Critical concentration and scaling exponents of one soluble polyimide-from dilute to semidilute entangled solutions

- A soluble polyimide was synthesized and it can be dissolved in common organic solvents in various concentration ranges.
- Deviation of scaling exponents in different concentration ranges is found.
- Mechanism of the deviation of scaling exponents is discussed comprehensively.

A soluble polyimide (6FDA-TFDB) was synthesized and its properties in solution were investigated. The relationship between specific viscosity and concentration is established using rheometer and applying Zimm model (dilute solution), Rouse-Zimm model (semidilute unentangled solution), and Doi-Edwards model (semidilute entangled solution). In addition, the overlapped concentration (C*) and semidilute entangled concentration (Ce) are determined. Results showed that all of the scaling exponents are higher than the theoretical values. The influence of factors, namely, electrostatic interaction, hydrogen bonding, dipole-dipole interaction and polydispersity index under different conditions (i.e., temperature, salt, and solvent) on critical concentration and scaling exponents are investigated extensively. In order to confirm the related conclusions, two soluble polyimides with different chemical structures are also synthesized and compared with the above results. The reasons for the deviation of scaling exponents are also discussed.

257