JPH07109352A - Crosslinked star-shaped nylon and production of molding thereof - Google Patents

Abstract

PURPOSE:To provide a crosslinked star-shaped nylon exhibiting a low viscosity and excellent in mechanical properties and a method for producing molding thereof. CONSTITUTION:In this crosslinked star-shaped nylon, a molecular structure of a star-shaped nylon is produced by forming nylon polymer chains from the respective polymerization initiation groups in a polymerization nuclei compound having three or more polymerization initiation groups as the starting points and a crosslinked structure is formed through a crosslinking-coupling molecule having two or more functional groups reactive with the terminals between the terminals of the respective polymer chains of different star-shaped nylon molecules. The method for production of a crosslinked star-shaped nylon molding is carried out by heating the star-shaped nylon up to the melting temperature, admixing a crosslinking-coupling molecule therewith, casting the molten mixture before formation of the crosslinked structure and then forming the crosslinking structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked star-shaped nylon and a method for producing a molded body thereof, and more specifically, it is a star-shaped nylon which is one of the characteristics of star-shaped nylon and is too low in the pursuit of low melt viscosity during molding. As a countermeasure against problems such as excessively low molecular weight, resulting in a star-shaped nylon molded body with poor mechanical properties, molding the star-shaped nylon while maintaining its low melt viscosity. The present invention relates to a crosslinked star nylon and a method for producing a molded article thereof, which is intended to improve the mechanical properties of the body.

[0002]

2. Description of the Related Art A so-called star-shaped polymer is a polymer compound having a structure in which a plurality of polymer chains are radially extended from a main polymer nucleus. Has a low molecular weight and is characterized by a chemical structure in which each polymer chain is bound through a polymer nucleus. Therefore, in the molten state, the star-shaped polymer has relatively little entanglement of polymer chains, and therefore has a relatively low melt viscosity, which enables so-called thin injection molding, and is good with other polymers. In many cases, it exhibits desirable compatibility and is accompanied by desirable physical properties such as expanding the possibility of polymer blending.

As for nylon, such star-shaped nylon has been studied so far, and U.S. Pat. S. P. 4,5
No. 99,400, American Chemica
Polymer Prepri issued by lSociety
nts, Vol. 130, No. 1, P117 ~ (19
89) and so on. For example, a star-shaped nylon 6 in which an amine compound having a plurality of amino groups at positions distant from each other in one molecule is used as a polymerization nucleus and a nylon monomer ε-caprolactam is subjected to ring-opening polymerization for each amino group is It is disclosed.

On the other hand, the applicant of the present invention, as a novel star-shaped nylon having superior properties to the above-mentioned star-shaped nylon, has three or more polymerizations in which aromatic carbons are substituted for each carbon at positions separated by one or more. A star type nylon having a polymerization nucleus of an aromatic compound having an initiation group and a polymer chain of nylon originating from each of the polymerization initiation groups has already been proposed (Japanese Patent Application No. 5-62896).

[0005]

However, in the star-shaped nylon using the above amine compound as a polymerization nucleus, due to the fact that the polymerization nucleus does not have a rigid molecular structure, etc. It shows no decrease in melt viscosity. On the other hand, in the star nylon of Japanese Patent Application No. 5-62896 proposed by the applicant of the present invention, since the polymerization nucleus is an aromatic compound having a rigid molecular structure, at least the theoretically expected melt viscosity can be expected. Can be ensured.

However, even with the star nylon of Japanese Patent Application No. 5-62896, if the star nylon is made to have an excessively low molecular weight so as to pursue a low melt viscosity, the molded article will have a range corresponding to this. It is unavoidable that the mechanical properties are relatively deteriorated to some extent.

Therefore, it is an object of the present invention to improve the mechanical properties of the molded product while maintaining the low melt viscosity of the star nylon.

[0008]

[Means for Solving the Problems]

(Structure of the first invention) The structure of the first invention of the present application (the invention of claim 1) for solving the above-mentioned problems is the structure of the polymerization initiation group in the polymerization nucleus compound having three or more polymerization initiation groups. Star-shaped nylon molecules are formed by forming polymer chains of nylon from each of the starting points, and between the ends of the polymer chains of different molecules of the star-shaped nylon, two or more having reactivity with the ends. It is a cross-linked star-shaped nylon that forms a cross-linked structure through a cross-linking connecting molecule having the functional group of.

(Structure of the Second Invention) The structure of the second invention of the present application (the invention according to claim 2) for solving the above-mentioned problems is a part or all of the linking molecule for crosslinking in the first invention. Is a crosslinked star nylon having a polyether moiety or a polyolefin moiety having a predetermined molecular weight sufficient to improve the brittleness of the star nylon, between the two or more functional groups.

(Structure of Third Invention) The structure of the third invention of the present application (the invention according to claim 3) for solving the above-mentioned problems is the first invention in a molten state of the star-shaped nylon in the first invention. Mixed with the linking molecule for crosslinking in the invention,
Casting the molten mixture before a crosslinked structure is formed, and then forming the crosslinked structure to obtain the crosslinked star nylon molded product according to the first aspect of the present invention. Is the way.

[0011]

[Action]

(Operation of the first invention) The crosslinked star nylon of the first invention exhibits more excellent mechanical properties than the uncrosslinked star nylon of the same molecular weight because of its crosslinked structure.

(Operation of the Second Invention) In the crosslinked star nylon of the second invention, the crosslinking linking molecule functions as a so-called soft component, and the mechanical properties of the star nylon are improved.
It is particularly effective in improving brittleness.

(Operation of the Third Invention) In the method for producing a crosslinked star-shaped nylon molded article according to the third invention, thin injection molding or the like is effectively performed by utilizing the low melt viscosity of the star-shaped nylon before crosslinking. Further, the mechanical properties of the molded product can be improved by forming the crosslinked structure after casting.

[0014]

【The invention's effect】

(Effect of the first invention) The crosslinked star-shaped nylon of the first invention can provide a novel nylon material which can be molded into a thin material and has excellent mechanical properties as a molded body as compared with the star-shaped nylon. .

(Effect of the Second Invention) The crosslinked star nylon of the second invention provides a novel nylon material having improved brittleness, in particular, compared with the effect of the first invention, in addition to the effect of the first invention. it can.

(Effect of the Third Invention) By the method for producing a crosslinked star nylon molded body according to the third invention, thin injection molding or the like is effectively performed by utilizing the low melt viscosity of the star nylon before crosslinking. In addition, the mechanical properties of the molded product can be improved by forming a crosslinked structure after casting.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the first to third inventions will be described. The star-shaped nylon polymer compound used in the present invention is 3
It has at least one nylon polymerization initiation group. A typical example thereof is one having three or more polymerization initiating groups which are substituted for every carbon at every other position in the aromatic ring of the aromatic compound.

When such an aromatic polymer nucleus compound is used, the polymer nucleus serves as an effective spacer, and it is difficult for the polymer chains in the same molecule to come into contact with each other at the initial stage of polymerization of nylon, and the active polymer chain is active. The formation of intermolecular crosslinks between them is prevented. As a result, intermolecular hydrogen bond formation is promoted during solidification after the completion of nylon polymerization, and good crystallization is possible.

Furthermore, since the aromatic ring has a polygonal plate shape,
At the time of solidification after the completion of polymerization, these plate-like aromatic rings tend to be aligned and oriented in a stacked state in the thickness direction. As a result, the polymer chains of each star-shaped nylon molecule also tend to be oriented parallel to each other between the molecules, further promoting the formation of intermolecular hydrogen bonds.

The aromatic ring of the above aromatic compound includes a benzene ring, naphthalene ring, anthracene ring, pyridine ring, pyrrole ring, indole ring, furan ring, thiophene ring, purine ring, quinoline ring, phenanthrene ring, porphyrin ring, A phthalocyanine ring and a naphthalocyanine ring are included. Particularly, the porphyrin ring, the phthalocyanine ring, and the naphthalocyanine ring are large-sized cyclic structures, and have an advantage that many polymerization initiation groups can be set as compared with the benzene ring and the like.

The skeleton structure of the aromatic compound may be composed of only the above-mentioned various aromatic rings or condensed rings thereof, and biphenyl, triphenyl, in which two or more aromatic rings are bonded without being condensed, It may be composed of bipyridine or the like. Further, it may have a structure having a portion containing an alkylene group, an arylene group, an arylene group, a diazo group, a carbonyl group, an ether group, an amide group, an ester group, an amino group or the like between two or more aromatic rings. .

An amino group or a carboxyl group is most suitable as the polymerization initiation group for the aromatic compound, but other polymerization initiation groups having a polymerization initiation action for the nylon monomer can also be used.

The polymerization initiating group does not necessarily have to be directly bonded to the carbon of the aromatic ring, but may be bonded through a specific intermediate structure portion. Examples of such an intermediate structure portion include an alkylene group, an arylene group, and an arylene group.

Some typical examples of the polymerization nuclei are as follows. 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-naphthalene tetracarboxylic acid 1,3,6,8-acridine tetracarboxylic acid 3,5,3 ', 5'-benzophenone tetracarboxylic acid 1,3,5-triaminobenzene 1,3 , 5-tri (aminomethyl) benzene 3,5,3 ', 5'-tetraaminobiphenyl 2,4,6-triaminopyridine 3,5,3', 5'-tetraaminobipyridyl 1,3,5,5 7-Tetraaminonaphthalene 1,3,6,8-tetraaminoacridine 3,5,3 ′, 5′-tetraaminobenzophenone

A typical porphyrin-based polymer nucleus is, for example, metal-free tetrakis (carboxyphenyl).
There are porphyrin, aluminum tetrakis (carboxyphenyl) porphyrin, titanium tetrakis (carboxyphenyl) porphyrin, nickel tetrakis (carboxyphenyl) porphyrin, rhodium tetrakis (carboxyphenyl) porphyrin and the like.

Typical examples of the phthalocyanine-based polymerization nucleus include, for example, metal-free tetracarboxyphthalocyanine, chloro (tetracarboxyphthalocyaninate) aluminum, and (tetracarboxyphthalocyaninate).
Cobalt, (Tetracarboxyphthalocyanineate)
Copper, (tetracarboxyphthalocyaninato) nickel, (tetracarboxyphthalocyaninato) iron, (tetracarboxyphthalocyaninato) oxovanadium, (tetracarboxyphthalocyaninato) lead, (tetracarboxyphthalocyaninato) )magnesium,
Examples include (tetracarboxyphthalocyaninato) tin and (tetracarboxyphthalocyaninato) zinc.

Typical examples of naphthalocyanine-based polymerization nuclei include metal-free tetracarboxynaphthalocyanine and metal tetracarboxynaphthalocyanine.

In addition to the above, as the polymerization nucleus compound, an aliphatic compound having three or more amino groups or carboxyl groups in the molecule can be used.

The nylon monomer is not particularly limited. Preferably valerolactam, caprolactam, 2-
Nylon monomers such as azacyclotridecanone, 2-azacyclotridecanone (laurolactam), and 1,8-diazacyclotetradecane-2,7-dione can be used.

The method for preparing the star nylon used in the present invention is not particularly limited. However, when polymerizing a nylon monomer, if a polymerization initiator other than the polymerization nucleus compound (for example, water or acid) is mixed, linear nylon is also generated, so be careful not to mix these polymerization initiators. Should be.

The star nylon polymerization process is preferably carried out under reduced pressure in order to eliminate water and oxygen contained in the reaction system material, and in a sealed tube to prevent volatilization of volatile nylon monomer. It is desirable to polymerize.

The molecular weight of the star-shaped nylon, which is theoretically predicted, is determined by the number of polymerization initiating groups in the polymerization nucleus and the charging ratio with the nylon monomer. The molecular weight of each polymer chain in the star-shaped nylon molecule is approximately equal to the total molecular weight divided by the number of polymer chains.

As the cross-linking molecule, for star-shaped nylon having a carboxyl group at the end of the polymer chain, a compound having two or more amino groups, such as a diamino compound, is used. For star-shaped nylon having a terminal, a compound having two or more carboxyl groups such as dicarboxylic acid or a diisocyanate compound is used.

A method according to claim 1, which has two or more amino groups.
Alternatively, typical examples of the connecting molecule described in 2 are m-xylylenediamine, p-xylylenediamine, m-diaminobenzene, p-diaminobenzene, H ₂ N- (C
H ₂ ) _n —NH ₂ (n is an integer of 2 to 20), polymers having a molecular weight of about 500 to 5,000 and having amino groups at both ends (polyethylene oxide, polypropylene oxide, polybutadiene, polyisoprene, etc.) and the like.

Representative examples of the linking molecule having two or more carboxyl groups described above are isophthalic acid, terephthalic acid and HOOC- (CH ₂ ) _n-.
COOH (n is an integer of 2 to 20), a polymer having a carboxyl group at both ends and a molecular weight of about 500 to 5,000 (polyethylene oxide, polypropylene oxide, polybutadiene, polyisoprene, etc.) and the like.

Representative examples of the linking molecule which is the above-mentioned isocyanate compound according to claim 1 or 2 are m-xylylene diisocyanate, p-xylylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate and O = C. = N- (CH _{2) n} -N
= C = O (n is an integer of 2 to 20), and polymers having an isocyanate group at both ends and a molecular weight of about 500 to 5,000 (polyethylene oxide, polypropylene oxide, polybutadiene, polyisoprene, etc.) and the like.

An embodiment of the method for producing a crosslinked star nylon molding according to claim 3 will be described.
The mixing ratio of the star-shaped nylon and the cross-linking connecting molecule is such that the concentration of the terminal group of the polymer chain of the star-shaped nylon-which is a carboxyl group or an amino group-and the functional group of the connecting molecule-the carboxyl group,
It can be determined by the concentration of-which is an amino group or an isocyanate group.

The terminal group concentration (mol / g) of the polymer chain is obtained by the following formula. Terminal group concentration = (1 / molecular weight of star-shaped nylon) × number of polymer chains of star-shaped nylon On the other hand, the functional group concentration (mol / g) of the linking molecule is determined by the following formula. Functional group concentration = (1 / molecular weight of linked molecule) x number of functional groups in one molecule

Theoretically, when the terminal group concentration and the functional group concentration are equal, the terminal group of the polymer chain of star-shaped nylon and the functional group of the cross-linking linking molecule are all involved in the cross-linking formation, Is most developed. However, in reality, there is a problem of homogeneity of the mixing of the star-shaped nylon and the linking molecule, and it is not always necessary that all the terminal groups and the functional groups react with each other in order to improve the mechanical properties. Therefore, even if the ratio of terminal group concentration / functional group concentration is narrow, it is better to allow a margin in the range of 5 to 0.3.

The proportion of the linking molecule having a polyether moiety or polyolefin moiety in the linking molecule for cross-linking, or the molecular weight of the polyether moiety or polyolefin moiety is particularly determined for cross-linked star nylon. It is relatively different depending on whether such physical properties are strongly demanded, and it cannot always be specified uniformly. However, it is generally desirable that the proportion of the polyether portion or the polyolefin portion in the crosslinked star nylon is 5 to 50 wt%. If it is less than this range, the brittleness of the star nylon is insufficiently improved, and if it is more than this range, the strength and elastic modulus of the crosslinked star nylon are reduced.

The mixing of the star-shaped nylon and the linking molecule for crosslinking is performed in a molten state. The temperature at that time is not less than the melting point of star-shaped nylon and not more than the thermal decomposition temperature of nylon. Note that in this temperature range, it takes time to melt the star-shaped nylon at a temperature almost the same as the melting point and the productivity tends to be relatively reduced, and at a temperature close to the upper limit, the star-shaped nylon and the crosslinking linking molecule are It is necessary to take care so that the crosslinking reaction of (1) does not proceed too quickly and the viscosity does not rise before casting. As an example of the melting temperature, in the case of the low molecular weight star type nylon 6, the melting temperature is 200 ° C. or higher, preferably 220 to 260 ° C.

The casting of the molten mixture is carried out before the crosslinking reaction in the molten mixture has proceeded sufficiently. Otherwise, the viscosity of the molten mixture will increase due to the progress of the crosslinking reaction, and the required casting pressure will increase, so that the advantages of the low-viscosity casting of the third invention cannot be secured. Therefore, it is best to cast immediately after the nylon melts. There is a possibility that the star-shaped nylon and the cross-linking linking molecule are sufficiently mixed in the casting step itself, and a known mixing promoting means may be applied to the injection passage and the injection port of the molten mixture. If the mixing is still insufficient, it is advisable to mix the nylon immediately after it is melted by a suitable stirring means and then cast it immediately.

After the molten mixture is cast, the cross-linking reaction between the star-shaped nylon and the cross-linking linking molecule may be rapidly advanced at a temperature as high as possible, as long as the decomposition temperature of the nylon is not reached. For example, when low molecular weight star type nylon 6 is used, the heating temperature after casting is 200 ° C. or higher, preferably 220 to 260 ° C. Also, the heating time after casting required to cause an effective degree of crosslinking reaction is
Although it depends on the heating temperature, it is about 1 to 20 minutes. If the above heating temperature or heating time is insufficient, the degree of crosslinking becomes insufficient, and the mechanical properties of the crosslinked star nylon tend to be unsatisfactory. Further, if the heating temperature and the heating time are excessive, the physical properties of nylon tend to be deteriorated due to thermal decomposition of nylon.

[0044]

【Example】

(Synthesis of Polymer Nucleus Compound) 5-Bromoisophthalic Acid 51.
0 g was dissolved in an aqueous solution of 120 ml of water and 33.3 g of caustic soda, and PdCl ₂ .2NaCl was added to the solution in an amount of 0.
330 g were added and the temperature was raised to 90 ° C. 30 ml of water, 6.66 g of methanol, 9.57 g of formic acid during the temperature raising process
Was added dropwise over 1 hour. After the temperature was raised, the mixture was stirred at 90 ° C. for 4 hours, and then Pd was removed by filtration. 1 water in this filtrate
00 ml was added, and while cooling with ice, 90% of 36% hydrochloric acid solution was added.
When g was added, a white solid precipitated. The white solid was filtered and then recrystallized with dimethylformamide to obtain 13.0 g of 3,5,3 ′, 5′-biphenyltetracarboxylic acid.

(Synthesis of Star Nylon 6) 7.60 g of the sufficiently dried 3,5,3 ′, 5′-biphenyltetracarboxylic acid and 115 g of ε-caprolactam were placed in a glass container and the pressure was reduced by a vacuum pump. I sealed the tube below. This container was heated in an oven at 120 ° C. for 2 hours to melt ε-caprolactam, and then shaken and stirred for 3,5,5.
3 ', 5'-biphenyltetracarboxylic acid was dissolved in a uniform mixed state. Then raise the temperature to 250 ° C and
After reacting for a period of time, the mixture was cooled and the sealed tube was opened. The polymerized resin was taken out, freeze-pulverized, thoroughly washed and then vacuum dried to obtain 4-chain star nylon 6 having a molecular weight of 4,450 ( Hereinafter this is referred to as "star nylon sample".)

[Example 1] In this example, the physical properties of the crosslinked star nylon according to claim 1, the crosslinked star nylon and the uncrosslinked star nylon according to claim 2 were evaluated as follows. went.

Experimental Example 1 Star-shaped nylon sample 10.0 g
And m-xylylenediamine (0.306 g) are mixed to prepare C
It was placed in a cylinder of a Mini Max molding machine CS-183 manufactured by SI Co., and melted at 230 ° C. for 2 minutes. Then, this molten mixture was cast into a mold heated to 230 ° C. in which a test piece having the shape and size shown in FIG. 1 was molded, and the mold was further heated for 7 minutes at that temperature, and then the mold was cooled. The test piece was taken out. Tensile speed 0.06 for this test piece
30 cm / min. When the tensile test was conducted at (2.0 rpm), the yield strength was 66.1 MPa and the elastic modulus was 812 M.
Pa and elongation at break were 15%.

(Experimental Example 2) Star nylon sample 12.0 g
And 3.0 g of polyethylene oxide having amino groups at both ends (manufactured by Koei Chemical Industry, molecular weight 1,000) is mixed with CS
It was put in a cylinder of a Mini Max molding machine CS-183 manufactured by I Co. and melted at 230 ° C. for 2 minutes. Then, this molten mixture was cast into the same mold as in Experimental Example 1 heated to 230 ° C., the mold was heated at that temperature for 10 minutes, and then the mold was cooled to take out a test piece. The tensile speed of this test piece was 0.0630 cm / min. (2.0 r.p.
m.) tensile test showed that the yield strength was 17.5 M
Pa, elastic modulus was 271 MPa, and elongation at break was 118%.

Comparative Experimental Example 1 Star Nylon Sample 2.0
g was placed in a cylinder of a CSI Mini Max molding machine CS-183 and melted at 230 ° C. for 2 minutes. Then, Experimental Example 1 in which the melt was heated to 90 ° C
After casting in the same mold, the mold was cooled and the test piece was taken out. Tensile speed 0.0630 cm /
min. When the tensile test was performed at (2.0 rpm),
The yield strength was 14.9 MPa, the elastic modulus was 404 MPa, and the elongation at break was 4%.

(Evaluation of Example 1) In Experimental Example 1, as compared with Comparative Experimental Example 1, improvement in strength and elastic modulus was observed, and the strength of commercially available nylon (linear chain, molecular weight 13,000) , And was about the same as the elastic modulus. In Experimental Example 2, the elongation at break was improved to the same level as commercial nylon (straight chain, molecular weight 13,000),
The brittleness was remarkably improved as compared with Comparative Experimental Example 1.

[Example 2] This example relates to a method for producing a crosslinked star type nylon molding according to claim 3, wherein a crosslinked star type nylon, an uncrosslinked star type nylon and a linear type nylon are melted under a certain condition. The viscosity or casting pressure was evaluated as follows.

(Experimental Example 3) 200 between the male type and the female type
Into the female mold of the mold having a void of μm, 10.0 g of a star-shaped nylon sample and 0.306 g of m-xylylenediamine
3.0 g of a mixture with and was melted at 230 ° C. for 2 minutes. Then, 2 male with a force of 2 kg / cm ²
It was pressed in for about 2 seconds and then heated at 230 ° C for another 10 minutes. After cooling, pulling out the male mold gives 20
A 0 μm thick cross-linked star nylon film was uniformly coated.

(Comparative Experimental Example 2) 3.0 g of the same mixture as in Experimental Example 3 was placed in a female mold of the same mold as in Experimental Example 3 and the temperature was 230 °.
Heating was continued at C for 12 minutes. Then, an attempt was made to press fit the male type into the female type, but the force could not be applied even with a force of 25 kg / cm ² for 5 minutes.

COMPARATIVE EXPERIMENTAL EXAMPLE 3 A four-chain star-shaped nylon 6 (molecular weight of 13,000) was added to the same female mold as in Experimental Example 3.
0) 3.0 g was put and heated and melted at 230 ° C. for 2 minutes. Then, it took 10 seconds with a force of 20 kg / cm ² to press-fit the male mold. After cooling, pull out the male mold to get 2
It was coated with a star-shaped nylon film having a thickness of 00 μm.

(Comparative Experimental Example 4) A linear nylon 6 (molecular weight 13,000) was added to a female mold having the same mold as in Experimental Example 3.
3.0 g was added and the mixture was heated and melted at 230 ° C. for 2 minutes. After that, an attempt was made to press-fit the male type, but the press-fitting could not be performed even with a force of 25 kg / cm ² for 5 minutes.

(Evaluation of Example 2) In Experimental Example 3, the comparative experimental example 2 is uncrosslinked, and the comparative experimental example 3 has a low molecular weight. For No. 4, because of the star-shaped structure, it was possible to shorten the casting time and the casting pressure, respectively.

[Brief description of drawings]

FIG. 1 is a diagram showing the shape and dimensions of a sample piece.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Takahashi 1st 41st Yokomichi, Nagakute Town, Nagakute Town, Aichi District, Aichi Prefecture Toyota Central Research Institute Co., Ltd.

Claims (3)

[Claims] 1. A star-shaped nylon molecule is formed by forming a polymer chain of nylon starting from each of the polymerization initiation groups in a polymerization nucleus compound having three or more polymerization initiation groups, and wherein the star-shaped nylon molecule is formed. Between the ends of the polymer chains of different molecules of type nylon, a cross-linking structure is constituted through a cross-linking linking molecule having two or more functional groups reactive with the ends. Cross-linked star nylon. 2. A part or all of the cross-linking linking molecule has, between its two or more functional groups, a polyether moiety or polyolefin moiety having a predetermined molecular weight sufficient to improve the brittleness of star nylon. The crosslinked star nylon according to claim 1, wherein 3. The star-shaped nylon according to claim 1 is mixed in a molten state with the linking molecule for crosslinking according to claim 1, and the molten mixture is formed before the crosslinked structure according to claim 1 is formed. The method for producing a crosslinked star-shaped nylon molded article according to claim 1, wherein the crosslinked star-shaped nylon molded article according to claim 1 is obtained by casting into a mold and then forming the crosslinked structure.