LASER-LIGHT SCATTERING STUDIES OF SOLUBLE HIGH-PERFORMANCE FLUORINE-CONTAINING POLYIMIDES .1. POLYIMIDE SYNTHESIZED FROM 2,2'-BIS(3,4-DICARBOXYPHENYL)HEXAFLUOROPROPANE DIANHYDRIDE AND 2,2'-(TRIFLUOROMETHYL)-4,4'-BIPHENYLDIAMINE

Five fractions of a polyimide synthesized from 2,2'-bis(3,4-dicarboxyp henyl)hexafluoropropane dianhydride (6FDA) and 2,2'-(trifluoromethyl)- 4,4'-biphenyldiamine (PFMB) (6FDA/PFMB) in tetrahydrofuran (THF) at 30 degrees C were investigated by a combination of static and dynamic la ser light scattering (LLS). The relations of [R-h] (nm) = 2.38 x 10(-2 ) (M) over bar(w)(-0.560) and A(2) (mol.cm(-3).g(-2)) = 2.1 x 10(-1) ( M) over bar(w)(0.43) were established, where (M) over bar (R-h) and A( 2) are weight-average molecular weight, average hydrodynamic radius an d second virial coefficient, respectively. A combination of (M) over b ar w and the translational diffusion coefficient distribution G(D) lea ds to a relation of D(cm(2)/s) = 2.41 x 10(-4) M-0.564. With this rela tion, we successfully convert each G(D) into a corresponding molecular weight distribution (MWD). On the basis of the Benoit-Doty theory, we found that the persistence length and the Flory characteristic ratio C-infinity of the 6FDA-PFMB chain are similar to 3.3 nm and similar to 40, respectively, indicating that the 6FDA-PFMB chain is more extende d than typical random-coil chains. On the other hand, the ratio of the radius of gyration to the hydrodynamic radius, i.e., [R-g]/[R-h] simi lar to 1.8, together with the values of the exponents (similar to 0.56 ) indicate that the 6FDA PFMB chain has a coil chain conformation. The refore, the 6FDA-PFMB chain has an extended coil conformation in THF a t 30 degrees C.