PROCESS FOR PRODUCING 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 a polyamine of formula A with an aldehyde of formula B in order to obtain the polybenzoxazine monomer of formula C, the chemical formulas being provided below: ##STR00009## in these formulas: N.sub.1 is an integer greater than or equal to 2; A.sub.2 is selected from linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon chains interrupted by one or more monocyclic or polycyclic, substituted or unsubstituted, aromatic carbocyclic or aromatic heterocyclic groups, or uninterrupted; in formula A, the groups A.sub.1 are identical or different and each have the above formula A.sub.1 with: R.sub.1.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; *-designates the bond to A.sub.2; B.sub.1 is selected from: monocyclic or polycyclic, substituted or unsubstituted aromatic carbocyclic or aromatic heterocyclic groups.

2. (canceled)

3. The process as claimed in claim 1, wherein A.sub.2 is a substituted or unsubstituted xylylene group.

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

5. (canceled)

6. The process as claimed in claim 1, wherein B.sub.1 is a substituted or unsubstituted benzene ring.

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

8. 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.

9. The process as claimed in claim 8, 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: ##STR00010## 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 unsubstituted hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms.

10. The manufacturing process as claimed in claim 8, comprising crosslinking of a mixture comprising the polybenzoxazine monomer of formula C and an additional polybenzoxazine monomer of formula E, formula E being provided below: ##STR00011## R.sub.1.sup.e is selected from: substituted or unsubstituted furfuryl groups; saturated, unsaturated or aromatic, monocyclic or polycyclic carbocyclic or heterocyclic groups; substituted or unsubstituted aralkyl groups; substituted or unsubstituted, linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms; 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; E.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 unsubstituted hydrocarbon chains, interrupted or not interrupted by one or more heteroatoms; and N.sub.2 is an integer greater than or equal to 2.

11. A process for manufacturing a thruster nozzle comprising manufacturing the crosslinked product by carrying out the process as claimed in claim 8 and manufacturing the thruster nozzle with said crosslinked product.

12. A process for manufacturing an atmospheric reentry body comprising manufacturing the crosslinked product by carrying out the process as claimed in claim 8 and manufacturing the atmospheric reentry body by using said crosslinked product.

13. The process as claimed in claim 3, wherein n.sup.a is equal to 0.

14. The process as claimed in claim 3, wherein B.sub.1 is a substituted or unsubstituted benzene ring.

15. The process as claimed in claim 4, wherein B.sub.1 is a substituted or unsubstituted benzene ring.

16. The process as claimed in claim 3, wherein N.sub.1 is an integer equal to 2.

17. The process as claimed in claim 4, wherein N.sub.1 is an integer equal to 2.

18. The process as claimed in claim 6, wherein N.sub.1 is an integer equal to 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 is a DSC thermogram of an example of a polybenzoxazine monomer of formula C obtained by carrying out the invention,

[0066] FIG. 2 is a result of thermogravimetric analysis (TGA) of a crosslinked product obtained by crosslinking this polybenzoxazine monomer.

[0067] FIG. 3 is a DSC thermogram of another example of a polybenzoxazine monomer of formula C obtained by carrying out the invention.

[0068] FIG. 4 is a thermogravimetric analysis result of a crosslinked product obtained by crosslinking this other polybenzoxazine monomer.

[0069] FIG. 5 is a DSC thermogram of an example of an additional polybenzoxazine monomer of formula E suitable for use in the context of the process according to the invention.

[0070] FIG. 6 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 Meta-Xylylene-Aminomethylphenol and Benzaldehyde and Subsequent Crosslinking

[0071] 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, followed by heating 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 solid at room temperature. The product was characterized by NMR and the structure was confirmed.

##STR00006##

[0072] Thermal characterization by DSC revealed an enthalpy of polymerization of 68 J/g. The DSC thermogram obtained is provided in FIG. 1. Thermogravimetric 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. 2 and shows good thermal stability and charring properties.

Example 2. Synthesis of a Polybenzoxazine Monomer from 1,10-Decanediaminomethylphenol and Benzaldehyde and Subsequent Crosslinking

[0073] 1,10-Diaminodecane 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, followed by heating at reflux for 2 hours. The 1,10-decanediaminomethylphenol 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 solid at room temperature. The product was characterized by NMR and the structure was confirmed.

##STR00007##

[0074] Thermal characterization by differential scanning calorimetry (DSC) revealed a melting temperature of 65° C. as well as an exothermic reaction between 209 and 260° C., representing 66 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. 3, Thermogravimetric analysis of a crosslinked sample showed a coke content of 46% under nitrogen atmosphere at 900° C. as well as a degradation temperature of 10% of the total mass of 404° C. The thermogravimetric analysis graph obtained is provided in FIG. 4 and shows good thermal stability and charring properties.

Example 3: Study of a Mixture of a Polybenzoxazine Monomer Synthesized Polyamine with an Additional Polybenzoxazine Monomer Synthesized from a Polyaldehyde

[0075] An additional polybenzoxazine monomer was synthesized from a polyaldehyde in the following manner.

[0076] 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 synthesized furfurylaminomethylphenol 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.

##STR00008##

[0077] Thermal characterization by differential scanning calorimetry (DSC) revealed a melting temperature of 150° C. as well as an exothermic reaction between 190 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. 5.

[0078] 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: 20° C./min). The thermogravimetric analysis graph obtained is provided in FIG. 6. 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%).

[0079] The additional polybenzoxazine monomer synthesized from the polyaldehyde was mixed with the polybenzoxazine monomer obtained in Example 1. The additional polybenzoxazine monomer synthesized from the polyaldehyde advantageously has a higher coke content when crosslinked compared with the crosslinked polybenzoxazine of Example 1.

[0080] A mixture was made comprising the additional polybenzoxazine monomer obtained from polyaldehyde in an amount of 25% by mass and the 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.

[0081] Thermogravimetric analysis of this crosslinked mixture was performed under nitrogen up to 900° C. The results are provided in Table 1 below. It can be noted that the tested polybenzoxazine mixture has an intermediate coke content between the products crosslinked from pure polybenzoxazines. The addition of the additional polybenzoxazine monomer synthesized from polyaldehyde increased the coke content. In Table 1 below, the polybenzoxazine monomer synthesized from the polyamine is denoted “bzx MXDA” and the additional polybenzoxazine monomer synthesized from the polyaldehyde is denoted “bzx TPA”. The mixture is also suitable for application as an ablative resin for thruster nozzles.

TABLE-US-00001 TABLE 1 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.

[0082] The expression “comprised between . . . and . . . ” should be understood as including the bounds.