Process for manufacturing a cross-linked product

Abstract

A process for manufacturing a cross-linked product has improved charring and thermal stability properties in which there is cross-linking of a benzoxazine monomer.

Claims

1. A process for manufacturing a cross-linked product comprising the cross-linking of a benzoxazine monomer of formula A provided below: ##STR00009## in this formula: A.sub.1 is selected from: (i) saturated, unsaturated or aromatic, monocyclic or polycyclic carbocyclic or heterocyclic groups, substituted by a cross-linkable group, (ii) saturated or unsaturated, linear or branched hydrocarbon chains, optionally interrupted by one or more heteroatoms, substituted by a cross-linkable group, in the alternative (i) or (ii), said cross-linkable group is selected from: a hydroxyl group, an amine group, a maleimide group, an acetylene group, an allyl group, a carbonitrile group, a phthalimide group, a phthalonitrile group, an epoxy group, R.sub.1.sup.a 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, linear or branched, saturated or unsaturated, substituted or unsubstituted hydrocarbon chains, optionally interrupted by one or more heteroatoms, n.sup.a is an integer comprised between 0 and 2, 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, optionally interrupted by one or more heteroatoms, saturated, unsaturated or aromatic, substituted or unsubstituted carbocyclic or heterocyclic groups.

2. The process as claimed in claim 1, wherein A.sub.1 is a monocyclic or polycyclic aromatic carbocyclic or aromatic heterocyclic group substituted by the cross-linkable group.

3. The process as claimed in claim 2, wherein A.sub.1 is a benzene ring substituted by the cross-linkable group.

4. The process as claimed in claim 1, wherein the cross-linkable group is a hydroxyl group.

5. The process as claimed in claim 1, wherein R.sub.1.sup.a is selected from: substituted or unsubstituted furfuryl groups, monocyclic or polycyclic, substituted or unsubstituted carbocyclic aromatic or heterocyclic aromatic groups, substituted or unsubstituted aralkyl groups.

6. The process as claimed in claim 5, wherein R.sub.1.sup.a is a substituted or unsubstituted furfuryl group.

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

8. A rocket nozzle obtained by using a cross-linked product obtained by the process as claimed in claim 1.

9. A re-entry vehicle obtained by using a cross-linked product obtained by the process as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a thermogram obtained by differential scanning calorimetry (DSC) of a first example of benzoxazine monomer according to the invention.

(2) FIG. 2 is a result of thermogravimetric analysis (TGA) of a cross-linked product obtained by cross-linking this first example of benzoxazine monomer.

(3) FIG. 3 is a DSC thermogram of a second example of benzoxazine monomer according to the invention.

(4) FIG. 4 is a thermogravimetric analysis result of a cross-linked product obtained by cross-linking this second example of benzoxazine monomer.

DETAILED DESCRIPTION

EXAMPLES

Example 1: Synthesis of a Benzoxazine Monomer from Furfurylaminomethylphenol and Para-Hydroxybenzaldehyde and Subsequent Cross-Linking

(5) Furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 in order to form the corresponding imine. The imine is reduced to an 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 hours. The furfurylaminomethylphenol thus synthesized is dissolved in toluene with 1 equivalent of para-hydroxybenzaldehyde, 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, followed by proton NMR.

(6) After evaporation of the solvent under reduced pressure, the isolated benzoxazine is a pale yellow solid. The product was characterized by NMR and infrared spectroscopy and the structure was confirmed.

(7) Thermal characterization by DSC revealed a melting temperature of 130° C. as well as an exothermic reaction between 140° C. and 250° C. corresponding to cross-linking, representing 2833 J/g enthalpy with respect to the reference, with a ramp rate of 10° C./min in high-pressure sealed steel crucibles. The resulting DSC thermogram is shown in FIG. 1.

(8) Thermogravimetric analysis showed a coke rate after in situ polymerization of 64% under nitrogen atmosphere, as well as a degradation temperature of 10% of the total mass of 402° C. (heating ramp rate: 10° C./min). This shows excellent thermal stability for this resin. The thermogravimetric analysis graph obtained is provided in FIG. 2.

Example 2: Synthesis of a Benzoxazine Monomer from Furfurylaminomethylphenol and Para-Phthalonitrile-Benzaldehyde and Subsequent Cross-Linking

(9) Para-hydroxybenzaldehyde is reacted with 1 equivalent of K.sub.2CO.sub.3 in dimethylformamide at 0° C. 1.1 equivalent of 4-nitrophthalonitrile is added gradually at 0° C. It is left stirring at room temperature overnight. The reaction medium is then precipitated in 50 times the volume of ice water. The heterogeneous yellow-colored medium is then filtered under vacuum, and an off-white viscous solid is obtained. This solid is dissolved in dichloromethane and washed 3 times with a saturated sodium chloride solution. The organic phase is isolated, dried over magnesium sulfate and the product recovered by evaporation of the solvent under reduced pressure. The product is an off-white powder.

(10) The furfurylamine is reacted with salicylaldehyde in stoichiometric proportions in methanol at reflux for 2 h, in order to form the corresponding imine. The imine is reduced to an 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 hours. The furfurylaminomethylphenol thus synthesized is dissolved in toluene with 1 equivalent of para-phthalonitrile-benzaldehyde, then refluxed in a Dean Stark apparatus to remove the water generated during the condensation reaction. The reaction is stopped when the aldehyde conversion has reached its maximum, followed by proton NMR. After evaporation of the solvent under reduced pressure, the isolated benzoxazine is an off-white viscous solid. The product was characterized by NMR and the structure was confirmed.

(11) Thermal characterization by DSC revealed an exothermic reaction between 170° C. and 278° C., representing 4303 J/g of enthalpy relative to the reference, with a ramp rate of 10° C./min in high-pressure sealed steel crucibles. The resulting DSC thermogram is shown in FIG. 3.

(12) The thermogravimetric analysis showed a coke rate after in situ polymerization of 62% under nitrogen atmosphere, as well as a degradation temperature of 10% of the total mass of 444° C. (heating ramp rate: 10° C./min). The thermogravimetric analysis graph obtained is provided in FIG. 4.