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 amide;   dissolving said imide in a reactive solvent esterifying agent to exterify said imide;   adding thereto a diamine;   drying the 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 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 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## where "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 foamable product produced by the following process steps: 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 and about 0.05:1 to produce an N-substituted aliphatic imide;   dissolving said imide in a reactive solvent esterifying agent to esterify said imide; 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.  A foamable product produced by the following process steps: reacting an aromatic dianhydride with an oxoimine having the general formula:.Iaddend. ##STR13## .Iadd.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 esterify said imide; and   adding fillers or reinforcing materials to the solution prior to drying;   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.16.  A foamable product produced from the following process steps: 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. ##STR14## .Iadd.wherein "x" is an integer from 2 to 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'-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; 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 polymide resin..Iaddend. .Iadd.17.  A foamable product produced from the following process steps: 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. ##STR15## .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.