Copolyimides containing a hexafluoropropylidene group are prepared by the stepwise monomer addition method as well as the conventional one-shot method. The stepwise addition method goes through an oligomeric imide prepolymer. The molecular weight distribution of the prepolymers approximately follows the Flory’s statistical distribution in the fluorinated imide prepolymer. Except for the final molecular weight, the conventional one-shot method does not give a significant difference in the copolymer character from the stepwise method, indicating that the segmental distribution in the copolyimides is practically statistical in the present monomer combination. The observed difference in the molecular weight by the preparation method may be related to the reactivity difference of the two monomer pairs.