PROCESS FOR THE PRODUCTION OF A POLYBENZOXAZINE MONOMER

Abstract

A process for manufacturing a polybenzoxazine monomer, crosslinking the latter, and using the crosslinked product to form an ablative thermal protection system for a thruster nozzle or atmospheric reentry body.

Claims

1. A process for manufacturing a polybenzoxazine monomer comprising condensing an amine of formula A with a polyaldehyde of formula B in order to obtain the polybenzoxazine monomer of formula C, formulas A, B and C being provided below: ##STR00014## in these formulas: R.sub.1.sup.a is a substituted or unsubstituted furfuryl group or a substituted or unsubstituted benzyl group, R.sub.2.sup.a is selected from: electron-withdrawing groups; saturated or unsaturated, substituted or unsubstituted, linear or branched hydrocarbon chains comprising between 1 and 6 carbon atoms, interrupted or not interrupted by one or more heteroatoms; saturated, unsaturated or aromatic, substituted or unsubstituted carbocyclic or heterocyclic groups; n.sup.a is an integer comprised between 0 and 2; B.sub.1 is selected from: monocyclic or polycyclic, substituted or unsubstituted aromatic carbocyclic or aromatic heterocyclic groups; and N.sub.1 is an integer greater than or equal to 2.

2. The process as claimed in claim 1, wherein n.sup.a is equal to 0.

3. (canceled)

4. The process as claimed in claim 1, wherein B.sub.1 is a substituted or unsubstituted benzene ring and, in this case, N.sub.1=2 or 3.

5. The process as claimed in claim 1, wherein N.sub.1 is an integer equal to 2.

6. A process for manufacturing a crosslinked product comprising: manufacturing a polybenzoxazine monomer of formula C by carrying out the process as claimed in claim 1, and crosslinking the polybenzoxazine monomer of formula C.

7. The process as claimed in claim 6, comprising crosslinking of a mixture comprising the polybenzoxazine monomer of formula C and an additional monobenzoxazine monomer of formula D, formula D being provided below: ##STR00015## formula in which: R.sub.1.sup.d is selected from: substituted or unsubstituted furfuryl groups; saturated, unsaturated or aromatic, monocyclic or polycyclic, substituted or unsubstituted carbocyclic or heterocyclic groups; substituted or unsubstituted aralkyl groups; saturated or unsaturated, substituted or unsubstituted, linear or branched hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms or by one or more saturated, unsaturated or aromatic, monocyclic or polycyclic, substituted or unsubstituted carbocyclic or heterocyclic groups; R.sub.2.sup.d is selected from: electron-withdrawing groups; saturated or unsaturated, substituted or unsubstituted, linear or branched hydrocarbon chains comprising between 1 and 6 carbon atoms, interrupted or not interrupted by one or more heteroatoms; saturated, unsaturated or aromatic, substituted or unsubstituted carbocyclic or heterocyclic groups; n.sup.d is an integer comprised between 0 and 2; D.sub.1 is selected from: saturated, unsaturated or aromatic, monocyclic or polycyclic, substituted or unsubstituted carbocyclic or heterocyclic groups; linear or branched, saturated or unsaturated, substituted or un substituted hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms.

8. The process as claimed in claim 6, wherein there is crosslinking of a mixture comprising the polybenzoxazine monomer of formula C and an additional polybenzoxazine monomer of formula E, formula E being provided below: ##STR00016## in this formula E: N.sub.2 is an integer greater than or equal to 2; E.sub.2 is selected from saturated or unsaturated, substituted or unsubstituted, linear or branched hydrocarbon chains interrupted by one or more heteroatoms or by one or more saturated, unsaturated or aromatic, monocyclic or polycyclic, substituted or unsubstituted, carbocyclic or heterocyclic groups, or uninterrupted; the groups of formula E.sub.1 are identical or different and each has the formula below: ##STR00017## in this formula E.sub.1: R.sub.1.sup.e is selected from: saturated, unsaturated or aromatic, monocyclic or polycyclic, substituted or unsubstituted carbocyclic or heterocyclic groups; linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms; and R.sub.2.sup.e is selected from: electron-withdrawing groups; saturated or unsaturated, substituted or unsubstituted, linear or branched hydrocarbon chains comprising between 1 and 6 carbon atoms, interrupted or not interrupted by one or more heteroatoms; saturated, unsaturated or aromatic, substituted or unsubstituted carbocyclic or heterocyclic groups; n.sup.e is an integer comprised between 0 and 2; *- denotes the bond to E.sub.2.

9. A process for manufacturing a thruster nozzle comprising manufacturing the crosslinked product by carrying out the process as claimed in claim 6 and manufacturing the nozzle with said crosslinked product.

10. A process for manufacturing an atmospheric reentry body comprising manufacturing the crosslinked product by carrying out the process as claimed in claim 6 and manufacturing the atmospheric reentry body with said crosslinked product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 is a DSC thermogram of an example of a polybenzoxazine monomer of formula C obtained by carrying out the invention.

[0055] FIG. 2 is a result of thermogravimetric analysis (TGA) of a crosslinked product obtained by crosslinking this polybenzoxazine monomer.

[0056] FIG. 3 is a DSC thermogram of an example of a polybenzoxazine monomer of formula C obtained by carrying out the invention.

[0057] FIG. 4 is a thermogravimetric analysis result of a crosslinked product obtained by crosslinking this polybenzoxazine monomer.

[0058] FIG. 5 is a DSC thermogram of an example of a polybenzoxazine monomer of formula C obtained by carrying out the invention.

[0059] FIG. 6 is a themiogravimetric analysis result of a crosslinked product obtained by crosslinking this polybenzoxazine monomer.

[0060] FIG. 7 is a DSC thermogram of an example of an additional polybenzoxazine monomer of formula E suitable for use in the context of the process in accordance with the invention.

[0061] FIG. 8 is a thermogravimetric analysis result of a crosslinked product obtained by crosslinking this polybenzoxazine monomer.

DESCRIPTION OF THE EMBODIMENTS

Examples

Example 1: Synthesis of a Polybenzoxazine Monomer from Furfurylaminomethylphenol and Terephthalaldehyde and Subsequent Crosslinking

[0062] Furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 h to form the corresponding imine. The imine is reduced to the amine with 1 equivalent of NaBH.sub.4 added at 0° C. in a solution of the imine in MeOH, followed by heating at reflux for 2 h. The furfurylaminomethylphenol thus synthesized is dissolved in toluene with 0.5 equivalents of terephthalaldehyde and refluxed in a Dean-Stark apparatus to remove water generated during the condensation reaction. The reaction is stopped when the conversion of aldehydes has reached its maximum, monitored by proton NMR. After evaporation of the solvent under reduced pressure, the isolated bisbenzoxazine is an off-white solid. The product was characterized by NMR and infrared spectroscopy and the structure was confirmed.

##STR00006## ##STR00007##

[0063] Thermal characterization by differential scanning calorimetry (DSC) revealed a melting temperature of 150° C. as well as an exothermic reaction between 190° C. and 280° C., representing 261 J/g of enthalpy compared with the reference, with a ramp of 20° C./min in high-pressure sealed steel crucibles. The resulting DSC thermogram is provided in FIG. 1.

[0064] A bisbenzoxazine sample was crosslinked at 180° C. for 4 hours and showed no residual signal in DSC. Thermogravimetric analysis showed a coke content of 62% under nitrogen atmosphere, after 1 h at 900° C. as well as a degradation temperature of 10% of the total mass of 403° C. (heating ramp: 5° C./min). The thermogravimetric analysis graph obtained is provided in FIG. 2. The crosslinked product obtained was insoluble in dichloromethane (the insolubility rate after 24 h at room temperature in dichloromethane, followed by drying under vacuum at 60° C. for 24 h was measured to be 100±0.1%).

Example 2 Synthesis of a Polybenzoxazine Monomer from Furfurylaminomethylphenol and Isophthalaldehyde and Subsequent Crosslinking

[0065] Furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 h to form the corresponding imine. The imine is reduced to the amine with 1 equivalent of NaBH.sub.4 added at 0° C. in a solution of the imine in MeOH, followed by heating at reflux for 2 h. The furfurylaminomethylphenol thus synthesized is dissolved in toluene with 0.5 equivalents of isophthalaldehyde and then refluxed in a Dean-Stark apparatus to remove the water generated during the condensation reaction. The reaction is stopped when the conversion of aldehydes has reached its maximum, monitored by proton NMR. After evaporation of the solvent under reduced pressure, the isolated bisbenzoxazine is an off-white solid. The product was characterized by NMR and the structure was confirmed.

##STR00008##

[0066] Thermal characterization by differential scanning calorimetry (DSC) revealed an exothermic reaction between 190° C. and 280° C., representing 260 J/g enthalpy compared with the reference, with a ramp of 10° C./min in high-pressure sealed steel crucibles. The resulting DSC thermogram is provided in FIG. 3.

[0067] A bisbenzoxazine sample was crosslinked at 200° C. for 10 hours and showed no residual signal in DSC. Thermogravimetric analysis showed a coke content of 66% under nitrogen atmosphere, after 1 h at 900° C. as well as a degradation temperature of 10% of the total mass of 403° C. (heating ramp: 5° C./min). The thermogravimetric analysis graph obtained is provided in FIG. 4.

Example 3: Synthesis of a Polybenzoxazine Monomer from Benzylaminomethylphenol and Terephthalaldehyde and Subsequent Crosslinking

[0068] Benzylamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 h to form the corresponding imine. The imine is reduced to the amine with 1 equivalent of NaBH.sub.4 added at 0° C. in a solution of the imine in MeOH, followed by heating at reflux for 2 h. The benzylaminomethylphenol thus synthesized is dissolved in toluene with 0.5 equivalents of terephthalaldehyde and then refluxed in a Dean-Stark apparatus to remove the water generated during the condensation reaction. The reaction is stopped when the conversion of aldehydes has reached its maximum, monitored by proton NMR. After evaporation of the solvent under reduced pressure, the isolated bisbenzoxazine is a colorless solid. The product was characterized by NMR and the structure was confirmed.

##STR00009## ##STR00010##

[0069] Thermal characterization by differential scanning calorimetry (DSC) revealed an exothermic reaction between 240° C. and 310° C., representing 99 J/g enthalpy compared with the reference, with a ramp of 10° C./min in high-pressure sealed steel crucibles. The resulting DSC thermogram is provided in FIG. 5.

[0070] A bisbenzoxazine sample was crosslinked at 200° C. for 7 hours and showed no residual signal in DSC. Thermogravimetric analysis showed a coke content of 59% under nitrogen atmosphere, as well as a degradation temperature of 10% of the total mass of 401° C. (heating ramp: 10° C./min). The thermogravimetric analysis graph obtained is provided in FIG. 6.

Example 4; Study of a Mixture of a Polybenzoxazine Monomer with an Additional Monobenzoxazine Monomer

[0071] An additional monobenzoxazine monomer was synthesized following a similar procedure as in Example 1 from benzaldehyde and furfuryl aminomethylphenol with 1:1 ratios between these two constituents. The melting temperature of the additional monobenzoxazine monomer is 52° C. The chemical structure of the additional monobenzoxazine monomer obtained is provided below.

##STR00011##

[0072] Mixtures of the polybenzoxazine monomer of Example 1 and the additional monobenzoxazine monomer were then prepared. It was found that the viscosity of the resulting mixtures was significantly lower than that of a medium consisting of the polybenzoxazine monomer alone. The monobenzoxazine/polybenzoxazine mass ratios of the prepared mixtures were 25/75, 50/50 and 65/35.

[0073] These mixtures of these two benzoxazines were crosslinked at 200° C. for 4 h, resulting in a fully crosslinked material, insoluble in dichloromethane (the rate of insolubility after 24 h at room temperature in dichloromethane, followed by drying under vacuum at 60° C. for 24 h was measured to be 100±0.1%)

[0074] The results obtained after thermogravimetric analysis for these crosslinked mixtures are provided in Table 1 below.

TABLE-US-00001 TABLE 1 Mono/poly Coke content Rate of ratio at 900° C. T.sub.d 10% insolubility   0/100 62% 403° C. >99.9% ± 0.1% 25/75 61% 392° C. >99.9% ± 0.1% 50/50 58% 381° C. >99.9% ± 0.1% 65/35 56% 375° C. >99.9% ± 0.1%

[0075] Themiogravimetric analysis of the monobenzoxazine/polybenzoxazine mixtures produced showed only a small decrease in coke content compared with the use of polybenzoxazine alone. The degradation temperature of 10% of the total mass (T.sub.d10%) was also not significantly affected. These measurements were conducted with a ramp of 10° C./min to 900° C., with a 1 h isotherm at 900° C., under nitrogen atmosphere.

[0076] The additional monobenzoxazine monomer synthesized has the advantage of exhibiting a liquid character when heated to moderate temperature. Its addition thus facilitates the obtaining of a liquid phase compared with the use of the polybenzoxazine monomer alone, without significantly affecting the thermal stability and charring properties.

Example 5: Study of a Mixture of a Polybenzoxazine Monomer Synthesized from a Polyaldehyde with an Additional Polybenzoxazine Monomer Synthesized from a Polyamine

[0077] An additional polybenzoxazine monomer was synthesized from a polyamine in the following manner.

[0078] Meta-xylylenediamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 h to form the corresponding imine. The imine is reduced to the amine with 2 equivalents of NaBH.sub.4 added at 0° C. in a solution of the imine in ethanol, heating is then carried out at reflux for 2 hours. The meta-xylylene-aminomethylphenol thus synthesized is dissolved in toluene with 2 equivalents of benzaldehyde and then refluxed in a Dean-Stark apparatus to remove the water generated during condensation. After evaporation of the solvent under reduced pressure, the product obtained is a viscous liquid with an orange color when hot, and a pale yellow sold at room temperature. The product was characterized by NMR and the structure was confirmed,

##STR00012## ##STR00013##

[0079] Thermal characterization by DSC revealed an enthalpy of polymerization of 68 Ng. The DSC thermogram obtained is provided in FIG. 7. Themiogravimetric analysis of a crosslinked sample showed a coke content of 57% under nitrogen atmosphere at 900° C. as well as a degradation temperature of 10% of the total mass of 448° C., The thermogravimetric analysis graph obtained is provided in FIG. 8.

[0080] The additional polybenzoxazine monomer synthesized from the polyamine was mixed with the polybenzoxazine monomer obtained in Example 1. The additional polybenzoxazine monomer synthesized from the polyamine advantageously exhibits a liquid character when heated to moderate temperature. Its addition thus facilitates the obtaining of a liquid phase compared with the use of the polybenzoxazine monomer of Example 1 alone.

[0081] A mixture was made comprising the polybenzoxazine monomer obtained from polyaldehyde in an amount of 25% by mass and the additional polybenzoxazine monomer synthesized from polyamine in an amount of 75% by mass. The mixture was heated to 80° C. using a water bath, then the mixture was homogenized with a spatula and then crosslinked by heat treatment at 200° C.

[0082] Thermogravimetric analysis of this crosslinked mixture was performed under nitrogen up to 900° C. The results are provided in Table 2 below. It can be noted that the tested polybenzoxazine mixture has an intermediate coke content between the products crosslinked from pure polybenzoxazines. Adding the additional polybenzoxazine monomer synthesized from the polyamine significantly decreases the viscosity, which facilitates the use of certain types of techniques such as resin transfer molding. In Table 2 below, the additional polybenzoxazine monomer synthesized from the polyamine is denoted “bzx MXDA” and the polybenzoxazine monomer synthesized from the polyaldehyde is denoted “bzx TPA”, It is found that the thermal and charring properties of the mixture remain compatible with the application as an ablative resin for thruster nozzles.

TABLE-US-00002 TABLE 2 bzx MXDA/bzx TPA ratio Coke content at 900° C. T.sub.d 10% 100/0 57% 448° C. 75/25 59% 411° C. 0/100 62% 405° C.

[0083] The expression “comprised between . . . and . . . ” should be understood as including the bounds.