Modified polyimide foams and methods of making same

Abstract

Methods of making modified polyimide/polyimide-amide foams and the resulting compositions. An N-substituted aliphatic imide is prepared by reacting a suitable aromatic dianhydride with a suitable oxoimine. A polyimide forming material is prepared by dissolving the N-substituted aliphatic imide in an esterifying solvent, then adding a suitable aromatic diamine. This material is dried to a powder or film. A foam is produced by heating the material to reaction temperature for a period sufficient to produce a stable foam. The material melts, then spontaneously expands into a foam which becomes self supporting and cures to a resilient flexible foam. Depending upon heating conditions, a polyimide, polyimide-amide or mixture thereof may be produced, resulting in foams having varying physical properties.

I claim: 
     
       1. The method of making a resilient, flame resistant modified polyimide foam which comprises the steps of: reacting an aromatic dianhydride with an oximine having the general formula: ##STR8## wherein "X" is an integer from 2 to 4, in a mole ratio of oxoimine to dianhydride between about 1.5:1 and about 0.05:1 to produce an N-substituted aliphatic imide;   dissolving said imide in a reactive solvent esterifying agent to exterify said imide;   adding thereto a diamine;   drying the resulting solution; and   heating the dry material to a selected foaming temperature of from about 120° C. to about 320° C. for a period of from about 10 to about 60 minutes;   whereby a resilient foam having good flame resistance is produced comprising polyimide and polyimide-amide with proportions depending on the selected foaming temperature.   
     
     
       2. The method according to claim 1 wherein said foaming temperature is in the range of from about 230° C. and about 320° C. and the resulting foam comprises primarily a polyimide. 
     
     
       3. The method according to claim 1 wherein said foaming temperature is in the range of from about 120° C. and about 220° C. and the resulting foam is primarily a polyimide-amide. 
     
     
       4. The method according to claim 1 wherein said aromatic dianhydride is pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride or mixtures thereof. 
     
     
       5. The method according to claim 1 wherein said oxoimine is caprolactam. 
     
     
       6. The method according to claim 1 wherein said reactive solvent is methyl alcohol. 
     
     
       7. The method according to claim 1 wherein said diamine is 4,4'-diaminophenyl methane. 
     
     
       8. The method according to claim 1 wherein said diamine comprises at least two different diamines, at least one of which is an aromatic diamine. 
     
     
       9. The method according to claim 1 further including the step of adding from about 0.01 to about 2 wt % of a surfactant to the solution prior to drying. 
     
     
       10. The method according to claim 1 further including the step of adding fillers or reinforcing materials to the solution prior to drying. 
     
     
       11. The method of making a modified polyimide foam comprising a mixture of polyimide and polyimide-amide resins with the polyimide-amide predominating which comprises the steps of: mixing together an aromatic dianhydride selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof and an oxoimine having the general formula: ##STR9## wherein "x" is an integer from 2 to 4, the mole ratio of oxoimine to dianhydride being from about 1.5:1 to about 0.05:1;   heating the mixture to a temperature of from about 150° C. to about 200° C. for from about 5 to about 90 minutes ro react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide;   cooling the mixture to a temperature of from about 40° C. to about 70° C.;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide;   heating the imide solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of from about 60 to about 90 minutes to esterify said imide;   adding thereto about 1.0M 4,4'-diaminodiphenyl methane per 1.0M of dianhydride;   heating the resulting solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of about 2 to about 30 minutes;   drying the solution at a temperature of from about 60° C. to about 70° C. for a period of about 60 to about 240 minutes to produce a dry material; and   foaming said dry material by heating to a temperature of about 120° C. to about 220° C. in a pre-heated oven for from about 10 to about 40 minutes;   whereby a resilient, flame resistant modified polyimide foam is produced consisting primarily of polyimide-amide resin.   
     
     
       12. The method of making a modified polyimide foam comprising a mixture of polyimide and polyimide-amide with the polyimide predominating which comprises the steps of: mixing together an aromatic dianhydride selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof and an oxoimine having the general formula: ##STR10## wherein "x" is an integer from 2 to 4, the mole ratio of oxoimine to dianhydride being from about 1.5:1 to about 0.05:1;   heating the mixture to a temperature of from about 150° C. to about 200° C. for from about 5 to about 90 minutes to react with dianhydride with said oxoimine to produce an N-substituted aliphatic imide;   cooling the mixture to a temperature of from about 40° C. to about 70° C.;   dissolving said imide in a reacting solvent esterifying agent to esterify said imide;   heating the imide solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of from about 60 to about 90 minutes to esterify said imide;   adding thereto about 1.0M 4,4'-diaminodiphenyl methane per about 1.0M of dianhydride;   heating the resulting solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of about 2 to about 30 minutes;   drying the solution at a temperature of from about 60° C. to about 70° C. for a period of about 60 to about 240 minutes to produce a dry material; and   foaming said dry material by heating to a temperature of about 230° C. to about 320° C. in a pre-heated oven for about 30 to about 60 minutes;   whereby a resilient flame resistant modified polyimide foam is produced consisting primarily of polyimide resin.   
     
     
       13. The method of making a modified polyimide foam comprising a mixture of polyimide and polyimide-amide with significant portions of both polyimide and polyimide-amide which comprises the steps of: mixing together an aromatic dianhydride selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof and an oxoimine having the general formula: ##STR11## wherein "x" is an integer from 2 to 4, the mole ratio of oxoimine to dianhydride being from about 1.5:1 to about 0.05:1;   heating the mixture to a temperature of from about 150° C. to about 200° C. for from about 5 to about 90 minutes to react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide;   cooling the mixture to a temperature of from about 40° C. to about 70° C.;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide;   heating the imide solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of from about 60 to about 90 minutes to esterify said imide;   adding thereto about 1.0M 4,4'-diaminodiphenyl methane per about 1.0M of dianhydride;   heating the resulting solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of about 2 to about 30 minutes;   drying the solution at a temperature of from about 60° C. to about 70° C. for a period of about 60 to about 240 minutes to produce a dry material; and   foaming said dry material by heating to a temperature of from about 210° C. to about 250° C. for a period of about 30 to about 45 minutes;   whereby a resilient flame resistant modified polyimide foam is produced containing significant portions of both polyimide and polyimide-amide resins. .Iadd.   
     
     
       14.  A method of making a foamable modified polyimide which comprises the steps of: reacting an aromatic dianhydride with an oxoimine having the general formula: .Iaddend. ##STR12## .Iadd.wherein "x" is an integer from 2 to 4, in a mole ratio of oxoimine to dianhydride between about 1.5:1 to about 0.05:1 to produce an N-substituted aliphatic imide;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide;   adding thereto a diamine; and   drying the resulting solution, whereby the dried solution when heated to a temperature of from about 120° C. to about 320° C. for a period of from about 10 to about 60 minutes, forms a resilient foam having good flame resistance. .Iaddend. .Iadd.     
     
     
       15.  The method according to claim 14 comprising the additional step of forming said resulting solution into free-flowing powder or flakes. .Iaddend. .Iadd.16. The method according to claim 14 wherein said aromatic dianhydride is pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride or a mixture thereof. .Iaddend. .Iadd.17. The method according to claim 14 wherein said oxoimine is caprolactam. .Iaddend. .Iadd.18. The method according to claim 14 wherein said reactive 
     
     
        solvent is methyl alcohol. .Iaddend. .Iadd.19.  The method according to claim 14 wherein said diamine is 4,4-diaminophenyl methane. .Iaddend. .Iadd.20. The method according to claim 14 wherein said diamine comprises at least two different diamines, at least one of which is an aromatic diamine. .Iaddend. .Iadd.21. The method according to claim 14 further comprising the step of adding from about 0.01 to about 2 wt. % of a surfactant to the solution prior to drying. .Iaddend. .Iadd.22. The method according to claim 14 further comprising the step of adding fillers or reinforcing materials to the solution prior to drying. .Iaddend. .Iadd.23. The method of making a modified polyimide foamable material comprising a mixture of polyimide and polyimide-amide with the polyimide-amide predominating which comprises the steps of: mixing together an aromatic dianhydride selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof and an oxomine having the general formula: .Iaddend. ##STR13## .Iadd.wherein "x" is an integer from 2-4, the mole ratio oxoimine to dianhydride being from about 1.5:1 to about 0.05:1;   heating the mixture to a temperature of from about 150° C. to about 200° C. for about 5 to 90 minutes to react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide;   cooling the mixture to a temperature of from about 40° C. to about 70° C.;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide;   heating the imide solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of from about 60 to about 90 minutes to esterify said imide;   adding thereto about 1.0M 4,4'-diamino-diphenyl methane per 1.0M of dianhydride;   heating the resulting solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of about 2 to about 30 minutes; and   drying the solution at a temperature of from about 60° C. to about 70° C. for a period of about 60 to about 240 minutes to produce a dry material, whereby the dry material when heated to a temperature of about 230° C. to about 320° C. for about 30 to 60 minutes produces a resilient flame resistant, modified polyimide foam consisting   
     
     
        primarily of polyimide resin. .Iaddend. .Iadd.24.  The method of making a modified polyimide foamable material comprising a mixture of polyimide and polyimide-amide with significant portions of both polyimide and polyimide-amide which comprises the steps of: mixing together an aromatic dianhydride selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof and an oxoimine having the general formula: .Iaddend. ##STR14## .Iadd.wherein "x" is an integer from 2 to 4, the mole ratio of oxoimine to dianhydride being from about 1.5:1 to about 0.05:1;   heating the mixture to a temperature of from about 150° C. to about 200° C. for from about 5 to about 90 minutes to react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide;   cooling the mixture to a temperature of from about 40° C. to about 70° C.;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide;   heating the inside solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of from about 60 to about 90 minutes to esterify said imide;   adding thereto about 1.0M 4,4'-diaminodiphenyl methane per about 1.0M of dianhydride;   heating the resulting solution to reflux at a temperature of from about 70° C. to about 80° C. for a period of about 2 to about 30 minutes; and   drying the solution at a temperature of from about 60° C. to about 70° C. for a period of about 60 to about 240 minutes to produce a dry material,   whereby the dry material when heated to a temperature of from about 210° C. to about 250° C. for a period of about 30 to 45 minutes produces a resilient flame resistant modified polyimide foam containing significant portions of both polyimide and polyimide-amide resins. .Iaddend.