Polyimides from 4-(3-aminophenoxy)benzoic acid

Thermoplastic poly(imide-esters) and poly(imide-amides) with repeat units derived from the title amino acid. In the polymer the amino group becomes part of an imide group and the carboxyl group becomes part of an ester or amide group. The polymers have a good balance of properties, making them useful for melt forming shaped articles, films and fibers.

FIELD OF THE INVENTION 
This invention concerns poly(imide-esters) and poly(imide-amides) prepared 
using 4-(3-aminophenoxy)benzoic acid, a cyclic aromatic (di)carboxylic 
anhydride, and a diol or Ddiamine, or their reactive equivalents. These 
polymers are useful as molding resins and fibers. 
TECHNICAL BACKGROUND 
Polymers having a combination of high strengths and moduli, good high 
temperature properties, and ease of preparation are always of interest for 
typical thermoplastic uses, such as molding resins and fibers. Disclosed 
herein are poly(imide-esters) and poly(imideamides), which have such 
properties, and are particularly easy to form into useful shapes by melt 
processing. These polyimides are based on 4-(3-aminophenoxy)benzoic acid 
(herein sometimes abbreviated as APBA) as one of the monomeric units. 
Polyimides made with this repeat unit usually have an exceptional balance 
of good physical properties and melt formability. 
German Patent 3,910,276 describes a preparation of (3-aminophenoxy)benzoic 
acids. It generally states that they may be used in polymers. 
SUMMARY OF THE INVENTION 
This invention concerns thermoplastic, comprising, a poly(imide-ester) or a 
poly(imide-amide), which contains a repeat unit of the formula 
##STR1## 
wherein the nitrogen atom is part of an aromatic imide group, and the 
carbonyl group is part of an ester or amide group. 
DETAILS OF THE INVENTION 
The present invention concerns certain thermoplastic polyimides. By 
thermoplastic herein is meant that the polyimide has a glass transition 
temperature (Tg) and/or melting point (Tm) above ambient temperature 
(usually taken as about 25.degree. C.), and may be melt processed at a 
temperature below which significant thermal degradation takes place. This 
would normally mean it is melt processable at a temperature of about 
400.degree. C. or less. It is preferred if the polyimides herein are 
isotropic (not liquid crystalline in the melt). 
The instant polyimides contain an "aromatic imide group". By this is meant 
that in the imide grouping, 
##STR2## 
the bond marked "a" will be part of an aromatic ring. Since imides are 
most commonly made from cyclic anhydrides, at least some of the imide 
groups in the instant polyimides could be said to be derived from cyclic 
aromatic carboxylic anhydrides. As can be seen from the Examples, such 
anhydrides can be monoanhydrides or dianhydrides. 
Most commonly, cyclic imides are made from the corresponding cyclic 
carboxylic anhydrides, and herein, cyclic aromatic carboxylic anhydrides. 
In order to form a polymer, these anhydrides must be difunctional in the 
polymerization sense, i.e., contain 2 functional groups that can react to 
incorporate the anhydride into the polymer chain (except for capping 
groups, see below). Thus the anhydrides may be a dianhydride, or contain 
another functional group, preferably carboxyl. Preferred cyclic aromatic 
carboxylic anhydrides are trimellitic anhydride, pyromellitic dianhydride, 
benzophenone dianhydride, biphenyl dianhydride, oxydiphthalic anhydride, 
hexafluoroisopropylidenediphthalic anhydride, or an arylenedioxydiphthalic 
anhydride. More preferred anhydrides are trimellitic anhydride, 
pyromellitic anhydride and benzophenone dianhydride. 
At least some of the imide linkages in the polyimide contain the amino 
group in APBA. These linkages would normally be formed by reaction of this 
amino group with an aromatic cyclic carboxylic anhydride group. Imide 
linkages formed from other amino groups may also be present in minor 
amounts (less than 50 molar percent of the total number of imide linkages 
in the polymer), but it is preferred if essentially all of the imide 
linkages are formed by the amino group of APBA. 
The carboxyl group (or its reactive equivalent) is formed into an amide or 
ester group by reaction with a diamine or diol or their reactive 
equivalents, respectively. By reactive equivalent herein is meant a group 
that will react to form the desired derivative (for example ester or 
amide) group of the "parent" or "nominal" group (for instance carboxylic 
acid or amine). Included within the meaning of poly(imide-ester) and 
poly(imide-amide) are "mixed" polyimides which contain both ester and 
amide linkages in the polymer main chain (and are formed by using diols 
and diamines, and/or aminophenols as monomer units). 
While any diamine which contains primary and/or secondary amine groups may 
be used, aromatic diamines are preferred, and preferred aromatic diamines 
of the formula 
##STR3## 
wherein X is a covalent bond, --O--, --C(O)--, --CH.sub.2 --, 
--C(CH.sub.3).sub.2 --, --S--, or --S(O).sub.2 --. Similarly, any diol may 
be used, but preferred diols are aromatic diols, and an especially 
preferred diol is a substituted hydroquinone, resorcinol, a substituted 
resorcinol, 2,6-naphthalenediol, 2,7-naphthalenediol, and compounds of the 
formula 
##STR4## 
wherein X is a covalent bond, --O--, --C(O)--, --CH.sub.2 --, 
--C(CH.sub.3).sub.2 --, --S--, or --S(O).sub.2 --. Similar aminephenols 
may also be used The polyimide may be a "copolymer", for example, one or 
more diols, diamines, and cyclic aromatic carboxylic anhydrides may be 
used. When aromatic diamines and/or diols and/or aminehydroxyl compound 
are used, if the bonds connecting the two functional groups to the 
aromatic ring(s) are linear with respect to one another, and/or the 
compound is highly symmetrical, the polyimide formed is more likely to 
melt higher than 400.degree. C. Such compounds include hydroquinone, 
p-phenylenediamine and p-aminophenol. If it is desired to use such a 
monomer, simple synthesis of the desired polymer will readily determine 
with little experimental work whether the resulting polyimide is suitable 
for melt forming. 
To remove reactive end groups and/or regulate molecular weight the ends of 
the polymer may be capped by appropriate monofunctional (in a 
polymerization sense) compounds. For instance a monocarboxylic acid (e.g., 
benzoic acid), a monofunctional cyclic aromatic anhydride (phthalic 
anhydride), or a monoamine (aniline). 
The polymers described herein may be readily made by a variety of 
procedures. The polymers may be made in the melt or in solution; melt 
synthesis is preferred. Particularly for higher melting crystalline 
polymers, the polymer molecular weight may be increased by solid state 
polymerization (see Example 3). Some polymers, depending on their 
structure, can be made in a one step process from the monomers (see 
Example 8), or by a two step process (see Example 1 with Examples 3, 4, 
and 5 and Example 2 with Examples 6 and 7). If the diol used herein 
contains one or two aromatic hydroxyl groups (bound directly to an 
aromatic ring), the esters of such hydroxyl groups are readily formed from 
a reactive equivalent of those hydroxyl groups, their acetate (or other 
monocarboxylic acid) esters. Similarly, amide groups are readily formed 
from amides and carboxylic acids by using an amide of a lower 
monocarboxylic acid (e.g., acetic acid) as a reactive equivalent of an 
amine. Preparation of such starting materials is known, and some are 
illustrated in the Experiments. Methods for imidization and formation of 
the ester and/or amide linkages of the final polymer are well known to the 
art skilled, and can be used to make the instant polymers. Generally 
speaking, when a poly(imide-ester) is being made the polymerization may be 
done in one step, with the amine group to form the imide being introduced 
(as the amine) the same time the diol (or its reactive equivalent) is 
added. If a specific (in terms of which amine forms that imide and amides 
present) poly(imideamide) is desired, a two step reaction is often used, 
although a one step reaction is possible with a combination of amine (to 
form the imide) and (acet)amide to form polymeric amide linkages. 
The polyimides described herein often have an elevated Tg, and if 
crystalline, Tm (as determined by DSC). While viscous melts are produced, 
they are generally within the range needed for melt forming of various 
articles by extrusion and injection molding, for example. The polymers are 
tough and readily form fibers if they have a high enough molecular weight 
(fiber forming molecular weight). They generally start to decompose at 
relatively high temperatures, above the Tg and Tm (if present) of the 
polyimides. The polyimides may be used for films (for packaging 
applications), fibers (for fabrics and ropes), and for shaped articles 
(parts requiring good mechanical properties and/or heat resistance), and 
all of these can be formed by appropriate melt forming techniques known to 
the artisan. 
When melt formed, the polyimides described herein may contain other 
ingredients typically used in thermoplastics, such as fillers, reinforcing 
materials (e.g., glass fiber) colorants, pigments, antioxidants, other 
stabilizers, etc.

In the Examples, the following abbreviations are used: 
DMAc--N,N-dimethylacetamide 
DMF--N,N-dimethylformamide 
DMSO--dimethylsulfoxide 
DSC--differential scanning calorimetry 
EtOAc--ethyl acetate 
NMP--n-methylpyrrolidone 
TGA--thermogravimetric analysis 
TLC--thin layer chromatography 
EXPERIMENT 1 
4-(3-Aminophenoxybenzoic acid) (I) 
4-Methyl-3'-nitrophenyl ether (II) 
A stirred mixture of 1,3-dinitrobenzene (78.7 g; 0.0468 mole), p-cresol 
(39.4 g; 0.364 mole), K.sub.2 CO.sub.3 (64.5 g; 0.467 mole) , and 
tris[2-(2-methoxyethoxy)ethyl]amine (0.8 g; 2 mmol) in DMF (360 mL) was 
heated at reflux for 40 hr. Solids were removed from the cooled reaction 
mixture by filtration. The filtrate was spin-evaporated in vacuo to an 
oily residue. The residue was chromatographed on a silica gel column (750 
g) packed in and eluted with hexanes-EtOAc (4:1) (5.0 L) . Appropriate 
fractions, as determined by TLC, were combined and spin-evaporated in 
vacuo to give 75.9 g (91.0%) of an oil suitable for further 
transformation. An additional 458.8 g of this material was synthesized in 
a similar manner. 
Benzoic acids, 4-(3-nitrophenoxy)-(III) 
To a hot (90.degree. C.), stirred solution of (II) (75.6 g; 0.330 mole) , 
NaOH (30.2 g; 0.755 mole), and pyridine (600 mL) in H.sub.2 O (600 mL) was 
added KMnO.sub.4 (179.9 g; 1.138 mole) , portionwise, over 1.5 hr. The 
resulting mixture was stirred at 90.degree. C. for 18 hr. The reaction 
mixture was cooled and solids removed by filtration. The filtrate was 
washed with CH.sub.2 Cl.sub.2 (2.times.500 mL) and then spin-evaporated in 
vacuo to a solid residue. This solid was dissolved in H.sub.2 O (1.0 L) 
and the stirred solution was acidified with excess conc. HCl (40 mL). The 
resulting precipitate was collected by filtration and dried to constant 
weight in vacuo at 45.degree. C. to give 53.4 g (62.5%) of product 
suitable for further transformation. An additional 331.3 g of comparable 
material was synthesized in a similar fashion. 
Benzoic acid, 4-(3-aminophenoxy)-(I) 
A stirred suspension of (III) (55.9 g; 0.216 mole) in H.sub.2 O (1.0 L) was 
treated with NaOH (8.60 g; 0.216 mole) to affect solubilization as the 
sodium carboxylate. NaHCO.sub.3 (16.8 g; 0.200 mole) and 5% Pd.C (50% 
water-wet) (5.6 g) were added and the mixture was stirred under H.sub.2 
(70 psig) for 4 hr. The catalyst was removed by filtration. The filtrate 
was acidified to pH=5.0 using conc. HCl (.about.35 mL). The resulting 
precipitate was collected by filtration and dried to constant weight in 
vacuo at 40.degree. C. to give 45.4 g (91.7%) of crude product. Additional 
reductions were performed to give a total of 236.8 g of comparably pure 
material. The combined crude products were filtered through a silica gel 
pad (800 g) packed in and eluted with acetone (6.0 L). The eluate was 
spin-evaporated in vacuo to an oil. This oil was blended into 50% aq. EtOH 
(2.0 L) . The resulting precipitate was collected by filtration and then 
triply recrystallized from refluxing 50% aq. EtOH (3.times.2.0 L), using 
decolorizing carbon (.about.5 g) on the second and third 
recrystallizations. The purified product was dried to constant weight in 
vacuo at 40.degree. C. to give 125.1 g (52.8% recovery) of material; m.p., 
145.degree.-147.degree. C. (corr.). 
EXAMPLE 1 
N,N'-Bis(4-carboxyphenoxy-3-phenyl)pyromellitimide (IV) 
##STR5## 
(I) (9.16 g; 0.04 mole) in anhydrous DMAc (100 mL) at room temperature, 
with stirring, was treated with freshly-dried (160.degree. C./4 hr) 
pyromellitic dianhydride to give a clear brown solution. After 30 min. 
acetic anhydride (8.0 mL; ca. 100% excess), followed by anhydrous pyridine 
(7.0 mL), was added, stirred at 21.degree. C. for 30 min., then at 
90.degree. C. for 45 min. The cooled solution was combined with 300 mL 
cold water to afford a yellow precipitate. This was filtered, washed with 
DMAc, then water, and dried in vacuo at 100.degree. C. Yield 12.5 g. M.p., 
417.degree. C. by DSC. 
EXPERIMENT 2 
3,4'-Diacetamidodiphenyl ether (V) 
3,4'-Diaminodiphenyl ether (100 g) in NMP (800 mL) at 5.degree. C. with 
stirring was treated with acetyl chloride (78.5 g), whereupon temperature 
rose to 60.degree. C. After a further 20 min. stirring at room 
temperature, the solution was poured into 5 liters ice-water. A gummy pink 
solid separated but, after standing overnight and thorough washing with 
deionized water, filtration yielded 133 g white solid, m.p. 
195.0.degree.-197.5.degree. C. 
EXAMPLE 2 
4-[3-(N-Trimellitimido)phenoxy]benzoic acid (VI) 
To a solution of (I) (18.32 g; 0.08 mole) in anhydrous DMAc (160 mL) was 
added trimellitic anhydride (15.36 g; 0.08 mole) and the solution stirred 
30 min. Acetic anhydride (16 mL) followed by pyridine (14 mL) was added, 
stirred 30 min. at 21.degree. C., then at 110.degree.-115.degree. C. for 
45 min. The cooled solution was poured onto 800 mL ice-water. The gummy 
solid, which separated, yielded after several treatments with water in a 
blender, a yellowish-white solid, m.p. 282.degree.-9.degree. C. 
Recrystallization from boiling DMAc gave m.p. 284.degree.-7.degree. C. 
EXAMPLE 3 
Melt polymerization of (IV) with phenylhydroquinone diacetate 
(IV) (9.66 g; 0.0150 mole) and phenylhydroquinone diacetate (4.33 g; 0.0161 
mole; 7% excess) were polymerized in a three-necked flask equipped with an 
air-driven stirrer, distillation take-off, slow bleed of supernatant 
argon, and external heating by a Wood's metal bath. Temperature was raised 
from 240.degree. C. to 310.degree. C. under argon during 5.7 hr. Acetic 
acid was evolved but the mixture remained a solid cake. It was cooled, 
ground finely, and solid phase polymerized for 4 hr/315.degree. C./0.01 mm 
Hg to give a polymer stick temperature of 325.degree. C. and a melting 
temperature of 355.degree. C. The melt was not very viscous. Further 
heating 7 hr/335.degree. C./0.01 mm Hg did not alter its appearance as an 
opaque, brown solid but stick temperature increased to 344.degree. C. and 
melting temperature to 366.degree. C. Somewhat greater viscosity permitted 
drawing of short, brittle fibers. The polymer was insoluble in 
pentafluorophenol and o-dichlorobenzene. DSC indicated sharp crystalline 
melting at 360.degree. C. but no discernible Tg. TGA showed incipient 
weight loss at 400.degree. C. 
EXAMPLE 4 
Melt polymerization of (IV) with carbonyl-3,4'-(bisphenylacetate) 
(IV) (9.66 g; 0.0150 mole) and carbonyl-3,6'-bisphenyldiacetate (4.47 g; 
0.0161 mole; 7% excess) were polymerized as above by heating from 
140.degree. C. to 355.degree. C. during 4 hr under argon, and then at 
355.degree. C. during 3 hr at 27 Pa. The dark brown, clear polymer was 
tough and had inherent viscosity of 0.42 in pentafluorophenol. Sticking 
temperature was 260.degree. C. and melting temperature 335.degree. C. Long 
fibers were readily drawn from the melt. DSC showed Tg=214.degree. C. and 
no crystalline melting. TGA showed incipient weight loss at 450.degree. C. 
EXAMPLE 5 
Polymerization of (IV) with 3,4'-diacetamidodiphenylether 
(IV) (7.08 g; 0.011 mole) and 3,4-diacetamidodiphenylether (3.16 g; 0.011 
mole) were heated under argon with stirring from 230.degree.-300.degree. 
C. during 5 hr. The semi-solid product was cooled, ground up, and solid 
phase polymerized for 7 hr at 290.degree. C./1.3 Pa to yield a brown, 
opaque solid, insoluble in pentafluorophenol, NMP, and DMSO. Polymer stick 
temperature was 308.degree. C. and polymer melt temperature 350.degree. C. 
DSC showed Tg=223.degree. C. and crystalline melting at 365.degree. C. 
Fibers could be pulled from the melt. TGA showed incipient weight loss at 
about 370.degree. C. 
EXAMPLE 6 
Polymerization of (VI) with carbonyl (3,4'-bisphenyldiacetate) 
(VI) (7.75 g; 0.018 mole) and carbonyl (3,4'-bisphenyldiacetate) (5.63 g; 
0.018 mole) were polymerized at 200.degree.-245.degree. C. during 95 min. 
under argon, then at 245.degree.-255.degree. C. at 0.02 mm for 5 hr to 
give a clear, tough, amber-colored polymer with .eta..sub.inh =0.37 in 
pentafluorophenol. Stick temperature was 209.degree. C. and melting 
temperature 253.degree. C.; the viscous melt readily yielded fibers. DSC 
showed a Tg of 166.degree. C. on initial heat-up and 183.degree. C. on 
second heat-up, but no trace of crystalline melting. TGA showed initial 
weight loss at about 380.degree. C. 
EXAMPLE 7 
Polymer from (VI) and (V) 
(VI) (8.06 g; 0.02 mole) and (V) (5.74 g; 0.02 mole) were polymerized under 
argon at 205.degree.-260.degree. C. during 4.5 hr, then at 260.degree. C. 
for 1 hr at 1.3 Pa to give a very viscous melt. The brown, glassy polymer 
had .eta..sub.inh =0.23 in pentafluorophenol, sticking temperature of 
211.degree. C. and melting temperature of 253.degree. C. and gave fibers 
from the melt. DSC showed Tg=193.degree. C. on first cycle and 236.degree. 
C. on second cycle but no trace of crystalline melting. TGA showed 
incipient weight loss at 350.degree. C. 
The same polymer was melt polymerized further for 5 hr under vacuum at 
270.degree. C. .eta..sub.inh was now 0.46, with sticking at 242.degree. C. 
and melting at 286.degree. C. The polymer was now much tougher and readily 
gave superior fibers. Tg was now 208.degree. C. (first cycle) and 
232.degree. C. second cycle but there still was no crystalline melting 
point. 
EXAMPLE 8 
Polymer from trimellitic anhydride, (I), and phenylhydroquinone diacetate 
(single stage) 
##STR6## 
Trimellitic anhydride (9.60 g; 0.05 mole), (V) (11.45 g; 0.05 mole), and 
phenylhydroquinone diacetate (13.90 g; 0.05 mole) were polymerized at 
180.degree.-285.degree. C. during 7 hr under argon, then at 
285.degree.-300.degree. C. at 0.05 mm Hg for 5 hr. (The brittle, 
glass-like polymer at this stage melted at 225.degree. C.) Polymerization 
was continued at 310.degree.-320.degree. C. for a further 5 hr at 13 Pa to 
give clear brown tough polymer, of .eta..sub.inh =0.48 in 
pentafluorophenol, sticking temperature of 218.degree. C. and melting 
temperature of 292.degree. C. The viscous melt readily yielded long 
fibers.