GB2137214A - Resoles containing metal atoms - Google Patents

Abstract

There are disclosed thermosetting resoles containing chemically bonded boron, tungsten and/or zirconium atoms. These modified phenolics are prepared by reacting a resol with zirconyl acetate, boric acid, or a tungsten carbonyl/pyrrolidine reaction product. The metal containing resoles of this invention are useful, for example, as reimpregnation resins for carbon/carbon composites.

Description

SPECIFICATION Resoles containing metal atoms This invention relates to resoles containing one or more metal atoms in the polymer chain.

A reimpregnation resin is a thermosetting polymer introduced as a liquid into the characteristic void of a carbon/carbon composite.

The resin is subsequently cured and heat treated, thus increasing the density of the composite. Selected polymers impart specific desired characteristics to the composite depending upon the ultimate application. Viable reimpregnation resins must maintain a suitably low viscosity during the reimpregnation process and, in addition, exhibit a relatively high char yield.

U.S. Patent No. 4,185,043 to Robert C.

Shaffer discloses thermoplastic and thermosetting polymers which incorporate tungsten and/or molybdenum metal atoms. The metal atoms are incorporated into the polymer by reacting a monomer or polymer containing at least one free carboxyl group with a reaction product of tungsten or molybdenum carbonyl and pyrrolidine to obtain a polymer. It is disclosed that the polymers are useful as reimpregnation resins.

It has now been discovered that the properties of base catalyzed thermosetting phenolic resins known as resoles may be improved by incorporating therein one or more metal atoms selected from the group consisting of boron, tungsten and/or zirconium. Such thermosetting modified phenolic resins can be prepared by reacting a resol with zirconyl acetate, boric acid or a tungsten carbonyl/pyrrolidine reaction product. The metals are chemically bonded into the backbone of the polymer.

These polymers show improved heat resistance and their respective chars display improved oxidation resistance which render them particularly useful for carbon/carbon composites.

The thermosetting modified resol resins of this invention are viscous polymers at room temperature but become much less viscous as the temperature is raised. The basic structural unit of these polymers is that formed from the reaction of hydroxy benzenes and formaldehyde in the presence of a base. The metallic precursors participate both as chain modifiers and as cross-linking agents without signifi cantly changing the basic properties of the phenolic resin.

The resoles used in the practice of this invention are well known in the art. They are obtained by reacting a phenol with an al-dehyde such as formaldehyde using an alkaline catalyst. Resoles are also known as Astage resins. For a discussion of resoles see Polymers And Resins by Golding, D. Van Nostrand Company Inc., pages 245-247 (1959), the disclosure of which is incorporated herein by reference. The resoles can be prepared from mono- or dihydroxy benzenes and formaldehyde.

The amount of zirconyl acetate added to the initial resin can be varied in such a manner as to obtain a resin containing from 0 to 16% zirconium.

The amount of boric acid added to the initial resin can be varied in such a manner as to obtain a resin containing from 0 to 7% boron in the cured product. Up to 15% glycerol may be added to this resin in order to improve castability.

The amount of tungsten carbonyl/pyrrolidine reaction product added to the initial resin can be varied in such a manner as to obtain a resin containing from 0 to 20% tungsten. The reaction between the tungsten carbonyl and pyrrolidine may be accomplished in one of several methods found in the literature, e.g., an article by Fowles et al entitled "The Reactions Of Group VI Metal Carbonyls With Pyrrolidine, Piperazine and Morpholine", Inorganic Chemistry, Vol. 3, No. 2, 1964, pages 257-259. The reaction product consisting of the pyrrolidine-tungsten carbonyl complex is ground to a fine powder for subsequent reaction. The reaction product of the pyrrolidinetungsten carbonyl complex is believed to contain at least two moles of pyrrolidine to one mole of tungsten carbonyl.

The amount of metal in the metal containing resoles may be varied by increasing or decreasing the amount of resol used in the reaction with the zirconyl acetate, boric acid or tungsten carbonyl/pyrrolidine reaction product. The zirconyl acetate, boric acid or tungsten carbonyl/pyrrolidine reaction product is reacted with the resol by combining the two materials and heating the reaction mixture, preferably within the range of about 100 to 200"C for from about + to 2 hours. The amount of metal containing reactant and resol may vary widely depending upon the amount of metal desired in the final product.

Any of these metal containing resoles can be polymerized with another in any desired ratio, thus permitting the incorporation of metals into the resultant copolymer in a wide range of ratios. The only limiting factor is the maximum metal content in the primary metal resin.

The metal containing resoles of this invention display high graphitization yields which render them more desirable than other organometallic resins for use in reimpregnation of carbon/carbon composites. These resins, when carbonized or graphitized, exhibit unique energy absorbing characteristics and display improved oxidation resistance.

The metal containing polymers of this invention are also useful in preparing carbonized, high-temperature, corrosion resistant and ablative products under conditions known to those skilled in the art. Specifically, high silica fabric materials prepared by leaching glass fibers, as set forth in U.S. Patent Nos.

2,491,761; 2,624,658; and 3,262,761 or carbonaceous fibers prepared by pyrolyzing cellulosic materials such as cotton, rayon and the like under controlled conditions, as disclosed, for example, in U.S. Patent No.

3,294,489 may be impregnated with the metal containing resins of the present invention and thereafter pyrolyzed at temperatures of between about 800' and 5500'F. The resulting products retain a substantial and desirable amount of the original resin volume and weight, and yet are characterized by the improved ablative and temperature and corrosion resistant properties taken on as a result of the pyrolysis.

The impregnated fibrous material may be used to form molded articles, such as rocket engine nozzles and reentry materials, such as rocket nose cones. The presence of the metal atoms in the resin renders the material capable of absorbing large quantities of energy and also results in a higher density material which generally produces improved ablative properties.

The metal containing polymers of this invention may also be used to form films, coatings or castings. They may be used in combination with conventional adjuvants such as film forming prepolymers, fillers, etc. with which they are compatible. The metal containing polymers may also be cured and then carbonized and/or treated at graphitizing temperatures and the resultant material ground to provide particles which may be used as a filler in resins, elastomers, etc. to impart energy absorbing characteristics of the metal containing polymers.

The following examples illustrate the best modes contemplated for carrying out this invention.

Example 1 A hot solution containing 45.0 parts by weight of zirconyl acetate in 80 parts by weight of 80% acetic acid and 40 parts by weight of ethanol were added to an open resin kettle containing 131.0 parts by weight of a phenolic resol at 66.0% by weight solids.

The resol was prepared from 1.5 moles of formaldehyde and 1.0 moles of phenol. This mixture was stirred well and heated to 111 C over a 30 minute period. To this clear, amber product were added 50 parts by weight of dimethylformamide to solvate the resin. The product can be thermally set within two hours at 160"C.

Example 2 To 15.0 parts by weight of boric acid were added 87.0 parts by weight of the phenolic resol at 66.0% by weight solids described in Example 1. This mixture was heated to 160"C over a one hour period with stirring. To the clear, amber product thus obtained were added 60 parts by weight of dimethylformamide to solvate the product. The product can be thermally set within 20 hours at 200"C.

Example 3 One mole equivalent of tungsten hexacarbonyl and an excess of pyrrolidine are reacted to form the metal pyrrolidine complex. At the completion of the reaction, the product is washed and ground to a fine powder. A mixture of 9.0 parts by weight of this complex and 1 3.3 parts by weight of a phenolic resol at 66.0% solids as described in Example 1 was heated in an open resin kettle to 140 (:: over a one hour period. The resulting clear, brown resin was then solvated in six parts by weight of dimethylformamide. This resin can be thermoset within 20 hours at 200 C.

The following example shows the copolymerization of the three metal bearing resins prepared in each of Examples 1, 2 and 3.

Example 4 In an open resin kettle were mixed 20.0 parts by weight of the zirconium phenolic prepared as described in Example 1, 20.0 parts by weight of the boron phenolic prepared as described in Example 2 and 20.0 parts by weight of the tungsten phenolic prepared as described in Example 3. This solution was constantly stirred over a 20 minute period as the temperature was brought to 160"C. Stirring was continued and 60 parts by weight of dimethylformamide were added to further solvate. The solution was then brought back up to 120"C over a ten minute period. This resin can be thermoset within 1 7 hours at 160"C.

Claims (14)

1. A thermosetting resol resin containing one or more chemically bonded metal atoms selected from boron atoms, tungsten atoms and/or zirconium atoms.

2. A thermosetting resol resin as claimed in claim 1 containing chemically bonded boron atoms.

3. A thermosetting resol resin as claimed in claim 1 containing chemically bonded tungsten atoms.

4. A thermosetting resol resin as claimed in claim 1 containing chemically bonded zirconium atoms.

5. A thermosetting resol as claimed in claim 1 containing a combination of chemically bonded boron, tungsten and zirconium atoms.

6. A process for preparing a thermosetting resol resin containing one or more chemically bonded boron, tungsten and/or zirconium atoms which comprises reacting a resol resin with zirconyl acetate, boric acid and/or a tungsten carbonyl /pyrrolidine reaction product.

7. A process as claimed in claim 6 wherein the resol resin is reacted with zirconyl acetate.

8. A process as claimed in claim 6 wherein the resol resin is reacted with boric acid.

9. A process as claimed in claim 6 wherein the resol resin is reacted with a tungsten carbonyl/pyrrolidine reaction product.

10. A process for preparing a thermosetting resol resin containing chemically bonded boron atoms, tungsten atoms and zirconium atoms which comprises reacting together a thermosetting resol resin containing chemically bonded boron atoms, a thermosetting resol resin containing chemically bonded tungsten atoms and a thermosetting resol resin containing chemically bonded zirconium atoms.

11. A process as claimed in claim 6 substantially as hereinbefore described with reference to any one of Examples 1 to 3.

12. A processas claimed in claim 10 substantially as hereinbefore described with reference to Example 4.

1 3. A thermosetting resol resin whenever prepared by a process as claimed in any one of claims 6 to 12.

14. A carbon/carbon composite which has been subjected to multi-cycle reimpregnation with a resin as claimed in claim 1 3.