Melt-processible polyimides with high Tg

A process for preparing a polyimide having a glass transition temperature of from 220 to 330 degrees Celsius and melt viscosity of less than 5.0.times.10.sup.4 Pa s at 360 degrees Celsius comprising:

• a. forming a precursor resin solution by preparing a solution of biphenyl dianhydride as an ester/acid in a polar aprotic solvent selected from N-methylpyrrolidinone either alone or in combination with an aliphatic alcohol having from 1 to 4 carbons, optionally including pyromellitic dianhydride as an ester/acid and reacting with a mixture of diamines consisting of 1,4-bis(4-aminophenoxy)-2-phenylbenzene and either m-phenylene diamine or p-phenylene diamine, and an end-capping agent selected from the group consisting of phthalic anhydride, phenylethynylaniline and phenylethynyl phthalic anhydride, there being a molar-excess of at least 2% of either the dianhydrides or diamines, said pyromellitic dianhydride constituting 0 to 60 mole % of the dianhydride component, the m-phenylene diamine if present, constituting from 20 to 75 mole % of the diamine mixture and the p-phenylene diamine, if present, constituting from 20 to 70 mole % of the diamine mixture and
• b. heating the precursor solution to devolatilize and polymerize the precursor solution to the polyimide.

A polyimide having a glass transition temperature of from 220 to 330 degrees Celsius and melt viscosity of less than 5.0.times.10.sup.4 Pa s at 360 degrees Celsius consisting essentially of ##STR7## where Z is ##STR8## and Q is ##STR9## wherein said A or B units being in molar excess of at least 2% and said molar excess being partially or fully end-capped with a reactive end-capping agent selected from the group consisting of phenylethynyl phthalic anhydride and phenylethynylaniline or the non-reactive end-capping agent phthalic anhydride.