ABSTRACT
Aromaticpolyimidesarewellestablishedashighperformancepolymericmaterialsbecauseoftheirexcellentheatresistance,electricalinsulatingpropertiesas wellasmechanicalcharacteristicsandarewidelyusedaselectronicmaterials,adhesives,compositematerials,fiberandfilmmaterials[1-6].Unlesscarefullydesigned,however,polyirnidesareofteninsolubleandintractableintheirfully imidizedform,presentingseriousprocessingdifficulties.Therefore,preparation ofsolubleorthermoplasticpolyirnideshasbeenamajorresearchinterest.The conceptsforstructuralmodificationssuchasincorporationofflexiblebridging linkages[7-9]ormeta-orientedphenyleneringsintothepolymerbackboneand introductionofbulkysubstituents[10-16]alongpolymerskeletonhavebeenused toenhancethesolubilityandtolowertheglasstransitiontemperature.Ithasbeen generallyrecognizedthataromaticetherlinkagesinsertedinthearomaticmain
chains provide them with a significantly lower energy of internal rotation. In general, such a structural modification leads to a lower glass transition temperature (Tg) and crystalline melting temperature (Tm), as well as significant improvements in solubility and other process characteristics of the polymers without greatly sacrificing thermal stability. Increasing the chain flexibility could also result in an increase in the rate of crystallization of polyimide. Semicrystalline polyimides offer further advantages of increased solvent resistance and retention of mechanical properties above the glass transition temperature.
