Laser light-scattering studies of soluble high performance fluorine-containing polyimides

Two sets of soluble high performance polyimides synthesized from 2,2'-bis(3 ,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2'-(trifluoro methyl)4,4'-diaminobiphenyl diamine (PFMB), and from 2,2'-bis(trifluorometh yl)-4,4',5,5'-biphenyl-tetracarboxylic dianhydride (HFBPDA) and 2,2 '-(trif luoromethyl) -4,4'-diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser Light scattering (LLS) in tetrahydrofuran (THF) a t 30 degrees C. The calibrations, for 6FDA-PFMB: <R-9> (nm) = 3.87 x 10(-2) <M-w> (0.568), <R-h> (nm) = 2.38 x 10(-2) <M-w>(0.560) and <D> (cm(2)/s) = 2.13 x 10(-4) <M-w>(-0.560); for HFBPDA-PFMB: <R-g> (nm) = 2.24 x 10(-2) < M-w>(0.626), <R-h> (nm) = 1.27 x 10(-2) <M-w>(0.621) and <D> (cm(2)/s) = 3. 99 x 10(-4) <M-w>(-0.621), have been established, where <M-w>, <R-g> <R-h> and <D> are the weight-average molar mass, the root mean square z-average r adius of gyration, the z-average hydrodynamic radius and the z-average tran slational diffusion coefficient, respectively. A combination of <M-w> and t he translational diffusion coefficient distribution G(D) leads to the calib rations of D (cm(2)/s) = 2.41 x 10(-4)M(-0.564) and D (cm(2)/s) = 6.16 x 10 (-4)M(-0.656) for 6FDA-PFMB and HFBPDA-PFMB, respectively, where D and M co rrespond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distribution G(D) into a corresponding molar mass distribution f(w)(M). On the basis of the Kratky-Porod wormlike chain model, the persistence lengths (q) were found to be similar to 3.3 n m and similar to 4.5 nm, respectively, for 6FDA-PFMB and HFBPDA-PFMB, which indicates that both polyimide chains have an extended conformation. In add ition, <R-g>/<R-h> similar to (1.7-1.9) shows that they are in coil conform ation. Therefore, we conclude that both polyimides have an extended coil co nformation.