Modified polyimide/polyimide-amide foams and methods of making same

The method of making a modified polyimide foam having a selected compressive resistance 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 selected within the range of from about 1.5:1 to about 1.05:1 in accordance with the final foam compressive resistance desired;
• mixing therewith an effective quantity of an alcohol;
• heating the mixture to a temperature of from about 60.degree. to about 120.degree. C. for from about 30 to about 90 minutes to react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide and further to esterify said imide;
• cooling the mixture to a temperature of from about 40.degree. C. to about 70.degree. C.;
• 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.degree. C. to about 80.degree. C. for a period of about 2 to about 30 minutes;
• drying the solution at a temperature of from about 60.degree. C. to about 70.degree. 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.degree. C. to about 220.degree. C. in a pre-heated oven for from about 10 to about 40 minutes;
• whereby a resilient foam is formed having a selected compressive resistance in accordance with the selected oxoimine to dianhydride mole ratio, the compressive resistance being inversely proportional to the oxoimine quantity.

The method of making a modified polyimide foam having a selected compressive resistance 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 selected within the range of from about 1.5:1 to about 0.05:1 in accordance with the desired final foam compressive resistance, said compressive resistance being inversely proportional to the oxoimine quantity;
• mixing therewith from about 5 to 10 moles alcohol per 100 mole dianhydride,
• heating the mixture to a temperature of from about 60.degree. to about 120.degree. C. for from about 30 to about 90 minutes to react said dianhydride with said oxoimine to produce an N-substituted aliphatic imide and substantially simultaneously esterify said imide;
• cooling the mixture to a temperature of from about 40.degree. C. to about 70.degree. C.;
• 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.degree. C. to about 80.degree. C. for a period of about 2 to about 30 minutes;
• drying the solution at a temperature of from about 60.degree. C. to about 70.degree. 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.degree. C. to about 320.degree. C. in a pre-heated oven for about 30 to about 60 minutes;
• whereby a resilient flame resistant modified polyimide foam having selected compressive resistance characteristics is produced, consisting primarily of polyimide resin.