Purification of acetylene-terminated polyimide oligomers

A process for purifying an acetylene-terminated polyimide oligomer containing a residual amount of the solvent used as the reaction medium in its synthesis which comprises the steps of:

• (a) dissolving the oligomer in the same solvent used as the reaction medium in its synthesis;
• (b) mixing the resulting solution with an aqueous solution of potassium or sodium chloride, thereby causing the oligomer to precipitate from solution;
• (c) separating the precipitated oligomer from the aqueous solution;
• (d) successively washing the separated oligomer at least once in each of a series of five liquid baths of decreasing polarity, the first of said baths consisting essentially of water, the second of said baths consisting essentially of a mixture of methanol and water, the third of said baths consisting essentially of methanol, the fourth of said baths consisting essentially of a mixture of ether and methanol, and the fifth of said baths consisting essentially of ether;
• and
• (e) recovering and drying the purified oligomer from the said fifth bath.