Polyimide coating compositions based on meta-dialkyldihydrogen pyromellitate and aromatic diamines

Abstract

A composition for the application of a planar polymide coating having a glass transition temperature above 300° C. comprises a solution in an anhydrous, aprotic solvent of .Iadd.the reaction product .Iaddend.of an aromatic diamine and a .[.dialkyldihydrogen.]. .Iadd.dialkyl .Iaddend.pyromellitate .Iadd.diacyl chloride .Iaddend.which .[.is more than.]. .Iadd.comprises about .Iaddend.90% .Iadd.or more .Iaddend.meta isomer.

We claim: 
     
       1. A composition for applying to a substrate a planar polyimide coating having a glass transition temperature over 300° C., said composition comprising a solution, in anhydrous, aprotic solvent, of .Iadd.the reaction product of .Iaddend.an aromatic diamine and a .[.dialkyldihydrogen.]. .Iadd.dialkyl .Iaddend.pyromellitate .Iadd.diacyl chloride .Iaddend.which .[.is more than.]. .Iadd.comprises about .Iaddend.90% .Iadd.or more .Iaddend.meta isomer. 
     
     
       2. A composition as claimed in claim 1 wherein the .[.dialkyldihydrogen.]. .Iadd.dialkyl .Iaddend.pyromellitate .Iadd.diacyl chloride .Iaddend.is the diethyl compound. 
     
     
       3. A composition as claimed in claim 1 wherein the aromatic diamine is p-phenylene diamine or 4,4'-diaminodiphenylether. 
     
     
       4. A composition as claimed in claim 1 wherein the solvent is N-methyl pyrrolidone. 
     
     
       5. A composition as claimed in claim 4 wherein the solvent also contains about 10% of N-cyclohexyl pyrrolidone. .Iadd.6. A polyimide coating precursor comprising a polyisophthalamide polymer which is the reaction product of an aromatic diamine and an alkyl pyromellitate diacyl chloride which comprises about 90% or ore meta isomer. .Iaddend. .Iadd.7. The precursor as claimed in claim 6 wherein the dialkylpyromellitate diacyl chloride is the diethyl compound. .Iaddend. .Iadd.8. The precursor as claimed in claim 6 wherein the aromatic diamine is p-phenylene diamine or 4,4'-diaminodiphenylether. .Iaddend.