. . . "ng substantially 0.33 molar portion of an aromatic triamine thereto, and C. Adding substantially 1.0 molar portion of a vinyl substituted aromatic monoamine to the product of step (B);said aromatic tetracarboxylic acid dianhydride having the formula: ##STR31## where R has the structure: ##STR32## where X is ##STR33## or a bond; said aromatic triamine having the formula: ##STR34## where R' is an ar" .