Structure-property relations in processing high-performance polyisoimide–imide resins

Abstract

The processing of high-performance polyimides via their processible isoimide modifications is of great interest to aeronautical and aerospace applications. Rheological characterization during the isoimide-to-imide conversion, essential for identifying the processing conditions of such reactive polymers and their polymer blends, is reported. Using dynamic shear measurements, we obtained rheological information for a series of polyisoimide–imide resins as a function of temperature and cure history. Both homopolymers and copolymers have been investigated. We found that the processibility (e.g., melt viscosity of isoimide) and ultimate product properties (e.g., Tg of polyimide) can be systematically varied by changing the chemical constituents and rigidity of the polymer backbone. Such correlations of chemical structures, rheological behavior, and processing characteristics provide the necessary database for tailor making new polymer systems with desirable processibility and mechanical properties. Practical considerations and difficulties in measuring the viscoelasticity of these materials are also addressed.