Chain Conformation and Local Rigidity of Soluble Polyimides(Ⅱ): Isomerized Polyimides in THF

摘要

Two soluble isomerized polyimides(PIs)synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane 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 ℃.The corresponding parameters related to conformations α and v,evaluated from the scaling relationships[η]=KηMa and Rg=KgMv,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 lp and shift factor ML(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 lp and ML showed that the two PIs in THF are flexible chains and exhibit some local rigidity to some extent.