Abstract: Two soluble isomerized polyimides(PIs) synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropro- pane dianhydride(6FDA) with either 2,2′-dimethylbenzidine(2,2′-DMB) or 3,3′-DMB were investigated by means of size-exclusion chromatography coupled with multi-angle laser light scattering, a viscometer and a refractive index detector in tetrahydrofuran(THF) with tetrabutylammonium bromide(TBAB) at 35 °C. The corresponding parameters related to conformations α and ν, evaluated from the scaling relationships [η]=K_ηM^α and R_g=K_gM^ν, respectively, were 0.66±0.01 and 0.55±0.02 for poly(6FDA/3,3′-DMB), and 0.67±0.01 and 0.56±0.01 for poly(6FDA/2,2′-DMB), indicating a random coil conformation for both the samples in this mobile system. The persistence length l_p and shift factor M_L(relative molecular weight per unit contour length) were estimated from the relationship between intrinsic viscosity and molecular weight for the wormlike cylinder model proposed by Bohdanecky. Both l_p and M_L showed that the two PIs in THF are flexible chains and exhibit some local rigidity to some extent.

Key words: Isomerized polyimide, Chain conformation, Local rigidity, Wormlike chain, Persistence length