Star-shaped nylons, methods for their preparation, tetrasubstituted carboxylic acids and methods for their preparation

Star-shaped nylons with low melt viscosities and excellent mechanical properties, methods for their preparation, a novel tetrasubstituted carboxylic acid for use as a polymerization core therefor and methods for its preparation are provided. A star-shaped nylon has polymer chains emanating from 3 or more polymerization initiation groups which are substituents bonded to every other or more separated carbon atoms on an aromatic ring of an aromatic compound. The star-shaped nylon is produced by homogeneously mixing the aromatic compound with molten nylon monomer and polymerizing the nylon monomer with the respective polymerization initiation groups as the starting points. A novel tetrasubstituted carboxylic acid having a structure of 3,5,3',5'-biphenyltetracarboxylic acid is useful as a polymerization core for star-shaped nylons.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to star-shaped nylons, methods for their 
preparation, tetrasubstituted carboxylic acids and methods for their 
preparation. More particularly, it is concerned with star-shaped nylons 
with desired properties provided by use of characteristic polymerization 
cores, new tetrasubstituted carboxylic acids for use as the aforementioned 
polymerization cores and methods for their preparation. 
2. Description of the Related Art 
The so-called star-shaped polymers are macro molecules of a structure where 
a plurality of radial polymer chains emanate from a polymerization core as 
a center, their chemical structure being characterized in that, as 
compared with the conventional linear polymers, the molecular weight per 
polymer chain is less, and the respective polymer chains combine with each 
other through the polymerization core. Therefore, star-shaped polymers 
have relatively less entanglement of respective polymer chains, which 
contributes to their relatively low melt viscosities. This often leads to 
their preferable physical properties to enable injection molding into 
films, or leads to excellent compatibility with other polymers to broaden 
the possibilities of polymer blends. 
Also relating to nylons, those of star-shaped type have been investigated 
as exemplified in U.S. Pat. No. 4,599,400 and "Polymer Preprints," 30(1), 
pp117-118, American Chemical Society, 1989. For example, a star-shaped 
nylon 6 is described therein which is prepared by making use of a 
star-shaped amine compound with plural amino groups on separate positions 
in a molecule as a polymerization core, and subjecting the respective 
amino groups to ring-opening polymerization with .epsilon.-caprolactam or 
a nylon monomer. 
The above-mentioned type of star-shaped nylon, however, does not always 
exhibit low melt viscosity, nor good mechanical properties (e.g. tensile 
strength, tensile modulus, etc.). These drawbacks are assumed to be due to 
the following causes characteristic of nylons. 
That is, polymer chains of nylon contain numerous amide bond (--CO--NH--) 
portions which are indispensable to crystallization due to formation of 
hydrogen bonds between nylon molecules upon solidification, and eventually 
contribute to improvement in various mechanical properties of nylon 
materials. 
In the early stage of polymerization for star-shaped nylons, however, the 
respective polymer chains in the same molecule are present in close 
vicinity to each other near the polymerization core, and further the 
reactivity of the amide bond portions of the respective polymer chains 
remain high until completion of polymerization. So the mutual contact of 
the respective polymer chains in the same molecule causes radical 
formation due to deprotonation at the amide bond portions and thus 
formation of intramolecular network structure among the polymer chains. 
Such intramolecular network structure is known to cause an increase in 
melt viscosity of nylon. 
The intramolecular network structure formed between the amide bond portions 
prevents formation of hydrogen bonds among nylon molecules caused by amide 
bonds upon the solidification, resulting in poor crystallization which 
provides nylon materials with inferior mechanical properties. 
For the foregoing reasons, it is necessary to keep the respective polymer 
chains in the molecule from their mutual close contact in the early stage 
of polymerization in order to prepare star-shaped nylons having low melt 
viscosities and excellent mechanical properties. 
According to the prior art, however, a star-shaped amine compound as a 
polymerization core is not of a rigid molecular structure, and eventually 
infallible separation of the respective polymer chains from each other 
cannot be attained in the course of polymerization, thereby failing to 
prevent formation of the intramolecular network structure discussed above, 
even if a plurality of amino groups are positioned separated from each 
other in the molecule so that the respective polymer chains in the 
molecule do not mutually contact. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide star-shaped 
nylons with low melt viscosities and excellent mechanical properties due 
to no formation of the aforementioned intramolecular network structure 
upon polymerization of nylon monomers and due to satisfactory 
crystallization upon solidification, and processes for preparations 
thereof. Another object of the present invention resides in a plentiful 
supply of types of polymerization cores which enable the provision of the 
star-shaped nylons mentioned above. 
In a first aspect, the present invention provides a star-shaped nylon with 
nylon polymer chains emanating from 3 or more polymerization initiation 
groups which are substituents bonded to every other or more separated 
carbon atoms on the aromatic ring of an aromatic compound. 
In a second aspect, the present invention provides a process for the 
preparation of a star-shaped nylon, which comprises: preparing an aromatic 
compound substituted with 3 or more polymerization initiation groups for 
nylon monomers, which are bonded to every other or more separated carbon 
atoms on an aromatic ring of an aromatic compound; homogeneously mixing 
the aromatic compound with molten nylon monomers under a condition where 
no other polymerization initiators for nylon monomers are present; and 
polymerizing the nylon monomer starting from the respective polymerization 
initiation groups of the aromatic compound mentioned above. 
According to the aforementioned first and second aspects, an aromatic 
compound of rigid molecular structure is employed as the polymerization 
core for a star-shaped nylon, and polymerization initiation groups as 
substituents are bonded to every other or more separated carbon atoms on 
an aromatic ring of an aromatic compound, so that the polymerization core 
functions as an effective spacer to place the respective polymer chains in 
the same molecule for scarce mutual contact thereof early in the course of 
polymerization for nylon. 
Therefore, no formation is performed of intramolecular network structure 
between amide bond portions during the polymerization for star-shaped 
nylons, leading to promotion of formation of intramolecular hydrogen bonds 
upon solidification with satisfactory crystallization. 
Here, aromatic rings of aromatic compounds are in a form of flat hexagonal 
plates or more complicated polygonal plates, and thus, at solidification 
after the completion of polymerization, these plate-like aromatic rings 
tend to be oriented in a pile in the perpendicular thereof. For this 
reason, the respective polymer chains of star-shaped nylon molecules also 
have a tendency to be oriented horizontally among the molecules, thus 
promoting more efficient formation of intermolecular hydrogen bonds. 
Next, the polymerization core of a star-shaped nylon according to the 
present invention, which bears 3 or more polymerization initiation groups, 
has a lower molecular weight per polymer chain than conventional linear 
polymers, and maintains a structural characteristic peculiar to 
star-shaped polymers in that the respective polymer chains combine with 
each other through the polymerization core. 
In addition, in the method for the preparation of star-shaped nylons 
according to the second aspect, an aromatic compound as a polymerization 
core is homogeneously mixed with molten nylon monomers under a condition 
where no other polymerization initiators for nylon monomers are present, 
and then the nylon monomers are subjected to polymerization starting from 
each of the polymerization initiation groups of the above-mentioned 
compound. Accordingly, the physical properties cannot be spoiled due to 
formation of linear nylon molecules which may be produced because of the 
presence of other types of polymerization initiator for nylon monomers. 
The aforementioned aspects contribute to the provision of star-shaped 
nylons with low melt viscosities and various excellent mechanical 
properties. In this connection, star-shaped nylons are of structure 
constructed by combining polymer chains, which are shorter than those of 
linear nylons, through a polymerization core, which structure causes an 
increase in glass transition temperature, an index of thermal stability. 
The third aspect of the present invention resides in tetrasubstituted 
carboxylic acids of chemical structure generically named 
3,5,3',5'-biphenyltetracarboxylic acids according to the nomenclature of 
International Union of Pure and Applied Chemistry (IU). The chemical 
structure of this tetrasubstituted carboxylic acid is represented by 
Formula 1 given below. 
##STR1## 
Tetrasubstituted carboxylic acid, which has 4 polymerization initiation 
groups (carboxyl groups) as substituents bonded to every other or more 
separated carbon atoms on an aromatic ring (biphenyl ring) of an aromatic 
compound, is a novel compound which may be used as the polymerization core 
in the first and second aspects of the present invention. 
In a fourth aspect, the present invention provides a method for the 
preparation of the tetrasubstituted carboxylic acid, which comprises 
dissolving a 1,3-dicarboxy 5-halobenzene in a solvent, followed by 
dehalogenation condensation in the presence of a catalyst of metal 
belonging to group X of the periodic table. 
This method for the preparation of the tetrasubstituted carboxylic acid 
serves to produce tetrasubstituted carboxylic acid according to the third 
aspect. 
Usually, the preparation of tetrasubstituted carboxylic acids involves 
coupling of 5-diazonium salts of 1,3-dicarboxybenzene with copper or the 
like. The following of this process by the present inventors, however, led 
to the synthesis of the diazo compound represented by Formula 2 shown 
below, but not to the synthesis of the tetrasubstituted carboxylic acid 
according to the third aspect. Considering this fact, the present 
inventors undertook the multi-faceted research on synthesis methods, 
resulting in the completion of a method for the preparation of the 
tetrasubstituted carboxylic acid according to the fourth aspect.

DETAILED DESCRIPTION OF THE INVENTION 
Hereunder, the first to fourth aspects of the present invention will be 
explained in detail. 
The aromatic compounds used in the present invention include all compounds 
with an aromatic ring and their derivatives in general. 
The aromatic ring includes benzene ring, naphthalene ring, anthracene ring, 
etc., and further heterocycles such as pyridine ring, pyrrole ring, indole 
ring, furane ring, thiophene ring, purine ring, quinoline ring, 
phenanthrene ring, porphyrin ring, phthalocyanine ring, naphthalocyanine 
ring and the like. 
Particularly, porphyrin ring, phthalocyanine ring and naphthalocyanine ring 
are of large cyclic structure which is expected to provide a general 
advantage in that, as compared with benzene ring or the like, more 
polymerization initiation groups as substituents may be bonded to every 
other or more separated carbon atoms on an aromatic ring. 
The skeleton of the aromatic compounds of the present invention may consist 
only of any one of the various aromatic rings discussed above and their 
condensed rings, and further it can be composed of biphenyl, triphenyl, 
bipyridine, etc., i.e. 2 or more aromatic rings combined without 
condensation. In addition, the structure may be such that, between the 2 
or more aromatic rings there exists a portion comprising an alkylene 
group, allylene group, arylene group, diazo group, carbonyl group, ether 
group, amido group, ester group, amino group or the like. 
In the aromatic compounds according to the present invention, a hydrogen 
atom may bond to the carbon atoms on an aromatic ring, to which no 
polymerization initiation groups bond, or a variety of groups not capable 
of preventing the preparation of a star-shaped nylon may be bonded thereto 
as substituents. 
For the aromatic compounds according to the present invention, the most 
suitable polymerization initiation group is amino or carboxyl group, but 
other polymerization initiation groups may be used which can initiate 
polymerization for nylon monomers. 
Preferably, the aforementioned polymerization initiation groups as 
substituents bond to every other or more distant or separated carbon atoms 
on an aromatic ring of an aromatic compound. This is because bonding to 
carbon atoms at neighboring positions on the aromatic ring not only causes 
formation of the aforementioned intramolecular network of polymer chains, 
but also is apt to induce so-called steric hindrance or a side reaction 
such as imide cyclization between the polymerization initiation groups, 
thus failing to produce a star-shaped nylon with desired physical 
properties. 
In addition, preferably, the aromatic compounds may be substituted with 3 
or more polymerization initiation groups, because substitution of the 
aromatic compounds with only 1 or 2 polymerization initiation groups 
results in the formation of 1 or 2 polymerization chains emanating 
therefrom, thereby producing nylon molecules in a linear state rather than 
in a star-shape when viewed as a whole. More preferably, the aromatic 
compounds have not less than 3, but not more than 10 polymerization 
initiation groups as substituents, for the reason that the presence of 10 
or more polymerization initiation groups leads to the production of 10 or 
more intramolecular polymer chains, which may cause a jam of 
intramolecular polymer chains around the core of the star-shaped nylon, 
which should be undesirable in view of the above-mentioned intramolecular 
network or crystallization properties. 
The polymerization initiation groups do not necessarily bond directly to 
the carbon atoms on the aromatic ring, and may bond thereto through 
certain intermediate structural portions. Such intermediate structural 
portions include an alkylene group, allylene group, arylene group, etc. 
and in effect any intermediate structural portion may be utilized so long 
as it hinders neither the action of the polymerization initiation groups 
to initiate the polymerization nor that of the polymerization core to 
separate the intramolecular polymer chains in the molecule. 
Several typical examples of such polymerization cores are illustrated 
hereunder. 
1,3,5-benzenetricarboxylic acid (trimesic acid); 
3,5,3',5'-biphenyltetracarboxylic acid; 
2,4,6-pyridinetricarboxylic acid; 
3,5,3',5'-bipyridyltetracarboxylic acid; 
1,3,5,7-naphthalenetetracarboxylic acid; 
1,3,6,8-acridinetetracarboxylic acid; 
3,5,3',5'-benzophenonetetracarboxylic acid; 
1,3,5-triaminobenzene; 
1,3,5-tri(aminomethyl)benzene; 
3,5,3',5'-tetraaminobiphenyl; 
2,4,6-triaminopyridine; 
3,5,3,',5'-tetraaminobipyridine; 
1,3,5,7-tetraaminoaphthalene; 
1,3,6,8-tetraaminoacridine; and 
3,5,3',5'-tetraaminobenzophenone. 
Typical examples of porphyrin polymerization cores are 
tetrakis(carboxyphenyl)porphyrin represented by Formula 3, aluminum 
tetrakis(carboxypenyl)porphyrin, titanium 
tetrakis(carboxyphenyl)porphyrin, nickel tetrakis (carboxyphenyl) 
porphyrin, rhodium tetrakis(carboxyphenyl)porphyrin, etc. 
##STR3## 
Typical examples of phthalocyanine polymerization cores are 
tetracarboxyphthalocyanine represented by Formula 4, 
chloro(tetracarboxyphthalocyaninate)aluminum, 
(tetracarboxyphthalocyaninate)cobalt, 
(tetracarboxyphthalocyaninate)copper, and (tetracarboxyphthalocyaninate) 
nickel represented by Formula 5, (tetracarboxyphthalocyaninate)iron, 
(tetracarboxyphthalocyaninate)oxovanadium, 
(tetracarboxyphthalocyaninate)lead, 
(tetracarboxyphthalocyaninate)magnesium, 
(tetracarboxyphthalocyaninate)tin, (tetracarboxyphthalocyaninate)zinc, 
etc. 
##STR4## 
Typical examples of naphthalocyanine polymerization cores are 
tetracarboxynaphthalocyanine represented by Formula 6, metallic 
tetracarboxynaphthalocyanine represented by Formula 7 (wherein M is a 
metal atom). 
##STR5## 
The nylon monomers are not particularly limited. Preferably, nylon monomers 
such as valerolactam, caprolactam, 2-azacyclododecanone, 
2-azacyclotridecanone (laurolactam), 1,8-diazacyclotetradecane-2,7-dione, 
etc. are employed. 
The conventional polymerization for nylons is often carried out in the 
presence of water or a small amount of acid. However, as the co-presence 
of water or acid capable of initiating polymerization causes formation of 
linear nylons, water, acid or other polymerization initiators must be 
substantially excluded prior to the polymerization for nylons according to 
the preparation method of the present invention. 
The process for the polymerization for nylons is preferred to be conducted 
under vacuum (desirably, under reduced pressure of around 10.sup.-2 Torr). 
This is because the water and oxygen contained in the reactive materials 
may be excluded under vacuum. Further, it is preferred that the process 
for the polymerization for nylons is carried out in a sealed tube. This is 
because the polymerization reaction of star-shaped nylons does not always 
proceed readily, and thus it becomes necessary to prevent evaporation of 
volatile nylon monomers during the progress of the reaction. 
The molecular weight per polymer chain of the star-shaped nylon depends on 
the ratio of the number of the polymerization initiation groups on the 
polymerization core to the amount of the nylon monomer charged. For 
example, to state simply, around 100-mers are synthesized if 100 molecules 
of nylon monomer is used per polymerization initiation group. The 
molecular weight of the star-shaped nylons according to the present 
invention is not particularly limited; but, the number average molecular 
weight Mn is prefereably controlled in the range of 5,000-50,000, most 
preferably, in the range of 10,000-30,000 for better mechanical properties 
and lower melt viscosity. 
The above-mentioned molecular weight is of the entire star-shaped nylon, 
and the molecular weight per polymer chain in the molecule almost equals 
the value calculated by dividing the total molecular weight by the number 
of the polymer chains. 
In the fourth aspect of the present invention, the halogen in 
1,3-dicarboxy-5-halobenzene is preferred to be bromine, but other halogens 
such as iodine, chlorine and fluorine may be used as well. 
Palladium, nickel or platinum, which belong to group X of the periodic 
table, may be used as the metallic catalyst for dehalogenation 
condensation of the 1,3-dicarboxy-5-halobenzene. 
In order to bring about the dehalogenation condensation, it is necessary to 
keep the 1,3-dicarboxy-5-halo benzene in solution, preferably in an 
aqueous solvent in order to maintain the activity of the aforementioned 
catalyst. Most desirably, the 1,3-dicarboxy-5-halobenzene is treated with 
an alkali such as caustic soda to convert its 2 carboxylic groups to an 
alkaline salt thereby, imparting water-solubility to the compound. 
To simplify the processes, the 1,3-dicarboxy-5-halobenzene may be dissolved 
directly in a certain organic solvent. The certain organic solvent 
includes dimethylsulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, 
N-methylpyrrolidone, etc. Because of their water-miscible property, both 
these solvents alone and their mixture with water can be used as a 
reaction solvent. 
If the carboxyl groups of the 1,3-dicarboxy-5-halobenzene have been 
converted into an alkaline salt considering solubility, the 
tetrasubstituted carboxylic acid produced by dehalogenation condensation 
is also an alkaline salt. In this case, the treatment thereof with any of 
various acids, particularly an inorganic strong acid provides 
3,5,3',5'-biphenyltetracarboxylic acid. 
Hereunder mention will be made of the examples of the present invention. 
Example 1 
A 6.37-g portion of trimesic acid and 500 g of .epsilon.-caprolactam, both 
having been well dried beforehand, were placed in a glass vessel, and 
sealed under vacuum to 10.sup.-2 Torr with a vacuum pump. The sealed 
vessel was shaken for 2 hours in an oven while heating at 120.degree. C., 
for melting and homogeneously mixing the trimesic acid and the 
.epsilon.-caprolactam. Then the mixture was allowed to stand to increase 
its temperature to 250.degree. C., and a polymerization reaction was 
carried out for 72 hours. Next, the above sealed vessel was cooled and 
then opened, thereby producing a crude resin of the star-shaped nylon of 
the present example. 
The crude resin referred to above was freezed to a glassy state and then 
crushed, washed with hot water at 80.degree. C. and filtered to remove 
unreacted monomer, after which the water was removed by vacuum drying to 
yield a purified resin of the present example. The star-shaped nylon 
molecular structure of the purified resin according to the present example 
was confirmed by the results of determination of the terminal carboxylic 
group (--COOH) in the molecule and by other means for the confirmation of 
the structure. (The similar confirmation was also made in other Examples.) 
The star-shaped nylon resin of the present example comprises molecules of 
nylon 6 with 3 polymer chains and having a molecular weight of about 
13,200. 
Samples of the aforementioned purified resin of Example 1 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
TABLE 1 
__________________________________________________________________________ 
Example 1 Example 2 
Example 3 
Example 4 
Example 5 
Comparison 1 
__________________________________________________________________________ 
Tensile 
625 523 613 530 470 621 
strength 
(kg/cm.sup.2) 
Tensile 
6700 5100 7340 4300 3300 8910 
modulus 
(kg/cm.sup.2) 
Tensile 
57 25 99 &gt;200 &gt;200 137 
elongation 
(%) 
__________________________________________________________________________ 
Samples of the aforementioned purified resin of Example 1 were measured for 
their melt viscosities at 230.degree. C. and 240.degree. C., using a 
capillary rheometer (capirograph) manufactured by Toyo, Inc., with a die 
having a diameter of 1 mm. The results are shown in FIGS. 1 and 2, 
respectively. 
Example 2 
In the same manner as in Example 1 except that the amount of trimesic acid 
was changed to 10.5 g, Example 2 was carried out to yield a purified resin 
of star-shaped nylon. The star-shaped nylon resin of the present example 
comprises molecules of nylon 6 with 3 polymer chains and having a 
molecular weight of about 8,300. 
Samples of the aforementioned purified resin of Example 2 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
Example 3 
In the same manner as in Example 1 except that the 6.37 g of trimesic acid 
was replaced by 11.0 g of 3,5,3',5'-biphenyltetracarboxylic acid, Example 
3 was carried out to yield a purified resin of star-shaped nylon. The 
star-shaped nylon resin of the present example comprises molecules of 
nylon 6 with 4 polymer chains and having a molecular weight of about 
13,350. 
Samples of the aforementioned purified resin of Example 3 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
Samples of the aforementioned purified resin of Example 1 were measured for 
their melt viscosities at 230.degree. C. and 240.degree. C., using a 
capillary rheometer (capirograph) manufactured by Toyo, Inc., with a die 
having a diameter of 1 mm. The results are shown in FIGS. 1 and 2, 
respectively. 
Example 4 
In the same manner as in Example 1 except that the 500 g of 
.epsilon.-caprolactam was replaced by 810 g of 2-azacyclododecanone, 
Example 4 was carried out to yield a purified resin of star-shaped nylon. 
The star-shaped nylon resin of the present example comprises molecules of 
nylon 11 with 3 polymer chains and having a molecular weight of about 
21,000. 
Samples of the aforementioned purified resin of Example 4 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
Example 5 
In the same manner as in Example 1 except that the 500 g of 
.epsilon.-caprolactam was replaced by 872 g of 2-azacyclododecanone, 
Example 5 was carried out to yield a purified resin of star-shaped nylon. 
The star-shaped nylon resin of the present example comprises molecules of 
nylon 12 with 3 polymer chains and having a molecular weight of about 
22,000. 
Samples of the aforementioned purified resin of Example 5 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
Comparison 1 
For comparison, samples of the conventional nylon 6 (comprising molecules 
of linear nylon with a molecular weight of about 13,000) were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation thereof. The results are shown in 
Table 1. 
In addition, samples of Comparison 1 were measured for their melt 
viscosities at 230.degree. C. and 240.degree. C., using a capillary 
rheometer (capirograph) manufactured by Toyo, Inc., with a die having a 
diameter of 1 mm. The results are shown in FIGS. 1 and 2, respectively. 
Evaluation of Examples 1-5 
As is clearly shown in Table 1, the star-shaped nylon of each of the 
examples of the present invention, with a molecular weight per polymer 
chain in the nylon molecule being only 1/4-1/3 of that of the linear nylon 
in Comparison 1, exhibited tensile strength, tensile modulus and tensile 
elongation not being much different from those of Comparison 1. 
As FIGS. 1 and 2 show apparently, the star-shaped nylons of Examples 1 and 
3 have melt viscosities at 230.degree. C. and 240.degree. C. being lower 
than those of the linear nylon of Comparison 1 almost by one figure. 
Example 6 
In the same manner as in Example 1 except that the trimesic acid was 
replaced by 1.04 g of tetrakis(4-carboxyphenyl)porphyrin, and the amount 
of .epsilon.-caprolactam was changed into 17.13 g, polymerization and 
purification were carried out to yield a star-shaped nylon with 4 chains 
and a porphyrin ring as the core, which had a molecular weight of about 
12,800. 
Example 7 
In the same manner as in Example 1 except that the trimesic acid was 
replaced by 0.876 g of tetrakis(carboxyphthalocyaninate)Fe(II), and the 
amount of .epsilon.-caprolactam was changed into 20.00 g, polymerization 
and purification were carried out to yield a star-shaped nylon with 4 
chains and a phthalocyanine ring (Fe) as the core, which had a molecular 
weight of about 15,300. 
Example 8 
In the same manner as in Example 1 except that the trimesic acid was 
replaced by 0,879 g of tetrakis(carboxyphthalocyaninate)Ni(II), and the 
amount of .epsilon.-caprolactam was changed into 20.00 g, polymerization 
and purification were carried out to yield a star-shaped nylon with 4 
chains and a phthalocyanine ring (Ni) as the core, which had a molecular 
weight of about 15,100. 
Tensile tests 
Samples of the respective purified nylons of Examples 6-8 were subjected to 
tensile tests according to ASTM D638M, to evaluate the tensile strength, 
tensile modulus and tensile elongation-thereof. The results are shown in 
Table 2. 
TABLE 2 
______________________________________ 
Example 6 Example 7 Example 8 
______________________________________ 
Tensile 644 620 650 
strength 
(kg/cm.sup.2) 
Tensile 7230 6710 6540 
modulus 
(kg/cm.sup.2) 
Tensile 67 50 50 
elongation 
(%) 
______________________________________ 
Measurement of Melt Viscosities 
Samples of the respective purified star-shaped nylons of Examples 6-8 were 
measured for their melt viscosities at 230.degree. C., using a capillary 
rheometer (capirograph) manufactured by Toyo, Inc., with a projecting die 
having a diameter of 1 mm. The shear rate used here was 
1.217.times.10.sup.3 (1/sec). The results of measurement are shown in 
Table 3. 
TABLE 3 
______________________________________ 
Example 6 Example 7 Example 8 
______________________________________ 
Melt viscosity 
200 305 298 
(poise) 
______________________________________ 
Evaluation of Examples 6-8 
As is clearly shown in Table 2, the star-shaped nylon of Examples 6-8 , 
with a molecular weight per polymer chain in the nylon molecule being only 
1/4-1/3 of that of the linear nylon in Comparison 1, exhibited tensile 
strength, tensile modulus and tensile elongation not being much different 
from those of Comparison 1. 
As is clearly shown in Table 3, the star-shaped nylons of Examples 6-8 have 
melt viscosities at 230.degree. C. being lower than those of the linear 
nylon of Comparison 1 almost by one figure. 
Measurement of Glass Transition Temperatures 
The star-shaped and linear nylons of Examples 1, 3, 6, 7 and 8 and 
Comparison 1 were measured for their dynamic visco-elasticities with a 
visco-elasticity spectrometer VES-F manufactured by Iwamoto Seisakusho, 
Inc., to determine the glass transition temperatures thereof. The results 
are shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Exmaple 1 
Example 3 
Example 6 
Example 7 
Example 8 
Comparison 1 
__________________________________________________________________________ 
Glass 70 72 84 80 72 65 
transition 
temperature 
(.degree.C.) 
__________________________________________________________________________ 
As is apparently shown in Table 4, the star-shaped nylons of Examples 1, 3, 
6, 7 and 8 have higher glass transition temperatures or an index of 
thermal stability, than the linear nylon of Comparison 1. 
Example 9 
In this example, the polymerization core used in Example 3 or the 
3,5,3',5'-biphenyltetracarboxylic acid represented by Formula 1 was 
synthesized as described hereunder. 
A 51.0-g portion of 1,3-dicarboxy-5-bromobenzene was dissolved in a 
solution of 33.3 g of sodium hydroxide and 120 ml of water, followed by 
addition of 0.330 g of PdCl.sub.2.2NaCl to the solution, after which the 
temperature was increased to 90.degree. C. In the course of 
temperature-increasing, a solution of 30 ml of water, 6.66 g of methanol 
and 9.57 g of formic acid was added dropwise to the mixture over a period 
of 1 hour. After the completion of the addition, the mixture was stirred 
for 4 hours while keeping the temperature at 90.degree. C. 
After the above-mentioned reaction was over, the Pd was filtered off, and 
100 ml of water was added to the filtrate, followed by addition of 90 g of 
36% hydrochloric acid solution while cooling with ice, thereby 
precipitating a white solid. This white solid was filtered off from the 
liquid phase and purified by recrystallization operation with 
N,N-dimethylformamide. The yield was 13.0 g (38.0%). 
The white crystals mentioned above were confirmed to have the chemical 
structure represented by Formula 1 by measurement of .sup.1 H-NMR and IR 
and by elementary analysis thereof. The results showed that the product is 
a novel compound not reported so far, so the present inventors named it 
3,5,3',5'-biphenyltetracarboxylic acid according to the nomenclature of 
IU (International Union of Pure and Applied Chemistry).