Process for producing thermoplastically processable aromatic polyamide with phosphorus catalyst

The invention relates to a process for producing aromatic polyamides by melt condensation of PA1 (i) aromatic diamines of the formula EQU H.sub.2 N--Ar'--X--Ar"--Y--Ar"--X--Ar--NH.sub.2 where X=--O-- and Y=--SO.sub.2 -- or X=--SO.sub.2 -- and Y=--O-- and Ar' and Ar"=meta-, para-phenylene, which can be replaced up to 70 mole percent by an aromatic diamine of the formula EQU H.sub.2 N--Ar--((Z)q--Ar).sub.r --NH.sub.2 where Ar=meta-- or para-phenylene; Z=--O--, --S--, --SO.sub.2 --, --CO--, or --C(CH.sub.3).sub.2 -- or mixtures thereof; q=0 or 1; r=0, 1 or 2 and of PA1 (ii) isophthalic acid, which can be replaced up to 60 mole % by terephthalic acid, while both acids can be substituted for by an acid with the formula ##STR1## or a dicarboxylic acid with the general formula EQU HO.sub.2 C--Ar--(A--Ar).sub.p --CO.sub.2 H, where A=--O--, --S--, --SO.sub.2 --, --CO-- or a single bond; and p=0 or 1; in the presence of triphenylphosphite or an acid with the formula H.sub.3 PO.sub.n, where n=2, 3 or 4. The invention further relates to the aromatic polyamides produced by this process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to aromatic polyamides which have high 
temperature resistance and good mechanical properties, and which are 
thermoplastically processible. 
2. Discussion of the Background 
Aromatic polyamides with the repeating unit: 
EQU --CO--Ar--CO--NH--Ar'--X--Ar"--Y--Ar"--X--Ar'--NH-- (I) 
not only display high temperature resistance and good mechanical 
properties; they are also thermoplastically processable (see 
Elias/Vohwinkel, New Polymer Materials for Industrial Use, 2nd Ed. Carl 
Hanser Verlag 1983, pp. 242 ff). In repeating unit (I), X and Y 
alternatively stand For an ether and a sulfonyl group, and Ar, Ar' and Ar" 
stand independently of one another for the para- and meta- phenylene 
group. 
Prior art processes for producing aromatic polyamides include the 
following: 
1. Low temperature solution polycondensation by reacting aromatic 
dicarboxylic acid dichlorides with aromatic diamines in polar solvents 
(See U.S. Pat. Nos. 3,287,324; 3,541,056; 3,600,350; 3,819,587; 3,767,756; 
3,869,429; 3,673,143; 3,817,941; 3,063,966; and German No. AS5 22 19 703). 
The subject of U.S. Pat. No. 3,859,252 is thermoplastic condensation 
polymers with an aromatic bisamide structure. The compound in which R=H, 
X=SO.sub.2 and Y=O contains repeating unit (I). It is produced from 
isophthaloylchloride and the corresponding diamine. 
2. Interface polycondensation by reaction between an aromatic dicarboxylic 
acid dichloride and an aromatic diamine at the interface of an organic and 
an aqueous phase (See German No. OS 19 08 297 and OS 23 25 139; and German 
Pat. No. 30 06 899). 
Aromatic polyamides can also be prepared by the reaction of aromatic 
dicarboxylic acids with aromatic diisocyanates (German Pat. No. 19 28 435) 
and by reacting aromatic dicarboxylic acid diaryl esters with aromatic 
diamines. 
For example, Brode et al. describe the preparation of 4,4'- [sulfonylbis 
(p-phenyleneoxy)] to dianiline (X=0, Y=SO.sub.2) from p-aminophenol and 
4,4'-dichlorodiphenylsulfone and its condensation with aromatic acid 
chlorides such as terephthalic acid chloride, for example, to produce 
aromatic polyamides with glass temperatures (Tg) between 230.degree. and 
320.degree. C. (See Polymer Prepr. Am. Chem. Soc. Div. Pol. Chem. 15, 761 
(1974) and Adv. Chem. Ser. 142 (1975); See CA 84, 5530 s). 
This process has the disadvantage that it calls for the use of activated, 
hard-to-handle monomers, such as dicarboxylic acid chlorides. 
Processes are also known by which one can obtain aromatic polyamides 
directly by reaction of aromatic dicarboxylic acids and aromatic diamines 
in the presence of aromatic phosphites. N-methyl acid amides, particularly 
N-methylpyrrolidone, have been found to be good solvents for this process. 
With other dipolar aprotic solvents, such as dimethylsulfoxide, no polymer 
amides are obtained (See F. Higashi et al., J. Polym. Sci., Polym. Chem. 
Ed. 18, 1711 ff (1980). 
In a summary (See S. M. Aharoni et al., J. Polym. Sci., Polym. Chem. Ed. 
22, 2579 (1984), it is concluded that: 
(i) the phosphite to be used must contain aryl groups and should preferably 
be a triphenyl phosphite; 
(ii) the aryl phosphites must be used in at least such quantities that for 
each mole of amide to be substituted, one mole of a compound containing 
the grouping 
EQU Ar--O--P&lt; 
is added, since this grouping will be consumed during the course of the 
reaction, and this reaction is the driving force behind the 
transformation; and 
(iii) pyridine is not required for the reaction, but does have the effect 
of speeding up the reaction. 
Finally, in European Pat. No. 0 099 997, a process for producing aromatic 
polyamides is disclosed in which aromatic dicarboxylic acids are reacted 
with aromatic diamines in a polar solvent in the presence of a dehydrating 
catalyst, such as a phosphorus-containing compound, for example. The 
polyamides disclosed cannot be thermoplastically processed because of 
their high softening points, which lie in the area of the decomposition 
temperature or even higher. If electron-rich aromatic diamines, such as 
4,4'-diaminodiphenylether, are used in this process, long reaction times 
are required to obtain products of high molecular weight, and these 
products are heavily colored due to the formation of unidentified 
by-products. If, on the other hand electron-poor diamines such as 
4,4'diaminodiphenylsulfone are used, the process according to European 
Pat. No. 0 099 997 fails to work altogether. All that is obtained are 
heavily colored oligomers. 
In addition to these processes, in which condensation is performed in a 
solvent, attempts have also been made to produce polyamides in the melt. 
Thus, U.S. Pat. No. 3,109,836 discloses a process for producing polyamides 
with repeating units of (CO--Ar--NH) that consists of heating 
acetamidobenzoic acid for three hours in a vacuum at 200.degree. to 
300.degree. C. 
Contrary to the allegations in this patent, this process does not yield 
thermoplastically processable products, since the melting points of the 
products of the reaction lie in the area of the decomposition temperature 
or higher. 
It has also been suggested that aromatic polyamides can be produced by 
amidation of acylated aromatic amines in the melt. Apart from the fact 
that such a proceeding would require the prior production of the acylated 
amines, the results obtained with this process must be considered highly 
unsatisfactory. In order to improve processibility, the starting compounds 
are not purely aromatic compounds, but rather a mixture including 
aliphatic compounds. The diamines are only partially, not completely 
acylated. Finally, acetic acid, an acetic anhydride, dimethyl acetamide or 
another agent is added to the reaction melt to improve the flowability. 
(See Keske et al., Polymer Prepr. 25, Part XXV, p. 25 (1984) and U.S. Pat. 
No. 3,654,227). 
Even though Buhler's standard work on the subject, Spezialplaste 
(Specialized Plastics), Akademieverlag, Berlin (1978), states on page 412 
that the method of melt polycondensation is not applicable to the 
preparation of aromatic polyamides from aromatic dicarboxylic acids and 
simple aromatic diamines, there exists a need for a process for producing 
aromatic polyamides by just this melt polycondensation method. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the present invention is to provide a process 
for producing thermoplastic aromatic polyamides by a melt polycondensation 
method while avoiding the production of heavily colored compounds. 
These objects and other objects of the present invention which will become 
apparent from the following specification have been achieved by the 
process of the present invention which produces high molecular weight 
aromatic polyamides by condensing an aromatic diamine and an aromatic 
dicarboxylic acid in the presence of a phosphorus-containing catalyst, 
wherein 
(i) said aromatic diamine has the formula 
EQU H.sub.2 N--Ar'--X--Ar"--Y--Ar"--X--Ar'--NH.sub.2 
wherein Ar' and Ar" are a meta- or para-phenylene radical; X=--O--and 
Y=--SO.sub.2 -- or X=--SO.sub.2 -- and Y=--O--; wherein said aromatic 
diamine can be replaced up to 70 mole % by aromatic diamines with the 
formula 
EQU H.sub.2 N--Ar ((Z).sub.q --Ar).sub.r --NH.sub.2 
wherein Ar is meta-phenylene, para-phenylene; Z is --O--, --S--, --SO.sub.2 
--, --CO-- or --C(CH.sub.3).sub.2 -- or mixtures thereof; q is 0 or 1; and 
r is 0, 1 or 2; 
(ii) said aromatic dicarboxylic acid is 
(a) isophthalic acid, which may be replaced up to 60 mole % by terephthalic 
acid, wherein said isophthalic acid and said terephthalic acid may be 
substituted by at least one C.sub.1 -C.sub.6 alkyl radical, alkyl-or 
aryl-substituted phenyl radical, C.sub.1 -C.sub.6 alkoxy radical, phenoxy 
radical in which the phenyl ring can be alkyl- or aryl-substituted, or a 
halogen; 
(b) an acid with the formula 
##STR2## 
(c) or a dicarboxylic acid with the general formula 
EQU HO.sub.2 C--Ar--(A--Ar).sub.p --CO.sub.2 H 
wherein Ar is meta-phenylene or para-phenylene; A is --O--, --S--, 
--SO.sub.2 --, --CO-- or a single bond; and p=O or 1, and wherein said 
catalyst is triphenylphosphite or an acid derived from phosphorus having 
the formula H.sub.3 PO.sub.n, where n=2, 3 or 4 and 
(iii) said condensing step is performed in the melt of the starting 
materials. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A process has now been found with which certain aromatic diamines can be 
reacted with certain aromatic dicarboxylic acids in the melt to yield 
aromatic polyamides. Surprisingly, the products obtained are not only 
thermoplastically processible, as known in the art, but display double 
refraction in the melt. The characterizing of liquid crystal phases by 
double refraction in the melt is described in U.S. Pat. No. 4,118,732. 
Thus, a new class of technically interesting aromatic polyamides has been 
uncovered. 
The process for producing the polyamides of the present invention consists 
of reacting an approximately equimolar mixture of aromatic dicarboxylic 
acid and aromatic diamine in the presence of at least the minimum 
catalytically effective quantity of triphenylphosphite or an acid derived 
from phosphorus with the formula H.sub.3 PO.sub.n where 
2.ltoreq.n.ltoreq.4 or a catalytically effective quantity of a mixture of 
the abovementioned phosphorus compounds and a 4-dialkylaminopyridine in 
the melt at temperatures between 200.degree. and 380.degree. C. 
The addition of the tiny quantity of co-catalyst has the following 
substantial effects on the formation of the polyamide: 
the viscosity number, which is a reflection of molecular weight, is 
substantially increased; 
the color quality of the polymer is markedly improved; 
the polycondensation time is drastically reduced; 
the reaction temperature is greatly lowered; and 
the molecular weight of the polyamides obtained lies between 10,000 and 
200,000, preferably between 20,000 and 70,000. 
The following aromatic dicarboxylic acids or mixtures thereof may be used 
according to the invention: 
(a) Isophthalic acid, which can be replaced by terephthalic acid up to 60 
mole percent, while both acid groups may be substituted by at least one of 
the following radicals: 
(a) C1-C6 alkyl; 
(b) a phenyl radical which can be alkyl- or aryl-substituled 
(c) alkoxy radical with 1-6 C-atoms: 
(d) phenoxy radicals, with alkyl- or aryl-substitution of the phenyl ring; 
or 
(e) a halogen, particularly chlorine and bromine, 
(b) a dicarboxylic acid with the formula 
##STR3## 
(See Lorenz et al., Macromolecular Chemistry 130, 65 (1969)). 
(c) or a dicarboxylic acid of the general formula 
EQU HO.sub.2 C--Ar--(A--Ar).sub.p --CO.sub.2 H 
where Ar=meta-phenylene or para-phenylene; A=--O--, --S--, --SO.sub.2 --, 
--SO--or a single bond; and p=0 or 1. 
The following aromatic diamines or mixtures thereof may be used according 
to the invention: 
EQU H.sub.2 N--Ar'--X--Ar"--Y--Ar"--X--Ar'--NH.sub.2 
where Ar' and Ar" stand for meta- or in particular para-phenylene radicals; 
particularly: 
4,4'-bis(4-aminophenoxy)diphenylsulfone (X=O, Y=SO.sub.2) and 
4,4'-bis(4-aminophenylenesulfonyl)diphenylether (X=SO.sub.2, Y=O). 
The compound where X=O and Y=SO.sub.2 is obtained by reaction of 
p-aminophenol with 4,4'-dichlorodiphenylsulfone. The preparation of the 
compound where X=SO.sub.2 and Y=O is described in U.S. Pat. No. 3,859,252. 
Up to 70 mole percent of the diamines thus described can be replaced by the 
following aromatic diamines: 
Aromatic diamines of the general formula: 
EQU H.sub.2 N--Ar ((Z).sub.q --Ar).sub.r --NH.sub.2 
where Ar=meta-phenylene, para-phenylene; Z=at least one type of radical 
selected from the group --O--, --S--, --SO.sub.2 --, --CO--, or 
--C(CH.sub.3).sub.2 ; q=0 or 1; and r=0, 1 or 2. 
For one mole of aromatic diamines, 0.95 to 1.05 mole, preferably 1.0 mole 
of aromatic dicarboxylic acid is used. 
The aromatic dicarboxylic acids are reacted with the diamines in the 
presence of a catalytic quantity of a phosphorus-containing compound or in 
the presence of a catalytic quantity of a mixture of said phosphorus 
containing compound and a 4-dialkylaminopyridine. 
Suitable phosphorus-containing compounds are triphenylphosphite, 
hypophosphorous acid, phosphorous acid and phosphoric acid. 
The 4-dialkylaminopyridines used as a co-catalyst have the following 
structure: 
##STR4## 
where R.sub.1 and R.sub.2 either stand independently of one another for a 
C.sub.1 -C.sub.10 alkyl radical or together with the amino nitrogen can 
form a pyrrolidine or alkyl piperidine ring. 
Preferred 4-dialkylaminopyrrolines are: 4-dimethylaminopyridine, 
4-dibutylaminopyridine, 4-di-n-hexylaminopyridine, and 
4-piperidinylpyridine. 
The pyridine derivatives can be produced according to Synthesis 844 (1978). 
High-boiling organic bases with tertiary nitrogen atoms can also be used as 
the co-catalyst, such as isoquinoline or quinoline, and inorganic basic 
salts, particularly alkali and alkaline earth carbonates, such as calcium 
carbonate. 
For 100 moles of dicarboxylic acid used, 0.1 to 10 moles, preferably 1 to 5 
moles each of the phosphorus-containing compound and the catalyst are 
used. 
Normally, the operation is performed under inert gas at normal pressure. It 
is possible however, when desirable for one reason or another, to work at 
a pressure slightly above or below normal. The reaction times required to 
obtain sufficiently high molecular weight products are between 1 and 4 
hours. 
The polycondensation process is performed in the melt at temperatures 
between 200.degree. and 380.degree. C., preferable between 250.degree. and 
350.degree. C. Three preferred embodiments of the process are as follows: 
(1) The reactants and the catalysts are melted together and pre-condensed 
at temperatures of between 200.degree. and 250.degree. C. The temperature 
is then increased to a maximum of from 350.degree. to 380.degree. C., and 
the pre-polymers are further condensed. The build-up of molecular weight 
that takes place is revealed by the sharp increase in the mel viscosity. 
(2) A powdered mixture of the reactants and catalysts is processed in a 
kneader with a gradual increase in temperature from 220.degree. to 
290.degree. C., until the water produced by condensation is eliminated. 
Alternatively, it is also possible to perform the polycondensation in an 
extruder. Here again, a powdered mixture of the components is fed into the 
apparatus, and the reaction water is completely eliminated by suitable 
adjustment of temperature. 
(3) Finally, it is possible as in Embodiment (1) to transform the starting 
products first to a precondensate at a temperature of from 200.degree. to 
280.degree. C. and then to further condense the precondensate in a kneader 
or extruder. In the extruder, temperatures of from 280.degree. to 
350.degree. C., preferably from 290.degree. to 330.degree. C., will then 
normally be required. This embodiment is particularly preferred. 
If the end product still does not have a sufficiently high molecular 
weight, it is possible to increase molecular weight by secondary solid 
phase condensation. A person skilled in the art will be familiar with such 
a process. 
The catalyst generally remains in the product. If it is desirable, however, 
it may be removed by dissolving and precipitating the reaction product in 
a suitable solvent, such as N-methylpyrrolidone. 
In order to produce sufficiently high-molecular-weight products, it is 
necessary to remove the water formed during polycondensation from the 
reaction system. In Embodiment 1), this is accomplished by passing inert 
gas over or through it. The use of a vacuum is also effective. 
Upon completion of the polycondensation, one obtains a more or less viscous 
melt of the polymer that can then be directly processed into a granulate. 
The resulting products can be fabricated into films by pressing at high 
temperature ( &gt;200.degree. C.). Organic solutions of the polyamides in 
suitable aprotic polar solvents may also be made into cast sheets in a 
conventional manner. 
The viscosity number J of the polyamides obtained which constitutes a 
measure of the relative molar mass, is determined in the following tests 
in mixtures of 1,2-dichlorobenzene and phenol in the volume ratio 1:1 as 
per DIN (German Industrial Standard) 53,728. 
Other features of the invention will become apparent in the course of the 
following examples of the exemplary embodiments which are given for 
illustration of the invention and are not intended to be limiting thereof.

EXAMPLES 
EXAMPLE 1 
11.52 g (0.07 mole) of isophthalic acid, 30.00 g (0.07 mole) of 
4,4'-bis(4-aminophenoxy)diphenylsulfone and 0.22 g triphenylphosphite are 
melted at 220.degree. C. After 60 minutes, the temperature is increased to 
250.degree. C. During these 60 minutes at 250.degree. C., the viscosity of 
the melt sharply increases. Next, the temperature is increased to 
350.degree. C. for another 30 minutes. A polyamide with the following 
properties is obtained: J=120 cm.sup.3 /g and T.sub.g =245.degree. C. At 
300.degree. C. the product can be pressed into transparent plates. 
EXAMPLE 2 
11.52 g (0.07 mole) of isophthalic acid and 30,000 g (0.07 mole) of 
bis-4-4'(4-aminophenoxy)diphenylsulfone are stirred with 112.8 mg (1.37 m 
mole) of phosphorous acid and 88.7 mg (0.69 m mole) of isoquinoline under 
nitrogen for 20 minutes at 250.degree. C. and then for 20 minutes at 
350.degree. C. The water produced by the reaction and separated out during 
the course of the reaction is distilled off in the process. A polyamide 
with J=63 cm.sup.3 /g is obtained. 
EXAMPLE 3 
1,800 g (4.16 mole) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 694 g (4.18 
mole) of isophthalic acid, 26.20 g (0.08 mole) of triphenylphosphite and 
18.00 g (0.18 mole) of calcium carbonate are melted at 250.degree. C. 
under nitrogen and then condensed with stirring for 45 minutes at 
290.degree. C. The water separated out during condensation is removed with 
the inert gas. The pale yellow, transparent oligomer has a J-value of 14 
cm.sup.3 /g in a mixture of 50 parts each of phenol and 
1,2-dichlorobenzene. The second condensation is carried out in a vacuum 
(120 mbar) in a twin-screw extruder at a condensation temperature of 
320.degree. C. and an extrusion temperature of 345.degree. C. and results 
in a viscosity figure of J=55 cm.sup.3 /g. 
EXAMPLE 4 
48.00 g (0.11 mole) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 3.00 g of 
m-phenylenediamine, 23.04 g (0.14 mole) of isophthalic acid, 0.60 ml of a 
50% aqueous solution of hypophosphorous acid and 0.672 g of 
4-dimethylaminopyridine are stirred under nitrogen for 30 minutes at 
250.degree. C. Over the course of 20 minutes the temperature is increased 
to 350.degree. C. and the product is then allowed to cool. The golden 
brown, transparent co-polyamide has a J-value of 33 cm.sup.3 /g. 
EXAMPLE 5 
30.00 g (0.07 mole) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 2.30 g 
(0.014 mole) of terephthalic acid, 9.22 g (0.056 mole) of isophthalic 
acid, 0.44 g (0.0014 mole) of triphenylphosphite and 0.30 g (0.003 mole) 
of calcium carbonate are stirred for 20 minutes at 250.degree. C. and the 
temperature is increased to 300.degree. C. over the course of 10 minutes. 
A colorless, transparent product is obtained with a J-value of 37 cm.sup.3 
/g. 
EXAMPLE 6 
900 g (2.08 moles) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 347 g (2.09 
moles) of isophthalic acid, 7.63 g (0.06 mole) of 4-dimethylaminopyridine 
and 3.41 g (0.04 mole) of phosphorous acid are melted together and stirred 
for 25 minutes at 290.degree. C. An oligomer with a J-value of 13 cm.sup.3 
/g is obtained. The second condensation in the twin-screw extruder at 
320.degree. C. in a vacuum yields a polyamide with a J-value of 55 
cm.sup.3 /g. 
EXAMPLE 7 
60.00 g (0.14 mole) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 23.04 g 
(0.14 mole) of isophthalic acid, 504 mg of 4-dimethylaminopyridine and 
225.6 mg of phosphorous acid are kneaded in a Haake-Rheomix Laboratory 
Kneader at 220.degree. to 290.degree. C., during which process the water 
resulting from condensation is eliminated. After 20 minutes a polyamide is 
obtained with a J-value of 21 cm.sup.3 /g. 
EXAMPLE 8 
60.0 g (0.14 mole) of 4,4'-bis(4-aminophenoxy)diphenylsulfone, 11.52 g 
(0.07 mole) of terephthalic acid, 11.52 g (0.07 mole) of isophthalic acid, 
225.6 mg of phosphorous acid and 504 mg of 4-dimethylaminopyridine are 
polycondensed for 20 minutes at 250.degree. C. and for 25 minutes at 
250.degree. to 370.degree. C. The polyamide obtained with a J-value of 33 
cm.sup.3 /g is condensed again in the laboratory kneader at 335.degree. C. 
After 4 minutes, the melt has a rotation moment of 9.4 Nm. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.