WO1981001293A1

WO1981001293A1 - Acetylene terminated imide oligomers having improved solubilities and lower melting points

Info

Publication number: WO1981001293A1
Application number: PCT/US1980/001415
Authority: WO
Inventors: R Boschan; N Bilow; A Landis
Original assignee: Hughes Aircraft Co
Priority date: 1979-11-05
Filing date: 1980-10-23
Publication date: 1981-05-14
Also published as: IT1146143B; IT8050063A0

Abstract

Acetylene-substituted polyimides fabricated from 2,2-bis(3,4-diacarboxyphenyl) hexafluoropropane dianhydride exhibit very low melting points and are soluble in low boiling solvents. The processing characteristics of these oligomers are superior to that of prior art acetylene-substituted imide oligomers.

Description

ACETYLENE TERMINATED IMIDE OLIGOMERS HAVING IMPROVED SOLUBILITIES AND LOWER MELTING POINTS

TECHNICAL FIELD This invention relates generally to the preparation of acetylene-substituted imide oligomers and more particularly to the preparation of imide oligomers which exhibit low melting points, better solubilities, lower cure temperatures and improved processing characteristics.

BACKGROUND ART Acetylene terminated imide oligomers have been shown to be useful as high temperature adhesives, as matrix resins for high temperature lubricants, and as resins for high strength, high temperature resistance composite structural materials. The principal disadvantages of these prior art acetylene terminated oligomers are their relatively low solubilities in low boiling solvents and their high melting points. These disadvantages tend to limit their usefulness because of processing difficulties.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide oligomers which exhibit low melting points, are soluble in low boiling solvents, and cure via homopolymerization at relatively low temperatures to yield void free resins that are thermally stable and structurally strong. In accomplishing this objective while avoiding the disadvantages of the prior art and retaining the advantages of said art, we have discovered that acetylene-substituted polyiinide oligomers prepared from 2 , 2-bis ( 3 , 4-dicarboxyphenyl) hexafluoropropane dianhydride exhibit low melting points, are soluble in low boiling solvents and exhibit excellent processing, curing and structural characteristics.

The oligomers of this invention have the following structure;

Wherein n may range from 1 to 10 and Ar is derived from 1,3-bis(3-aminophenoxy) benzene or other aryldiamines. It is the use of this novel dianhydride structure which is directly responsible for the improved solubilities, lowered melting points and lowered cure temperatures which are characteristics of this present invention.

It is therefore an objective of this invention to provide addition curing acetylene substituted polyimide oligomers with significantly improved processing characteristics in part due to substantially lower melting points relative to state-of-the art acetylene-substituted oligomers. A further objective is to provide acetylene- substituted polyimide oligomers with improved solubility characteristics.

A third objective of this invention is to provide acetylene-substituted polyimide oligomers with improved melt flow characteristics.

A fourth objective is to provide oligomers of the type described with longer gel times in their moltenstate. A fifth objective is to provide oligomers of the type described which when fabricated into prepregs exhibit better tack and drape than prior art. imide oligomers.

That we have accomplished the above stated objectives while avoiding the disadvantages of the prior art and retaining most, if not all, of the advantages of said art will be apparent upon reference to the following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

We have discovered that oligomers synthesized in accordance with the following reaction sequence:

2 (DAM) + BAPB

DAM- BAPB-DAM ; and

DAM-BAPB-DAM +2 (APA)

APA-DAM-BAPB-DAM-APA

where APA i s an aminophenylacetylene, DAM is a dianhydride moiety and BAPB i s an aminophenoxy benzene, exhibit substantially better processing characteristics when 2, 2-bis(3,4- di carboxyphenyl ) hexafluoropropane dianhydride is used to provide the required dianhydride moiety. The reacti on sequence shown above yi elds polyi mi de oli gomers whi ch mel t a t 140-150 ° C whose s tructures are :

where Ar is a divalent organic moiety whose structure is

wherein X' may be O, S, CO, SO₂ or CH₂ and m range from 1 to 10 N' may be 0, 1, 2, 3 or 4 and X¹ may be O, S, CO, S0₂ or CH₂. The value of n is determined by the stoichiometry of of the reactants. For example, defining the reactants as above, the following molar ratios of APA: DAM:BAPB may be used to achieve higher molecular weight oligomers; 2:n+l:n. To obtain the desired product the preferred addition is to first slowly add the stoichiometric amount of BAPB to DAM, which yields an anhydride terminated diamine, and then add the APA to obtain the desired acetylene terminated oligomer. These oligomers are soluble in low boiling solvents such as acetone and can be homopolymerized without the use of a catalyst by heating to approximately 210°C or above. Their relatively low melting points and high solubilities in lov; boiling solvents such as acetone or tetrahydrofuran facilitates their use as molding resins, varnishes, laminating resins, and as matrix resins for composite solid lubricants. The gel time, of these oligomers at their melting points, is on the order of 5-10 minutes. By way of comparison, our prior art oligomers exhibiting gel times of from 2 to 3 minutes at their melting points.

While we prefer to prepare oligomers with 3-aminophenyl acetylene to obtain the lowest melting point product, the use of 2, 2-bis(3, 4-dicarboxyphenyl) hexafluoropropane in the above-reaction sequence allows, us to synthesize oligomers v/ith 4-aminophenylacetylene and still obtain a processable product.

The polyimide oligomer of formula I was prepared in accordance v/ith the following example:

Example 1 A solution of 1,3-bis (3-aminophenoxy)benzene (32.9 grams, 0.JU.3 mole) in N-methylpyrrolidinone (250 ml) was added drop-wise to a solution of 2,2-bis

(3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (100 grams, 0.225 mole) and N-methylpyrrolidinone (750 ml) at 50°C. After heating at 50°C for thirty minutes, 3-aminophenylacetylene (26.4 grams, 0.225 mole) in N-methylpyrrolidinone (100 ml) was added all at once. Sufficient benzene was added so that the pot temperature at reflux was 139°C. The mixture was heated at a vigorous reflux rate for 22 hours employing a Dean-Stark trap to remove the water. The solvent was removed by evaporation on a rotary film evaporator and the oligomer was triturated with ethanol several times and dried at 80°C for 72 hours. The yield was 134 grams, and its melting point was 147-152°C. The compound was found to be soluble in acetone

Example 2_ The oligomers of Example 1 cured into tough resinous products when heated to 220°C in air.

Example 3 The para-substituted analogue of Example 1 is prepared by substituting tetrahydrofuran for N-methyl pyrrolidinone as a solvent, using 4-aminophenylacetylene instead of 3-aminophenylacelytene, isolating the polyamic acid and imidizing with acetic anhydride. A product having a melting point slightly higher than the meta substituted analogue prepared in Example 1, is obtained. temperature was 149°C during reflux. The mixture was heated at a vigorous reflux rate for 13 hours employing Dean-Stark water trap to remove water. The solvent v/as removed using a rotary film evaporator and the oligomer was triturated with ethanol several times. The product was recrystallized from ethanol. A yield of 58 grams, melting point 190-194°C was obtained.

INDUSTRIAL APPLICABILITY

Acetylene-terminated imide oligomers prepared in accordance v/ith this invention are useful as molding compounds and or matrix resins for solid lubricants. They are curable by addition reactions, at relatively low temperatures, into void free resins that are thermally stable and structurally strong. As such, they have utility in the fabrication of lightweight structure for aerospace, military and domestic applications. Having fully disclosed our invention and provided teachings to enable others to make and use the same, the scope of our claims may now be understood as follows:

Claims

1. An acetylene substituted imide oligomer that is soluble in low boiling solvents whose structure is

where n may range from 1 to 10, n¹ may range from 0 to 4 where X is 0, S, CO, SO₂ or CH₂, and Ar is a divalent organic moiety whose structure is

wherein X' may be O, S, CO, SO₂ or CH₂ and m may range from 0 to 4.

2. An oligomer in accordance with claim 1 wherein the acetylene terminal group is attached to the phenylene ring at a meta position with respect to the imide linkage.

3. An oligomer of claim 1 wherein n is 1, m is o, and X is 0.

4. An oligomer of claim 2 wherein n is 1, m is o and X is 0.

5. A polyimide oligomer comprising a molecular chain consisting of a center pivital section, selected from a diphenylene diamine, joined by imide linkages at its ends to two intermediate sections consisting of tetravalent organic morities that are joined by imide linkages to acetylene substituted phenylene terminal groups wherein said tetravalent organic morety is derived from 2,2-bis (3 ,4-dicarboxyphenyl) hexaf luorapropane dianhydride which thereby rendered said oligomer soluble in low boiling organic solvents and lowers its melting point.

6. The polymide oligomer of Claim 5 wherein said diamine is 1, 3-bis (3-aminophenoxy ) benzene.