Some of the preferred polyimides have repeating units of the formula: ##STR1## wherein R is a tetravalent organic radical and R' is a divalent organic radical selected from the group consisting of aromatic, aliphatic, cycloaliphatic, heterocyclic, combinations of aromatic and aliphatic, and substituted groups thereof (e.g. with halogen and methyl substituents and/or other substituents known to tho