METHOD FOR PRODUCING AN ABLATIVE RESIN

Abstract

A method for producing a propulsion nozzle, wherein the nozzle is produced from an ablative resin, the method including a step of pre-polymerization wherein an innovative aldehyde compound is used.

Claims

1. A method for producing a propulsion nozzle, wherein the nozzle is produced from a phenolic resin obtained at least by carrying out the following step: a) pre-polymerization of an aromatic aldehyde compound with a phenolic compound in order to obtain the phenolic resin, the aromatic aldehyde compound having one or other of the following formulae A and B: ##STR00026## the aromatic aldehyde compound being polyfunctional and formulae A and B being such that n.sub.1 is an integer between 0 and 4 and when n.sub.1 is greater than or equal to 2, the substituents R.sub.1 are identical or different, n.sub.2 is an integer between 0 and 5 and when n.sub.2 is greater than or equal to 2, the substituents R.sub.2 are identical or different and n.sub.3 is an integer between 1 and 6, and formulae A and B being such that the substituents R.sub.1 and R.sub.2 are chosen independently from one another from: OH, COOH, CHO, the groups O-Alk wherein Alk denotes a substituted or unsubstituted alkyl chain of 1 to 4 carbon atoms, saturated or unsaturated, substituted or unsubstituted hydrocarbon-based chains comprising between 1 and 20 carbon atoms, interrupted or not interrupted with one or more heteroatoms, and having or not having one or more carbonyl or carboxylic acid functions, substituted or unsubstituted, monocyclic or polycyclic, saturated, unsaturated or aromatic carbocyclic or heterocyclic groups having or not having one or more carbonyl or carboxylic acid functions, and substituted or unsubstituted aryl groups having or not having one or more carbonyl or carboxylic acid functions, R.sub.2 also denoting or not denoting a radical of formula A1 in formula A above or a radical of formula B1 in formula B above and R.sub.1 also denoting or not denoting a radical of formula A2 in formula A above, formulae A1, A2 and B1 being the following: ##STR00027## in formulae A1, A2 and B1, R.sub.1, R.sub.2, n.sub.1, n.sub.2 and n.sub.3 are as defined above.

2. The method as claimed in claim 1, wherein the aromatic aldehyde compound used during step a) has the formula A and wherein the method comprises, in addition, before step a), a step of producing said aromatic aldehyde compound by aromatic nucleophilic substitution reaction between a compound having the formula A3 and a compound having the formula A4 wherein X denotes a leaving group, the formulae A3 and A4 being the following: ##STR00028##

3. The method as claimed in claim 1, wherein the aromatic aldehyde compound used during step a) has the formula B and wherein the method comprises, in addition, before step a), the following two steps: a) a nucleophilic substitution reaction between a compound of formula A3 and a compound of formula B2 in order to obtain a compound of formula B3, wherein Z is a protective group making it possible to obtain an aldehyde function after deprotection and Y is a leaving group, and b) a reaction for deprotection of the compound of formula B3 in order to obtain the aromatic aldehyde compound of formula B, the formulae A3, B2, B3 being the following: ##STR00029##

4. The method as claimed in claim 1, wherein the substituents R.sub.1 and R.sub.2 are chosen independently from one another from: OH, CHO, the groups O-Alk wherein Alk denotes a substituted or unsubstituted alkyl chain of 1 to 4 carbon atoms, COOH, and substituted or unsubstituted aryl groups having or not having one or more carbonyl or carboxylic acid functions, R.sub.2 also denoting or not denoting a radical of formula A1 in formula A above or a radical of formula B1 in formula B above and R.sub.1 also denoting or not denoting a radical of formula A2 in formula A above; in formulae A1, A2 and B1, R.sub.1 and R.sub.2 are as defined above in this claim.

5. The method as claimed in claim 4, wherein the substituents R.sub.1 and R.sub.2 are chosen independently from one another from: OH, CHO, OMe wherein Me denotes a methyl group, and substituted or unsubstituted aryl groups having or not having one or more carbonyl or carboxylic acid functions.

6. The method as claimed in claim 1, wherein n.sub.1 is between 0 and 2 and n.sub.2 is between 0 and 3 for formula A.

7. The method as claimed in claim 1, wherein n.sub.2 is between 0 and 3 and n.sub.3 is between 1 and 3 for formula B.

8. The method as claimed in claim 2, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: simple phenols, polyphenolic compounds, hydroxybenzoic aldehydes, hydroxybenzoic acids, hydroxybenzyl alcohols, hydroxycinnamyl alcohols, hydroxycinnamic acids, phenylpropenes, coumarins, naphthoquinones, stilbenoids, flavonoids, isoflavonoids, anthocyans, lignans, lignins, condensed tannins, hydrolyzable tannins, depolymerized tannins, and resol and novolac resins.

9. The method as claimed in claim 8, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: simple phenols and hydroxybenzoic aldehydes.

10. The method as claimed in claim 8, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: phenol, pyrocatechol, resorcinol, hydroquinone, phloroglucinol, pyrogallol, guaiacol, syringol, bis-phenol A, bis-phenol S, para-hydroxyb enzaldehyde, vanillin, syringaldehyde, dehydrodivanillin, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, vanillyl alcohol, syringyl alcohol, para-coumaryl alcohol, coniferyl alcohol, sinapyl alcohol, ferulic acid, para-hydroxybenzoic acid, gallic acid, para-coumaric acid, eugenol, isoeugenol, cardanols, cardols, anacardic acids, catechin, umbelliferone, juglone, trans-resveratrol, kaempferol, daidzein, delphinidol, enterodiol, lignins, procyanidins, gallotannins, condensed tannins, and resol and novolac resins.

11. (canceled)

12. The method as claimed in claim 1, wherein the nozzle is produced from a phenolic resin obtained by carrying out the pre-polymerization step or from a crosslinked phenolic resin obtained after carrying out a step wherein a heat treatment is carried out so as to crosslink phenolic resins obtained by carrying out the pre-polymerization step.

13.-14. (canceled)

15. The method as claimed in claim 3, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: simple phenols, polyphenolic compounds, hydroxybenzoic aldehydes, hydroxybenzoic acids, hydroxybenzyl alcohols, hydroxycinnamyl alcohols, hydroxycinnamic acids, phenylpropenes, coumarins, naphthoguinones, stilbenoids, flavonoids, isoflavonoids, anthocyans, lignans, lignins, condensed tannins, hydrolyzable tannins, depolymerized tannins, and resol and novolac resins.

16. The method as claimed in claim 15, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: simple phenols and hydroxybenzoic aldehydes.

17. The method as claimed in claim 15, wherein the compound of formula A3 used for producing the aromatic aldehyde compound is chosen from: phenol, pyrocatechol, resorcinol, hydroguinone, phloroglucinol, pyrogallol, guaiacol, syringol, bis-phenol A, bis-phenol S, para-hydroxybenzaldehyde, vanillin, syringaldehyde, dehydrodivanillin, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, vanillyl alcohol, syringyl alcohol, para-coumaryl alcohol, coniferyl alcohol, sinapyl alcohol. ferulic acid, para-hydroxybenzoic acid, gallic acid, para-coumaric acid, eugenol, isoeugenol, cardanols, cardols, anacardic acids, catechin, umbelliferone, juglone, trans-resveratrol, kaempferol, daidzein, delphinidol, enterodiol, lignins, procyanidins, gallotannins, condensed tannins, and resol and novolac resins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other characteristics and advantages of the invention will emerge from the following description with reference to the appended drawings, wherein:

[0052] FIGS. 1 and 2 represent results of thermogravimetric analyses comparing the properties of resins obtained by means of a method according to the invention and of the Ablaphene RS 101 resin.

EXAMPLES

Example 1: Grafting of Aromatic Aldehyde Functions (Synthesis of 4-Phenoxybenzaldehyde and Application of the Latter in Synthesis of Phenolic Resin without Formaldehyde)

[0053] Phenol (5 g, 1 eq., 53 mmol), 4-fluorobenzaldehyde (5.4 g, 0.82 eq., 43.5 mmol), potassium carbonate (14.68 g, 2 eq., 106 mmol) and 50 ml of N,N-dimethylformamide are placed in a 100 ml round-bottomed flask equipped with a condenser, with magnetic stirring and under an argon atmosphere. The round-bottomed flask is immersed in a bath of oil thermostated at 110 C. for 15 hours. At the end of the 15 hours of reaction, the .sup.1H NMR analysis of the reaction crude indicates that the conversion of the 4-fluorobenzaldehyde to 4-phenoxybenzaldehyde is total. The reaction medium is filtered through filter paper, and the filtrate is recovered and then distilled under reduced pressure in order to remove the DMF. The product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered and washed three times with a concentrated sodium hydroxide solution at 1 mol/l. The purpose of these washes is to remove the residual phenol and the residual DMF. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. 4.93 g of 4-phenoxybenzaldehyde product are recovered. The product analyzed by .sup.1H and .sup.13C NMR is pure. Appearance: colorless oil. Weight yield=57%.

[0054] This reaction is summarized by the synthesis scheme below.

##STR00011##

[0055] A phenolic resin was then synthesized without formaldehyde from 4-phenoxybenzaldehyde according to the operating protocol detailed below.

[0056] 4-Phenoxybenzaldehyde (6.32 g, 1.5 eq., 31.9 mmol), phenol (2 g, 1 eq., 21.3 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.41 g, 0.5 eq., 10.3 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 20 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black, rigid and totally insoluble in acetone.

[0057] These reactions are summarized by the synthesis scheme below.

##STR00012##

Example 2: Grafting of Aromatic Aldehyde Functions (Synthesis of 4-Hydroxybenzaldehyde-Benzaldehyde and Application of the Latter in Synthesis of Phenolic Resin without Formaldehyde)

[0058] 4-Hydroxybenzaldehyde (20 g, 1 eq., 164 mmol), 4-fluorobenzaldehyde (41.7 g, 2 eq., 329 mmol), potassium carbonate (45.5 g, 2 eq., 329 mmol) and 155 ml of N,N-dimethylformamide are placed in a 500 ml round-bottomed flask equipped with a condenser, with magnetic stirring and under an argon atmosphere. The round-bottomed flask is immersed in a bath of oil thermostated at 110 C. for 6 hours. At the end of the 6 hours of reaction, the conversion of the 4-hydroxybenzaldehyde to 4-hydroxybenzaldehyde-benzaldehyde, determined by .sup.1H NMR analyses of the reaction crude, is total. The reaction medium is filtered through filter paper, and the filtrate is recovered and then distilled under reduced pressure in order to remove the DMF. The product is purified by liquid-liquid extraction with EtOAc/H.sub.2O and then washed three times with a brine solution in order to remove the residual DMF. The organic phases are recovered, dried over anhydrous magnesium sulfate and then concentrated under reduced pressure. The excess 4-fluorobenzaldehyde reagent is distilled off under vacuum (T=80 C., P=510.sup.3 mbar). 35.4 g of 4-hydroxybenzaldehyde-benzaldehyde product are recovered. The .sup.1H and .sup.13C NMR analyses indicate that the product is pure. Appearance: white powder. Weight yield=95%.

[0059] This reaction is summarized by the synthesis scheme below.

##STR00013##

A phenolic resin was then synthesized without formaldehyde from 4-hydroxybenzaldehyde-benzaldehyde according to the operating protocol detailed below.

[0060] 4-Hydroxybenzaldehyde-benzaldehyde (1.24 g, 035 eq., 5.5 mmol), phenol (0.686 g, 1 eq., 7.3 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.09 g, 0.3 eq., 2.2 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 15 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black, rigid and totally insoluble in acetone.

[0061] These reactions are summarized by the synthesis scheme below.

##STR00014##

Example 3: Grafting of Aromatic Aldehyde Functions (Synthesis of Vanillin-Benzaldehyde and Application of the Latter in Synthesis of Phenolic Resin without Formaldehyde)

[0062] Vanillin (1.62 g, 1 eq., 10.6 mmol), 4-fluorobenzaldehyde (2.63 g, 2 eq., 21.2 mmol), potassium carbonate (2.94 g, 2 eq., 21.2 mmol) and 10 ml of N,N-dimethylformamide are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring and under an argon atmosphere. The round-bottomed flask is immersed in a bath of oil thermostated at 110 C. for 42 hours. The vanillin used can, for example, be obtained from a biobased synthesis route as described in the article: M. B. Hocking, Vanillin: synthetic flavoring from spent sulfite liquor, J. Chem. Educ., 74 (1997) 1055-1059. At the end of the 42 hours of reaction, the conversion of the vanillin to vanillin-benzaldehyde, determined by .sup.1H NMR analysis of the reaction crude, is total. The reaction medium is filtered through filter paper, and the filtrate is recovered and then distilled under reduced pressure in order to remove the DMF. The product is purified by liquid-liquid extraction with EtOAc/H.sub.2O and then washed three times with a brine solution in order to remove the residual DMF. The organic phases are recovered, dried over anhydrous magnesium sulfate and then concentrated under reduced pressure. The vanillin-benzaldehyde product is separated from the excess 4-fluorobenzaldehyde reagent by separative silica chromatography with the eluent: 90% cyclohexane/10% EtOAc. 2.04 g of product are recovered. The .sup.1H and .sup.13C NMR analyses indicate that the product is pure. Appearance: white powder. Weight yield=75%.

[0063] This reaction is summarized by the synthesis scheme below.

##STR00015##

[0064] A phenolic resin was then synthesized without formaldehyde from the vanillin-benzaldehyde according to the operating protocol detailed below.

[0065] Vanillin-benzaldehyde (1.4 g, 0.75 eq., 5.5 mmol), phenol (0.686 g, 1 eq., 7.3 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.1 g, 0.3 eq., 2.5 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 20 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black, rigid and totally insoluble in acetone.

[0066] These reactions are summarized by the synthesis scheme below.

##STR00016##

Example 4: Grafting of Aliphatic Aldehyde Functions for the Preparation of Phenolic Resins without Formaldehyde

[0067] In this example, 2-(phenoxymethyl)-1,3-dioxolane was first of all synthesized according to the operating protocol described below.

[0068] Phenol (3 g, 1 eq., 31.9 mmol), potassium carbonate (8.81 g, 2 eq., 63.8 mmol), 2-bromomethyl-1,3-dioxolane (10.65 g, 2 eq., 46.1 mmol) and butyronitrile 30 ml) are placed in a 100 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The medium is placed at reflux of the butyronitrile, at 115 C. After 58 hours of reaction, the conversion of the phenol to 2-(phenoxymethyl)-1,3-dioxolane, determined by .sup.1H NMR analysis of the reaction crude, is total. The reaction medium is filtered through filter paper and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residual dioxolane reagent present in the product is distilled off under secondary vacuum (T=100 C., P=210.sup.2 mbar). 4.12 g of 2-(phenoxymethyl)-1,3-dioxolane are obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: colorless liquid. Weight yield=72%.

[0069] This reaction is summarized by the synthesis scheme below.

##STR00017##

[0070] Starting from the 2-(phenoxymethyl)-1,3-dioxolane, 2-phenoxyacetaldehyde was then synthesized by carrying out the operating protocol described below.

[0071] The 2-(phenoxymethyl)-1,3-dioxolane compound (0.756 g, 1 eq., 4.2 mmol) and the mixture of solvents consisting of 32 ml of HCl solution at 1 mol/l (7.6 eq., 32 mmol) and of 32 ml of 1,4-dioxane are placed in a 250 ml round-bottomed flask with magnetic stirring and equipped with a condenser. The round-bottomed flask is placed in a bath of oil thermostated at 80 C. for 5 h. At the end of this reaction, the pH of the reaction medium is neutralized with a saturated NaHCO.sub.3 solution, the dioxane solvent is evaporated off under reduced pressure and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The product is isolated pure by separative chromatography with a mixture of EtOAc/cyclohexane eluent: 20/80. 0.35 g of 2-phenoxyacetaldehyde product are obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: colorless oil. Weight yield=62%.

[0072] This reaction for deprotection of the 2-(phenoxymethyl)-1,3-dioxolane to give 2-phenoxyacetaldehyde is summarized by the synthesis scheme below.

##STR00018##

[0073] A phenolic resin was then synthesized without formaldehyde from 2-phenoxyacetaldehyde according to the operating protocol detailed below.

[0074] 2-Phenoxyacetaldehyde (2 g, 1.5 eq., 14.7 mmol), phenol (0.922 g, 1 eq., 9.8 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.15 g, 0.4 eq., 16 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 10 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black and rigid.

[0075] This reaction is summarized by the synthesis scheme below.

##STR00019##

Example 5: Grafting of Aliphatic Aldehyde Functions for the Preparation of Phenolic Resins without Formaldehyde

[0076] In this example, 4-hydroxybenzaldehyde-diethoxyethane was first of all synthesized according to the operating protocol described below.

[0077] 4-Hydroxybenzaldehyde (4.15 g, 1 eq., 34 mmol), potassium carbonate (9.4 g, 2 eq., 68 mmol), 2-bromo-1,1-diethoxyethane (13.4 g, 2 eq., 68 mmol) and butyronitrile (30 ml) are placed in a 100 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The medium is placed at reflux of the butyronitrile, at 115 C. After 5 days of reaction, the conversion of the 4-hydroxybenzaldehyde to 4-hydroxybenzaldehyde-diethoxyethane, determined by .sup.1H NMR analyses of the reaction crude, is total. The reaction medium is filtered through filter paper and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residual acetal reagent present in the product is distilled off under secondary vacuum (T=100 C., P=210.sup.2 mbar). 6.9 g of 4-hydroxybenzaldehyde-diethoxyethane product are obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: yellow oil. Weight yield=85%. This reaction is summarized by the synthesis scheme below.

##STR00020##

[0078] Starting from the 4-hydroxybenzaldehyde-diethoxyethane, 4-hydroxybenzaldehyde-acetaldehyde was then synthesized by carrying out the operating protocol described below.

[0079] The 4-hydroxybenzaldehyde-diethoxyethane compound (1 g, 1 eq., 4.2 mmol) and the mixture of solvents consisting of 16 ml of HCl solution at 1 mol/l (3.8 eq., 16 mmol) and of 16 ml of tetrahydrofuran are placed in a 100 ml round-bottomed flask with magnetic stirring and equipped with a condenser. The round-bottomed flask is placed in a bath of oil thermostated at 60 C. for 5 hours. At the end of this reaction, the pH of the reaction medium is neutralized with a saturated NaHCO.sub.3 solution, the THF solvent is evaporated off under reduced pressure and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. 0.6 g of 4-hydroxybenzaldehyde-acetaldehyde product is obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: white powder. Weight yield=87%.

[0080] This reaction is summarized by the synthesis figure below.

##STR00021##

[0081] A phenolic resin was then synthesized without formaldehyde from 4-hydroxybenzaldehyde-acetaldehyde according to the operating protocol detailed below.

[0082] 4-Hydroxybenzaldehyde-acetaldehyde (1.69 g, 0.75 eq., 10.3 mmol), phenol (1.29 g, 1 eq., 131 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.16 g, 0.3 eq., 4 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 15 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black, rigid and totally insoluble in acetone.

[0083] This reaction is summarized by the synthesis figure below.

##STR00022##

Example 6: Grafting of Aliphatic Aldehyde Functions for the Preparation of Phenolic Resins without Formaldehyde

[0084] In this example, vanillin-dimethoxyethane was first of all synthesized according to the operating protocol described below.

[0085] Vanillin (11.25 g, 1 eq., 74 mmol), potassium carbonate (40.9 g, 4 eq., 296 mmol), 2-bromo-1,1-dimethoxyethane (25 g, 2 eq., 147.9 mmol) and butyronitrile (240 ml) are placed in a 500 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The medium is placed at reflux of the butyronitrile, at 115 C. After four days of reaction, the conversion of the vanillin to vanillin-dimethoxyethane, determined by .sup.1H NMR analysis of the reaction crude, is total. The reaction medium is filtered through filter paper and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residual acetal reagent present in the product is distilled off under secondary vacuum (T=100 C., P=210.sup.2 mbar). 16.74 g of vanillin-dimethoxyethane product are obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: yellow oil. Weight yield=94%. This reaction is summarized by the synthesis scheme below.

##STR00023##

[0086] Starting from the vanillin-dimethoxyethane, vanillin-acetaldehyde was then synthesized by carrying out the operating protocol described below.

[0087] The vanillin-dimethoxyethane compound (1 g, 1 eq., 4.2 mmol) and the mixture of solvents consisting of 16 ml of HCl solution at 1 mol/l (3.8 eq., 16 mmol) and of 16 ml of tetrahydrofuran are placed in a 100 ml round-bottomed flask with magnetic stirring and equipped with a condenser. The round-bottomed flask is placed in a bath of oil thermostated at 60 C. for 22 hours. At the end of this reaction, the pH of the reaction medium is neutralized with a saturated NaHCO.sub.3 solution, the THF solvent is evaporated off under reduced pressure and the product is purified by liquid-liquid extraction with EtOAc/H.sub.2O. The organic phases are recovered, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. 0.75 g of vanillin-acetaldehyde product is obtained. The product characterized by .sup.1H and .sup.13C NMR is pure. Appearance: white powder. Weight yield=90%.

[0088] This reaction is summarized by the synthesis figure below.

##STR00024##

[0089] A phenolic resin was then synthesized without formaldehyde from vanillin-acetaldehyde according to the operating protocol detailed below.

[0090] Vanillin-acetaldehyde (2 g, 0.75 eq., 10.3 mmol), phenol (1.29 g, 1 eq., 13.7 mmol) and sodium hydroxide in aqueous solution at 50% by weight (0.16 g, 0.3 eq., 4 mmol) are placed in a 50 ml round-bottomed flask equipped with a condenser, with magnetic stirring. The round-bottomed flask is immersed in a bath of oil thermostated at 130 C. for 5 minutes. At the end of this reaction, the mixture is in homogeneous and viscous resitol form. It is recovered, placed in an aluminum dish and baked in an oven, under atmospheric pressure, according to a baking program consisting of an increase in temperature from 40 C. to 180 C. at the rate of 3 C./h and of a stationary temperature phase of 24 h at 180 C. The resite material obtained at the end of this baking is black, rigid and totally insoluble in acetone.

[0091] This reaction is summarized by the synthesis figure below.

##STR00025##

Example 7: Analysis of the Heat Stability and Carbonizing Properties of the Crosslinked Phenolic Resins Obtained

[0092] The measurements of the coke contents of the synthesized resites were carried out by thermogravimetric analyses (TGA) on a Q50 instrument sold by the company TA Instruments. A 30 mg sample of resite in monolithic form is placed on a platinum cradle and then heated, under a nitrogen stream (60 ml/min) according to the following program: [0093] Linear increase from 20 C. to 160 C. at the rate of 10 C./min. [0094] Stationary temperature phase for one hour at 160 C. (iw). [0095] Linear increase from 160 C. to 900 C. at the rate of 10 C./min. [0096] Stationary temperature phase for one hour at 900 C. (fw).

[0097] The coke content is calculated according to the following equation, wherein the parameters iw and fw represent the weights of the sample at the end of the stationary temperature phases at 160 C. and 900 C., respectively:

Coke content=fw/iw.

[0098] FIG. 1 represents the results obtained by TGA for the resins synthesized in examples 1 (4-phenoxybenzaldehyde/phenol resite), 2 (4-hydroxybenzaldehyde-benzaldehyde/phenol resite) and 3 (vanillin-benzaldehyde/phenol resite) in comparison with the results obtained for Ablaphene RS101.

[0099] FIG. 2 represents the results obtained by TGA for the resins synthesized in examples 4 (2-phenoxyacetaldehyde/phenol resite), 5 (4-hydroxybenzaldehyde-acetaldehyde/phenol) and 6 (vanillin-acetaldehyde/phenol) in comparison with the results obtained for Ablaphene RS101.

[0100] The coke content and also the degradation temperatures at 10% by weight (Td10%) of the resins tested are reported in tables 1 and 2 below.

TABLE-US-00001 TABLE 1 Coke Resite Td10% content 4-Phenoxybenzaldehyde/Phenol 375 C. 56% 4-Hydroxybenzaldehyde- 497 C. 66% benzaldehyde/phenol Vanillin-benzaldehyde/Phenol 440 C. 68% Ablaphene RS101 370 C. 63%

TABLE-US-00002 TABLE 2 Coke Resite Td10% content 2-Phenoxyacetaldehyde/Phenol 260 C. 44% 4-Hydroxybenzaldehyde- 352 C. 61% acetaldehyde/phenol Vanillin-acetaldehyde/Phenol 330 C. 51% Ablaphene RS101 370 C. 63%

[0101] These results show that the resins produced by means of the method according to the invention can have heat stability and carbonizing properties that are similar to, or even better than, those of the Ablaphene RS101 reference resin. This method thus gives access to phenolic resins which can advantageously replace the conventional formo-phenolic resins for the production of aeronautical parts such as propulsion nozzles. In addition, these results show that the use of a polyfunctional aromatic aldehyde compound (4-hydroxybenzaldehyde-acetaldehyde, vanillin-acetaldehyde, 4-hydroxybenzaldehyde-benzaldehyde or vanillin-benzaldehyde) advantageously makes it possible to obtain improved heat stability and carbonizing properties compared with the use of monofunctional aromatic aldehyde compounds (2-phenoxyacetaldehyde and 4-phenoxybenzaldehyde).

[0102] The expression comprising/containing a should be understood as comprising/containing at least one.

[0103] The expression between . . . and . . . or from . . . to . . . should be understood as including the limits.