EP0672044A1

EP0672044A1 - Bisnadimides

Info

Publication number: EP0672044A1
Application number: EP94901690A
Authority: EP
Inventors: Jonathan Howard Hodgkin; Mervyn Benjamin Jackson; Trevor Charles Morton
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 1992-12-07
Filing date: 1993-12-07
Publication date: 1995-09-20
Also published as: CA2150566A1; EP0672044A4; AU5619094A; WO1994013669A1; NZ258488A; JPH08504196A

Abstract

The invention relates to a method for the preparation of a bisnadimide of formula (II) substantially free of oligomeric, amidic and uncyclized impurities wherein: Ar is an optionally substituted aryl, optionally substituted bridged or bonded di- or poly- aryl or optionally substituted heteroaryl group; Ar' is an optionally substituted aryl or heteroaryl group which provides for good conjugation between the nitrogen containing groups; X is hydrogen, halogen or an alkyl group; and m is 0 to 6 which comprises reacting a diaminobisimide of formula (III); wherein Ar and Ar' are as defined in formula (II) with nadic acid or a reactive derivative thereof which is optionally substituted with an alkyl group. The invention also relates to bisnadimides of formula (II) and high temperature resistant matrix polymers for composites made therefrom.

Description

BISNADIMIDES

The invention is concerned with bisnadimides and polymers, particularly high temperature resistant matrix polymers for composites, made therefrom.

In recent years the most practical of the high temperature thermostable polyimide matrix resins developed for the aerospace industry has been the Polymerizable Monomeric Reactants (PMR)-type, produced by workers in NASA, USA. These resins are monomeric mixtures of aromatic examines with nadic anhydride and aromatic dianhydride based esters. These mixtures were reported to react at intermediate temperatures to give nadimide capped oligomers of Formula (I) as shown below.

Formula (I) At higher cure temperatures, these oligomers melt and crosslink to form a continuous stable matrix in advanced composite structures. Recent work (J.N. Hay, J.D. Boyle, P.G. James, J.R. Walton, and D. Wilson, "Polymerisation Mechanisms in PMR 15 Polyimide,", in Polyimides: Materials, Chemistry and Characterization, C. Feger, M.M. Khojasteh, and J.E. McGrath Eds., Elsevier, Amsterdam, 1989, pages 305 to 320) has shown that the oligomers formed have much more complex structures with unreacted ester and acid groups as well as uncyclized structures. This complexity and partial reaction means that consistent resin properties are not possible and also lead to brittleness, microcracking and voids in the final composites. The aromatic diamine monomers present in the resins often have toxicity and stability problems, for example, diaminodiphenylmethane - the most commonly used aromatic diamine in industry.

An alternative approach to improve composite toughness, etc., has been to use higher molecular weight or fluorinated monomers in the initial resin mixtures and hence improve molecular mobility and processability. The difficult challenge however is to prepare relatively homogeneous materials without increasing material costs greatly.

International Patent Publication No. WO 92/06078 by the present applicant which is incorporated herein by reference describes a process for the low cost production of novel, high molecular weight monomeric c aminobisimides (hereinafter referred to as "OABIs") of well defined structure and substantially free of oligomeric, amidic and uncyclized impurities. These aromatic diamines have also been found to be non-toxic and stable. International Patent Publication No. WO 92/06078 also discloses the use of DABIs as hardeners for epoxy resins.

In European Patent Publication No. 0 479 722 A2, Kramer et al disclose oligomeric polyimides of Formula (I) as defined above wherein Ar is Cgl^ and 5 <n< 150. These polyimides are stated to be soluble and useful as tougheners in crossiinked resin systems. We have now found that DABIs produced by the process disclosed in International Patent Pubhcation No. WO 92/06078 can be used to make bisnadimides which crosshnk on heating to give thermally stable polyimide resins having superior properties.

According to one aspect of the present invention there is provided a method for the preparation of a bisnadimide of Formula (II) substantially free of ohgomeric, amidic and uncyclized impurities

Formula (II) wherein

Ar is an optionally substituted aryl, optionally substituted bridged or bonded di- or poly- aryl or optionally substituted heteroaryl group;

Ar' is an optionally substituted aryl or heteroaryl group which provides for good conjugation between the nitrogen containing groups; X is hydrogen, halogen or an alkyl group; and m is 0 to 6 which comprises reacting a diaminobisimide of the Formula (HI)

Formula (III) wherein Ar and Ar' are as defined in Formula (II) above with nadic acid or a reactive derivative thereof which is optionally substituted with an alkyl group.

As used herein the term "good conjugation" means that during formation of the ώaminobisimide precursor from a diamine of Formula (IV) shown below, substitution of an electron-withdrawing group on one of the nitrogen atoms suppresses the reactivity of the other nitrogen atom during the reaction.

H₂N-Ar^,-NH₂

Formula (IV)

Preferably the aromatic diamine of the Formula (IV) is stericaUy hindered, such as in compounds of Formulae (V) and (VI)

Formula (VI)

wherein R^, R^, R^ and R° are the same or different and each may be selected from alkyl, aryl, heteroaryl, nitro and halogen groups. Ar or Ar' may be substituted with one or more alkyl, alkoxy, alkylthio, aryl, heteroaryl, aryloxy, carboxy, alkylthio, alkylamino, dialkylamino, amino, nitro, cyano or halo groups.

"Aryl" means an aromatic carbocylic group, such as phenyl, naphthyl, and the like.

"Bridged or bonded di- or poly- aryl" means a group consisting of two or more aromatic carboxylic ring systems, such as phenyl, naphthyl or the like joined by a bond, such as in biphenyl, or a bridging group, such as in sulphonyldiphenyl.

'Bridging group" includes for example SO2, CO, CH₂ and O such as in compounds of the Formula (Vila)

wherein R^ is a divalent group such as -SO2-, -CO-, -CH₂- and -O-.

Generally the group Ar' maybe selected from the groups listed above for Ar. However, because of the constraints imposed by the requirement of "good conjugation" (as defined above) some bridged di- or poly- aryl groups may not be suitable. Thus for Ar', the bridging group (if present) must provide good conjugation between the amino groups of the diamine moiety (IV). For example in groups of the Formula (VLIb)

wherein R* is CH₂ or where the diamine is 3,3'-sulphonyldianiline, there is insufficient conjugation and ohgomeric diaminoimides are present in the precursor c arninobisimides. In contrast, benzidine and 4,4'-sulphonyldianilines have sufficient conjugation and give the desired predominantly monomeric diaminobisimide compound and hence a substantially monomeric bisnadimide.

"Heteroaryl" means aromatic monocyclic or polycyclic groups containing at least one heteroatom such as nitrogen, oxygen or sulfur. Examples of suitable "heteroaryl" groups are: 3- to 8- membered, more preferably 5- or 6- membered heteromonocychc groups containing 1 to 4 nitrogen atom(s), for example, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrimidyl, pyrazinyl, pyridazinyl, triazinyl; condensed heterocyclic groups containing 1 to 5 nitrogen atom(s), for example, indolyl, isoindolyl, indolizinyl, benzimidazolyl, quinolyl, isoquinolyl, indazolyl, benzotriazolyl, etc.; 3- to 8- membered heteromonocychc groups containing 1 or 2 sulfur atom(s) and 1 to 3 nitrogen atom(s), for example, thiazolyl, isothiazolyl, thiadiazolyl, etc.; 3- to 8- membered heteromonocychc groups containing 1 to 2 sulfur atom(s), for example thienyl, etc.; condensed heterocyclic groups containing 1 to 2 sulfur atom(s) and 1 to 3 nitrogen atom(s), for example, benzothiazolyl; benzothiadiazolyl, etc.; 3 to 8- membered heteromonocychc groups containing an oxygen atom, for example, furyl, etc.; condensed heterocyclic groups containing 1 to 2 sulfur atom(s), for • example, benzothienyi, etc.; and condensed heterocyclic groups containing 1 or 2 oxygen atom(s), for example, benzofuranyl, etc.

The alkyl group may be straight chain or branched and contain 1 to 20 carbon atoms. Suitable alkyl groups are methyl, ethyl, propyl, iro-propyl, /rbutyl, irø-butyl, ter bvLtyl, /rpentyl, ύσ-pentyi, neo-pentyl, n-octyl, iso-octyl, decyl, cetyl, stearyl, and the like.

"Alkoxy" and "alkylthio" mean groups in which the alkyl moiety is a branched or unbranched saturated hydrocarbon group containing from one to eight carbon atoms, such as methyl, ethyl, propyl, isσ-propyl, wbutyl, iro-butyl, tertbutyl and the like.

"Alkanoyl" may be formyl, acetyl, propionyl, butyryl, valeryl, isσvaleryl, pivaloyl, hexanoyl, and the like.

Preferably, the diaminobisimide of the Formula (III) is produced by the process disclosed in International Patent Pubhcation No. WO 92/06078 as such a compound is substantially free of oligomeric, amidic and uncyclized impurities.

However, it will be appreciated that the diarninobisimide of the Formula (HI) used in the method of the invention may be produced by any suitable known process.

The reaction is preferably carried out using nadic anhydride or an alkyl- substituted nadic anhydride in the molten state as the solvent.The reaction may also be performed in the presence of a solvent such as an organic solvent, for example, dimethyl formamide, dimethylacetamide or xylene. If a solvent is used, because pure cyclized bisnadimides are formed and can be separated from the solvent as solids, unlike the case in standard PMR type resins, the products can be cured into final resins and composites without the porosity problems caused by strongly bound solvents.

Preferably the reaction is performed at elevated temperatures, such as, for example, above about 120 °C. The method of the invention allows very high yields of substantially pure bisnadimides, even with very insoluble DABIs, to be prepared.

Excess optionally substituted nadic anhydride maybe removed from the final product by washing with a suitable solvent, such as, for example, ethanol or hot water.

The bisnadimides of Formula (II) are also novel and form another aspect of the present invention. The invention also provides bisnadimides of Formula (II) whenever prepared by a method as defined above.

The bisnadimides of the invention, which are substantially free of ohgomeric, amidic and uncyclized impurities, may be used in a curable formulation to produce impregnated fibre reinforced materials and to form crosslinked polyimide polymers which can be used in advanced composite materials.

By utilising the present invention, the PMR composition containing a toxic, reactive diamine of conventional practice is replaced by a safe, stable bisnadimide which can be readily handled during composite fabrication. Furthermore, on a weight of resin basis, much lower quantities of volatile cyclization products are evolved during the curing step as at least half the groups are already cyclized.

The bisnadimides of the invention can be reacted with or without curing agents to form crosslinked polyimide polymers which are useful for a variety of applications including adhesives, bars, films, electronic encapsulation, moulded components and composites. On curing at elevated temperatures, the bisnadimides of Formula (II) may be converted into crosslinked polyimide polymers having improved properties.

Thus, the invention further provides a curable formulation which comprises a bisnadimide of the Formula (II) as defined above.

The bisnadimides of the invention are particularly useful in the manufacture of fibre reinforced composite materials. For example, curable formulations containing the bisnadimides of the invention maybe applied to reinforcing cloth such as uni-directional or woven carbon fibre either from solution (preferably a lower aliphatic ketone or halogenated hydrocarbon solvent) or from a hot melt. Apphcation may be performed manually or by machine and includes techniques involving transfer from a precoated transfer medium. Therefore, the present invention also provides an impregnated fibre reinforced material (commonly known as a "prepreg") wherein the fibre reinforcements are coated with a curable formulation as defined above.

Thus, according to another aspect of the present invention there is provided a crosslinked polyimide polymer which is formed from a bisnadimide monomer of Formula (II) as defined above.

According to a further aspect of the present invention there is provided a method for the preparation of the crosslinked polyimide polymer defined above which comprises heating a bisnadimide of Formula (II) as defined above.

The bisnadimides are preferably heated to temperatures above about 250 °C. The heating may occur under pressure.

While the prior art describes very few co-reactants for curing PMR type resins, it has been found that trans-stilbene is a particularly good curing additive for the bisnadimides of the invention. Such additives provide cyclizable and aromatizable double bond compounds which are capable of reacting with reactive groups liberated by the bisnadimide type cure. Another additive particularly useful in the production of void-free resin bars from the bisnadimides of the invention is the addition of a small percentage of hydroquinone or other additives to prevent "■skinning" and hence entrapment of residual volatiles during the early stages of cure.

The impregnated fibre reinforced material defined above are also suitable for use in the production of advanced composite materials. The impregnated fibre materials may be laid down by any suitable known method for making composite materials, such as, for example, vacuum bagging on a caul plate or an appropriate tool. Accordingly, the present invention also provides an advanced composite material which comprises an assembly of reinforcing fibres in a matrix of a crosslinked polyimide polymer as defined above.

Alternatively, the bisnadimides of the invention can be used in an appropriate resin formulation for resin transfer moulding or for the manufacture of sheet moulded material. Another envisaged apphcation is in pultrusion.

The invention is illustrated by the following Examples. These Examples are not to be construed as limiting the invention in any way.

The systematic names used in the Examples are based on the Chemical Abstracts names of related compounds.

Example 1

Bisnadimide resin, CBR-116, Formula (II) wherein XisH, Aris C_βH₃COC I₃ and Ar' is 1 disubstituted methyldiethylphenyl

A mixture of 400g of nadic anhydride and 200g of 5,5'-carbonylbis {2-[3- amino(methyldiethyl)phenyl]}-lH-isoindole-l^(2H)-dione prepared by the method described in International Patent Pubhcation No. WO 92/06078 were mixed together as finely divided solids and then heated slowly with stirring to 180 °C. The nadic anhydride melted at about 160 ^βC and dissolved the diamine as well as reacting with it to liberate water. After heating with stirring for 8 hours the toffee-like mixture was cooled, ground and washed with very hot water to remove the large excess of unreacted anhydride.

The remaining solid was dried and then dissolved in the minimum amount of methylene chloride and poured into excess ethanol to give the pure solid bisnadimide as a light brown powder with infrared spectra showing peaks at 1776, 1724, 1710cm^-1 (imide), 1182, 1106 and 723cm^"1. Example 2

Bisnadimide resin CBR-412, Formula (II) wherein X is CH_j, Ar is Ar' is I -disubstauted methyldiethylpheπyl

(a) Neat

2,6-bis(3-amino(methyldiethyl)phenyl)-benzo[l,2-c:4,5c']-dipyrrole- l,3,5,7(lH,6H)-tetrone (CBH-103) (2.6g, 0.0049 mole) prepared by the method described in International Patent Pubhcation No. WO 92/06078 was added to liquid methyl nadic anhydride (1.8g, 0.01 mole) and the stirred solution heated at 180 °C for 2 hours and at 200 °C for 2 hours and allowed to cool. The FTIR was consistent with the expected product which was soluble in CH₂C1₂, acetone, THF and DMF and insoluble in ethanol. The GPC showed one main peak with Mn= 830 (expected value 858). It had no sharp melting point, but softened with decomposition at about 300 °C. Recrystallization from CHCI3 /ethanol made no difference to the properties. Curing a sample in the DSC resulted in an endotherm centred at 260 ^βC, attributed to the retro Diels-Alder reaction, and a broad exotherm commencing at about 300 °C.

(b) In DMF A solution of CBH-103 (10.7g, 0.02 mole) and methyl nadic anhydride (6.9 ml,

0.048 mole) in DMF (50 ml) was refluxed with stirring under nitrogen for 4 hours. After cooling, it was poured into cold water (500 ml) with stirring, the precipitate filtered off, washed repeatedly with water and dried in vacua at 40 ° C to constant weight. It was purified by dissolving in chloroform and precipitated into ethanol. Its properties were the same as those of the material prepared without solvent.

(c) In xylene solvent

A mixture of CBH-103 (5.35g, 0.01 mole) and methyl nadic anhydride (3.45 ml, 0.024 mole) in xylene (50 ml) was refluxed in a flask fitted with a Dean Stark trap until the theoretical amount of water had been evolved and then cooled and the product filtered off and dried in vacua at 40 ^βC to constant weight. Its properties were the same as those of the material prepared without solvent.

Examples 3 to 10

Other bisnadimides prepared by methods similar to those described in Examples 1 and 2 are shown in Table 1. Their infrared and nuclear magnetic resonance spectra and their gel permeation chromatographs were in agreement with the proposed structures.

Table 1: Other Bisnadimides of Formula (π)

Example X Ar Ar' Niimber

3 H (C₆H₃OC₆H₄)₂C(CH₃)₂ 1,4 disubstituted phenyl

4 H (C₆H₃OC₆H₄)₂C(CH₃)₂ 1,3 disubstituted methyl diethylphenyl

5 H C₆H₃CH₂C₆H₃ 1,4 disubstituted phenyl

6 CH₃ (C₆H₃OC₆H₄)₂C(CH₃)₂ 1,4 disubstituted phenyl

7 CH₃ (C₆H₃OC₆H₄)₂C(CH₃)₂ 1 disubstituted methyl diethylphenyl

8 CH₃ C₆H₃COC₆H₃ 1,3 disubstituted methyl diethylphenyl

9 CH₃ ^C6^H3^CH2^C6^H3 1,4 disubstituted phenyl

10 CH₃ C_fiH₃C(CH )₂C_fiH 1,4 disubstituted phenyl

Example 11

A matrix resin formulation was prepared for coating carbon fibre by dissolving

78% of the resin of Example 1, 18.0% trans-stilbene and 4% hydroquine in four volumes of dichloromethane with stirring. After coating with this solution to give a 40% total resin content on the fibres after drying, the cloth was laid up in a 5 layer test part and cured in a heated press as follows. 25 °C to 250 °C in 3 hrs, 250 - 310 °C in 1 hr, 310 °C for 1 hr and then cooled to room temperature over 2 hrs. Measurements by DMTA indicated a T_g of 386 "C.

Example 12

A 20% (w/v) solution of the bisnadimide of Example 6 in methylene chloride was coated on to a carbon fibre cloth to give approximately a 40% resin content on the fibres after drying, the cloth was laid up in a 5 layer test part and cured in a heated press from 25 °C to 180 °C in 0.5 h, 180 ^βC/l h, 200 "C/1.5 h, 250 °C/6 h and 315 °C/2 h.

Examples 13 to 18

Other bisnadimides were apphed to carbon fibre cloth and cured by methods similar to those of Example 12. Some of the properties of the cured laminates are listed in Table 2. The value of the T_g for most of the examples can be increased by up to 50% by a post cure at 315 ^βC for several hours.

Table 2: Preparation and properties of some cured bisnadimide 5-ply carbon fibre laminate

Example Bisnadimide Prepregging Maximum Wt% Thickness T_g by DMTA Water Weight Loss of Example Solvent Cure Resin of laminate (°C) uptake at at 250°C

Number CO (mm) 71°C after after 7 7 days (%) days (%)

12 6 CH2CI2 315 42 1.18 263 0.9 0.37

13 6 DMF 315 30 1.07 294 2.7 0.8

14 6 NMP 315 30 1.10 295 4.1 1.2

15 3 DMF 315 35 1.05 325 3.7 0.6

16 4 CH2CI2 315 42 1.13 312 1.4 2.3

17 7 CH2CI2 315 42 1.09 286 1.4 2.4

10 18 9 CH₂Cl2 315 42 1.18 374 1.7 0.31

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A method for the preparation of a bisnadimide of Formula (II) substantiaUy free of ohgomeric, amidic and uncyclized impurities

Formula (II) wherein Ar is an optionaUy substituted aryl, optionaUy substituted bridged or bonded di- or poly- aryl or optionaUy substituted heteroaryl group,

Ar' is an optionaUy substituted aryl or heteroaryl group which provides for good conjugation between the nitrogen containing groups; X is hydrogen, halogen or an alkyl group; and m is 0 to 6 which comprises reacting a diarninobisimide of the Formula (III)

Formula (III)

wherein Ar and Ar' are as defined in Formula (II) above with nadic acid or a reactive derivative thereof which is optionaUy substituted with an alkyl group.

2. A method according to Claim 1, wherein the nadic acid derivative is nadic anhydride or an alkyl ester of nadic acid.

3. A method according to Claim 1 or Claim 2, wherein the reaction is performed at an elevated temperature.

4. A method according to Claim 3, wherein the temperature is above about 120 °C.

5. A method according to any one of the preceding claims, wherein the reaction is performed in the presence of a solvent.

6. A method according to Claim 5, wherein the solvent is an organic solvent.

7. A method according to Claim 5 or Claim 6, wherein the solvent is dimethylformamide, dimethylacetamide or xylene.

8. A bisnadimide of Formula (II) as defined in Claim 1 whenever prepared by the method of any one of the preceding claims.

9. A bisnadimide of Formula (II) as defined in Claim 1.

10. A curable formulation which comprises a bisnadimide of the Formula (II) as defined in Claim 8 or Claim 9.

11. A crosslinked polyimide polymer which is formed from a bisnadimide monomer of Formula (II) as defined in Claim 8 or Claim 9.

12. A method for the preparation of a crosslinked polyimide polymer as defined in Claim 11 which comprises heating a bisnadimide of Formula (II) as defined in Claim 8 or Claim 9.

13. A method according to Claim 13, wherein the heating occurs in the presence of a curing additive.

14. A method according to Claim 13, wherein the curing additive is trans-stilbene and/or hydroquinone.

15. An adhesive, bar, film or moulded component which is composed whoUy or partly of the crosslinked polyimide polymer defined in Claim 11.

16. An impregnated fibre reinforced material wherein the fibre reinforcements are coated with the curable formulation defined in Claim 10.

17. An advanced composite material which comprises an assembly of reinforcing fibres in a matrix of the crosslinked polyimide polymer defined in Claim 11.