A product selected from the group consisting of:A. An end-capped polyimide oligomer whose principal component has the structure: ##STR10## where R has the structure: ##STR11## where X is ##STR12## or a bond; where R' is an aryl group; and where R is an aryl group bearing a substituent having the structure: --CH═CH2 ; B. A first precursor of an end-capped polyimide oligomer of (A) whose prin