioned sol-vents, for example, are suitable as developers.
The polymer coating of the material accarding to Appli-cation No. 495,286 has a photosensitivity which is sufficient for many applicat;on purposes and in some cases is high, and it ran be photocrosslinked directly. The protective films and relief images are distinguished by a high adhesion and resistance to heat, mechanical stresses and chemicals. Only slight shrinkage is observed during after-treatment with heat. Additives for producing or increasing photosensitivity can furthermore be avoided. The material is stable on stor-age, but should advantageously be protected from the effect of light.
The following examples illustrate the invention in more detail. The glass transition temperatures are deter-mined by differential scanning calorimetry.

13106~

A) Preparat;on of the starting substances Example a) Preparation of \ / 3 H2N~ D C~
C~ \CH ~9/ \COO~

1) - 68.5 g of n-butylamine are added dropwise to a solu-tion of 185 9 of trimellit;c anhydride in the course of 15 minutes. The mixture is then heated to the boiling point and some of the solvent is distilled off, together with the uater of reaction. The solution which remains is poured into water and the product which has precipitated is filtered off and dried.
The dry product is then heated to the reflux tempera-ture with 265 ml of thionyl chloride in the course of one hour and the mixture is kept at this temperature for a further 2 hours. When the excess thionyl chloride has been removed by distillation, the residue is recrystallised from one litre of cyclohexane. The yield of pure trimellitic acid n-butylimide-chloride (A) is 168.9 9, melting point 77-78C~
2) 1S.5 g of Durol and 56 9 of AlCl3 in 150 ml of CS2 are introduced into a flask and 28 g of A are added in por-tions in the course of 15 minutes. After one hour, the mix-ture is poured onto ice-water and 100 ml of concentrated HCl are added.
The organic layer is separated off~ the aqueous layer is extracted with CH2Cl2 and the combined organic phases are washed with water, dried over Na2so4 and evaporated to dryness. The residue is boiled up with 200 ml of ethanol, the mixture is filtered hot and the filtrate is cooled. S-(2,3,5,6-Tetramethylbenzoyl)-phthalic acid n-butylimide (B) thereby precipitates as crystals. After filtering off and drying, 20.5 9 of product ~3 with a melting point of 127C
are obtained.

```` 1310~

Elemental analysis:
calculatedfound C76.01 76.2 H6.93 7.0 N3.85 3.7 013.21 13.2 3) 17 9 of product B are added in portions to a mixture of 48 ml of concentrated H2S04 and 40 ml of 65X HN03 at O to 2C. When the addition has ended, the mixture is stirred at 0C for a further 2 hours, the somewhat cloudy solution is filtered and the filtrate is poured onto ice-water. The 5-(4-nitro-2,3,5,6-tetramethylbenzoyl)phthalic acid n-butylimide (C) which has precipitated is filtered off, washed with water and dried, and, without further purifica-tion, is hydrogenated in dimethylformamide with hydrogen under catalysis by Raney nickel under atmospheric pressure.
The hydrogenation product is purified over a coLumn 50 cm long and 10 cm thick filled with silica gel 60, using toluene/ethyl acetate (80/20) as the mobile phase. 8.9 9 of 5-t4-amino-2,3,5,6-tetramethylbenzoyl)phthalir acid n-butyl-imide ~D) are obtained.
4) To prepare the free dicarboxylic acid, compound D is refluxed with alcoholic KOH for 24 hours. During this treat-ment, the potassium salt precipitates gradually as the hydrolysis progresses.
The potassium salt is filtered off and dissolved in water and 2N HCl is added until the isoelectric point (pH
5-6) is reached. The 5-(4-amino-2,3,5,6-tetramethylbenzoyl)-phthalic acid (E) which thereby precipitates is filtered off and dried.
Elemental analysis:
calculated found C66.85 65.66 H5.61 5.89 N4.10 4.'l2 023.44 24.01 5) 1 9 of aminodicarboxylic acid (E) is heated at 2500C

131~6~

in vacuo for 10 hours, the corresponding anhydride (F) being formed, uith water being detached.
Elemental analysis:
calculated found C 70.58 70.67 H 5.30 5.35 N 4.33 4.49 0 19.79 19.57 Example 1:
Polycondensation of E
0.5 9 of E is dissolved in S ml of m-cresol and the solution is kept under reflux (about 205C) for 4 hours.
The solution is cooled and the polyimide is precipitated with alcohol. The intrinsic viscosity is 0.41 dl/g.
Example 2:
0.5 9 of aminoanhydride F is dissolved in 5 m~ of N-methylpyrrolidone and the solution is stirred at room tem-perature for 16 hours.
0.5 ml of triethylamine and 1.3 ml of acetic anhyd-ride are then added and the mixture is stirred for a further 24 hours.
The polymer is then precipitated by stirring into water and is dried.
Intrinsic viscosity: 0.32 dl/g Glass transition temperature: 386C (differential scanning calorimetry).
Example 3:
1.642 9 of 3,6-diaminodurol are dissolved in 22 ml of N-methylpyrrolidone (NMP) in a condensation vessel and 0.45 9 of the aminoanhydride F is added, with stirring. After one hour, 3.22 9 of benzophenonetetracarboxylic acid dianhydride (~TDA) are added. Five hours later, a further 32.2 mg of ~TDA are added. After 2 hours, a mixture of 3 ml of ~ri-ethylamine and 8.5 ml of acetic anhydride is added to the polyamide acid solution and stirring is continued for 20 hours.
The polyimide ;s worked up by stirring the solution into water and filtering off and drying the product which .

precipitates.
Intrinsic viscosity: 1.04 dl/g Tg: 430C~
Application Example:
A thin film is produced on a sheet of plastic, which has been laminated with copper on one side, by whirling on a 10% solution of the polymer according to Example 1 in N-methylpyrrolidone and then removing the solvent in a cir-culating air oven. The sheet thus coated is then exposed through a photo-mask (Stouffer wedge) at room temperature with a UV lamp (1,000 watt) from a distance of 18 cm for 360 seconds.
The exposed sheet is developed with N-methylpyrroli-done, the non-exposed portions being dissolved away. The relief image is then rendered visible by etching away the exposed copper layer with FeCl3 solution.
The photosensitivity according to the "21 step Stouffer sensitivity guide" is 4 steps.
The copolyimide according to Example 3 has a photo-sensitivity of 7-8 steps using the same method with an exposure time of Z0 seconds.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An aminodicarboxylic acid of the formula IVa (IVa), in which R4, R5, R6 and R 7 are C1-C4-alkyl, or the polyimide forming derivatives thereof selected from the group consisting of the esters, amides, halides and anhydrides.

2. An acid according to claim 1 in which R4 , R5 , R6 and R7 are methyl or ethyl.

3. The acid according to claim 1 which is 4. The acid anhydride according to claim 1 which is