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Bis~maleimides are prepared, as is known in the art, by the reaction of maleic anhydride and a diamine. The bis-maleimides used in the present process can be pre› pared as known in the art or by the azeotroping process described in my copending application Ser. No. 363,800 filed May 25, 1973. The bis-maleimides useful in the present invention have the structural formula 

<img src='content_image/948358.jpg'>

wherein 

Ar is a divalent aromatic organic radical, 

Ar’ is a tetravalent aromatic organic radical, the four carbonyl groups being attached directly to separate carbon atoms and each pair of carbonyl groups being attached to adjacent carbon atoms in the Ar’ radical, and 

n is O or a positive integer of 1 to 20. 

The divalent aromatic radical Ar and the tetravalent aromatic radical Ar’ can be any of the radicals de› scribed in polyimide patents known in the art that are derived from an aromatic diamine and an aromatic dian› hydride respectively. Ar’ preferably contains at least one ring of six carbon atoms characterized by benze› noid unsaturation. Any of the aromatic tetracarboxylic acid dianhydrides known in the prior art can be used to provide Ar’. Among the useful dianhydrides are 3,3’ ,4,4’ -benzophenonetetracarboxylic acid dianhy- dride, pyromellitic dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 3,3’,4,4’-diphenyl tet› racarboxylic acid dianhydride, 1,2,5,6-naphthalene tet› racarboxylic acid dianhydride, 2,2’ ,3,3’ -diphenyl tetra› carboxylic acid dianhydride, 2,2-bis-(3,4-dicarboxy- phenyl)propane dianhydride, 3,4,9, 10-perylene tetra› carboxylic acid dianhydride, bis(3,4-dicarboxy› phenyl)ether dianhydride, naphthalene-1,2,4,5-tetracar› boxylic acid dianhydride, naphthalene-1,4,5,8-tetracar› boxylic acid dianhydride, decahydronaphthalene- 1,4,5,8-tetracarboxylic acid dianhydride, 4,8-dimethyl- 1,2,3,5,6,7-hexahydronaphthalene-l,2,5,6-tetracarboxy- lie acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8- tetracarboxylic acid dianhydride, 2,7-dichloronaphtha› lene-1,4,5,&tetracarboxylic acid dianhydride, 2,3,6,7-tet- rachloronaphthalene-1,4,5,8-tetracarboxylic acid dian› hydride, phenanthrene-1,8,9,10-tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid 

dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dian- hydride, . 2,2-bis(2,3-dicarboxyphenyl)propane dianhy- dride, 1, l-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1, l-bis-(3,4-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4- dicarboxyphenyl)methane dianhydride, bis(3,4-dicar- boxyphenyl)sulfone dianhydride, benzene-1,2,3,4-tet- racarboxylic acid dianhydride and thiophene-2,3,4,5- tetracarboxy1ic acid dianhydride. Preferred Ar’ radicals are 

<img src='content_image/948359.jpg'>

Ar is a divalent benzenoid radical selected from the group consisting of 

<img src='content_image/948360.jpg'>

and multiples thereof connected to each other by R, for example, 

wherein R is an alkylene chain of 1-3 carbon atoms, -CH==CH-, 

<img src='content_image/948362.jpg'>

wherein R’ and R" are each selected from the group consisting of alkyl and aryl of 1 to 6 carbon atoms. Ar is preferably 

<img src='content_image/948363.jpg'>

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