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′‐(trifluoromethyl)‐4,4′‐diaminobiphenyl diamine (PFMB), and from 2,2′‐bis(trifluoromethyl)‐4,4′,5,5′‐biphenyl‐tetracarboxylic dianhydride (HFBPDA) and 2,2′‐(trifluoromethyl)‐4,4′‐diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser light scattering (LLS) in tetrahydrofuran (THF) at 30°C. The calibrations, for 6FDA‐PFMB: <Rg> (nm) = 3.87 × 10−2 <Mw> 0.568, <Rh> (nm) = 2.38 × 10−2 <Mw>0.560 and <D> (cm2/s) = 2.13 × 10−4 <Mw>−0.560; for HFBPDA‐PFMB: <Rg> (nm) = 2.24 × 10−2 <Mw>0.626, <Rh> (nm) = 1.27 × 10−2 <Mw>0.621 and <D> (cm2/s) = 3.99 × 10−4 <Mw>−0.621, have been established, where <M2>, <Rg>, <Rh> and <D> are the weight‐average molar mass, the root mean square z‐average radius of gyration, the z‐average hydrodynamic radius and the z‐average translational diffusion coefficient, respectively. A combination of <Mw> and the translational diffusion coefficient distribution G(D) leads to the calibrations of D (cm2/s) = 2.41 × 10−4M−0.564 and D (cm2/s) = 6.16 × 10−4M−0.656 for 6FDA‐PFMB and HFBPDA‐PFMB, respectively, where D and M correspond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distribution G(D) into a corresponding molar mass distribution fw(M). On the basis of the Kratky‐Porod wormlike chain model, the persistence lengths (q) were found to be ˜ 3.3 nm and ˜ 4.5 nm, respectively, for 6FDA‐PFMB and HFBPDA‐PFMB, which indicates that both polyimide chains have an extended conformation. In addition, <Rg> / <Rh> ˜ (1.7‐1.9) shows that they are in coil conformation. Therefore, we conclude that both polyimides have an extended coil conformation.