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

Abstract

Abstract Five fractions of a polyimide synthesized from 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′‐(trifluoromethyl)‐4,4′‐biphenyldiamine (PFMB) (6FDA/PFMB) in tetrahydrofuran (THF) at 30°C were investigated by a combination of static and dynamic laser light scattering (LLS). The relations of 〈 R h 〉 (nm) = 2.38 x 10 −2 M w 0.560 and A 2 (mol · cm −3 · g −2 ) = 2.1 × 10 −1 M w −0.43 were established, where M w , 〈 R h 〉 and A 2 are weight‐average molecular weight, average hydrodynamic radius and second virial coefficient, respectively. A combination of M w and the translational diffusion coefficient distribution G(D) leads to a relation of D (cm 2 /s) = 2.41 × 10 −4 M 0.564 . With this relation, 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 ∞ of the 6FDA‐PFMB chain are ∼3.3 nm and ∼40, respectively, indicating that the 6FDA‐PFMB chain is more extended 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 〉 ∼ 1.8, together with the values of the exponents (∼0.56) indicate that the 6FDA‐PFMB chain has a coil chain conformation. Therefore, the 6FDA‐PFMB chain has an extended coil conformation in THF at 30°C.