Thermomechanical and thermogravimetric analyses of systematic series of polyimides

摘要

AbstractTwelve polyimides which differ systematically in chemical structure were investigated in nitrogen through the temperature range −190° rlhar2; 500°C by torsional braid analysis. The degradative regions were also examined in nitrogen by thermogravimetric analysis. Relationships between chemical structure/thermal history, processibility, thermomechanical behavior, and weight loss are discussed. A logical thermal program for converting the precursor polyamic acid solutions to solid polyimides was developed. High‐temperature, thermally induced chemical reactions could be regulated so as to preferentially freeze out longer‐range relaxations and extend the glass state behavior to well above its original load‐limitingTg. Materials made from more flexible molecules had lower glass transitions, softened more through theTg, and had simpler damping spectra and lower thermal stability than materials made from more rigid molecules. A commercially available polyimide film and polyimide‐forming varnish of undisclosed structures were examined by torsional pendulum and torsional braid analyses, respectively. The thermomechanical spectra of the film and cured varnish were similar to the spectra of one structural type o