3  4,118,377  4  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  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  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  wherein  R’  and  R"  are each  selected  from the  group  consisting  of alkyl  and aryl  of 1 to  6  carbon  atoms. Ar  is  preferably  wherein  R  is an  alkylene  chain of  1-3  carbon  atoms,  -CH==CH-,  and  multiples  thereof  connected  to each  other by  R,  for  example,  Ar  is a  divalent  benzenoid  radical  selected  from the  group  consisting  of  wherein  TABLE  I-continued  R$_{1 }$ - Position  (2)  (3)  (4)  (5)  y  B.P. "C.  H  ~H1  H  H  0  H  H  C3H1  0  C4H9  H  H  H  0  H  H  HC 4 H9 0  CH$_{3 }$ H  C~ 7  H  0  CH 3  CH 3  C  3  CH 3  0  H  CH  H  H  s  H  ~ii7  H  H  H  H  ~H1  s  C4Hg  H  H  H  H  HC 4 H 9  S  CH 3  H  Ct1  H  s  CH 3  CH 3  C  3  CH 3  H  H  H  H  s  84  0  II  r-C~N  0  0  II  II  C  C  I  \  I  \  0  II  /\C-ICIH  Ar-N  Ar’  N  Ar-N  CH-C  II  0  \  I  \  I  C  C  II  II  0  0  C-CH  II  0  ...  ~~  0  R’  II  I  -C-,  -0-,  -s-,  -S0$_{2}$ -,  -N-,  -Si-,  I  I  R  R"  R’  R’  R’  I  I  I  -O-Si-0-,  -o-P-0-,  and  -P- l  II  II  R"  0  0  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. 