JPH0547565B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a terminal capping agent for polyimide. More specifically, the present invention relates to an end-capping agent for polyimide that is suitable as a matrix resin that has good storage stability in varnish and high mechanical properties in fiber-reinforced composite materials.

[Prior art and problems to be solved by the invention] Condensation polymerization type polyimides become insoluble in organic solvents as the degree of polymerization increases, so when used as a matrix resin for composite materials, so-called amic acid prepolymers before dehydration and ring closure are used. NMP, DMF in the state of
It has been used by dissolving it in a high boiling point solvent such as and impregnating it into reinforcing fibers.

However, with this method, it is difficult to remove condensed water and high-boiling point solvents that are generated due to ring closure during molding, so these volatile components remain in the molded product, creating voids and reducing physical properties. There was a problem.

Therefore, addition-curing polyimide was developed to solve this problem. Addition-curing polyimide is an oligomer with a molecular weight of about 1,500 that has addition-reactive nadzic acid at the end. It becomes a polyimide polymer through an amic acid prepolymer, and then is crosslinked through a ring-opening addition reaction of the nadzic acid at the end. It is a synthetic resin.

However, addition-curing polyimides also include NMP and DMF.
It has the problem that it is only soluble in high boiling point solvents such as. Therefore, as a result of research to improve solubility, PMR type polyimide (in-situ
Polymerization of Monomeric Reactants) was developed by TRW Systems in the United States [Journal of Applied Polymer Science (J.
Appl.Polym.Sci.). 16, (1972), 905]. In other words, PMR type polyimide is characterized in that the varnish is prepared by dissolving the monomer in a low boiling point solvent, whereas with conventional polyimide, the varnish is prepared by dissolving the amic acid prepolymer in a high boiling point solvent. . For example, PMR-15, a typical resin among PMR type polyimides, has 3,3′4,
A varnish was prepared by directly dissolving 4'-benzophenone tetracarboxylic acid dimethyl ester (BTDE), nadic acid monomethyl ester (NE), and 4,4'-diaminodiphenylmethane (DDM) in methanol. Prepreg is manufactured using a wet method. However, NE
Compared to aromatic tetracarboxylic acid diesters such as BTDE, they are highly reactive with diamines such as DDM, and therefore are not easily reacted with NE during varnish storage.
The problem was that the reaction with DDM proceeded preferentially, producing low molecular weight bisdiimide (BNI) [ACS Organic Coatings and Plastics (ACS
Organic Coatings and Plastics), 40, (1979),
935; Journal of Applied Polymer Science (J.Appl.Polym.Sci.), 27 (1982),
4295]. As described above, since the monomer composition in the prepared resin solution changes during storage, it has been extremely difficult to produce a prepreg with stable quality.

When a large amount of BNI is produced, the remaining monomers form oligomers with high molecular weight, which changes the molecular weight distribution of the entire resin, which reduces fluidity during molding and worsens moldability. In addition, the composite materials obtained in this way deteriorated mechanical properties such as interlaminar shear strength and bending strength, and also had an adverse effect on heat resistance such as a decrease in thermal decomposition temperature [National Sanpe Symposium
SAMPE Symposium), 26, (1981), 89].

Therefore, the present inventors conducted intensive studies on terminal capping agents suitable for PMR type polyimide that do not have the above-mentioned drawbacks and have excellent storage stability, and as a result, they arrived at the following invention.

[Means for Solving the Problems] The present invention has the following configuration in order to solve the above problems. That is, it is an end-capping agent for polyimide represented by the formula [].

It goes without saying that the terminal capping agent for polyimide of the present invention can be used for other types than the PMR type, but as described below, the effect of the present invention is greatest in the case of the PMR type.

A conventional nadic acid-type end capping agent, nadic acid monoalkyl ester (NE), forms BNI during storage.
As a result of research into the causes of this formation, we have reached the following conclusion. In other words, BTDE, which is a monomer constituting the main chain of PMR polyimide, is an aromatic tetracarboxylic acid dialkyl ester, while NE is an alicyclic dicarboxylic acid monoalkyl ester, which is a chemical structural difference. There was a fundamental cause. The reaction between aromatic disulfonic acid monoalkyl ester and aromatic amine
In contrast, alicyclic dicarboxylic acid monoalkyl esters are highly reactive, so the reaction with aromatic amines proceeds easily even at room temperature. Therefore, in order to solve this problem, it is necessary to reduce the reactivity of the terminal capping agent so that it has the same reactivity as other monomers that constitute the main chain of PMR type polyimide.

Therefore, the present inventors conducted intensive studies on terminal capping agents with controlled reactivity, and found that a nadimide-type terminal capping agent having an aromatic amine as a reactive moiety as shown in formula [] met this requirement. I found that it satisfies me. In other words, by introducing an aromatic amine instead of using a highly reactive alicyclic dicarboxylic acid monoester as the reactive part of the terminal capping agent, it is possible to provide reactivity equivalent to that of other monomers. I made it.

Now, the end-capping agent according to the present invention is produced by, for example, reacting nadichic acid anhydride and nitroaniline in an acetamide solution to synthesize nadimidonitrobenzene as an intermediate, and then reducing this using stannous chloride ( ) can be synthesized by the method shown in the reaction formula.

In addition to this, there is also a method shown in the reaction formula () in which maleimidonitrobenzene is synthesized in advance, cyclopentadiene is added, and the nitro group is finally reduced, so the synthesis method is not limited to ().

In addition, in the PMR type polyimide varnish using the terminal capping agent of the present invention, heat resistance and Resins with different physical properties, moldability, etc. can be obtained.

As the average molecular weight of the resin obtained from PMR type polyimide varnish increases when it is oligomerized, its mechanical properties improve, but its heat resistance and moldability deteriorate. Therefore, the average number of repeating units n when oligomerized is preferably in the range of 0 to 10, especially n
A range of 0.4 to 2 is well-balanced in terms of heat resistance, moldability, and physical properties, and is suitable as a PMR type polyimide varnish.

When the PMR type polyimide varnish using the terminal capping agent of the present invention is impregnated into reinforcing fibers, it has good prepreg tack and drapability and excellent moldability, and the resin obtained by curing it has excellent properties. Due to its heat resistance and mechanical properties, it is an excellent matrix resin for fiber-reinforced composite materials.
In addition, it is suitable as an adhesive or a molding material.

When using the PMR type polyimide varnish using the terminal capping agent of the present invention as a matrix for fiber-reinforced composite materials, the best effect can be obtained when carbon fiber is used as the reinforcing fiber, especially when high-strength carbon fiber is used. It will be done. In addition to carbon fibers, glass fibers can also be used as reinforcing fibers, and different types of fibers can also be mixed. The form of the fibers may be any form such as long fibers, woven fabrics, knitted fabrics, matte fibers, and cut fibers.

[Example] The present invention will be explained in further detail by the following example.

Example 1 Synthesis of 1-amino-4-nadiimidobenzene a 1-nitro-4-nadiimidobenzene 138 g of 1-amino-4-nitrobenzene was dissolved in 500 ml of dimethylacetamide, and 164
A solution of 500 ml of dimethylacetamide dissolved in 500 ml of dimethylacetamide was added dropwise while stirring at room temperature. After the dropwise addition was completed, the mixture was stirred at room temperature for 1 hour, and then 150 ml of triethylamine and 150 ml of benzene were added and reacted at 140°C for 3 hours. After the reaction was completed, the mixture was left at room temperature overnight. The orange precipitate was filtered, washed with water, and dried under vacuum.

Yield 236g (83%) Elemental analysis results (calculated value) C; 63.98 (63.38) H; 4.11 (4.23) N; 10.02
(9.86) b 1-amino-4-nadimidobenzene 200 g of 1-nitro-4-nadimidobenzene
Dissolve in acetonitrile and add 850 g of ferric chloride.
Tin dihydrate was added and reacted at 60°C for 2 hours. After cooling to room temperature, the reaction solution was poured into water and neutralized with sodium carbonate. The precipitate was filtered, dried in vacuo, and then Soxhlet extracted with acetonitrile. Acetonitrile was distilled off under reduced pressure to obtain a white solid.

Yield 130g (75%) Elemental analysis result (calculated value) C; 70.32 (70.87 H; 5.68 (5.51) N; 10.87
(11.02) Example 2 Ethanol was added to 3,3',4,4'-benzophenonetetracarboxylic acid, and the mixture was refluxed at boiling point for 3 hours to completely dissolve it to obtain a solution of diester compound (BTED). Next, terminal capping agents 1-amino-4-nadiimidobenzene (ANB) and 4,4'-diaminodiphenylmethane (DDM) were dissolved in this solution. At this time, ANB:
The molar ratio of BTDE:DDM was 2:3:2. Excess ethanol was distilled off from this solution under reduced pressure to obtain a PMR type polyimide varnish.

When this varnish was stored at 20℃ and subjected to high-performance liquid chromatography analysis over time, it was found that 60
There was no change in its components even after a day had passed, and its stability was good.

A prepreg was created by the hot melt method using varnish that had been stored at 20°C for 60 days and "Toray Card" T400 manufactured by Toray Industries, Inc. The resin content of the obtained pre-reg was 39.6%. The prepreg obtained there was cut into pieces of 30 cm in length and 20 cm in width, which were then stacked and placed in an autoclave at 160°C and pressurized to 14Kg/ ^cm2 , then heated to 290°C, held for 2 hours, and then brought to room temperature. After cooling, the molded product was taken out from the autoclave. The obtained molded product was after-cured at 316° C. for 6 hours to obtain a molded product. The volume content of carbon fiber in the obtained molded product was 60.2%, and the glass transition temperature measured by the DSC method was 332°C, indicating that it had good heat resistance.

Next, a test piece was cut out from the obtained molded product according to ASTM D-790 and its bending properties were measured, and the bending strength was 190Kg/mm ² and the bending modulus was 13.8t/
mm ² and had excellent mechanical properties.

Comparative Example A PMR type polyimide varnish was prepared in the same manner as in Example 2, except that nadic acid monomethyl ester (NE) was used as the terminal capping agent and the molar ratio of NE:BTDE:DDM was 2:2:3. did.

When this varnish was stored at 20℃ and subjected to high-performance liquid chromatography analysis over time, it was found that 60
After a day had passed, 13% of bisnadimide had been produced, and the composition of the varnish had changed. A prepreg was made using this varnish in the same manner as in Example 2, and the bending properties of ^the composite material were measured.
It was 13.6t/mm ² and showed poor physical properties.

[Effects of the Invention] The polyimide varnish of the present invention using the terminal capping agent for polyimide has good storage stability and is suitable as a matrix resin for fiber-reinforced composite materials having high mechanical properties.

Claims (1)

[Claims] 1. An end-capping agent for polyimide represented by the formula [].